Posterior dislocation of meniscal bearing insert in mobile bearing unicompartmental knee arthroplasty mimicking a Baker cyst.

Unicompartmental knee arthroplasty (UKA) is a well-established procedure for isolated medial compartment osteoarthritis. Meniscal dislocation is a well-recognized complication in mobile bearing UKA especially when performed for the lateral compartment. Dislocation in medial UKA is relatively uncommon and is usually anterior when encountered. We would like to report a case of posterior dislocation of the bearing insert in a mobile bearing medial UKA presenting as a Baker cyst, which was subsequently revised to total knee arthroplasty.