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.
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
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:
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
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.