Issue: July 2013
Perspective from Jack M. Bert, MD
July 01, 2013
3 min read

Study highlights important factors that explain why partial knee arthroplasties fail

Most patients were revised due to aseptic loosening, other factors included lateral progression and wear.

Issue: July 2013
Perspective from Jack M. Bert, MD
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CHICAGO — A study presented at the Knee Society Specialty Day highlighted aseptic loosening as the cause of failure in half of unicompartmental knee arthroplasties and that they are more likely to fail due to pain than total knees.

“Unicompartmentals are revised earlier than total knees,” Michael E. Berend, MD, of the Center for Hip & Knee Surgery in Mooresville, Ind., said during his presentation. “[Unicompartmentals are] much more likely to be revised for pain with unknown outcomes. Fixation remains an issue in the future.”

Bias toward early revision

Berend pointed out there is a bias toward early revision of unicompartmental knee arthroplasty (UKA), but not for total knee arthroplasty (TKA). He said many studies do not consider other factors for failure such as loosening, progressive arthritis, infection, issues with bearings, patient dissatisfaction or pain.

“We have been lulled into thinking all of our total knee replacements do well,” Berend said. “Increasing information from London, Ontario, [Canada] and other places show that it is as high as one in five patients who receive a total knee replacement are not satisfied with their arthroplasty. We need to look at the archer and the arrow when we evaluate our results.”

Michael E. Berend

Michael E. Berend

Causes of failure

To examine the cause for failure of UKAs, Berend and colleagues conducted a retrospective multicenter study that included 813 revision knee arthroplasties performed during a 2-year period. Ten percent of the cohort was UKAs converted to TKAs. The average patient age was 62 years, and the average body mass index was 33. The average time to revision was 4.1 years. The researchers did not determine the number of unrevised UKAs.

The researchers discovered 57% of the patients were revised for aseptic loosening, 11% were revised for pain, 9% involved lateral progression, 6% were revised for instability, 5% for wear, 3% for malalignment and 2% for infection or fracture. The researchers found the rate of revision for pain was 13% for TKA vs. 2% for UKA. Patients who underwent TKAs required revisions at an average of 5.8 years compared to 4.1 years for UKAs. No patients needed revisions for isolated patellofemoral progression.


Berend said the study was limited by its retrospective nature and lack of clear definitions for aseptic loosening and pain levels that necessitated revision.

“The effect of surgical volume of UKA and TKA for surgeons performing partial knee replacement needs to be significantly considered in future studies,” Berend said. “The registry data concludes that there is a higher ‘failure’ rate. The is an apples to oranges comparison between total knees and partial knee replacements. It only accounts for revision and not really failure. Dissatisfied TKA patients are counted as a success in registries that do not get revised. Other authors have reported a five-fold higher revision rate for partial knee replacement compared to TKAs with equal outcome scores. This highlights the difference in thresholds for revision for UKA compared to TKA.” – by Renee Blisard Buddle

Berend K. Why unicompartmental knee arthroplasty fails. Presented at: Knee Society Specialty Day; March 23, 2013; Chicago.
For more information:
Michael E. Berend, MD, can be reached at the Center for Hip & Knee Surgery, 1199 Hadley Rd., Mooresville, IN 46158; email:
Disclosure: Berend receives research support and intellectual property royalties from Biomet for partial and total knee replacement products.