ACL impaction injury

Case
This young football player presented with a painful, swollen knee following an innocuous twisting injury. She described a feeling of “something going out of place”, a snapping sensation and immediate pain. She was unable to continue. 

The player had a restricted ROM and a moderate-large effusion. She had pronounced tenderness about the lateral joint line and gross laxity with Lachman’s test.

Findings
This lateral x-ray image shows an impaction injury involving the lateral femoral condyle. This is further demonstrated on a sagittal MRI image where there is pronounced increased signal involving the lateral femoral condyle and posterolateral tibia. The MRI images also show a large effusion.

Discussion
The patient was managed with an ACL reconstruction. This was done using hamstrings autograft. The player returned to football nine months following the surgery.

An impaction injury is a common MRI finding after an ACL injury. As the ligament ruptures the knee transiently ‘dislocates’ allowing the posterolateral tibial to strike the lateral femoral condyle. While a degree of increased signal is almost always seen on MRI following ACL injuries it is less common to see this on x-ray. On a normal x-ray the lateral femoral condyle has a notch. Following an ACL injury the notch is deeper than 2mm or has a significant change in the contour. While the impaction injury itself requires no specific treatment, the associated injury often requires surgical management. 

When an x-ray image shows a prominent sulcus affecting the lateral femoral condyle it is important to consider whether a player has had an injury to their ACL. Other x-ray findings consistent with ACL injuries are a Segond fracture, a lipohaemarthrosis or an avulsion from the tibial spines.

Important notice
FIFA does not bear any responsibility for the accuracy and completeness of any information provided in the “Radiology Review” features and cannot be held liable with regard to the information provided or any acts or omissions occurring on the basis of this information.

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