According to researchers from the University of Iowa (UI), thigh size in bariatric total hip anthroplasty (THA) patients plays a key role in hip implant failure in total hip replacement patients. During a recent study, the researchers simulated hip dislocations, mirroring how they occur in humans. The results indicate that increased thigh girth facilitates hip instability in morbidly obese patients.

To combat this effect, researchers recommend that surgeons modify surgical procedures in order to minimize the chance of dislocation in bariatric patients and consider alternate designs of hip replacement implants for this patient population. 

Jacob Elkins, MS, UI graduate student, first author of the study, reports that the team has shown morbidly obese patients’ thighs push each other outward and force the implant out of its socket, “Studies have shown up to a 6.9-fold higher dislocation rate for morbidly obese patients compared to normal weight patients,” Elkins and the research team explain.

A University of Iowa news release notes that during the study, Elkins and research collaborators used a computational model to understand how the implant functions in patients and analyzed 146 healthy adults and six cadaver pelvises. Researchers say they investigated the effects of thigh-on-thigh pressure on the hip implant during a wide range of movements from sitting to standing. The release notes that researchers also assessed different implants’ performances in bodies of varying size and type. 

The results suggest that thigh soft tissue impingement increased the risk of dislocation for body mass indexes (BMIs) of 40 or greater. The results also indicate that implants with a larger femoral head diameter did not substantially improve joint stability. 

Thomas Brown, PhD, the study’s senior author, UI professor of orthopedic surgery, recommends that to combat dislocation in this patient population, surgeons can use a high offset femoral stem to effectively shift the leg further away from the center rotation of the joint.

Source: University of Iowa