PM1072: Atypical Patella Tendon Injury in an Adolescent Football Athlete

Introduction: A 15-year-old male presented to a pediatric sports medicine clinic for evaluation of acute anterior knee pain during football practice. The patient has past medical history significant for long standing tibial tuberosity apophysitis that has since resolved.

Case Description: Three weeks prior to presentation he jumped to catch a ball and landed awkwardly causing a twisting motion of the knee. He reports that he felt a pop in the front of the knee with no assocaited instability. Additionally, he noted persistent pain and swelling over the anterior aspect of the knee. The patient rested for approximately three weeks, which resulted in improvement. However, after returning to activity the pain returned. On physical exam, the patient had full range of motion of the left knee with 5/5 strength knee flexion and 4/5 strength knee extension. He had swelling over the lower anterior knee not associated with tenderness to the tibial tuberosity however tenderness to the distal pole of the patella tendon was present. Specialist tests including Lachman test and McMurray test were negative and no extensor lag was noted.

A 2 view X-ray series of AP and lateral images were performed prior to the initial visit which showed irregular ossification of the tibial tuberosity consistent with previous history of tibial tuberosity apophysitis. A bedside musculoskeletal ultrasound was performed of the anterior knee which revealed a hypoechoic region within the distal patella tendon as well as an anechoic fluid collection deep to the patella tendon (figure 1), consistent with a partial tear of the patella tendon associated with deep infrapatella bursitis. To further asses the ultrasound images an MRI was obtained. The MRI confirmed a partial distal patellar tendon deep substance partial tear as well as mild to moderate deep infrapatellar bursitis (figure 2).

Treatment included an ultrasound guided aspiration of the deep infrapatellar bursa in conjunction with a needle tenotomy of the partially torn fibers, followed by physical therapy. After 8 weeks of physical therapy the patient has returned to near baseline with plans to return to practice.

Discussion: The mechanism of injury for a partial tear at the distal patellar tendon is likely an acute traumatic event asscoiated with an aggressive quadriceps contraction. The differential diagnosis of an acute anterior extensor mechanism injury of the knee in adolescents includes tibial tuberosity avulsion fractures, distally, or patella sleeve injuries from the distal pole of the patella.

Conclusion: Distal patella tendon partial tears in the adolescent athlete population are rare. Due to lack of reported incidence on partial distal patellar tendon tear in the literature, there is no definitive treatment protocol and reccurence rate is not known. The case highlights the diagnostic benefits of bedside ultrasound in a pediatric sports medicine clinic.