Ouch. And yes, there is a correlation between patients with larger thighs and hip failure, according to a study conducted by the University of Iowa (UI). Although you might think this is an obvious conclusion, it isn’t. Although weight bearing puts stress on the hip (and any other joint, for that matter), dislocation generally occurs as a result of excessive range of motion. But such an action, as you might imagine, is more difficult for an obese patient to perform.

So a UI grad student decided to dig further to find out exactly why clinical studies have found that the risk for dislocation is higher among the obese. The student, Jacob Elkins, created a computation model that allowed his team to assess the movement of patients of many sizes and thus implants of many difference sizes.

The team found that patients with a BMI of 40 or higher have a greater risk of dislocation due to thigh soft tissue impingement. Other findings were that implants that had a larger femoral head diameter weren’t more stable, and using an implant that has a high-offset femoral stem can lower the risk of dislocation.

What do these findings mean? Well they can help surgeons who treat obese patients, suggest the researchers. They say that the study finds could help surgeons choose better implant designs and alter procedures to reduce the change of hip dislocation in the obese. The UI study was published in the Clinical Orthopaedics and Related Research.

Check out UI’s site for a video simulation of a hip implant dislocation in a morbidly obese patient.

Maria Fontanazza is managing editor at UBM Canon. Follow her on Twitter @MariaFontanazza.