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.
Revision Knee Replacement
Whilst most knee replacements do perform very well and 90% of them are still functioning 20 years after insertion, some knee replacements fail prematurely. The reasons for premature failure can include infection, fracture, loosening or excessive wear.
Whatever the reason, a revision knee replacement is a major undertaking.
The surgery is more difficult than the primary replacement, requires special skill on the part of the Orthopaedic Surgeon and special ancillary support within the hospital environment.
The rehabilitation procedure is usually longer and more difficult. The outcome is usually less certain than the primary knee replacement surgery.
Whilst revision knee replacement is not to be sought after or revered, it is sometimes unavoidable. This is an issue that your Orthopaedic Surgeon will discuss with you very carefully.
Partial Knee Replacement
Some patients who have failed a thorough non-operative therapeutic programme and still have pain that is intolerable, will not require a total joint replacement. That is, of the three compartments in the joint – the medial compartment, the lateral compartment and the patellofemoral compartment – it may be that only one of those compartments is truly degenerate.
In this special circumstance, a so-called “partial knee replacement” can be performed. It is usually restricted to the medial compartment of the knee but sometimes it can be performed in the lateral compartment or the patellofemoral compartment.
The invasiveness of the procedure is usually less than a total knee replacement. The recovery is usually faster.
The results of partial knee replacement, whilst good, are not necessarily as good as those for a total knee replacement.
In addition, should a partial knee replacement fail and it requires conversion to a total knee replacement, the results are even less certain.
For these and many other reasons, not all Orthopaedic Surgeons favour partial knee replacement.
This is an issue that you should discuss very carefully with your Orthopaedic Surgeon.
The term “arthroscopy” is of Latin origin. The word “arthro” means joint and the word “scopy” means telescope or viewing instrument.
An arthroscope is a long, thin device (a little bit like a straw) which has an eye piece attached to one end. The narrow end can be passed into a knee joint through a tiny nick in the skin. This is so-called “keyhole surgery”. The arthroscope (or telescope) has a solid state camera attached to the eye piece end. A cable runs off to a colour television set and whilst the Orthopaedic Surgeon is sitting beside the patient, moving the viewing end of the telescope in and around the joint, he or she is usually looking at the television screen overhead.
The modern arthroscope is an outstanding device. It allows excellent and direct visualisation of almost every part of the joint. It is orders of magnitude better than it was 30 years ago when we used to open the joint to inspect the meniscus or the ligaments or the cartilage.
Knee arthroscopy is usually performed under a general anaesthetic but it can be performed under local anaesthesia or even regional anaesthesia. Three small nicks in the skin are usually used. One is for the insertion of the arthroscope, one is for the insertion of instruments that can be used to trim, shave or smooth the joint internally and the third is for the insertion of a drainage tube. Whilst the Orthopaedic Surgeon is performing the arthroscopic procedure, the joint is being washed or lavaged with an appropriate solution. This aids visualisation using the arthroscope and also removes debris or rubbish from the joint.
Most knee arthroscopic procedures can be performed as day surgery cases. A bandage is usually applied to the joint overnight but thereafter it can be removed. Physiotherapy can start within the next few days. Depending upon the procedure performed, your Orthopaedic Surgeon is likely to see you within the next week or two.
The types of operations that can be performed through the arthroscope include partial or complete meniscal removal, meniscal repairs, loose body removal, smoothing of the joint surfaces (chondroplasty), ligament reconstructions, microfracture of bare areas of the bone or lavage following infection.
As our techniques develop and the instruments become even more sophisticated, the list of procedures that can be performed within the joint through the arthroscope is forever increasing.
You will recall that the anterior cruciate ligament is one of two very important ligaments within the joint that provide stability both forwards and backwards, and when the joint is being rotated.
Some patients can cope with the loss of an anterior cruciate ligament and perform quite satisfactorily with most activities of daily living.
Others are not so fortunate. They require a so-called “cruciate ligament reconstruction”.
Once the ligament is ruptured, simply suturing it together is of no great use. The environment within the knee joint prevents the ligament healing. It is therefore necessary to use some form of graft to reconstruct the ruptured cruciate ligament.
The graft is usually in the form of tendons taken from the patient’s own thigh. These are the so-called “hamstring tendons” of semitendinosus and gracilis. They can be harvested through a small incision just below the knee joint, can then be bound together and then passed up through a tunnel in the upper end of the shin bone, out through a tunnel in the lower end of the thigh bone to reconstruct the cruciate ligament that has been ruptured.
The operation itself is not particularly difficult although it does require special technical expertise.
The post-operative recovery is very important. Many Orthopaedic Surgeons ask their patients to wear a limited range of motion brace for three weeks or so. Thereafter, intensive physiotherapy is required with a gradual reintroduction of usual social, recreational, domestic and remunerative activities. Rigorous bipedal sporting pursuits are usually delayed for up to twelve months.
The word “osteotomy” refers to a division of a bone. It is like a controlled fracture.
This operation is less common than it used to be but it is used to redirect load bearing forces around the knee joint. Sometimes patients have arthritis on the inside of the knee which gives rise to a marked bowing of the joint as though they had been riding a horse for too long. An osteotomy can be performed through the upper end of the shin bone. A wedge of bone can be removed and rather than being bow-legged, the patient can be reconverted to the usual knock-kneed alignment.
A similar approach can be adopted with the lower end of the thigh bone if excessive knock-kneedness is experienced by the patient. A wedge of bone can be taken from the medial side or inner side of the lower end of the thigh bone and convert the knock-kneed alignment into a limb which is now straight.
Whilst uncommon, osteotomies still have a role to play. They are typically used in patients who have quite significant deformity, who are suffering pain and who are too young to consider or should consider a joint replacement.
Other Ligamentous Repairs and Reconstructions
The most common ligament reconstruction that occurs in or around the knee joint relates to the anterior cruciate ligament.
Sometimes, the posterior cruciate ligament can be ruptured and on occasions, it also requires reconstruction.
In addition, there are ligaments on the medial side and lateral side of the knee (the collateral ligaments) which can be disrupted. The need for repair or reconstruction is less frequent but it does exist.
Sometimes, capsular disruptions can occur that may also require repair.
The decision to reconstruct or otherwise depends upon the severity of the injury, the morbidity or discomfort that ensues, the relative instability that persists and the views and advice of your Orthopaedic Surgeon. The level of activity of daily living that you aspire to will also be an indicator. For example, if you intend to spend the remaining years of your life in a chair watching television, a ligament reconstruction is not likely to be required. Conversely, if you want to return to A grade sport at a competitive level, a ligament reconstruction does become more desirable.
These are issues that your Orthopaedic Surgeon will help you understand.