A 34-year-old female recreational football player sustained an acute injury to her left knee during a game. She felt a popping sensation when she planted and pivoted, followed by immediate pain and swelling. She was unable to continue playing. On examination she was found to have a positive Lachman test and a pivot glide. There was also tenderness at the posterior lateral tibial plateau.
X-rays showed no fractures or dislocations. A subsequent MRI demonstrated a complete femoral avulsion of the ACL with Increased signal within the lateral femoral condyle and posterior tibial plateau. This high signal is consistent with osseous contusions/impaction injury.
This player elected to have an ACL reconstruction and had an uncomplicated recovery. The impaction injury does not require any specific management.
Bone contusions (bruises) in association with acute ACL tears are a common finding on MRI, seen in about 70% of cases. These injuries are generally best seen on T2 weighted or STIR images. The location of the contusion correlates with the mechanism of injury and position of the knee. With a flexed knee/pivoting stress the bone bruises typically occur at the lateral femoral condyle and posterior tibial plateau. A hyperextension mechanism may result in contusions of the anterior femur and tibial plateau. Contusions seen on the medial side are more often associated with multi-ligament injuries.
While the presence of bone bruises may cause increased pain, there is no correlation between the presence of bone bruises and functional outcomes during rehabilitation. It is however unclear whether there is an increased risk of developing long-term chondral lesions and associated osteoarthritis when these bone bruises are present.
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