Structural Integrity and Clinical Function of the Subscapularis Musculotendinous Unit After Arthroscopic and Open Shoulder Stabilization

Abstract

Background: Postoperative subscapularis dysfunction after open shoulder stabilization has recently received increasing attention. The potential advantage of arthroscopic stabilization procedures is that they do not violate the subscapularis musculotendinous unit, which might preserve its structural integrity and clinical function, which would lead to superior clinical results.

Hypothesis: Arthroscopic shoulder stabilization does not lead to clinical and radiological signs of subscapularis insufficiency.

Study Design: Cohort study; Level of evidence, 3.

Methods: Twenty-two patients who underwent arthroscopic (group I, n = 12; average age, 30.9 years; mean follow-up, 37 months) or open (group II, n = 10; average age, 28.8 years; mean follow-up, 35.9 months) shoulder stabilization procedure were followed up clinically (clinical subscapularis tests and signs, Constant Score, Rowe Score, Walch-Duplay Score, Western Ontario Shoulder Instability Index and Melbourne Instability Shoulder Score) and by magnetic resonance imaging (subscapularis tendon integrity, cross-sectional area, defined muscle diameters, and signal intensity analysis [ratio infraspinatus/upper subscapularis and infraspinatus/lower subscapularis]). A third group (group 0) of 12 healthy volunteers served as a control.

Results: Clinical signs for subscapularis insufficiency were present in 0% of cases in group I and in 70% of cases in group II. There were no statistically significant differences in either group regarding Constant Score, Rowe Score, Walch-Duplay Score, Western Ontario Shoulder Instability Index, and Melbourne Instability Shoulder Score (P > .05). On magnetic resonance image, no subscapularis tendon ruptures were found. The cross-sectional area, the mean vertical diameter, and the mean transverse diameter of the upper and lower subscapularis muscle portion was significantly less in group II than in group 0 (P < .05). The signal intensity analysis revealed the infraspinatus/upper subscapularis ratio was significantly lower in group II than in group I or group 0. The infraspinatus/lower subscapularis ratio did not significantly differ in all 3 groups (P > .05).

Conclusion: This study confirms previous observations that open shoulder stabilization using a subscapularis tenotomy may lead to atrophy and fatty infiltration of the subscapularis muscle, resulting in postoperative subscapularis dysfunction. As expected, arthroscopic procedures do not significantly compromise clinical subscapularis function and structural integrity. However, no significant differences were observed in the overall outcome.