Background 

The Knee Injury and Osteoarthritis Outcome Score (KOOS) is well known and commonly used to assess young, active patients with ACL injuries. However, this application of the outcome measure has been called into question. There is currently no evidence supporting the structural validity of the KOOS for this patient population. Structural validity refers to whether a questionnaire meant to provide scores on different subscales behaves as intended in the populations of interest. Structural validity should be assessed for all questionnaire measures with multiple items or subscales.

Questions/purposes 

Does the KOOS demonstrate adequate structural validity in young, active patients with ACL tears, when evaluated using (1) exploratory and (2) confirmatory factor analyses?

Methods 

Between January 2014 and March 2017, 1033 patients were screened for eligibility in the Stability 1 randomized controlled trial from nine centers in Canada and Europe. Patients were eligible if they had an ACL deficient knee, were between 14 and 25 years old, and were thought to be at higher risk of reinjury based on the presence of two or more of the following factors: participation in pivoting sports, presence of a Grade 2 pivot shift or greater, generalized ligamentous laxity (Beighton score of 4 or greater), or genu recurvatum greater than 10°. Based on this criteria, 367 patients were ineligible and another 48 declined to participate. In total, 618 patients were randomized into the trial. Of the trial participants, 98% (605 of 618) of patients had complete baseline KOOS questionnaire data available for this analysis. Based on study inclusion criteria, the baseline KOOS data from the Stability 1 trial represents an appropriate sample to investigate the structural validity of the KOOS, specifically for the young, active ACL deficient population.

A cross sectional retrospective secondary data analysis of the Stability 1 baseline KOOS data was completed to assess the structural validity of the KOOS using exploratory and confirmatory factor analyses. Exploratory factor analysis investigates how all questionnaire items group together based on their conceptual similarity in a specific sample. Confirmatory factor analysis is similar but used often in a second stage to test and confirm a proposed structure of the subscales. These methods were used to assess the established five-factor structure of the KOOS (symptoms [seven items], pain [nine items], activities of daily living [17 items], sport and recreation [five items], and quality of life [four items]) in young active patients with ACL tears. Incremental posthoc modifications, such as correlating questionnaire items or moving items to different subscales, were made to the model structure until adequate fit was achieved. Model fit was assessed using chi-square, root mean square error of approximation (RMSEA) and an associated 90% confidence interval, comparative fit index (CFI), Tucker-Lewis index (TLI), as well as standardized root mean square residual (SRMR). Adequate fit was defined as a CFI and TLI > 0.9, and RMSEA and SRMR < 0.08.

Results 

Structural validity of the KOOS was not confirmed when evaluated using (1) exploratory or (2) confirmatory factor analyses. The exploratory factor analysis, where the 42 KOOS items were allowed to group naturally, did not reflect adequate fit for a five-factor model (TLI = 0.828). Similarly, the confirmatory factor analysis used to investigate the KOOS structure as it was originally developed, revealed inadequate fit in our sample (RMSEA = 0.088 [90% CI 0.086 to 0.091]). Our analysis suggested a modified four-factor structure may be more appropriate in young, active ACL deficient patients; however, the final version presented here is not appropriate for clinical use because of the number and nature of post-hoc modifications required to reach adequate fit indices.

Conclusion 

The established five-factor structure of the KOOS did not hold true in our sample of young, active patients undergoing ACL reconstruction, indicating poor structural validity.

Clinical Relevance 

We question the utility and interpretability of KOOS subscale scores for young, active patients with ACL tears with the current form of the KOOS. A modified version of the KOOS, adjusted for this patient population, is needed to better reflect and interpret the outcomes and recovery trajectory in this high-functioning group. A separate analysis with a defined a priori development plan would be needed to create a valid alternative.

