A firm mass may be palpable. Pain is reproduced by extension against forced resistance. Some patients may have quadriceps atrophy. The etiology is controversial, but it clearly is exacerbated by exercise. Chronic microtrauma to the tibial tuberosity secondary to overuse of the quadriceps muscle is a leading theory.
Histologic studies support a traumatic etiology.
Laboratory evaluation is not indicated unless other diagnoses are being entertained. The OS lesion is best seen on the lateral view with the knee in slight internal rotation. Not all patients with OS disease need radiographs since the diagnosis is primarily clinical. Plain films are helpful to rule out other etiologies, such as neoplasm and infection. Therapy is conservative.