Tag Archives: Knee

Knee dislocation imaging…

April 12, 2013


A couple days ago I asked what other imaging modality is recommended with knee dislocations.  The answer is CT angiogram of the lower extremity.  As you recall we had an image of a patient with a knee dislocation, here is his CT angiogram of the left lower extremity:

CT angiogram LLE

This image shows no evidence of injury to the popliteal artery with contrast reaching the distal vasculature.  Please note that the bolus timing was optimized only for the left side thus the right side is not completely imaged.  Remember this imaging modality in knee dislocations to rule out vascular injury.

I came across an article written in 2007 published in Emergency Medicine Clinics of North America which has a good review section on knee dislocation (1).  The article also discusses other important emergency medicine orthopedic injuries.  According to the article, popliteal artery injury occurs in approximately 40% of high-energy knee dislocations.  Peroneal nerve injury occurs in 14-35% of cases.  Some classic mechanisms of dislocation include when a car bumper strikes the femur above a planted leg and when the knee strikes the dashboard in a high-energy frontal MVC.  Patients with findings consistent with arterial injury need emergent vascular surgery, ideally within 6 hours.  Compartment syndrome can occur and a delay in repair can result in need for amputation.  Furthermore, delayed spasm or compartment syndrome can occur and it is recommended that all patients be observed for 24 hours with serial clinical exams.

Author:  Russell Jones, MD


1.  Newton EJ, Love J.  Emergency Department Management of Selected Orthopedic Injuries.  Emerg Med Clin N Am 25; 2007: 763-793.

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Patient fell, now with knee pain…

April 9, 2013


Knee dislocation

This patient has a knee dislocation with an avulsion fragment seen in the joint space.  The tibia/fibula are both rotated facing medial with the patella displaced to the medial side as well.  Lateral projections were unable to be obtained due to the patient being very uncomfortable however clinically the tibia seemed to be posterior to the distal femur. 

Knee post-reduction 2Knee post-reduction 1

MRI later showed complete tears of the anterior and posterior cruciate ligaments as well as the medial collateral and fibular collateral ligaments.  It also showed the tibial plateu fracture and a compression fracture of the distal femur.

What other imaging would you recommend for this patient in the emergent setting?

Author:  Russell Jones, MD

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Patella Fracture

December 20, 2012

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I saw a nice elderly female with anterior knee pain after tripping on the curb and falling to her knees. Here is her knee X-ray:

Patella fx 3Patella fx 2Patella fx 1

The AP and lateral knee radiographs demonstrate a non-displaced transverse patellar fracture. Sometimes these can be difficult to see on AP and lateral films. Another view that can sometimes be helpful is the “sunrise” view of the patella.

Most patella fractures are managed non-operatively.  If, however, the patella fragments are displaced more than 3-4 mm on xray there is a higher chance of retinacula compromise requiring operative repair (1).  Clinically if the patient cannot maintain their knee in extension against gravity this is concerning for retinacular tear. 

This patient has a high chance, despite age, of having a good outcome with non-operative management (she had intact extensor mechanism of the knee). 


1.  Wheeless’ Textbook of Orthopedics.  http://www.wheelessonline.com/ortho/fractures_of_the_patella

Author:  Russell Jones, MD

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15 yo male twisted his knee…

October 11, 2012


The other day I was working in pediatrics and a 15 year-old male came in from his Friday night high-school football game with knee pain.  He is a running back; he twisted his knee when he was tackled and has diffuse knee pain with a slight effusion on exam.  Here is his lateral x-ray:

Fig. 1:  Lateral knee x-ray

Can you identify the abnormality?  This is a hard one…

The patient demonstrates a “deep lateral femoral notch sign” and a small effusion.

A what?  This was a radiology interpretation which I missed entirely (and I would guess many ED physicians would as well).  The lateral femoral notch sign is an abnormally deep depression of the lateral condylopatellar sulcus (See the arrow in Fig. 2).  On the lateral projection the lateral condylopatellar sulcus (aka the lateral femoral notch) is normally a shallow groove in the middle of the femoral condyle.  An unusually deep lateral femoral notch is an indirect sign of an ACL tear (1).

Fig. 2:  Arrow indicates the lateral condylopatellar sulcus (aka lateral femoral notch)

The most common mechanism of ACL tear is rotation and valgus stress.  This causes the posteriolateral tibial plateau to impact the anteriolateral femoral condyle and can cause a impaction at the site of the lateral femoral notch.  Thus…the “Lateral Femoral Notch Sign.”

To measure the depth of the lateral femoral notch draw a tangent line across the sulcus on the anterior surface of the lateral femoral condyle.  Measure the depth with a perpendicular line to the deepest portion.  Normal depth is around 1mm.  If the depth is >2.0mm this is highly suggestive of an ACL injury.

Luckily I had suspected an ACL tear from the beginning and treated accordingly…


1.  Pao DG.  The Lateral Femoral Notch Sign.  Radiology 2001; 219: 800-801.

Author:  Russell Jones, M.D.

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