Knee Went Out

Author: R  "Max" Lystrup, MD, CAQSM

Peer-reviewer:  M. Terese Whipple, MD

Editor: Alex Tomesch, MD

32 year-old male was doing a 425 lbs back squat and felt a painful "pop" in his anterior R knee above the kneecap and dropped to the ground. He has been unable to walk and his knee is extremely swollen.  X-rays are read as normal but he cannot extend his knee on exam.

Image 1: Ultrasound of the R anterior knee.  Robert Lystrup's  images.

1. What is your suspected diagnosis?

2. What is your initial workup in the ED?

3. What imaging confirms the diagnosis?

4. What is your management and disposition?

-- see below for answers --

1. What is your suspected diagnosis?

Quad tendon rupture. 

• Pearl: Quad tendon ruptures are often missed in the ED and are more common in older patients

2. What physical exam maneuver can help confirm your diagnosis?

Unassisted straight leg raise: If a patient cannot lift their lower leg off the bed while lying flat there may be a failure of the extensor mechanism, such as from a patellar or quad tendon rupture, or patellar fracture.

3. What is your initial workup in the ED?

A quad tendon rupture is largely a clinical diagnosis, supported by a palpable defect in the tendon with inability to extend the lower leg at the knee. Bedside ultrasound can help confirm the diagnosis. 

4. What imaging confirms the diagnosis?

Imaging is not necessary to make the diagnosis of quad tendon rupture. If the diagnosis is in question, ultrasound (Image 1)  or MRI (Image 2) can be used to confirm the diagnosis. MRI can be obtained on an outpatient basis. 

Image 2: MRI of the R knee demonstrating an acute tear of the quadriceps tendon with retraction. Robert Lystrup's images.

5. What is your management and disposition?

Patients with complete disruption of the quadriceps tendon should be made non-weight-bearing, splinted in knee extension, and referred to orthopedics within 1-3 days. Due to the powerful retractive forces of the quadriceps muscles, any operative intervention should be performed as quickly as possible [1].  

Resources:

Ilan DI, Tejwani N, Keschner M, Leibman M.  "Quadriceps tendon rupture." Journal of the American Academy of Orthopaedic Surgeons. 2003; 11(3): 192-200.

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