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Do short stems influence the cervico-diaphyseal angle and the medullary filling after reverse shoulder arthroplasties?
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Original article
Do short stems influence the cervico-diaphyseal angle and the medullary filling after reverse shoulder arthroplasties? Alexandre Lädermann a,b,c,d , Joe Chih-Hao Chiu e , Grégory Cunningham a,c , Anthony Hervé f , Sébastien Piotton a , Hugo Bothorel g,∗ , Philippe Collin f a
Division of Orthopaedics and Trauma Surgery, La Tour Hospital, Meyrin, Switzerland Faculty of Medicine, University of Geneva, Geneva, Switzerland c Division of Orthopaedics and Trauma Surgery, Department of Surgery, Geneva University Hospitals, Geneva, Switzerland d Division of Orthopaedics and Trauma Surgery, Hirslanden Clinique La Colline, Geneva, Switzerland e Department of Orthopaedic Sports Medicine, Chang Gung Memorial Hospital, Taoyuan City, Taiwan f Centre Hospitalier Privé Saint-Grégoire (Vivalto Santé), Saint-Grégoire, France g ReSurg SA, Rue Saint-Jean 22, 1260 Nyon, Switzerland b
a r t i c l e
i n f o
Article history: Received 20 August 2019 Accepted 18 December 2019 Available online xxx Keywords: Reverse shoulder arthroplasty Neck shaft angle Canal Fill Ratio Short stem Varus Valgus
a b s t r a c t Background: Shorter humeral stems were developed to improve bone preservation, vascularity and osteointegration in reverse total shoulder arthroplasty (RSA). While some studies examined the relationship between canal filling and radiographic changes, none evaluated the association between stem alignment and canal fill ratio (CFR). Hypothesis: The hypothesis was that stem misalignment after RSA would be associated with lower CFR. Patients and methods: The authors retrospectively reviewed immediate postoperative radiographs of 157 patients, comprising 56 men (36%), who underwent RSA with a short uncemented stem with neck shaft angle (NSA) default of 145◦ . The parameters included postoperative NSA and metaphyseal CFR, both measured with excellent inter-observer agreement. Uni- and multivariable linear regressions were performed to determine associations between postoperative NSA and 5 variables (CFR, gender, age, BMI, and surgical approach). Results: Postoperative NSA was 149◦ ± 8◦ , exceeding 5◦ of varus in 15 shoulders (9%) and 5◦ of valgus in 60 shoulders (38%), and CFR was 58% ± 8%. CFR was lower in shoulders with varus stem alignment (54% ± 6%) than shoulders with neutral stem alignment (59% ± 8%, p = 0.033). Multivariable regression revealed that postoperative NSA increased with age (beta: 0.20; p = 0.008), was higher for shoulders operated with the subscapularis- and deltoid-sparing approach (beta: 3.82; p = 0.040) but lower for men (beta: −4.14; p = 0.002). Conclusions: Stem misalignment exceeded 5◦ in 47% of the shoulders. Women, older age, and subscapularis- and deltoid-sparing approach are associated with greater risks of valgus stem positioning, while lower CFR seems to be associated with greater risks of varus stem positioning. Level of evidence: IV; case series. © 2020 Elsevier Masson SAS. All rights reserved.
1. Introduction Reverse total shoulder arthroplasty (RSA) is a procedure commonly used to treat patients with rotator cuff deficiencies [1–3], and is increasingly performed worldwide due to aging populations and expanding indications [4,5]. While RSA grants satisfactory functional improvements and pain relief, it is frequently
∗ Corresponding author. E-mail address: [email protected] (H. Bothorel).
associated with scapular notching [6]. The incidence of this complication can be decreased with greater lateralization [7–11], eccentricity [7–15], and size [16,17] of the glenosphere, thereby increasing range of motion in external rotation. Low postoperative neck shaft angle (NSA) can also reduce scapular notching and thereby improve adduction range [18], but on the other hand could lead to impingement of the greater tuberosity on the acromion and hence limit the abduction range [19]. Shorter humeral stems were developed to improve bone preservation, vascularity and osteointegration as well as to facilitate revision [20]. Despite promising results [21–23], short stems are
https://doi.org/10.1016/j.otsr.2019.12.010 1877-0568/© 2020 Elsevier Masson SAS. All rights reserved.
Please cite this article in press as: Lädermann A, et al. Do short stems influence the cervico-diaphyseal angle and the medullary filling after reverse shoulder arthroplasties? Orthop Traumatol Surg Res (2020), https://doi.org/10.1016/j.otsr.2019.12.010
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2 Table 1 Patient characteristics.
2.2. Implant and surgical technique Entire cohort (n = 159 shoulders)
Male sex Operated side: right Age (yrs) BMI Canal fill ratio (%) Neck shaft angle (◦ ) Implant by default Postoperative Post minus default
Mean ± SD
Range
57 (35.8%) 109 (68.6%) 74.3 ± 8.0 27.0 ± 4.6 57.7 ± 8.2
(48.0–93.0) (17.6–48.3) (38.6 74.0)
145.0 149.0 4.0 ± 7.9
(133.5–176.5) (−11.5 to −31.5)
SDS: subscapularis- and deltoid-sparing; Post: postoperative.
