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Radiographic changes and clinical outcomes associated with an adjustable diaphyseal press-fit humeral stem in primary reverse shoulder arthroplasty
ARTICLE IN PRESS J Shoulder Elbow Surg (2017) ■■, ■■–■■
www.elsevier.com/locate/ymse
ORIGINAL ARTICLE
Radiographic changes and clinical outcomes associated with an adjustable diaphyseal press-fit humeral stem in primary reverse shoulder arthroplasty Samuel M. Harmsen, MDa,*, Tom R. Norris, MDb a
The Orthopedic Clinic Association, Phoenix, AZ, USA The San Francisco Shoulder, Elbow and Hand Clinic, San Francisco, CA, USA
b
Background: Press-fit humeral fixation in reverse shoulder arthroplasty (RSA) has become increasingly popular; however, radiographic analysis of these stems is limited. We aimed to evaluate the radiographic and clinical outcomes of an adjustable diaphyseal press-fit humeral stem in primary RSA. Methods: We conducted a retrospective review of 232 primary RSAs in 219 patients performed by a single surgeon using this system. Radiographic outcomes were evaluated in patients with at least 2 years of radiographic follow-up. Standardized postoperative digital radiographs were analyzed for loosening, osteolysis, and stress shielding. Clinical outcomes in patients who also had complete clinical data sets were evaluated at the most recent follow-up. Results: Radiographic evidence of loosening was identified in 1 RSA (0.4%) associated with deep infection. Aseptic loosening was not observed. No stems were identified as being at high risk for loosening. Internal stress shielding was observed proximal to the coated diaphyseal component in 226 shoulders (97.4%). This finding was often visible at 3 months (92.7%) and predictably progressed on subsequent radiographs. Progression beyond the 2-year period was rarely seen (4.4%). No external stress shielding or osteolysis was observed. Thirty-six complications occurred in 33 patients (15.1%). At an average follow-up of 36.6 months, significant improvements were identified in all measured clinical outcomes (P < .001). Conclusion: Predictable fixation is achieved using an adjustable diaphyseal press-fit humeral system in primary RSA. Internal stress shielding is commonly observed but does not appear to compromise quality of fixation or clinical outcomes. Level of evidence: Level IV; Case Series; Treatment Study © 2017 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved. Keywords: Reverse shoulder arthroplasty; press-fit; stress shielding; humeral loosening; radiographic analysis; adjustable reverse
The California Pacific Medical Research Institute Institutional Review Board approved this study, study number 27.007. *Reprint requests: Samuel M. Harmsen, MD, The Orthopedic Clinic Association, PC, 2222 E Highland Ave, #300, Phoenix, AZ 85016, USA. E-mail address: [email protected] (S.M. Harmsen).
Shoulder replacement surgery is associated with good to excellent results for a variety of shoulder pathologies7,12,16,27,37,41,49-51 and has become increasingly popular.11,22 As the incidence of these operations increases,
1058-2746/$ - see front matter © 2017 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved. http://dx.doi.org/10.1016/j.jse.2017.02.006
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S.M. Harmsen, T.R. Norris
the number of complications will inevitably increase as well. Complication profiles have been well documented and suggest that glenoid component loosening is the primary mode of failure.2,35,37,46,55 Humeral component loosening is much less common. Historically, successful humeral fixation with low loosening rates has been achieved with cementation techniques.23,24,39,43 Recently, however, the use of press-fit humeral components has become more prevalent.12,14,18,28,38,45,54 Proposed advantages of press-fit fixation include decreased operative time and lower complication rates with stem removal during revision surgery. Early-generation press-fit humeral components were associated with high loosening rates and poor results.44,48,51 With improvements in technology and techniques, later-generation implants have shown much more favorable results with low loosening rates.12,14,18,24,28,38,45,54 However, significant radiographic humeral changes, including stress shielding, osteolysis, and radiolucent lines, have been observed.28,29,34,38,45 Stress shielding and osteolysis of the femur have been associated with poor clinical outcomes with hip arthroplasty,13,34,38 but these radiographic changes have not yet been shown to correlate with poor clinical results in anatomic shoulder arthroplasty. Reverse shoulder arthroplasty (RSA) has revolutionized the care of patients with cuff-deficient shoulder pathologies.5,6,8-10,15,26,31,33,36,56 As with anatomic shoulder arthroplasty, humeral component loosening has not been reported with high incidence, and a shift toward the use of press-fit humeral systems has been seen with successful clinical outcomes. However, few studies have assessed the radiographic changes seen with press-fit stems in RSA.17,30,59 This study evaluated the radiographic and clinical outcomes of an adjustable diaphyseal press-fit humeral system in primary RSA. This system consists of a fully hydroxyapatite-coated diaphyseal component, optional smooth segmental stacking inserts if required, and a detachable smooth inset metaphyseal component (Fig. 1). Height and version can be adjusted at the time of initial implantation or revision surgery without the need to remove the fixed diaphyseal component. We hypothesize that this system will (1) provide predictable press-fit fixation with low loosening rates, (2) have
Figure 1
Adjustable diaphyseal press-fit humeral system.
a high rate of proximal stress shielding secondary to solid diaphyseal fixation, and (3) be associated with excellent clinical outcomes, consistent with the RSA literature, that are unaffected by the radiographic changes observed.
Materials and methods We retrospectively reviewed all primary RSAs performed by the senior author (T.R.N.) using the adjustable press-fit humeral system between 2007 and 2013. All patients in this series were entered in a prospectively gathered database intended for outcome analysis of shoulder replacement surgery. All patients provided consent for inclusion in the database before surgical intervention. The inclusion criteria for this study were primary RSA using the Aequalis Adjustable Reverse Shoulder System (AARS; Tornier, Inc., Edina, MN, USA) for any indication, minimum of 2-year radiographic follow-up, and complete radiographic series at each followup interval. All revision operations were excluded. As a secondary outcome, clinical results in those patients who met the inclusion criteria and who also had complete preoperative and postoperative clinical data sets extending to or beyond 24-months were also evaluated. All preoperative, intraoperative, and postoperative records and imaging were reviewed. Patient demographics, indications for surgery, complications, and radiographic findings were reviewed. If revision surgery was required, the utility of the adjustable system for improving stability with height or version changes, the ability to retain and reuse the diaphyseal component, and any complications associated with removal of the diaphyseal component, if required, were also assessed.
Radiographic evaluation Postoperative digital radiographs were obtained at time 0, 3 months, 6 months, 1 year, 2 years, and at the most recent follow-up. Standard radiographs included true anteroposterior (with the humerus in neutral rotation), scapular Y, and axillary views. Axillary views were not obtained at time 0 but were obtained at all other scheduled times. All preoperative and postoperative radiographs were obtained using a standardized technique and performed by the same technician. All radiographs were assessed for subsidence or migration of the humeral component, presence of radiolucent lines around the humeral component, osteolysis, and stress shielding by three American Shoulder and Elbow Surgeons (ASES) shoulder and elbow fellowship-trained orthopedic surgeons. A consensus was reached on all radiographic changes identified. The humeral component was divided into 7 zones.5,44,48 Zones 1 and 7 included the metaphyseal component and extended to the level of the diaphyseal/metaphyseal component junction. This junction represented the transition zone from smooth to the hydroxyapatite-coated implant. If stack spacers had been placed, these zones were extended beyond the metaphysis distally to the level of the smooth spacer/coated stem junction. Zones 2 and 6 represented the proximal half of the diaphyseal component. Zones 3 and 5 represented the distal half of the diaphyseal component. Zone 4 represented the area distal to the tip of the stem (Fig. 2). Radiolucent lines were assessed according to Sperling et al49: measured in 0.5-mm increments up to 2 mm and then identified as >2 mm. If radiolucent lines were identified, each subsequent radio-
ARTICLE IN PRESS Adjustable press-fit humeral stem in RSA
Figure 2 Humeral zones for radiographic analysis. (A) The humeral stem was divided into 7 zones. (B) Zones 1 and 7 were proximal to the junction of the smooth metaphyseal component and the coated diaphyseal component. The remaining zones were distal to this junction (indicated by arrow) and surrounded the press-fit diaphyseal component as above. graphic series was critically evaluated for progression of lucency. Progression was defined as an increase in width of >0.5 mm or extension along the implant into the adjacent zone, or both. If radiolucent lines >2 mm were present in ≥3 zones, the implant was considered to be at high risk for loosening. If subsidence or stem migration was identified, the implant was deemed loose. Radiographs were also assessed for cortical resorption and stress shielding.34
Clinical evaluation Functional outcome scores (FOS), active range of motion (AROM), and strength measurements were collected preoperatively and at each annual postoperative visit. FOS included the ASES score,40 the Simple Assessment Numeric Evaluation,57 and the visual analog scale for pain. AROM was measured in 5° increments using a goniometer with a standardized method in the seated position. Motions included forward flexion and external rotation with the arm held at 0° of abduction and at 90° of abduction. Abduction strength in the scapular plane was measured using a dynamometer as described by Moeller et al.32 FOS, AROM, and strength at the most recent follow-up were compared with preoperative values using a paired Student t test. Reviewers were blinded to the radiographic outcomes of each patient. Statistical significance was set at P < .01. Data were analyzed with Excel software (Microsoft Corp., Redmond, WA, USA).
