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

Abstract

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.

Prior Acromioplasty Provides Similar Outcomes and Rate of Postoperative Complications Including Acromial Fracture After Reverse Total Shoulder Arthroplasty: A Retrospective Matched-Cohort Analysis

“…The rate of post-RTSA acromial fracture (2.2%) in both the study group and the control group was lower than the rates reported in the most recent literature (3.7%-10%). 5 , 11 , 12 However, the cited studies were able to evaluate larger populations of patients undergoing RTSA compared with our study. 11 , 12 Prior studies have evaluated patient factors and sequelae of operative techniques that predispose patients to acromial fractures after RTSA.…”

“…The incidence of acromial and scapular spine stress fractures after RTSA has been reported as up to 10%. 5 Preoperative patient factors including female sex, osteoporosis, and acromial anatomy, as well as the biomechanical changes and excess stress placed on the acromion inherent to RTSA, have been identified as risk factors. 5 …”

Acromial and Scapular Spine Fractures following Reverse Total Shoulder Arthroplasty—A Systematic Review of Fixation Constructs and Techniques

“…Although we were unable to determine the fixation construct with the best clinical performance, our study of pooled results suggests that using a single locking plating for lateral acromion and acromial base fractures (Levy Type I and II), and a dual plating construct for more medial fractures (Levy Type II and III) delivers a high union rate and a reasonably low complication rate. Together with the current biomechanical knowledge about acromion and scapular spine fractures following RSA [ 5 ] and plating techniques [ 35 ], it seems that dual plating reveals a stronger fixation construct than single plating and may yield superior outcomes in more medial fractures, although the latter is yet to be proven.…”

“…Several RSA-specific factors influence acromial/scapular spine strain, with glenoid lateralization being one of the main factors leading to increased strain [ 5 ]. Thus the growing trend towards increased lateralization of the center of rotation (COR) may exacerbate the difficult problem of acromion or scapular spine fractures following RSA [ 2 , 6 ].…”

Mitigating Fracture of the Acromion and Scapular Spine After Reverse Shoulder Arthroplasty

“…The authors found significantly increased strain in all Levy zones at 0° flexion when glenoid lateralization was increased from 0 to +10 mm. Furthermore, a systematic review by Paszicsnyek et al 50 that included 6 studies with 36 cadavers and 11 CT reconstructions concluded that there was a linear relationship between increased glenoid lateralization and increased acromion and SS strain based on 4 included studies demonstrating a positive relationship 45,47,51,52 . However, the influence of glenoid lateralization is likely dependent on humeral lateralization; Shah et al 47 found that cases with greater humeral onlay (+10 or +13 mm) demonstrated a significant increase in acromial strain when lateralizing the glenoid from 0 to +6 mm.…”