more difficult to align than long stems, where the distal portion serves as an intramedullary guide. To date, few studies [24–26] have reported stem misalignment, whether due to imprecise humeral resections and entry point, insufficient canal filling, or a combination thereof. While some studies examined the relationship between canal filling and radiographic changes [25–27], none evaluated the association between stem alignment and canal fill ratio (CFR). The purpose of this study was therefore to evaluate humeral stem alignment after RSA (difference between default NSA and postoperative NSA), and to evaluate whether it was associated with CFR. The hypothesis was that stem misalignment would be associated with lower canal fill. 2. Material and methods 2.1. Patients The authors retrospectively reviewed immediate postoperative radiographs of 205 consecutive patients who underwent primary RSA between May 2013 and December 2017 by two experienced surgeons. The inclusion criteria were: • presence of primary gleno-humeral osteoarthritis, cuff tear arthritis, massive cuff tears or rheumatoid arthritis without avascular necrosis of the humeral head; • RSA performed using the Aequalis AscendTM Flex short stem (Tornier SAS–Wright Medical Inc® , Bloomington, MN, USA). The authors did not include patients with massive cuff tears without gleno-humeral osteoarthritis, because this rare etiology is increasingly treated by partial or complete rotator cuff repair, with satisfactory long-term outcomes [28,29]. The exclusion criteria were: • presence of postoperative humeral fractures (n = 2); • loose implant stems (n = 1); • with unusable radiographs due to incorrect beam incidence (n = 45). This left a cohort of 157 patients (159 shoulders), comprising 56 men (57 shoulders) and 101 women (102 shoulders), aged 74.3 ± 8.0 (median: 74.0; range: 48.8–93.0) at index surgery with a body mass index (BMI) of 27.0 ± 4.6 (median: 26.4; range: 17.6–48.3) (Table 1). The operations involved the right shoulder in 108 patients (69%), the left shoulder in 47 patients (30%) and both in 2 patients (1%). The study protocol was approved by the Medical Ethics Committee of the Clinique Vivalto Santé (CERC-VS-2016-071) and of the “Association des Médecins du Canton de Genève et Société Médicale” (protocol 12-26).
The Aequalis AscendTM Flex is a second-generation convertible stem made of titanium, and proximally coated with titanium plasma spray for metaphyseal press-fit fixation. Its onlay design with a reversed tray of low (1.5 mm) or high (3 mm) offset has a total inclination angle of 145◦ (132.5◦ inclination of the stem + 12.5◦ inclination of the asymmetric polyethylene insert). Whilst the Aequalis AscendTM Flex is available in standard and short lengths, this series comprised exclusively short stems (66 mm to 94 mm), with geometrically proportional diameter. A deltopectoral approach was used in 140 shoulders and a subscapularis- and deltoid-sparing approach in 19 shoulders [30]. Humeral osteophytes at the anatomic neck were resected. Where the deltopectoral approach was taken, a guide was used to perform the neck resection with 132.5◦ . Where the subscapularis- and deltoid-sparing approach was taken, an electrocoagulation device and a retroversion guide were used to delineate the osteotomy line on the humeral head, and a free-hand osteotomy was performed. If the inclination was suboptimal, subsequent revisions were performed to maximize the anatomic fit between the prosthesis and the resected bone area. In most shoulders, the humeral shaft was first sized using sounders. Metaphyseal bone was compacted to grant optimal rotational stability. A surface planer ensured adequate contact between the stem and the reversed tray. 2.3. Radiographic assessment Standard radiographs of the operated shoulders were assessed immediately after RSA, in a true anteroposterior view, defined by the visualization of the Morse taper. Radiographs were analyzed using a DICOM viewer (Osirix© v.5.8.1, Pixmeo, Bernex, Geneva, Switzerland) according to the method described by Goetzmann et al. [24] The parameters measured included NSA (defined as the angle between the diaphyseal axis and the perpendicular of the reversed tray, Fig. 1A), and CFR (calculated by dividing the mediolateral width of the stem by that of the inner bone cortex, both taken perpendicular to the diaphyseal axis 1 cm below the medial calcar-prosthesis junction, Fig. 1B). The authors preferred to study CFR at the metaphysis rather than at the diaphysis to ensure that measurements are comparable to those published by Goetzmann et al. [24]. In order to evaluate misalignment, postoperative NSA were compared to the default 145◦ . NSA of 145 ± 5◦ were considered normal, NSA > 150◦ were considered valgus and NSA < 140◦ varus. 2.4. Statistical analysis The NSA and CFR were measured on radiographs by a second observer (AH) for all 159 RSAs, to evaluate inter-observer agreement. The intra-class correlation coefficients (ICC) were excellent for both NSA (ICC = 0.85; CI: 0.80–0.89), and CFR (ICC = 0.81; CI: 0.71–0.87). The authors used the measurements performed by the first observer (JC) who was more experienced. Descriptive statistics were used to summarize the data. Shapiro–Wilk tests were used to assess the normality of distributions. For non-Gaussian continuous data, differences between groups were evaluated using Wilcoxon rank-sum tests (Mann–Whitney U test). For categorical data, differences between groups were evaluated using Fisher exact tests. For continuous variables, correlations were analysed using Pearson’s coefficients. Uni- and multivariable linear regressions were performed to determine associations between postoperative NSA and 5 independent variables (CFR, gender, patient age, BMI, and surgical approach). With a sample size of 159 shoulders, our regression model including 5 variables was deemed sufficiently powered, considering the
Please cite this article in press as: Lädermann A, et al. Do short stems influence the cervico-diaphyseal angle and the medullary filling after reverse shoulder arthroplasties? Orthop Traumatol Surg Res (2020), https://doi.org/10.1016/j.otsr.2019.12.010
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Fig. 1. True anteroposterior radiographs illustrating measurements of (A) Canal Fill Ratio: stem diameter (S)/humeral diameter (H); (B) Neck Shaft Angle.
