What is a knee prosthesis?
A knee prosthesis is the replacement of the joint by a synthetic piece, through a surgical intervention. It is an implant that is placed in the damaged structure and replaces its function, allowing the patient to move the joint again, eliminating the pain he/she may have. During the intervention, the damaged bone and cartilage are removed. The patient will be given either general anesthesia or regional anesthesia (spinal or epidural). The anesthesiology specialist will determine this together with the orthopedic surgeon, in order to cause the least discomfort to the patient and to make the procedure as comfortable as possible.
Why is it performed?
The most common reason why a prosthesis is placed is due to osteoarthritis of the knee (gonarthrosis), which is damaging the joint. But also some fractures in which there is a great damage of the subchondral bone or certain bone tumors make necessary an implant or knee prosthesis.
The knee prosthesis allows the patient to recover the mobility and stability of the joint.
What does it consist of?
The knee prosthesis surgery lasts about two hours and consists of removing the damaged cartilage and bone of the joint, placing in its place artificial pieces. These pieces can be placed in different places of the knee: lower end of the femur (piece made of metal), upper end of the tibia (piece of strong plastic and metal) or on the back side of the kneecap (prosthesis made of strong plastic).
Once anesthesia has been applied to the patient, the specialist in Traumatology will make an incision in the joint to open it, about 20cm. Then, the following procedure will follow:
- Remove the patella and cut the ends of the femur and tibia, in order to accommodate the prosthesis to the joint space.
- Also cut the lower part of the patella so that the new piece fits well.
- To fix the two parts of the prosthesis to the different bones, one glued to the femur and the other to the tibia, with cement or screws.
- Repair the tendons and muscles of the joint, as well as close the incision.
Depending on the lesion and the amount of bone removed from the patient, the prostheses can be:
- Total or tricompartmental: the joint is totally replaced (also the patella). Among them are the prostheses of rigid axis (only allows a movement, the flexoextension, so they are almost not used), the prostheses of substitution of articular surfaces (isolated resection of the damaged joint), the prostheses with linked components (provide much stability by the link between the tibia and femur, as well as flexion-extension and rotation movements, but they are also in disuse) and self-stable prostheses (they replace the damaged surface and provide stability and functionality due to their design, the most common being the “medial pivot”).
- Monocompartmental: they are used in delimited lesions of the joint. They usually have a metallic femoral part that is placed in the injured femoral condyle, and a polyethylene component in the tibial part.
Like any surgical intervention, knee prostheses can also have their complications. In the following monograph of the Spanish Society of Orthopedic Surgery and Traumatology (SECOT) they explain it.
Preparation for the knee prosthesis
The specialist in Traumatology and the anesthesiologist will recommend to the patient what steps to follow before the intervention. It is important that the patient communicates the medication he/she is taking, so that it does not interfere in the evolution of the surgery. On the other hand, the specialist will perform a series of preoperative tests on the patient, such as electrocardiogram, magnetic resonance imaging, X-rays and other procedures that will make the operation easier and will allow him to access the joint with full knowledge of the injury suffered by the patient.
Care after the intervention
After the intervention of knee prosthesis the patient must be very strict, following the advice of the traumatologist and physiotherapist, so that the recovery is complete and successful. Thus, the specialist in Physiotherapy will design a series of exercises adapted to the patient and the injury suffered, which will increase in intensity over time, as the patient recovers the mobility of the joint. The objective is to recover and increase muscle strength, correct any instability and deformity, relieve any pain the patient may have, eliminate any scar adhesions and improve the patient’s physical function.
A series of recommendations can be added to this rehabilitation: alternate flexion and extension movements when sitting, wear comfortable, well-laced footwear, avoid sudden changes in weight to avoid overloading the joint, remove any furniture that may cause the patient to trip and fall, perform exercises at home (always recommended by the specialist), apply cold to the area after the rehabilitation exercises, follow the specialist’s instructions for sitting, walking and going down stairs and, above all, keep the wound clean and disinfected.
Alternatives to this treatment
There is no alternative to knee prosthesis surgery. It is an intervention that is only performed in extreme cases, when the joint is very damaged and the injury cannot be solved with another therapy or intervention. The specialist will be the one to study the injury and decide on the best treatment or alternative.