Figure 1. Anteroposterior radiograph of right knee. Figure 2. Lateral image of right knee.
A 16-year-old boy presents with right knee pain 3 days after sustaining an injury. The patient felt a sharp pain in the right knee after he attempted to jump on a trampoline. He is able to walk but bending the knee causes severe pain. The patient reports injuring his right knee 5 years ago during a bicycle accident; he fully recovered. On physical examination the patient has a trace effusion with tenderness to palpation over the tibial tubercle. Radiographic images taken in the emergency department (Figures 1 and 2) are positive for calcification in the patella ligament of unknown significance.
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The patient has a minimally displaced tibial tubercle avulsion fracture. Interestingly, the calcification in the patella ligament seen on the radiographic images was likely related to his older bicycle injury and proved to be a distraction from the acute tibial tubercle avulsion injury.
Avulsion fractures of the lower extremity in the pediatric population can be easily missed without a careful radiographic evaluation and high clinical suspicion.1 To the untrained eye, growth plates at varying degrees of skeletal maturity can be confused with fractures and vice versa.
The tibial tubercle is an attachment site for the patella ligament and is critical for knee extension. The tibial tubercle apophysis generally fuses to the tibial epiphysis between the ages of 14 and 18 years.2 Tibial tubercle avulsion fractures typically occur in boys as they approach skeletal maturity (aged 12-15 years). Tibial tubercle avulsion fractures can present with varying degrees of fracture displacement and fracture extension.1,2
Fractures can range from minimally displaced, such as in this case, to a fracture that extends through the entire proximal tibia physis. Fractures with minimal displacement can be treated in a long leg cast or brace with the goal of keeping the knee in extension at all times for approximately 6 weeks. A quadriceps contraction could cause displacement of the avulsed fragment. Displaced fractures of more than 2 mm require surgical fixation.1,2
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor in chief of the Journal of Orthopedics for Physician Assistants.
1. Schiller J, DeFroda S, Blood T. Lower extremity avulsion fractures in the pediatric and adolescent athlete. J Am Acad Orthop Surg. 2017;25(4):251-259. doi:10.5435/JAAOS-D-15-00328
2. Steffes MJ, Shirley E. Tibial tubercle fracture. Ortho Bullets. Accessed March 8, 2021. https://www.orthobullets.com/pediatrics/4023/tibial-tubercle-fracture