What Do These Images Reveal?Knee pain in an adolescent soccer player

A 13-year-old boy has had mild right knee pain for about 1 week; the pain was exacerbated by a collision and subsequent fall during soccer practice. He recently began playing soccer on a team that practices every weekday and has games on the weekends. He has played since his collision, but the knee pain has progressively worsened.

This well-developed adolescent is in no acute distress. His temperature is 37.2°C (99°F); heart rate, 85 beats per minute; respiration rate, 16 breaths per minute; and blood pressure, 110/75 mm Hg. Head, neck, heart, lungs, abdomen, and upper extremities are all normal.

Examination of the right lower extremity reveals significant tenderness in the volar aspect of the proximal tibia. There is full passive range of motion in the right knee; active range of motion is restricted during extension of the knee because of tenderness in the volar aspect of the proximal tibia. Pulses and sensation in the right lower extremity are normal. The left lower extremity is normal.

You order radiographs of the right knee. Based on these films, what do you include in the differential and what further action will you take to arrive at a diagnosis?

(Answer begins on page 495.)

Knee pain in an adolescent soccer player: Both the frontal and lateral radiographs of the knee are normal in this skeletally immature patient (A, B). Normal radiographs make infection or tumor very unlikely diagnoses. The differential diagnosis includes stress fracture, bone contusion, injury to the patellar tendon, and Osgood-Schlatter disease, all of which can be radiographically occult.

A stress fracture is possible, although this occurs more typically at the junction of the metaphysis and diaphysis in the proximal tibia. A bone contusion at the site of this patient's pain, which might have resulted from forgotten direct trauma, could produce this clinical picture. An injury to the patellar tendon could also produce similar findings. Finally, the presentation of Osgood-Schlatter disease can be similar to that seen here, although this condition is sometimes associated with radiographic abnormalities that include irregularity of the tibial tuberosity and overlying soft tissue swelling.

You order an MRI scan to narrow the differential. A sagittal T2-weighted image of the right knee shows increased signal with- in the tibial tuberosity at the site of insertion of the patellar tendon (C, arrow). A coronal T2-weighted image also demonstrates increased signal within the tibial tuberosity; in this view, the signal is localized to the central third of the volar aspect of the proximal tibia (D, arrow). A sagittal T1-weighted image of the knee shows decreased signal within the tibial tuberosity at the site of insertion of the patellar tendon (E, arrow). The increased signal on the T2-weighted images and the decreased signal on the T1-weighted image are consistent with marrow edema.

The MRI findings are diagnostic of Osgood-Schlatter disease. The condition is most likely an avulsion injury caused by the patellar tendon's pulling against an area of rapidly growing, slightly immature bone. The marrow edema represents an inflammatory response of the bone to the avulsion force from the tendon.

Osgood-Schlatter disease is seen in adolescents--usually following a rapid growth spurt. In boys, such spurts typically occur at age 13 to 14 years, and in girls, at age 10 to 11 years.

The risk of Osgood-Schlatter disease increases in proportion to a young person's participation in sports that involve frequent contractions of the quadriceps. Thus, it is most common in adolescents who play soccer, basketball, or tennis; these sports all involve quick and frequent changes of direction, which require rapid flexion of the quadriceps. In about 25% of patients, both knees are involved. Typically, prolonged rest ameliorates symptoms. However, if the patient continues to engage in aggravating activities, the pain will persist and the avulsion injury may progress to a fracture.

Outcome of this case. The patient was restricted from playing soccer for 2 months, and the knee pain diminished. He was advised to resume playing gradually and to have intervals of rest during training (for example, 1 or 2 days of rest between practices and a game). *