Incomplete, Intrasubstance Strain Injuries of the Rectus Femoris Muscle

Abstract

Rectus femoris muscle strain injuries commonly occur at the distal muscle-tendon junction of the quadriceps tendon. However, we have recently recognized a pat tern of strain injury that consists of an incomplete in trasubstance tear at the muscle-tendon junction formed by the deep tendon of the muscle's indirect head and those muscle fibers originating from this tendon. These injuries are found more proximally within the thigh than the "classic" distal rectus femoris muscle strain. We re viewed 10 athletes with these intrasubstance tears, all of whom had diagnostic imaging performed using com puted tomography or magnetic resonance imaging or both. Two of these patients required surgical interven tion. The mechanism of injury usually involved kicking or sprinting. All patients had chronic thigh pain or an anterior thigh mass or both. Physical examination re vealed thigh asymmetry and a nontender to mildly ten der intrasubstance muscle mass. Magnetic resonance imaging demonstrated abnormal signal intensity cen tered about the intramuscular tendon of the indirect head of the muscle. Surgical findings included a mass of fibrous scar and fatty tissue encasing the deep ten don. Surgical removal of this fibrous mass appears curative. We contrast this injury from distal strains of the rectus femoris muscle, as well as from soft tissue neoplasms.