Table 2 Patient characteristics by surgical approach. SDS approach (n = 19 shoulders)
Deltopectoral approach (n = 140 shoulders) Mean ± SD Male sex Operated side: right Age (yrs) BMI Canal fill ratio (%) Neck shaft angle (◦ ) Implant by default Postoperative Post minus default Stem alignment Neutral Varus Valgus
p-value
Range
Mean ± SD
54 (38.6%) 96 (68.6%) 74.0 ± 8.2 27.0 ± 4.5 58.0 ± 8.1
(48.0–93.0) (17.6–48.3) (40.8–74.0)
3 (15.8%) 13 (68.4%) 76.9 ± 5.9 27.0 ± 5.2 55.5 ± 8.7
(66.0–86.0) (19.8–43.4) (38.6–70.4)
145.0 148.3 ± 7.5 3.3 ± 7.5
(133.5–176.5) (−11.5 to 31.5)
145.0 154.0 ± 9.0 9.0 ± 9.0
(137.5–172.5) (−7.5 to 27.5)
79 (56.4%) 14 (10.0%) 47 (33.6%)
Range 0.073 1.000 0.109 0.953 0.266
0.004 0.004 0.009
5 (26.3%) 1 (5.3%) 13 (68.4%)
SDS: subscapularis- and deltoid-sparing; Post: postoperative; p-values in bold indicate significant differences.
recommendations of Austin and Steyerberg of a minimum of 2 subjects per variable for linear regression models [31]. Statistical analyses were performed using R version 3.3.3 (R Foundation for Statistical Computing, Vienna, Austria). p-values < 0.05 were considered statistically significant.
3. Results Postoperative NSA was 149.0◦ ± 7.9◦ (median, 147.9◦ ; range, 133.5◦ –176.5◦ ) and CFR was 57.7% ± 8.2% (median, 56.9%; range, 38.6%–74.0%) (Tables 1 and 2). The postoperative NSA was greater than default 145◦ by 4.0◦ ± 7.9◦ (median: 2.9◦ ; range: −11.5◦ to 31.5◦ ), exceeding 5◦ of varus in 15 shoulders (9.4%) and exceeding 5◦ of valgus in 60 shoulders (37.7%) (Fig. 2A and B).
Varus stem positioning was more present in men (66.7%), while valgus stem positioning was more present in women (78.3%) (Table 3). Of the 19 patients operated with the subscapularisand deltoid-sparing approach, 13 (68.4%) had a valgus stem position, while of the 140 patients operated with a deltopectoral approach, 47 (33.6%) had a valgus stem position (p = 0.015) (Table 2). Shoulders with varus stem positioning had lower CFR than shoulders with neutral stem positioning (53.8% ± 5.5% vs. 58.9% ± 8.3%, p = 0.033) (Fig. 3). Univariable regression revealed that postoperative NSA significantly increased with age (beta: 0.24; CI: 0.09–0.39; p = 0.002), but was lower for men (beta: −4.27; CI: −6.76 to −1.79; p = 0.001) and higher for shoulders operated by the subscapularis- and deltoid-sparing approach (beta: 5.67; CI: 1.97–9.37; p = 0.003) (Table 4). Multivariable regression confirmed that postoperative NSA independently increased with age (beta:
Please cite this article in press as: Lädermann A, et al. Do short stems influence the cervico-diaphyseal angle and the medullary filling after reverse shoulder arthroplasties? Orthop Traumatol Surg Res (2020), https://doi.org/10.1016/j.otsr.2019.12.010
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Fig. 2. True anteroposterior radiographs illustrating stem misalignments: (A) varus (B) valgus.
Table 3 Patient characteristics stratified by stem alignment.
Male sex Operated side: right Surgical approach Deltopectoral SDS Age (yrs) BMI Canal fill ratio (%) Post NSA (◦ )
Neutral stem position (n = 84) 140◦ < Postop NSA < 150◦
Valgus stem position (n = 15) Postop NSA ≤ 140◦
Mean ± SD
Mean ± SD
Range
34 (40.5%) 55 (65.5%)
10 (66.7%) 11 (73.3%)
79 (94.0%) 5 (6.0%) 72.8 ± 8.3 26.6 ± 4.7 58.9 ± 8.3 145.5 ± 2.8
14 (93.3%) 1 (6.7%) 74.1 ± 6.3 28.6 ± 5.9 53.8 ± 5.5 137.2 ± 2.1
(48.0–87.0) (19.7–48.3) (40.8–73.1) (140.2–149.9)
Range
(63.0–85.0) (21.7–44.6) (43.2–64.3) (133.5–140.0)
Valgus stem position (n = 60) Postop NSA ≥ 150◦ p-valuea
Mean ± SD
0.089 0.767 1.000
13 (21.7%) 43 (71.7%)
0.732 0.220 0.033 –
47 (78.3%) 13 (21.7%) 76.6 ± 7.5 27.2 ± 4.1 57.0 ± 8.3 156.9 ± 6.1
Range
p-valuea 0.020 0.472 0.009
(60.0–93.0) (17.6–43.4) (38.6–74.0) (150.5–176.5)
0.012 0.240 0.264 –
NSA: neck shaft angle; Post: postoperative; SDS: subscapularis- and deltoid-sparing; p-values in bold indicate significant differences. a Compared with the neutral stem position group.
