Good long-term results in older UKR patients

Researchers found only a 14% failure rate at 21 years follow-up.

Older patients who had unicompartmental knee replacement showed promising results in a 21-year follow-up study.

The study did not address the results of unicompartmental knee replacement (UKR) in younger patients, since only 22% of participants were younger than 65 at the time of surgery, said John J. Callaghan, MD, University of Iowa.

“We really wanted to answer a few questions, such as what is the long-term durability of unicompartmental replacement vs. total knee replacement,” he said during a poster presentation at the 118th Annual Meeting of the American Orthopaedic Association.

Fairly durable operation

“From this standpoint ... we thought this was a relatively durable operation, with only a 14% failure rate at 21 years, especially when one considers we included patients who would be better suited with total knee replacement today,” Callaghan said.

His colleague, Richard C. Johnston, MD, performed 136 UKRs in 103 patients between 1975 and 1982. Researchers clinically evaluated the patients using the Hospital for Special Surgery (HSS) knee rating as well as the Knee Society clinical and functional knee scores. They evaluated radiographs for both femoral and tibial loosening and disease progression in the opposite compartment and in the patellofemoral joint.

The patients’ average age was 70.9 years, and their average weight was 175 lbs. “By Iowa standards, that’s really light,” Callaghan said.

At the minimum 21-year follow-up, 14 patients with 19 knee replacements were living; only two patients were lost to the follow-up. The average preoperative and follow-up HSS knee scores were 58 and 74, respectively. The average Knee Society final follow-up clinical score was 72 and the average functional score was 53, Callaghan reported in the abstract.

19 knees revised

Johnston and his associates revised 19 knees during the 21-year follow-up: nine for disease progression, eight for loosening and two for pain. The results were less durable in patients who were younger than 65 years at the time of surgery, the authors wrote in their abstract. The patients with disease progression were typically overcorrected; the patients with aseptic loosening were undercorrected, according to Callaghan.

“I think the data are the key to our conclusion from a technical standpoint,” Callaghan said. “These days, what I try to do is just slightly undercorrect. I think that’s pretty much what most surgeons today agree upon. And the only other important thing is radiographically, there really were not many changes other than the wear of the plastic, this was gamma radiated in air.

“These were all performed using the inlaid technique; Johnston took a burr to prepare the tibia much like Repicci does in his procedure,” Callaghan said. “He burred out the tibia to accept the plastic and, on the femoral side, used the jig mostly for sizing."

“The caveat to overinterpreting these data is that these were patients were relatively old and also had relatively large deformities. The question is whether some of the newer designs, with tighter indications for surgery, will do any better,” Callaghan said.

For more information:
Callaghan JJ, Gardner J, Goetz D, et al. Unicompartmental knee replacement: A minimum 21-year follow-up end result study. #AR5. Presented at the 118th Annual Meeting of the American Orthopaedic Association. June 22-25, 2005. Huntington Beach, Calif.