- Email: [email protected]
The relationship between scapular notching and reverse shoulder arthroplasty prosthesis design
J Shoulder Elbow Surg (2012) 21, 1430-1441
www.elsevier.com/locate/ymse
The relationship between scapular notching and reverse shoulder arthroplasty prosthesis design Marc S. Kowalsky, MDa, Leesa M. Galatz, MDb, Derek S. Shia, MDc, Karen Steger-May, MAd, Jay D. Keener, MDb,* a
Department of Orthopaedic Surgery, Lenox Hill Hospital, Park Lenox Orthopaedics, New York, NY, USA Department of Orthopaedic Surgery, Washington University, St. Louis, MO, USA c The Portland Clinic, Portland, OR, USA d Division of Biostatistics, Washington University, St. Louis, MO, USA b
Background: Inferior scapular notching is a common radiographic complication of reverse shoulder arthroplasty. The purpose of this study is to determine the impact of prosthesis design on the incidence and severity of notching. Materials and methods: Eighty-eight patients (mean age, 72 years) who underwent reverse shoulder arthroplasty with a minimum of 12 months’ follow-up (mean, 31 months) were retrospectively reviewed. Patients were grouped based on prosthesis design: Tornier (Stafford, TX, USA) (45%), Zimmer (Warsaw, IN, USA) with a nonretentive liner (35%), and Zimmer with a retentive liner (19%). Notching on final radiographs was graded by use of the Sirveaux classification system and a novel classification system. Results: The incidence of notching was significantly higher with the Tornier prosthesis (92%) compared with the Zimmer prosthesis with nonretentive liners (58%) and retentive liners (71%) (P < .05). The incidence of high-grade notching and the median grade were significantly higher with the Tornier prosthesis compared with the Zimmer prosthesis (P < .05). By use of the novel grading system, there was a higher incidence of notching involving the baseplate with the Tornier prosthesis (68%) compared with the Zimmer prosthesis (33%) (P < .05). The addition of a retentive liner was not associated with greater notching than a nonretentive liner for the Zimmer implant. Diagnosis had no significant influence on notching. Conclusions: A higher incidence and severity of notching were observed with the Tornier reverse arthroplasty compared with the Zimmer reverse arthroplasty at short-term follow-up. These findings may be because of the different morphology of the polyethylene component and/or differences in glenosphere offset between the prosthetic systems. In addition to surgical technique, consideration should be given to prosthesis design in mitigating the risk of scapular notching. Level of evidence: Level III, Case-Control Design, Treatment Study. Ó 2012 Journal of Shoulder and Elbow Surgery Board of Trustees. Keywords: Reverse arthroplasty; scapular notching; notching; shoulder arthroplasty; implant
Institutional review board approval: Washington University (08-1130). *Reprint requests: Jay D. Keener, MD, Department of Orthopaedic Surgery, Washington University, 660 S Euclid Ave, CB 8233, St. Louis, MO 63110, USA. E-mail address: [email protected] (J.D. Keener).
Scapular notching is by far the most common complication of reverse shoulder arthroplasty; yet, its etiology and clinical significance remain controversial. Notching occurs with alarmingly high frequency in most reported series but is not consistently associated with failure of the
1058-2746/$ - see front matter Ó 2012 Journal of Shoulder and Elbow Surgery Board of Trustees. doi:10.1016/j.jse.2011.08.051
Scapular notching and reverse shoulder arthroplasty design
1431
glenosphere.1,3-5,10,17,19,22,27-30,32 Multiple biomechanical and cadaveric studies have focused on the influence of glenoid placement and surgical technique on the development of notching, leading to the nearly universal principles of inferior glenosphere positioning with some inferior tilt.14,23,25 This ideology assumes that notching occurs as a result of adduction impingement. More recently, notching has been recognized as a 3-dimensional phenomenon, with acknowledgment of the possible rotational impingement that occurs between the liner and the scapular neck.21,26 Regardless, the ideal surgical parameters to minimize notching and a reliable classification system have not been established. Essential elements of modern reverse arthroplasty designs include a center of rotation that is translated distal and medial to improve the lever arm of the deltoid and recruit more deltoid fibers for glenohumeral elevation.11,12 The medialized center of rotation also localizes the shear force on the glenoid component to the glenoid face at the point of fixation, which mitigates the risk of glenosphere failure.2 These innovations have led to improved functional outcomes and survivorship in comparison to earlier constrained and semiconstrained reverse implant designs.6,8,13,24,28,30 Whereas a medialized center of rotation is one of the hallmarks of most contemporary reverse shoulder arthroplasty designs essential to their success, this feature comes at a cost. Medialization of the glenosphere decreases the surface arc of motion, resulting in impingement of the humeral component on the inferior scapular neck. This in turn results in scapular notching, or characteristic bone loss along the inferior scapular neck at the location of impingement. Scapular notching is commonly reported in association with implant designs with a medialized center of rotation, with a prevalence as high as 96%.31 Conflicting reports exist in the literature regarding the relationship between notching and functional outcomes.1,21,26,28 Furthermore, whereas a theoretic concern exists that notching may lead to catastrophic glenosphere baseplate loosening, no definitive association thereof has yet been established. Most published studies of reverse shoulder arthroplasty rely on 2 commonly used classification systems for scapular notching, offered by Nerot and colleagues29 and Sirveaux et al.27,28 However, several fundamental problems exist with these grading systems. The Nerot classification system attempts to distinguish between notching that involves only the lateral pillar (grade 1) and notching that involves the lateral pillar with ‘‘condensation’’ indicating stability (grade 2). This subjective interpretation potentially undermines the reliability of this grading system. Furthermore, both classification schemes grade severity of notching in reference to the position of the inferior screw. However, the optimal technique for screw insertion has changed over time. Initially, it was advocated to direct the inferior screw with caudal orientation down the lateral pillar to maximize screw depth. Recent literature has shown that optimal inferior screw orientation should instead be
more horizontal, maximizing screw length and bony purchase.25 Furthermore, with variable-angle screws, this is not a consistent landmark either among patients or among surgeons. Therefore, the ideal classification system should be independent of the trajectory of the inferior screw. Lastly, in both classification systems, notching that extends beneath the baseplate qualifies as a distinct grade (grade 4). However, the size and location of the notch relative to the baseplate are independent phenomena and should thus be addressed independently. The purpose of this study is to investigate the impact of prosthesis design on the prevalence and severity of notching using 2 different implant designs. In addition, the influence of factors such as glenosphere position and revision surgery on scapular notching was examined. Lastly, an alternative classification system that is independent of inferior screw position is described and analyzed in this investigation.
Materials and methods Inclusion and exclusion criteria We identified 175 consecutive patients who underwent a reverse shoulder arthroplasty in 179 shoulders by 1 of 3 fellowship-trained shoulder and elbow surgeons (K.Y., L.M.G., and J.D.K.) from July 2004 until January 2008. Of these patients, 107 who had been followed up for at least 12 months postoperatively with radiographs were considered for this investigation. Exclusion criteria included inadequate or poor-quality radiographs (7 patients), glenosphere failure (1 patient with early postoperative glenoid vault fracture treated nonoperatively), intraoperative or postoperative conversion to hemiarthroplasty (1 patient with inadequate bone stock for glenosphere placement and 2 with intraoperative glenoid fracture during glenoid preparation), or postoperative instability requiring conversion from nonretentive to retentive polyethylene liners (3 patients). Because glenosphere positioning has been shown to be an independent risk factor for notching, patients were also excluded if the glenosphere was implanted above the level of the inferior glenoid rim (5 patients). A total of 88 patients participated in the study. The mean age of the patients at the time of surgery was 72 9 years (range, 42-88 years). The mean age was 74.1 8 years for patients treated with the Tornier prosthesis (Stafford, TX, USA) and 70.6 10 years for patients treated with the Zimmer prosthesis (Warsaw, IN, USA) (68.7 11 years for Zimmer prosthesis with nonretentive liner [Zimmer N] and 74.0 7 years for Zimmer prosthesis with retentive liner [Zimmer R]) (Table I). Overall, age was not statistically different between the Tornier and Zimmer groups (P ¼ .164); however, there was a statistically significant difference between the Tornier and Zimmer N groups (P ¼ .013). The mean duration of follow-up was 31 12 months (range, 12-68 months). Mean follow-up for the Tornier and Zimmer groups was 2.9 1.3 years and 2.2 0.6 years, respectively (2.3 0.7 years for Zimmer N and 1.9 0.5 years for Zimmer R). This difference was statistically significant, primarily because of the difference between the Tornier and Zimmer R groups (P ¼ .002). There were 38 men (43%) and 50 women (57%). The
1432 Table I
M.S. Kowalsky et al. Subject characteristics by implant design P value for 2-group comparison
P value for 3-group comparison
17 74.0 7
P ¼ .164
2.3 0.7
1.9 0.5
P ¼ .002 P ¼ .754
P ¼ .030 Tornier vs Zimmer N, P ¼ .013 Zimmer N vs Zimmer R, P ¼ .052 P ¼ .006 Tornier vs Zimmer R, P ¼ .002 P ¼ .900
20 1 1 3 1 1 1 3
10 0 2 2 1 0 2 0
P ¼ .868
P ¼ .735
Tornier
Zimmer
Zimmer N
Zimmer R
N Age at surgery (y)
40 74.1 8
48 70.6 10
31 68.7 11
Follow-up (y)
2.9 1.3
2.2 0.6
26 1 1 6 1 1 2 2
30 1 3 5 2 1 3 3
Diagnosis CTA Failed hemi for arthritis Failed hemi for CTA Failed hemi for fracture Failed TSA Irreparable RCT Proximal humeral fx Proximal humeral fx sequelae Primary/revision Revision Primary
(65%) (2.5%) (2.5%) (15%) (2.5%) (2.5%) (5%) (5%)
9 (22%) 31 (78%)
(62%) (2%) (6%) (10%) (4%) (2%) (6%) (6%)
11 (23%) 37 (77%)
(65%) (3%) (3%) (10%) (3%) (3%) (3%) (10%)
6 (19%) 25 (81%)
(59%) (12%) (12%) (6%) (12%)
5 (29%) 12 (71%)
CTA, Cuff tear arthropathy; hemi, hemiarthroplasty; TSA, total shoulder arthroplasty; RCT, rotator cuff tear; fx, fracture.
primary diagnoses in these patients included the following: cuff tear arthropathy (56 patients [64%]), failed hemiarthroplasty for fracture (11 patients [13%]), proximal humeral fracture nonunion or malunion (5 patients [6%]), acute proximal humeral fracture (5 patients [6%]), failed hemiarthroplasty for cuff tear arthropathy (4 patients [5%]), failed total shoulder arthroplasty (3 patients [3%]), irreparable rotator cuff tear (2 patients [2%]), and failed hemiarthroplasty for arthritis (2 patients [2%]). For 68 patients (77%), the reverse shoulder arthroplasty was the primary procedure, whereas 20 patients (23%) had undergone previous procedures. There was no significant difference among groups with respect to the distribution of diagnoses or the percentage of patients in each group who had undergone previous procedures. The Tornier Aequalis Reversed Shoulder was used in 40 patients (45%) until December 2007 (Fig. 1). Beginning in May 2006, the Zimmer Trabecular Metal Reverse Shoulder System was used in 48 patients (55%). Of these patients, 31 (65%) received a nonretentive humeral polyethylene liner and 17 received a retentive liner (35%).
metaphyseal geometry with trabecular metal surface coating. The diameter of the metaphyseal portion is 41 mm. The angle of inclination of the humeral component is 53 , and this increases to 60 with a nonretentive liner and to 65 with a retentive liner. Therefore, there is some angulation built into the liner itself. Importantly, the polyethylene liner is not symmetric around the circumference. The medial aspect has maximum thickness, with decreasing thickness as it traverses laterally. This design feature may have significant implications in notching because of rotational impingement. Both the Tornier and Zimmer prostheses implement a hemispherical glenosphere design. In this study, only 36-mm-diameter glenospheres were used. When considering the glenosphereetoe glenoid baseplate Morse taper relationship, there is potentially a significant design difference between the two systems: a 2.5-mm lateral offset is seen with the Zimmer implant compared with no offset with the Tornier system.