0.20; CI: 0.05–0.35; p = 0.008), was higher for shoulders operated by the subscapularis- and deltoid-sparing approach (beta: 3.82; CI: 0.18–7.46; p = 0.040), but lower for men (beta: −4.14; CI: −6.72 to −1.57; p = 0.002). 4. Discussion The principal finding of the study was that 47% of stems were misaligned, with up to 12◦ of varus and 32◦ of valgus. Compared to shoulders with neutral stem positioning, shoulders with varus stems had lower CFR, confirming our hypothesis that stem misalignment is associated with lower canal fill. Misalignment of short humeral stems is a common but underreported problem. Raiss et al. [25] observed that 16% of RSA short stems had a > 5◦ misalignment, of which 4% were in varus and 12% in valgus position. In our series, 47% of RSA stems were misaligned, of which 9% in varus and 38% in valgus position. Goetzmann et al. [24] reported a maximum varus and valgus stem misalignment of 1.5◦ and 11.5◦ , while we reported up to 12◦ of varus and 32◦ of valgus misalignment. Multivariable analysis revealed that postoperative NSA was higher for women and increased with older age, likely due to poorer bone quality [32]. It is worth noting that surgical approaches can also have a real impact on stem alignment,
as multivariable analyses confirmed that shoulders operated by subscapularis- and deltoid-sparing approach had 4 more degrees of NSA compared to shoulders operated by deltopectoral approach. Our results revealed that shoulders with varus stems had lower CFR compared to those with neutral stem alignment. Interestingly, it seems that CFR was not associated with valgus stem positioning, which could explain why linear regressions did not confirm any association between CFR and postoperative NSA. Surgeons should therefore be cautious not to undersize RSA humeral stems to avoid varus stem positioning, which could increase the humeral offset, and decrease abduction range due to impingement of the greater tuberosity upon the acromion [19]. Short humeral stems rely on proximal fixation, and their size should be selected to ensure optimal canal filling, avoiding bone remodeling (due to oversizing) or insufficient primary fixation (due to undersizing). In their anatomic and reverse shoulder arthroplasty series, Schnetzke et al. [26] and Goetzman et al. [24] reported that, at 2-year follow-up, greater canal filling was associated with stress shielding (condensation lines, cortical bone resorption and spot welds). A recent consecutive series of RSA corroborated that patients with greater CFR (≥ 74%) are at higher risk of stress shielding than lower CFR (≤ 64%) [25]. It is worth noting that none of our shoulders had CFR greater than 74%.
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Table 4 Uni- and multivariable regression analysis of postoperative NSA. Univariable
Multivariable (159 shoulders)
Variable

95% CI
p-value

95% CI
p-value
Canal fill ratio Male gender Surgical approach Deltopectoral SDS Age BMI
−5.87 −4.27
(−21.04 to −9.30) (−6.76 to −1.79)
0.446 0.001
−12.45 −4.14
(−27.46 to 2.55) (−6.72 to −1.57)
0.103 0.002
REF 5.67 0.24 −0.35
(1.97–9.37) (0.09–0.39) (−0.22 to 0.19)
0.003 0.002 0.573
REF 3.82 0.20 0.02
(0.18–7.46) (0.05–0.35) (−0.23 to 0.28)
0.040 0.008 0.853
NSA: neck shaft angle; SDS: subscapularis- and deltoid-sparing; p-values in bold indicate significant differences.
alignment and CFR, with a sizeable series of RSA using a single stem design. 5. Conclusion While short uncemented stems offer several advantages in RSA, they remain challenging to align within the humerus. In our series, stem misalignment exceeded 5◦ in 47% of the shoulders. Women, older age and subscapularis- and deltoid-sparing approach are independently associated with greater risks of valgus stem alignment while lower canal filling is associated with greater risks of varus stem positioning. Surgeons and engineers should collaborate to develop new techniques and surgical tools to reduce alignment errors, which may compromise long-term clinical and radiographic outcomes. Disclosure of interest Author AL receives royalties from Wright and consulting fees from Medacta, Arthrex and Wright. Author PC declares royalties from Wright, Stortz and Advanced Medical Applications, as well as consulting fees from Wright, Smith and Nephew and ConMed. The other authors declare that they have no competing interest. Fig. 3. Boxplots illustrating the Canal Fill Ratio (%) for shoulders with different stem alignments (varus, neutral or valgus). Horizontal line = median; top and bottom of box = third and first quartiles; top and bottom of whiskers = 95% confidence interval.
Correct positioning of RSA stems is essential to optimize postoperative range of motion and limit potential mechanical complications. New surgical techniques are needed to improve stem positioning, not only for standard [33], but also for short stems that are more susceptible to misalignment. In fact, limited joint space could render the use of surgical guides difficult, leading to freehand osteotomy. Moreover, improvements in medical devices and surgical tools are required to optimize the entry point of the stem and canal filling, while ensuring adequate stem alignment. The limitations of this multicentric study include: • its retrospective design; • the heterogeneity of surgical techniques; • the fact that only one of the two surgeons used the subscapularisand deltoid-sparing approach; • the lack of postoperative clinical and radiographic data; • the inability to evaluate the influence of etiology, bone quality and diaphyseal canal filling; • the small number of shoulders with varus stems which prevented us from performing logistic regression analyses or establishing a cut-off value of CFR for which varus misalignment is more likely. Notwithstanding these limitations, to the authors’ knowledge, this study is the first to evaluate the association between stem
Funding sources This study was funded by a non-profit foundation for Research and Teaching in Orthopaedics, Sports Medicine, Trauma and Imaging (FORE), with no commercial interest in the present study. The source of funds was involved in data analysis and manuscript redaction. Contribution of authors AL participated in study design, data collection, manuscript writing and manuscript editing. JCHC participated in data collection, manuscript editing. GV, PC participated in study design, data collection, manuscript editing. AH participated in data collection, manuscript editing. SP participated in data collection, manuscript editing. HB participated in statistical analysis, manuscript writing. All authors approved the final manuscript. Acknowledgments The authors are grateful to Aude Michelet for her help in manuscript redaction. References [1] Boileau P, Sinnerton RJ, Chuinard C, et al. Arthroplasty of the shoulder. J Bone Joint Surg Br 2006;88:562–75. [2] Nolan BM, Ankerson E, Wiater JM. Reverse total shoulder arthroplasty improves function in cuff tear arthropathy. Clin Orthop Relat Res 2011;469:2476–82.
