Analysis of osseous shoulder morphology and muscle volume in concentric and eccentric osteoarthritis of the shoulder.

BACKGROUND

The etiology of primary eccentric osteoarthritis (OA) is multifactorial involving glenoid shape alterations, acromion abnormalities, and rotator cuff pathologies. However, none of the changes described for eccentric OA are either consistent or do satisfactorily explain the condition. Up to now, potential individual risk factors contributing to the development of concentric or eccentric OA have been studied mostly independently of each other. This study examined the differences of osseous shoulder morphology and muscle volume in concentric and eccentric OA of the shoulder as a potential risk factor for the development of posterior glenoid wear.

METHODS

A retrospective, comparative study was conducted, analyzing computed tomography scans of 114 shoulders in 86 patients with primary OA at a single center between 2010 and 2023. These patients were divided into 2 groups-according to an underlying concentric or eccentric OA. As parameters, the osseous shoulder morphology (glenoid offset, glenoid version, posterior humeral head subluxation, anterior acromial coverage, posterior acromial coverage, posterior acromial tilt, posterior acromial height, and critical shoulder angle (CSA)) and muscle volume (subscapularis, infraspinatus/teres minor, supraspinatus), were measured and compared between the groups. Computed tomography images were classified according to the modified Walch classification.

RESULTS

The mean age of the patients was 68.9 ± 9.9 years and 62.3% of the patients were female (54 of 86). A total of 25 shoulders were included in the concentric group and 89 shoulders in the eccentric group. Patients with eccentric OA had a significantly increased glenoid retroversion according to Friedmann (12.6° ± 8.2° vs. 4.3° ± 3.4°; < .001) and relative to scapular blade axis (10.6° ± 7.6° vs. 3.1° ± 3.6°; < .001), increased scapulohumeral subluxation index (0.67 ± 0.01 vs. 0.55 ± 0.05; < 001), increased glenohumeral subluxation index (0.56 ± 0.06 vs. 0.52 ± 0.05; = .004), and increased CSA (26.3° ± 5.0° vs. 23.1° ± 4.2°; = .006) compared to patients with concentric OA. No significant differences in anterior glenoid offset and other parameters of acromial roof morphology were found between the 2 experimental groups. No significant differences in volumes of supraspinatus, subscapularis and infraspinatus/teres minor muscles could be detected between the 2 experimental groups.

CONCLUSION

Patients with primary eccentric OA show significant differences in glenoid retroversion, posterior scapulohumeral/glenohumeral subluxation, and CSA. However, there are no significant differences regarding the acromion roof morphology and rotator cuff volume compared to patients with concentric OA.