Atraumatic dislocation of a modern rotating hinge total-knee prosthesis. A rare but devastating complication.

The number of total knee arthroplasties (TKA) is rising in many countries along with the numbers of the revision TKA. Rotating hinge knee (RHK) implants have a fundamental role in the revision TKA and their design has evolved during the last years becoming appealing to many surgeons worldwide. They are mainly used in cases where large bone defects and severe soft tissue imbalance exist. However, despite their recent advancements, they are still associated with high complication rates such as infection, periprosthetic fractures and insufficiency of the extensor apparatus. An uncommon complication of the latest rotating hinge implants is their mechanical component failure. Here we present a rare case of such a devastating complication where a modern RHK prosthesis dislocated without a preceding traumatic event, a review of the corresponding literature and a potential cause for the failure of the mechanism. Moreover, insight on key aspects that need to be addressed is provided, like intrinsic and extrinsic factors which play a crucial role and shouldn't be overlooked for a successful outcome.