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Original article
Do short stems influence the cervico-diaphyseal angle and the medullary filling after reverse shoulder arthroplasties? Alexandre Lädermann a,b,c,d , Joe Chih-Hao Chiu e , Grégory Cunningham a,c , Anthony Hervé f , Sébastien Piotton a , Hugo Bothorel g,∗ , Philippe Collin f a
Division of Orthopaedics and Trauma Surgery, La Tour Hospital, Meyrin, Switzerland Faculty of Medicine, University of Geneva, Geneva, Switzerland c Division of Orthopaedics and Trauma Surgery, Department of Surgery, Geneva University Hospitals, Geneva, Switzerland d Division of Orthopaedics and Trauma Surgery, Hirslanden Clinique La Colline, Geneva, Switzerland e Department of Orthopaedic Sports Medicine, Chang Gung Memorial Hospital, Taoyuan City, Taiwan f Centre Hospitalier Privé Saint-Grégoire (Vivalto Santé), Saint-Grégoire, France g ReSurg SA, Rue Saint-Jean 22, 1260 Nyon, Switzerland b
a r t i c l e
i n f o
Article history: Received 20 August 2019 Accepted 18 December 2019 Available online xxx Keywords: Reverse shoulder arthroplasty Neck shaft angle Canal Fill Ratio Short stem Varus Valgus
a b s t r a c t Background: Shorter humeral stems were developed to improve bone preservation, vascularity and osteointegration in reverse total shoulder arthroplasty (RSA). While some studies examined the relationship between canal filling and radiographic changes, none evaluated the association between stem alignment and canal fill ratio (CFR). Hypothesis: The hypothesis was that stem misalignment after RSA would be associated with lower CFR. Patients and methods: The authors retrospectively reviewed immediate postoperative radiographs of 157 patients, comprising 56 men (36%), who underwent RSA with a short uncemented stem with neck shaft angle (NSA) default of 145◦ . The parameters included postoperative NSA and metaphyseal CFR, both measured with excellent inter-observer agreement. Uni- and multivariable linear regressions were performed to determine associations between postoperative NSA and 5 variables (CFR, gender, age, BMI, and surgical approach). Results: Postoperative NSA was 149◦ ± 8◦ , exceeding 5◦ of varus in 15 shoulders (9%) and 5◦ of valgus in 60 shoulders (38%), and CFR was 58% ± 8%. CFR was lower in shoulders with varus stem alignment (54% ± 6%) than shoulders with neutral stem alignment (59% ± 8%, p = 0.033). Multivariable regression revealed that postoperative NSA increased with age (beta: 0.20; p = 0.008), was higher for shoulders operated with the subscapularis- and deltoid-sparing approach (beta: 3.82; p = 0.040) but lower for men (beta: −4.14; p = 0.002). Conclusions: Stem misalignment exceeded 5◦ in 47% of the shoulders. Women, older age, and subscapularis- and deltoid-sparing approach are associated with greater risks of valgus stem positioning, while lower CFR seems to be associated with greater risks of varus stem positioning. Level of evidence: IV; case series. © 2020 Elsevier Masson SAS. All rights reserved.
1. Introduction Reverse total shoulder arthroplasty (RSA) is a procedure commonly used to treat patients with rotator cuff deficiencies [1–3], and is increasingly performed worldwide due to aging populations and expanding indications [4,5]. While RSA grants satisfactory functional improvements and pain relief, it is frequently
∗ Corresponding author. E-mail address: [email protected] (H. Bothorel).
associated with scapular notching [6]. The incidence of this complication can be decreased with greater lateralization [7–11], eccentricity [7–15], and size [16,17] of the glenosphere, thereby increasing range of motion in external rotation. Low postoperative neck shaft angle (NSA) can also reduce scapular notching and thereby improve adduction range [18], but on the other hand could lead to impingement of the greater tuberosity on the acromion and hence limit the abduction range [19]. Shorter humeral stems were developed to improve bone preservation, vascularity and osteointegration as well as to facilitate revision [20]. Despite promising results [21–23], short stems are
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2 Table 1 Patient characteristics.
2.2. Implant and surgical technique Entire cohort (n = 159 shoulders)
Male sex Operated side: right Age (yrs) BMI Canal fill ratio (%) Neck shaft angle (◦ ) Implant by default Postoperative Post minus default
Mean ± SD
Range
57 (35.8%) 109 (68.6%) 74.3 ± 8.0 27.0 ± 4.6 57.7 ± 8.2
(48.0–93.0) (17.6–48.3) (38.6 74.0)
145.0 149.0 4.0 ± 7.9
(133.5–176.5) (−11.5 to −31.5)
SDS: subscapularis- and deltoid-sparing; Post: postoperative.
