[Open dislocation of the mobile bearing in a unicondylar knee arthroplasty. A rare complication].

Unicompartmental knee arthroplasty can be viewed as a procedure with reliable medium- to long-term success. However, complications occur. To the authors' knowledge, this is the first report on an open dislocation of the tibial component (polyethylene plate) of a mobile bearing unicondylar knee prosthesis. Twelve days after a unicompartmental knee arthroplasty a 69-year-old patient suffered an open knee trauma due to a simple fall on the ground. The clinical examination showed wound dehiscence of the former mid-line approach, ventral dislocation of the polyethylene plate and a rupture of the anterior cruciate ligament. A pragmatic surgical treatment consisting of a jet lavage with saline solution, disinfection and relocation of the polyethylene plate and application of prophylactic antibiotics was performed. No peri- or postoperative complications were observed. The 6-month follow-up revealed a range of motion of 0-0-120° for extension-flexion and an isolated anterior instability. The patient was satisfied. This case report adds an uncommon and previously unpublished complication associated with unicompartmental knee arthroplasty. Surgical management in revision knee arthroplasty is challenging, although pragmatic approaches might be successful. Open dislocation of the bearing in a unicondylar knee prosthesis demands immediate revision. The manner of treatment depends on clinical findings and the surgeon's experience with arthroplasty.