A Cam-Post Mechanism Is No Longer Necessary in Modern Primary Total Knee Arthroplasty

Conclusive evidence supporting a clinical difference between posterior-stabilized (PS) and cruciate-retaining (CR) designs in total knee arthroplasty (TKA) does not currently exist, despite both designs being used for decades. Proponents of PS designs that employ a cam-and-post mechanism cite in vivo fluoroscopic data that demonstrate improved posterior rollback; however, optimal rollback has never been correlated to superior clinical outcomes. Recently, anterior-lipped and more conforming CR bearings, such as ultracongruent, medial pivot, and dual-pivot designs, have been used to substitute for the posterior cruciate ligament and obviate the need for the cam-post mechanism of a traditional PS design. Advantages of avoiding a PS TKA include eliminating the risk of box cut induced femoral condylar fracture, improving operative efficiency by removing procedural steps, removing the articulation that is a source of wear, postdeformation, breakage, or dislocation, and eliminating patellar clunk. Health care reform efforts mandate cost reduction, and procedural efficiencies and minimizing inventory through the removal of unnecessary bearing options foster that initiative.