When someone has a flexible joint, we usually ascribe the increased range of motion to ligamentous laxity (i.e. loose ligaments). As it turns out, rotational hip flexibility is largely determined not by the ligaments, but rather by the bony alignment of the femur (ball) and acetabulum (socket). We recently published our results in the prestigious Journal of Bone and Joint Surgery (see link) and I’d like to take a moment to describe the significance of our findings.
You may have noticed that children have a remarkable ability to sit on the floor with their legs rotated out to the sides in what is called the “W” position (opposite of cross-legged). This is because we are all born with our femur bones rotated about 40 degrees to the front. As we mature into adults, our femur bones “derotate” to a final rotation of approximately 15 degrees to the front or 15 degrees femoral antetorsion. This change in rotational alignment also changes our hip’s rotational flexibility, which is why you seldom see adults sitting in the “W” position. In rare instances, the femur bone either fails to derotate or does so excessively resulting in an abnormal rotational alignment with correspondingly abnormal rotational range of motion.
Our study demonstrates that by accurately measuring range of motion in clinic, we can predict the rotational alignment of the bones and take them into account in our hip preservation algorithm. Abnormal femoral rotation may contribute to femoroacetabular impingement (FAI) or hip instability and, if severe enough, corrective surgery (derotational femoral osteotomy (DFO)) may be indicated to restore normal alignment.
At SCHI we are actively studying the effects of bony alignment on hip pathology and the need for corrective surgery. Our goal is to provide the least invasive treatment option to get rid of your pain and get you back to the active lifestyle that you enjoy!
Dr. Tigran Garabekyan is a board certified orthopedic surgeon specializing in hip preservation. To learn more about Southern California Hip Institute or to schedule a consultation, click here to contact us. Serving patients in Encino, Sherman Oaks, Van Nuys, North Hollywood, Burbank, Glendale, West Hollywood, Century City, Beverly Hills, Santa Monica, Los Angeles, and other neighboring cities in the greater Los Angeles area.