Factors Influencing Acromial and Scapular Spine Strain after Reverse Total Shoulder Arthroplasty: A Systematic Review of Biomechanical Studies

Background: Acromial and scapular spine fractures after reverse total shoulder arthroplasty (RTSA) can be devastating complications leading to substantial functional impairments. The purpose of this study was to review factors associated with increased acromial and scapular spine strain after RTSA from a biomechanical standpoint. Methods: A systematic review of the literature was conducted based on PRISMA guidelines. PubMed, Embase, OVID Medline, and CENTRAL databases were searched and strict inclusion and exclusion criteria were applied. Each article was assessed using the modified Downs and Black checklist to appraise the quality of included studies. Study selection, extraction of data, and assessment of methodological quality were carried out independently by two of the authors. Only biomechanical studies were considered. Results: Six biomechanical studies evaluated factors associated with increased acromial and scapular spine strain and stress. Significant increases in acromial and scapular spine strain were found with increasing lateralization of the glenosphere in four of the included studies. In two studies, glenosphere inferiorization consistently reduced acromial strain. The results concerning humeral lateralization were variable between four studies. Humeral component neck-shaft angle had no significant effect on acromial strain as analysed in one study. One study showed that scapular spine strain was significantly increased with a more posteriorly oriented acromion (55° vs. 43°; p < 0.001). Another study showed that the transection of the coracoacromial ligament increased scapular spine strain in all abduction angles (p < 0.05). Conclusions: Glenoid lateralization was consistently associated with increased acromial and scapular spine strain, whereas inferiorization of the glenosphere reduced strain in the biomechanical studies analysed in this systematic review. Humeral-sided lateralization may increase or decrease acromial or scapular spine strain. Independent of different design parameters, the transection of the coracoacromial ligament resulted in significantly increased strains and scapular spine strains were also increased when the acromion was more posteriorly oriented. The results found in this systematic review of biomechanical in-silico and in-vitro studies may help in the surgical planning of RTSA to mitigate complications associated with acromion and scapular spine fracture.

Is reverse total shoulder arthroplasty (rTSA) more advantageous than anatomic TSA (aTSA) for osteoarthritis with intact cuff tendon? A systematic review and meta-analysis

Purpose We aimed to compare the outcomes and complications of anatomical shoulder arthroplasty (aTSA) and reverse total shoulder arthroplasty (rTSA) for primary glenohumeral osteoarthritis with intact cuff tissue. Materials and methods The MEDLINE, Embase, and Cochrane Library databases were systematically searched for studies published before March 2, 2021 using the PRISMA guidelines. Studies were included if they directly compared aTSA and rTSA for treating primary glenohumeral arthritis. A meta-analysis was performed using six studies that compared radiologic outcomes, functional scores, and range of motion (ROM). All the data were pooled using a random-effects model. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated as dichotomous data, while continuous data were analyzed using mean differences with 95% CIs. Results Two independent researchers reviewed 1,061 studies. Six studies met the inclusion criteria. The range of motion, especially external rotation, was better for aTSA than for rTSA (MD = − 10.28, 95% CI: − 16.69 to − 3.88, P = 0.002). Functional scores showed no difference between aTSA and rTSA. Glenoid loosening (OR = 0.17, 95% CI: 0.06–0.50, P = 0.001) was more common with aTSA, and scapula notching (OR = 10.63, 95% CI: 1.73–65.27, P = 0.01) with rTSA. In the mid-term follow-up, the overall revision rate showed no difference between aTSA and rTSA, with a pooled OR of 0.33 (95% CI: 0.07–1.57, P = 0.16). Conclusion A better ROM was achieved after aTSA than after rTSA. There was no difference in the revision rate at mid-term follow-up between aTSA and rTSA. Glenoid loosening was more common with aTSA, and scapula notching with rTSA. Level of evidence: Level IV, Meta-analysis.

Comparison of Lateralized Versus Medialized Reverse Total Shoulder Arthroplasty: A Systematic Review and Meta-analysis

Background: Reverse total shoulder arthroplasty (rTSA) is an established procedure for cuff tear arthropathy. More lateralized prostheses have been designed to overcome the reported adverse outcomes of Grammont-style rTSA. Purpose: To compare the clinical and radiological outcomes of medialized and lateralized center of rotation (COR) in rTSA. Study Design: Systematic review; Level of evidence, 3. Methods: This review followed the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Included were studies with a level of evidence ≥3 that compared medialized and lateralized rTSA with a minimum follow-up of 12 months. Functional scores including the American Shoulder and Elbow Surgeons (ASES) score and Constant score (CSS), range of motion at final follow-up, gain of external rotation (ER), visual analog scale (VAS) pain score, scapular notching, and heterotopic ossification (HO) were compared. Data were analyzed using random-effects or fixed-effects models in accordance with heterogeneity. Results: Five retrospective cohort studies and 1 randomized controlled study (n = 594 patients) were included. Lateralized rTSA resulted in greater improvement in ER degree ( P < .001), a lower VAS pain score (standardized mean difference [SMD], –0.39; P = .002), and a lower rate of scapular notching (risk ratio [RR], 0.40; P < .001) and HO (RR, 0.52; P < .001). Final forward flexion (SMD, –0.14; P = .629) and ER (SMD, 0.21; P = .238) did not differ significantly between the 2 groups. Overall functional scores, including ASES score (SMD, 0.22; P = .310) and CSS (SMD, 0.37; P = .077), also did not differ significantly (SMD, 0.28; P = .062). The overall complication rate did not differ significantly between the 2 groups (RR, 0.71; P = .339). Conclusion: Compared with medialized rTSA, lateralized COR rTSA results in greater improvement in ER and the VAS pain score, decreased rates of scapular notching and HO, and no significant changes in functional outcome scores or the complication rate.

Medialized versus Lateralized Center of Rotation in Reverse Total Shoulder Arthroplasty: A Systematic Review and Meta-Analysis

One of the original biomechanical principles of reverse total shoulder arthroplasty (RTSA) is medialization of the center of rotation (COR) relative to the native level of the glenoid. Several authors have proposed the lateralized center of rotation, which is characterized by a lateralized (L) glenoid and medialized (M) humeral component. The aim of this review is to compare the clinical and functional outcomes of COR in medialized (M-RTSA) and lateralized (L-RTSA) RTSA in patients with uniform indications and treatment through a meta-analysis. A PRISMA-guided literature search of PubMed, Medline, Embase, Scopus, Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews and Cochrane Clinical Answers was conducted from April to May 2021. Twenty-four studies were included in the qualitative synthesis, and 19 studies were included in the meta-analysis. Treatment with RTSA resulted in positive post-operative outcomes and low complication rates for both groups. Statistically relevant differences between L-RTSA group and M-RTSA group were found in post-operative improvement in external rotation with arm-at-side (20.4° and 8.3°, respectively), scapular notching rates (6.6% and 47.7%) and post-operative infection rates (1% and 7.7%). Both lateralized and medialized designs were shown to improve the postoperative outcomes. Nevertheless, a lateralized COR resulted in greater post-operative external rotation.