Surgical technique Implant design Both the Tornier and Zimmer reverse arthroplasty designs implement a glenoid component design with a medialized center of rotation. For both systems, the humeral prostheses are cobaltchrome implants with a fluted distal geometry (Fig. 1). The Tornier Aequalis Reversed Shoulder humeral prosthesis has a conical metaphyseal geometry with a smooth metal surface finish. The diameter of the metaphyseal component is either 36 or 42 mm, depending on glenosphere size. The angle of inclination is 65 and does not change with the addition of the polyethylene liner. That is, the liner is symmetric around its entire circumference, without any angulation built into the liner itself. The Zimmer Trabecular Metal Reverse Shoulder System humeral prosthesis has a conical
All procedures were performed with the patient in the beach-chair position under general anesthesia with or without regional anesthesia. A deltopectoral approach was used in all but 2 cases, in which an anterosuperior transdeltoid approach was used. The proximal 1 to 2 cm of pectoralis major tendon was released to improve exposure. A biceps tenotomy was performed if the tendon was still present within the joint. The subscapularis tendon, if intact, was released from the lesser tuberosity. The humeral osteotomy was performed to establish between 0 and 20 of retroversion, depending on the integrity of the posterior rotator cuff. The prosthesis was placed in 0 of retroversion if the teres minor was absent as evidenced by a positive hornblower’s sign on physical examination. All other prostheses were placed in 20 of
Scapular notching and reverse shoulder arthroplasty design
1433
Figure 1 Implant designs: Tornier Aequalis Reversed Shoulder (A), Zimmer Trabecular Metal Reverse Shoulder System (B), Zimmer nonretentive polyethylene liner with 60 angle of inclination (C), and Zimmer retentive polyethylene liner with 65 angle of inclination (D). retroversion. Alignment rods defining 0 and 20 of retroversion were placed into the humeral cutting guide, proximal metaphyseal reamers, and stem inserter to ensure appropriate version. Glenoid exposure was facilitated with aggressive anterior and inferior capsular releases, with care taken to identify and protect the axillary nerve. The origin of the long head of the triceps brachii was released and the inferior capsulolabral tissue was excised to ensure inferior placement of the glenoid baseplate. A drill guide was used to place a guidewire to allow baseplate insertion flush with the inferior glenoid rim. During placement of the guidewire, inferior tilt of 5 to 10 relative to the horizontal was established to allow inferior tilt of the baseplate during glenoid preparation and implant insertion. In addition, preoperative axial imaging assisted in determination of the required correction to establish acceptable glenoid version. The Tornier Aequalis Reversed Shoulder allowed placement of 4 nonlocking glenoid screws, whereas the Zimmer Trabecular Metal Reverse Shoulder System allowed placement of 2 screws stabilized with locking caps (Fig. 1). With all implants, the superior screw was angled cephalad and anterior toward the coracoid base. Initially, the inferior screw was angled caudad in line with the inferior pillar. However, over
time, the technique evolved with placement of the inferior screw more perpendicular to the baseplate. A 36-mm glenosphere was used in all cases. The humeral stem was inserted with antibioticimpregnated bone cement. A polyethylene humeral insert of sufficient thickness was chosen to establish appropriate stability of the prosthesis. If necessary, a spacer was placed between the humeral stem and polyethylene liner to enhance longitudinal stability. Once it became commercially available with the Zimmer system, a retentive liner with an angle of inclination of 65 (155 in reference to the long axis of the humerus) was used at the surgeon’s discretion, to improve stability without increasing humeral length. The subscapularis tendon or its remnant was repaired to the medial aspect of the lesser tuberosity when sufficient tissue was present. A suction drain for self-suctioning was placed in the subdeltoid space in all patients. The operative extremity was immobilized in a sling with an abduction pillow. Patients did not receive any physical therapy, nor were they permitted any shoulder motion, for the first 2 to 4 weeks. They were, however, encouraged to remove the sling 3 times daily for elbow, wrist, and finger motion. After 2 to 4 weeks, the patients were instructed
1434
Figure 2 Sirveaux classification system: grade 1 notching involves only the lateral pillar (a), grade 2 notching contacts the inferior screw (b), grade 3 notching extends beyond the inferior screw (c), and grade 4 notching extends under the baseplate (d). with regard to a home exercise program consisting primarily of active-assisted forward elevation.
Patient evaluation The patients were evaluated at a minimum of 12 months postoperatively with anteroposterior, true anteroposterior, scapular lateral, and axillary lateral radiographs of the operative shoulder. Only the radiographs obtained at latest follow-up evaluation were examined for study purposes. The initial postoperative radiographs were available for reference to evaluate initial baseplate position relative to the scapular neck. Radiographs were evaluated by 3 observers (2 fellowship-trained shoulder and elbow surgeons [J.D.K. and L.M.G.] and 1 shoulder and elbow surgery fellow [M.S.K.]) for scapular notching. The degree of scapular notching was graded according to the system of Sirveaux et al27,28 (Fig. 2). According to this classification system, grade 1 notching involves only the lateral pillar, grade 2 notching contacts the inferior screw, grade 3 notching extends beyond the inferior screw, and grade 4 notching extends beneath the baseplate. Radiographs were also interpreted by use of a novel classification system that references the size of the notch relative to the central peg, which is not variable (Fig. 3). Accordingly, the maximum height of the notch from the inferior pillar is measured (notch height [NH]) and compared with the distance from the inferior pillar to the central peg at that location (pillar-to-peg distance [PPD]). Grade 0 indicates no notching, grade 1 indicates notching in which the
M.S. Kowalsky et al.
Figure 3 Novel classification system: grade 1 indicates notching in which the ratio of NH (a) to PPD (b) is less than two-thirds, and grade 2 indicates notching in which the NH-PPD ratio is two-thirds or greater. The dotted line indicates notching that does not involve the baseplate (type A), and the solid line indicates notching that involves the baseplate (type B).
NH-PPD ratio is less than two-thirds, and grade 2 indicates notching in which the NH-PPD ratio is greater than or equal to two-thirds (Fig. 4). Notching was then examined to determine whether it also contacted the baseplate (type A, does not contact baseplate; type B, does contact baseplate) (Fig. 5). In addition, the radiographs were examined for the presence of heterotopic ossification or osteophyte formation along the inferior glenoid.
Statistical analysis Inter-rater agreement for the Sirveaux and novel classification systems, as well as the presence of heterotopic ossification, was assessed with Cohen k coefficients and corresponding 95% confidence intervals (CIs). For variables measured on an ordered polytomous scale, weighted k values were reported. The weighted k is a refinement of the k coefficient that takes into account the magnitude of the disagreement between ratings. For data analysis, the consensus grading of at least 2 readers was used, with the exception of 1 case for which no consensus existed. In this case, all 3 readers reviewed the radiographs together, and a unanimous decision was made regarding the ultimate grading. Continuous variables (ie, age and length of followup) were compared across the 3 groups (Tornier, Zimmer N, and Zimmer R) via analysis of variance. When significant (P .05)
Scapular notching and reverse shoulder arthroplasty design
1435
Figure 4 Scapular notching according to novel classification system. (A) No scapular notching. (B) Grade 1 scapular notching with an NH-PPD ratio of less than two-thirds. (C) Grade 2 scapular notching with an NH-PPD ratio of two-thirds or greater.
Figure 5 Scapular notching and baseplate involvement. (A) Scapular notching that does not involve the baseplate (type A). (B) Scapular notching that does involve the baseplate (type B).
and within the analysis of variance model, statistical contrasts were used to compare (1) Tornier versus Zimmer N, (2) Tornier versus Zimmer R, (3) Zimmer N versus Zimmer R, and (4) Tornier versus all Zimmer. Binary and ordinal-scaled variables were compared across the 3 groups by generalized estimating equations. Binary outcomes were modeled with binomial probability distributions and logit link functions. Ordinal-scaled variables were modeled with a multinomial probability distribution and a cumulative logit link function to account for the ordering of the response categories. When significant (P .05) and within the generalized estimating equation model, statistical contrasts were used to compare (1) Tornier versus Zimmer N, (2) Tornier versus
Zimmer R, (3) Zimmer N versus Zimmer R, and (4) Tornier versus all Zimmer. Analyses were performed with SAS software, version 9.2, of the SAS System for Linux (SAS Institute, Cary, NC, USA).
Results Reliability Weighted k coefficients were calculated for the analysis of scapular notching using both the Sirveaux and novel
1436 Table II
M.S. Kowalsky et al. Scapular notching by implant design Tornier
New grade 0, none 1, mild/moderate 2, severe Median new grade New grade severity Low grade (0-1) High grade (2) Baseplate involvement A (no) B (yes) Sirveaux grade 0 1 2 3 4 Median Sirveaux grade Sirveaux grade severity Low grade (0-2) High grade (3-4) Heterotopic ossification No Yes
Zimmer
Zimmer N
Zimmer R
3 (8%) 24 (60%) 13 (32%) 1
18 (38%) 24 (50%) 6 (12%) 1
13 (42%) 14 (45%) 4 (13%) 1
5 (29%) 10 (59%) 2 (12%) 1
27 (68%) 13 (32%)
42 (88%) 6 (12%)
27 (87%) 4 (13%)
15 (88%) 2 (12%)
12/37 (32%) 25/37 (68%)
20/30 (67%) 10/30 (33%)
10/18 (56%) 8/18 (44%)
10/12 (83%) 2/12 (17%)
3 (8%)
18 (38%)
13 (42%)
5 (29%)
12 (30%) 10 (25%) 9 (22%) 6 (15%) 2
24 (50%) 4 (8%) 2 (4%) 0 1
14 (45%) 2 (6%) 2 (6%) 0 1
10 (59%) 2 (12%) 0 0 1
25 (62%) 15 (38%)
10 (25%) 30 (75%)
46 (96%) 2 (4%)
12 (25%) 36 (75%)
29 (94%) 2 (6%)
11 (35%) 20 (65%)
classification systems by the 3 observers on the radiographs of 88 shoulders. With the Sirveaux classification system, the weighted k coefficient was 0.69 (95% CI, 0.62-0.75), indicating substantial interobserver agreement according to the guidelines established by Landis and Koch.20 With the novel classification system, the weighted k coefficient for grade was 0.73 (95% CI, 0.65-0.80). The k coefficient for involvement of the baseplate was 0.70 (95% CI, 0.62-0.78). These values also indicate substantial interobserver agreement. For the presence of heterotopic ossification, the k coefficient was 0.68 (95% CI, 0.58-0.79).
Prosthesis type versus notching The overall prevalence of scapular notching was 76% by use of both the Sirveaux and novel classification systems (Table II). The prevalence of notching in the Tornier group was 92%, as compared with 62% in the Zimmer group (58% for Zimmer N and 71% for Zimmer R). The prevalence of notching was significantly higher in the Tornier group compared with both Zimmer groups (P ¼ .002), but there was no difference between Zimmer groups.
