Horseshoes and Total Knee Arthroplasty
OrthoBuzz occasionally receives posts from guest bloggers. This guest post comes from Matthew Herring, MD, in response to a recent JBJS article.
The old adage that “close only counts in horseshoes” may also apply to total knee arthroplasty (TKA). Much attention has been paid to coronal alignment during TKA based on conventional wisdom that prosthetic durability and patient function are strongly dependent on that parameter. To re-check that hypothesis, in the March 21, 2018 issue of JBJS, Abdel et al. evaluated the influence of coronal plane alignment on implant survival by analyzing results from a large cohort of patients who underwent primary TKA 20 years ago.
In 2010, Abdel’s group reviewed a consecutive series of 398 primary cemented TKAs done between 1985 and 1990. Knees were divided into 2 groups based on their mechanical alignment as measured using a full-length hip-knee-ankle radiograph. Knees in the “aligned group” (n = 292) were defined as having alignment within 0° ± 3° of the mechanical axis, and knees in the “outlier group” (n = 106) were defined as having alignment >3° in varus or valgus. Implant survival was evaluated based on the need for revision, and the specific indications for revisions were recorded.
In the current study, at 20 years of follow-up, the authors found revision rates that were not significantly different between the same 2 groups—19.5% in the mechanically aligned group and 15.1% in the outliers. Multivariate analysis controlling for patient age and BMI did not demonstrate any implant survivorship benefit for the mechanically well aligned group as compared to the outliers.
This study seems to call into question the dogma that a neutral mechanical axis protects against mechanical failure. The effort, time, and money spent on techniques and devices to improve coronal plane alignment by a few degrees (i.e., computer navigation, custom jigs, and robotics) may not translate into meaningful improvements in patient outcomes.
It is important to note that in this group’s 2010 study evaluating the same cohort, 66% of knees in the outlier group were only 4° shy of neutral and only 12% (13 knees) were >6° off. So, while we should still strive for neutral mechanical alignment, it seems that we may miss the neutral mark by a few degrees without harming our patients.
Matthew Herring, MD is a senior orthopaedic resident at the University of Minnesota and a member of the JBJS Social Media Advisory Board.