Summary

A study was performed for monitoring scapular kinematics in patients with rotator cuff tears (RCT) and scheduled for arthroscopic repair. The 3D scapular kinematics was measured by using an acromion marker cluster both on the healthy and pathologic side during arm elevation. Patients with RCT exhibit scapular dyskinesis with decreased humeral elevation and increased scapular internal rotation.

Abstract

Background

Monitoring scapular movements is valuable in managing patients with abnormal scapular motion patterns, such as those suffering from rotator cuff tears (RCT). Measuring scapular kinematics is challenging due to the sliding nature of the scapula over the thorax and the complex variation in its orientation during movements. Among the methods proposed in the literature for monitoring scapular kinematics is the acromion marker cluster (AMC) method. The AMC overcomes the high level of invasiveness of the method using bone pin insertion, considered the gold standard.

AIMS
To compare the scapular kinematics of the pathologic side of patients with RCT and scheduled for arthroscopic repair vs. the healthy side before surgery.

Methods

An L-shaped AMC consisting of three photo-reflective markers was placed on the flat portion of the acromion, with the long side along the scapular spine and the short side pointing anteriorly to the scapular plane. Through a static calibration procedure, a relationship is defined between the anatomical scapular landmarks and the markers on the cluster to follow dynamically scapular kinematics. Enrolled patients were asked to perform bilateral elevations and lowerings in the frontal, scapular, and sagittal planes at a self-selected speed. Patients repeated the movements five times in each trial, but only the central three repetitions were selected for subsequent analysis. Kinematic analysis was performed in Visual 3D software after pre-processing markers trajectories acquired with the Qualisys™ stereophotogrammetric system. The following kinematic variables were calculated: humerothoracic elevations, scapular internal-external rotation, medial-lateral rotation, and anterior-posterior tilt at 30°, 45°, 60°, and 90° of humeral elevation. Statistical analysis was executed in SPSS v28. The nonparametric Wilcoxon rank-sum test was applied as a statistical method (p-value < 0.05).

Results

In the sagittal plane flexion, the maximum mean arm elevation was 112.04° (range: 76.42°-143.29°) for the healthy side and 98.56° (range: 20.89°-133.66°) for the pathological side. In the scapular plane, the maximum mean arm elevation was 93.94° (range: 77.96°-113.20°) for the healthy side and 87.48° (range: 8.92°-114.17°) for the pathological side. In the frontal plane, the maximum mean arm elevation was 102.14° (range: 89.10°-117.00°) for the healthy side and 86.07° (range: 21.86°-112.61°) for the pathological side. At the maximum humeral elevation in the sagittal plane, the mean scapular upward rotation, internal rotation, and posterior tilting were 32.58°±8.60°, 13.50°±8.46°, 10.92°± 9.16° for the healthy side, and 32.63°±11.63°, 17.05°±11.01°, 9.46°±10.23° for the pathological side. No significant differences were observed in scapular kinematics at 30°, 45°, 60°, and 90° of humeral elevation.

Discussion

In this study, the 3D scapular kinematics was evaluated between shoulders with RCT and the contralateral healthy shoulders. According to our study, before treatment, comparable or increased scapular motions in the affected shoulders with respect to the contralateral healthy side may result from adaptive movements of the pathological side to maintain humeral elevation. Patients with RCT exhibit scapular dyskinesis with decreased humeral elevation and increased scapular internal rotation.