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Background: Functional internal rotation (fIR) of the shoulder is frequently limited after reverse shoulder arthroplasty (RTSA). The objective of this study was to study a cohort of satisfied patients after RTSA who had comparable active mobility except for fIR and to identify factors associated with selective loss of fIR. Methods: A retrospective cohort study was conducted to compare 2 patient groups with either poor (≤ 2 points in the Constant-Murley score [CS]) or excellent (≥8 points in CS) fIR after RTSA at a minimum follow-up of 2 years. Influencing factors (demographic, surgical or implant related, radiographic parameters) and clinical outcome were analyzed. Results: Fifty-two patients with a mean age of 72.8 (±9.3) and a mean follow-up of 41 months were included in the IR≤2 group and 63 patients with a mean age of 72.1 (±8.0) and a mean follow-up of 59 months in the IR≥8 group. All patients had undergone RTSA with the same implant type and only 2 different glenosphere sizes (36 and 40) for comparable indications. A multivariate analysis identified the following significant risk factors for poor postoperative fIR: poor preoperative fIR (pts in CS: 3 [range: 2-6] vs. 6 [range: 4-8], P

Background: With the increase in utility and popularity of the reverse total shoulder arthroplasty (RTSA) within the last decades, indications for RTSA have expanded. As well as the established indications such as cuff tear arthropathy and massive irreparable rotator cuff tears, RTSA for complex proximal humeral fractures in elderly patients has been proven to be a reliable treatment option. Methods: A prospectively enrolled RTSA database of 1457 RTSAs implanted between September 2005 and November 2020 was reviewed. Patients treated with RTSA for a complex proximal humerus fracture and fracture sequalae (F-RTSA) were 1:1 matched with a group of patients who were treated electively with RTSA for indications other than a fracture (E-RTSA). Matching criteria included sex, age, length of follow-up and body mass index. Evaluation after a minimum of 2 years follow-up included evaluation of the absolute and relative Constant–Murley score (aCS; rCS), subjective shoulder value (SSV), range of motion (ROM) assessment and complications. Results: Each of the matched cohorts comprised 134 patients with a mean follow-up of 58 ± 41 months for the fracture group and 58 ± 36 months for the elective group. The mean age for both groups was 69 ± 11 years in the F-RTSA and 70 ± 9 years for the E-RTSA group. There were no significant differences in clinical outcome measures including aCS, rCS and SSV (p > 0.05). There was a significant difference in mean active external rotation with 20° ± 18° in the F-RTSA group compared with 25° ± 19° in the E-RTSA group (p = 0.017). The complication rate was not significantly different, with 41 complications in 36 shoulders in the F-RTSA and 40 complications in 32 shoulders in the E-RTSA group (p = 0.73). The main complication for the F-RTSA group was dislocation of the greater tuberosity (6%), whereas acromial fractures (9%) were the leading complication in the E-RTSA group. There was also no significant difference in revision rate comparing F-RTSA with E-RTSA (10% vs. 14%; p = 0.25). Conclusions: RTSA for complex proximal humeral fractures and its sequalae leads to a comparable clinical outcome as that for patients treated electively with RTSA for indications other than fracture. There was, however, a significant difference in active external rotation, with inferior rotation in patients undergoing RTSA for fracture. This valuable information can help in requesting informed consent of patients with proximal humeral fractures.

Background Little guidance exists regarding the minimum screw length and screw quantity necessary to achieve fixation in reverse total shoulder arthroplasty (rTSA); to that end, this study quantified the displacement of 2 different sizes of glenoid baseplates using multiple different screw lengths and quantities of screws in a low-density polyurethane bone-substitute model. Methods Testing of rTSA glenoid loosening was conducted according to ASTM F 2028-17. To independently evaluate the impact of screw quantity and screw length on rTSA glenoid fixation for 2 different sizes of glenoid baseplates, baseplates were constructed using 2 screws, 4 screws, or 6 screws (with the latter being used for the larger baseplate only) with 3 different poly-axial locking compression screw lengths. Results Both sizes of glenoid baseplates remained well fixed after cyclic loading regardless of screw length or screw quantity. Baseplates with 2 screws had significantly greater displacement than baseplates with 4 or 6 screws. No differences were observed between baseplates with 4 screws and those with 6 screws (used for the larger baseplate). Both sizes of baseplates with 18-mm screws had significantly greater displacement than baseplates with 30- or 46-mm screws. For larger baseplates, those with 30-mm screws had significantly greater displacement than those with 46-mm screws in the superior-inferior direction. Discussion For the 2 different sizes of baseplates tested in this study, rTSA glenoid fixation was impacted by both screw quantity and screw length. Irrespective of screw quantity, longer screws showed significantly better fixation. Irrespective of screw length, the use of more screws showed significantly better fixation, up to a point, as the use of more than 4 screws showed no incremental benefit. Finally, longer screws can be used as a substitute for additional fixation if it is not feasible to use more screws.

