N. D. Clement, M. Bardgett, D. Weir, J. Holland, C. Gerrand, D. J. Deehan, Department of Orthopaedics, Freeman Hospital, Newcastle upon Tyne, United Kingdom.
Clin Orthop Relat Res. 2018 Oct;476(10):2005-2014. doi: 10.1097/CORR.0000000000000444.
The WOMAC score is a validated outcome measure for use in patients undergoing TKA. Defining meaningful changes in the WOMAC score is important for sample-size calculations in clinical research and for interpreting published studies. However, inconsistencies among published studies regarding key definitions for changes in the WOMAC score after TKA potentially could result in incorrectly powered studies and the misinterpretation of clinical research results.
QUESTIONS/PURPOSES: (1) To identify the minimum clinically important difference (MCID) for the total WOMAC score and its components 1 year after TKA using an anchor-based methodology. (2) To define the minimum important change (MIC) and the minimum detectable change with 95% confidence (MDC95) for the total WOMAC score and its components 1 year after TKA.
Between 2003 and 2013, 3641 patients underwent primary TKA at one center. Of those, 460 patients (13%) were excluded from this retrospective study for prespecified reasons (mainly secondary OA and bilateral surgery), and 592 patients (16%) were either lost to followup or could not be included because of incomplete questionnaires. WOMAC scores were recorded preoperatively and at 1 year postoperatively. Patient demographics and preoperative Short Form-12 and WOMAC scores were no different for the 16% of patients who were lost to followup or failed to complete 1-year questionnaires and the study cohort (n = 2589). At 1 year, patients were asked "How much did the knee replacement surgery improve the quality of your life?" Their responses were recorded as: a great improvement, moderate improvement, little improvement, no improvement at all, or the quality of my life is worse. The MCID was defined as the difference in the mean change in the WOMAC score between patients with no improvement compared with those with little improvement according to the anchor question. The MIC was defined as the change in the WOMAC score relative to the baseline score for patients who reported a little improvement in their quality of life. The MDC is the smallest change for an individual who is likely to be beyond the measurement error of the scoring tool and represents true change rather than variability in the scoring measure; we report it with 95% confidence bounds defining real change rather than variability in the scoring measure (MDC95). We calculated this with distribution-based methods for the whole cohort. Patients recording a little improvement (n = 211) and no improvement (n = 115) were used as anchor responses to calculate the MCID (using regression analysis to adjust for potential confounding variables such as age, gender, BMI and preoperative Short Form-12 or WOMAC scores) and the MIC (using receiver operative characteristics curves).
After adjusting for confounding variables such as age, gender, BMI as well as preoperative Short Form-12 and WOMAC scores, the MCID was 11 for pain, 9 for function, 8 for stiffness and 10 for the total WOMAC score. The MIC was 21 for pain, 16 for function, 13 for stiffness and 17 for the total WOMAC score. The MDC95 was 23 for pain, 11 for function, 27 for stiffness and 12 for the total WOMAC score.
The MCID and MIC for the WOMAC score represent the smallest meaningful effect sizes when comparing the outcome of two groups (difference in mean change between the groups) or when assessing a cohort (a change in score for the group) after TKA, respectively, helping the reader to distinguish between a clinically important effect size and a mere statistical difference. We determined that the error in measurement (based on the MDC95) for the function component and total WOMAC scores were less than the MIC, which suggests changes beyond the MIC are clinically real and not due to uncertainty in the score. These parameters are essential to interpret TKA outcomes research and to ensure clinical research studies are amply powered to detect meaningful differences. Future studies using the WOMAC score to assess TKA outcomes should report not only the statistical significance (a p value) but also the clinical importance using the reported MCID and MIC values.
Level III, diagnostic study.
WOMAC 评分是一种经过验证的用于接受 TKA 患者的疗效评估工具。定义 WOMAC 评分的有意义变化对于临床研究中的样本量计算和解释已发表的研究结果非常重要。然而，由于手术后 WOMAC 评分变化的关键定义在发表的研究中存在不一致，可能导致研究结果的统计学差异，以及对临床研究结果的错误解释。
问题/目的：（1）使用基于锚定的方法确定 TKA 后 1 年 WOMAC 总分及其各分量的最小临床重要差异（MCID）。（2）定义 TKA 后 1 年 WOMAC 总分及其各分量的最小重要变化（MIC）和 95%置信区间的最小可检测变化（MDC95）。
2003 年至 2013 年间，一家中心对 3641 例患者进行了初次 TKA。其中，460 例（13%）由于规定的原因（主要为继发性 OA 和双侧手术）被排除在这项回顾性研究之外，592 例（16%）因随访丢失或因问卷不完整而无法纳入研究。WOMAC 评分在术前和术后 1 年记录。随访丢失或无法完成 1 年问卷的患者（n=592）和研究队列（n=2589）的患者在丢失率或未完成率、人口统计学特征和术前短表-12 和 WOMAC 评分方面没有差异。在术后 1 年，患者被问到“膝关节置换手术对您的生活质量有多大改善？”他们的回答记录为：“很大改善”、“中度改善”、“略有改善”、“没有改善”或“生活质量更差”。MCID 定义为根据锚定问题，无改善组和略有改善组之间 WOMAC 评分平均变化的差异。MIC 定义为报告生活质量略有改善的患者相对于基线评分的 WOMAC 评分变化。MDC 是个体最有可能超出评分工具测量误差的最小变化，代表真正的变化而不是评分工具的变异性；我们以 95%置信区间（MDC95）报告它，以定义真正的变化而不是评分工具的变异性。我们使用基于分布的方法对整个队列进行了计算。记录略有改善（n=211）和无改善（n=115）的患者被用作锚定反应来计算 MCID（使用回归分析调整潜在混杂变量，如年龄、性别、BMI 以及术前短表-12 或 WOMAC 评分）和 MIC（使用接收器工作特征曲线）。
在调整了年龄、性别、BMI 以及术前短表-12 和 WOMAC 评分等混杂变量后，疼痛的 MCID 为 11，功能的 MCID 为 9，僵硬的 MCID 为 8，WOMAC 总分的 MCID 为 10。疼痛的 MIC 为 21，功能的 MIC 为 16，僵硬的 MIC 为 13，WOMAC 总分的 MIC 为 17。疼痛的 MDC95 为 23，功能的 MDC95 为 11，僵硬的 MDC95 为 27，WOMAC 总分的 MDC95 为 12。
WOMAC 评分的 MCID 和 MIC 分别代表比较两组之间的疗效（组间平均变化差异）或评估队列时（组内评分变化）的最小有意义的效应大小，有助于读者区分临床重要的效应大小和单纯的统计学差异。我们确定功能成分和 WOMAC 总分的测量误差（基于 MDC95）小于 MIC，这表明超过 MIC 的变化在临床上是真实的，而不是由于评分的不确定性。这些参数对于解释 TKA 结果研究以及确保临床研究有足够的能力检测有意义的差异非常重要。未来使用 WOMAC 评分评估 TKA 结果的研究应该不仅报告统计显著性（p 值），还应该使用报告的 MCID 和 MIC 值报告临床重要性。
III 级，诊断性研究。
