What is the diagnosis?

Patellar tendon rupture

• Pearl: Patellar tendon ruptures are most frequently seen in men younger than 40. This is opposed to quadricep tendon ruptures, which are typically seen in older patients [1].  Common comorbidities include diabetes mellitus, chronic renal failure, and gout. Rupture usually occurs at the inferior pole of the patella.

What is the mechanism of injury?

There are three main mechanisms of injury for a patellar tendon injury [2]:

• Indirect low energy trauma, which usually occurs after eccentric contraction of the quadriceps muscle

• Indirect high energy trauma, which is usually associated with other ligamentous, bony, and cartilaginous injuries of the knee

• Direct injury to the tendon itself, e.g. penetrating injury

What physical exam findings are expected?

• Weakness or loss of active extension. About 20 degrees of extension can still be expected in complete rupture, as the patella only begins to engage the trochlea at this angle [3]. 

• Anterior swelling of the knee inferior to the patella, which can be severe enough to mask the expected palpable tendon defect in complete rupture.

• Superiorly displaced patella can be seen in complete rupture.

Which imaging modalities can be used?

1. X-rays: Can show a superiorly displaced patella, known as patella alta (see Image 2 for example), as well as avulsion fractures from the inferior pole of patella and, less frequently, the tibial tuberosity [2]. 

• Pearl: Insall-Salvati ratio (ratio of patellar tendon length to diagonal length of patella) >1.2 suggests patellar tendon tear (image 3) [2,5]. For more on patella alta x-rays, click here. 

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Image 4: Normal lateral knee radiograph demonstrating typical location of the patella; case courtesy of Dr. Matt Skalski, Radiopaedia.org, rID: 30420.

2. Ultrasound: Useful but operator dependent and has been associated with a false positive rate of 33.3% in one study [2,4].

3. MRI is the gold standard but not necessary in the emergency department [2].

Image 5. MRI showing sagittal view of complete rupture of patellar tendon. Author’s own images.

What is the management in the ED?

All patients should be immobilized in a non-hinged knee immobilizer or posterior long leg splint, made non-weight bearing, and given crutches. 

When do you consult Orthopedics?

Orthopedics does not typically need to be consulted in the emergency department. Consult orthopedics if follow up cannot be arranged in less than 2 weeks.

• Pearl: Primary surgical repair for complete rupture should happen within 2 weeks for optimal outcomes [1,2,6].

• Pearl: Partial tears may be managed conservatively with immobilization in extension. Chronic tears can be conservatively managed or with reconstruction surgical techniques.