中文翻译：

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膝关节损伤和骨关节炎结果评分对于年轻、活跃的 ACL 撕裂患者没有足够的结构有效性

背景 

膝关节损伤和骨关节炎结果评分 (KOOS) 众所周知，通常用于评估年轻、活跃的 ACL 损伤患者。然而，结果测量的这种应用受到了质疑。目前没有证据支持 KOOS 对于该患者群体的结构有效性。结构效度是指旨在提供不同分量表分数的调查问卷在感兴趣的人群中是否按预期表现。应评估所有具有多个项目或子量表的问卷测量的结构效度。

问题/目的 

当使用 (1) 探索性因素分析和 (2) 验证性因素分析进行​​评估时，KOOS 是否在患有 ACL 撕裂的年轻活跃患者中表现出足够的结构有效性？

方法 

2014 年 1 月至 2017 年 3 月期间，来自加拿大和欧洲 9 个中心的 1033 名患者接受了 Stability 1 随机对照试验的资格筛查。如果患者的膝盖有 ACL 缺陷，年龄在 14 至 25 岁之间，并且由于以下两个或多个因素的存在而被认为再次受伤的风险较高：参加旋转运动、存在2 级枢轴移位或更大、全身韧带松弛（Beighton 评分为 4 或更高）或膝关节反曲大于 10°。根据这一标准，367 名患者不符合资格，另外 48 名患者拒绝参加。总共 618 名患者被随机分配参加试验。在试验参与者中，98%（618 名中的 605 名）患者拥有可用于此分析的完整基线 KOOS 问卷数据。根据研究纳入标准，稳定性 1 试验的基线 KOOS 数据代表了研究 KOOS 结构有效性的适当样本，特别是针对年轻、活跃的 ACL 缺陷人群。

完成了稳定性 1 基线 KOOS 数据的横断面回顾性二次数据分析，以使用探索性和验证性因素分析评估 KOOS 的结构有效性。探索性因素分析调查所有问卷项目如何根据特定样本中的概念相似性分组在一起。验证性因素分析类似，但经常在第二阶段使用，以测试和确认子量表的拟议结构。这些方法用于评估已建立的 KOOS 五因素结构（症状 [7 项]、疼痛 [9 项]、日常生活活动 [17 项]、运动和娱乐 [5 项] 以及生活质量 [四项]）年轻活跃的 ACL 撕裂患者。对模型结构进行增量事后修改，例如关联问卷项目或将项目移动到不同的子量表，直到达到足够的拟合。使用卡方、均方根近似误差 (RMSEA) 和相关的 90% 置信区间、比较拟合指数 (CFI)、Tucker-Lewis 指数 (TLI) 以及标准化均方根残差 ( SRMR）。充分拟合定义为 CFI 和 TLI > 0.9，RMSEA 和 SRMR < 0.08。

结果 

当使用 (1) 探索性或 (2) 验证性因素分析进行​​评估时，KOOS 的结构有效性并未得到证实。探索性因素分析（其中 42 个 KOOS 项目被允许自然分组）并未反映出五因素模型的充分拟合（TLI = 0.828）。同样，最初开发的用于研究 KOOS 结构的验证性因素分析显示，与我们的样本拟合不充分（RMSEA = 0.088 [90% CI 0.086 至 0.091]）。我们的分析表明，改良的四因素结构可能更适合年轻、活跃的 ACL 缺陷患者；然而，由于达到足够的拟合指数所需的事后修改的数量和性质，此处提出的最终版本并不适合临床使用。

结论 

已建立的 KOOS 五因素结构在我们接受 ACL 重建的年轻、活跃患者样本中并不成立，表明结构有效性较差。

临床相关性 

我们质疑当前 KOOS 形式的 KOOS 子量表评分对于患有 ACL 撕裂的年轻活跃患者的实用性和可解释性。需要针对该患者群体调整 KOOS 的修改版本，以更好地反映和解释这个高功能群体的结果和恢复轨迹。需要进行单独分析并确定先验开发计划，以创建有效的替代方案。