[Dislocation of the femoral component of an unicondylar knee prosthesis. Apropos of a case].

INTRODUCTION: Femoral component dislocation in unicondylar knee arthroplasty is rare. One case is reported.

MATERIAL AND METHODS: A 59 years old man required revision of his unicondylar knee arthroplasty for loosening and dislocation of the femoral component 3 years after its insertion. Revision was performed and we found a technical error: distal and posterior femoral cut was too thin, and with components in place, there was a tendancy for the components to "rock" as the knee was flexed. The implants were too tight in flexion. A new unicondylar knee arthroplasty was performed.

DISCUSSION: The posterior condylar bone resection should reach at least the thickness of the metal implant. It is better to resect slightly too much of the posterior condyle than too little in order to avoid tightening of the knee in flexion. The femoral component must accurately reproduces the anterior-posterior dimension of the femoral condyle.

CONCLUSION: With better selection of patients and surgeons who are more familiar to this type of procedure loosening and dislocation of an unicondylar knee arthroplasty should be avoided.