2021 ISAKOS Biennial Congress Paper
Introducing The Impingement Index: A Study Of The Combined Effect Of Alpha Angle And Femoral Version On Outcomes After Hip Arthroscopy For Fai
Danyal H. Nawabi, MD, FRCS(Orth), New York, NY UNITED STATES
Ronak M. Patel, MD, Manvel, TX UNITED STATES
Ryan S. Selley, MD, New York, New York UNITED STATES
Matthew S. Dooley, MA, Madison, Wisconsin UNITED STATES
Stephanie S Buza, MD, New York, New York UNITED STATES
Anil S. Ranawat, MD, New York, NY UNITED STATES
Bryan T. Kelly, MD, New York, NY UNITED STATES
Hospital for Special Surgery, New York, NY, UNITED STATES
FDA Status Not Applicable
Summary
Patients with significant femoral retroversion and large cam lesions may experience less overall improvement compared with normal or increased version.
Abstract
Introduction
Many studies within the recent literature have sought to identify the effect of femoral version and other morphologic characteristics on outcomes after primary hip arthroscopy for femoral acetabular impingement (FAI). In addition to femoral version and combined version, our group has recently begun to use the 'Impingement Index' to stratify patients undergoing this procedure. We define the impingement index as the alpha angle minus the femoral version.
Purpose
The purpose of the current study is to determine the impact of femoral version, combined version and impingement index on patient reported outcomes after primary hip arthroscopy for FAI.
Methods
A retrospective chart review of prospectively collected data was conducted from 2010-2016 to identify consecutive patients who underwent primary hip arthroscopy for treatment of FAI. Inclusion criteria are pre-operative CT scan, <Tonnis grade 1 degenerative changes, and minimum 1-year follow-up. Demographics, CT measurements (femoral version, acetabular version, alpha angle, and lateral center edge angle), and patient-reported outcomes scores (mHHS, HOS ADL, HOS Sport, QOL), were evaluated. McKibbin and impingement indices were calculated from CT measurements.
Results
A total of 456 hips (200 males, 256 females) met inclusion criteria. The mean age at time of surgery was 28.2 years (+/-10). Average follow-up was 2.6 years (range 23-59 months). The cohort experienced clinical improvement (p<0.001) in all patient-reported outcome measures. The mean improvement was 21.4 points for mHHS, 17.4 for HOS ADL, 29.5 for HOS Sport, and 34.3 for QOL. There was no significant difference in outcomes scores when stratified by femoral version (<5, 5-20, >20), including at the extremes of femoral version (<-5, >30). There was also no significant difference in outcomes scores when patients were stratified by Mckibbin Index (<25, 25-40, >40). The net change in mean HOS Sport for impingement index >75 was also significantly lower than any other category (14.5 (>75) vs. 28.1 (45-75) vs. 25.7 (<45).
Conclusion
Clinically significant improvements can be expected for all femoral version values when a thoughtful algorithm is employed for indicating patients for hip arthroscopy with version abnormalities. However, patients with significant femoral retroversion and large cam lesions may experience less overall improvement compared to patients with normal or increased version. The impingement index may be a valuable tool for predicting outcomes of primary hip arthroscopy for FAI.