P value for 2-group comparison
P value for 3-group comparison
P ¼ .0007
P ¼ .001 Tornier vs Zimmer N, P ¼ .0009 Tornier vs Zimmer R, P ¼ .026
P ¼ .024
P ¼ .074
P ¼ .002
P ¼ .005 Tornier vs Zimmer R, P ¼ .006
P < .0001
P < .0001 Tornier vs Zimmer N, P < .0001 Tornier vs Zimmer R, P ¼ .0002
P < .0001
P < .0001 Tornier vs Zimmer N, P ¼ .007 Tornier vs Zimmer R, P < .0001
P ¼ .349
P ¼ .048 Zimmer N vs Zimmer R, P ¼ .047
17 (100%) 0
1 (6%) 16 (94%)
The prevalence of high-grade notching, as defined by Sirveaux grades 3 and 4 or novel grade 2, was significantly higher in the Tornier group (38% and 32%, respectively) as compared with the Zimmer group (4% and 12%, respectively) (P < .0001 and P ¼ .024, respectively). Although comparison among all 3 groups (Tornier, Zimmer N, and Zimmer R) showed only a trend toward significance based on the novel grading system (P ¼ .074), a significantly higher prevalence of high-grade notching was observed in the Tornier group compared with both the Zimmer N and Zimmer R groups based on the Sirveaux classification (P ¼ .007 and P < .0001, respectively), with no difference between Zimmer groups. Moreover, the median notching grade by use of the Sirveaux grading system was higher in the Tornier group (2), as compared with both the Zimmer N group (1) and Zimmer R group (1) (P < .0001 and P ¼ .0002, respectively). The prevalence of notching that extends beneath the baseplate was higher with the Tornier prosthesis than the Zimmer prosthesis (68% vs 33%, P ¼ .002), primarily because of a difference between the Tornier and Zimmer R groups (P ¼ .006). The Zimmer R group showed the
Scapular notching by glenosphere position, primary versus revision procedure, and diagnosis Glenosphere position At (n ¼ 23)
New grade 0, none 1, mild/moderate 2, severe Median new grade New grade severity Low grade (0-1) High grade (2) Baseplate involvement A (no) B (yes) Sirveaux grade 0 1 2 3 4 Median Sirveaux grade Sirveaux grade severity Low grade (0-2) High grade (3-4)
Procedure
Below (n ¼ 65)
P value
Primary (n ¼ 68)
Diagnosis Revision (n ¼ 20)
.106 2 (9%) 15 (65%) 6 (26%) 1
19 (29%) 33 (51%) 13 (20%) 1
17 (74%) 6 (26%)
52 (80%) 13 (20%)
16 (24%) 37 (54%) 15 (22%) 1
16 (80%) 4 (20%)
53 (78%) 15 (22%)
2 (9%) 9 (39%) 5 (22%) 3 (13%) 4 (17%) 2
19 (29%) 27 (42%) 9 (14%) 8 (12%) 2 (3%) 1
6/15 (40%) 9/15 (60%)
26/52 (50%) 26/52 (50%) 16 30 8 9 5 1
(24%) (44%) (12%) (13%) (7%)
.129 55 (85%) 10 (15%)
16 (24%) 37 (54%) 15 (22%) 1
25 (78%) 7 (22%)
44 (79%) 12 (21%)
.961
.431 9/22 (41%) 13/22 (59%)
23/45 (51%) 22/45 (49%)
10 (31%) 11 (34%) 6 (19%) 3 (9%) 2 (6%) 1
11 (20%) 25 (45%) 8 (14%) 8 (14%) 4 (7%) 1
.766 5 (25%) 6 (30%) 6 (30%) 2 (10%) 1 (5%) 1
.404
.569 17 (85%) 3 (15%)
54 (79%) 14 (21%)
P value .442
10 (31%) 15 (47%) 7 (22%) 1
.493
.012
16 (70%) 7 (30%)
Not CTA (n ¼ 32)
.843
.283 24/46 (52%) 22/46 (48%)
CTA (n ¼ 56)
.838 5 (25%) 11 (55%) 4 (20%) 1
.548
8/21 (38%) 13/21 (62%)
P value
Scapular notching and reverse shoulder arthroplasty design
Table III
.502 27 (84%) 5 (16%)
44 (79%) 12 (21%)
CTA, Cuff tear arthropathy.
1437
1438 highest prevalence of heterotopic ossification as compared with the Zimmer N and Tornier groups (94% vs 65% and 75%, respectively), but the difference between the Zimmer groups was the only comparison achieving statistical significance (P ¼ .047).
Glenosphere position versus notching Because superior positioning of the glenosphere has been shown to increase the risk of scapular notching, 5 patients with a glenosphere position above the inferior glenoid rim were excluded from this investigation. Analysis of scapular notching was then performed between patients with glenosphere position either at (n ¼ 23) or below (n ¼ 65) the inferior glenoid rim (Table III). The former group showed increased severity of notching, with a higher median notching grade (2 vs 1), with use of only the Sirveaux classification system (P ¼ .012). The prevalence of notching was also higher in this group (91% vs 71%), but this difference was not statistically significant (P ¼ .106). Glenosphere position had no significant effect on the incidence of high- versus low-grade notching with either grading system (P ¼ .129 for Sirveaux system and P ¼ .548 for novel system).
Discussion Scapular notching, a nearly ubiquitous phenomenon after reverse shoulder arthroplasty, occurred in 76% of cases overall in our series; however, the prevalence and severity of severe notching were significantly influenced by prosthetic design. The Tornier group showed the highest prevalence of notching, the highest prevalence of high-grade notching, and the highest median notching grade compared with the Zimmer N and Zimmer R groups. In addition, the Tornier group had the highest prevalence of notching that involved the glenoid baseplate. These differences were observed despite consistent surgical technique, implicating prosthetic design with the development of notching. The increased neck-shaft angle (valgus inclination) of the Tornier humeral component may account for the increased prevalence and severity of notching in this group as compared with the Zimmer N group. However, the fact that notching in both the Zimmer R and Zimmer N groups was less than that of the Tornier group challenges this assumption, because the Zimmer neck-shaft angle, when assembled with the retentive polyethylene liner, is equivalent to that of the Tornier implant. This suggests that perhaps the more significant notching associated with the Tornier implant may be multifactorial. As described previously, the geometry of the polyethylene liners differs among implant designs. Moreover, previous studies have shown that notching is a 3-dimensional phenomenon that occurs not only inferiorly but also posteriorly.21,26 Therefore, the difference between the Tornier and Zimmer groups
M.S. Kowalsky et al. may have resulted in part from an angulated polyethylene insert that mitigates the occurrence of notching. Furthermore, a difference exists in the glenoid implant design of the Tornier and Zimmer prostheses. With the Zimmer implant, the glenosphere does not sit flush with the baseplate; that is, when the Morse taper is fully engaged, there is 2.5 mm of lateral offset. In contrast, the Tornier glenosphere has no appreciable lateral offset relative to the baseplate. This increase in lateral offset may explain in part the decreased notching observed with the Zimmer prostheses. The findings of this investigation are consistent with those of a similar study by Kempton et al.18 They compared the incidence and severity of notching using the same 2 implant designs with minimum 1-year follow-up; however, they did not distinguish between groups of patients who received a Zimmer implant with a nonretentive versus a retentive liner. Their investigation confirmed increased incidence and severity of notching associated with the Tornier implant design, with a neckshaft angle of 155 and no lateral offset of the glenosphere. Our study also examined the impact of diagnosis and glenosphere position on the prevalence of scapular notching. We did not discover an increased prevalence or severity of notching in patients treated with reverse shoulder arthroplasty for cuff tear arthropathy. This finding contrasts with findings of previous studies.1,21 In accordance with previous studies, decreased prevalence and severity of notching were observed when the glenosphere was placed below the inferior glenoid rim. Nyffeler et al24 confirmed the importance of glenoid component insertion technique on the development of scapular notching. In their investigation using cadaveric shoulder specimens, the authors showed that the highest adduction angles were achieved with glenosphere placement below the inferior glenoid. They concluded that these improved adduction angles theoretically decrease the risk of notching by avoiding impingement of the humeral component on the lateral pillar of the scapula. These findings have been supported in clinical series.21 Simovitch et al26 similarly examined the consequences of surgical technique on the risk of scapular notching in a clinical series of 77 patients treated with reverse shoulder arthroplasty for cuff tear arthropathy or irreparable rotator cuff tear. This investigation underscored the importance of inferior placement of the glenoid component to avoid impingement with adduction and scapular notching. The results of our study support, though not fully, the notion that an inferior-positioned glenosphere can decrease the incidence and severity of scapular notching. However, high-grade notching was still evident in 15% to 20% of shoulders with a glenosphere positioned below the glenoid rim. Perhaps the most comprehensive examination to date of those factors relevant to the development of scapular notching was offered by Gutierrez et al.14 In a biomechanical study, they analyzed the impact of several surgical and implant-related factors on the risk of scapular notching.
Scapular notching and reverse shoulder arthroplasty design
1439
This study confirms that inferior glenoid position and inferior tilt serve to avoid adduction range-of-motion deficits, which theoretically decreases the risk of notching. In addition, glenoid implant design influences the risk of notching. Larger-diameter glenospheres and those that increase lateral offset both serve to increase impingementfree adduction, thus mitigating the risk of notching. This has been confirmed in other biomechanical and clinical reports.6-9,14,15 However, earlier implant designs that lateralize the center of rotation beyond the glenoid face have been associated with catastrophic loosening due to inadequate fixation to withstand the significant shear force exerted on the implant.6,13 Novel glenosphere designs have evolved in an attempt to further diminish the risk of scapular notching. For example, eccentric implants with increased overhang beyond the inferior glenoid rim or those with inferior extension beneath the inferior pillar have been introduced to increase impingement-free adduction.7 An investigation by Gutierrez et al16 was the first to directly examine the importance of humeral component design on adduction deficits and theoretic notching risk. In fact, this study showed that humeral neck-shaft angle was the single most important parameter influencing impingement-free adduction range of motion. An adduction deficit of 5.8 associated with a neck-shaft angle of 130 increased to 36.9 associated with a neck-shaft angle of 170 . Moreover, when examined in conjunction with other relevant factors (such as inferior glenoid position, inferior glenoid tilt, lateral offset of glenosphere, and large glenosphere), it was impossible to avoid inferior impingement with a 170 neckshaft angle by manipulating the other parameters. It appears from our data that when one is using the Zimmer arthroplasty system, a retentive liner can be used when needed for stability without a significant increased risk of scapular notching. There were no differences in the median notching grade or the severity of high-grade notching between the Zimmer prosthesis with a retentive liner and the Zimmer prosthesis with a nonretentive liner. If inclination angle alone was responsible for the development of scapular notching, one would think that the Zimmer R shoulders would be associated with similar rates of notching to the Tornier implant (both angled 65 valgus). However, other design parameters such as the geometry of the polyethylene liner and the slightly increased lateral offset of the glenosphere may mitigate inferior notching to some degree. In addition, it appears that the pattern of notching with the retentive liner is different as well, given that the majority of notching was more medial (not involving the baseplate) in the retentive group as compared with the nonretentive group. However, the inferior impingement associated with the retentive liner did result in a greater incidence of heterotopic bone formation inferior to the scapular neck. The clinical significance of this finding is unknown, and caution should be used when assessing differences in the retentive and nonretentive liner groups because our study may be underpowered to draw conclusions.
