ASSESSMENT OF SUBSCAPULARIS MUSCLE FUNCTION AFTER RECONSTRUCTION OF ISOLATED AND COMBINED SUBSCAPULARIS TENDON TEARS – A MRI CONTROLLED STUDY

Abstract

In this retrospective study postoperative subscapularis (SSC) function was measured with an electronic force measurement plate (FMP) and clinical scores and correlated with SSC-muscle cross sectional area on defined MRI-sequences.

82 patients with subscapularis tears (34 isolated SSC tears and 48 combined SSC/SSP tears) were followed up at a mean of 38 (24–72) months after tendon reconstruction with the Constant score (CS) and clinical SSC-tests (Napoleon test, Lift off test). SSC-muscle function was assessed in the belly-press- and the lift off position using a custom made electronic FMP (force in Newton). SSC muscle strength values were compared with the contra-lateral side. SSC-muscle atrophy (muscle cross sectional area in mm²) was measured on standardised sagittal MRI-planes and compared with a healthy matched control group (CG) (Mann-Whitney-U-Test).

The mean CS improved from 51p to 81p in isolated tears (group 1) and from an average 47 p to 78 p in combined tears (group 2) (each p< 0.01). Overall 85% of the patients rated their result as good or excellent. Positive and intermediate postop. Napoleon tests were still present in 30% in group 1 and in 25% in group 2. Mean postoperative SSC-muscle strength in the belly-press position averaged 64 N (contralatera sidel-CL: 86 N) in group 1 and 81 N (CL: 91 N) in group 2. Lift-off test strength averaged 36 N (CL: 69 N) in group 1 and 50 N (CL: 63 N) in group 2 (each p< 0.05). Postoperative MRI revealed a significant reduced SSC muscle cross sectional area for the operated side compared with the CG (group 1: SSC: 1974 mm²; CG 2980 mm² p< 0,05; group 2: SSC: 1829 mm²; CG 2406 mm² − SSP: 570 mm²; CG 812 mm² each p< 0,05).

Despite good clinical results after reconstruction of isolated and combined subscapularis tears a marked subscapularis strength deficit remains that is not reflected in the Constant Score, but can be detected with the new measurement device. Additionally a subscapularis muscle atrophy remains in the postoperative course that cannot be reversed by surgery.