Unicompartmental Knee Replacement
Uncompartmental knee replacement (UKR), also known as partial knee replacement or half knee replacement is an excellent option in patients where joint damage is confined to one section of the knee. There are 3 main “compartments” of the knee, the medial compartment, the lateral compartment, and the patellofemoral compartment.
Uncompartmental knee replacement involves replacing the surfaces of both the tibia and femur (in the case of medial or lateral UKR), or femur and patella (in the case of patellofemoral joint replacement). The remainder of the knee is left alone, except for the removal of any osteophytes, which are bone growths resulting from arthritis. Importantly, the cruciate ligaments, which are sacrificed in total knee replacement, are kept. This helps maintain normal joint motion and joint position sense.
UKR has many benefits over total knee replacement. The operation is smaller that having a total knee replacement, and as such is associated with
- reduced pain after surgery
- reduced blood loss
- better movement
- earlier return to function
Patients report a much more “normal” feeling knee, as more of the knee is preserved, and the knee rotates in a more normal motion. Studies on UKR have shown a greater proportion of highly satisfied patients when compared to total knee replacement, and fewer dissatisfied patients. Patients report a higher level of activity, and an increased ability to perform more difficult and strenuous activities.
UKR targets only the failing areas of a joint and is a more individualized treatment for a patient’s knee arthritis. Total knee replacement, although very successful, is a one-size-fits-all solution.
Not everyone is suitable for UKR. It is very important to perform a thorough assessment prior to proceeding with surgery, involving a careful history of the pain and symptoms, physical examination, x-rays, and perhaps an MRI scan.
UKR is suitable for your knee if
- the pain is confined only to that segment of the knee
- the other compartments of the knee are normal on imaging
- you have a stable knee with no significant ligament problems
- you have good movement in the knee
- you do not suffer from an inflammatory joint condition such as rheumatoid arthritis
UKR may be seen as a single-step solution to patients with isolated single compartment arthritis. Typically, these patients are older, and lower in their activity levels. Alternatively, it can be used in younger patients as a smaller intervention allowing better function and earlier return to activity. This might be considered to be a staged intervention where years later a total knee replacement may need to be performed if the UKR were to wear out. Young patients who have this option can potentially enjoy the benefits of UKR while they are more active, and have a total knee replacement later in life when activity levels tend to be less.
Rates of UKR have fallen in Australia due to a perception that they are not as successful as Total Knee Replacement. The Australian National Joint Replacement Registry shows that there is a higher risk that a UKR will have to be re-done compared to a total knee replacement. After 10 years, 15.2% of UKR’s will have been re-done, compared with 5.5% of total knee replacements. The most common reasons for this are the implants loosening, or arthritis affecting the other areas of the knee.
Some of this difference in re-do rates may be because surgeons are more likely to revise a failing UKR than a failing total knee replacement because the surgery is more straightforward.
Regardless, it is important that UKR is done in a carefully selected patient, and by a surgeon with experience and a particular interest in UKR. Multiple studies have highlighted that surgeons with a higher rate of UKR have better overall results.
Yes. Bilateral surgery is very well tolerated and is often the best way to proceed if the knees are equally affected. Of course, your general health would need to be taken into account to see whether the anaesthetic and surgery could be performed safely.
Usually around 3-4 nights following surgery for single sided surgery, and 4-5 nights for bilateral surgery.
I am happy for my patients to drive when their knee is bending well, and they are not in pain, and are off any sedating medications. Typically this is around 1-2 weeks following UKR surgery. Typically, office workers will return to work after 2-4 weeks and manual worker at around 4-6 weeks.
The risks of UKR include (but are not limited to):
- Infection – rare but potentially catastrophic. Infection may need further operations to wash out or revise the implants.
- Bleeding – this is minimal in UKR, and modern techniques cause minimal blood loss.
- Stiffness – stiffness can occur after scarring within the knee after surgery. Generally most patients have a similar range of movement to their pre-operative range.
- Pain – pain is expected after surgery, and usually settles within weeks. However some patients may have some mild ongoing pains.
- Wear – the polyethylene in the knee can wear with time, requiring surgery. Sometimes a new polyethylene can be inserted, but occasionally the wear is associated with loosening of the metal components. In this situation, the UKR will have to be revised.
- Loosening – the bond between the metal and the bone can fail, leading to loosening and pain. This requires revision surgery.
- Adjacent compartment arthritis – arthritis may begin to affect the other areas of the knee not replaced by UKR surgery. If this occurs, that area may either be suitable for another UKR, or the entire knee revised to a total knee replacement.
- Dislocation or instability – the components of the knee replacement may jump or slide abnormally, leading to giving way of the joint. This may require revision to a total knee replacement.
- DVT/PE – Deep Vein Thrombosis (DVT) involves formation of blood clot in the deep calf veins. This may occur after surgery, trauma, or even spontaneously. Knee replacement is associated with a higher risk of DVT. Special precautions are usually taken, including compression socks, pneumatic pumps, and either blood thinning tablets or injections. Even despite these measures, DVT can occur. DVT by itself causes calf pain and swelling, but its most concerning consequence is when the clot breaks free and travels to the lungs (called Pulmonary Embolism or PE), causing shortness of breath or chest pain. Very occasionally this can be serious or even life-threatening.
- Fracture – a very rare complication. If this occurs, further surgery or splinting may be required.
- Injury to nearby nerves and blood vessels – very rare, but may be associated with impaired log term function.
- Anaesthetic problems – Anaesthetic agents have been associated with allergic and anaphylactic reactions. In addition, the medications can depress the function of the heart and lungs. In older or more prone patients this may lead to heart attack, stroke, or cardiac failure.