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The Effect of Knee Alignment on the Outcome of Unicondylar Knee Replacement Stephen R. Ridgeway, MD, James P. McAuley, MD, Deborah J. Ammeen, BS, Gerard A. Engh, MD To be published in The Journal of Bone and Joint Surgery

Abstract

Background: Many authors have recommended undercorrection of deformity when performing unicompartmental knee arthroplasty (UKA). However, the isolated effect of knee alignment on the outcome of UKA has received little attention in the literature. We undertook this study to evaluate and quantify the effect of alignment on the outcome of UKA.

Methods: One hundred eighty-five UKAs performed by a single surgeon using metal-backed tibial components to manage medial compartment arthritis were reviewed at a minimum five-years after the operation. We measured the tibiofemoral angle preoperatively, four months postoperatively, and at the most recent evaluation. The amount of tibiofemoral angle correction and the subsequent loss of tibiofemoral angle correction were recorded.

Results:  While adjusting for the confounding effects of age, weight, gender, implant type and implant thickness, the mean amount of tibiofemoral angle correction was significantly different between the group of UKAs with a Marmor score of failure (6.8°) and the group with excellent Marmor scores (9.2°) (p =0.034, Multiple Linear Regression). Likewise, the mean amount of correction was also significantly different between patients with Marmor scores of failure (6.8°) and those with poor Marmor scores (11.1°) (p=0.039, Multiple Linear Regression). Similarly, there was a significant difference in the mean amount of tibiofemoral angle correction between the UKAs that were revised (6.6°) and those that were not revised (9.1°) (p=0.033, Multiple Linear Regression). In addition, the revised group of UKAs had a statistically higher percentage of thinner tibial implants (< 8 mm) (19/30 or 63%) than the surviving group of UKAs (42/155 or 27%) (p<0.001, Fisher's Exact test).

Conclusions/Clinical Implications: These statistically significant findings indicate that undercorrection of the tibiofemoral angle in medial compartment UKA should be avoided, particularly if a thin tibial implant (thin polyethylene) is being used.

 

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