How modern total knee replacements have developed
The concept of inserting an artificial joint after the removal of a diseased joint has been considered for centuries. But it was not until the 19th century that a Romanian surgeon called Themistocles Glück began practicing total knee replacement with ivory devices fixed with ‘bone cement’. The concept had merit, but was prone to failure for a variety of reasons including material choice, patient selection and infection. Other designs followed, with alternative materials and more suitable patients. But they all had a common feature: some form of mechanical hinge that imposed too much constraint for normal knee function and invariably led to high rates of mechanical failure.
Modern total knee replacement (TKR) designs were born in a particularly innovative period in the 1970s.
In 1969, the late Professor Michael Freeman implanted the first ever ‘total condylar knee replacement’ at the Royal London Hospital in Whitechapel, London. The knee was developed with Alan Swanson, an engineer at Imperial College London, and its design was based on recent success in hip replacement surgery by Sir John Charnley. The design was unique in that it replaced only the worn cartilage in the knee with two components intended to articulate as a ‘low friction’ bearing: it did not include a hinge.
The components had just enough built-in constraint to allow the joint to flex in a normal way and remain stable using the joint capsule. So that the joint capsule could work normally around the implanted components, a stepwise technique was developed with special instruments to resect (cut) minimal bone and measure gaps between bone ends in the flexed and straight leg. Techniques were also developed to work with the ligaments to reliably correct angular deformities to obtain a straight leg that was stable in flexion and extension.
Unlike the comparatively simple ball-and-socket hip bearing, the knee has a more complex pattern of movement that simple hinged devices cannot restore. Without a hinge an implant could be designed to work with the natural knee structures. It would allow as normal a range of motion as possible while at the same time provide a normal degree of stability. That is, as long as the designers understood how the knee works.
The concept of attempting to understand the natural pattern and freedom of movement in a normal joint, and developing a low friction bearing that allowed the joint to work normally with its own guiding and stabilising structures, was a milestone in joint replacement surgery. The challenge to find the perfect bearing design is principally what led to a plethora of knee designs in the 1970s and a challenge that remains to this day.
Refs. Glück https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3824904/ ; history Ranawats (although poor errors) https://page-one.springer.com/pdf/preview/10.1007/978-2-287-99353-4_63; robinson;