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Patellar Tendon Rupture

Lee A Fox, MD
Daniel S Williamson, MD, PhD

August 28, 1996

Presentation

A 42-year-old woman presented to the Emergency Department with right knee pain after she fell while exercising on a treadmill machine. She could not bear weight on her right leg.

Physical examination revealed a tender, swollen right knee. The patient was unable to perform active knee extension.

Imaging Findings

AP radiograph of the right knee
Lateral radiograph of the right knee
Tangential patellar radiograph of the knees

Anteroposterior (AP), lateral, and tangential patellar views demonstrate that the right patella is displaced superiorly (right patella alta). A cortical step-off in the inferior patella (black arrow), increased soft tissue density (white arrows) in the infrapatellar region, and a small right suprapatellar effusion are visible. There is no evidence of proximal tibial fracture.

Diagnosis

Acute patellar tendon rupture

Discussion

The patellar tendon spans from the inferior patellar border to the tibial tubercle. Patellar tendon rupture is one type of knee extension injury. The mechanism of injury is often, as demonstrated in this patient, knee flexion followed by a strong quadriceps contraction. The tendon is almost always disrupted at one of the points of its bony attachment. The most common site of injury is the inferior patellar insertion site. Such an injury is usually accompanied by a small avulsion fracture.

Plain film study classically reveals a superiorly displaced patella, best seen on the lateral view. A small avulsion fragment from the tibial or patellar attachment site may be identified. Soft tissue swelling and joint effusion may also be visible.

Clinically, patients with patellar tendon rupture present with pain and are unable to perform active knee extension. The patella may be more mobile than usual and an infrapatellar soft tissue defect can often be palpated. Surgical repair of the tendon is required to restore knee extensor function.

References

1. Rockwood CA, Green DP. Fractures in adults, vol 2. 2nd ed. Philadelphia: Lippincott, 1984.

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