Anteroposterior Thickening of the Femoral Neck With Aging Decreases the “Offset” in Men

Abstract

Background: The contour of the femoral head-neck junction has been shown to have an effect on femoroacetabular impingement (FAI), which can lead to early osteoarthritis of the hip. This study uses computed tomography (CT) to investigate changes in the femoral head, femoral neck, and joint space with aging. Hypothesis: The ratio of the diameter of the femoral head to the diameter of the femoral neck would decrease with increasing age, thus diminishing the “offset” of the femoral neck and being a possible mechanism for cam-type FAI and resultant osteoarthritis. Study Design: Cross-sectional study; Level of evidence, 3. Methods: There were 20 male and 20 female patients from each decade, aged 20 to 80 years, who received pelvic and abdominal CT scans. In the axial plane, the femoral head and neck were measured from anterior to posterior, and the joint space was measured anteromedially. The ratio of the diameter of the femoral head to the diameter of the femoral neck was calculated, and patients with radiographic signs of osteoarthritis were noted. Regression analysis was performed to examine the significance of the relationships between these variables, age, and osteoarthritis. Results: Male and female patients showed significant increases in femoral head diameter and femoral neck diameter as well as decreases in joint space width with increasing age. Male patients showed a decrease in the femoral head-neck ratio (relative neck thickening) of 0.0053 per year (P < .0001) or an average 18% decrease from age 20 to 80 years, while female patients did not show a significant relationship (P = .29). Male patients with signs of osteoarthritis had a smaller femoral head-neck ratio (P < .0001) than those without, while female patients did not (P = .25). Male and female patients with signs of osteoarthritis had a larger femoral head and femoral neck and a more narrow joint space width than those without. Conclusion: Our results suggest that, as men age, they develop a relatively thicker femoral neck that could result in increasing cam impingement, which contributes to the known higher prevalence of osteoarthritis in men. This does not seem to be the case in women, as their femoral neck does not appear to grow as quickly.