Whoever coined the phrase, “a picture is worth a thousand words” never treated a patient with knee osteoarthritis (OA). While knee OA is one of the most common conditions encountered in orthopaedic practice and its diagnosis and treatment are fairly straightforward, predicting the outcomes of total knee arthroplasty (TKA)—the definitive treatment for most cases of end-stage knee OA—can be challenging. The severity of OA on radiographs has long been debated as a tool to aid surgeons in predicting post-TKA outcomes and framing expectations for patients. In general, we tend to say, “The worse the x-ray, the better the patient-reported outcome,” and conversely, “The better the x-ray, the worse the patient-reported outcome.”
Lange et al. investigated this assumption in a study published in JBJS Open Access on July 9, 2020. The authors leveraged data from a 2-arm, randomized controlled trial that evaluated the role of “motivational interviewing” in enhancing rehabilitation following TKA. In their cohort analysis, Lange et al. compared pre- and postoperative WOMAC pain scores and KOOS activities-of-daily-living (ADL) scores with preoperative radiographic severity of knee OA, as measured by the Osteoarthritis Research Society International (OARSI) Atlas score. Among the 240 patients who had 2-year outcome measures and imaging available, the median preoperative OARSI score was 10 (on a scale of 0 to 18), and the authors defined “milder OA” as an OARSI score of <10 and “more severe OA” as a score of ≥10.
The researchers found a cohort-wide postoperative improvement in WOMAC pain and KOOS ADL scores of ~30 points, but they did not find any significant or clinically important differences in pain and function scores between patients with “milder OA” and “more severe OA.” The authors were also unable to demonstrate any correlation between radiographic severity and pain and function scores preoperatively.
Additionally, Lange et al. looked for associations between the WOMAC and KOOS improvements and 4 four other radiographic assessments of knee OA severity (Kellgren-Lawrence grade, compartment-specific OARSI score, compartment-specific joint-space-narrowing score, and 4-level OARSI score). Again, they failed to observe any clinically important postoperative differences in pain or function between the subjects with radiographically milder or more severe OA.
These findings provide further evidence that radiographs should represent only one piece in the puzzle of diagnosis and treatment planning for our patients with knee OA. To me, it’s worth noting that the study capitalized on data from a trial investigating motivational interviewing, which aims to improve outcomes by empowering patients—yet in the multivariable analysis that adjusted for several confounders, use of motivational interviewing was not among them. Still, the many aspects of outcome prediction following knee replacement are most definitely worthy and in need of continued investigation.
David Vizurraga, MD is a San Antonio-based orthopaedic surgeon specializing in adult hip and knee reconstruction and a member of the JBJS Social Media Advisory Board.