Rates of TKA Based on OA Location and Severity

The number of knee replacements in the US alone is over 600,000 per year, which is more than double the number of hip replacements or any other joint. The factors that lead to a total knee arthroplasty (TKA) include clinical symptoms and radiknee ographic evidence of osteoarthritis (OA). However, there are often discrepancies between radiographic findings and clinical symptoms. Furthermore, there is a scarcity of information in the literature as these findings relate to nonoperative symptom progression and rate of TKA based on the location and severity of OA.

Our research and physical therapy staff at the Shelbourne Knee Center performed a study looking at the rates of TKA based on an individual’s location and severity of OA in the knee joint. The severity of OA is graded by the amount of joint space narrowing on radiographs, mild (<50%), moderate (50-99%) or severe (complete loss of joint space). There are three compartments, or locations, in the knee joint that can develop OA, and some individuals can develop OA in all three, or in just one compartment. The compartments are the medial (inside), lateral (outside), and patellofemoral (PF).

This study looked at 337 patients with knee OA between the years of 2013-2019, and they were divided into 9 groups based on their maximum radiographic grade of OA (mild, moderate, severe) and their location (medial, lateral, or PF). In this study, they excluded anyone who had more than one compartment with the same maximum grade. The enrolled subjects all participated in a standard rehabilitation program focusing first on range of motion (ROM) and then progressing to strength, with a goal of limb symmetry. These patients were then further categorized as “TKA yes” or “TKA no”, which was retrieved from a surgical database or via survey response from the most recent patient contact, which was a mean of 49 months from enrollment. The Knee Injury and Osteoarthritis Outcome Scores (KOOS) were collected at enrollment, 1, 3, 6, and 12 months after enrollment. This survey was stopped if a patient decided to do TKA.

Study Findings

The results of this study showed that patients with medial compartment OA showed statistically significantly different rates of TKA between grades (mild 9%, moderate 20%, severe 43%, p<.001). The lateral and PF compartment rates of having a TKA increased as the severity increased; however, no statistically significant differences were found. Those patients with severe OA were found to have statistically significantly different rates of TKA based on location (medial 43%, lateral 17%, and PF 9%), p=.001, but no differences were found for mild or moderate OA. The subjective KOOS scores were statistically significantly higher for those in the “TKA no” group at 3 and 6 months, p<.05. Patients that showed no improvement or got worse on the KOOS from 1 to 3 months were more likely to have surgery compared to those that improved in the same timeframe. There was not a statistically significant difference in KOOS scores at enrollment based on OA severity or having a TKA in the future.

This study tells us that patients tend to have a TKA at a higher rate when OA at enrollment is severe and the location is in the medial compartment of the knee. Subjective scores at enrollment were similar between OA grades and future “TKA yes” or “TKA no”. Those that did go on to have a TKA had lower scores at 3 and 6 months after enrollment and patients that plateau or regress between 1 and 3 months are 4.8 times more likely to have a TKA compared to those that improve in the same timeframe.

Clinically, patients with knee OA can see improvement in symptoms with conservative treatment and avoid TKA procedures, but these results differ by severity and location of the OA.

This study was submitted and accepted for poster presentations at the 2023 CSM meeting in San Diego, CA and at the AAOS annual meeting in Las Vegas, NV.