more difficult to align than long stems, where the distal portion serves as an intramedullary guide. To date, few studies [24–26] have reported stem misalignment, whether due to imprecise humeral resections and entry point, insufficient canal filling, or a combination thereof. While some studies examined the relationship between canal filling and radiographic changes [25–27], none evaluated the association between stem alignment and canal fill ratio (CFR). The purpose of this study was therefore to evaluate humeral stem alignment after RSA (difference between default NSA and postoperative NSA), and to evaluate whether it was associated with CFR. The hypothesis was that stem misalignment would be associated with lower canal fill. 2. Material and methods 2.1. Patients The authors retrospectively reviewed immediate postoperative radiographs of 205 consecutive patients who underwent primary RSA between May 2013 and December 2017 by two experienced surgeons. The inclusion criteria were: • presence of primary gleno-humeral osteoarthritis, cuff tear arthritis, massive cuff tears or rheumatoid arthritis without avascular necrosis of the humeral head; • RSA performed using the Aequalis AscendTM Flex short stem (Tornier SAS–Wright Medical Inc® , Bloomington, MN, USA). The authors did not include patients with massive cuff tears without gleno-humeral osteoarthritis, because this rare etiology is increasingly treated by partial or complete rotator cuff repair, with satisfactory long-term outcomes [28,29]. The exclusion criteria were: • presence of postoperative humeral fractures (n = 2); • loose implant stems (n = 1); • with unusable radiographs due to incorrect beam incidence (n = 45). This left a cohort of 157 patients (159 shoulders), comprising 56 men (57 shoulders) and 101 women (102 shoulders), aged 74.3 ± 8.0 (median: 74.0; range: 48.8–93.0) at index surgery with a body mass index (BMI) of 27.0 ± 4.6 (median: 26.4; range: 17.6–48.3) (Table 1). The operations involved the right shoulder in 108 patients (69%), the left shoulder in 47 patients (30%) and both in 2 patients (1%). The study protocol was approved by the Medical Ethics Committee of the Clinique Vivalto Santé (CERC-VS-2016-071) and of the “Association des Médecins du Canton de Genève et Société Médicale” (protocol 12-26).
The Aequalis AscendTM Flex is a second-generation convertible stem made of titanium, and proximally coated with titanium plasma spray for metaphyseal press-fit fixation. Its onlay design with a reversed tray of low (1.5 mm) or high (3 mm) offset has a total inclination angle of 145◦ (132.5◦ inclination of the stem + 12.5◦ inclination of the asymmetric polyethylene insert). Whilst the Aequalis AscendTM Flex is available in standard and short lengths, this series comprised exclusively short stems (66 mm to 94 mm), with geometrically proportional diameter. A deltopectoral approach was used in 140 shoulders and a subscapularis- and deltoid-sparing approach in 19 shoulders [30]. Humeral osteophytes at the anatomic neck were resected. Where the deltopectoral approach was taken, a guide was used to perform the neck resection with 132.5◦ . Where the subscapularis- and deltoid-sparing approach was taken, an electrocoagulation device and a retroversion guide were used to delineate the osteotomy line on the humeral head, and a free-hand osteotomy was performed. If the inclination was suboptimal, subsequent revisions were performed to maximize the anatomic fit between the prosthesis and the resected bone area. In most shoulders, the humeral shaft was first sized using sounders. Metaphyseal bone was compacted to grant optimal rotational stability. A surface planer ensured adequate contact between the stem and the reversed tray. 2.3. Radiographic assessment Standard radiographs of the operated shoulders were assessed immediately after RSA, in a true anteroposterior view, defined by the visualization of the Morse taper. Radiographs were analyzed using a DICOM viewer (Osirix© v.5.8.1, Pixmeo, Bernex, Geneva, Switzerland) according to the method described by Goetzmann et al. [24] The parameters measured included NSA (defined as the angle between the diaphyseal axis and the perpendicular of the reversed tray, Fig. 1A), and CFR (calculated by dividing the mediolateral width of the stem by that of the inner bone cortex, both taken perpendicular to the diaphyseal axis 1 cm below the medial calcar-prosthesis junction, Fig. 1B). The authors preferred to study CFR at the metaphysis rather than at the diaphysis to ensure that measurements are comparable to those published by Goetzmann et al. [24]. In order to evaluate misalignment, postoperative NSA were compared to the default 145◦ . NSA of 145 ± 5◦ were considered normal, NSA > 150◦ were considered valgus and NSA < 140◦ varus. 2.4. Statistical analysis The NSA and CFR were measured on radiographs by a second observer (AH) for all 159 RSAs, to evaluate inter-observer agreement. The intra-class correlation coefficients (ICC) were excellent for both NSA (ICC = 0.85; CI: 0.80–0.89), and CFR (ICC = 0.81; CI: 0.71–0.87). The authors used the measurements performed by the first observer (JC) who was more experienced. Descriptive statistics were used to summarize the data. Shapiro–Wilk tests were used to assess the normality of distributions. For non-Gaussian continuous data, differences between groups were evaluated using Wilcoxon rank-sum tests (Mann–Whitney U test). For categorical data, differences between groups were evaluated using Fisher exact tests. For continuous variables, correlations were analysed using Pearson’s coefficients. Uni- and multivariable linear regressions were performed to determine associations between postoperative NSA and 5 independent variables (CFR, gender, patient age, BMI, and surgical approach). With a sample size of 159 shoulders, our regression model including 5 variables was deemed sufficiently powered, considering the
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Fig. 1. True anteroposterior radiographs illustrating measurements of (A) Canal Fill Ratio: stem diameter (S)/humeral diameter (H); (B) Neck Shaft Angle.
