The knee is the hinge between the leg and the thigh. This weight-bearing joint is always under strain as it supports the weight of the body and enables movement. It is formed between the ends of three bones: the femur, the tibia and the patella, and joined by ligaments and the joint capsule. The cartilage protects the bone and facilitates movement by enabling the different parts to slide easily and painlessly over each other. When the cartilage is destroyed or damaged, the knee no longer functions correctly.
This deterioration of the joint cartilage has various origins: osteoarthritis, inflammatory arthritis, necrosis, bone or joint trauma, ultimately leading to severe pain, stiffening or swelling resulting in disability that can range from minor impairment in daily activities to a real loss of autonomy.
When medical treatments no longer provide any satisfactory solution, a total knee replacement is the only way to restore the joint and thus decrease or even eliminate the pain and recover mobility.
What is a total knee remplacement ?
Contrary to a partial or “unicompartmental” knee replacement that is performed when only part of the joint is damaged, a total knee replacement involves the replacement of the entire joint.
The most common implants are referred to as fixed or mobile bearing. They provide better results and greater freedom of movement than “hinge” implants for which indications are now rather limited.
The implants are generally made of metal (titanium, chromium-cobalt alloy, stainless steel) and a very high density polyethylene.
Briefly, a total knee replacement implant comprises two metallic parts fixed to the bone to replace the worn parts of bone and cartilage on the femur and tibia, and a central part implanted on the patella so the different parts can glide over each other.
The aim is to recover, as far as possible, normal knee mechanics.
Nowadays, health care professionals have good command of this operation that is becoming increasingly routine thanks to scientific progress in anesthesia and surgery. However, it is still a major procedure for patients due to the need for a general anesthetic and several weeks of functional rehabilitation.
The operation needs to be carefully prepared. A pre-op assessment is necessary to determine the patient’s state of health and to avoid any possible complications during or after the operation. Arrangements should also be made for when the patient leaves hospital so that the functional rehabilitation, essential to recover physical ability and autonomy, can begin as rapidly as possible.
Complications are rare and vary in severity. However, they can be avoided through daily surveillance in hospital and follow-up consultations of which the frequency varies according to the initial pathology and the circumstances of the operation.
The patient stays in hospital for one or two weeks on average. This is necessary to ensure the effective management of the pain caused in part by the healing process, to watch out for any immediate complications – in particular infection or thromboembolism – and to initiate rehabilitation.
Rehabilitation and results
Rehabilitation begins almost immediately after the operation with passive mobilization of the limb before resuming movement using machines and exercises with the physiotherapist.
It is essential to continue rehabilitation for at least one month after leaving hospital in order to rapidly recover autonomy in daily life and everyday movements. It can be carried out at home, but it is highly recommended that it be performed at a functional rehabilitation center.
Recovery of movement is generally very satisfactory and improves during the first year. It does however depend on the condition, pre-op knee mobility, and the initial physical condition of the patient. Excess weight and muscle loss often play a prominent role. Prolonged pre or post-op rehabilitation can be proposed in some cases.
For most patients, the pain ultimately disappears or is significantly reduced. Walking and driving can generally be resumed rapidly. After a few months, most patients can return to activities such as swimming, dancing or cycling. However, some sports such as skiing or running are not recommended to avoid shocks or rotations of the knee that could deteriorate the implant.
After the operation, the orthopedic surgeon will prescribe an x-ray every two or three years to monitor the progressive appearance of loosening or wear. However, the lifespan of a knee implant is generally 15 to 20 years, and the latest studies suggest that the lifespan of new generation implants will probably be much longer.