Magnetic Resonance Markers of Supraspinatus Muscle Microvascular Function and Energetics Following a Rotator Cuff Tear

Rotator cuff tears (RCT) cause pain and disability in adults. Histological studies indicate that the degenerative process following a rotator cuff tear may disrupt the vascularity and energetics of the shoulder muscles. Magnetic resonance imaging (MRI) post-contractile blood oxygen level-dependent (BOLD) response and 31phosphorus magnetic resonance spectroscopy (31P‑MRS) offer methods to non-invasively assess muscle microvascular function and energetic status in vivo. This study aimed to evaluate the post-contractile BOLD response and 31P-MRS as potential markers of microvascular function and energetic status of the supraspinatus muscle in individuals with chronic full‑thickness supraspinatus tendon tears and healthy individuals without a tear. Using a 3‑T MR Phillips system, all participants performed five 2‑s maximal isometric shoulder abductions to obtain a post-contractile BOLD response using a custom MR‑compatible dynamometer. Dixon fat/water imaging was used to quantify muscle fat fraction (FF). A surface 31P‑MRS coil acquired spectra concentrations of high energy phosphates and intracellular pH from the supraspinatus and surrounding muscles. Results revealed a lower peak BOLD response (P < 0.01) and longer time-to-peak (P = 0.02) in RCT, indicating impaired microvascular function. Analysis of 31P-MRS spectra showed elevated unlocalized Pi/PCr (P = 0.04) and PDE (P < 0.01) concentrations in RCT, consistent with muscle damage. No differences in muscle PCr (P = 0.30) or pH (P = 0.50) were observed. Overall, these findings support that the post-contractile BOLD response and 31P-MRS may be valuable markers to assess shoulder muscle health status and evaluate therapeutic interventions aimed at improving clinical outcomes following a rotator cuff tear.