Partial knee replacement surgery

Unicompartmental knee replacement surgery is used to address 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. This particular pattern of arthritis is commonly seen in younger individuals who have possibly had previous knee surgery, for example, resection of a torn cartilage. As there is significant concern regarding performing a total knee replacement surgery in younger individuals, unicompartmental or partial knee replacement surgery is generally preferred.

Type of anaesthesia

Partial knee replacement surgery can be carried out under a general anaesthetic (where you will be asleep) or a regional type of anaesthetic (spinal or epidural anaesthetic, where your legs are numb for the duration of the operation).

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 component on the lower end of the femur (thigh bone) and a plastic component on the upper end of the tibia (shin bone). The components are fixed to bone with bone cement.

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 and a drain is used to drain the blood away from the knee.

What happens after the partial knee replacement?

The day after your partial knee replacement surgery you start exercising your knee with the help of a physiotherapist after removal of the drain. Your knee is X-rayed to confirm accurate placement of the knee replacement components and you are encouraged to walk and bend the knee with the help of the physiotherapist. As the recovery is faster as compared to a total knee replacement you should be able to go home within 3-5 days 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 physiotherapist can help you to achieve these goals. Two weeks following the partial knee replacement surgery your skin clips will be removed. It can take up to six weeks for the knee to settle down following the knee surgery and you may notice swelling and bruising in relation to the knee in this period. You will be reviewed in clinic at six weeks following your surgery to check your progress and then you will be kept under review on a six monthly basis for the first year following partial knee replacement surgery.

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 dissection inside is significantly less and hence can lead to a faster recovery and better flexion (bend) of the knee.

What can I expect from my partial knee replacement surgery?

Following partial knee replacement surgery you will be able to carry out most 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 following your partial knee replacement. Exercises and activities leading to impact onthe artificial knee are generally not advisable.  If the arthritis progresses in the rest of the knee which has not been replaced, the partial knee replacement may need to be converted to a total knee replacement. Though the long term results of partial knee replacement surgery are not yet known it is a useful procedure for young patients with arthritis affecting partof the knee.

What are the risks of undergoing partial knee replacement surgery?

The significant and common risks are as follows:

• Infection (around 1%): despite giving antibiotics and operating in sterile conditions (laminar air flow theatres), infection can occur.  This usually manifests by the incision becoming red, hot and painful, with possible discharge of fluid.  A superficial infection not going deep to the joint can be treated with antibiotics and an operation to wash the wound.  In case of deep infection the artificial knee may need to be removed and replaced at a later date after the infection has been controlled.
• 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 can go to the lungs, which is termed as a pulmonary embolus.  To reduce the risk of DVT you will be given medications as well as stockings on your legs.  One of the best ways to prevent a DVT is to get the leg muscles moving as quickly as possible following the surgery.
• 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.

Less common complications include persistent pain following knee replacement surgery, knee stiffness, nerve and blood vessel damage.