Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Background The transverse force couple (TFC) of the rotator cuff (subscapularis vs. infraspinatus and teres minor muscle) is an important dynamic stabilizer of the shoulder joint in the anterior-posterior direction. In patients with posterior static subluxation of the humeral head (PSSH), decentration of the humeral head posteriorly occurs, which is associated with premature arthritis. We hypothesize that not only pathologic glenoid retroversion but also chronic muscle volume imbalance in the transverse force couple leads to PSSH. Methods A retrospective analysis of the TFC muscle volumes of 9 patients with symptomatic, atraumatic PSSH, within 8 were treated with glenoid correction osteotomy, was conducted. The imaging data (CT) of 9 patients/10 shoulders of the full scapula and shoulder were analyzed, and the muscle volumes of the subscapularis (SSC), infraspinatus (ISP) and teres minor muscles (TMM) were measured by manually marking the muscle contours on transverse slices and calculating the volume from software. Furthermore, the glenoid retroversion and glenohumeral distance were measured. Results The mean glenoid retroversion was − 16° (− 7° to − 31°). The observed mean glenohumeral distance was 4.0 mm (0 to 6.8 mm). Our study population showed a significant muscle volume imbalance between the subscapularis muscle and the infraspinatus and teres minor muscles (192 vs. 170 ml; p = 0.005). There was no significant correlation between the subscapularis muscle volume and the glenohumeral distance (r = 0.068), (p = 0.872). Conclusion The muscle volume of the SSC in patients with PSSH was significantly higher than the muscle volume of the posterior force couple (ISP and TMM). This novel finding, albeit in a small series of patients, may support the theory that transverse force couple imbalance is associated with PSSH. Level of evidence Level 4 – Case series with no comparison group.

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Purpose Purpose of this study was to evaluate the mid- to long-term outcome after conservatively treated first-time posterior shoulder dislocations and to determine structural defects associated with failure. Methods In this multi-centric retrospective study, 29 shoulders in 28 patients with first-time acute posterior shoulder dislocation (Type A1 or A2 according to the ABC classification) and available cross-sectional imaging were included. Outcome scores as well as radiological and magnetic resonance imaging were obtained at a mean follow-up of 8.3 ± 2.7 years (minimum: 5 years). The association of structural defects with redislocation, need for secondary surgery, and inferior clinical outcomes were analysed. Results Redislocation occurred in six (21%) shoulders and nine shoulders (31%) underwent secondary surgery due to persistent symptoms. The posttraumatic posterior glenohumeral subluxation was higher in the redislocation group compared to the no redislocation group; however, statistical significance was not reached (61.9 ± 12.5% vs. 50.6 ± 6.4%). Furthermore, a higher adapted gamma angle was observed in the failed conservative treatment group versus the conservative treatment group, similarly without statistically significant difference (97.8° ± 7.2°, vs. 93.3° ± 9.7°). The adapted gamma angle was higher than 90° in all patients of failed conservative therapy and the redislocation group. An older age at the time of dislocation showed a significant correlation with better clinical outcomes (SSV: r = 0.543, p = 0.02; ROWE: r = 0.418, p = 0.035 and WOSI: r = 0.478, p = 0.045). Posterior glenohumeral subluxation after trauma correlated with a worse WOSI (r = − 0.59, p = 0.02) and follow-up posterior glenohumeral decentring (r = 0.68, p = 0.007). The gamma angle (r = 0.396, p = 0.039) and depth of the reverse Hill–Sachs lesion (r = 0.437, p = 0.023) correlated significantly with the grade of osteoarthritis at follow-up. Conclusion Conservative treatment is a viable option in patients with an acute traumatic posterior shoulder dislocation with good outcome after mid- and long-term follow-up especially in patients with centred joint, low gamma angle, and middle or old age. Level of evidence IV.

Purpose The purpose of this study was to evaluate sleep disturbance prospectively before and after short-stem hip arthroplasty. Methods A prospective study on 25 patients undergoing a primary unilateral total short-stem hip replacement was conducted. Patients were observed for six months. To evaluate the sleep quality and daytime sleepiness, the Pittsburgh Sleep Quality Index and Epworth Sleepiness Scale were used. To assess the general physical health status, we used the Short Form 36 Health Survey (SF-36). Pain was recorded on a visual analog scale. Results The physical health status of the patients improved significantly (p < 0.05) during the six month follow-up period in seven out of nine categories. During the first post-operative week, the sleep quality stayed on an equal level to the pre-operative state, following a steady improvement over the next months (6 months p = 0.00). The daytime sleepiness showed a significant improvement during all the follow-ups (6 months p = 0.00). Pain decreased significantly from baseline to six months postoperatively (p = 0.00). There was no correlation between pain and sleep quality or pain and daytime sleepiness. Conclusion According to our results, patients undergoing short-stem total hip arthroplasty can expect a 50% improvement of sleep quality and physical function six months after surgery.