The indications for unicompartmental knee arthroplasty are symptomatic single compartment arthritic disease within the knee.
Any condition involving the whole of the knee joint is a contraindication to a unicompartmental knee replacement. The most common contraindication would be an inflammatory arthritis, which would by definition involve the whole of the knee joint.
A patient would usually complain of localised pain on the medial side of the knee which is worse with walking and may be resistant to non-surgical treatment. Occasionally the patient may have had other surgical treatment, such as arthroscopic debridement, but have once again become symptomatic.
Advantages of unicompartmental knee replacement
Total knee replacement is the surgical gold standard for knee arthritis. The problems, however, with total knee arthroplasty include the fact that it is a major operation that carries a number of risks. It can take a number of weeks/months to rehabilitate from it in the acute period. It can involve a longer period of inpatient stay in a hospital. It is, however, a very effective operation.
The current thinking is that if the arthritis of the knee is truly limited to one compartment, then the sensible option is to just replace one compartment. I undertake less invasive unicompartmental knee replacement using a small incision (below) which involves less soft tissue dissection and trauma.
The advantages of less invasive unicompartmental knee replacement over standard incision total knee replacement are:
– Less major operation
– Less pain
– Less bleeding
– Quicker recovery
– Greater range of motion achieved
– Shorter in-patient stay of one to two days
– Quicker return to function
– Greater ability to return to selective recreational activities
– Easier to revise to a total knee replacement if the unicompartmental eventually wears out compared to revising a total knee to a second knee replacement, if the first knee replacement wears out
– Cosmetically appealing as smaller scars than a total knee replacement
MIUKR is a technically demanding operation and requires experience to prevent mal-alignment positioning which can cause early failure of the knee replacement. The x-rays below are of a mal-aligned and mal-rotated MIUKR, done elsewhere.
Indications for a unicompartmental knee replacement
There is some controversy regarding the indications for this surgery. Some surgeons believe that it should not be done in young patients, whereas others feel that it is an ideal operation for older patients. There is some evidence in the literature to suggest that the ideal patient is a slim, female patient between the age of 55 and 70. Most surgeons would agree that young, male patients, involved in heavy manual work or sports are not a suitable candidate for a unicompartmental knee replacement.
Contraindications to MIUKR
Inflammatory arthritis – Any disease involving the whole of the knee joint cannot by definition be truly unicompartmental and therefore, there is no point just doing a unicompartmental knee replacement in such conditions. In these patients who require arthroplasty surgery, the option would be a total knee replacement. Therefore patients with rheumatoid arthritis and similar conditions are not suitable for this operation.
Patients who are grossly overweight – The literature shows that gross obesity or a BMI over 30 to 35, does result in an increased rate of failure of unicompartmental knee replacements and so should not be considered in patients who are obese.
Deformity – The presence of gross contractures/deformities around the knee are also contraindications. Up to 10° of varus, valgus and fixed flexion deformity can be accepted, but more than this is not accepted. The reason for this is that, unlike a total knee replacement, where significant soft tissue releasing and tissue balancing can be carried out to correct the alignment of the knee, this is not done in unicompartmental knee replacement. The aim of unicompartmental knee replacement is to allow the mechanical access to load the replaced compartment, rather than to over correct the joint and cause the mechanical axis to load the other compartments of the knee. Thus in severe deformities which cannot be corrected, the loading forces are too great for the unicompartmental knee replacement and will lead to early wear and failure of the prosthesis.
Knee stiffness – In order to undertake unicompartmental knee replacement, it is a pre-requisite that the knee has a range of motion greater than 90°, which is well accepted by surgeons. Therefore a very stiff knee is not suitable for this procedure.
Other contraindications for MIUKR are similar to those described for total knee replacement.
Isolated patellofemoral joint replacement
Knee arthritis can occasionally involve the patellofemoral compartment primarily. This is more commonly seen in women than it is in men. The patients commonly complain of pain in the anterior knee joint, which is worse going up and down stairs and with prolonged sitting. It can also be painful with squatting.
The radiographs will show severe patellofemoral arthritis, with relative sparing of the tibiofemoral compartment.
Rehabilitation following unicompartmental knee replacement
The rehabilitation protocols are similar for less invasive total knee replacement. They entail swelling control, immediate commencement of a routine of motion exercises and strengthening exercises.
Patients are usually kept in hospital one night to two nights on a CPM machine, to help with elevation and range of motion exercises.
A cold compression device is used to minimise swelling and help with pain relief. A TED stocking is also used to provide graduated compression up the leg and to help prevent deep venous thrombosis.
The patients are discharged home on appropriate oral analgesia with outpatient physiotherapy arrangements made. Patients will normally use crutches for the first few weeks to help with mobilisation and to allow them to walk with a normal gait pattern so as not to limp.