The artificial replacement of a knee can be either partial or total.
Whichever type is engaged, it does involve removing some of the bone and cartilage from the joint and replacing the worn surfaces with metal and plastic. Occasionally bone cement (grout) is used to secure the metal on the bone.
In total knee replacements, the entire lower end of the thigh bone is resurfaced, the entire upper end of the shin bone is resurfaced and more often than not, the wearing surface of the kneecap (the patella) is also resurfaced.
The Orthopaedic Surgeon is able to open the joint but preserve the attachments of ligaments and tendons. The anterior cruciate ligament is always sacrificed but sometimes, the posterior cruciate ligament is preserved.
The metal typically used to resurface the lower end of the thigh bone (the femur) is an alloy of cobalt and chrome.
The material used to resurface the upper end of the shin bone (the tibia) is titanium.
Rather than having the two metal surfaces rub together, a plastic or polyethylene piece is attached to the shin bone tray. This is a so-called “interposition arthroplasty” with the plastic interposed between the two metal surfaces. The kneecap component (the patellar component) is also made of polyethylene.
Knee replacements were first performed in the mid to late 1960’s. Considerable advancements were made during the 1970’s and 1980’s.
There are now more than 150 types of knee replacement available. They all have many similarities although there is a number of subtle differences. Orthopaedic Surgeons tend to favour one type over another for various reasons. This is an issue that you should discuss with your Orthopaedic Surgeon.
Most patients with arthritis are treated without operation. Unless there is a specific indication for a knee replacement, it should not be considered. The most important considerations include unremitting pain and a failure of all other non-operative measures to assist with the reduction of that pain.
A knee replacement procedure is not desperately difficult for an Orthopaedic Surgeon but it is quite an undertaking for a patient. It is much more difficult to recover from than a hip replacement.
It involves a 15-20cm incision down the front of the knee, an operation that takes an hour or two, a five to seven day hospital stay and intensive physiotherapy and a home exercise programme for the next four to six weeks. Many patients say that following a total knee replacement, although their condition is dramatically improved quite quickly, they do not reach their peak or zenith for eighteen months or so.
Importantly, whilst 85% of patients are good or excellent following a knee replacement, the remaining 15% of patients are fair or poor.
Whilst knee replacements have an excellent reputation and a 90% 20-year survivorship, it is not something that you should rush into.