This study has some inherent weaknesses. First, it is a retrospective review, which may introduce selection bias among groups. However, with the exception of a small difference in patient age, the distribution of diagnosis and revision surgery status were similar among groups. Furthermore, the duration of follow-up varied slightly among groups, and this difference was statistically significant. Importantly, however, we believe that the minimum 1-year follow-up period for this radiographic study is justified, because 2 previous studies have shown that scapular notching appeared at a mean of 4.5 months postoperatively and did not progress after 1 year in the majority of cases.24,26 The study period may have included a learning curve for each participating surgeon. This may have introduced bias that might have contributed to the increased prevalence and severity of notching of the implant used early in the study period. However, attempts were made to mitigate the effect of the learning curve by controlling those aspects of technique that might have contributed to notching, such as the coronal position of the glenosphere. This study is also limited because we examined only radiographic outcomes with no attempted correlation to functional outcomes. The clinical implications of scapular notching remain controversial. Whereas certain studies have shown a relationship between notching and poor clinical outcomes,26,28 others have failed to confirm this relationship.1,21,24 Certainly, further study with longterm follow-up is warranted to elucidate the clinical relevance of this phenomenon. A fundamental strength of this radiographic investigation lies in the novel classification system for scapular notching described and applied herein. The weaknesses of previously described classification systems, in our opinion, have been minimized in the development of this novel grading system. First, any subjective criteria, such as interpretation of the chronicity or stability of the lesion, have been eliminated. Second, the novel grading system references the constant central peg rather than the variable position of the inferior screw. Third, the novel system recognizes that baseplate involvement is an independent phenomenon that is addressed with a qualifier in grading scapular notching. This novel grading system showed substantial interobserver reliability that is, at a minimum, comparable to that of the commonly used Sirveaux classification system. Further studies are needed to validate this classification system and further define its clinical applicability.
Conclusions A higher incidence and severity of notching were observed with the Tornier reverse arthroplasty compared with the Zimmer reverse arthroplasty at short-term follow-up. These findings may be because of the different morphology of the polyethylene component
1440 (despite equal varus/valgus inclination angle between systems) and/or differences in glenosphere offset between the prosthetic systems. The use of a retentive polyethylene liner with a more valgus angle of inclination did not influence scapular notching with the Zimmer implant. We found no influence of diagnosis on scapular notching; however, the incidence of notching was decreased when the glenosphere was positioned below the glenoid rim. A novel classification system of scapular notching that takes into account the location of scapular notching in relation to (adjacent to or separate from) the glenoid baseplate should be considered and has been shown to have substantial interobserver agreement. In addition to surgical technique, consideration should be given to prosthesis design in mitigating the risk of scapular notching.
Disclaimer The authors, their immediate families, and any research foundations with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.
References 1. Boileau P, Watkinson D, Hatzidakis AM, Havorka I. Neer Award 2005: the Grammont reverse shoulder prosthesis: results in cuff tear arthritis, fracture sequelae, and revision arthroplasty. J Shoulder Elbow Surg 2006;15:527-40. doi:10.1016/j.jse.2006.01.003 2. Boileau P, Watkinson DJ, Hatzidakis AM, Balg F. Grammont reverse prosthesis: design, rationale, and biomechanics. J Shoulder Elbow Surg 2005;14:147S-61S. doi:10.1016/j.jse.2004.10.006 3. Bufquin T, Hersan A, Hubert L, Massin P. Reverse shoulder arthroplasty for the treatment of three- and four-part fractures of the proximal humerus in the elderly: a prospective review of 43 cases with a short-term follow-up. J Bone Joint Surg Br 2007;89:516-20. doi:10. 1302/0301-620X.89B4.18435 4. Cazeneuve JF, Cristofari DJ. The reverse shoulder prosthesis in the treatment of fractures of the proximal humerus in the elderly. J Bone Joint Surg Br 2010;92:535-9. doi:10.1302/0301-620X.92B4.224506 5. Cazeneuve JF, Cristofari DJ. Delta III reverse shoulder arthroplasty: radiological outcome for acute complex fractures of the proximal humerus in elderly patients. Orthop Traumatol Surg Res 2009;95:3259. doi:10.1016/j.otsr.2009.03.018 6. Chacon A, Virani N, Shannon R, Levy JC, Pupello D, Frankle M. Revision arthroplasty with use of a reverse shoulder prosthesisallograft composite. J Bone Joint Surg Am 2009;91:119-27. doi:10. 2106/JBJS.H.00094 7. Chou J, Malak SF, Anderson IA, Astley T, Poon PC. Biomechanical evaluation of different designs of glenospheres in the SMR reverse total shoulder prosthesis: range of motion and risk of scapular notching. J Shoulder Elbow Surg 2009;18:354-9. doi:10.1016/j.jse. 2009.01.015
M.S. Kowalsky et al. 8. Cuff D, Pupello D, Virani N, Levy J, Frankle M. Reverse shoulder arthroplasty for the treatment of rotator cuff deficiency. J Bone Joint Surg Am 2008;90:1244-51. doi:10.2106/JBJS.G.00775 9. de Wilde LF, Poncet D, Middernacht B, Ekelund A. Prosthetic overhang is the most effective way to prevent scapular conflict in a reverse total shoulder prosthesis. Acta Orthop 2010;81:719-26. doi:10.3109/ 17453674.2010.538354 10. Gallinet D, Clappaz P, Garbuio P, Tropet Y, Obert L. Three or four parts complex proximal humerus fractures: hemiarthroplasty versus reverse prosthesis: a comparative study of 40 cases. Orthop Traumatol Surg Res 2009;95:48-55. doi:10.1016/j.otsr.2008.09.002 11. Grammont PM, Baulot E. Delta shoulder prosthesis for rotator cuff rupture. Orthopedics 1993;16:65-8. 12. Grammont PM, Trouilloud P, Laffay JP. Etude et realisationd’une novelle prothese d’epaule. Rhumatologie 1987;39:17-22. 13. Guery J, Favard L, Sirveaux F, Oudet D, Mole D, Walch G. Reverse total shoulder arthroplasty. Survivorship analysis of eighty replacements followed for five to ten years. J Bone Joint Surg Am 2006;88: 1742-7. doi:10.2106/JBJS.E.00851 14. Gutierrez S, Comiskey CA IV, Luzzo ZP, Pupello DR, Frankle MA. Range of impingement-free abduction and adduction deficit after reverse shoulder arthroplasty. Hierarchy of surgical and implantdesign-related factors. J Bone Joint Surg Am 2008;90:2606-15. doi: 10.2106/JBJS.H.00012 15. Gutierrez S, Levy JC, Frankle MA, Cuff D, Keller TS, Pupello DR, et al. Evaluation of abduction range of motion and avoidance of inferior scapular impingement in a reverse shoulder model. J Shoulder Elbow Surg 2008;17:608-15. doi:10.1016/j.jse.2007.11.010 16. Gutierrez S, Levy JC, Lee WE III, Keller TS, Maitland ME. Center of rotation affects abduction range of motion of reverse shoulder arthroplasty. Clin Orthop Relat Res 2007;458:78-82. doi:10.1097/ BLO.0b013e31803d0f57 17. John M, Pap G, Angst F, Flury MP, Lieske S, Schwyzer HK, et al. Short-term results after reversed shoulder arthroplasty (Delta III) in patients with rheumatoid arthritis and irreparable rotator cuff tear. Int Orthop 2010;34:71-7. doi:10.1007/s00264-009-0733-1 18. Kempton LB, Balasubramaniam M, Ankerson E, Wiater JM. A radiographic analysis of the effects of prosthesis design on scapular notching following reverse total shoulder arthroplasty. J Shoulder Elbow Surg 2011;20:571-6. doi:10.1016/j.jse.2010.08.024 19. Klein M, Juschka M, Hinkenjann B, Scherger B, Ostermann PA. Treatment of comminuted fractures of the proximal humerus in elderly patients with the Delta III reverse shoulder prosthesis. J Orthop Trauma 2008;22:698-704. doi:10.1097/BOT.0b013e31818afe40 20. Landis JR, Koch GG. The measurement of observer agreement for categorical data. Biometrics 1977;33:159-74. 21. Levigne C, Boileau P, Favard L, Garaud P, Mole D, Sirveaux F, et al. Scapular notching in reverse shoulder arthroplasty. J Shoulder Elbow Surg 2008;17:925-35. doi:10.1016/j.jse.2008.02.010 22. McFarland EG, Sanguanjit P, Tasaki A, Keyurapan E, Fishman EK, Fayad LM. The reverse shoulder prosthesis: a review of imaging features and complications. Skeletal Radiol 2006;35:488-96. doi:10. 1007/s00256-006-0109-1 23. Middernacht B, De Roo PJ, Van Maele G, de Wilde LF. Consequences of scapular anatomy for reversed total shoulder arthroplasty. Clin Orthop Relat Res 2008;466:1410-8. doi:10.1007/s11999-008-0187-6 24. Nyffeler RW, Werner CM, Gerber C. Biomechanical relevance of glenoid component positioning in the reverse Delta III total shoulder prosthesis. J Shoulder Elbow Surg 2005;14:524-8. doi:10.1016/j.jse. 2004.09.010 25. Parsons BO, Gruson KI, Accousti KJ, Klug RA, Flatow EL. Optimal rotation and screw positioning for initial glenosphere baseplate fixation in reverse shoulder arthroplasty. J Shoulder Elbow Surg 2009;18: 886-91. doi:10.1016/j.jse.2008.11.002 26. Simovitch RW, Zumstein MA, Lohri E, Helmy N, Gerber C. Predictors of scapular notching in patients managed with the Delta III reverse
Scapular notching and reverse shoulder arthroplasty design total shoulder replacement. J Bone Joint Surg Am 2007;89:588-600. doi:10.2106/JBJS.F.00226 27. Sirveaux F. La prothese de Grammont dans le traitement des arthropathies de l’epaule a coiffe detruite. A propos d’une serie mulicentrique de 42 cas. Nancy: L’Universite de Nancy; Thesis; 1997. p. 245. 28. Sirveaux F, Favard L, Oudet D, Huquet D, Walch G, Mole D. Grammont inverted total shoulder arthroplasty in the treatment of glenohumeral osteoarthritis with massive rupture of the cuff. Results of a multicentre study of 80 shoulders. J Bone Joint Surg Br 2004;86: 388-95. doi:10.1302/0301-620X.86B3 29. Valenti PH, Boutens D, Nerot C. Delta 3 reversed prosthesis for osteoarthritis with massive rotator cuff tear: long term results (> 5 years). In: Walch G, Boileau P, Mole D, editors. 2000 Shoulder
1441 Prostheses: Two to Ten Year Follow-up. Montpellier: Sauramps Medical; 2001. p. 253-9. 30. Vanhove B, Beugnies A. Grammont’s reverse shoulder prosthesis for rotator cuff arthropathy. A retrospective study of 32 cases. Acta Orthop Belg 2004;70:219-25. 31. Werner CM, Steinmann PA, Gilbart M, Gerber C. Treatment of painful pseudoparesis due to irreparable rotator cuff dysfunction with the Delta III reverse-ball-and-socket total shoulder prosthesis. J Bone Joint Surg Am 2005;87:1476-86. doi:10.2106/JBJS.D.02342 32. Wierks C, Skolasky RL, Ji JH, McFarland EG. Reverse total shoulder replacement: intraoperative and early postoperative complications. Clin Orthop Relat Res 2009;467:225-34. doi:10.1007/s11999-0080406-1
www.elsevier.com/locate/ymse
The relationship between scapular notching and reverse shoulder arthroplasty prosthesis design Marc S. Kowalsky, MDa, Leesa M. Galatz, MDb, Derek S. Shia, MDc, Karen Steger-May, MAd, Jay D. Keener, MDb,* a
Department of Orthopaedic Surgery, Lenox Hill Hospital, Park Lenox Orthopaedics, New York, NY, USA Department of Orthopaedic Surgery, Washington University, St. Louis, MO, USA c The Portland Clinic, Portland, OR, USA d Division of Biostatistics, Washington University, St. Louis, MO, USA b
Background: Inferior scapular notching is a common radiographic complication of reverse shoulder arthroplasty. The purpose of this study is to determine the impact of prosthesis design on the incidence and severity of notching. Materials and methods: Eighty-eight patients (mean age, 72 years) who underwent reverse shoulder arthroplasty with a minimum of 12 months’ follow-up (mean, 31 months) were retrospectively reviewed. Patients were grouped based on prosthesis design: Tornier (Stafford, TX, USA) (45%), Zimmer (Warsaw, IN, USA) with a nonretentive liner (35%), and Zimmer with a retentive liner (19%). Notching on final radiographs was graded by use of the Sirveaux classification system and a novel classification system. Results: The incidence of notching was significantly higher with the Tornier prosthesis (92%) compared with the Zimmer prosthesis with nonretentive liners (58%) and retentive liners (71%) (P < .05). The incidence of high-grade notching and the median grade were significantly higher with the Tornier prosthesis compared with the Zimmer prosthesis (P < .05). By use of the novel grading system, there was a higher incidence of notching involving the baseplate with the Tornier prosthesis (68%) compared with the Zimmer prosthesis (33%) (P < .05). The addition of a retentive liner was not associated with greater notching than a nonretentive liner for the Zimmer implant. Diagnosis had no significant influence on notching. Conclusions: A higher incidence and severity of notching were observed with the Tornier reverse arthroplasty compared with the Zimmer reverse arthroplasty at short-term follow-up. These findings may be because of the different morphology of the polyethylene component and/or differences in glenosphere offset between the prosthetic systems. In addition to surgical technique, consideration should be given to prosthesis design in mitigating the risk of scapular notching. Level of evidence: Level III, Case-Control Design, Treatment Study. Ó 2012 Journal of Shoulder and Elbow Surgery Board of Trustees. Keywords: Reverse arthroplasty; scapular notching; notching; shoulder arthroplasty; implant
Institutional review board approval: Washington University (08-1130). *Reprint requests: Jay D. Keener, MD, Department of Orthopaedic Surgery, Washington University, 660 S Euclid Ave, CB 8233, St. Louis, MO 63110, USA. E-mail address: [email protected] (J.D. Keener).
