UNASSIGNED: Peripheral nerve injury is a recognized complication after reverse shoulder arthroplasty (RSA) that has mainly been studied at the level of the brachial plexus and its proximal branches. However, the impact of RSA on distal peripheral nerves and the influence of elbow and wrist position is not known. This cadaveric study aimed to analyze the effect of RSA implantation and upper limb position on tension in the distal median and radial nerves. The hypothesis was that RSA increased distal nerve tension, which could be further affected by elbow and wrist position.
UNASSIGNED: 12 upper limbs in 9 full fresh-frozen cadavers were dissected. Nerve tension was measured in the median nerve at the level of the proximal arm, elbow, and distal forearm, and in the radial nerve at the level of the elbow, using a customized three-point tensiometer. Measurements were carried out before and after RSA implantation, using a semi-inlay implant (Medacta, Castel San Pietro, Switzerland). Two different configurations were tested, using the smallest and largest available implant sizes. Three upper-limb key positions were considered (plexus at risk, plexus relief, and neutral), from which the effect of elbow and wrist position was further tested.
UNASSIGNED: RSA implantation significantly increased median and radial nerve tension throughout the upper limb. The distal nerve segments were particularly dependent on elbow and wrist position. The plexus at risk position induced the most tension in all nerve segments, especially with the large implant configuration. On the other hand, the plexus relief position induced the least amount of tension. Flexing the elbow was the most efficient way to decrease nerve tension in all tested nerve segments and key positions. Wrist flexion significantly decreased nerve tension in the median nerve, whereas wrist extension decreased tension in the radial nerve.
UNASSIGNED: RSA significantly increases tension in the median and radial nerves and makes them more susceptible to wrist and elbow positioning. The mechanism behind distal peripheral neuropathy after RSA may thus result from increased compression of tensioned nerves against anatomical fulcrums rather than nerve elongation alone. Elbow flexion was the most effective way to decrease nerve tension, while elbow extension should be avoided when implanting the humeral component. Further studies are needed to assess the ulnar nerve.

BACKGROUND: Acromial fractures after Reverse Total Shoulder Arthroplasty (RTSA) are a common complication. Nevertheless, only a few studies have identified risk factors for acromial fractures after RTSA. High delta angle (combination of inferiorization and medialization of the center of rotation) after RTSA was identified as a risk factor in recent studies. The aim of this study was the biomechanical exploration of different delta angles and implant configurations with regard to the acromial stress.
METHODS: In a rigid body model of the upper extremity muscle, forces of the deltoid muscle were calculated before and after implanting RTSA in different arm and implant positions. The deltoid muscle was divided into an anterior, middle, and posterior part. Implant positions of the glenoid components were changed in the medialization, lateralization and inferiorization of the center of rotation (COR) as well as lateralization of the humeral component. Further, in a finite element model of the upper extremity, the stresses of the acromion in the same implant design configurations were measured.
RESULTS: Differences in acromial stress between different delta angle model configurations were observed. Lateralization (5 mm, 10 mm) of the glenosphere reduced maximal acromial stress by 21% (1.5 MPa) and 31% (1.3 MPa), respectively. Inferiorization (5 mm, 10 mm) of the glenosphere increased maximal acromial stress by 5% (2.0 MPa) and 15% (2.2MPa), respectively. Changes in positioning the humeral component was found to have the highest impact in this model configuration. A 10 mm lateralized humeral component reduced acromial stress by 37% (1.2 MPa) while in the 6 mm medialized configuration, an increase in acromial stress by 83% (3.48 MPa) was observed. There was a high correlation between delta angle and acromial stress (R-squared = 0.967).
CONCLUSIONS: Implant design configuration has an impact on the acromial stress. High delta angles correlate with an increase in acromial stress. Both lateralization of the COR and the humerus decreased the acromial stress in our study. The lateralization of the humerus has the highest impact in influencing acromial stress. Due to contrary results in the current literature, further studies with focus on the acromial stress influenced by different anatomical variants of the shoulder and the acromion are needed before a clinical recommendation can be made.

