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Mid-Journey on the Road to the Forgotten Knee

In the last 45 years, numerous achievements have been made in modern total knee replacement (TKR) in areas of materials, design and computer technology. As it stands today, primary TKR reliably results in a durable joint with low potential for revision, but most patients sense the artificial knee and some studies estimate that about 20% are dissatisfied with their TKR.

TKR traces its origin to the early 1970s at the Hospital for Special Surgery, where John Insall collaborated with surgeons Chitiranjan Ranawat and Allan Inglis, along with engineer Peter Walker, Ph.D., to develop the total condylar knee. In the mid-1970s, cruciate sacrificing (posterior stabilized) total knee and resurfacing designs for the patellofemoral joint were also developed. The biomaterials that made up the implant components at that time remain the same today, with polyethylene for tibial and patellar bearing surfaces, CoCr alloy for the femur and titanium or CoCr alloy for the tibial base plate (or “all-poly”), with PMMA-cement dominating fixation to bone.

The design of articulating surfaces has ranged from unconstrained to fully constrained with everything in-between, including mobile bearings, rotating platforms, nearly flat on radiused femurs, posterior-stabilized, conforming femorotibial articulation and medial pivot. Throughout most of this history, knees have been mechanically aligned with compensation in component position to better match anatomical rotation and joint line, with ligament balancing and attention to flexion-extension gaps being controlled in planning pre-operatively and via surgery intra-operatively.

Also noteworthy from the past 15+ years are products and procedures focused on localized pathologies of the knee, with unicompartmental knee surgery becoming a mainstay in knee arthroplasty, and cellular, drug and traditional materials solutions to osteochondral defects in various R&D phases in the U.S. today.

Before we predict what TKR will look like in the future, let’s review notable changes to the procedure over its lifetime and ways that materials of choice have changed (or remain unchanged, in many cases).

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