Operative technique The surgical technique for RSA has been well described.4,20,56 Most of this procedure, including exposure, head cut, metaphyseal preparation, and glenoid preparation, follows these standard techniques. Humeral sizing, implant assembly, and techniques for adjustments in height and version are specific to the AARS system. Once the metaphyseal preparation is complete, the canal is sized with pro-
3 gressive trials until snug fixation of the trial stem is achieved. Height is then measured using the markings on the trial stem inserter in relation to the greater tuberosity. If necessary, smooth inserts can be added to achieve stable diaphyseal fixation when in-between stem sizes. The final component, including the appropriate diameter diaphyseal stem, smooth inserts, if necessary, and the smooth metaphyseal component, is assembled and secured with a locking screw securitization system. The assembled component is then impacted into the humeral canal in the desired version. Humeral inserts are trialed in a standard fashion, and the appropriate insert is impacted onto the metaphyseal component. If necessary, version can be adjusted in 10° increments without removing the press-fit diaphyseal stem by removing the securitization system and turning the metaphysis. Spacers can also be added if the height needs to be adjusted. The RSA is then reduced in standard fashion. The addition of a stacking insert was needed in 13 shoulders to obtain stable distal fixation at time of the primary surgery. For example, if a 9-mm stem was too small and an 11-mm stem was too large to gain stable press-fit fixation, additional stem length was obtained by adding stacking spacers of various lengths to the 9-mm stem. The added length facilitates the ability to gain stable fixation further distal as the humeral canal narrows. All humeral head cuts were made at 155° of inclination and 30° of retroversion. All but 13 shoulders were performed using the Bony Increased Offset (BIO)RSA technique (Tornier) on the glenoid side for glenoid bone defect grafting, lateralization, or both. All procedures were performed with the patient under general anesthesia with regional interscalene nerve block in the beach chair position through a standard deltopectoral approach. All operations were completed by or under the direction of the senior author.
Postoperative protocol All shoulders were immobilized with a sling and abduction pillow for 4 to 6 weeks, coming out of the sling 3 times a day to do pendulum, elbow, wrist, and hand exercises. Patients were also allowed to come out of the sling for hygiene. The hand could be used for simple tasks; however, no active lifting was allowed. After 4 to 6 weeks, the sling was discontinued, physical therapy consisting of gradual range of motion and progressive strengthening exercises was initiated, and progression of activities as tolerated was allowed.
Results Radiographic analysis A total of 232 RSA in 219 patients with a mean follow-up of 26.4 months (range, 23.7-82.2 months) met the inclusion criteria for radiographic analysis. Migration and clear radiographic loosening was seen in 1 shoulder (0.4%). This shoulder was diagnosed with a deep infection (Propionibacterium acnes) and underwent 2-stage revision RSA with an AARS. No shoulder met criteria for high risk of loosening. No radiolucent lines >1 mm were identified around the diaphyseal component (zones 2-6). Radiolucent lines ≤1 mm in width were identified in zones 2-6 in 14 shoulders (6.0%). Of these shoulders, only 2 had radiolucent lines in >1 zone, both of
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S.M. Harmsen, T.R. Norris Table I
Patient demographics
Variable
Radiographic analysis
Clinical analysis*
Reverse shoulder arthroplasty, No. Left Right Sex, No. Male Female Age at time of surgery, average (range), y Follow-up, mean (range), mo Indication, % Cuff tear arthropathy Massive rotator cuff tear Primary osteoarthritis with posterior glenoid bone loss Post-traumatic sequela Rheumatoid arthritis Primary osteoarthritis with rotator cuff tear Postinfectious arthropathy Acute proximal humeral fracture
232 88 144 219 116 103 67.7 (35-89) 26.4 (23.7-82.2)
174 70 104 164 82 82 68.2 (35-89) 36.6 (23.7-82.2)
89 69 31 21 10 5 5 2
69 49 29 16 8 2 3 2
* 55 patients from the radiographic analysis did not have complete clinical data sets and therefore were excluded.
which had lines in zones 2 and 6. Radiolucent lines were identified around the smooth metaphyseal component (zones 1 and 7) in 226 shoulders (97.4%) This finding was observed in 215 shoulders (92.7%) at 3 months. Advancement in radiolucent line width was seen in all but 2 of these shoulders during the first 2 years. However, in 70 shoulders that had radiographs at and after 24-months (mean, 42.2; range, 31.3-82.2 months), further advancement was rarely seen (4.3%). No radiolucent lines had a width >3 mm. No progression of radiolucent lines into the adjacent zones (from zone 1 to 2 or zone 7 to 6) was identified. No cortical resorption was identified. Osteolysis involving the humerus was not identified, despite 3 shoulders with radiographic evidence of osteolysis of the glenoid and 30 shoulders with scapular notching.
Clinical analysis There were 174 RSAs in 164 patients, with an average followup of 36.6 months (range 23.7-82.2 months), that met inclusion criteria for clinical analysis. Of the patients included in the radiographic analysis, 25% were excluded because of incomplete clinical data sets, resulting in a 75% recruitment rate. It is important to note that radiographic changes consistent with proximal zone radiolucencies described above were identified in 171 of the 174 RSAs (98.3%) included in the clinical analysis. Demographic information is listed in Table I. Significant improvement in FOS, ROM, and abduction strength in the scapular plane was observed (P < .01). The ASES score improved from 32.3 preoperatively to 77.5 postoperatively (P < .001). Forward flexion increased from 81° to 123°. All clinical results are listed in Table II. When all patients, with or without complete clinical data sets, were included, 36 complications occurred in 33 pa-
tients (15.1%). Complications included acromial/scapular spine stress fracture (n = 7), deep infection (n = 7), baseplate failure (n = 6), dislocation (n = 5), transient neuropathy (n = 4), superficial infection (n = 3), postoperative periprosthetic Vancouver C humeral shaft fracture (n = 1), humeral shaft fracture during implant removal (n = 1), baseplate malposition (n = 1), and retained drill fragment (n = 1). Failures, defined as requiring revision surgery, were documented in 17 RSAs. In 11 of these shoulders, the diaphyseal component was retained and used for revision RSA. These included 6 baseplate failures and 1 baseplate malposition that required revision. In these revisions, the ability to easily remove and replace the metaphyseal component facilitated glenoid visualization without the need for humeral stem removal. Segmental stacking inserts were easily added to increase the height and improve tension in 3 cases for correction of instability. The other retained stem was left in place during stage 1 of a 2-stage revision RSA for treatment of a deep infection. This stem was successfully reused at the time of the second stage (Fig. 3). Six stems were removed for treatment of deep infection. One of these stems was loose and was easily removed. The other 5 stems were well fixed and were explanted using various stem removal techniques. An iatrogenic humeral shaft fracture occurred in 1 patient. No other complications occurred during stem removal.