BACKGROUND: Reverse shoulder arthroplasty (RSA) offers promising functional outcomes for young patients, yet challenges persist in restoring internal rotation (IR). This study aimed to assess the restoration of IR after RSA in patients younger than 60 years of age and analyze the factors affecting IR recovery.
METHODS: A retrospective multicenter study was conducted, examining the functional outcome of patients who underwent RSA, with a minimum follow-up period of 2 years. Two subgroups of patients who underwent primary RSA were analyzed separately with respect to active internal rotation with the elbow at the side (AIR1): \"difficult AIR1\" and \"easy AIR1.\"
RESULTS: The study included 136 patients (overall series) with a mean age of 51.6 years. The overall series showed statistically significant improvement in active range of motion (RoM), pain, and Constant scores, especially with active IR (p ​< ​0.01). According to etiology, statistically significant improvement (p ​< ​0.05) in active IR was observed for fracture sequelae, primary osteoarthritis, and rheumatoid arthritis, whereas no statistically significant improvement in IR was observed for tumor, revision, and cuff-tear arthropathy (p ​> ​0.05). In subgroup analysis, patients with easy AIR1 displayed a statistically significant lower body mass index and better Constant score mobility, as well as improved motion in forward elevation and active IR (p ​< ​0.05). No statistically significant associations were found between improved IR and prosthetic design or subscapularis repair. Scapular notch, lysis of the graft, and teres minor atrophy were significantly associated with better active IR (p ​< ​0.05).
CONCLUSIONS: RSA improves active RoM, pain, and functional outcomes in patients aged under 60. However, the degree of improvement in IR may vary depending on several factors and the underlying etiologies. These insights are crucial for patient selection and counseling, guiding RSA optimization efforts.
METHODS: IV.

BACKGROUND: Pre-operative planning for reverse shoulder arthroplasty (RSA) poses challenges, particularly when dealing with glenoid bone loss. This modified Delphi study aimed to assess expert consensus on RSA planning processes and rationale, specifically targeting low-resourced institutions. Our objective was to offer pre-operative decision-making algorithms tailored for surgeons practising in resource-constrained hospitals with limited access to computed tomography (CT) scans.
METHODS: A working group generated statements on pre-operative imaging and glenoid of glenoid morphology and intra-operative decision-making. The study was conducted in three stages, with virtual consensus meetings in between. Stages 2 and 3 consisted only of closed questions/statements. The statements with over 70% were considered consensus achieved and those with less than 10% were considered disagreement consensus achieved.
RESULTS: Twelve shoulder surgeons participated, with 67% having over five years of experience in shoulder arthroplasty. In the absence of glenoid bone loss, the sole use of plain radiographs for pre-operative planning reached consensus and is recommended by these groups, while 100% advise using CT scans when bone loss is present. Most surgeons (70%) recommend using patient-specific instrumentation (PSI) in cases of structural bone loss. Most of the statements on intra-operative decision-making related to component placement and enhancing stability failed to reach consensus.
CONCLUSIONS: While consensus was achieved on most aspects of pre-operative imaging and planning, technical aspects of surgery lacked consensus. Planning for patients with structural glenoid bone loss necessitates CT scans and planning tools.

BACKGROUND: Reverse shoulder arthroplasty (RSA) is a common procedure for treating a variety of shoulder pathologies. However, many patients struggle with postoperative internal rotation (IR) deficits, which often hinder their activities of daily living. The conjoint tendon provides an anatomic barrier that can impede the postoperative IR of the shoulder, and this study aims to evaluate the effect of a conjoint tendon lengthening on the glenohumeral range of motion (ROM) following RSA.
METHODS: This study used ten fresh-frozen cadaver specimens of the upper extremity. An RSA was implanted using a standard deltopectoral approach, and the ROM was assessed postimplantation. Following this, the conjoint tendon was identified and lengthened using a tendon sheath z-plasty, and the ROM was rerecorded. Statistical significance for the ROM gains after conjoint tendon lengthening was determined with a significance level of P < .05.
RESULTS: Following the lengthening of the conjoint tendon, there were statistically significant improvements in all ROMs (P < .05). Subjects demonstrated a notable gain in IR to the back by 10.3 cm (P < .01), and all ROMs increased by at least 10°, except for forward flexion, which increased by 6° (P < .001).
CONCLUSIONS: This study suggests that lengthening the conjoint tendon improves postoperative ROM of the glenohumeral joint after RSA, offering a potential solution to considerable IR deficits that are commonly encountered post-RSA. Subsequent clinical and biomechanical studies should assess the stability of the shoulder joint following conjoint tendon lengthening.

