Medical Physics and Biophysics

Rotator cuff tears result in muscle atrophy and fat infiltration within the rotator cuff muscles. Surgical options available and the extensibility of a torn cuff tendon and muscle are highly individualized. A decrease in the extensibility can lead to incomplete reconstruction and may require additional surgical procedures. Additionally, excessive tensile forces during surgery can lead to gap formation and failure at the repair site. An estimation of the supraspinatus (SSP) muscle extensibility is useful in selecting the most appropriate surgical procedure. The purpose of this study was to determine if non-invasive quantitative assessment of intramuscular fat using magnetic resonance imaging (MRI) could be used to predict extensibility of the SSP. Seventeen cadaveric shoulders were imaged to 1) qualitatively assess intramuscular fat using classification systems routinely used in the clinic, and 2) quantitatively assess fat infiltration (fat fraction). The SSP muscles were secured in a custom-designed set-up which allowed for extensibility (mm) and load (N) recordings. Muscles were stained with H&E for fatty evaluation. Pearson correlation coefficients and t-test were used to assess significant differences. Fat fraction positively correlated with histological findings. Fat fraction also presented a positive and high correlation with extensibility (r=0.69; p=0.002). Interestingly, extensibility was not significantly different between shoulders graded with a higher fat content vs. those with low fat when implementing clinical classification systems. A non-invasive prediction of whole-muscle extensibility can directly guide in pre-operative planning to determine if the torn edge could efficiently cover the original footprint; aid in prognosis, and postoperative evaluation of rotator cuff repair.