What is Unicompartmental Knee Replacement?
A Unicompartmental Knee Replacement is also known as a Partial Knee Replacement. It is very similar to a Total Knee Replacement but it has a smaller incision and faster recovery. However, the problem is that it cannot be used in patients with very advanced arthritis. This procedure involves removing the damaged cartilage whilst preserving the healthy cartilage as opposed to removing all the cartilage. Then a prosthetic is inserted to replace the removed cartilage.
Who is this operation for?
A partial knee replacement suits people whose arthritis is confined to one part of the knee — most often the inner, or medial, side.
It is generally considered when:
- Pain and X-ray changes are limited to one compartment of the knee
- The knee still bends and straightens reasonably well
- The ligaments, particularly the anterior cruciate ligament, are intact
- There is no significant bowing or knock-knee deformity
It is not suitable where arthritis affects the whole knee, in inflammatory arthritis such as rheumatoid disease, or where the knee is stiff or badly deformed. In those situations a total knee replacement is used instead.
How it differs from a total knee replacement
- Only the worn compartment is resurfaced. The healthy cartilage, the ligaments and the rest of the joint are left alone.
- The incision is smaller and less bone is removed.
- Recovery is usually quicker, and the knee tends to feel more natural because your own ligaments are preserved.
- The hospital stay is generally shorter.
- Over the long term, a partial knee replacement is more likely than a total to need further surgery, because arthritis can progress in the compartments that were left.
If arthritis does spread later, a partial knee replacement can usually be converted to a total knee replacement.
Alternatives to surgery
Before considering a partial knee replacement, most people will have tried:
- Simple pain relief and anti-inflammatory medication
- Losing weight, which reduces the load going through the knee
- Physiotherapy and strengthening, particularly of the quadriceps
- A walking stick or other walking aid
- Injections into the knee
In younger, active people with wear on one side of the knee, an osteotomy — cutting and realigning the bone to shift load away from the worn side — is sometimes considered instead.
Benefits of the operation
- Relief of the pain coming from the arthritic compartment
- More of your own knee is kept, including the ligaments
- Faster recovery and a shorter hospital stay than a total knee replacement
- Movement often feels more natural than after a total replacement
Complications
As with any operation there are risks. General risks include infection, blood clots in the leg or lung, and risks related to the anaesthetic.
Risks more specific to this operation:
- Pain that does not settle as hoped
- Arthritis progressing in the other compartments of the knee, which may eventually need conversion to a total knee replacement
- Loosening or wear of the implant over time
- Stiffness
- Fracture of the bone around the implant, which is uncommon
The Operation
A partial knee replacement usually takes about an hour to an hour and a half.
You will have either a general anaesthetic, or a spinal anaesthetic with sedation. Through a smaller incision than a total knee replacement, the worn surfaces of the affected compartment are removed and replaced with metal components, with a plastic bearing between them. The rest of the knee is left untouched.
Most people go home within one to three days.
What happens before and around the operation — the pre-admission clinic, tests, medications, preparing your skin and organising help at home — is the same as for any joint replacement. See Preparing for Surgery.
Recovery and Rehabilitation
Most people are up and walking with a frame or crutches on the day of surgery or the day after.
- Physiotherapy starts in hospital and continues at home
- Most people are off walking aids within two to four weeks
- Driving is usually possible somewhere between two and six weeks, depending on which leg was operated on and whether you can perform an emergency stop comfortably
- Swelling can come and go for several months, which is normal
- Low-impact activity such as walking, swimming, cycling and golf is encouraged; running and jumping sports are generally discouraged
F.A.Q. | Frequently Asked Questions
How long does a partial knee replacement last?
Most last many years. Published figures vary between studies and depend heavily on your age and activity level, so your surgeon is the best person to give you a realistic figure for your own knee.
Will I need a total knee replacement later?
Some people do, if arthritis progresses in the parts of the knee that were left alone. A partial replacement can usually be converted to a total knee replacement if that happens.
How does recovery compare with a total knee replacement?
It is generally quicker, with a shorter hospital stay and less time on walking aids, because less bone is removed and your own ligaments are kept.
Can I kneel afterwards?
Many people can, though it is often uncomfortable at first and some never find it comfortable. This is worth raising with your surgeon beforehand if kneeling matters for your work or your faith.
What activities can I go back to?
Walking, swimming, cycling, golf and similar low-impact activities are encouraged. High-impact sport puts the implant under load it was not designed for and is generally advised against.
References
Miller, M. (2000). Review of Orthopaedics, Saunders.