Scapular Morphologic Characteristics and Rotator Cuff Tear Pattern Are Independently Associated With Chronic Pseudoparalyis: A Matched-Pair Analysis of Patients With Massive Rotator Cuff Tears.

Background: It is unclear which structural parameters determine the development or the absence of chronic pseudoparalysis (PP) in patients with massive rotator cuff tears (mRCTs). Purpose: To determine whether scapular morphologic characteristics and extent of rotator cuff tearing are independent factors associated with chronic PP. Study Design: Case-control study; Level of evidence, 3. Methods: In this retrospective case-control study, 50 patients with chronic mRCT (>= 2 fully detached tendons) and active scapular plane abduction less than 90 degrees (PP group) were age- and sex-matched with a cohort of 50 patients with chronic mRCT and an active scapular plane abduction greater than 90 degrees (non-PP; NPP group). Analysis of standardized, plain radiographs included measurement of the critical shoulder angle (CSA) and the acromiohumeral distance (ACHD) on anteroposterior views and measurement of posterior acromial tilt, anterior and posterior acromial coverage, and posterior acromial height on standardized outlet views. Measurements on magnetic resonance imaging included fatty muscle infiltration, anterior (subscapularis) and posterior (infraspinatus/teres minor) tear extension, and global tear extension (anterior + posterior tear extension) in the parasagittal plane. Results: Overall, no significant difference was found in patients' demographic characteristics (P> .05). Univariate analyses confirmed significant differences between the PP and NPP groups in active scapular plane abduction (51 degrees +/- 22 degrees vs 135 degrees +/- 29 degrees;P< .001). Multivariate analyses revealed independent factors associated with PP compared with the NPP group: CSA (38.2 degrees +/- 4.6 degrees vs 35.2 degrees +/- 3.7 degrees;P= .001); ACHD (4.7 +/- 2.2 vs 7.3 +/- 2.6 mm;P< .001); posterior acromial height (22 +/- 10 vs 17 +/- 7 mm;P= .005); and anterior (-9 degrees +/- 21 degrees vs 25 degrees +/- 12 degrees;P< .001) and posterior (-18 degrees +/- 14 degrees vs 2 degrees +/- 14 degrees;P< .001) tear extension. The NPP group had significantly less involvement and fatty infiltration of the subscapularis (1.4 +/- 0.6) compared with the PP group (2.2 +/- 0.9) (P< .001). Conclusion: This study confirms that global RCT extension and the quality of the inferior half of the subscapularis are significantly associated with chronic pseudoparalysis. The study further shows that acromial morphologic characteristics are relevant in the development of pseudoparalysis. Patients with pseudoparalysis have a larger CSA, less ACHD, and a higher positioned acromion in the sagittal plane.