GENETIC INFLUENCES IN THE AETIOLOGY OF FEMOROACETABULAR IMPINGEMENT: A SIBLING STUDY

Abstract

Introduction: Femoroacetabular impingement (FAI) is an important cause of hip pain in young adults and a precursor to osteoarthritis. Genetic factors are important in the aetiology of osteoarthritis of the hip. From a research perspective, FAI is an example of how subtle morphological abnormality results in a predictable pattern of cartilage damage, and thereby offers great potential as a model to study early degenerative disease.

Although many causes of FAI are described, the vast majority of patients give no history of previous hip disease. The purpose of this study was to investigate the extent to which FAI has an underlying genetic basis, by studying the siblings of patients undergoing surgery for FAI and comparing them with controls.

Methods: 66 patients (probands, 29 male, 37 female, mean age 39.1 years) treated surgically for FAI provided siblings for the study. These patients were classified as having cam, pincer or mixed FAI. 101 siblings (55 male, 56 female, mean age 38.2 years) were recruited. The control group consisted of the 77 partners of those siblings (40 male, 37 female, mean age 41.9 years). All subjects underwent clinical (interview, examination, and hip scores) and radiological assessment (standardised AP Pelvic and cross-table lateral radiographs of each hip). Radiographs were scored for the presence of osteoarthritis, and cam- and pincer-type abnormalities.

Results: Participants were classified as a) Normal morphology with no clinical features, b) Abnormal morphology but no clinical features c) Abnormal morphology with clinical signs but no symptoms, and d) Abnormal morphology with symptoms and signs. The sibling relative risks were significant for groups b, c, and d, supporting the hypothesis of an underlying genetic predisposition to FAI. Siblings usually demonstrated the same type of abnormal morphology as the proband. Gender specificity was apparent however, with pincer abnormalities which were usually apparent in female probands being common in sisters but less common in brothers. The brothers of probands with cam deformities almost universally demonstrated the same deformity, although only 50% of sisters did so.

Discussion: Genetic influences are important in the aetiology of FAI. Whether the morphological abnormality is determined at conception or by an inherited predisposition to an acquired event during maturity warrants further study. We have identified a spectrum of disease with a proportion of siblings with abnormal morphology currently asymptomatic. These cohorts present an opportunity to prospectively study the natural history of the condition, improve our understanding of the mechanisms and pathology in early degenerative disease, and potentially to be recruited into clinical trials of surgical and adjuvant treatments.