Patient factors predict severity of hip symptoms to a greater extent than abnormal bony hip morphology in femoroacetabular impingement syndrome

Abstract

Introduction: Femoroacetabular impingement (FAI) syndrome is a common cause of hip pain in active young adults and a primary contributor to the future development of hip osteoarthritis. Diagnostic imaging is essential for identification of cam and/or pincer morphology in FAI syndrome, though precise diagnostic criteria remain elusive. Patient factors may require consideration, in conjunction with measures of bony morphology, to predict symptom-related consequences in FAI syndrome. This study aimed to determine the morphological parameter(s) and patient factor(s) associated with symptom severity in FAI syndrome. Methods: Ninety-nine participants diagnosed with FAI syndrome (symptoms, clinical examination, and imaging) received standardised plain radiographs and magnetic resonance scans of their affected hip. Alpha angle was measured in four reconstructed radial planes at 30° intervals from superior to anterior. Acetabular version, femoral version, lateral centre edge angle, femoral neck-shaft angle, and anterior centre edge angle were also measured from imaging. Participants completed the international Hip Outcome Tool–33 (iHOT–33) and the 11–point modified UCLA activity score. Univariate linear regression was used to assess the relationship between iHOT–33 score and each morphological parameter and patient factor (i.e. age, sex, body mass index, symptom duration, annual income, health care system) measured. Variables with p < 0.2 were used in a backward stepwise regression model to establish which, if any, were independent predictors of iHOT–33 score. Results: Participants (age 32.9 ± 10.5 years, 44 % female) had an average iHOT–33 score of 41.9 ± 18.8. Higher anterior centre edge angle was associated with a higher iHOT-33 score (p = 0.027). Lower income (p = 0.002) and lower modified UCLA activity score (p < 0.001) were associated with a lower iHOT-33 score. Female participants had worse iHOT–33 scores than males (mean difference –8.6 [95 %CI–1.2, –16.1], p = 0.026) and participants who accessed the public healthcare system had worse iHOT-33 scores than those who accessed the private healthcare system (mean difference –16.7 [95 %CI–9.7,–23.8], p < 0.001). After backwards stepwise elimination, anterior centre edge angle, modified UCLA activity score, sex, and health care system remained as independent predictors of the iHOT–33 score. Discussion: Abnormal bony hip morphology, which by definition is a cornerstone of FAI syndrome, may influence hip-related quality of life to a lesser extent than potentially modifiable factors like activity level. Anterior centre edge angle was the only measure of hip morphology associated with the iHOT–33 score, despite comprehensive bony morphological measurement. Longitudinal prospective investigations are required to establish whether the patient factors identified can predict subsequent structural deterioration in individuals with FAI syndrome.