A 14-year-old boy is brought to the clinic for evaluation of progressive pain in his left knee over the past 4 months. He is an avid basketball player and notes that the pain is most intense when he is jumping or running during games. The pain improves significantly with rest. Past medical history is negative. On physical examination, there is a prominent, exquisitely tender osteocartilaginous bump over the anterior aspect of the proximal tibia, just below the patella. There is no joint effusion, and the range of motion of the knee is full. There is no ligamentous laxity. Resisted knee extension reproduces the pain.
Which of the following is the most likely underlying mechanism of this patient's condition?
The correct answer is:
B) Microavulsion fractures at the bone-tendon interface
The patient is presenting with Osgood-Schlatter disease, which is technically an overuse traction apophysitis of the tibial tubercle. It occurs most commonly in active adolescents (boys aged 12–15, girls aged 10–12) during a period of rapid growth. The repetitive contraction of the quadriceps muscle group transmits force through the patellar tendon to its insertion at the immature tibial tubercle. This repetitive stress leads to microavulsion fractures and chronic inflammation at the bone-tendon interface. Over time, the body attempts to repair this with new bone formation, resulting in the classic visible and palpable bump on the anterior tibia.
Answer choice A: Avascular necrosis of the femoral head, is incorrect. This is the pathophysiology of Legg-Calvé-Perthes disease, which causes hip/groin pain in younger children.
Answer choice C: Rupture of the anterior cruciate ligament, is incorrect. An ACL tear is typically an acute, traumatic injury resulting in immediate swelling (hemarthrosis) and instability, rather than chronic, localized pain at the tibial tubercle. This patient has no ligamentous laxity, which is inconsistent with an ACL tear.
Answer choice D: Stretching of the pes anserine bursa, is incorrect. Pes anserine bursitis causes pain on the medial aspect of the proximal tibia at the insertion of the sartorius, gracilis, and semitendinosus, not the anterior midline at the tibial tubercle.
Answer choice E: Traction apophysitis of the medial epicondyle, is incorrect. This describes "little league elbow," which is an overuse injury of the medial elbow in young overhead-throwing athletes.
Key Learning Point
Osgood-Schlatter disease is a clinical diagnosis characterized by pain and swelling at the tibial tuberosity in active adolescents. It is caused by repetitive strain and microavulsion at the insertion of the patellar tendon. Management is conservative, focusing on activity modification, icing, and NSAIDs. The condition is self-limiting and usually resolves when the growth plate closes.