Discussion Recently, there has been a trend toward the use of press-fit humeral stems in shoulder replacement surgery. Although a number of studies have evaluated the radiographic changes observed with these implants, most analyzed results with anatomic shoulder replacement.14,18,24,28,29,38,45,48,51,52,54 Early
ARTICLE IN PRESS Adjustable press-fit humeral stem in RSA
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Table II Mean clinical outcomes in primary reverse shoulder arthroplasty using the Aequalis Adjustable Reverse Shoulder System* pressfit humeral stem† Variable‡
Preoperative Postoperative** Improvement
Functional outcome scores
Objective clinical measurements
ASES
SANE
VAS pain
AFF (°)
AER (°)
ABER (°)
STR§ (lbs)
32.2 (16.9) 77.5 (15) 45.2
23.4 (18.7) 76.7 (17) 53.3
6.5 (2.0) 0.9 (1.4) –5.6
81 (36) 123 (26) 42
20 (20) 32 (17) 12
37 (31) 58 (24) 21
3.0 (3.8) 7.4 (4.4) 4.4
ABER, abduction, external rotation; AER, active external rotation; AFF, active forward flexion; ASES, American Shoulder and Elbow Surgeons; SANE, Simple Assessment Numeric Evaluation; STR, strength; VAS, visual analog scale. * Tornier, Inc., Edina, MN, USA. † All changes statistically significant with P < .001 (paired t test). ‡ Data are shown as mean (standard deviation). § Measured with arm in 90° of abduction in the scapular plane with a dynamometer. ** Mean 36.6 mo.
Figure 3 Utility of Aequalis Adjustable Reverse Shoulder System (Tornier, Inc., Edina, MN, USA) in revision reverse shoulder arthroplasty (RSA). This patient was treated for a deep infection with a 2-stage RSA. (A) The diaphyseal press-fit component was retained at stage 1. The patient underwent treatment with an antibiotic loaded cement spacer and 6 weeks of intravenous antibiotics. (B) The well-fixed adjustable stem was built upon at the time of the second-stage RSA with a new metaphyseal component, providing solid fixation at time 0. Intraoperative cultures at this point showed no growth at 14 days. The patient went on to full recovery.
experience with the press-fit technique showed a high failure rate. Torchia et al51 reviewed the long-term results seen with press-fit stems that were initially designed for cemented total shoulder arthroplasty and found evidence of shift in the humeral component in 49% of press-fit shoulders compared with 0% of those that were cemented. Sanchez-Sotelo et al44 saw similarly poor results with this implant and reported a radiographic risk of loosening in 55.6% at medium- to longterm follow-up. As improvements in design, coating, and configuration have been made with later generations of press-
fit humeral stems, loosening rates have significantly improved, with rates approaching 0.0%.24,38,45,54 As a result, press-fit humeral stems have become increasingly popular in anatomic shoulder replacement. Humeral component loosening has been identified as a cause for revision in RSA.3,47 Boileau et al3 reported 10 RSAs that required revision for humeral loosening, accounting for 17% of the revisions performed during a 12-year period. Whether these stems were press-fit or cemented is not clear. A number of studies have reported very low loosening rates of press-fit humeral stems with RSA.17,18,30,42,59 Our loosening rate of 0.4% is comparable to the literature, particularly because the single case of loosening within our series was attributable to infection. In addition, radiolucent lines around the diaphyseal component (zones 2-6), even in single zones, were rarely seen with this implant and occurred much less frequently than those seen with other RSA implants. This finding may be secondary to the location of fixation achieved. This system achieves fixation in the diaphysis alone, whereas other systems achieve fixation in the metaphysis or in both the diaphysis and metaphysis. Although the loosening rate with modern press-fit humeral stems approaches 0.0%, alarming rates of other radiographic changes, such as stress shielding and osteolysis, have been reported.24,28,29,34,38,45 Stress shielding is defined as an adaptation of the bone to changes in stress distribution, following Wolff’s law.34,58 These changes can manifest as “external” (thinning and resorption of the external cortex) and “internal” (increasing porosity and resorption of cancellous bone) remodeling. In our study, we saw no evidence of osteolysis or external stress shielding; however, we did appreciate a consistent radiolucent line around the smooth metaphyseal component in most cases. The width of these radiolucent lines predictably increased over time through the first 2 years, indicating resorption of the surrounding cancellous bone. Although we would not expect to see bony ongrowth in these areas, we also did not expect resorption of the immediate surrounding
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S.M. Harmsen, T.R. Norris
Figure 4 Internal stress shielding observed over time. (A) Immediate postoperative radiograph shows no radiolucency. (B) At 3 months, a small 0.5-mm lucency can be seen around the smooth metaphyseal component. (C) At 22 months, the width of the lucency has increased compared to that seen at 3 months. (D) At 46 months (most recent), no significant change is seen in lucency width compared with that seen at 22 months. The lucencies do not extend beyond the smooth metaphyseal component. No lucencies are seen distal to the smooth/fullycoated junction. This is thought to represent internal stress shielding.
cancellous bone. This resorption was thought to represent internal stress shielding (Fig. 4). Our observed rate of stress shielding of 97.4% is much higher than reported rates in shoulder arthroplasty with a pressfit humeral stems: 9% by Nagels et al,34 63% by Raiss et al,38 62% by McElwain and English,29 51.9% by Schnetzke et al,45 and 58.8% by Matsen et al.28 Comparing these results, however, is difficult and confounding. We observed internal stress shielding with no occurrences of external stress shielding, whereas a number of prior studies identified external stress shielding with the presence of bone islands or cortical thinning and resorption, or both. Furthermore, Huiskes21 reported that fully ingrown diaphyseal stems are associated with higher rates of stress shielding then proximally ingrown stems. The implant used in this study is a complete diaphyseal fit stem, whereas stems in the other mentioned studies are metaphyseal only or are combined fit implants. As such, we should expect a higher rate of stress shielding with this stem. Lastly, our study evaluated changes seen in RSA, whereas the others investigated changes seen in anatomic systems. It may be that the intrinsic semiconstrained design of the RSA leads to increased stress shielding caused by altered stresses across the humeral component. There are conflicting studies within the hip literature regarding the clinical effect of stress shielding; however, the general consensus is that it can lead to inferior results.1,13,19,25,52,53 The effect of stress shielding in shoulder arthroplasty, particularly RSA, is unclear. Studies that evaluate stress shielding in anatomic shoulder replacement suggest that the adaptive changes seen are not associated with a negative effect on functional outcomes.29,38,45 In our study, excellent clinical results were obtained at short- to midterm follow-up in primary RSA despite the high incidence of internal stress shielding observed. Whether results will change with longer follow-up, with concerns of progression and eventual component loosening,
is unclear. However, we observed a maturity, or halt of progression, of the internal stress shielding beyond 2 years. In addition, we did not appreciate any progression of radiolucency into adjacent diaphyseal zones over time. If these findings hold true over time, the observed internal stress shielding may not have a significant effect on clinical results through long-term follow-up. More studies with longer followup are needed to better understand the clinical effect of stress shielding in both anatomic and reverse shoulder arthroplasty. The adjustable nature of this system proved beneficial both at the time of implantation and during revision surgery. Quick and easy lengthening of the prosthesis allowed for diaphyseal press-fit fixation in cases where the humeral canal was in between stem sizes proximally. Removal of the smooth metaphyseal component also provided for safe, adequate glenoid exposure in revision surgery without the need to remove the well-fixed humeral component, avoiding potential complications. In these cases, the metaphyseal component was able to be reconnected to the well-fixed diaphyseal component with version adjustment performed as needed. Three cases of instability were successfully addressed by adding stack spacers to the well-fixed stem. It is important to note that instability with RSA is much more complicated than tension and version alone and may require other revision options to correct; however, increasing tension was successful in treating the instability in these 3 patients. These features could prove beneficial if revision surgery is required. This study has a number of limitations. Although the data were prospectively gathered, the inherent limitations of a retrospective review and single-surgeon study are present. The study evaluated a large cohort of patients, but the follow-up duration was short. Longer follow-up is needed to better understand the effect of stress shielding on RSA outcomes over time.