© 2020 Elsevier Ltd Reverse total shoulder arthroplasty (RTSA) is an effective treatment for several shoulder conditions, however scapular notching is common and results in damage to the polyethylene humeral cup. This study assessed the simulator wear of RTSA implants, with and without the presence of simulated scapular notching rim damage. A shoulder wear simulator applied representative shoulder circumduction with a 900 N peak force to five clinically available RTSA implants. The lubricant was alpha calf fraction with a protein concentration of 30 g/L, sodium hyaluronate at 1.5 g/L, and antimycotic antibiotic at 1%. Simulated scapular notching damage was progressively applied every 0.25 Mc. Wear was assessed gravimetrically and load soak controls allowed for the correction of fluid uptake. A finite element model also permitted the investigation of the effects of the simulated damage on articular contact area and stress. All humeral cups showed signs of articular wear in the inferior aspect. After the simulated rim damage, a secondary wear band formed at the inferior edge of the cup, and the finite element analysis showed a reduction of articular contact area and an increase in maximum contact stress at this location. The average volumetric wear rate of the intended articular surface during testing was 25.30 ± 0.92 mm3/Mc and while the wear rate was reduced slightly by the simulated scapular notching damage, likely a result of the reduced articular contact area, the magnitudes of the changes were small. The articular wear zone moved inferiorly as the damage progressed.

Background:Increased passive deltoid tension after reverse total shoulder arthroplasty (RTSA) potentially leads to displacement or tilting of a preexisting os acromiale.Purpose:To analyze patients with an os acromiale who underwent RTSA and compare their outcomes and complications with a matched control group without an os acromiale.Study Design:Cohort study; Level of evidence, 3.Methods:In this study, 45 shoulders in 42 patients with an os acromiale (cases) were matched to 133 patients without os acromiale (controls) who underwent RTSA between 2005 and 2016. The mean follow-up was 52 ± 32 months. Matching criteria included sex, type of surgery, duration of follow-up, and age. The Constant score (CS), Subjective Shoulder Value (SSV), and radiological outcomes were assessed postoperatively at 1-year, 2-year, and final follow-up visits.Results:The mean CS, SSV, and range of motion improved from preoperative levels to the final follow-up in both groups ( P < .01). Patients with an os acromiale had a relative CS of 70 ± 23 versus 76 ± 21 points ( P = .15) and an SSV of 70 ± 30 versus 73 ± 24 ( P = .52) compared with controls at the final follow-up visit. Patients with an os acromiale had significantly decreased active flexion of 104° ± 33° versus 114° ± 33° ( P = .03) at 1 year and active abduction of 103° ± 37° versus 121° ± 38° at 2 years postoperatively ( P = .02). A postoperatively painful os acromiale was found in 12 cases (27%) and spontaneously resolved in 8 cases after a mean of 33 months (range, 12-47 months; P = .04).Conclusion:RTSA reliably restores patient satisfaction despite the presence of an os acromiale, with a slightly impaired range of motion. Postoperative local tenderness at the os acromiale can be expected in 1 out of 4 patients, but this resolves spontaneously over time in the majority of patients.

© 2016 Journal of Shoulder and Elbow Surgery Board of Trustees Introduction There is disagreement regarding whether, when possible, the rotator cuff should be repaired in conjunction with reverse total shoulder arthroplasty (RTSA). Therefore, we investigated the effects of rotator cuff repair in RTSA models with varying magnitudes of humeral and glenosphere lateralization. Methods Six fresh frozen cadaveric shoulders were tested on a validated in vitro muscle-driven motion simulator. Each specimen was implanted with a custom adjustable, load-sensing RTSA after creation of a simulated rotator cuff tear. The effects of 4 RTSA configurations (0 and 10 mm of humeral lateralization and glenosphere lateralization) on deltoid force and joint load during abduction with and without rotator cuff repair were assessed. Results Deltoid force was significantly affected by increasing humeral lateralization (−2.5% ± 1.7% body weight [BW], P = .016) and glenosphere lateralization (+7.7% ± 5.6% BW, P = .016). Rotator cuff repair interacted with humeral and glenosphere lateralization (P = .005), such that with no humeral lateralization, glenosphere lateralization increased deltoid force without cuff repair (8.1% ± 5.1% BW, P = .012). This effect was increased with cuff repair (12.8% ± 7.8% BW, P = .010), but the addition of humeral lateralization mitigated this effect. Rotator cuff repair increased joint load (+11.9% ± 5.1% BW, P = .002), as did glenosphere lateralization (+13.3% ± 3.7% BW, P

Copyright © 2014 by ASME. In vitro active shoulder motion simulation can provide improved understanding of shoulder biomechanics; however, accurate simulators using advanced control theory have not been developed. Therefore, our objective was to develop and evaluate a simulator which uses real-time kinematic feedback and closed loop proportional integral differential (PID) control to produce motion. The simulator's ability to investigate a clinically relevant variable - namely muscle loading changes resulting from reverse total shoulder arthroplasty (RTSA) - was evaluated and compared to previous findings to further demonstrate its efficacy. Motion control of cadaveric shoulders was achieved by applying continuously variable forces to seven muscle groups. Muscle forces controlling each of the three glenohumeral rotational degrees of freedom (DOF) were modulated using three independent PID controllers running in parallel, each using measured Euler angles as their process variable. Each PID controller was configured and tuned to control the loading of a set of muscles which, from previous in vivo investigations, were found to be primarily responsible for movement in the PID's DOF. The simulator's ability to follow setpoint profiles for abduction, axial rotation, and horizontal extension was assessed using root mean squared error (RMSE) and average standard deviation (ASD) for multiple levels of arm mass replacement. A specimen was then implanted with an RTSA, and the effect of joint lateralization (0, 5, 10 mm) on the total deltoid force required to produce motion was assessed. Maximum profiling error was