Stress analysis of a polyethylene acetabular component in the extreme flexion position—a finite element analysis

Background: Many factors cause impingement of the femoral neck and polyethylene liners. Impingements definitely increase the rate of polyethylene wear. This effect has been a major cause of revision hip surgery. Squatting and sitting cross-legged are specific sitting positions typically used by Asian people, including Thai. These types of positions may cause impingements and abnormal stress distributions, resulting in massive destruction of polyethylene liners.

Objective: To analyze the effects of squatting and sitting in a cross-legged position in total hip replacement patients using finite element analysis.

Methods: A three-dimensional finite element model was developed to study the effects of squatting and sitting in a cross-legged position. The study was divided into two parts. First, mean hip ranges of motion of sitting positions were analyzed. Second, hip ranges of motion at one standard deviation were also analyzed. Locations of the impingement area and stress distribution were demonstrated using finite element software.

Results: Squatting and sitting cross-legged at one standard deviation obviously cause significant impingement at the superior part of the polyethylene liner. Maximum principal stresses are 103 MPa and 24.5 MPa in squatting and sitting cross-legged, respectively. There is no impingement when the mean hip ranges of motion are used. The distance between the neck and cup are 4.05 mm and 4.15 mm in squatting and sitting cross-legged, respectively.

Conclusion: Squatting and sitting cross-legged can cause significant impingement in commonly used total hip replacements. Massive destruction of the prostheses can develop by the process of the impingement.