The Minimal Clinically Important Difference (MCID) for the WOMAC and Factors Related to Achievement of the MCID After Medial Opening Wedge High Tibial Osteotomy for Knee Osteoarthritis

Abstract

Background: Many approaches have been used to determine the minimal clinically important difference (MCID) in patients undergoing total knee arthroplasty, but the MCID for outcome measures after medial opening wedge high tibial osteotomy (MOWHTO) for the treatment of medial compartment knee osteoarthritis (OA) has not been reported. Purpose: To define the MCID for the Western Ontario and McMaster Universities Arthritis Index (WOMAC) after MOWHTO and to identify risk factors for not achieving the MCID. Study Design: Case-control study; Level of evidence, 3. Methods: Among patients with medial compartment knee OA who underwent MOWHTO, 174 patients who were followed for 2 years were included in the study. The MCID and substantial clinical benefit (SCB) for the WOMAC were determined using the anchor-based method with a 15-item questionnaire. Preoperative OA severity was measured by the Kellgren-Lawrence (K-L) grading system, and the acceptable range of the postoperative weightbearing line ratio was 50% to 70%. Patients were divided into 2 groups based on whether the MCID and SCB were achieved, and then factors related to failure to achieve the MCID and SCB were analyzed using multivariate logistic regression analysis. Results: The MCID for the WOMAC was 4.2 points for the pain subscale, 1.9 points for the stiffness subscale, 10.1 points for the function subscale, and 16.1 points for the total. Additionally, the SCB for the WOMAC was 6.4 for pain, 2.6 for stiffness, 16.4 for function, and 25.3 for the total. Overall, 116 (66.7%), 99 (56.9%), 127 (73.0%), and 128 (73.6%) patients achieved the MCID for the WOMAC pain, stiffness, function, and total, respectively, after MOWHTO. The odds of not achieving the MCID for the WOMAC total were 1.09 times greater (95% CI, 1.05-1.13; P < .001) in patients with a low preoperative WOMAC total score (cutoff values: 10.5 for pain, 3.5 for stiffness, 34.5 for function, and 51.0 for the total), 11.77 times greater (95% CI, 3.68-37.70; P < .001) in patients with K-L grade 4 OA compared with K-L grades 2 or 3 OA, and 8.39 times greater (95% CI, 2.98-23.63; P < .001) in patients with undercorrection or overcorrection. A low preoperative WOMAC score, K-L grade 4 OA, and undercorrection or overcorrection were also associated with not achieving the SCB for the WOMAC total (all P < .05). Conclusion: Patients treated with a MOWHTO require a 16.1-point improvement in the WOMAC total score to achieve a MCID from the procedure. Low preoperative WOMAC scores, severe OA, and undercorrection or overcorrection were related to failure to achieve the MCID.

Avoiding Overcorrection to Increase Patient Satisfaction After Open Wedge High Tibial Osteotomy

“…Among these are factors not related to surgery or surgeon, including preoperative medial compartmental cartilage status or patient expectations. 11,28 In our study, not only was greater postoperative WBL ratio associated with inferior postoperative IKDC score, but higher BMI was also correlated with an inferior result. Being overweight is known to be a major factor for increasing knee pain in patients with knee osteoarthritis.…”

“…Some studies noted poor clinical outcomes in patients with overcorrected alignment, but other studies did not demonstrate a significant correlation between overcorrection and inferior clinical outcomes. 7,11,18,27 In our study, overcorrected postoperative alignment was associated with inferior PROs. Taken together, these results allow us to say that overcorrection could lead to less patient satisfaction rather than necessarily to poor results.…”

“…The terms undercorrection and residual varus after high tibial osteotomy are used interchangeably in many studies. 5,10,11,34 It is widely agreed that postoperative residual varus induced poor clinical outcomes after high tibial osteotomy. Conversely, postoperative correction between neutral alignment and targeted alignment showed comparable clinical outcomes.…”

Clinical Usefulness of SPECT/CT for Assessing Postoperative Outcomes After Medial Opening-Wedge High Tibial Osteotomy

“…Among the 61 knees, 26 were excluded for the following reasons: missing preoperative WOMAC score (n ¼ 1), no preoperative SPECT/CT raw data (n ¼ 3), refusal to undergo 3-year follow-up SPECT/CT (n ¼ 20), and 3-year follow-up SPECT/CT examination without hardware removal (n ¼ 2). The final study cohort included 35 knees (31 patients), which were divided into 2 groups based on an MCID threshold of 16.1 points in total WOMAC score according to Kim et al 16 : above-MCID group (n ¼ 22 knees, 62.9%) and below-MCID group (n ¼ 13 knees, 37.1%). Figure 1 outlines the patient inclusion process.…”

“…As clinical results after MOWHTO may vary by individual, 12 the MCID has attracted attention because the results above a clinically meaningful threshold are considered relevant for patients. 2,13 According to Kim et al, 16 the MCID of MOWHTO is 16.1 points for the total WOMAC score. Specifically, patients report that their knee OA symptoms and function improve with MOWHTO only if their postoperative total WOMAC score is at least 16.1 points better than the preoperative total.…”