ARTICLE IN PRESS Adjustable press-fit humeral stem in RSA Multivariate analysis was not performed to assess for correlations between variables and the radiographic changes seen. However, the changes seen were almost universal, and as such, specific correlations likely do not exist. Of the RSAs and patients with a radiographic evaluation, 25% did not meet inclusion criteria for clinical analysis. Correlations between radiographic changes and clinical outcomes are therefore limited. However, in the 174 RSA that met inclusion for both radiographic and clinical analysis, 98.3% of shoulders had radiographic changes of internal stress shielding. Lastly, although good to excellent interobserver and intraobserver reliability has been shown when evaluating for radiolucent lines on digital radiographs, we did not perform our own reliability analysis. Strengths of this study include the large study size, consistent prospective radiographic and clinical data collection techniques, blinding of reviewers to radiographic changes and clinical outcomes, and complete data collection. This is the first study to evaluate radiographic or clinical outcomes of an all-diaphyseal press-fit humeral system in RSA and is the largest study of which we are aware to evaluate the radiographic changes associated with press-fit humeral stems of any kind in RSA.
Conclusion The adjustable diaphyseal press-fit humeral system provides predictable, stable humeral fixation in primary RSA and is associated with excellent short- to midterm clinical outcomes that are consistent with the RSA literature.6,8-10,15,26,31,33,36,56 A high rate of internal stress shielding is consistently observed in the early postoperative period and predictably progresses over the short-term. Progression beyond 2 years rarely occurs. These radiographic humeral changes do not adversely affect clinical outcomes in short- to midterm follow-up. The adjustability of the system can be successfully used in primary and revision situations. This system can be recommended for use in primary RSA.
Disclaimer Tornier, Inc. provided funding for database management, which was performed by User Friendly Custom Software Inc. (Houston, TX, USA). Tom Norris reports that he received royalties and consultant payments from Tornier Inc., which were related to the subject of this work, and also received financial support from Tornier, Inc. for the database used in the study. Samuel M. Harmsen, his immediate family, and any research foundations with which they are affiliated did not receive any financial payments or other benefits from any commercial entity related to the subject of this article.
7
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ARTICLE IN PRESS 8 17. Gilot G, Alvarez-Pinzon AM, Wright TW, Flurin PH, Krill M, Routman HD, et al. The incidence of radiographic aseptic loosening of the humeral component in reverse total shoulder arthroplasty. J Shoulder Elbow Surg 2015;24:1555-9. http://dx.doi.org/10.1016/j.jse.2015.02.007 18. Giuseffi SA, Streubel P, Sperling J, Sanchez-Sotelo J. Short-stem uncemented primary reverse shoulder arthroplasty: clinical and radiological outcomes. J Bone Joint Surg Br 2014;96:526-9. http://dx.doi.org/10.1302/0301-620X.96B3.32702 19. Han CW, Yang IH, Lee HY, Han CD. Long-term follow-up results of a second-generation cementless femoral prosthesis with a collar and straight distal fixation channels. Yonsei Med J 2012;53:186-92. http://dx.doi.org/10.3349/ymj.2012.53.1.186 20. Hatzidakis AM, Norris TR, Boileau P. Reverse shoulder arthroplasty indications, technique, and results. Tech Shoulder Elbow Surg 2005;6:135-49. 21. Huiskes R. The various stress patterns of press-fit, ingrown, and cemented femoral stems. Clin Orthop Relat Res 1990;261:27-38. 22. Jain NB, Higgins LD, Guller U, Pietrobon R, Katz JN. Trends in the epidemiology of total shoulder arthroplasty in the United States from 1990–2000. Arthritis Rheum 2006;55:591-7. http://dx.doi.org/10.1002/ art.22102 23. Kasten P, Pape G, Raiss P, Bruckner T, Rickert M, Zeifang F, et al. Mid-term survivorship analysis of a shoulder replacement with a keeled glenoid and a modern cementing technique. J Bone Joint Surg Br 2010;92:387-92. http://dx.doi.org/10.1302/0301-620X.92B3.23073 24. Khan A, Bunker TD, Kitson JB. Clinical and radiological follow-up of the Aequalis third-generation cemented total shoulder replacement: a minimum ten-year study. J Bone Joint Surg Br 2009;91:1594-600. http://dx.doi.org/10.1302/0301-620X.91B12.22139 25. Kim YH, Park JW, Kim JS, Kang JS. Long-term results and bone remodeling after THA with a short, metaphyseal-fitting anatomic cementless stem. Clin Orthop Relat Res 2014;472:943-50. http://dx.doi.org/10.1007/s11999-013-3354-3 26. Lederman ES, Harmsen S, Hatzidakis AM, Kelly JD, Edwards TB. Reverse total shoulder arthroplasty is associated with good clinical outcomes that are sustained through mid-term follow-up: a prospective cohort study. J Shoulder Elbow Surg 2014;9:e229. http://dx.doi.org/ 10.1016/j.jse.2014.06.004 27. Lo IK, Litchfield RB, Griffin S, Faber K, Patterson SD, Kirkley A. Quality-of-life outcome following hemiarthroplasty or total shoulder arthroplasty in patients with osteoarthritis. J Bone Joint Surg Am 2005;87:2178-85. http://dx.doi.org/10.2106/JBJS.D.02198 28. Matsen FA, Iannotti JP, Rockwood CA. Humeral fixation by press-fitting of a tapered metaphyseal stem. J Bone Joint Surg Am 2003;85:3048. 29. McElwain JP, English E. The early results of porous-coated total shoulder arthroplasty. Clin Orthop Relat Res 1987;218:217-24. 30. Melis B, DeFranco M, Laedermann A, Mole D, Favard L, Nérot C, et al. An evaluation of the radiological changes around the Grammont reverse geometry shoulder arthroplasty after eight to 12 years. J Bone Joint Surg Br 2011;93:1240-6. http://dx.doi.org/10.1302/0301-620X.93B9.25926 31. Mizuno N, Denard PJ, Raiss P, Walch G. Reverse total shoulder arthroplasty for primary glenohumeral osteoarthritis in patients with a biconcave glenoid. J Bone Joint Surg Am 2013;95:1297. http://dx.doi.org/ 10.2106/JBJS.L.00820 32. Moeller AD, Thorsen RR, Torabi TP, Bjoerkman AS, Christensen EH, Maribo T, et al. The Danish version of the modified Constant-Murley shoulder score: reliability, agreement, and construct validity. J Orthop Sports Phys Ther 2014;44:336-40. http://dx.doi.org/10.2519/ jospt.2014.5008 33. Mulieri P, Dunning P, Klein S, Pupello D, Frankle M. Reverse shoulder arthroplasty for the treatment of irreparable rotator cuff tear without glenohumeral arthritis. J Bone Joint Surg Am 2010;92:2544-56. http://dx.doi.org/10.2106/JBJS.I.00912 34. Nagels J, Stokdijk M, Rozing PM. Stress shielding and bone resorption in shoulder arthroplasty. J Shoulder Elbow Surg 2003;12:35-9. http://dx.doi.org/10.1067/mse.2003.22
