The aim of this study was to analyse human muscle tissue before
and after rotator cuff repair to look for evidence of regeneration,
and to characterise the changes seen in the type of muscle fibre. Patients were assessed pre-operatively and one year post-operatively
using the Oxford Shoulder Score (OSS) and MRI. The cross-sectional
area and distribution of the type of muscle fibre were assessed
on biopsies, which were taken at surgery and one year post-operatively.
Paired samples from eight patients were analysed. There were three
men and five women with a mean age of 63 years (50 to 73).Aims
Patients and Methods
Our aim was to accurately determine whether muscle atrophy and fatty infiltration are reversible following cuff repair. Patients with a repairable cuff-tear were recruited and assessed clinically and radiologically (Magnetic Resonance Imaging). At surgery, supraspinatus was biopsied. Post-operatively, patients underwent clinical evaluation at standardised intervals, with further MRI and an ultrasound guided biopsy of supraspinatus at 12 months. MRI was used to characterize cuff-tears and determine the degree of muscle atrophy and fatty infiltration. Biopsy samples were fixed on-site and transported for processing. Morphometric assessments of myofibres were made and mean cross-sectional areas calculated using validated techniques. The pathologist was blinded to sample details. Statistical analysis was performed to assess differences in mean myofibre area following cuff repair and correlated with radiological findings. Eight patients were available for completed histological and radiological analysis. Six (two re-tears) demonstrated sizeable and highly statistically significant improvements in mean myofibre cross-sectional area (P=0.000–0.0253). Of the two not showing any increase in myofibre area, neither result was statistically significant (P=0.06, 0.2); one was a re-tear and one was a repair of a partial-thickness tear. Radiologically, the muscle and fatty changes had not demonstrably changed. Our finding that myofibre cross-sectional area increases following cuff repair suggests muscle atrophy is a potentially reversible process. Even with re-tears, improvements were seen. MRI features of fatty infiltration and muscle atrophy were not seen to improve however. It is likely that radiological assessment is not sensitive enough to demonstrate the reversibility of muscle atrophy seen on histological analysis at one year.
