[Magnetic resonance analysis of the subscapularis muscle after open anterior shoulder stabilization]

Analysis of the magnetic resonance imaging of the subscapularis musculotendinous unit (SSC) after primary and revision open shoulder stabilization and their correlation with the clinical function.

In a retrospective cohort study, 13 patients (mean age of group A: 36.5 years) after primary and 12 (mean age of group B: 34.2 years) after revision open stabilization underwent postoperative MRI of the shoulder. The digital data was analyzed with respect to the vertical und transverse diameters (V[slashed circle], T[slashed circle]) in a defined image slice. A signal intensity analysis was performed (infraspinatus/subscapularis signal-to-noise ratio = ISP/SSC SNR). The clinical examination included the SSC tests and signs and the Constant and Rowe score. Twelve healthy volunteers (group C) served as the control.

From group C to group B, the mean V[slashed circle] of the SSC decreased significantly (p < 0.05) as did the mean T[slashed circle] of the cranial part of the SSC muscle (= crSSC) (p < 0.05). The mean T[slashed circle] of the caudal part of the SSC muscle (= caSSC) did not differ significantly between all groups (p > 0.05). The ISP-SSC SNR was significantly lower (p < 0.05) in the crSSC of groups A und B than in group C. In the caSSC, the SNR increased in groups A and B. In 53.8 % of group A and 92.3 % of group B, clinical signs of SSC insufficiency were found. There was no significant difference between the Constant and the Rowe score in both groups (p > 0.05). Complete tendon ruptures were not observed in any case.

MRI enables semi-quantitative analysis of the postoperative changes of the subscapularis muscle. The decrease of the ISP/SSC SNR points to a fatty degeneration in the crSSC. The results provide indications of the causes of the clinical dysfunction of the subscapularis musculotendinous unit after open shoulder stabilization.