Measurement Qualities of Hip and Groin Outcome Scores: Letter to the Editor

Dear Editor: It was with great interest that we read the article by Kemp et al, ‘‘Psychometric Properties of Patient-Reported Outcome Measures for Hip Arthroscopic Surgery,’’ and we commend the importance of head-to-head psychometric comparisons of patient-reported outcomes (PROs) for younger patients with hip and groin pain, such as the Copenhagen Hip and Groin Outcome Score (HAGOS), International Hip Outcome Tool (iHOT-33), Hip Outcome Score (HOS), modified Harris Hip Score (mHHS), and now also the Hip Disability and Osteoarthritis Outcome Score (HOOS). Unfortunately, the conclusion in the article by Kemp et al—that parts of the HAGOS, HOS, and mHHS have poor psychometric properties and should not be used for patients undergoing hip arthroscopic surgery because of insufficient responsiveness or content validity—is not supported by the data provided. Furthermore, this recommendation concerning the HAGOS is in direct contrast to the conclusion of a most recent systematic review on study methodology and measurement qualities of existing hip and groin outcome measures for patients undergoing treatment for femoroacetabular impingement. In this review, published in the Journal of the American Academy of Orthopedic Surgeons in July 2013, independent reviewers rated the HAGOS and iHOT-33 to have the best scores regarding quality. The purpose of this commentary is to provide additional clinical insights to some of the methodological limitations in the study by Kemp et al. As stated by Kemp et al in the discussion section, the evaluation of responsiveness and the minimal important change (MIC) of hip and groin outcome scores in their study can only be extrapolated to patients 12 to 24 months after undergoing hip arthroscopic surgery. The clinical rationale for conducting head-to-head comparisons of responsiveness and the MIC during this specific time period only, without including the immediate preoperative and postoperative period, is not clear to us. At the Arthroscopic Centre Amager, Copenhagen, we have prospectively followed our patients undergoing hip arthroscopic surgery for the past 5 years, evaluating PROs using the mHHS and HAGOS, preoperatively and at 3, 6, 12, and 24 months. When using these outcome measures, including all subscales of the HAGOS, we see large clinical improvements (effect sizes ranging from 1-2) within the initial 3 to 6 months after surgery. This observation is in accordance with the existing literature documenting PROs after hip arthroscopic surgery, which shows that the main changes in PROs seem to occur within the first 6 months after surgery, with no or only minimal changes occurring between 12 and 24 months in patients’ pain, physical function, and general health. The data provided by Kemp et al also support this notion by documenting trivial to small effect sizes (\0.3) during this time period (12-24 months after hip arthroscopic surgery) in 12 of the 15 hip and groin outcome measures being evaluated in their study. It therefore seems an illogical choice to evaluate responsiveness—the scores’ ability to detect clinically relevant changes over time—and the MIC of hip and groin outcome scores during a time period in which no or only minimal changes occur. Kemp et al conclude, based on a priori hypotheses, that psychometric properties of hip and groin outcome scores that correlate 0.40 with changes in the global health status, using a global rating scale (GRS), are ‘‘reduced’’ and ‘‘less valuable’’ compared with scores that correlate . 0.40. Interestingly, even though correlations for the HOS (activities of daily living) and mHHS live up to these a priori hypotheses (.0.40) provided by Kemp et al, they are still deemed ‘‘reduced’’ and ‘‘less valuable. ’’ This conclusion by Kemp et al is apparently based on the presence of ceiling effects and the lack of content validity in these measures. However, this conclusion is even more confusing, as the HOOS, which does not have content validity for the patient group in question and also displays ceiling effects, is deemed valuable for patients undergoing hip arthroscopic surgery. Unfortunately, these inconsistencies show that the conclusions provided by Kemp et al are primarily based on personal opinion instead of scientific data. Furthermore, it is important to note that, while correlation sizes are recommended for hypothesis testing of responsiveness for individual PROs, the correlation sizes provided for head-to-head comparisons of the different outcome scores in the study by Kemp et al need to be supported by confidence intervals before conclusions can be made as to which outcome scores/subscales are more or less ‘‘valuable’’ for patients undergoing hip arthroscopic surgery. Correlation sizes of 0.23 to 0.59, including only 32 to 45 data points in the analyses, will provide The American Journal of Sports Medicine, Vol. 42, No. 1 DOI: 10.1177/0363546513514718 2014 The Author(s)