When arthritis is confined to only one side of the knee, patients may be suitable for a partial or unicondylar knee replacement. In this operation only one half of the end of the femur and one half of the end of the tibia are replaced, leaving the rest of the joint and the cruciate ligaments alone. It is much more common for this to involve the inside or medial portion of the knee.
A knee for a unicondylar replacement should have minimal deformity and should bend to beyond 90 degrees and come out almost completely straight prior to surgery. All major ligaments in the knee should also in general be intact. Patients with inflammatory types of arthritis such as rheumatoid arthritis, psoriatic arthritis or ankylosing spondylitis should not have a unicondylar knee due to the potential for their disease process to involve the rest of the knee in future.
A unicondylar knee replacement involves a smaller operation than a total knee replacement and thus patients tend to recover from the procedure more rapidly. In most instances, you will be able to be discharged by day 2 or 3 following surgery as opposed to day 3 to 5 following a total knee replacement. In addition, because the anterior and posterior cruciate ligaments are both preserved, the knee will feel and move much more like a natural knee.
Most types of knee replacements are performed under a spinal anaesthetic, where the legs are numbed from an injection of local anaesthetic into the back. This can be combined with sedation if you prefer not to be aware of the surgery. Occasionally a general anaesthetic is used for various medical reasons, but ultimately this is the decision of the Anaesthetist looking after you and can be discussed with them prior to surgery.
An incision is made down along the front of the knee just to the inside of the kneecap. It is usually roughly 10cm in length or roughly half of that used for a total knee replacement. The tissue on the side of the kneecap is also cut to allow access to the joint but the kneecap is not turned over as for a total knee replacement. Instead it is just pushed to the side and the rest of the joint is carefully inspected to ensure it is suitable for a partial knee.
Using either special jigs or computer navigation cutting blocks, the inside end of the femur and the inside of the tibia are both prepared for the implants. The chosen implants are carefully checked to ensure that the knee has full movement and is well balanced and aligned. The components can be either cemented in place or impacted on and a special coating allows bone to grow onto the back of them.
The joint is then thoroughly washed out and closed in layers and dressings applied.
As the rest of the knee is not replaced, there is always a small chance that arthritis can progress and that you will require further surgery in the future. This would normally require a conversion to a total knee replacement but it is possible to occasionally just replace another worn segment.
The bulky wool & crepe bandage can be removed 24 hours after surgery. The dressing underneath can remain in place for several days & only if it leaks blood will the nurse change it. As a general rule, the less the wound is interfered with, the better. It is fine to shower but avoid getting too much water directly on the dressings. The paper stitches can remain in place for 2 weeks. At this point, you can shower without the dressing on & the paper stitches will peel off easily when wet.
At the end of the procedure, some local anaesthetic is injected around the knee joint. This will usually ensure minimal pain following the surgery. As the local anaesthetic begins to wear off (usually after 12 - 24 hours), discomfort can return. This can be minimised with a combination of simple analgesia such as paracetamol, an anti-inflammatory & a stronger morphine-like tablet or injection (depending on patient tolerances / allergies). If you are in significant pain, call the nursing staff to help get some more analgesia. In general, most patients report significantly less pain after a partial knee than after a total knee replacement.
When patients return home, they often forget to continue using ice packs. These when combined with a few minutes elevation can really help reduce pain & swelling. Try to adopt the motto “work hard, rest hard”, by performing your exercises regularly as directed by the physiotherapist but then getting the leg up on a couple of pillows with an icepack. A frozen bag of peas wrapped in a towel works fine.
A small scar will run down along the front of the knee, slightly to the inside of the kneecap. This is closed with a dissolvable suture under the skin with additional paper stitches (like pieces of tape) on top. It is normal to have an area of numbness especially on the outer part of the knee but this should diminish over 12 - 18 months and should be considerably smaller than with a total knee replacement. The scar itself is quite red and raised initially and matures over 6 - 12 months when it will be flat and slightly lighter than the surrounding skin.
It must be stressed that recovery from any type of a knee replacement is not easy, although patients with unicondylar knee replacements do tend to progress more rapidly than with a total knee replacement. Beginning to bend a swollen, bruised leg involves a degree of discomfort and determination. Your physiotherapist will be there to supervise and encourage you & rapidly you will start to notice improvements. Exercises should be performed regularly and diligently as directed by the physiotherapist. It is often useful to take some simple analgesia 30 minutes before your exercises.
Roughly 4 - 6 weeks following surgery is reasonable. If you have an automatic car and it is your left leg, then perhaps you can start earlier. Bear in mind that sitting in a car involves a significant knee bend and anything longer than a few minutes can be very uncomfortable.
Roughly 6 weeks following surgery is reasonable. If you have an automatic car and it is your left leg, then perhaps you can start earlier. Bear in mind that sitting in a car involves a significant knee bend and anything longer than a few minutes can be very uncomfortable.
This is obviously dependent on the nature of the work. Office based workers may be able to return after 6 weeks but for manual workers, 3 months is a more realistic goal. Don’t forget to think about how you normally get to & from work when contemplating returning.
Ultimately it may be possible to return to many sports as a unicondylar knee replacement feels more natural than a total knee replacement. However it is important that you are realistic as well; any high impact sports should be avoided and even prolonged jogging is not recommended due to the risk of early loosening of the replacement.
Sports such as tennis, cycling, skiing and golf should all be fine.
🏊🏼 You can slowly return to swimming after 3 weeks as long as the wound has fully healed.
🚴🏻 You can start back on a stationary bicycle with the seat raised at 2 weeks.
You will usually be reviewed 4 weeks following surgery. This allows us to ensure that the incisions are healing and check the motion. It is often the best time to have a talk about the procedure and ask any questions regarding returning to normal activities.
You should seek advice if the pain dramatically worsens after discharge. Also call if the knee becomes a lot more swollen or you get a large amount of bleeding. Any symptoms such as calf swelling or tenderness or simply feeling unwell or shortness of breath should also be assessed.
Compiled October 2015
Review date: March 2016
Review date: March 2016