Highlights
- •Scapulothoracic kinematics are significantly altered in anterior instability vs. controls.
- •In abduction reduced glenohumeral motion is compensated by increased scapular rotation.
- •In apprehension position greater glenohumeral joint angles, but normal humeral translation.
- •This suggests altered neuromuscular control of the unstable shoulder.
- •The observed differences in shoulder kinematics may be used for targeted rehabilitation.
Abstract
Background
Altered shoulder kinematics in patients with recurrent anterior shoulder instability
remains poorly understood. This prospective study aimed to quantify in vivo glenohumeral and scapulothoracic joint kinematics and joint-contact positions in
patients with shoulder instability and healthy controls.
Methods
Twenty patients with recurrent anterior shoulder instability (mean 28 years) and five
patients without shoulder pathology (mean 39 years) were scanned using open CT in
six static upper limb positions including 90° of abduction, combined abduction and
external rotation, 90° of flexion, lift-off position (i.e. reaching behind the back) and the neutral shoulder with external rotation. Image
datasets were digitally reconstructed to quantify shoulder joint kinematics and glenohumeral
translation.
Findings
At 90° of abduction, instability patients demonstrated significantly less glenohumeral
abduction and a reciprocal increase in upward scapulothoracic rotation compared to
controls (mean difference: 13.3°, p = 0.038). With the shoulder in combined abduction and external rotation, instability
patients showed a significant increase in glenohumeral rotation and a reciprocal decrease
in scapulothoracic rotation compared to controls (mean difference: 5.0°, p = 0.042). There were no significant differences in humeral head translation in the
sagittal plane (anterior-posterior axis) for all motions tested (p > 0.05).
Interpretation
Scapulothoracic and glenohumeral kinematics are significantly different between patients
with recurrent anterior shoulder instability and those with a healthy shoulder. Instability
patients compensate for reduced glenohumeral function during abduction by increasing
scapular rotation. With the shoulder in combined abduction and external rotation position,
greater glenohumeral joint angles without significantly increased humeral head translation
suggest altered neuromuscular control in the unstable shoulder.
Keywords
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Article info
Publication history
Published online: September 30, 2022
Accepted:
September 27,
2022
Received:
April 19,
2022
Identification
Copyright
© 2022 Elsevier Ltd. All rights reserved.
