Hip OA and Hip Shape

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Estimates of the prevalence of hip osteoarthritis vary widely, from <1% to 27% of adults, with symptomatic hip OA less frequent than radiographic OA; hip OA leads to the majority of hip replacements performed in the U.S (more than 450,000 in 2011).  The risk factors for hip OA are not as well understood as those for knee OA, but include age, genetics, occupational factors, and prior inflammatory arthritis.  In addition, there are local risk factors, such as injury, prior slipped capital femoral epiphysis, and congenital dysplasia of the hip that are specific to the hip joint.  Femoroacetabular impingement (FAI), an entity described since the 1930’s but only recently widely recognized and studied, also appears to be an important risk factor for the development of hip OA.  FAI encompasses a variety of morphologic variations of the femoral or acetabular side of the joint, or both, and is generally measured using a variety of geometric assessments on hip images.  Conventional radiography has been most widely used in OA cohort studies, but smaller surgical series often report on cross-sectional imaging such as MRI or CT.

Dr. Nelson’s K23 award from NIH/NIAMS is funding her work to make assessments of hip shape on films available from the Johnston County Osteoarthritis Project.  She is using both traditional geometric measures and more advanced modeling methods, such as active shape modeling, to describe and compare hip shape by gender, race, and hip OA outcomes.

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This image shows the geometric measures for femoroacetabular impingement and dysplasia as made on a conventional radiograph from the Johnston County Osteoarthritis Project.

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This figure shows an example of variation in a mode of shape using active shape modeling, where the blue line represents the mean shape, the red line is -2 standard deviations and the green line is +2 standard deviations from that shape in the studied population.

 

Dr. Nelson’s work will lead to a better understanding of the frequency of FAI findings in the population, particularly among African Americans, underrepresented in studies to date, as well as the functional and symptomatic impact of these shape alterations. She is also working with international collaborators to better understand the definitions of FAI and to apply shape models to other joint sites.