Biomechanical engineers at the University of Iowa, Iowa City, determined that thigh size in obese people is a reason their hip implants are more likely to fail. In a study, the team simulated hip dislocations as they occur in humans and determined that increased thigh girth creates hip instability in morbidly obese patients.
They suggest that surgeons modify surgical procedures to minimize the chance of dislocation and are select better implant designs for hip replacement implants in obese patients.
“We have shown that morbidly obese patients’ thighs are so large that they are actually pushing each other outward and forcing the implant out of its socket,” says Jacob Elkins, a UI graduate student and first author of the paper published in the journal, Clinical Orthopaedics and Related Research. “When your thighs are real big, they push on the hips.”
They say the best thing surgeons can do is called a “high offset femoral stem,” the portion of the implant that attaches to the patient’s upper thigh bone. The implant’s femoral stem is longer, so it effectively shifts the leg further away from the center rotation of the joint. The thighs then would need to move even further inward before they would push against each another and generate the forces needed for dislocation.
The National Institutes of Health, the Veterans Administration, and the National Center for Resource Resources funded the research.
