Studies have shown that the trees minor plays an important role after total (TSA) and reverse (RSA) shoulder arthroplasty, as well as in maintenance of function in the setting of infraspinatus wasting. In this regard, teres minor hypertrophy has been described as a compensatory change in response to this infraspinatus wasting, and has been suggested that this compensatory hypertrophy may mitigate the loss of infraspinatus function in the patient with a large rotator cuff tear. The purpose of this study was to determine the prevalence of teres minor hypertrophy in a cohort of patients undergoing rotator cuff repair, and to determine its prognostic effect, if any, on outcomes after surgical repair. Over a 3 year period, all rotator cuff repairs performed in a single practice by 3 ASES member surgeons were collected. Inclusion criteria included both preoperative and postoperative validated outcomes measures (minimum 2 year), and preoperative Magnetic Resonance Imaging (MRI) scanning. 144 patients met all criteria. MRIs were evaluated for rotator cuff tear tendon involvement, tear size, and Goutallier changes of each muscle. In addition, occupational ratios were determined for the supraspinatus, infraspinatus, and teres minor muscles. Patients were divided into 2 groups, based upon whether they had teres minor hypertrophy or not, based on a previously established definition. A 2 way ANOVA was used to determine the effect of teres minor hypertrophy(tear size by hypertrophy) and Goutallier. Teres minor hypertrophy was a relatively common finding in this cohort of rotator cuff patients, with 51% of all shoulders demonstrating hypertrophy. Interestingly, in patients without an infraspinatus tear, teres minor hypertrophy was still present in 19/40 (48%) of patients. Teres minor hypertrophy had a significant, negative effect ASES scores after rotator cuff repair in patients with and without infraspinatus tearing, infraspinatus atrophy, and fatty infiltrative changes (P<0.05). In general, the presence of teres minor hypertrophy showed 10–15% less improvement (Figure 1) than when no hypertrophy was present, and this was consistent across all tear sizes, independent of Goutallier changes. Teres minor hypertrophy is a common finding in the setting of rotator cuff tearing, including in the absence of infraspinatus tearing. Contrary to previous publications, the presence of teres minor hypertrophy in patients with rotator cuff repair does not appear to be protective as a compensatory mechanism. While further study is necessary to determine the mechanism or implication of teres minor hypertrophy in setting of rotator cuff repair, our results show it is not a positive of outcomes following rotator cuff repair

Abstract

Purpose. While treating fracture sequelae (FS) with unconstrained prostheses has been shown to give inferior or unpredictable outcomes, the literature is still scant regarding their treatment with reverse shoulder arthroplasty (RSA). This study was performed to determine the suitability of RSA as a solution for FS with severe tuberosity malunion/nonunion and rotator cuff dysfunction, and to identify any useful preoperative prognostic factors. Method. Between 1997 and 2007, RSA was performed in 26 cases for FS of type 4 according to the classification of Boileau et al., previously treated either operatively or nonoperatively. Prior treatment with hemiarthroplasty was an exclusion criteria, as was follow-up of less than two years, leaving 20 patients who had undergone an average of one surgery prior to the index RSA (range, 1–3) and were followed up for a mean of 4.8 years. Preoperatively, the mean global fatty degeneration index (GFDI) was 1.8 (range, 0.7–2.9), and almost half the patients had an atrophic or ruptured teres minor. The mean age at surgery was 70 years (range, 50–91). Clinical evaluation was performed by two independent observers with the help of the Constant score (CS) and Subjective Shoulder Value (SSV). Results. Three patients (15%) had five complications, all of which were treated with reoperation. No infections and only one case of instability occurred. Overall, 82% were satisfied or very satisfied, and the mean relative CS improved by 45% (from 35% to 80%). The best range-of-motion gains were made in active anterior elevation, which improved by 53 (from 62 to 115), although gains were generally variable. Teres minor and subscapularis insufficiency was observed in many patients. Worse clinical outcomes were associated with these preoperative variables: prior surgical treatment, medical comorbidity, a lack of active external rotation, and a GFDI of 2.0 or more. However, the numbers available did not produce statistically significant correlations. Radiographic humeral-component loosening was seen in one patient (5%), and either the humeral or the glenoid component was considered at-risk in three patients (15%), although no revisions were performed for loosening. Conclusion. These results show that in the medium term, RSA is a very good treatment option for elderly patients with severe FS and rotator cuff dysfunction. They are better than previously published results of RSA performed for FS but not as good as those of RSA for CTA. High satisfaction rates may be related to the severity of preoperative disability and good patient education. The association of prior surgical treatment with worse results may be related to the negative effect of surgery on the rotator cuff and anterior deltoid. Much can be learned from the reported complications, and outcomes will probably improve with improved prosthetic design and surgical techniques, as well as with better surgeon and patient awareness of the surgical pitfalls and variable clinical gains, especially in rotation

Lateralizing the center of rotation in reverse shoulder arthroplasty has been the subject of renewed interest due to complications associated with medialized center of rotation implants. Benefits of lateralization include: increased joint stability, decreased incidence of scapular notching, increased range of motion, and cosmetic appeal. However, lateralization may be associated with increased risk of glenoid loosening, which may result from the increased shear forces and the bending stresses that manifest at the bone-implant interface. To address glenoid loosening in reverse implants with lateralized joint centers, recent studies have focused on testing and improving implant fixation. However, these studies use loads derived from literature specific to subjects with normal anatomy. The aim of this study is to characterize how joint center lateralization affects the loading in reverse shoulder arthroplasty. Using an established computational shoulder model that describes the geometry of a commercial reverse prosthesis (DELTA® III, DePuy), motion in abduction, scapular plane elevation, and forward flexion was simulated. The simulations were run for five progressively lateralized centers of rotation: −5, 0, +5, +10, and +15 mm (Figure 1). The model was modified to simulate a full thickness rotator cuff tear, where all cuff musculature except Teres Minor were excluded, to reflect the clinical indication for reverse shoulder arthroplasty on cuff tear arthropathy patients. To analyze the joint contact forces, the resultant glenohumeral force was decomposed into compression, anterior-posterior shear, and superior-inferior shear on the glenoid. Joint center lateralization was found to affect the glenohumeral joint contact forces and glenoid loads increased by up to 18% when the center was lateralized from −5 mm to +15 mm. Compressive forces were found to be more sensitive to lateralization in abduction, while changes in shear forces were more affected in forward flexion and scapular plane abduction. On average, the superior shear component showed the largest increases due to lateralization (up to a 21% increase), while the anterior-posterior shear component showed larger changes than those of compression, except in the most lateralized center position (Figure 2). The higher joint loads in the lateralized joint centers reflect a shortening of the Deltoid muscle moment arms (Figure 3), since the muscle needs to exert more force to provide the desired motions. The additional shear forces generated by the lateralization may increase the risk of the ‘rocking-horse’ effect. Together with the lateralized joint center, this creates an additional bending stress at the bone-implant interface that puts the implant at further risk of loosening (Figure 1). Current studies on implant fixation tend to use loads in compression and superior shear that exceed the forces seen in this study but have not investigated anterior-posterior shear loads. Our data support that loading in anterior-posterior direction can be significant. Using inappropriate loads to design fixation may result in excessive loss of bone stock and/or unforeseen implant loosening. The implication is that future studies may be performed using this more relevant data set to navigate the tradeoff between fixation and bone conservation