BACKGROUND:
Postoperative subscapularis muscle insufficiency after open shoulder stabilization procedures represents an unrecognized condition.

HYPOTHESIS:
Primary and revision open shoulder stabilization using the inverted L-shaped tenotomy approach impairs subscapularis muscle recovery and affects final clinical outcome.

STUDY DESIGN:
Cohort study; Level of evidence, 3.

METHODS:
Twenty-five patients who underwent primary (group 1: n = 13; mean age, 36.5 years; follow-up, 48 months) or revision (group 2: n = 12; mean age, 34.2 years; follow-up, 52 months) open shoulder stabilization procedures were followed up clinically (clinical subscapularis tests and signs, Constant score, and Rowe score) and by magnetic resonance imaging (tendon integrity, defined muscle diameters, and signal intensity analysis [ratio infraspinatus/upper subscapularis muscle and infraspinatus/lower subscapularis muscle]). A third group (group 0) of 12 healthy volunteers served as a control.

RESULTS:
Clinical signs for subscapularis muscle insufficiency were present in 53.8% of cases in group 1 and 91.6% of cases in group 2. There were no significant differences between groups with regard to Constant and Rowe scores (P > .05). On magnetic resonance imaging, no complete tendon ruptures were found. The mean vertical diameter of the subscapularis muscle and the mean transverse diameter of the upper subscapularis muscle portion were significantly greater in group 0 than in group 1 and greater in group 1 than in group 2 (P < .05). The mean transverse diameter of the lower subscapularis muscle was comparable in all groups (P > .05). The signal intensity analysis revealed the infraspinatus/upper subscapularis muscle ratio was greater in group 0 than in group 1 and greater in group 1 than in group 2 (P < .05). The infraspinatus/lower subscapularis muscle ratio was lower in group 0 than in groups 1 and 2 (P < .05).

CONCLUSION:
Open shoulder stabilization using an inverted L-shaped tenotomy approach may lead to atrophy and fatty infiltration, particularly of the upper part of the subscapularis muscle, resulting in postoperative subscapularis muscle insufficiency. Revision procedures using the same approach may further compromise clinical subscapularis muscle function and structure. The lower portion of the subscapularis muscle seems to have a compensating effect that may, in addition to a meticulous capsulolabral reconstruction, account for the uncompromised overall clinical outcome.





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