| Description |
- Funding Acknowledgement: This study was supported by a grant from the Orthopaedic Research and Education Foundation
Background: The glenohumeral joint is the most frequently dislocated joint in the human body, and recurrent instability is common with non-operative treatment. Shoulder stabilization surgery can decrease the risk of recurrent instability. However, surgery has not been shown to decrease osteoarthritis rates at long-term follow-up, which has been reported as high as 55%. Arthritis after joint stabilization surgery remains poorly understood and difficult to detect. It is unclear how cartilage mechanical properties change after shoulder instability and subsequent surgery and how those changes relate to early signs of cartilage degeneration. Thus, the purpose of this study was to evaluate the role of advanced MRI imaging for detecting cartilage changes in the postoperative period with the hope that early detection could improve treatment decisions and understanding of the pathology. Two hypotheses were investigated. 1) Compared to healthy controls, patients with shoulder instability will have an increased compressive cartilage strain. 2) Following surgical treatment, the compressive cartilage strain will be higher than prior to surgical treatment.
Methods: 12 patients with anterior shoulder instability were treated with arthroscopic shoulder stabilization surgery. Patients underwent T1 VIBE MRI imaging at two time points: 4-6 weeks after initial injury and 6 months after surgery. At each time point, participants underwent MRI scans before and after completing 30 standardized pushups. 3-dimensional models of the scapula and humerus were created for each scan. A semi-automated segmentation tool was developed and validated that leveraged gradients in spacial signal intensity to isolate bony cortices with speed and repeatability. Bone-to-bone distance was measured between the glenoid and humeral head at 9 locations allowing for 6 regional comparisons in the anterior-posterior and superior-inferior axes. Percent change in bone-to-bone distance was measured between pre- and post-exercise bone models as a proxy for glenohumeral cartilage strain. The study group was compared to a cohort of 7 healthy participants with no history of shoulder injury.
Results: In the study group (n=12), there were 10 Males and 2 Females with an average age of 24.2±4.7 (16-42) years and a BMI of 23.9±2.2 (20-32). The healthy control group (n=7) contained 6 Males and 1 Female with an average age of 24.8±3.7 (17-31) years and BMI of 24.3±3.9 (19-32). The average percent change in bone-to-bone distance was found to be -1.01 ± 2.2% (mean ± 95% CI) for the study group and 0.32 ± 3.4% for the healthy control group (p=0.59). No site-specific differences were found in percent change in bone-to-bone distance in either the A-P axis (P=0.976) or the S-I axis (P=0.751). Six patients returned for post-surgery imaging. The average percent change in bone-to-bone distance was found to be 1.02 ±2.5% pre-surgery and -1.09 ± 4.4% post-surgery (p=0.51). No site-specific differences were found in percent change in bone-to-bone distance in either the A-P axis (P=0.809) or the S-I axis (P=0.427).
Conclusion: No significant differences were found between the study and the control group in percent change in bone-to-bone distance or bone-to-bone distance at global or site-specific measurements, and no significant differences were found between the pre- and post-surgery groups. These results may have been influenced by the applicability of bone-to-bone measurements in the shoulder, the XY resolution of the MRI protocol, or other factors. Further investigation may complete sub-pixel segmentation of the articular surfaces and/or analyze new parameters, such as labral and bony morphology, and how they are influenced by shoulder instability and subsequent surgery.
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