Three-dimensional analysis of shoulder movement patterns in shoulders with anterior instability: A comparison of kinematics with normal shoulders and the influence of stabilization surgery.

Abstract

Introduction: Movement analysis of the shoulder joint requires a system capable of analysing a complex interplay of movements in six degrees of freedom. This study was conducted to investigate the three dimensional kinematics of asymptomatic shoulders, shoulders with anterior instability and influence of surgical stabilization on kinematics.
Materials and Methods: Kinematic data and clinical scores were obtained from nine asymptomatic individuals who served as the control group. Data was also obtained from five patients with recurrent anterior instability who were awaiting stabilization surgery before and at least six months after arthroscopic stabilization and rehabilitation. Abduction in coronal plane, abduction in the scapular plane, forward flexion and circumduction movements were assessed.
Results: Unstable shoulders demonstrate a significant decrease in the range of movement when the shoulder is abducted in the coronal plane (p=0.002). There is a significant decrease in the area covered by the circumducting arm in instability when the movements are referenced to the trunk (p=0.002). Forward flexion (p=0.33) and scaption (p=0.075) remain unaffected in instability. Surgical stabilization failed to influence a significant change in any of the pre operative kinematic parameters
[Abduction in the coronal plane (p=0.673), abduction in the scapular plane (p=0.733), forward flexion (p=0.992) or circumduction (p=0.214)]. There was a significant difference in the clinical scores between the control group and the patients with anterior instability (Constant score; p=0.03, Oxford instability score p=0.001). The Oxford instability scores demonstrated a significant improvement after surgical intervention (p=0.011), whereas the Constant score did not change (p=0.58).
Conclusions: This study describes shoulder motion patterns using a non-invasive motion tracking system, which is capable of dynamic movement data capture in six degrees of freedom. There are significant differences in the kinematic characteristics and clinical scores between patients with anterior instability as compared to shoulders in healthy volunteers and the kinematic characteristics are not restored to normal after surgical stabilization and rehabilitation.