Scapular notching is by far the most common complication of reverse shoulder arthroplasty; yet, its etiology and clinical significance remain controversial. Notching occurs with alarmingly high frequency in most reported series but is not consistently associated with failure of the
1058-2746/$ - see front matter Ó 2012 Journal of Shoulder and Elbow Surgery Board of Trustees. doi:10.1016/j.jse.2011.08.051
Scapular notching and reverse shoulder arthroplasty design
1431
glenosphere.1,3-5,10,17,19,22,27-30,32 Multiple biomechanical and cadaveric studies have focused on the influence of glenoid placement and surgical technique on the development of notching, leading to the nearly universal principles of inferior glenosphere positioning with some inferior tilt.14,23,25 This ideology assumes that notching occurs as a result of adduction impingement. More recently, notching has been recognized as a 3-dimensional phenomenon, with acknowledgment of the possible rotational impingement that occurs between the liner and the scapular neck.21,26 Regardless, the ideal surgical parameters to minimize notching and a reliable classification system have not been established. Essential elements of modern reverse arthroplasty designs include a center of rotation that is translated distal and medial to improve the lever arm of the deltoid and recruit more deltoid fibers for glenohumeral elevation.11,12 The medialized center of rotation also localizes the shear force on the glenoid component to the glenoid face at the point of fixation, which mitigates the risk of glenosphere failure.2 These innovations have led to improved functional outcomes and survivorship in comparison to earlier constrained and semiconstrained reverse implant designs.6,8,13,24,28,30 Whereas a medialized center of rotation is one of the hallmarks of most contemporary reverse shoulder arthroplasty designs essential to their success, this feature comes at a cost. Medialization of the glenosphere decreases the surface arc of motion, resulting in impingement of the humeral component on the inferior scapular neck. This in turn results in scapular notching, or characteristic bone loss along the inferior scapular neck at the location of impingement. Scapular notching is commonly reported in association with implant designs with a medialized center of rotation, with a prevalence as high as 96%.31 Conflicting reports exist in the literature regarding the relationship between notching and functional outcomes.1,21,26,28 Furthermore, whereas a theoretic concern exists that notching may lead to catastrophic glenosphere baseplate loosening, no definitive association thereof has yet been established. Most published studies of reverse shoulder arthroplasty rely on 2 commonly used classification systems for scapular notching, offered by Nerot and colleagues29 and Sirveaux et al.27,28 However, several fundamental problems exist with these grading systems. The Nerot classification system attempts to distinguish between notching that involves only the lateral pillar (grade 1) and notching that involves the lateral pillar with ‘‘condensation’’ indicating stability (grade 2). This subjective interpretation potentially undermines the reliability of this grading system. Furthermore, both classification schemes grade severity of notching in reference to the position of the inferior screw. However, the optimal technique for screw insertion has changed over time. Initially, it was advocated to direct the inferior screw with caudal orientation down the lateral pillar to maximize screw depth. Recent literature has shown that optimal inferior screw orientation should instead be
more horizontal, maximizing screw length and bony purchase.25 Furthermore, with variable-angle screws, this is not a consistent landmark either among patients or among surgeons. Therefore, the ideal classification system should be independent of the trajectory of the inferior screw. Lastly, in both classification systems, notching that extends beneath the baseplate qualifies as a distinct grade (grade 4). However, the size and location of the notch relative to the baseplate are independent phenomena and should thus be addressed independently. The purpose of this study is to investigate the impact of prosthesis design on the prevalence and severity of notching using 2 different implant designs. In addition, the influence of factors such as glenosphere position and revision surgery on scapular notching was examined. Lastly, an alternative classification system that is independent of inferior screw position is described and analyzed in this investigation.
Materials and methods Inclusion and exclusion criteria We identified 175 consecutive patients who underwent a reverse shoulder arthroplasty in 179 shoulders by 1 of 3 fellowship-trained shoulder and elbow surgeons (K.Y., L.M.G., and J.D.K.) from July 2004 until January 2008. Of these patients, 107 who had been followed up for at least 12 months postoperatively with radiographs were considered for this investigation. Exclusion criteria included inadequate or poor-quality radiographs (7 patients), glenosphere failure (1 patient with early postoperative glenoid vault fracture treated nonoperatively), intraoperative or postoperative conversion to hemiarthroplasty (1 patient with inadequate bone stock for glenosphere placement and 2 with intraoperative glenoid fracture during glenoid preparation), or postoperative instability requiring conversion from nonretentive to retentive polyethylene liners (3 patients). Because glenosphere positioning has been shown to be an independent risk factor for notching, patients were also excluded if the glenosphere was implanted above the level of the inferior glenoid rim (5 patients). A total of 88 patients participated in the study. The mean age of the patients at the time of surgery was 72 9 years (range, 42-88 years). The mean age was 74.1 8 years for patients treated with the Tornier prosthesis (Stafford, TX, USA) and 70.6 10 years for patients treated with the Zimmer prosthesis (Warsaw, IN, USA) (68.7 11 years for Zimmer prosthesis with nonretentive liner [Zimmer N] and 74.0 7 years for Zimmer prosthesis with retentive liner [Zimmer R]) (Table I). Overall, age was not statistically different between the Tornier and Zimmer groups (P ¼ .164); however, there was a statistically significant difference between the Tornier and Zimmer N groups (P ¼ .013). The mean duration of follow-up was 31 12 months (range, 12-68 months). Mean follow-up for the Tornier and Zimmer groups was 2.9 1.3 years and 2.2 0.6 years, respectively (2.3 0.7 years for Zimmer N and 1.9 0.5 years for Zimmer R). This difference was statistically significant, primarily because of the difference between the Tornier and Zimmer R groups (P ¼ .002). There were 38 men (43%) and 50 women (57%). The
1432 Table I
M.S. Kowalsky et al. Subject characteristics by implant design P value for 2-group comparison
P value for 3-group comparison
17 74.0 7
P ¼ .164
2.3 0.7
1.9 0.5
P ¼ .002 P ¼ .754
P ¼ .030 Tornier vs Zimmer N, P ¼ .013 Zimmer N vs Zimmer R, P ¼ .052 P ¼ .006 Tornier vs Zimmer R, P ¼ .002 P ¼ .900
20 1 1 3 1 1 1 3
10 0 2 2 1 0 2 0
P ¼ .868
P ¼ .735
Tornier
Zimmer
Zimmer N
Zimmer R
N Age at surgery (y)
40 74.1 8
48 70.6 10
31 68.7 11
Follow-up (y)
2.9 1.3
2.2 0.6
26 1 1 6 1 1 2 2
30 1 3 5 2 1 3 3
Diagnosis CTA Failed hemi for arthritis Failed hemi for CTA Failed hemi for fracture Failed TSA Irreparable RCT Proximal humeral fx Proximal humeral fx sequelae Primary/revision Revision Primary
(65%) (2.5%) (2.5%) (15%) (2.5%) (2.5%) (5%) (5%)
9 (22%) 31 (78%)
(62%) (2%) (6%) (10%) (4%) (2%) (6%) (6%)
11 (23%) 37 (77%)
(65%) (3%) (3%) (10%) (3%) (3%) (3%) (10%)
6 (19%) 25 (81%)
(59%) (12%) (12%) (6%) (12%)
5 (29%) 12 (71%)
CTA, Cuff tear arthropathy; hemi, hemiarthroplasty; TSA, total shoulder arthroplasty; RCT, rotator cuff tear; fx, fracture.
primary diagnoses in these patients included the following: cuff tear arthropathy (56 patients [64%]), failed hemiarthroplasty for fracture (11 patients [13%]), proximal humeral fracture nonunion or malunion (5 patients [6%]), acute proximal humeral fracture (5 patients [6%]), failed hemiarthroplasty for cuff tear arthropathy (4 patients [5%]), failed total shoulder arthroplasty (3 patients [3%]), irreparable rotator cuff tear (2 patients [2%]), and failed hemiarthroplasty for arthritis (2 patients [2%]). For 68 patients (77%), the reverse shoulder arthroplasty was the primary procedure, whereas 20 patients (23%) had undergone previous procedures. There was no significant difference among groups with respect to the distribution of diagnoses or the percentage of patients in each group who had undergone previous procedures. The Tornier Aequalis Reversed Shoulder was used in 40 patients (45%) until December 2007 (Fig. 1). Beginning in May 2006, the Zimmer Trabecular Metal Reverse Shoulder System was used in 48 patients (55%). Of these patients, 31 (65%) received a nonretentive humeral polyethylene liner and 17 received a retentive liner (35%).
metaphyseal geometry with trabecular metal surface coating. The diameter of the metaphyseal portion is 41 mm. The angle of inclination of the humeral component is 53 , and this increases to 60 with a nonretentive liner and to 65 with a retentive liner. Therefore, there is some angulation built into the liner itself. Importantly, the polyethylene liner is not symmetric around the circumference. The medial aspect has maximum thickness, with decreasing thickness as it traverses laterally. This design feature may have significant implications in notching because of rotational impingement. Both the Tornier and Zimmer prostheses implement a hemispherical glenosphere design. In this study, only 36-mm-diameter glenospheres were used. When considering the glenosphereetoe glenoid baseplate Morse taper relationship, there is potentially a significant design difference between the two systems: a 2.5-mm lateral offset is seen with the Zimmer implant compared with no offset with the Tornier system.