S.M. Harmsen, T.R. Norris 35. Neer C, Watson KC, Stanton FJ. Recent experience in total shoulder replacement. J Bone Joint Surg Am 1982;64:319-37. 36. Nolan BM, Ankerson E, Wiater JM. Reverse total shoulder arthroplasty improves function in cuff tear arthropathy. Clin Orthop Relat Res 2011;469:2476-82. http://dx.doi.org/10.1007/s11999-010-1683-z 37. Norris TR, Iannotti JP. Functional outcome after shoulder arthroplasty for primary osteoarthritis: a multicenter study. J Shoulder Elbow Surg 2002;11:130-5. http://dx.doi.org/10.1067/mse.2002.121146 38. Raiss P, Edwards TB, Deutsch A, Shah A, Bruckner T, Loew M, et al. Radiographic changes around humeral components in shoulder arthroplasty. J Bone Joint Surg Am 2014;96:e54. http://dx.doi.org/ 10.2106/JBJS.M.00378 39. Raiss P, Schmitt M, Bruckner T, Kasten P, Pape G, Loew M, et al. Results of cemented total shoulder replacement with a minimum follow-up of ten years. J Bone Joint Surg Am 2012;94:e171. http://dx.doi.org/10.2106/JBJS.K.00580 40. Richards RR, An KN, Bigliani LU, Friedman RJ, Gartsman GM, Gristina AG, et al. A standardized method for the assessment of shoulder function. J Shoulder Elbow Surg 1994;3:347-52. 41. Rispoli DM, Sperling JW, Athwal GS, Schleck CD, Cofield RH. Humeral head replacement for the treatment of osteoarthritis. J Bone Joint Surg Am 2006;88:2637-44. http://dx.doi.org/10.2106/JBJS.E.01383 42. Saltzman BM, Chalmers PN, Gupta AK, Romeo AA, Nicholson GP. Complication rates comparing primary with revision reverse total shoulder arthroplasty. J Shoulder Elbow Surg 2014;23:1647-54. http://dx.doi.org/10.1016/j.jse.2014.04.015 43. Sanchez-Sotelo J, O’Driscoll SW, Torchia ME, Cofield RH, Rowland CM. Radiographic assessment of cemented humeral components in shoulder arthroplasty. J Shoulder Elbow Surg 2001;10:52631. 44. Sanchez-Sotelo J, Wright TW, O’Driscoll SW, Cofield RH, Rowland CM. Radiographic assessment of uncemented humeral components in total shoulder arthroplasty. J Arthroplasty 2001;16:180-7. 45. Schnetzke M, Coda S, Raiss P, Walch G, Loew M. Radiologic bone adaptations on a cementless short-stem shoulder prosthesis. J Shoulder Elbow Surg 2016;25:650-7. http://dx.doi.org/10.1016/j.jse.2015.08.044 46. Singh JA, Sperling JW, Cofield RH. Revision surgery following total shoulder arthroplasty: analysis of 2588 shoulders over three decades (1976 to 2008). J Bone Joint Surg Br 2011;93:1513-7. http://dx.doi.org/10.1302/0301-620X.93B11.26938 47. Smith CD, Guyver P, Bunker TD. Indications for reverse shoulder replacement: a systematic review. J Bone Joint Surg Br 2012;94:577-83. http://dx.doi.org/10.1302/0301-620X.94B5.27596 48. Sperling JW, Cofield RH, O’Driscoll SW, Torchia ME, Rowland CM. Radiographic assessment of ingrowth total shoulder arthroplasty. J Shoulder Elbow Surg 2000;9:507-13. 49. Sperling JW, Cofield RH, Rowland CM. Minimum fifteen-year follow-up of Neer hemiarthroplasty and total shoulder arthroplasty in patients aged fifty years or younger. J Shoulder Elbow Surg 2004;13:604-13. http://dx.doi.org/10.1016/j.jse.2004.03.013 50. Sperling JW, Cofield RH, Rowland CM. Neer hemiarthroplasty and Neer total shoulder arthroplasty in patients fifty years old or less. Long-term results. J Bone Joint Surg Am 1998;80:464-73. 51. Torchia ME, Cofield RH, Settergren CR. Total shoulder arthroplasty with the Neer prosthesis: long-term results. J Shoulder Elbow Surg 1997;6:495-505. 52. Turner TM, Sumner DR, Urban RM, Igloria R, Galante JO. Maintenance of proximal cortical bone with use of a less stiff femoral component in hemiarthroplasty of the hip without cement. An investigation in a canine model at six months and two years. J Bone Joint Surg Am 1997;79:138190. 53. Van Rietbergen B, Huiskes R, Weinans H, Sumner DR, Turner TM, Galante JO. The mechanism of bone remodeling and resorption around press-fitted THA stems. J Biomech 1993;26:369-82. 54. Verborgt O, El-Abiad R, Gazielly DF. Long-term results of uncemented humeral components in shoulder arthroplasty. J Shoulder Elbow Surg 2007;16:S13-8. http://dx.doi.org/10.1016/j.jse.2006.02.003
ARTICLE IN PRESS Adjustable press-fit humeral stem in RSA 55. Walch G, Young AA, Boileau P, Loew M, Gazielly D, Mole D. Patterns of loosening of polyethylene keeled glenoid components after shoulder arthroplasty for primary osteoarthritis: results of a multicenter study with more than five years of follow-up. J Bone Joint Surg Am 2012;94:145-50. http://dx.doi.org/10.2106/JBJS.J.00699 56. Wall B, Nové-Josserand L, O’Connor DP, Edwards TB, Walch G. Reverse total shoulder arthroplasty: a review of results according to etiology. J Bone Joint Surg Am 2007;89:1476-85. http://dx.doi.org/ 10.2106/JBJS.F.00666
9 57. Williams GN, Gangel TJ, Arciero RA, Uhorchak JM, Taylor DC. Comparison of the Single Assessment Numeric Evaluation method and two shoulder rating scales: outcomes measures after shoulder surgery. Am J Sports Med 1999;27:214-21. 58. Wolff J. The law of bone remodelling. Heidelberg: Springer-Verlag; 1986. 59. Youn SM, Deo S, Poon PC. Functional and radiologic outcomes of uncemented reverse shoulder arthroplasty in proximal humeral fractures: cementing the humeral component is not necessary. J Shoulder Elbow Surg 2016;25:e83-9. http://dx.doi.org/10.1016/j.jse.2015.09.007
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ORIGINAL ARTICLE
Radiographic changes and clinical outcomes associated with an adjustable diaphyseal press-fit humeral stem in primary reverse shoulder arthroplasty Samuel M. Harmsen, MDa,*, Tom R. Norris, MDb a
The Orthopedic Clinic Association, Phoenix, AZ, USA The San Francisco Shoulder, Elbow and Hand Clinic, San Francisco, CA, USA
b
Background: Press-fit humeral fixation in reverse shoulder arthroplasty (RSA) has become increasingly popular; however, radiographic analysis of these stems is limited. We aimed to evaluate the radiographic and clinical outcomes of an adjustable diaphyseal press-fit humeral stem in primary RSA. Methods: We conducted a retrospective review of 232 primary RSAs in 219 patients performed by a single surgeon using this system. Radiographic outcomes were evaluated in patients with at least 2 years of radiographic follow-up. Standardized postoperative digital radiographs were analyzed for loosening, osteolysis, and stress shielding. Clinical outcomes in patients who also had complete clinical data sets were evaluated at the most recent follow-up. Results: Radiographic evidence of loosening was identified in 1 RSA (0.4%) associated with deep infection. Aseptic loosening was not observed. No stems were identified as being at high risk for loosening. Internal stress shielding was observed proximal to the coated diaphyseal component in 226 shoulders (97.4%). This finding was often visible at 3 months (92.7%) and predictably progressed on subsequent radiographs. Progression beyond the 2-year period was rarely seen (4.4%). No external stress shielding or osteolysis was observed. Thirty-six complications occurred in 33 patients (15.1%). At an average follow-up of 36.6 months, significant improvements were identified in all measured clinical outcomes (P < .001). Conclusion: Predictable fixation is achieved using an adjustable diaphyseal press-fit humeral system in primary RSA. Internal stress shielding is commonly observed but does not appear to compromise quality of fixation or clinical outcomes. Level of evidence: Level IV; Case Series; Treatment Study © 2017 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved. Keywords: Reverse shoulder arthroplasty; press-fit; stress shielding; humeral loosening; radiographic analysis; adjustable reverse
The California Pacific Medical Research Institute Institutional Review Board approved this study, study number 27.007. *Reprint requests: Samuel M. Harmsen, MD, The Orthopedic Clinic Association, PC, 2222 E Highland Ave, #300, Phoenix, AZ 85016, USA. E-mail address: [email protected] (S.M. Harmsen).
