Three-dimensional scapular morphology is associated with rotator cuff tears and alters the abduction moment arm of the supraspinatus. (August 2020)

• Record Type: Journal Article
• Authors: Lee, Erin C.S.; Roach, Neil T.; Clouthier, Allison L.; Bicknell, Ryan T.; Bey, Michael J.; Young, Nathan M.; Rainbow, Michael J.
• Is Part Of: Clinical biomechanics. Volume 78(2020)
• Publication Date: 2020-08
• Subjects: Shoulder -- Biplanar videoradiography -- Statistical shape modeling -- Rotator cuff -- Musculoskeletal modeling -- Imaging - computed tomography; Biomechanics -- Periodicals; Osteopathic medicine -- Periodicals; Biomechanics -- Periodicals; Osteopathic Medicine -- Periodicals; 612.76
• DOI: 10.1016/j.clinbiomech.2020.105091
• Languages: English
• ISSNs: 0268-0033

Abstract

Abstract: Background: Numerous studies have reported an association between rotator cuff injury and two-dimensional measures of scapular morphology. However, the mechanical underpinnings explaining how these shape features affect glenohumeral joint function and lead to injury are poorly understood. We hypothesized that three-dimensional features of scapular morphology differentiate asymptomatic shoulders from those with rotator cuff tears, and that these features would alter the mechanical advantage of the supraspinatus. Methods: Twenty-four individuals with supraspinatus tears and twenty-seven age-matched controls were recruited. A statistical shape analysis identified scapular features distinguishing symptomatic patients from asymptomatic controls. We examined the effect of injury-associated morphology on mechanics by developing a morphable model driven by six degree-of-freedom biplanar videoradiography data. We used the model to simulate abduction for a range of shapes and computed the supraspinatus moment arm. Findings: Rotator cuff injury was associated with a cranial orientation of the glenoid and scapular spine ( P = .011, d = 0.75) and/or decreased subacromial space ( P = .001, d = 0.94). The shape analysis also identified previously undocumented features associated with superior inclination and subacromial narrowing. In our computational model, warping the scapula from a cranial to a lateral orientation increased the supraspinatus moment arm at 20° of abduction and decreased the moment arm at 160° of abduction. Interpretations: Three-dimensional analysis of scapular morphology indicates a stronger relationship between morphology and cuff tears than two-dimensional measures. Insight into how morphological features affect rotator cuff mechanics may improve patient-specific strategies for prevention and treatment of cuff tears. Highlights: 3D scapular shape features are strongly correlated with supraspinatus tears. 3D analysis identified shape nuances not previously captured by 2D measures. Abduction was simulated for a range of shapes in data-driven musculoskeletal model. At-risk shape features decreased the supraspinatus moment arm for low abduction. At-risk shape features increased the supraspinatus moment arm for high abduction.