Sarcomere length of torn rotator cuff muscle

Background: Sarcomere length is one of the factors related to the contractile ability of muscle. There is no report about sarcomere length of torn rotator cuff muscles. The purpose of this study was to clarify sarcomere length of torn rotator cuff muscles. Materials and methods: Twenty-eight embalmed cadaver shoulders (14 shoulders with intact rotator cuff and 14 shoulders with full-thickness rotator cuff tears: an isolated tear of the supraspinatus in 3, a combined tear of the supraspinatus and infraspinatus in 4, and a combined tear of the supraspinatus, infraspinatus and subscapularis in 7) were used in this study. Muscle fiber length was measured using a digital caliper. Sarcomere length was measured by laser diffraction method. Results: Muscle fiber lengths of the supraspinatus and infraspinatus (33.0 ± 6.5 mm and 61.5 ± 14.0 mm, respectively) in the cuff tear group were significantly shorter than those in the intact cuff group (56.9 ± 10.1 mm and 74.2 ± 10.0 mm: P < .001 and P = .010). The sarcomere lengths of these muscles were 3.00 ± 0.44 μm and 3.12 ± 0.45 μm in the intact cuff group and 2.90 ± 0.34 μm and 3.01 ± 0.34 μm in the cuff tear group. The sarcomere lengths showed no significant difference (P = 0.46 and P = .37). Conclusion: The sarcomere lengths of the supraspinatus and infraspinatus with torn tendons were not significantly different from those with intact tendons, although the muscle fiber lengths were significantly shorter with torn tendons.