Dislocation and spontaneous reduction of the femoral implant against the femoral neck in an infected metal on metal hip resurfacing with complex collection

Metal on metal resurfacing hip implants are known to have complications unique to this type of implant. The case presented adds a further previously not described complication, the dislocation and spontaneous reduction of the pin of the femoral component against the femoral neck. The radiographic and CT findings are demonstrated. The dislocation was aided by bone loss due to an infection with a large periarticular collection. Periarticular collections in hip resurfacings are often due to a hypersensitivity type reaction to metal debris. However in the case presented it was due to infection. MRI was not able to discern the infection from a sterile collection. CT demonstrated bone loss and periosteal reaction suggestive of infection. In addition calcification of the pseudocapsule was seen, this is not a recognized feature of sterile collections.