Shoulder replacement surgery is associated with good to excellent results for a variety of shoulder pathologies7,12,16,27,37,41,49-51 and has become increasingly popular.11,22 As the incidence of these operations increases,
1058-2746/$ - see front matter © 2017 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved. http://dx.doi.org/10.1016/j.jse.2017.02.006
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S.M. Harmsen, T.R. Norris
the number of complications will inevitably increase as well. Complication profiles have been well documented and suggest that glenoid component loosening is the primary mode of failure.2,35,37,46,55 Humeral component loosening is much less common. Historically, successful humeral fixation with low loosening rates has been achieved with cementation techniques.23,24,39,43 Recently, however, the use of press-fit humeral components has become more prevalent.12,14,18,28,38,45,54 Proposed advantages of press-fit fixation include decreased operative time and lower complication rates with stem removal during revision surgery. Early-generation press-fit humeral components were associated with high loosening rates and poor results.44,48,51 With improvements in technology and techniques, later-generation implants have shown much more favorable results with low loosening rates.12,14,18,24,28,38,45,54 However, significant radiographic humeral changes, including stress shielding, osteolysis, and radiolucent lines, have been observed.28,29,34,38,45 Stress shielding and osteolysis of the femur have been associated with poor clinical outcomes with hip arthroplasty,13,34,38 but these radiographic changes have not yet been shown to correlate with poor clinical results in anatomic shoulder arthroplasty. Reverse shoulder arthroplasty (RSA) has revolutionized the care of patients with cuff-deficient shoulder pathologies.5,6,8-10,15,26,31,33,36,56 As with anatomic shoulder arthroplasty, humeral component loosening has not been reported with high incidence, and a shift toward the use of press-fit humeral systems has been seen with successful clinical outcomes. However, few studies have assessed the radiographic changes seen with press-fit stems in RSA.17,30,59 This study evaluated the radiographic and clinical outcomes of an adjustable diaphyseal press-fit humeral system in primary RSA. This system consists of a fully hydroxyapatite-coated diaphyseal component, optional smooth segmental stacking inserts if required, and a detachable smooth inset metaphyseal component (Fig. 1). Height and version can be adjusted at the time of initial implantation or revision surgery without the need to remove the fixed diaphyseal component. We hypothesize that this system will (1) provide predictable press-fit fixation with low loosening rates, (2) have
Figure 1
Adjustable diaphyseal press-fit humeral system.
a high rate of proximal stress shielding secondary to solid diaphyseal fixation, and (3) be associated with excellent clinical outcomes, consistent with the RSA literature, that are unaffected by the radiographic changes observed.
Materials and methods We retrospectively reviewed all primary RSAs performed by the senior author (T.R.N.) using the adjustable press-fit humeral system between 2007 and 2013. All patients in this series were entered in a prospectively gathered database intended for outcome analysis of shoulder replacement surgery. All patients provided consent for inclusion in the database before surgical intervention. The inclusion criteria for this study were primary RSA using the Aequalis Adjustable Reverse Shoulder System (AARS; Tornier, Inc., Edina, MN, USA) for any indication, minimum of 2-year radiographic follow-up, and complete radiographic series at each followup interval. All revision operations were excluded. As a secondary outcome, clinical results in those patients who met the inclusion criteria and who also had complete preoperative and postoperative clinical data sets extending to or beyond 24-months were also evaluated. All preoperative, intraoperative, and postoperative records and imaging were reviewed. Patient demographics, indications for surgery, complications, and radiographic findings were reviewed. If revision surgery was required, the utility of the adjustable system for improving stability with height or version changes, the ability to retain and reuse the diaphyseal component, and any complications associated with removal of the diaphyseal component, if required, were also assessed.
Radiographic evaluation Postoperative digital radiographs were obtained at time 0, 3 months, 6 months, 1 year, 2 years, and at the most recent follow-up. Standard radiographs included true anteroposterior (with the humerus in neutral rotation), scapular Y, and axillary views. Axillary views were not obtained at time 0 but were obtained at all other scheduled times. All preoperative and postoperative radiographs were obtained using a standardized technique and performed by the same technician. All radiographs were assessed for subsidence or migration of the humeral component, presence of radiolucent lines around the humeral component, osteolysis, and stress shielding by three American Shoulder and Elbow Surgeons (ASES) shoulder and elbow fellowship-trained orthopedic surgeons. A consensus was reached on all radiographic changes identified. The humeral component was divided into 7 zones.5,44,48 Zones 1 and 7 included the metaphyseal component and extended to the level of the diaphyseal/metaphyseal component junction. This junction represented the transition zone from smooth to the hydroxyapatite-coated implant. If stack spacers had been placed, these zones were extended beyond the metaphysis distally to the level of the smooth spacer/coated stem junction. Zones 2 and 6 represented the proximal half of the diaphyseal component. Zones 3 and 5 represented the distal half of the diaphyseal component. Zone 4 represented the area distal to the tip of the stem (Fig. 2). Radiolucent lines were assessed according to Sperling et al49: measured in 0.5-mm increments up to 2 mm and then identified as >2 mm. If radiolucent lines were identified, each subsequent radio-
ARTICLE IN PRESS Adjustable press-fit humeral stem in RSA
Figure 2 Humeral zones for radiographic analysis. (A) The humeral stem was divided into 7 zones. (B) Zones 1 and 7 were proximal to the junction of the smooth metaphyseal component and the coated diaphyseal component. The remaining zones were distal to this junction (indicated by arrow) and surrounded the press-fit diaphyseal component as above. graphic series was critically evaluated for progression of lucency. Progression was defined as an increase in width of >0.5 mm or extension along the implant into the adjacent zone, or both. If radiolucent lines >2 mm were present in ≥3 zones, the implant was considered to be at high risk for loosening. If subsidence or stem migration was identified, the implant was deemed loose. Radiographs were also assessed for cortical resorption and stress shielding.34
Clinical evaluation Functional outcome scores (FOS), active range of motion (AROM), and strength measurements were collected preoperatively and at each annual postoperative visit. FOS included the ASES score,40 the Simple Assessment Numeric Evaluation,57 and the visual analog scale for pain. AROM was measured in 5° increments using a goniometer with a standardized method in the seated position. Motions included forward flexion and external rotation with the arm held at 0° of abduction and at 90° of abduction. Abduction strength in the scapular plane was measured using a dynamometer as described by Moeller et al.32 FOS, AROM, and strength at the most recent follow-up were compared with preoperative values using a paired Student t test. Reviewers were blinded to the radiographic outcomes of each patient. Statistical significance was set at P < .01. Data were analyzed with Excel software (Microsoft Corp., Redmond, WA, USA).
Operative technique The surgical technique for RSA has been well described.4,20,56 Most of this procedure, including exposure, head cut, metaphyseal preparation, and glenoid preparation, follows these standard techniques. Humeral sizing, implant assembly, and techniques for adjustments in height and version are specific to the AARS system. Once the metaphyseal preparation is complete, the canal is sized with pro-
3 gressive trials until snug fixation of the trial stem is achieved. Height is then measured using the markings on the trial stem inserter in relation to the greater tuberosity. If necessary, smooth inserts can be added to achieve stable diaphyseal fixation when in-between stem sizes. The final component, including the appropriate diameter diaphyseal stem, smooth inserts, if necessary, and the smooth metaphyseal component, is assembled and secured with a locking screw securitization system. The assembled component is then impacted into the humeral canal in the desired version. Humeral inserts are trialed in a standard fashion, and the appropriate insert is impacted onto the metaphyseal component. If necessary, version can be adjusted in 10° increments without removing the press-fit diaphyseal stem by removing the securitization system and turning the metaphysis. Spacers can also be added if the height needs to be adjusted. The RSA is then reduced in standard fashion. The addition of a stacking insert was needed in 13 shoulders to obtain stable distal fixation at time of the primary surgery. For example, if a 9-mm stem was too small and an 11-mm stem was too large to gain stable press-fit fixation, additional stem length was obtained by adding stacking spacers of various lengths to the 9-mm stem. The added length facilitates the ability to gain stable fixation further distal as the humeral canal narrows. All humeral head cuts were made at 155° of inclination and 30° of retroversion. All but 13 shoulders were performed using the Bony Increased Offset (BIO)RSA technique (Tornier) on the glenoid side for glenoid bone defect grafting, lateralization, or both. All procedures were performed with the patient under general anesthesia with regional interscalene nerve block in the beach chair position through a standard deltopectoral approach. All operations were completed by or under the direction of the senior author.