Surgical technique Implant design Both the Tornier and Zimmer reverse arthroplasty designs implement a glenoid component design with a medialized center of rotation. For both systems, the humeral prostheses are cobaltchrome implants with a fluted distal geometry (Fig. 1). The Tornier Aequalis Reversed Shoulder humeral prosthesis has a conical metaphyseal geometry with a smooth metal surface finish. The diameter of the metaphyseal component is either 36 or 42 mm, depending on glenosphere size. The angle of inclination is 65 and does not change with the addition of the polyethylene liner. That is, the liner is symmetric around its entire circumference, without any angulation built into the liner itself. The Zimmer Trabecular Metal Reverse Shoulder System humeral prosthesis has a conical
All procedures were performed with the patient in the beach-chair position under general anesthesia with or without regional anesthesia. A deltopectoral approach was used in all but 2 cases, in which an anterosuperior transdeltoid approach was used. The proximal 1 to 2 cm of pectoralis major tendon was released to improve exposure. A biceps tenotomy was performed if the tendon was still present within the joint. The subscapularis tendon, if intact, was released from the lesser tuberosity. The humeral osteotomy was performed to establish between 0 and 20 of retroversion, depending on the integrity of the posterior rotator cuff. The prosthesis was placed in 0 of retroversion if the teres minor was absent as evidenced by a positive hornblower’s sign on physical examination. All other prostheses were placed in 20 of
Scapular notching and reverse shoulder arthroplasty design
1433
Figure 1 Implant designs: Tornier Aequalis Reversed Shoulder (A), Zimmer Trabecular Metal Reverse Shoulder System (B), Zimmer nonretentive polyethylene liner with 60 angle of inclination (C), and Zimmer retentive polyethylene liner with 65 angle of inclination (D). retroversion. Alignment rods defining 0 and 20 of retroversion were placed into the humeral cutting guide, proximal metaphyseal reamers, and stem inserter to ensure appropriate version. Glenoid exposure was facilitated with aggressive anterior and inferior capsular releases, with care taken to identify and protect the axillary nerve. The origin of the long head of the triceps brachii was released and the inferior capsulolabral tissue was excised to ensure inferior placement of the glenoid baseplate. A drill guide was used to place a guidewire to allow baseplate insertion flush with the inferior glenoid rim. During placement of the guidewire, inferior tilt of 5 to 10 relative to the horizontal was established to allow inferior tilt of the baseplate during glenoid preparation and implant insertion. In addition, preoperative axial imaging assisted in determination of the required correction to establish acceptable glenoid version. The Tornier Aequalis Reversed Shoulder allowed placement of 4 nonlocking glenoid screws, whereas the Zimmer Trabecular Metal Reverse Shoulder System allowed placement of 2 screws stabilized with locking caps (Fig. 1). With all implants, the superior screw was angled cephalad and anterior toward the coracoid base. Initially, the inferior screw was angled caudad in line with the inferior pillar. However, over
time, the technique evolved with placement of the inferior screw more perpendicular to the baseplate. A 36-mm glenosphere was used in all cases. The humeral stem was inserted with antibioticimpregnated bone cement. A polyethylene humeral insert of sufficient thickness was chosen to establish appropriate stability of the prosthesis. If necessary, a spacer was placed between the humeral stem and polyethylene liner to enhance longitudinal stability. Once it became commercially available with the Zimmer system, a retentive liner with an angle of inclination of 65 (155 in reference to the long axis of the humerus) was used at the surgeon’s discretion, to improve stability without increasing humeral length. The subscapularis tendon or its remnant was repaired to the medial aspect of the lesser tuberosity when sufficient tissue was present. A suction drain for self-suctioning was placed in the subdeltoid space in all patients. The operative extremity was immobilized in a sling with an abduction pillow. Patients did not receive any physical therapy, nor were they permitted any shoulder motion, for the first 2 to 4 weeks. They were, however, encouraged to remove the sling 3 times daily for elbow, wrist, and finger motion. After 2 to 4 weeks, the patients were instructed
1434
Figure 2 Sirveaux classification system: grade 1 notching involves only the lateral pillar (a), grade 2 notching contacts the inferior screw (b), grade 3 notching extends beyond the inferior screw (c), and grade 4 notching extends under the baseplate (d). with regard to a home exercise program consisting primarily of active-assisted forward elevation.
Patient evaluation The patients were evaluated at a minimum of 12 months postoperatively with anteroposterior, true anteroposterior, scapular lateral, and axillary lateral radiographs of the operative shoulder. Only the radiographs obtained at latest follow-up evaluation were examined for study purposes. The initial postoperative radiographs were available for reference to evaluate initial baseplate position relative to the scapular neck. Radiographs were evaluated by 3 observers (2 fellowship-trained shoulder and elbow surgeons [J.D.K. and L.M.G.] and 1 shoulder and elbow surgery fellow [M.S.K.]) for scapular notching. The degree of scapular notching was graded according to the system of Sirveaux et al27,28 (Fig. 2). According to this classification system, grade 1 notching involves only the lateral pillar, grade 2 notching contacts the inferior screw, grade 3 notching extends beyond the inferior screw, and grade 4 notching extends beneath the baseplate. Radiographs were also interpreted by use of a novel classification system that references the size of the notch relative to the central peg, which is not variable (Fig. 3). Accordingly, the maximum height of the notch from the inferior pillar is measured (notch height [NH]) and compared with the distance from the inferior pillar to the central peg at that location (pillar-to-peg distance [PPD]). Grade 0 indicates no notching, grade 1 indicates notching in which the
M.S. Kowalsky et al.
Figure 3 Novel classification system: grade 1 indicates notching in which the ratio of NH (a) to PPD (b) is less than two-thirds, and grade 2 indicates notching in which the NH-PPD ratio is two-thirds or greater. The dotted line indicates notching that does not involve the baseplate (type A), and the solid line indicates notching that involves the baseplate (type B).
NH-PPD ratio is less than two-thirds, and grade 2 indicates notching in which the NH-PPD ratio is greater than or equal to two-thirds (Fig. 4). Notching was then examined to determine whether it also contacted the baseplate (type A, does not contact baseplate; type B, does contact baseplate) (Fig. 5). In addition, the radiographs were examined for the presence of heterotopic ossification or osteophyte formation along the inferior glenoid.
Statistical analysis Inter-rater agreement for the Sirveaux and novel classification systems, as well as the presence of heterotopic ossification, was assessed with Cohen k coefficients and corresponding 95% confidence intervals (CIs). For variables measured on an ordered polytomous scale, weighted k values were reported. The weighted k is a refinement of the k coefficient that takes into account the magnitude of the disagreement between ratings. For data analysis, the consensus grading of at least 2 readers was used, with the exception of 1 case for which no consensus existed. In this case, all 3 readers reviewed the radiographs together, and a unanimous decision was made regarding the ultimate grading. Continuous variables (ie, age and length of followup) were compared across the 3 groups (Tornier, Zimmer N, and Zimmer R) via analysis of variance. When significant (P .05)
Scapular notching and reverse shoulder arthroplasty design
1435
Figure 4 Scapular notching according to novel classification system. (A) No scapular notching. (B) Grade 1 scapular notching with an NH-PPD ratio of less than two-thirds. (C) Grade 2 scapular notching with an NH-PPD ratio of two-thirds or greater.
Figure 5 Scapular notching and baseplate involvement. (A) Scapular notching that does not involve the baseplate (type A). (B) Scapular notching that does involve the baseplate (type B).
and within the analysis of variance model, statistical contrasts were used to compare (1) Tornier versus Zimmer N, (2) Tornier versus Zimmer R, (3) Zimmer N versus Zimmer R, and (4) Tornier versus all Zimmer. Binary and ordinal-scaled variables were compared across the 3 groups by generalized estimating equations. Binary outcomes were modeled with binomial probability distributions and logit link functions. Ordinal-scaled variables were modeled with a multinomial probability distribution and a cumulative logit link function to account for the ordering of the response categories. When significant (P .05) and within the generalized estimating equation model, statistical contrasts were used to compare (1) Tornier versus Zimmer N, (2) Tornier versus
Zimmer R, (3) Zimmer N versus Zimmer R, and (4) Tornier versus all Zimmer. Analyses were performed with SAS software, version 9.2, of the SAS System for Linux (SAS Institute, Cary, NC, USA).
Results Reliability Weighted k coefficients were calculated for the analysis of scapular notching using both the Sirveaux and novel
1436 Table II
M.S. Kowalsky et al. Scapular notching by implant design Tornier
New grade 0, none 1, mild/moderate 2, severe Median new grade New grade severity Low grade (0-1) High grade (2) Baseplate involvement A (no) B (yes) Sirveaux grade 0 1 2 3 4 Median Sirveaux grade Sirveaux grade severity Low grade (0-2) High grade (3-4) Heterotopic ossification No Yes
Zimmer
Zimmer N
Zimmer R
3 (8%) 24 (60%) 13 (32%) 1
18 (38%) 24 (50%) 6 (12%) 1
13 (42%) 14 (45%) 4 (13%) 1
5 (29%) 10 (59%) 2 (12%) 1
27 (68%) 13 (32%)
42 (88%) 6 (12%)
27 (87%) 4 (13%)
15 (88%) 2 (12%)
12/37 (32%) 25/37 (68%)
20/30 (67%) 10/30 (33%)
10/18 (56%) 8/18 (44%)
10/12 (83%) 2/12 (17%)
3 (8%)
18 (38%)
13 (42%)
5 (29%)
12 (30%) 10 (25%) 9 (22%) 6 (15%) 2
24 (50%) 4 (8%) 2 (4%) 0 1
14 (45%) 2 (6%) 2 (6%) 0 1
10 (59%) 2 (12%) 0 0 1
25 (62%) 15 (38%)
10 (25%) 30 (75%)
46 (96%) 2 (4%)
12 (25%) 36 (75%)
29 (94%) 2 (6%)
11 (35%) 20 (65%)
classification systems by the 3 observers on the radiographs of 88 shoulders. With the Sirveaux classification system, the weighted k coefficient was 0.69 (95% CI, 0.62-0.75), indicating substantial interobserver agreement according to the guidelines established by Landis and Koch.20 With the novel classification system, the weighted k coefficient for grade was 0.73 (95% CI, 0.65-0.80). The k coefficient for involvement of the baseplate was 0.70 (95% CI, 0.62-0.78). These values also indicate substantial interobserver agreement. For the presence of heterotopic ossification, the k coefficient was 0.68 (95% CI, 0.58-0.79).
Prosthesis type versus notching The overall prevalence of scapular notching was 76% by use of both the Sirveaux and novel classification systems (Table II). The prevalence of notching in the Tornier group was 92%, as compared with 62% in the Zimmer group (58% for Zimmer N and 71% for Zimmer R). The prevalence of notching was significantly higher in the Tornier group compared with both Zimmer groups (P ¼ .002), but there was no difference between Zimmer groups.
