Intraoperative avulsion fracture of the intercondylar eminence in Oxford mobile-bearing unicompartmental knee arthroplasty: Case report.

BACKGROUND: Unicompartmental knee arthroplasty (UKA) can provide good postoperative results and long term survival, but there may be complications. We present a rare case of avulsion fracture of the intercondylar eminence during UKA surgery.

CASE PRESENTATION: An 88-year-old man had right-knee pain with anteromedial osteoarthritis. Oxford partial knee UKA (Zimmer Biomet, Warsaw, IN) was performed by the senior author by the under-vastus approach using Microplasty instruments. During the final check of the range of motion, an avulsion fracture of the intercondylar eminence occurred at the terminal extension. A 4.0 mm cannulated cancellous screw was inserted into the intercondylar eminence from just in front of the anterior cruciate ligament to the posterior tibial cortex. Six months postoperatively, bony fusion was confirmed by lateral radiography. Two years after the surgery, the patient was fully satisfied. The flexion angle was 125°, but still with an extension limit of 10°.

DISCUSSION: Avulsion fracture of the intercondylar eminence can be caused by hyperextension and/or the ACL becoming tighter in full extension of the knee. In this patient, avulsion fracture also probably occurred due to increased tension of the ACL in the fully extended position. After making the horizontal cut, we inserted a thin metal plate to prevent deeper vertical cuts, but an excessive horizontal cut was a possible cause of the fracture. As treatment for avulsion fracture of the intercondylar eminence, fixation of the cannulated cancellous screw resulted in uneventful bone fusion. We recommend having a cannulated cancellous screw at hand for such complications and for other potential intraoperative problems, such as tibial plateau fracture. Further investigation into limited postoperative extension might be needed.

CONCLUSION: Our patient had intraoperative avulsion fracture of the intercondylar eminence, a relatively rare complication of Oxford UKA which is probably caused by the extension being tight and/or an excessive horizontal cut. Having a cannulated cancellous screw at hand is advised, and attention should be paid to postoperative limit of extension.