MRI Diagnosis of Bone Bruise

A 41-year-old man fell 3 ft into a bilge; he landed on his left leg and experienced immediate generalized pain in that knee. Three days later, he consulted his physician, who found minimal effusion in the knee and tenderness of the medial collateral ligament (MCL). No abnormalities were seen on plain x-ray films.

MRI scans (C, D, E, and F) revealed a bruise of the left lateral femoral condyle and a minimal sprain of the left MCL. This case illustrates the usefulness of MRI in knee trauma when the diagnosis is not evident from physical examination and plain films.

A bone contusion was defined on T1-weighted images (C and D) as a traumatic, nonlinear, dark area of signal loss involving the epiphysis and a portion of the metaphysis; the articular cartilage appeared normal. On the T2-weighted image (E), the signal intensity was increased (ie, it appeared lighter). The sprained MCL was gray on the T1-weighted image (F); normally, it would have been black.

In addition to assessing internal derangements of the knee (including sprains and tears of the cruciate and collateral ligaments, loose cartilaginous bodies, osteonecrosis, osteochondritis dissecans, and synovial disorders), MRI is also useful in evaluating occult traumatic lesions, such as bone contusions, osteochondral fractures, stress fractures, and suprachondral femoral and tibial plateau fractures.

Bone bruises revealed by MRI (the scan need not be repeated in uncomplicated cases) usually resolve within several months. In this case, the patient was given a knee splint and treated with an NSAID until his symptoms abated. He also required physical therapy for knee rehabilitation.