Vascular Changes in the Supraspinatus Muscle and Association with Intramuscular Fat Accumulation: An Experimental Study in Rabbits

Abstract

Supraspinatus (SSP) tendon tear leads to intramuscular fat accumulation in the SSP muscle and the mechanisms are currently unknown. The purpose of this study was to investigate changes in vascularization of the SSP muscle and the relationship to intramuscular fat accumulation following SSP tendon detachment with or without reattachment. One hundred and six rabbits underwent SSP tendon detachment. In groups of ten, thirty rabbits were sacrificed 4, 8, and 12 weeks following detachment. Forty rabbits underwent detachment and immediate reattachment and were sacrificed in groups of ten following 0, 1, 2, and 6 weeks of healing. In groups of twelve, the remaining thirty-six rabbits underwent SSP tendon reattachment 4, 8, and 12 weeks after detachment and were sacrificed 12 weeks later. Vascularization was quantified in each specimen using CD31 immunohistochemistry. Four weeks after SSP tendon detachment, there was an increase in vascularization of the distal SSP muscle that reached significance after 12 weeks of detachment (p=0.024). We found that vascularization was positively correlated with intramuscular fat accumulation after detachment only (r=0.29; p=0.008). After SSP tendon reattachment, immediate or delayed, the correlation between vascularization and intramuscular fat accumulation was not observed. Microscopically, some SSP muscle vascular structures in the reattachment group had thicker vascular walls which were further quantified using αSMA immunohistochemistry. The delayed reattachment group showed an increase in vascular wall thickness in the distal portion of the SSP muscle at 4+12 (p=0.012) and 12+12 (p=0.012) weeks and in the proximal portion at 4+12 (p=0.024) weeks. Further investigation is required to demonstrate a cause/effect relationship between increased vascularization and intramuscular fat accumulation in the context of rotator cuff tear and success of surgical repair.