OBJECTIVE: Reverse shoulder arthroplasty has demonstrated excellent clinical efficacy for patients with shoulder joint diseases and is increasingly in demand. Traditional surgery faces challenges such as limited exposed surfaces and a narrow field of vision, leading to a shorter prosthesis lifespan and a higher risk of complications. In this study, an optical navigation system was proposed to assist surgeons in real-time tracking of the surgical scene.
METHODS: Our optical navigation system was developed using the NDI Polaris Spectra device and several open-source platforms. The first step involved using the preoperative medical image to plan screw implantation paths. Real-time tracking of the patient phantom or cadaver and the surgical instrument was achieved through registration and calibration algorithms. Surgeons were guided on drilling through visualization methods. Postoperative results were compared with the planned implantation paths, and an algorithm was introduced to correct errors caused by the incorrect beginning points.
RESULTS: Experiments involved three scapula cadavers and their corresponding phantoms with identical anatomy. For each experiment, three holes were completed with drills with diameters of 3.2 mm and 8.0 mm, respectively. Comparisons between the postoperative actual screw implantation paths and the preoperative planned implantation paths revealed an entry error of 1.05 ± 0.15 mm and an angle error of 2.47 ± 0.55° for phantom experiments. For cadaver experiments, the entry error was 1.53 ± 0.22 mm, and the angle error was 4.91 ± 0.78°.
CONCLUSIONS: Our proposed optical navigation system successfully achieved real-time tracking of the surgical site, encompassing the patient phantom or cadaver and surgical instrument, thereby aiding surgeons in achieving precise surgical outcomes. Future study will explore the integration of robots to further enhance surgical efficiency and effectiveness.

BACKGROUND: The benefits of reverse shoulder arthroplasty compared to nonoperative treatment for patients presenting with complex proximal fractures have been rarely explored. The aim of this prospective study was to compare the functional results of reverse shoulder arthroplasty with those of nonsurgical treatment in patients with displaced proximal humeral fractures.
METHODS: A multicentric prospective randomized control trial of patients older than 70 years who sustained an acute proximal humeral fracture (3 or 4 parts), with less than 3 weeks of evolution, and had no previous condition or surgery on the affected shoulder was conducted. Patients were randomly assigned to the intervention group (implantation of a reverse shoulder arthroplasty and tuberosities reattachment) or the control group (nonoperative treatment). Functional outcome was assessed using the Constant-Murley score (CMS) at the 1-year follow-up. Complications and reinterventions were considered secondary outcomes. The power of the study relied on the inclusion of 81 patients to recognize a statistically significant difference of 10 points between CMS scores in the groups. Analysis was performed based on the intention to treat principle.
RESULTS: Eighty-one patients were randomized to surgical treatment or nonoperative treatment, while 66 patients completed the 1-year follow-up evaluation. There was no significant difference between the groups in terms of age (76.1 yo vs. 77.43 yo, P = .43), sex (81.08% women in the surgical group vs. 84.09% in the nonoperative group, P = .72), or type of fracture according to Neer\'s classification system (P = .06). At the 1-year follow-up, the group assigned to undergo the intervention had better functional outcomes than the nonoperative treatment group (mean CMS; 61.24, SD: 13.33 vs. mean CMS: 52.44, SD: 16.22, P: .02), with a mean difference of 8.84 points, 95% CI (1.57, 16.11). Two patients in the intervention group (6.5%) suffered major complications (periprosthetic joint infection and axillary nerve palsy). No major complications were observed in the nonoperative group. One patient in the intervention group underwent secondary surgery for a periprosthetic joint infection.
CONCLUSIONS: Treatment with reverse shoulder arthroplasty provides superior functional outcomes compared with conservative treatment for patients presenting with an acute proximal humeral fracture. The difference in CMS is close to the clinically significant thresholds, and some harms are associated with the operative treatment.

UNASSIGNED: Arthroscopic superior capsular reconstruction (ASCR) and reverse shoulder arthroplasty (RSA) have both shown favorable outcomes in patients with irreparable rotator cuff tears (IRCTs).
UNASSIGNED: To (1) compare the clinical outcomes of ASCR versus RSA in patients aged ≥65 years with IRCTs and (2) compare serial changes in clinical outcomes between treatment groups.
UNASSIGNED: Cohort study; Level of evidence, 3.
UNASSIGNED: This study included patients with IRCTs without glenohumeral osteoarthritis who underwent either ASCR or RSA between March 2013 and December 2020 and had at least 2 years of follow-up data. We assessed active range of motion, a visual analog scale (VAS) pain score, the American Shoulder and Elbow Surgeons (ASES) score, and the Single Assessment Numeric Evaluation (SANE) score at the preoperative, short-term (postoperative 6-12 months), and final follow-up times.
UNASSIGNED: In total, 64 patients (ASCR, 31 patients; RSA, 33 patients) were included. The mean age of patients was 71.3 ± 4.4 and 72.9 ± 4.1 years, and the mean final follow-up duration was 42 ± 21.8 and 37.7 ± 21.7 months in the ASCR and RSA groups, respectively. At the short-term follow-up, RSA achieved significant improvements in all clinical outcomes, except for internal rotation (IR), while ASCR only showed significant improvements in VAS pain, ASES, and SANE scores. Compared with the preoperative period, both ASCR and RSA achieved significant improvements in all clinical outcomes, except for IR in the RSA group at the final follow-up. The ASCR group achieved better IR and ASES scores at the final follow-up, while the time taken to recover from pseudoparalysis was shorter after RSA. The ASCR group showed a 67.8% graft healing rate at the 1-year follow-up, while the RSA group showed 12.1% of scapular notching at the final follow-up. No other postoperative complications were observed in either group.
UNASSIGNED: ASCR and RSA achieved favorable clinical outcomes in the study cohort. At the short-term follow-up, RSA showed significant improvements in all clinical outcomes, except for IR, while ASCR only showed significant improvements in VAS pain, ASES, and SANE scores. At the final follow-up, however, ASCR had better IR and ASES scores compared with RSA.