P value for 2-group comparison
P value for 3-group comparison
P ¼ .0007
P ¼ .001 Tornier vs Zimmer N, P ¼ .0009 Tornier vs Zimmer R, P ¼ .026
P ¼ .024
P ¼ .074
P ¼ .002
P ¼ .005 Tornier vs Zimmer R, P ¼ .006
P < .0001
P < .0001 Tornier vs Zimmer N, P < .0001 Tornier vs Zimmer R, P ¼ .0002
P < .0001
P < .0001 Tornier vs Zimmer N, P ¼ .007 Tornier vs Zimmer R, P < .0001
P ¼ .349
P ¼ .048 Zimmer N vs Zimmer R, P ¼ .047
17 (100%) 0
1 (6%) 16 (94%)
The prevalence of high-grade notching, as defined by Sirveaux grades 3 and 4 or novel grade 2, was significantly higher in the Tornier group (38% and 32%, respectively) as compared with the Zimmer group (4% and 12%, respectively) (P < .0001 and P ¼ .024, respectively). Although comparison among all 3 groups (Tornier, Zimmer N, and Zimmer R) showed only a trend toward significance based on the novel grading system (P ¼ .074), a significantly higher prevalence of high-grade notching was observed in the Tornier group compared with both the Zimmer N and Zimmer R groups based on the Sirveaux classification (P ¼ .007 and P < .0001, respectively), with no difference between Zimmer groups. Moreover, the median notching grade by use of the Sirveaux grading system was higher in the Tornier group (2), as compared with both the Zimmer N group (1) and Zimmer R group (1) (P < .0001 and P ¼ .0002, respectively). The prevalence of notching that extends beneath the baseplate was higher with the Tornier prosthesis than the Zimmer prosthesis (68% vs 33%, P ¼ .002), primarily because of a difference between the Tornier and Zimmer R groups (P ¼ .006). The Zimmer R group showed the
Scapular notching by glenosphere position, primary versus revision procedure, and diagnosis Glenosphere position At (n ¼ 23)
New grade 0, none 1, mild/moderate 2, severe Median new grade New grade severity Low grade (0-1) High grade (2) Baseplate involvement A (no) B (yes) Sirveaux grade 0 1 2 3 4 Median Sirveaux grade Sirveaux grade severity Low grade (0-2) High grade (3-4)
Procedure
Below (n ¼ 65)
P value
Primary (n ¼ 68)
Diagnosis Revision (n ¼ 20)
.106 2 (9%) 15 (65%) 6 (26%) 1
19 (29%) 33 (51%) 13 (20%) 1
17 (74%) 6 (26%)
52 (80%) 13 (20%)
16 (24%) 37 (54%) 15 (22%) 1
16 (80%) 4 (20%)
53 (78%) 15 (22%)
2 (9%) 9 (39%) 5 (22%) 3 (13%) 4 (17%) 2
19 (29%) 27 (42%) 9 (14%) 8 (12%) 2 (3%) 1
6/15 (40%) 9/15 (60%)
26/52 (50%) 26/52 (50%) 16 30 8 9 5 1
(24%) (44%) (12%) (13%) (7%)
.129 55 (85%) 10 (15%)
16 (24%) 37 (54%) 15 (22%) 1
25 (78%) 7 (22%)
44 (79%) 12 (21%)
.961
.431 9/22 (41%) 13/22 (59%)
23/45 (51%) 22/45 (49%)
10 (31%) 11 (34%) 6 (19%) 3 (9%) 2 (6%) 1
11 (20%) 25 (45%) 8 (14%) 8 (14%) 4 (7%) 1
.766 5 (25%) 6 (30%) 6 (30%) 2 (10%) 1 (5%) 1
.404
.569 17 (85%) 3 (15%)
54 (79%) 14 (21%)
P value .442
10 (31%) 15 (47%) 7 (22%) 1
.493
.012
16 (70%) 7 (30%)
Not CTA (n ¼ 32)
.843
.283 24/46 (52%) 22/46 (48%)
CTA (n ¼ 56)
.838 5 (25%) 11 (55%) 4 (20%) 1
.548
8/21 (38%) 13/21 (62%)
P value
Scapular notching and reverse shoulder arthroplasty design
Table III
.502 27 (84%) 5 (16%)
44 (79%) 12 (21%)
CTA, Cuff tear arthropathy.
1437
1438 highest prevalence of heterotopic ossification as compared with the Zimmer N and Tornier groups (94% vs 65% and 75%, respectively), but the difference between the Zimmer groups was the only comparison achieving statistical significance (P ¼ .047).
Glenosphere position versus notching Because superior positioning of the glenosphere has been shown to increase the risk of scapular notching, 5 patients with a glenosphere position above the inferior glenoid rim were excluded from this investigation. Analysis of scapular notching was then performed between patients with glenosphere position either at (n ¼ 23) or below (n ¼ 65) the inferior glenoid rim (Table III). The former group showed increased severity of notching, with a higher median notching grade (2 vs 1), with use of only the Sirveaux classification system (P ¼ .012). The prevalence of notching was also higher in this group (91% vs 71%), but this difference was not statistically significant (P ¼ .106). Glenosphere position had no significant effect on the incidence of high- versus low-grade notching with either grading system (P ¼ .129 for Sirveaux system and P ¼ .548 for novel system).
Discussion Scapular notching, a nearly ubiquitous phenomenon after reverse shoulder arthroplasty, occurred in 76% of cases overall in our series; however, the prevalence and severity of severe notching were significantly influenced by prosthetic design. The Tornier group showed the highest prevalence of notching, the highest prevalence of high-grade notching, and the highest median notching grade compared with the Zimmer N and Zimmer R groups. In addition, the Tornier group had the highest prevalence of notching that involved the glenoid baseplate. These differences were observed despite consistent surgical technique, implicating prosthetic design with the development of notching. The increased neck-shaft angle (valgus inclination) of the Tornier humeral component may account for the increased prevalence and severity of notching in this group as compared with the Zimmer N group. However, the fact that notching in both the Zimmer R and Zimmer N groups was less than that of the Tornier group challenges this assumption, because the Zimmer neck-shaft angle, when assembled with the retentive polyethylene liner, is equivalent to that of the Tornier implant. This suggests that perhaps the more significant notching associated with the Tornier implant may be multifactorial. As described previously, the geometry of the polyethylene liners differs among implant designs. Moreover, previous studies have shown that notching is a 3-dimensional phenomenon that occurs not only inferiorly but also posteriorly.21,26 Therefore, the difference between the Tornier and Zimmer groups
M.S. Kowalsky et al. may have resulted in part from an angulated polyethylene insert that mitigates the occurrence of notching. Furthermore, a difference exists in the glenoid implant design of the Tornier and Zimmer prostheses. With the Zimmer implant, the glenosphere does not sit flush with the baseplate; that is, when the Morse taper is fully engaged, there is 2.5 mm of lateral offset. In contrast, the Tornier glenosphere has no appreciable lateral offset relative to the baseplate. This increase in lateral offset may explain in part the decreased notching observed with the Zimmer prostheses. The findings of this investigation are consistent with those of a similar study by Kempton et al.18 They compared the incidence and severity of notching using the same 2 implant designs with minimum 1-year follow-up; however, they did not distinguish between groups of patients who received a Zimmer implant with a nonretentive versus a retentive liner. Their investigation confirmed increased incidence and severity of notching associated with the Tornier implant design, with a neckshaft angle of 155 and no lateral offset of the glenosphere. Our study also examined the impact of diagnosis and glenosphere position on the prevalence of scapular notching. We did not discover an increased prevalence or severity of notching in patients treated with reverse shoulder arthroplasty for cuff tear arthropathy. This finding contrasts with findings of previous studies.1,21 In accordance with previous studies, decreased prevalence and severity of notching were observed when the glenosphere was placed below the inferior glenoid rim. Nyffeler et al24 confirmed the importance of glenoid component insertion technique on the development of scapular notching. In their investigation using cadaveric shoulder specimens, the authors showed that the highest adduction angles were achieved with glenosphere placement below the inferior glenoid. They concluded that these improved adduction angles theoretically decrease the risk of notching by avoiding impingement of the humeral component on the lateral pillar of the scapula. These findings have been supported in clinical series.21 Simovitch et al26 similarly examined the consequences of surgical technique on the risk of scapular notching in a clinical series of 77 patients treated with reverse shoulder arthroplasty for cuff tear arthropathy or irreparable rotator cuff tear. This investigation underscored the importance of inferior placement of the glenoid component to avoid impingement with adduction and scapular notching. The results of our study support, though not fully, the notion that an inferior-positioned glenosphere can decrease the incidence and severity of scapular notching. However, high-grade notching was still evident in 15% to 20% of shoulders with a glenosphere positioned below the glenoid rim. Perhaps the most comprehensive examination to date of those factors relevant to the development of scapular notching was offered by Gutierrez et al.14 In a biomechanical study, they analyzed the impact of several surgical and implant-related factors on the risk of scapular notching.
Scapular notching and reverse shoulder arthroplasty design
1439
This study confirms that inferior glenoid position and inferior tilt serve to avoid adduction range-of-motion deficits, which theoretically decreases the risk of notching. In addition, glenoid implant design influences the risk of notching. Larger-diameter glenospheres and those that increase lateral offset both serve to increase impingementfree adduction, thus mitigating the risk of notching. This has been confirmed in other biomechanical and clinical reports.6-9,14,15 However, earlier implant designs that lateralize the center of rotation beyond the glenoid face have been associated with catastrophic loosening due to inadequate fixation to withstand the significant shear force exerted on the implant.6,13 Novel glenosphere designs have evolved in an attempt to further diminish the risk of scapular notching. For example, eccentric implants with increased overhang beyond the inferior glenoid rim or those with inferior extension beneath the inferior pillar have been introduced to increase impingement-free adduction.7 An investigation by Gutierrez et al16 was the first to directly examine the importance of humeral component design on adduction deficits and theoretic notching risk. In fact, this study showed that humeral neck-shaft angle was the single most important parameter influencing impingement-free adduction range of motion. An adduction deficit of 5.8 associated with a neck-shaft angle of 130 increased to 36.9 associated with a neck-shaft angle of 170 . Moreover, when examined in conjunction with other relevant factors (such as inferior glenoid position, inferior glenoid tilt, lateral offset of glenosphere, and large glenosphere), it was impossible to avoid inferior impingement with a 170 neckshaft angle by manipulating the other parameters. It appears from our data that when one is using the Zimmer arthroplasty system, a retentive liner can be used when needed for stability without a significant increased risk of scapular notching. There were no differences in the median notching grade or the severity of high-grade notching between the Zimmer prosthesis with a retentive liner and the Zimmer prosthesis with a nonretentive liner. If inclination angle alone was responsible for the development of scapular notching, one would think that the Zimmer R shoulders would be associated with similar rates of notching to the Tornier implant (both angled 65 valgus). However, other design parameters such as the geometry of the polyethylene liner and the slightly increased lateral offset of the glenosphere may mitigate inferior notching to some degree. In addition, it appears that the pattern of notching with the retentive liner is different as well, given that the majority of notching was more medial (not involving the baseplate) in the retentive group as compared with the nonretentive group. However, the inferior impingement associated with the retentive liner did result in a greater incidence of heterotopic bone formation inferior to the scapular neck. The clinical significance of this finding is unknown, and caution should be used when assessing differences in the retentive and nonretentive liner groups because our study may be underpowered to draw conclusions.
