Muscle Changes After Injury and the Hamstring Strain Exam

MRI shows persistent edema at return to play and scar tissue that appears permanent. A case of denervation edema in a college football player went unnoticed until research imaging. Athletes with recurrent injuries show about 12% atrophy of the biceps femoris long head with hypertrophy of the short head, which may hide weakness on knee flexion testing, and some older players show fat infiltration. Isokinetic testing finds weakness at return to play, especially at longer muscle lengths, which recovers by about six months. Strain concentrates next to the old scar, which may explain why reinjuries occur nearby. The exam starts with history: an acute onset and clear mechanism separate a strain from radiculopathy or chronic posterior thigh pain. A demonstration video covers the active knee extension test at 90-90 and in full hip flexion with an inclinometer, handheld dynamometer strength in several positions, and palpation to mark the length of painful tissue and the site of maximum pain. A greater distance from the ischial tuberosity suggests a quicker recovery.