Fossa-Foveolar Mismatch Is Highest in Dysplastic Hips and During External Rotation.

Purpose To identify which hip pathomorphologies and motions are associated with a high fossa-foveolar mismatch (FFM) index.Methods Three-dimensional models of hips with femoroacetabular impingement syndrome or developmental dysplasia of the hip (DDH) and control hips were analyzed. Simulations of the physiological range of motion and impingement tests were performed using validated collision detection software. The FFM index-the proportion of the fovea tracking outside the acetabular fossa-was calculated for each motion.Results A total of 183 hips with femoroacetabular impingement syndrome and 22 control hips were included. DDH hips showed the highest FFM index (median 0.4), followed by hips with excessive femoral version (median 0.3). Controls had the lowest values (median 0.2). External rotation had the highest FFM in all groups. Motions such as flexion, extension, and abduction had the lowest FFM values.Conclusions DDH and excessive femoral version were linked to increased FFM, while hips from the control group presented the lowest mismatch. From all analyzed motions, the highest FFM was found in external rotation in all groups.Level Of Evidence Level III, retrospective cohort study.