Distal disinsertion of the patellar ligament combined with avulsion fractures at the medial and lateral margins of the patella. A case report and an experimental study.

A 12-year-old boy presented with a proximally retracted patella 5 months after an injury to the left knee. The clinical and radiographic features and the findings at operation led to the conclusion that the original lesion had been a distal disinsertion of the patellar ligament combined with avulsion fractures at the medial and lateral margins of the patella, produced by the medial and lateral longitudinal patellar retinacula. Loading experiments on amputation and cadaver specimens showed that these retinacula, apart from being tendons for the vastus medialis and the vastus lateralis, respectively, constitute a direct fibrous connection of considerable strength between the patella and the tibia and thus are capable of producing avulsion fractures.