A 25-year-old football player was referred to see you with a suspected ‘patella fracture’. He describes a twisting injury on his planted right leg followed by a pop sensation and near immediate pain and swelling in his right knee. He was seen at a local emergency clinic and was told he had fractured his patella based on some x-rays taken while there.
An AP x-ray image shows a type III (supero-lateral) bipartate patella. In addition, this image also demonstrates a Segond fracture. A subsequent MRI (conducted to define the anterior cruciate ligament and not the patella) shows a normal synchondrosis with no oedema or other abnormality involving the patella. The ACL is ruptured.
This player was reassured that his patella was normal and that he had a common anatomical variant. Unfortunately, he required an ACL reconstruction and was out of football for ten months.
A bipartate patella is a common incidental finding on x-ray imaging. They occur in about 3% of the general population and are bilateral in more than 50% of cases. The morphology seen in this case (type III) is the most common variant. Type I bipartate patellae involve the inferior pole (see an earlier radiology review case for an example of this) while type II patellae involve the lateral margin. In the vast majority of cases this finding does not require any further investigation or follow-up. It is unlikely to be relevant in the case of acute knee trauma. It may be more important when a player describes an insidious onset or anterior knee pain.
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