Table 2 Patient characteristics by surgical approach. SDS approach (n = 19 shoulders)
Deltopectoral approach (n = 140 shoulders) Mean ± SD Male sex Operated side: right Age (yrs) BMI Canal fill ratio (%) Neck shaft angle (◦ ) Implant by default Postoperative Post minus default Stem alignment Neutral Varus Valgus
p-value
Range
Mean ± SD
54 (38.6%) 96 (68.6%) 74.0 ± 8.2 27.0 ± 4.5 58.0 ± 8.1
(48.0–93.0) (17.6–48.3) (40.8–74.0)
3 (15.8%) 13 (68.4%) 76.9 ± 5.9 27.0 ± 5.2 55.5 ± 8.7
(66.0–86.0) (19.8–43.4) (38.6–70.4)
145.0 148.3 ± 7.5 3.3 ± 7.5
(133.5–176.5) (−11.5 to 31.5)
145.0 154.0 ± 9.0 9.0 ± 9.0
(137.5–172.5) (−7.5 to 27.5)
79 (56.4%) 14 (10.0%) 47 (33.6%)
Range 0.073 1.000 0.109 0.953 0.266
0.004 0.004 0.009
5 (26.3%) 1 (5.3%) 13 (68.4%)
SDS: subscapularis- and deltoid-sparing; Post: postoperative; p-values in bold indicate significant differences.
recommendations of Austin and Steyerberg of a minimum of 2 subjects per variable for linear regression models [31]. Statistical analyses were performed using R version 3.3.3 (R Foundation for Statistical Computing, Vienna, Austria). p-values < 0.05 were considered statistically significant.
3. Results Postoperative NSA was 149.0◦ ± 7.9◦ (median, 147.9◦ ; range, 133.5◦ –176.5◦ ) and CFR was 57.7% ± 8.2% (median, 56.9%; range, 38.6%–74.0%) (Tables 1 and 2). The postoperative NSA was greater than default 145◦ by 4.0◦ ± 7.9◦ (median: 2.9◦ ; range: −11.5◦ to 31.5◦ ), exceeding 5◦ of varus in 15 shoulders (9.4%) and exceeding 5◦ of valgus in 60 shoulders (37.7%) (Fig. 2A and B).
Varus stem positioning was more present in men (66.7%), while valgus stem positioning was more present in women (78.3%) (Table 3). Of the 19 patients operated with the subscapularisand deltoid-sparing approach, 13 (68.4%) had a valgus stem position, while of the 140 patients operated with a deltopectoral approach, 47 (33.6%) had a valgus stem position (p = 0.015) (Table 2). Shoulders with varus stem positioning had lower CFR than shoulders with neutral stem positioning (53.8% ± 5.5% vs. 58.9% ± 8.3%, p = 0.033) (Fig. 3). Univariable regression revealed that postoperative NSA significantly increased with age (beta: 0.24; CI: 0.09–0.39; p = 0.002), but was lower for men (beta: −4.27; CI: −6.76 to −1.79; p = 0.001) and higher for shoulders operated by the subscapularis- and deltoid-sparing approach (beta: 5.67; CI: 1.97–9.37; p = 0.003) (Table 4). Multivariable regression confirmed that postoperative NSA independently increased with age (beta:
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Fig. 2. True anteroposterior radiographs illustrating stem misalignments: (A) varus (B) valgus.
Table 3 Patient characteristics stratified by stem alignment.
Male sex Operated side: right Surgical approach Deltopectoral SDS Age (yrs) BMI Canal fill ratio (%) Post NSA (◦ )
Neutral stem position (n = 84) 140◦ < Postop NSA < 150◦
Valgus stem position (n = 15) Postop NSA ≤ 140◦
Mean ± SD
Mean ± SD
Range
34 (40.5%) 55 (65.5%)
10 (66.7%) 11 (73.3%)
79 (94.0%) 5 (6.0%) 72.8 ± 8.3 26.6 ± 4.7 58.9 ± 8.3 145.5 ± 2.8
14 (93.3%) 1 (6.7%) 74.1 ± 6.3 28.6 ± 5.9 53.8 ± 5.5 137.2 ± 2.1
(48.0–87.0) (19.7–48.3) (40.8–73.1) (140.2–149.9)
Range
(63.0–85.0) (21.7–44.6) (43.2–64.3) (133.5–140.0)
Valgus stem position (n = 60) Postop NSA ≥ 150◦ p-valuea
Mean ± SD
0.089 0.767 1.000
13 (21.7%) 43 (71.7%)
0.732 0.220 0.033 –
47 (78.3%) 13 (21.7%) 76.6 ± 7.5 27.2 ± 4.1 57.0 ± 8.3 156.9 ± 6.1
Range
p-valuea 0.020 0.472 0.009
(60.0–93.0) (17.6–43.4) (38.6–74.0) (150.5–176.5)
0.012 0.240 0.264 –
NSA: neck shaft angle; Post: postoperative; SDS: subscapularis- and deltoid-sparing; p-values in bold indicate significant differences. a Compared with the neutral stem position group.
