INCOMPLETE, INTRASUBSTANCE STRAIN INJURIES OF THE RECTUS FEMORIS MUSCLE

Rectus femoris muscle strain injuries commonly occur at the distal mus cle-tendon junction of the quadriceps tendon. However, we have recentl y recognized a pattern of strain injury that consists of an incomplete intrasubstance tear at the muscle-tendon junction formed by the deep tendon of the muscle's indirect head and those muscle fibers originati ng from this tendon. These injuries are found more proximally within t he thigh than the ''classic'' distal rectus femoris muscle strain. We reviewed 10 athletes with these intrasubstance tears, all of whom had diagnostic imaging performed using computed tomography or magnetic res onance imaging or both. Two of these patients required surgical interv ention. The mechanism of injury usually involved kicking or sprinting. All patients had chronic thigh pain or an anterior thigh mass or both . Physical examination revealed thigh asymmetry and a nontender to mil dly tender intrasubstance muscle mass. Magnetic resonance imaging demo nstrated abnormal signal intensity centered about the intramuscular te ndon of the indirect head of the muscle. Surgical findings included a mass of fibrous scar and fatty tissue encasing the deep tendon. Surgic al removal of this fibrous mass appears curative. We contrast this inj ury from distal strains of the rectus femoris muscle, as well as from soft tissue neoplasms.