What is the cause of this teenage boy’s knee pain?

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A 14-year-old boy presents to the clinic with left knee pain of 1 month’s duration. He reports having pain when he leans on his knee. The pain increases when he climbs stairs or walks uphill. He denies any fever or trauma to the knee.

On physical examination, the anterior aspect of the left knee is mildly swollen and tender. There is no erythema. All joints have normal range of motion. There is no pain on straight leg–raising; however, squatting is painful. Extending the leg against resistance also elicits pain. Gait is normal. Remaining physical findings are unremarkable.

Anteroposterior and lateral views of the left knee are shown.

What is the cause of this teenage boy’s knee pain?

A. Avulsion fracture of the tibial tuberosity.

B. Osteochondritis of the tibial tuberosity.

C. Stress fracture of the proximal tibia.

D. Osteomyelitis.

E. Osteosarcoma.

(Answer and discussion on next page.)

Answer: B, Osteochondritis of the tibial tuberosity

The radiographs show no fracture dislocation, joint effusion, or destructive bony process. Fragmentation of the tibial tuberosity is noted with adjacent soft tissue swelling. There is no radiopaque foreign body. These findings are suggestive of Osgood-Schlatter disease.

Osgood-Schlatter disease, or osteochondritis of the tibial tuberosity, results from repetitive microtrauma or traction to the secondary ossification center (apophysis) of the tibial tuberosity. The traction forces, generated by quadriceps contractions, are typically transmitted through the apophysis—the patellar tendon insertion site.

This type of overuse injury typically occurs in pubertal children when they undergo a rapid growth spurt. Therefore, girls are affected earlier than boys. It is more common in athletes than in non-athletes. Sports that require cutting and jumping, or repetitive quadriceps contractions, such as soccer, volleyball, gymnastics, and basketball, frequently lead to Osgood-Schlatter disease.

Affected patients characteristically present with pain and prominence of the tibial tuberosity. The pain progresses with time and is exacerbated by physical activity. Patients may have some overlying soft tissue swelling, without warmth or erythema. They may report bilateral symptoms; however, the degree of involvement may be asymmetrical. Except for swelling and tenderness of
the tibial tuberosity, all other knee examination findings, including the range of motion, are essentially normal.

The diagnosis of Osgood-Schlatter disease is based on clinical features. Features that should alert one to other causes of knee pain include acute onset of pain, warmth and erythema overlying the tuberosity, pain unrelated to activity, pain at night, or presence of constitutional/systemic symptoms. These symptoms are frequently associated with osteomyelitis, tumor, avulsion fracture of the tibial tuberosity, stress fracture of the proximal tibia, and avulsion of the quadriceps tendon. Other items in the differential diagnosis include patellar peritendinitis, synovial impingement, patellar malalignment, and patellar instability. It is important to rule out hip pathology.

Radiographs are indicated in patients who report atypical symptoms. Although this patient’s symptoms were not atypical, radiographs were obtained to evaluate for stress fracture of the proximal tibia in view of the history of active participation in athletic activities. Plain radiographs, when obtained, may show fragmentation or irregular ossification of the tibial tuberosity. However, soft tissue swelling overlying the tuberosity may be the only finding.

Osgood-Schlatter disease is benign and self-limited. Symptoms usually wax and wane over 6 to 18 months and resolve completely once the growth plate ossifies. Management is conservative and involves adequate pain control, ice, and physical therapy. Physical therapy focuses on strengthening the quadriceps and hamstrings. NSAIDs and acetaminophen are frequently used to achieve analgesia. A counterforce brace may provide some symptomatic relief. Sports activity is generally allowed as tolerated.

Although Osgood-Schlatter disease is considered benign, an increased susceptibility to epiphyseal fractures has been described. Other complications include residual prominence of the tuberosity after resolution of symptoms, hyperextension of the knee, and painful ossicles in the distal patellar tendons. Tuberosity prominence results from callus formation during healing. Hyperextension of the knee is a consequence of premature closure of the anterior part of the growth plate. Ossicles occur in about 10% of patients and may be visible on radiographs of the knee. These ossicles can be surgically excised in the event of persistent pain, once skeletal maturity is achieved.

This patient was treated conservatively without any complications. At 1-year follow-up, he was pain-free, with minimal residual swelling of the left knee.