Sean, a 16-year-old male, presents with sudden-onset left knee pain while playing soccer.

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Sean, a 16-year-old male, presents with sudden-onset left knee pain while playing soccer. He describes feeling a popping sensation, followed by severe pain, on landing on the left leg after jumping up to attempt a header. He fell to the ground and is now unable to weight bear or extend his left knee, which is swollen and misshapen.

Sean is generally well. He has a history of Osgood-Schlatter disease in early adolescence, but stopped playing basketball and has not had any knee pain for at least a year.

On examination he is unable to extend the knee. There is an abnormal contour to the lateral side of the left thigh and a sharp protrusion at the anterior aspect of the left knee. Lateral view X-ray of the left knee is shown.

The answer is b. The X-ray shows a left tibial tubercle avulsion fracture, with an associated patella alta (high-riding patella).¹ The tibial tubercle is the secondary ossification centre of the proximal tibia. Complete bony fusion typically occurs by age 15 in females and 17 in males.¹

Avulsion fractures of the tibial tubercle typically occur when the quadriceps are forcefully contracted against resistance, such as when jumping, or when rapid knee flexion occurs with contracted quadriceps, such as during a jump landing.² Jumping sporting activity is therefore a risk factor for this injury.