Postoperative protocol All shoulders were immobilized with a sling and abduction pillow for 4 to 6 weeks, coming out of the sling 3 times a day to do pendulum, elbow, wrist, and hand exercises. Patients were also allowed to come out of the sling for hygiene. The hand could be used for simple tasks; however, no active lifting was allowed. After 4 to 6 weeks, the sling was discontinued, physical therapy consisting of gradual range of motion and progressive strengthening exercises was initiated, and progression of activities as tolerated was allowed.
Results Radiographic analysis A total of 232 RSA in 219 patients with a mean follow-up of 26.4 months (range, 23.7-82.2 months) met the inclusion criteria for radiographic analysis. Migration and clear radiographic loosening was seen in 1 shoulder (0.4%). This shoulder was diagnosed with a deep infection (Propionibacterium acnes) and underwent 2-stage revision RSA with an AARS. No shoulder met criteria for high risk of loosening. No radiolucent lines >1 mm were identified around the diaphyseal component (zones 2-6). Radiolucent lines ≤1 mm in width were identified in zones 2-6 in 14 shoulders (6.0%). Of these shoulders, only 2 had radiolucent lines in >1 zone, both of
ARTICLE IN PRESS 4
S.M. Harmsen, T.R. Norris Table I
Patient demographics
Variable
Radiographic analysis
Clinical analysis*
Reverse shoulder arthroplasty, No. Left Right Sex, No. Male Female Age at time of surgery, average (range), y Follow-up, mean (range), mo Indication, % Cuff tear arthropathy Massive rotator cuff tear Primary osteoarthritis with posterior glenoid bone loss Post-traumatic sequela Rheumatoid arthritis Primary osteoarthritis with rotator cuff tear Postinfectious arthropathy Acute proximal humeral fracture
232 88 144 219 116 103 67.7 (35-89) 26.4 (23.7-82.2)
174 70 104 164 82 82 68.2 (35-89) 36.6 (23.7-82.2)
89 69 31 21 10 5 5 2
69 49 29 16 8 2 3 2
* 55 patients from the radiographic analysis did not have complete clinical data sets and therefore were excluded.
which had lines in zones 2 and 6. Radiolucent lines were identified around the smooth metaphyseal component (zones 1 and 7) in 226 shoulders (97.4%) This finding was observed in 215 shoulders (92.7%) at 3 months. Advancement in radiolucent line width was seen in all but 2 of these shoulders during the first 2 years. However, in 70 shoulders that had radiographs at and after 24-months (mean, 42.2; range, 31.3-82.2 months), further advancement was rarely seen (4.3%). No radiolucent lines had a width >3 mm. No progression of radiolucent lines into the adjacent zones (from zone 1 to 2 or zone 7 to 6) was identified. No cortical resorption was identified. Osteolysis involving the humerus was not identified, despite 3 shoulders with radiographic evidence of osteolysis of the glenoid and 30 shoulders with scapular notching.
Clinical analysis There were 174 RSAs in 164 patients, with an average followup of 36.6 months (range 23.7-82.2 months), that met inclusion criteria for clinical analysis. Of the patients included in the radiographic analysis, 25% were excluded because of incomplete clinical data sets, resulting in a 75% recruitment rate. It is important to note that radiographic changes consistent with proximal zone radiolucencies described above were identified in 171 of the 174 RSAs (98.3%) included in the clinical analysis. Demographic information is listed in Table I. Significant improvement in FOS, ROM, and abduction strength in the scapular plane was observed (P < .01). The ASES score improved from 32.3 preoperatively to 77.5 postoperatively (P < .001). Forward flexion increased from 81° to 123°. All clinical results are listed in Table II. When all patients, with or without complete clinical data sets, were included, 36 complications occurred in 33 pa-
tients (15.1%). Complications included acromial/scapular spine stress fracture (n = 7), deep infection (n = 7), baseplate failure (n = 6), dislocation (n = 5), transient neuropathy (n = 4), superficial infection (n = 3), postoperative periprosthetic Vancouver C humeral shaft fracture (n = 1), humeral shaft fracture during implant removal (n = 1), baseplate malposition (n = 1), and retained drill fragment (n = 1). Failures, defined as requiring revision surgery, were documented in 17 RSAs. In 11 of these shoulders, the diaphyseal component was retained and used for revision RSA. These included 6 baseplate failures and 1 baseplate malposition that required revision. In these revisions, the ability to easily remove and replace the metaphyseal component facilitated glenoid visualization without the need for humeral stem removal. Segmental stacking inserts were easily added to increase the height and improve tension in 3 cases for correction of instability. The other retained stem was left in place during stage 1 of a 2-stage revision RSA for treatment of a deep infection. This stem was successfully reused at the time of the second stage (Fig. 3). Six stems were removed for treatment of deep infection. One of these stems was loose and was easily removed. The other 5 stems were well fixed and were explanted using various stem removal techniques. An iatrogenic humeral shaft fracture occurred in 1 patient. No other complications occurred during stem removal.
Discussion Recently, there has been a trend toward the use of press-fit humeral stems in shoulder replacement surgery. Although a number of studies have evaluated the radiographic changes observed with these implants, most analyzed results with anatomic shoulder replacement.14,18,24,28,29,38,45,48,51,52,54 Early
ARTICLE IN PRESS Adjustable press-fit humeral stem in RSA
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Table II Mean clinical outcomes in primary reverse shoulder arthroplasty using the Aequalis Adjustable Reverse Shoulder System* pressfit humeral stem† Variable‡
Preoperative Postoperative** Improvement
Functional outcome scores
Objective clinical measurements
ASES
SANE
VAS pain
AFF (°)
AER (°)
ABER (°)
STR§ (lbs)
32.2 (16.9) 77.5 (15) 45.2
23.4 (18.7) 76.7 (17) 53.3
6.5 (2.0) 0.9 (1.4) –5.6
81 (36) 123 (26) 42
20 (20) 32 (17) 12
37 (31) 58 (24) 21
3.0 (3.8) 7.4 (4.4) 4.4
ABER, abduction, external rotation; AER, active external rotation; AFF, active forward flexion; ASES, American Shoulder and Elbow Surgeons; SANE, Simple Assessment Numeric Evaluation; STR, strength; VAS, visual analog scale. * Tornier, Inc., Edina, MN, USA. † All changes statistically significant with P < .001 (paired t test). ‡ Data are shown as mean (standard deviation). § Measured with arm in 90° of abduction in the scapular plane with a dynamometer. ** Mean 36.6 mo.
Figure 3 Utility of Aequalis Adjustable Reverse Shoulder System (Tornier, Inc., Edina, MN, USA) in revision reverse shoulder arthroplasty (RSA). This patient was treated for a deep infection with a 2-stage RSA. (A) The diaphyseal press-fit component was retained at stage 1. The patient underwent treatment with an antibiotic loaded cement spacer and 6 weeks of intravenous antibiotics. (B) The well-fixed adjustable stem was built upon at the time of the second-stage RSA with a new metaphyseal component, providing solid fixation at time 0. Intraoperative cultures at this point showed no growth at 14 days. The patient went on to full recovery.
