Summary

No radiographic indices were found to be predictive of achieving the minimal clinically important difference (MCID) for the modified Hip Harris Score (mHHS), the Hip Outcome Score (both HOS-ADL and HOS-SS) or the international hip outcome tool (iHOT-33) in patients that underwent hip arthroscopy at either one or two-year postoperative follow-up.

Abstract

Background

The relationship between the pre-operative radiographic indices for femoroacetabular impingement syndrome (FAIS) and post-operative patient-reported outcome measures (PROMs) continues to be under investigation with inconsistent findings reported. The purpose of the present study was to apply a machine learning model to determine which preoperative radiographic indices, if any, among patients indicated for arthroscopic correction of FAIS predict whether a patient will achieve the minimal clinically important difference (MCID) for one- and two-year PROMs.

Methods

A total of 1,735 consecutive patients undergoing primary hip arthroscopy for FAIS were included from an institutional hip preservation registry. Patients underwent pre-operative computed tomography (CT) of the hip, from which the following radiographic indices were calculated by a musculoskeletal radiologist: alpha angle; beta angle; sagittal center edge angle; coronal center edge angle; neck shaft angle; acetabular version and femoral version angle. PROMs were completed preoperatively, one year postoperatively, and two years postoperatively for the modified Harris Hip Score (mHHS), the Hip Outcome Score (HOS) Activities of Daily Living Subscale (HOS-ADL) and Sport Specific Subscale (HOS-SS) as well as the international hip outcome tool (iHOT-33). Random forest models were created for each outcome measure at one and two years follow-up, with each outcome measures’ MCID used to establish clinical meaningfulness. Data inputted into the models included ethnicity, laterality, sex, age, body mass index (BMI), and radiographic indices. Comprehensive and separate models were built specifically to assess association for the alpha angle, femoral version angle, coronal center edge angle, McKibbin index, and hip impingement index with respect to each PROM.

Results

The mean difference between one-year and two-year PROMs compared to pre-operative levels exceeded the respective MCIDs for the cohort. As evidenced by poor AUCs and p-values > 0.05 for each model created, no combination of radiographic indices or isolated index (alpha angle, coronal center edge angle, femoral version angle, McKibbin index, hip impingement index) were significant predictors of clinically significant outcome improvement on the mHHS, HOS-ADL, HOS-SS, or iHOT-33.

Conclusion

In patients appropriately indicated for FAIS corrective surgery, clinical improvements can be achieved regardless of pre-operative radiographic indices, such as femoral version, coronal center edge angle and the alpha angle. No specific radiographic parameter or combination of indices was found to be predictive of reaching the MCID for any of the four studied hip specific PROMs at either one or two years follow-up.