0.20; CI: 0.05–0.35; p = 0.008), was higher for shoulders operated by the subscapularis- and deltoid-sparing approach (beta: 3.82; CI: 0.18–7.46; p = 0.040), but lower for men (beta: −4.14; CI: −6.72 to −1.57; p = 0.002). 4. Discussion The principal finding of the study was that 47% of stems were misaligned, with up to 12◦ of varus and 32◦ of valgus. Compared to shoulders with neutral stem positioning, shoulders with varus stems had lower CFR, confirming our hypothesis that stem misalignment is associated with lower canal fill. Misalignment of short humeral stems is a common but underreported problem. Raiss et al. [25] observed that 16% of RSA short stems had a > 5◦ misalignment, of which 4% were in varus and 12% in valgus position. In our series, 47% of RSA stems were misaligned, of which 9% in varus and 38% in valgus position. Goetzmann et al. [24] reported a maximum varus and valgus stem misalignment of 1.5◦ and 11.5◦ , while we reported up to 12◦ of varus and 32◦ of valgus misalignment. Multivariable analysis revealed that postoperative NSA was higher for women and increased with older age, likely due to poorer bone quality [32]. It is worth noting that surgical approaches can also have a real impact on stem alignment,
as multivariable analyses confirmed that shoulders operated by subscapularis- and deltoid-sparing approach had 4 more degrees of NSA compared to shoulders operated by deltopectoral approach. Our results revealed that shoulders with varus stems had lower CFR compared to those with neutral stem alignment. Interestingly, it seems that CFR was not associated with valgus stem positioning, which could explain why linear regressions did not confirm any association between CFR and postoperative NSA. Surgeons should therefore be cautious not to undersize RSA humeral stems to avoid varus stem positioning, which could increase the humeral offset, and decrease abduction range due to impingement of the greater tuberosity upon the acromion [19]. Short humeral stems rely on proximal fixation, and their size should be selected to ensure optimal canal filling, avoiding bone remodeling (due to oversizing) or insufficient primary fixation (due to undersizing). In their anatomic and reverse shoulder arthroplasty series, Schnetzke et al. [26] and Goetzman et al. [24] reported that, at 2-year follow-up, greater canal filling was associated with stress shielding (condensation lines, cortical bone resorption and spot welds). A recent consecutive series of RSA corroborated that patients with greater CFR (≥ 74%) are at higher risk of stress shielding than lower CFR (≤ 64%) [25]. It is worth noting that none of our shoulders had CFR greater than 74%.
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Table 4 Uni- and multivariable regression analysis of postoperative NSA. Univariable
Multivariable (159 shoulders)
Variable

95% CI
p-value

95% CI
p-value
Canal fill ratio Male gender Surgical approach Deltopectoral SDS Age BMI
−5.87 −4.27
(−21.04 to −9.30) (−6.76 to −1.79)
0.446 0.001
−12.45 −4.14
(−27.46 to 2.55) (−6.72 to −1.57)
0.103 0.002
REF 5.67 0.24 −0.35
(1.97–9.37) (0.09–0.39) (−0.22 to 0.19)
0.003 0.002 0.573
REF 3.82 0.20 0.02
(0.18–7.46) (0.05–0.35) (−0.23 to 0.28)
0.040 0.008 0.853
NSA: neck shaft angle; SDS: subscapularis- and deltoid-sparing; p-values in bold indicate significant differences.
alignment and CFR, with a sizeable series of RSA using a single stem design. 5. Conclusion While short uncemented stems offer several advantages in RSA, they remain challenging to align within the humerus. In our series, stem misalignment exceeded 5◦ in 47% of the shoulders. Women, older age and subscapularis- and deltoid-sparing approach are independently associated with greater risks of valgus stem alignment while lower canal filling is associated with greater risks of varus stem positioning. Surgeons and engineers should collaborate to develop new techniques and surgical tools to reduce alignment errors, which may compromise long-term clinical and radiographic outcomes. Disclosure of interest Author AL receives royalties from Wright and consulting fees from Medacta, Arthrex and Wright. Author PC declares royalties from Wright, Stortz and Advanced Medical Applications, as well as consulting fees from Wright, Smith and Nephew and ConMed. The other authors declare that they have no competing interest. Fig. 3. Boxplots illustrating the Canal Fill Ratio (%) for shoulders with different stem alignments (varus, neutral or valgus). Horizontal line = median; top and bottom of box = third and first quartiles; top and bottom of whiskers = 95% confidence interval.
Correct positioning of RSA stems is essential to optimize postoperative range of motion and limit potential mechanical complications. New surgical techniques are needed to improve stem positioning, not only for standard [33], but also for short stems that are more susceptible to misalignment. In fact, limited joint space could render the use of surgical guides difficult, leading to freehand osteotomy. Moreover, improvements in medical devices and surgical tools are required to optimize the entry point of the stem and canal filling, while ensuring adequate stem alignment. The limitations of this multicentric study include: • its retrospective design; • the heterogeneity of surgical techniques; • the fact that only one of the two surgeons used the subscapularisand deltoid-sparing approach; • the lack of postoperative clinical and radiographic data; • the inability to evaluate the influence of etiology, bone quality and diaphyseal canal filling; • the small number of shoulders with varus stems which prevented us from performing logistic regression analyses or establishing a cut-off value of CFR for which varus misalignment is more likely. Notwithstanding these limitations, to the authors’ knowledge, this study is the first to evaluate the association between stem
Funding sources This study was funded by a non-profit foundation for Research and Teaching in Orthopaedics, Sports Medicine, Trauma and Imaging (FORE), with no commercial interest in the present study. The source of funds was involved in data analysis and manuscript redaction. Contribution of authors AL participated in study design, data collection, manuscript writing and manuscript editing. JCHC participated in data collection, manuscript editing. GV, PC participated in study design, data collection, manuscript editing. AH participated in data collection, manuscript editing. SP participated in data collection, manuscript editing. HB participated in statistical analysis, manuscript writing. All authors approved the final manuscript. Acknowledgments The authors are grateful to Aude Michelet for her help in manuscript redaction. References [1] Boileau P, Sinnerton RJ, Chuinard C, et al. Arthroplasty of the shoulder. J Bone Joint Surg Br 2006;88:562–75. [2] Nolan BM, Ankerson E, Wiater JM. Reverse total shoulder arthroplasty improves function in cuff tear arthropathy. Clin Orthop Relat Res 2011;469:2476–82.
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Please cite this article in press as: Lädermann A, et al. Do short stems influence the cervico-diaphyseal angle and the medullary filling after reverse shoulder arthroplasties? Orthop Traumatol Surg Res (2020), https://doi.org/10.1016/j.otsr.2019.12.010