UNASSIGNED: In reverse shoulder arthroplasty (RSA), the ideal combination of baseplate lateralization (BL), glenosphere size (GS), and glenosphere overhang (GOH) with a commonly used 145° neck shaft angle (NSA) is unclear. This is the first study evaluating correlations of body height (BH), humeral head size (HS), glenoid height (GH), and association of gender with best glenoid configurations for range of motion (ROM) maintaining anatomic lateralization (aLAT) for optimized muscle length in 145° and less distalized 135° RSA.
UNASSIGNED: In this computer model study, 22 computed tomographies without joint narrowing were analyzed (11 male/female). A standardized semi-inlay 145° platform stem was combined with 20 glenoid configurations (baseplate [B] 25, 25 + 3/+6 lateralized [l], 29, 29 + 3/6l combined with glenosphere 36, 36 + 2 eccentric [e], 36 + 3l, 39, 39 + 3e, 39 + 3l , 42, 42 + 4e). Abduction-adduction, flexion-extension, external rotation-internal rotation, total ROM (TROM), and total notching relevant (TNR) ROM were computed, best TROM models respecting aLAT (-1 mm to +1 mm) and HS/GH recorded. Second, the 145° models (Ascend Flex stem; Stryker, Kalamazoo, MI, USA) were converted and compared to a 135° inlay RSA (New Perform stem; Stryker, Kalamazoo, MI, USA) maintaining GOH (6.5-7 mm) and aLAT.
UNASSIGNED: Best 145° models had eccentric glenospheres (mean BL: 3.5 mm, GOH 8.8 mm, GS 38.1 mm, distalization 23 mm). The 135° models had concentric glenospheres, mean BL 3.8 mm, GOH 6.9 mm, GS 39.7 mm, and distalization 14.1 mm. HS showed the strongest positive correlation with BL in 145° and 135° models (0.65/0.79). Despite reduced GOH in smaller females with a 135° NSA, adduction, external rotation, extension, TNR ROM, and TROM were significantly increased (P = .02, P = .005, P = .005, P = .004, P = .003), abduction however reduced (P = .02). The same trends were seen for males.
UNASSIGNED: HS is a practical measure in surgery or preoperatively, and the strong positive correlation with BL is a useful planning aid. Despite reduction of GOH, conversion to a less distalized 135° NSAinlay design is powerful to maintain and even significantly increase all components of TNR ROM (extension/external rotation/adduction) in small females with the drawback of reduced abduction which may however be compensated by scapula motion. Lateralization with a less distalized 135° RSA optimizes muscle length, may facilitate subscapularis repair, and maintains highest rigid body motion.

UNASSIGNED: To determine, from a sizable cohort of reverse shoulder arthroplasty (RSA), whether the deltopectoral (DP) or anterosuperior (AS) approach grant better outcomes at a minimum follow-up of 24 months.
UNASSIGNED: The authors reviewed 743 RSAs in patients with primary osteoarthritis (OA) with or without rotator cuff lesions and secondary OA due to rotator cuff tears. The DP approach was used in 540 and the AS approach in 203. Pre- and post-operative constant scores (CSs) and shoulder range of motion were recorded.
UNASSIGNED: Of the initial cohort of 743 shoulders, 193 (25.7%) were lost to follow-up, 16 (2.1%) died, and 33 (4.4%) were revised; 540 shoulders were operated using DP approach (73%), of which 22 were revised (4.1%), while 203 were operated using the AS approach (27%), of which 11 were revised (5.4%). Propensity score matching resulted in two groups: 172 shoulders operated by DP approach, and 88 shoulders operated by AS approach. Comparing outcomes of the matched groups at 2 or more years also revealed that, compared to the AS approach, the DP approach resulted in significantly better post-operative CSs (67.3 ± 14.0° vs 60.8 ± 18.3, P = 0.017), active forward elevation (137° ± 27.4° vs 129° ± 29.8; P = 0.031).
UNASSIGNED: At 2 or more years following RSA, the DP approach granted significantly better CS (by 6.5 points) and active forward elevation (by 8°) compared to the AS approach. The differences observed are clinically relevant and must be considered to manage patient expectations following RSA and for selecting surgical approach depending on their functional needs.
UNASSIGNED: III, comparative study.