No abstract

Introduction

Objectives We sought to describe the effect of alterations in hip morphology with respect to worsening hip OA in a community-based sample including African American (AA) and white men and women. Methods This nested case-control study defined case hips as Kellgren Lawrence grade (KLG)<3 on baseline supine pelvis radiographs and KLG≥3 or THR for OA at the 1st or 2nd follow-up visit (mean 6 and 13 years, respectively); control hips had KLG<3 at both visits, with gender/race distribution similar to cases. Hip morphology was assessed using HipMorf software (Oxford, UK). Descriptive means and standard errors were obtained from generalized estimating equation (GEE) models. Sex-stratified GEE regression models (accounting for within-person correlation), adjusted for age, race, BMI, and side were then employed. Results A total of 120 individuals (239 hips; 71 case/168 control) were included (25% male, 26% AA, mean age 62 years, BMI 30 kg/m2). Case hips tended to have greater baseline AP alpha angles, smaller minimum joint space width (mJSW) and more frequent triangular index signs. Adjusted results among men revealed that higher AP alpha angle, Gosvig ratio, and acetabular index were positively associated with case hips; coxa profunda was negatively associated. Among women, greater AP alpha angle, smaller mJSW, protrusio acetabuli, and triangular index sign were associated with case hips. Conclusions We confirmed an increased risk of worsening hip OA due to baseline features of cam deformity among men and women, as well as protrusio acetabuli among women, and provide the first estimates of these measures in AAs.

We report the first population-based prevalence estimates of radiographic hip morphologies relevant to femoroacetabular impingement (FAI) and dysplasia in the USA. These morphologies are very common, with ¼ men and 1/10 women having cam morphology, 1/3 of all adults having mild dysplasia, and 1/15 men and 1/10 women having pincer morphology in at least one hip.

Assessments were performed mid-season and included morphological MRI of both hips at 3T (in addition to a questionnaire, clinical examination, urine collection and physiological MRI). Morphological measurements were performed on 30 degree radial slices using Hipmorf software and included i) alpha angle measuring outline of bone ii) alpha angle measuring outline of cartilage iii) anterosuperior physeal extension (distance from medial femoral head to lateral extent of physis parallel with neck axis and divided by femoral head diameter) iv) metaphysis-neck offset (distance from metaphysis to outer border of femoral head perpendicular to neck axis and divided by femoral head diameter). Results: Maximum alpha angle measured on all radial slices increased with age (bone alpha angle r ¼ 0.47 p<0.0001, cartilage alpha angle r¼0.63 p<0.0001) and was higher in players with any degree of physeal closure (mean 78.6 degrees) compared with players with an open physis (mean 64.0 degrees) (p<0.0001). Alpha angle was highest at the 1 O'Clock position. Using a threshold of 60 degrees at this position, alpha angles were first raised for cartilage at 10 years of age and bone at 13 years of age. In the youngest age groups, raised cartilage alpha angles were secondary to hypertrophy of the outer border of the physis. Beyond 13 years of age, alpha angles were raised secondary to epiphyseal extension at the same site. The prevalence of cam morphology in participants aged over 16 years of age was 75% for bone alpha angle (mean 73.3) and 82% for cartilage alpha angle (mean 77.3). Cam morphology was bilateral in 91% cases and there was no statistically significant difference in the alpha angle between left and right hips. Alpha angle correlated with anterosuperior epiphyseal extension (cartilage r¼0.702 p<0.0001, bone r¼0.500 p<0.0001) but not metaphysis-neck offset (cartilage r¼0.040 p¼0.569, bone r¼0.041 p¼0.564). Absolute offset increased linearly with age at every radial slice (r ¼ 0.88 p<0.0001) and there was no evidence of SUFE. Conclusions: Cartilaginous hypertrophy at the femoral head-neck junction precedes the appearance of an ossified cam lesion. This is consistent with findings from studies that show internal rotation is lost prior to radiographic evidence of FAI. Early morphological changes appear to represent the novel finding of hypertrophy at the groove of Ranvier and perichondral ring of LaCroix that is followed by epiphyseal migration along the anterosuperior femoral neck. It is this mechanism that gives rise to cam morphology within this cohort and not SUFE. We hypothesise that this represents a physiological response to loading and this is compatible with the bilateral nature of the condition. We have now finished recruitment of an age-matched local population control group that will give further insight into cam lesion development.