UKA a viable option for monocompartment knee disease

Proper patient selection key for partial knee arthroplasty success.

Issue: April 2003

NEW ORLEANS — Proper patient selection and operative technique can result in unicompartmental knee arthroplasty results that surpass those of total knees, according to a Philadelphia orthopedist.

“There is no question that they work,” said Peter F. Sharkey, MD, associate professor at the Rothman Institute. “There are numerous studies now that show the results of UKA (unicompartmental knee arthroplasty) are predictable with a high percentage of good and excellent results.” Sharkey spoke at a symposium on surgical options for monocompartmental osteoarthritis of the knee presented at the American Academy of Orthopaedic Surgeons 70th Annual Meeting.

Ideal UKA candidates include patients with monocompartment disease such as osteoarthritis but not inflammatory arthritis. The patient’s anterior and posterior cruciate ligaments should be intact and have a good range of motion.

Surgical technique is paramount with this operation. “Data from the Swedish registry demonstrated that institutions that performed less than 23 unicompartmental procedures per year had an increase incidence for revision,” Sharkey said. “The most common reason for the revisions was too much bone resection on the tibial side, placing the implant in soft cancellous bone, which will cause the implant to subside and lead to aseptic loosening.”

Metal backed

He said one area of contention with UKA proponents is whether or not to use metal-backed tibial components. “The advantages are even distribution of pressure on the bone and enhanced fixation. However, the disadvantages are thinner polyethylene or more bone resection, both of which are bad. Thinner polyethylene leads to increased stress in the poly.” He noted there is no consensus on the issue.

Another difficulty facing UKA proponents is that instrumentation has yet to match that of the total knee. “The total knee has much better instrumentation, it makes it much more foolproof. Another difference is you are working through a much smaller incision, and [with] that lowered exposure, it is harder to ensure that your bone cuts and alignment are correct.”

Pitfalls

Pitfalls to avoid are overcorrection, which will lead to degenerative changes to the opposite compartment. Under correction and malalignment will lead to polyethylene wear. Poor fixation of the tibial component can lead to aseptic loosening.

Tibial component fixation is a historically documented problem with the uni knees. Sharkey addresses this through careful patient selection. “I try to pick patients who I feel will have long-lasting tibial fixation. “These are the lower demand patients, such as those who are older and thinner with good bone stock.”

Sharkey said that 10% to 15% of the knee arthroplasty patients in his practice are candidates for the partial knee procedure. His contraindications include severe deformity, severe flexion contracture, knee stiffness due to cruciate ligament involvement, inflammatory disease or young, high-demand individuals.

A temporizing procedure

One advantage of UKA is that it is a clock-slowing procedure, often giving a patient 10 to 12 years before needing a total knee.

“There is mounting scientific evidence that validates that premise, that it is a temporizing procedure and that it can be converted to a full knee replacement with good results.

“My opinion is that the pain is about 40% to 50% of a full knee, the recovery will be 40% to 50% of the time less than a total knee, and the overall function will feel 40% to 50% more normal than a total knee.”

For your information:

Sharkey PF. Unicompartmental knee replacement. Symposia G. Presented at the American Academy of Orthopaedic Surgeons 70th Annual Meeting. Feb. 5-9, 2003. New Orleans.