In a posterior-stabilised total knee arthroplasty, the polyethylene insert has a central cam-and-post mechanism. The PRIMARY purpose of this cam-post design is to:

• A Allow rotation of the tibia on the femur while blocking varus-valgus translation
• B Substitute for the absent posterior cruciate ligament by preventing posterior tibial subluxation during flexion ✓
• C Increase the contact area between femoral component and insert to reduce wear
• D Permit the bearing to translate freely, mimicking normal meniscal function

Explanation

In PS-TKA both cruciate ligaments are sacrificed. The tibial post engages the femoral cam in flexion, controlling rollback and preventing posterior tibial sag, thus substituting for the PCL. Free translation is blocked rather than allowed, and the design does not primarily increase contact area. Meniscal-style free translation describes mobile-bearing designs, not the fixed cam-post mechanism.

Reference: Miller's Review of Orthopaedics, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.