Higher critical shoulder angle and acromion index are associated with degenerative full-thickness rotator cuff tear.
Rotator cuff tear is one of the most common causes of shoulder pain and disability of shoulder function. Its etiology is multifactorial, and several risk factors predispose the individual to a higher risk of injury, including smoking habits, diabetes mellitus, abnormal biomechanics and anatomical variances. Within the anatomical variances, the bone morphology and morphometry have been proposed to increase the risk of degenerative rotator cuff tear. However, a systematic analysis of the bony morphology and morphometry influence on rotator cuff tear risk has not been performed. Hence, this systematic review aims to analyze the various shoulder bone morphology and morphometry parameters in rotator cuff tear risk, that are available in literature.
A systematic review of databases Pubmed, Scopus, EMBASE and Cochrane Library was performed in order to search for relevant studies reporting shoulder morphological or morphometrical potential risk factors for rotator cuff tear. The search collected all available studies up to the 30th of June of 2018, and was designed by combining the following keywords: "critical shoulder angle", "acromion index", "lateral acromial angle", "acromial index", morphology, morphometry, shoulder, acromi*, glenohumeral, scapul*, humerus, glenoid, "rotator cuff"; with resource to the Boolean operators (AND) and (OR) and the command [Ti/Ab]. Cochrane RevMan 5.3 was used for conducting random-effects inverse-variance meta-analysis of potential risk factors. Meta-analysis was considered only for degenerative full-thickness rotator cuff tears and when there were at least 5 studies for the considered potential risk factor.
A total of 48 studies comprising 7435 patients (34 years, 42% males, 53% left shoulder, 7577 shoulders) reporting shoulder bone morphology or morphometric parameters were included in this systematic review. When reporting (33 studies), rotator cuff tears were total (n=3004, 80%) or partial (n=740, 20%) and mostly involved the supraspinatus tendon. When comparing shoulders with full-thickness degenerative rotator cuff tears (n=750) against controls without rotator cuff injury (n=694), there was an increased critical shoulder angle (CSA) in rotator cuff injured group with a mean difference of 4.88º (95% confidence interval 3.97 to 5.79, p<0.001). Rotator cuff injured patients also showed an increased acromion index (AI) with a mean difference of 0.05 (95% confidence interval 0.02 to 0.08, p=0.001). Other bone morphology and morphometric risk factors were found and considered for qualitative analysis, but not eligible for meta-analysis. Considering a qualitative approach to outcomes studies, these reveled: 1) large CSA (>38º) was associated with higher retear rate and worst repaired rotator cuff integrity; 2) contradictory results regarding large CSA leading to worst pos-operative outcomes; 3) increased AI (>0.682) associated with lower satisfaction and worst functional outcomes.
Higher CSA and AI are associated with degenerative full-thickness rotator cuff tears. A large CSA (>38º) seems to be associated with higher risk of retear and worst rotator cuff integrity after surgical repair. An increased AI (>0.682) seems to be associated with lower postoperative outcomes.