AN EXPLANATION FOR VARIOUS RECTUS FEMORIS STRAIN INJURIES USING PREVIOUSLY UNDESCRIBED MUSCLE ARCHITECTURE

We performed cadaveric dissection of the rectus femoris muscle to corr elate the various lesions of strain injury seen with imaging studies t o the muscular anatomy. The proximal tendon is composed of a superfici al, anterior portion from the direct head, and a deep intramuscular po rtion from the indirect head. The muscle fibers arising from the anter ior superficial tendon of the direct head travel in a posterior and di stal direction to insert on the posterior tendon of insertion, giving the proximal muscle a unipennate architecture. Muscle fibers from the intramuscular tendon of the indirect head originate on both the medial and lateral sides of the tendon and insert on the distal posterior te ndon to create its bipennate structure. Three chronic strain injuries involving the midmuscle belly substance were explored grossly and micr oscopically. It appears that one type of acute strain injury occurs in the midmuscle belly with disruption of the muscle-tendon junction of the intramuscular tendon resulting in local hemorrhage and edema. More chronically, this hematoma organizes into a fatty, loose connective t issue encasement of the deep intramuscular proximal tendon. Serous flu id from the hematoma may remain within the connective tissue sheath, c reating a pseudocyst with the deep intramuscular tendon of the indirec t head at its center. The muscle's anatomy helps to explain a differen t rectus femoris strain injury.