Functional internal rotation is associated with subscapularis tendon healing and increased scapular tilt after Grammont style bony increased offset reverse shoulder arthroplasty with 155° humeral implant

Background: While forward flexion consistently improves after reverse shoulder arthroplasty (RSA), restoration of internal rotation behind the back (IR1) is much less predictable. This study aims to evaluate the role of the subscapularis tendon in restoration of IR and identify other factors that may influence IR such as anterior scapular tilt and postoperative passive internal rotation at 90° of abduction (IR2). The hypothesis was that IR1 is positively associated with both subscapularis healing, postoperative passive IR2, and anterior scapular tilt.

Methods: A retrospective review was performed on a consecutive series of Grammont style bony increased offset RSAs performed by a single surgeon between January 2014 and December 2015. Inclusion criteria were: (1) primary RSA for rotator cuff arthropathy, massive irreparable rotator cuff tear, or primary osteoarthritis with B2 glenoid morphology, (2) minimum of two years clinical follow-up, and (3) complete intraoperative repair of a repairable subscapularis tendon. The primary outcomes were postoperative return of IR1 compared to postoperative IR2, healing rate of subscapularis tendon, and scapular tilt.

Results: The cohort included 77 patients, aged 72.6 ± 7.0 years at index surgery and comprising 32 men (42%) and 45 women (58%). At a mean follow-up of 3.3 ± 1.0 years, ultrasound evaluation revealed a successful repair of the subscapularis in 41 patients (53%). Healed subscapularis repair was significantly associated with greater IR1 (85% vs. 53%, P = .031). A multivariate logistic regression revealed functional postoperative IR1 was independently associated with subscapularis healing (odds ratio [OR], 4.3; 95% confidence interval [CI] [1.1-20.2]; P = .046) as well as greater anterior tilt (OR, 1.2; 95% CI [1.1-1.5]; P = .008) and postoperative IR2 (OR, 1.09; 95% CI [1.05-1.14]; P < .001) but lower postoperative passive abduction (OR, 0.96; 95% CI [0.92-1.00], P = .045). The area under receiver operating characteristic curve obtained with the Youden index was 0.88 with a sensitivity of 81.8% and specificity of 90.6%.

Conclusions: This study revealed that in a Grammont-type RSA, postoperative IR1 recovery is first associated with subscapularis tendon healing, followed by IR2 and finally the ability to tilt the scapula anteriorly. Better understanding of these factors preoperatively may provide greater insight on expected return of functional internal after RSA.