Womac and Late Life Disability Index Important Improvement and Acceptable Symptom State in Knee Replacement

Purpose: Determining achievement of important improvement and or acceptable status from the patient's perspective following an intervention is critical to determine its success. Few studies have determined the Important Improvement (II) or the Patient Acceptable Symptom State (PASS) for WOMAC pain and function and even less so for measures of higher demand activities such as captured by the Late Life Disability Index (LLDI) in total knee replacement (TKR) patients. Also, some prior studies did not use currently accepted anchor-based methods. Finally, data are required to determine how similar or different II and PASS values are for measures applied for the same intervention in different countries. This study determined the WOMAC pain and function subscales and the LLDI limitations subscale II and PASS in people undergoing primary TKR for osteoarthritis (OA) in Ontario Canada. Methods: We followed 251 patients from pre-TKR to 1 year follow-up from one community and two academic hospitals. Participants completed the WOMAC pain and function and LLDI limitation subscales pre- and one-year post-TKR. All were scored 0–100 with higher scores indicating better outcome. At one year, participants also indicated if they were worse or better for each of pain, function, and higher demand activities on a scale ranging from −7 to 7. Those who indicated they were better with a score >5 (a good deal better or more vs moderately better or less) were characterized as having achieved an II. Participants also responded no/yes to questions for each of pain, function, and higher demand activities asking if they were at a level where they could “cope with it and do everything [they needed] to do in their daily life.” This enabled calculation of the PASS. Descriptive statistics were calculated for the sample. Using the anchor-based approach with our corresponding marker questions, II and PASS cut-points were determined using Youden's Index from receiving operating curve (ROC) methods to minimize misclassification bias. As the positive predictive value (PPV) increased when II was calculated by tertile (T) of baseline severity, we report those results. Results: Sample mean age was 65.1 years (range 43–90) and 55% were female. 80% reported at least one comorbid condition. For pain, T1 (mean 26.0, range 0–35) the II was 45; T2 (mean 48.7, range 40–55) the II was 30; and, T3 (mean 71.1, range 60–100) the II was 25. The overall PPV was 0.92. For function, T1 (mean 29.1, range 0–41) the II was 37; T2 (mean 50.6, range 43–59) the II was 20; and, T3 (mean 71.3, range 60–99) the II was 17. The overall PPV was 0.91. For higher demand activities, T1 (mean 49.3, range 18.7–56.2) the II was 8.8; T2 (mean 61.7, range 56.8–66.4) the II was 8.8; and, T3 (mean 75.6, range 67.3–100) the II was 5.3. The overall PPV was 0.87. Overall, 62%, 77% and 74% achieved the II for pain, function and high demand activities. The vast majority of participants responded ‘yes’ to the PASS anchor question (only 28, 29 and 33 (<15%) participants reported ‘no’ for pain, function and higher demand activities respectively) precluding PASS calculation by baseline severity. The PASS for each of pain, function and higher demand activities were 65.0, 68.0 and 70.2/100 respectively based on ROC analyses. The PPV ranged from 0.97–0.98. Conclusions: This work quantifies the II for the WOMAC pain and function subscales and, for the first time, for higher demand activities as measured by the LLDI limitations subscale. These II values accurately classified between 87 and 92% of participants. Given the known large effect for many with TKR, we determined cut-points based on a ‘good deal better or more’ resulting in somewhat higher values than those reported in some literature depending on baseline severity. Unlike other literature, the PASS was not a valuable discriminative metric in this sample as a very high proportion of people responded ‘yes’ to the marker question.