Determining Clinically Meaningful Thresholds for the Nonarthritic Hip Score in Patients Undergoing Arthroscopy for Femoroacetabular Impingement Syndrome

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Abstract
Purpose: The purpose of this study was to improve the interpretability of the Nonarthritic Hip Score (NAHS) by determining the minimal clinically important difference (MCID), patient acceptable symptomatic state (PASS), and substantial clinical benefit (SCB) after hip arthroscopy for femoroacetabular impingement. The secondary aim was to identify variables associated with achievement of the thresholds. Methods: Patients who underwent hip arthroscopy for femoroacetabular impingement and completed postoperative questionnaires between August 2019 and March 2020 were included. Patients were excluded if they underwent previous ipsilateral hip surgery, underwent gluteus medius repair, or had a previous hip condition. The MCID, PASS, and SCB thresholds were calculated for the NAHS at minimum 1‐, 2‐, and 5‐year follow‐up. Distribution‐ and anchor‐based methods with receiver operating characteristic analysis were used to determine the thresholds. Multivariate logistic regression was performed to determine predictors of achieving the MCID and PASS. Results: The study included 343 hips with an average follow‐up period of 48 months. On the basis of the distribution‐based approach, the MCID was 8.7 using a method in which the standard deviation of the baseline score was divided by 2. By use of a method in which the standard deviation of the change score was divided by 2, MCID scores of 9.1, 8.3, and 12.6 resulted at a minimum of 1, 2, and 5 years, respectively. The PASS thresholds for these time points were 81.9, 85.6, and 81.9. The absolute SCB thresholds were 91.9, 94.4, and 93.1 and the change score thresholds were 30.6, 24.4, and 29.3 for a minimum of 1, 2, and 5 years, respectively. The preoperative NAHS was positively associated with achievement of the PASS and inversely related to achievement of the MCID. Conclusions: This study provides important clinical thresholds for the NAHS. These thresholds were determined for minimum 1‐, 2‐, and 5‐year time points. The MCID was determined as 8.7, the PASS ranged between 81.9 and 85.6, and the absolute SCB value ranged from 91.9 to 94.4. The preoperative NAHS was found to be positively associated with achievement of the PASS and inversely related to achievement of the MCID. Level of Evidence: Level IV, retrospective case series.

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