Knee replacement surgery can be classified as either Partial or Total. In Partial knee replacement, only the worn part of the knee joint is replaced. In total knee replacement, the entire knee joint is replaced. Total knee Replacement is a far more common procedure than Partial knee Replacement.
Regardless of which form of knee replacement is performed, the concept remains the same – the surgery involves accessing the knee joint, removing the worn surface layer of the worn bone (and cartilage) and replacing the worn surfaces with new surfaces made of metal (with a plastic “bushing” in between). These components are rigidly fixed in place at the time of surgery, either using an acrylic cement to fix the components or utilising very precise, high friction, fitting of the parts to the bone.
In total knee replacements, the entire lower end of the thigh bone (femur) is resurfaced, the entire upper end of the shin bone (tibia) is resurfaced. Additionally, the rear surface of the kneecap (patella) is often resurfaced also.
This surgery preserves the tendons and muscles that move the joint as well the stabilising ligaments.
The components used in total knee replacement surgery are made of a variety of materials. The metal parts (femur and tibia components) are made from an alloy of cobalt and chrome (which is very hard, stiff, long-lasting and bio-compatible).
The material used to resurface the upper tibia is either made of the same cobalt-chrome alloy or from a titanium alloy.
These two metal surfaces do not rub against each other. A plastic bushing piece (made from polyethylene) fits securely between them. This plastic part can be thought of as being similar to cartilage in a normal knee. It is locked into place by being securely affixed to the tibia component. The new patella component is also made of polyethylene.
Most knees tend to develop a bow-legged shape as arthritis develops (a Varus deformity to the knee). In rarer instances, a knock-kneed deformity (Valgus deformity) can develop. Additionally, it is quite common for a flexion deformity of the knee (inability to fully straighten) to develop at the same time. As these deformities develop, the ligaments and fibrous capsule around the knee joint can tighten and contract on one side of the knee and sometime stretch and loosen on the other side.
Knee Replacement surgery requires the Orthopaedic Surgeon to accurately re-balance the knee and correct any knee deformities that may have developed as the arthritic process took hold. The alignment of the leg is corrected to remove Bow-legged or knock-kneed deformities that may have appeared.
Operative Information
As well as the very specialised surgical instruments, other high-technology devices are used during Knee Replacement Surgery to aid the surgeon achieve a successful outcome. Innovations such as computer navigation and stereoscopic guidance computers (computer systems that can see the leg being operated on in real time and provide feedback and guidance to the surgeon) and robotic devices are often employed in order to maximise the accuracy of knee replacement surgery.
Total knee replacement surgery requires a 15-20cm incision down the front of the knee. The operation itself takes only 60-120minutes. Most people stay in hospital for three to five days following surgery, during which an intensive physiotherapy programme is commenced. Full weight bearing is allowed straight away after surgery and the first physio session is usually undertaken only a few hours after the surgery is over (on the same day as the operation). A urinary catheter is only occasionally employed on a case-by-case basis.
Discharge home is usually allowed when people are able to walk without supervision (with the use of a stick or crutches for balance), bend the knee to at least 90 degrees and get up and down stairs independently.
At the time of surgery, the knee and surrounding regions are injected with a high volume of dilute local anaesthetic (as well as other pain relief medications) and the anaesthetist will often use an ultrasound machine to inject local anaesthetic next to the sensation nerves of the knee (a regional block or nerve block). Usually the knee is actually very comfortable in the immediate post-operative period and for the first 24 hours following surgery.
After Your Total Knee Replacement
As the local anaesthetic effect wears off, the knee can become sorer, requiring use of combinations of several different pain relief medications – it is found that lower doses of a variety of pain relievers produces a greater effect with less side effects than higher doses of a single drug. Nausea and vomiting is actually quite infrequent and can usually be managed very successfully with modern anti-nausea medications.
Full recovery after Total Knee Replacement requires a concerted effort on the recipients’ behalf, as well as patience. A supervised rehab programme under the guidance of a physiotherapist (either home-based or at the physios premises) is essential for success. This usually lasts from four to six weeks following discharge from hospital. For some people, a further stay in the rehab unit of the hospital prior to discharge home is useful – this is easily arranged either prior to admission or after surgery.
Experience suggests that following Total Knee Replacement, there is soreness of the knee that requires pain relief medication for the first 6 weeks following surgery. By 12 weeks following surgery, recovery is usually proceeding well and the people “can see the light at the end of the tunnel.” It is important to remain patient throughout this time and understand that recovery is often characterised by incremental advancements as well as periodic setbacks.
It is important to realise, however, that although the knee is often dramatically improved quite quickly, there is a substantial time period of further recovery and improvement for many months and most people do not reach their peak or maximal improvement for eighteen months to 2 years following surgery.
About 85% of patients report a “good” or “excellent” outcome following Knee Replacement. Although it is impossible to predict how long a Knee Replacement will last in any one individual, current data from the Australian Joint Replacement Registry demonstrates an 8.4% (less than one person in ten) rate of revision (re-do) surgery by the 17th year after surgery.