Knee surgery is not new - there is evidence which suggests that the ancient Egyptians operated on the knee joint, but probably for trauma, rather than for joint diseases. Joint surgery on the knee really began in the late nineteenth and early twentieth centuries and prosthetic knee joint replacements appeared just after the end of the Second World War. In 1947, Shiers, a British Orthopaedic Surgeon, developed the first true knee joint replacement, which was a simple hinge joint, pivoting around a central pin.

From this early design, other hinged types of knee prostheses evolved, but they all functioned in much the same way as a basic hinge joint, with no attempt made to replicate the motion of a normal knee. This was primarily because there was little knowledge of the way in which a physiologically normal knee moves. The knee rotates as it moves from extension into flexion and also pivots about the medial side.
 

The Modern Knee Replacement

The forebear of the first generation of modern knee designs was introduced in the late 1960's by Gunston, at Wrightington Hospital in Lancashire. The Gunston Knee was the first knee joint to have a metal to plastic articulation. Next came the Total Condylar Knee, designed by an English Surgeon, John Insall, working at the Hospital for Special Surgery in New York, closely followed by an improved design, the Insall Burstein Knee. Virtually all knee replacements are based on these two designs and look remarkably similar, although competing claims are made regarding their efficacy. In the mid- to late-1980's, some problems began to be seen with these earlier designs, with prosthetic loosenings, damage to bone stock and difficult revision surgery.

All modern knee designs are effectively a compromise between congruency, (making the components fit together as well as possible) and freedom of movement, which will tend to minimise the forces imparted to the prosthetic knee. These two conditions are, in the prosthetic knee, almost mutually exclusive.  Fixed bearing knees can and do provide excellent long-term results but, as the mean age of knee replacement patients decreases, the results tend to worsen, probably because younger, fitter patients will place greater demands on their replaced knees than older, less active patients.

The Solution

Are there any solutions to these problems? Fortunately, there are and, in the late 1970's, John Goodfellow, a Surgeon, and John O'Connor, a bio-engineer, both working in Oxford, developed a knee which was dramatically different to any preceding design of knee joint. Firstly, it was fully congruent and, secondly, it was unconstrained, as the plastic component moved freely between the femoral and tibial components. This knee has been shown to have excellent long-term clinical results; however, as it is designed to replace only one half of a knee joint, its applicability is somewhat limited.

In 1976-1977, Polyzoides, in Solihull, and Beuchel, in New Jersey, developed two similar products, both of which permitted rotation of the femur on the tibia and more physiologically normal movement than fixed bearing knees.

In the last few years, there has been a big swing towards the use of mobile bearing knees and the Rotaglide Mobile Bearing Knee * (Corin) has the longest clinical history of any total condylar type of knee which permits both rotation and front-to-back movement. It may be considered as a fourth generation knee replacement and provides more normal movement for a replaced knee than the older, fixed bearing designs.

The Rotaglide Knee *

One of the keys to implant longevity is minimising the production of polyethylene wear particles, as the body's defences can react to such debris and speed prosthetic loosening. How can this be best achieved? The easy answer would be to remove polyethylene from the prosthetic knee, but this is, as yet, not possible. However, if the knee is as congruent as possible, fewer wear particles will be produced because the high contact areas resulting from the high conformity mean that there will be low contact stresses and thus the chances of damaging the polyethylene are significantly reduced. The Rotaglide Knee has spherical, distal and posterior femoral condyles, articulating with polyethylene meniscal components, which have spherical contact areas of the same radius as the condyles of the femoral component.

This feature, combined with the ability of the meniscal bearings to rotate 12.5º either side of the midline of the tibial tray and to move up to 5mm anteriorly and posteriorly, means that congruency is maintained throughout the range of movement. In turn, this means that high contact areas of metal on polyethylene are maintained, thus yielding contact stresses well below those which are likely to cause material damage. *
 

It has been shown that knee replacements work as well as hip replacements, at least in the relatively elderly patient population and the challenge now is to extend this success to the younger, higher demand patient.

Mobile bearing knee replacements are becoming increasingly widely used as the surgical community accepts the benefits that these devices are likely to provide, but few devices currently available have much clinical history. Virtually every orthopaedic device manufacturer has introduced a mobile bearing knee within the last five years, recognising the need to be able to offer younger patients a long-term solution for their joint disease.

Knee replacements in the 21st century will increasingly be of the mobile bearing type and the Rotaglide Knee is a clinically proven and extensively tested design, which has been shown to have excellent mid-term results, with 99% survivorship at five to eight years. ¹ It has the longest clinical history of any total condylar mobile bearing meniscal knee which provides both rotation and antero-posterior movement and offers the more active patient the possibility of long lasting knee replacement.

* The Rotaglide Mobile Bearing Knee is not cleared or approved for use in the USA

¹ A. Hudd, K. Kunasingham, D. Ricketts, J. Bush: 'A 5 to 8 year follow-up stud of the Rotaglide mobile bearing total knee arthroplasty', International Orthopaedics (SICOT) 2008.