抄録
Structural changes of rotator cuff muscle after torn rotator cuff tendon are the muscle atrophy, the shortening of muscle fiber length, and fatty infiltration. However, there is no report about the sarcomere length which is one of the factors related to the contractile ability of muscle. The purpose of this study was to clarify the sarcomere length of torn rotator cuff muscle. 14 embalmed cadaver shoulders were enrolled in this study. The average age was 82 years old (range: 74-91). There were 7 full-thickness rotator cuff tear shoulders and 7 normal shoulders. Muscle fiber length was measured using a digital caliper. Sarcomere length of the rotator cuff muscle was determined by laser diffraction.
In the cuff tear group, muscle fiber length of the supraspinatus: SSP, infraspinatus: ISP, teres minor: TM, and subscapularis: SSC was 33.2±6.3mm, 70.6±9.9mm, 57.4±6.4mm, and 58.2±9.6mm, respectively. In the normal cuff group, that of SSP, ISP, TM, and SSC was 57.3±13.7mm, 73.4±14.0mm, 58.2±11.2mm, and 57.8±11.7mm, respectively. The muscle fiber length of SSP in the cuff tear group was significantly shorter than that of SSP in the normal cuff group (P=0.0157). ISP, TM, and SSC showed no significant difference in the muscle fiber length. In the cuff tear group, the sarcomere length of SSP, ISP, TM, and SSC were 3.07±0.41μm, 3.16±0.42μm, 2.80±0.27μm, and 2.41±0.21μm, respectively. In the normal cuff group, those of SSP, ISP, TM, and SSC were 3.18±0.46μm, 3.21±0.57μm, 3.13±0.34μm, and 2.60±0.22μm, respectively. There was no significant difference in the sarcomere length. Although the muscle fiber length of SSP with rotator cuff tear was significantly shorter than that of SSP without rotator cuff tear, the sarcomere length of SSP had no significant difference between the cuff tear group and the intact cuff group. These results indicate that the number of sarcomere may reduce to adapt the shortened muscle fiber length of supraspinatus to maintain muscle contractile ability.