This study has some inherent weaknesses. First, it is a retrospective review, which may introduce selection bias among groups. However, with the exception of a small difference in patient age, the distribution of diagnosis and revision surgery status were similar among groups. Furthermore, the duration of follow-up varied slightly among groups, and this difference was statistically significant. Importantly, however, we believe that the minimum 1-year follow-up period for this radiographic study is justified, because 2 previous studies have shown that scapular notching appeared at a mean of 4.5 months postoperatively and did not progress after 1 year in the majority of cases.24,26 The study period may have included a learning curve for each participating surgeon. This may have introduced bias that might have contributed to the increased prevalence and severity of notching of the implant used early in the study period. However, attempts were made to mitigate the effect of the learning curve by controlling those aspects of technique that might have contributed to notching, such as the coronal position of the glenosphere. This study is also limited because we examined only radiographic outcomes with no attempted correlation to functional outcomes. The clinical implications of scapular notching remain controversial. Whereas certain studies have shown a relationship between notching and poor clinical outcomes,26,28 others have failed to confirm this relationship.1,21,24 Certainly, further study with longterm follow-up is warranted to elucidate the clinical relevance of this phenomenon. A fundamental strength of this radiographic investigation lies in the novel classification system for scapular notching described and applied herein. The weaknesses of previously described classification systems, in our opinion, have been minimized in the development of this novel grading system. First, any subjective criteria, such as interpretation of the chronicity or stability of the lesion, have been eliminated. Second, the novel grading system references the constant central peg rather than the variable position of the inferior screw. Third, the novel system recognizes that baseplate involvement is an independent phenomenon that is addressed with a qualifier in grading scapular notching. This novel grading system showed substantial interobserver reliability that is, at a minimum, comparable to that of the commonly used Sirveaux classification system. Further studies are needed to validate this classification system and further define its clinical applicability.
Conclusions A higher incidence and severity of notching were observed with the Tornier reverse arthroplasty compared with the Zimmer reverse arthroplasty at short-term follow-up. These findings may be because of the different morphology of the polyethylene component
1440 (despite equal varus/valgus inclination angle between systems) and/or differences in glenosphere offset between the prosthetic systems. The use of a retentive polyethylene liner with a more valgus angle of inclination did not influence scapular notching with the Zimmer implant. We found no influence of diagnosis on scapular notching; however, the incidence of notching was decreased when the glenosphere was positioned below the glenoid rim. A novel classification system of scapular notching that takes into account the location of scapular notching in relation to (adjacent to or separate from) the glenoid baseplate should be considered and has been shown to have substantial interobserver agreement. In addition to surgical technique, consideration should be given to prosthesis design in mitigating the risk of scapular notching.
Disclaimer The authors, their immediate families, and any research foundations with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.
References 1. Boileau P, Watkinson D, Hatzidakis AM, Havorka I. Neer Award 2005: the Grammont reverse shoulder prosthesis: results in cuff tear arthritis, fracture sequelae, and revision arthroplasty. J Shoulder Elbow Surg 2006;15:527-40. doi:10.1016/j.jse.2006.01.003 2. Boileau P, Watkinson DJ, Hatzidakis AM, Balg F. Grammont reverse prosthesis: design, rationale, and biomechanics. J Shoulder Elbow Surg 2005;14:147S-61S. doi:10.1016/j.jse.2004.10.006 3. Bufquin T, Hersan A, Hubert L, Massin P. Reverse shoulder arthroplasty for the treatment of three- and four-part fractures of the proximal humerus in the elderly: a prospective review of 43 cases with a short-term follow-up. J Bone Joint Surg Br 2007;89:516-20. doi:10. 1302/0301-620X.89B4.18435 4. Cazeneuve JF, Cristofari DJ. The reverse shoulder prosthesis in the treatment of fractures of the proximal humerus in the elderly. J Bone Joint Surg Br 2010;92:535-9. doi:10.1302/0301-620X.92B4.224506 5. Cazeneuve JF, Cristofari DJ. Delta III reverse shoulder arthroplasty: radiological outcome for acute complex fractures of the proximal humerus in elderly patients. Orthop Traumatol Surg Res 2009;95:3259. doi:10.1016/j.otsr.2009.03.018 6. Chacon A, Virani N, Shannon R, Levy JC, Pupello D, Frankle M. Revision arthroplasty with use of a reverse shoulder prosthesisallograft composite. J Bone Joint Surg Am 2009;91:119-27. doi:10. 2106/JBJS.H.00094 7. Chou J, Malak SF, Anderson IA, Astley T, Poon PC. Biomechanical evaluation of different designs of glenospheres in the SMR reverse total shoulder prosthesis: range of motion and risk of scapular notching. J Shoulder Elbow Surg 2009;18:354-9. doi:10.1016/j.jse. 2009.01.015
M.S. Kowalsky et al. 8. Cuff D, Pupello D, Virani N, Levy J, Frankle M. Reverse shoulder arthroplasty for the treatment of rotator cuff deficiency. J Bone Joint Surg Am 2008;90:1244-51. doi:10.2106/JBJS.G.00775 9. de Wilde LF, Poncet D, Middernacht B, Ekelund A. Prosthetic overhang is the most effective way to prevent scapular conflict in a reverse total shoulder prosthesis. Acta Orthop 2010;81:719-26. doi:10.3109/ 17453674.2010.538354 10. Gallinet D, Clappaz P, Garbuio P, Tropet Y, Obert L. Three or four parts complex proximal humerus fractures: hemiarthroplasty versus reverse prosthesis: a comparative study of 40 cases. Orthop Traumatol Surg Res 2009;95:48-55. doi:10.1016/j.otsr.2008.09.002 11. Grammont PM, Baulot E. Delta shoulder prosthesis for rotator cuff rupture. Orthopedics 1993;16:65-8. 12. Grammont PM, Trouilloud P, Laffay JP. Etude et realisationd’une novelle prothese d’epaule. Rhumatologie 1987;39:17-22. 13. Guery J, Favard L, Sirveaux F, Oudet D, Mole D, Walch G. Reverse total shoulder arthroplasty. Survivorship analysis of eighty replacements followed for five to ten years. J Bone Joint Surg Am 2006;88: 1742-7. doi:10.2106/JBJS.E.00851 14. Gutierrez S, Comiskey CA IV, Luzzo ZP, Pupello DR, Frankle MA. Range of impingement-free abduction and adduction deficit after reverse shoulder arthroplasty. Hierarchy of surgical and implantdesign-related factors. J Bone Joint Surg Am 2008;90:2606-15. doi: 10.2106/JBJS.H.00012 15. Gutierrez S, Levy JC, Frankle MA, Cuff D, Keller TS, Pupello DR, et al. Evaluation of abduction range of motion and avoidance of inferior scapular impingement in a reverse shoulder model. J Shoulder Elbow Surg 2008;17:608-15. doi:10.1016/j.jse.2007.11.010 16. Gutierrez S, Levy JC, Lee WE III, Keller TS, Maitland ME. Center of rotation affects abduction range of motion of reverse shoulder arthroplasty. Clin Orthop Relat Res 2007;458:78-82. doi:10.1097/ BLO.0b013e31803d0f57 17. John M, Pap G, Angst F, Flury MP, Lieske S, Schwyzer HK, et al. Short-term results after reversed shoulder arthroplasty (Delta III) in patients with rheumatoid arthritis and irreparable rotator cuff tear. Int Orthop 2010;34:71-7. doi:10.1007/s00264-009-0733-1 18. Kempton LB, Balasubramaniam M, Ankerson E, Wiater JM. A radiographic analysis of the effects of prosthesis design on scapular notching following reverse total shoulder arthroplasty. J Shoulder Elbow Surg 2011;20:571-6. doi:10.1016/j.jse.2010.08.024 19. Klein M, Juschka M, Hinkenjann B, Scherger B, Ostermann PA. Treatment of comminuted fractures of the proximal humerus in elderly patients with the Delta III reverse shoulder prosthesis. J Orthop Trauma 2008;22:698-704. doi:10.1097/BOT.0b013e31818afe40 20. Landis JR, Koch GG. The measurement of observer agreement for categorical data. Biometrics 1977;33:159-74. 21. Levigne C, Boileau P, Favard L, Garaud P, Mole D, Sirveaux F, et al. Scapular notching in reverse shoulder arthroplasty. J Shoulder Elbow Surg 2008;17:925-35. doi:10.1016/j.jse.2008.02.010 22. McFarland EG, Sanguanjit P, Tasaki A, Keyurapan E, Fishman EK, Fayad LM. The reverse shoulder prosthesis: a review of imaging features and complications. Skeletal Radiol 2006;35:488-96. doi:10. 1007/s00256-006-0109-1 23. Middernacht B, De Roo PJ, Van Maele G, de Wilde LF. Consequences of scapular anatomy for reversed total shoulder arthroplasty. Clin Orthop Relat Res 2008;466:1410-8. doi:10.1007/s11999-008-0187-6 24. Nyffeler RW, Werner CM, Gerber C. Biomechanical relevance of glenoid component positioning in the reverse Delta III total shoulder prosthesis. J Shoulder Elbow Surg 2005;14:524-8. doi:10.1016/j.jse. 2004.09.010 25. Parsons BO, Gruson KI, Accousti KJ, Klug RA, Flatow EL. Optimal rotation and screw positioning for initial glenosphere baseplate fixation in reverse shoulder arthroplasty. J Shoulder Elbow Surg 2009;18: 886-91. doi:10.1016/j.jse.2008.11.002 26. Simovitch RW, Zumstein MA, Lohri E, Helmy N, Gerber C. Predictors of scapular notching in patients managed with the Delta III reverse
Scapular notching and reverse shoulder arthroplasty design total shoulder replacement. J Bone Joint Surg Am 2007;89:588-600. doi:10.2106/JBJS.F.00226 27. Sirveaux F. La prothese de Grammont dans le traitement des arthropathies de l’epaule a coiffe detruite. A propos d’une serie mulicentrique de 42 cas. Nancy: L’Universite de Nancy; Thesis; 1997. p. 245. 28. Sirveaux F, Favard L, Oudet D, Huquet D, Walch G, Mole D. Grammont inverted total shoulder arthroplasty in the treatment of glenohumeral osteoarthritis with massive rupture of the cuff. Results of a multicentre study of 80 shoulders. J Bone Joint Surg Br 2004;86: 388-95. doi:10.1302/0301-620X.86B3 29. Valenti PH, Boutens D, Nerot C. Delta 3 reversed prosthesis for osteoarthritis with massive rotator cuff tear: long term results (> 5 years). In: Walch G, Boileau P, Mole D, editors. 2000 Shoulder
1441 Prostheses: Two to Ten Year Follow-up. Montpellier: Sauramps Medical; 2001. p. 253-9. 30. Vanhove B, Beugnies A. Grammont’s reverse shoulder prosthesis for rotator cuff arthropathy. A retrospective study of 32 cases. Acta Orthop Belg 2004;70:219-25. 31. Werner CM, Steinmann PA, Gilbart M, Gerber C. Treatment of painful pseudoparesis due to irreparable rotator cuff dysfunction with the Delta III reverse-ball-and-socket total shoulder prosthesis. J Bone Joint Surg Am 2005;87:1476-86. doi:10.2106/JBJS.D.02342 32. Wierks C, Skolasky RL, Ji JH, McFarland EG. Reverse total shoulder replacement: intraoperative and early postoperative complications. Clin Orthop Relat Res 2009;467:225-34. doi:10.1007/s11999-0080406-1