experience with the press-fit technique showed a high failure rate. Torchia et al51 reviewed the long-term results seen with press-fit stems that were initially designed for cemented total shoulder arthroplasty and found evidence of shift in the humeral component in 49% of press-fit shoulders compared with 0% of those that were cemented. Sanchez-Sotelo et al44 saw similarly poor results with this implant and reported a radiographic risk of loosening in 55.6% at medium- to longterm follow-up. As improvements in design, coating, and configuration have been made with later generations of press-
fit humeral stems, loosening rates have significantly improved, with rates approaching 0.0%.24,38,45,54 As a result, press-fit humeral stems have become increasingly popular in anatomic shoulder replacement. Humeral component loosening has been identified as a cause for revision in RSA.3,47 Boileau et al3 reported 10 RSAs that required revision for humeral loosening, accounting for 17% of the revisions performed during a 12-year period. Whether these stems were press-fit or cemented is not clear. A number of studies have reported very low loosening rates of press-fit humeral stems with RSA.17,18,30,42,59 Our loosening rate of 0.4% is comparable to the literature, particularly because the single case of loosening within our series was attributable to infection. In addition, radiolucent lines around the diaphyseal component (zones 2-6), even in single zones, were rarely seen with this implant and occurred much less frequently than those seen with other RSA implants. This finding may be secondary to the location of fixation achieved. This system achieves fixation in the diaphysis alone, whereas other systems achieve fixation in the metaphysis or in both the diaphysis and metaphysis. Although the loosening rate with modern press-fit humeral stems approaches 0.0%, alarming rates of other radiographic changes, such as stress shielding and osteolysis, have been reported.24,28,29,34,38,45 Stress shielding is defined as an adaptation of the bone to changes in stress distribution, following Wolff’s law.34,58 These changes can manifest as “external” (thinning and resorption of the external cortex) and “internal” (increasing porosity and resorption of cancellous bone) remodeling. In our study, we saw no evidence of osteolysis or external stress shielding; however, we did appreciate a consistent radiolucent line around the smooth metaphyseal component in most cases. The width of these radiolucent lines predictably increased over time through the first 2 years, indicating resorption of the surrounding cancellous bone. Although we would not expect to see bony ongrowth in these areas, we also did not expect resorption of the immediate surrounding
ARTICLE IN PRESS 6
S.M. Harmsen, T.R. Norris
Figure 4 Internal stress shielding observed over time. (A) Immediate postoperative radiograph shows no radiolucency. (B) At 3 months, a small 0.5-mm lucency can be seen around the smooth metaphyseal component. (C) At 22 months, the width of the lucency has increased compared to that seen at 3 months. (D) At 46 months (most recent), no significant change is seen in lucency width compared with that seen at 22 months. The lucencies do not extend beyond the smooth metaphyseal component. No lucencies are seen distal to the smooth/fullycoated junction. This is thought to represent internal stress shielding.
cancellous bone. This resorption was thought to represent internal stress shielding (Fig. 4). Our observed rate of stress shielding of 97.4% is much higher than reported rates in shoulder arthroplasty with a pressfit humeral stems: 9% by Nagels et al,34 63% by Raiss et al,38 62% by McElwain and English,29 51.9% by Schnetzke et al,45 and 58.8% by Matsen et al.28 Comparing these results, however, is difficult and confounding. We observed internal stress shielding with no occurrences of external stress shielding, whereas a number of prior studies identified external stress shielding with the presence of bone islands or cortical thinning and resorption, or both. Furthermore, Huiskes21 reported that fully ingrown diaphyseal stems are associated with higher rates of stress shielding then proximally ingrown stems. The implant used in this study is a complete diaphyseal fit stem, whereas stems in the other mentioned studies are metaphyseal only or are combined fit implants. As such, we should expect a higher rate of stress shielding with this stem. Lastly, our study evaluated changes seen in RSA, whereas the others investigated changes seen in anatomic systems. It may be that the intrinsic semiconstrained design of the RSA leads to increased stress shielding caused by altered stresses across the humeral component. There are conflicting studies within the hip literature regarding the clinical effect of stress shielding; however, the general consensus is that it can lead to inferior results.1,13,19,25,52,53 The effect of stress shielding in shoulder arthroplasty, particularly RSA, is unclear. Studies that evaluate stress shielding in anatomic shoulder replacement suggest that the adaptive changes seen are not associated with a negative effect on functional outcomes.29,38,45 In our study, excellent clinical results were obtained at short- to midterm follow-up in primary RSA despite the high incidence of internal stress shielding observed. Whether results will change with longer follow-up, with concerns of progression and eventual component loosening,
is unclear. However, we observed a maturity, or halt of progression, of the internal stress shielding beyond 2 years. In addition, we did not appreciate any progression of radiolucency into adjacent diaphyseal zones over time. If these findings hold true over time, the observed internal stress shielding may not have a significant effect on clinical results through long-term follow-up. More studies with longer followup are needed to better understand the clinical effect of stress shielding in both anatomic and reverse shoulder arthroplasty. The adjustable nature of this system proved beneficial both at the time of implantation and during revision surgery. Quick and easy lengthening of the prosthesis allowed for diaphyseal press-fit fixation in cases where the humeral canal was in between stem sizes proximally. Removal of the smooth metaphyseal component also provided for safe, adequate glenoid exposure in revision surgery without the need to remove the well-fixed humeral component, avoiding potential complications. In these cases, the metaphyseal component was able to be reconnected to the well-fixed diaphyseal component with version adjustment performed as needed. Three cases of instability were successfully addressed by adding stack spacers to the well-fixed stem. It is important to note that instability with RSA is much more complicated than tension and version alone and may require other revision options to correct; however, increasing tension was successful in treating the instability in these 3 patients. These features could prove beneficial if revision surgery is required. This study has a number of limitations. Although the data were prospectively gathered, the inherent limitations of a retrospective review and single-surgeon study are present. The study evaluated a large cohort of patients, but the follow-up duration was short. Longer follow-up is needed to better understand the effect of stress shielding on RSA outcomes over time.
ARTICLE IN PRESS Adjustable press-fit humeral stem in RSA Multivariate analysis was not performed to assess for correlations between variables and the radiographic changes seen. However, the changes seen were almost universal, and as such, specific correlations likely do not exist. Of the RSAs and patients with a radiographic evaluation, 25% did not meet inclusion criteria for clinical analysis. Correlations between radiographic changes and clinical outcomes are therefore limited. However, in the 174 RSA that met inclusion for both radiographic and clinical analysis, 98.3% of shoulders had radiographic changes of internal stress shielding. Lastly, although good to excellent interobserver and intraobserver reliability has been shown when evaluating for radiolucent lines on digital radiographs, we did not perform our own reliability analysis. Strengths of this study include the large study size, consistent prospective radiographic and clinical data collection techniques, blinding of reviewers to radiographic changes and clinical outcomes, and complete data collection. This is the first study to evaluate radiographic or clinical outcomes of an all-diaphyseal press-fit humeral system in RSA and is the largest study of which we are aware to evaluate the radiographic changes associated with press-fit humeral stems of any kind in RSA.
Conclusion The adjustable diaphyseal press-fit humeral system provides predictable, stable humeral fixation in primary RSA and is associated with excellent short- to midterm clinical outcomes that are consistent with the RSA literature.6,8-10,15,26,31,33,36,56 A high rate of internal stress shielding is consistently observed in the early postoperative period and predictably progresses over the short-term. Progression beyond 2 years rarely occurs. These radiographic humeral changes do not adversely affect clinical outcomes in short- to midterm follow-up. The adjustability of the system can be successfully used in primary and revision situations. This system can be recommended for use in primary RSA.
Disclaimer Tornier, Inc. provided funding for database management, which was performed by User Friendly Custom Software Inc. (Houston, TX, USA). Tom Norris reports that he received royalties and consultant payments from Tornier Inc., which were related to the subject of this work, and also received financial support from Tornier, Inc. for the database used in the study. Samuel M. Harmsen, his immediate family, and any research foundations with which they are affiliated did not receive any financial payments or other benefits from any commercial entity related to the subject of this article.
7
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9 57. Williams GN, Gangel TJ, Arciero RA, Uhorchak JM, Taylor DC. Comparison of the Single Assessment Numeric Evaluation method and two shoulder rating scales: outcomes measures after shoulder surgery. Am J Sports Med 1999;27:214-21. 58. Wolff J. The law of bone remodelling. Heidelberg: Springer-Verlag; 1986. 59. Youn SM, Deo S, Poon PC. Functional and radiologic outcomes of uncemented reverse shoulder arthroplasty in proximal humeral fractures: cementing the humeral component is not necessary. J Shoulder Elbow Surg 2016;25:e83-9. http://dx.doi.org/10.1016/j.jse.2015.09.007