Summary

Changes in scapular and GH kinematics following superior capsular reconstruction suggest a convergence towards a more similar and potentially more efficient movement pattern following superior capsular reconstruction.

Abstract

Introduction

Patients with irreparable rotator cuff tears exhibit functional limitations while performing activities of daily living. One viable treatment is superior capsular reconstruction (SCR). SCR has been shown to restore stability of the glenohumeral (GH) joint in cadavers1, but its effect on in vivo scapular and humeral motion is unknown. The aims of this study were to determine the effect of SCR on in vivo scapular and humeral kinematics during a functional hand-to-head motion and to identify associations between shoulder kinematics and patient-reported outcomes (PROs). We hypothesized that the functional task would be accomplished by using more GH based movement and less scapular motion after SCR, and there would be a positive correlation between kinematics changes and improved PROs.

Methods

Ten patients (8M, 2F, age 63 ± 7 years) with irreparable RCT consented to participate in this prospective IRB-approved study. ASES, DASH, and WORC surveys were completed before (PRE) and 1-year after (1YR-POST) SCR. PRE and 1YR-POST, participants were seated and instructed to move their hand from their lap to the back of their head while synchronized biplane radiographs of the shoulder were collected at 50 images/s for 3 trials. Subject-specific CT-based bone models of the humerus and scapula were matched to the synchronized radiographs using a validated volumetric tracking technique2 to determine scapular and GH kinematics. PRE to 1YR-POST differences in end-range rotational orientation and the total contribution of each rotational component to the overall movement were evaluated using a paired t-test. Among-subject variability in rotational contributions to the motion was calculated each test day, and PRE to 1YR-POST differences were analyzed using a paired t-test. Correlations between rotation contributions and PROs were evaluated with Pearson’s correlation. Significance was set at p<0.05 for all tests.

Results

End-range GH I/E rotation was 12° lower (p=0.03) while end-range scapular protraction was 6° degrees higher 1YR-POST compared to PRE (p=0.01). Inter-subject variability in rotational contributions to the movement decreased 4.0% in GH abduction and 2.6% in GH I/E rotation (p=0.047, and p=0.005, respectively) from PRE to 1YR-POST. The PRE to 1YR POST change in contribution from GH abduction was positively correlated to the change in contribution from GH I/E rotation (R=0.8, p=0.001) and negatively correlated to the change in contribution from scapular protraction (R=-0.94, p=0.001). Changes in the horizontal plane elevation contribution were positively correlated with changes in ASES scores (R=0.635, p=0.048).

Discussion

Changes in rotational contributions of the scapula and humerus to the hand-to-head movement after SCR were inconsistent across subjects, however, inter-subject variability in GH abduction and I/E rotation were reduced following surgery, suggesting the participants’ movement strategy converged toward a more similar and possibly more efficient movement pattern following SCR. End-range I/E rotation decreased and scapular protraction increased, which contradicts our first hypothesis. In addition, increased GH horizontal plane elevation contribution following surgery was associated with improved ASES scores, supporting our second hypothesis. This may be consistent with improved glenohumeral kinematics and efficiency of movement during a functional task following SCR.