Partial knee replacement surgery

Partial/unicompartmental knee replacement surgery is used to treat arthritis affecting only one area of the knee joint provided the rest of the knee is not worn. Commonly the inner (medial) side of the knee joint is worn with the outer side of the knee having good cartilage. Due to long term concerns about total knee replacement surgery in younger individuals, partial knee replacement surgery is a preferable option, if suitable.

Type of anaesthesia

The surgical procedure is usually carried out under a regional anaesthetic (spinal anaesthetic where your legs are numb for the duration of the operation) and sedation. The procedure can be carried out under a general anaesthetic (where you are asleep). The appropriate anaesthetic is chosen after pre operative assessment and discussion with the anaesthetist. You are made comfortable during the surgery and are not in any pain.

What happens during partial knee replacement surgery?

During partial knee replacement surgery, the affected bearing surfaces of the knee joint (commonly the medial side) are removed and replaced with artificial bearing surfaces in the form of a metallic components on the lower end of the femur (thigh bone) and the upper end of the tibia (shin bone). A plastic bearing is inserted between the metal components.

As compared to total knee replacement the surgery is done through a smaller incision. As all the ligaments are kept intact during this procedure and not released, the recovery following partial knee replacement surgery is significantly quicker as compared to total knee replacement surgery.

At the end of the procedure, the skin is closed with metal clips. Local anaesthetic is infiltrated in and around the knee for good pain control.

What happens after the partial knee replacement?

Following your knee replacement surgery, you are made comfortable with pain killers as needed. Once you have recovered from the anaesthetic, physiotherapists will help you with your walking and knee exercises. You are given walking aids like crutches to help with your early mobilisation. Your knee is x-rayed after the operation to confirm accurate placement of the knee replacement. As the recovery is faster as compared to a total knee replacement you should be able to go home either the same day or the next day following the surgery.

What happens after discharge from the hospital?

You need to continue with the exercises to improve the bend in your new knee and to regain the strength in your muscles around the knee. The physiotherapists will work with you to achieve these goals. Two weeks following the partial knee replacement surgery the skin clips will be removed. It can take up to six to eight weeks for the knee to settle down following the knee surgery. You will be reviewed in clinic at eight weeks following your surgery to check your progress.

Is replacement of the kneecap a type of partial knee replacement?

In certain cases, arthritis of the knee can affect the under-surface of your kneecap and the underlying thigh bone on which the kneecap moves. If the main bearing surfaces between the femur (thigh bone) and tibia (shin bone) are satisfactory a type of partial knee replacement surgery can be done where the under-surface of the kneecap is replaced with a polyethylene button and the underlying surface of the thighbone is replaced with a small metallic component. Though the skin incision may be similar to a total knee replacement the work done inside is significantly less and hence can lead to a faster recovery and better flexion (bend) of the knee.

This type of partial knee replacement is falling out of favour due to concerns regarding higher rates of revision to total knee replacement

What can I expect from my partial knee replacement surgery?

Following partial knee replacement surgery, you will be able to carry out all of your daily activities. The bend in the knee is generally better as compared to a total knee replacement. You may find it difficult to kneel in the initial period following your partial knee replacement. Exercises and activities leading to repetitive impact on the knee are generally not advisable. If the arthritis progresses in the rest of the knee, the partial knee replacement may need to be converted to a total knee replacement. Good long term results of partial knee replacement surgery have shown it to be a useful procedure for younger patients with arthritis affecting part of the knee.

What are the risks of undergoing partial knee replacement surgery?

The significant and common risks are as follows:

Infection (around 1%): every effort is undertaken to avoid infection by performing the knee surgery in sterile conditions (laminar air flow theatre) and by giving antibiotics around the time of operation. Despite this infection can still occur. Infection usually manifests by the incision becoming red, hot and painful, with possible discharge of fluid. If this infection is superficial (not going deep to the joint) this can usually be treated with antibiotics and an operation to wash the wound. A change of plastic bearing may be needed at times. In case of deep infection, which is fortunately rare, the artificial knee may need to be removed and replaced at a later date after the infection has been controlled.
Bleeding: minimised by use of tourniquet during the surgery. Blood transfusion is kept on standby and may be required in the post-operative period.
Deep vein thrombosis and pulmonary embolus: deep vein thrombosis (DVT) is a blood clot in the veins of the leg. The blood clot can go into the general circulation and go to the lungs, which is termed as a pulmonary embolus. To reduce the risk of DVT you will be given blood thinners as well as stockings on your legs. One of the best ways to prevent a DVT is to get the calf muscles working by ankle exercises and keeping yourself well hydrated.
Swelling: swelling in and around your knee can take few weeks to settle down.
Stiffness: The knee can stiffen due to scar tissue on the front of the knee following the knee replacement surgery. Manipulation of the knee under anaesthetic may be needed at times to address significant stiffness.
Persistent pain: can occur in 10% of knee replacements due to scar tissue and overactivity of nerves around the knee. This may need input from pain clinic.
Loosening, wear and need for revision of the partial knee replacement: most partial knee replacements are expected to last for about 10 years or more. If there is loosening of the components or wearing of the polyethylene bearing of the knee or if the arthritis progresses in the rest of the knee the partial knee replacement may need to be changed to a total knee replacement.
Rare complications include nerve and blood vessel damage, fracture.