Abstract
In order to reduce the risk of dislocation larger femoral heads in total hip arthroplasty (THA) are being used by surgeons in recent years. The standard head size of 28 mm used in 73% of all hip procedures in 2003 was used in only 29% in 2016; whereas head sizes of 32 mm and 36 mm combined, were used in 70%. The increase of head size effectively reduces the thickness of the acetabular cup, altering the load transfer. Herein, this research work investigates the effect of increasing the femoral head size on the stresses of the periacetabular bone at two selected regions: A1 (superior) and A2 (anterior). Three Finite Element models were developed from CT scan data of a hemipelvis implanted with a cemented all-polyethylene acetabular cup with a 50 mm outer diameter and inner diameter to accommodate three head sizes: 28 mm, 32 mm and 36 mm. The peak reaction force at the hip joint during one leg stand for an overweight patient with a body weight of 100 Kg was simulated for head sizes investigated. We found that highest average von Mises stress was 5.7 MPa and occurred in the cortical bone of region A1 which is located within Zone 1 boundaries (Charnley &DeLee); whereas a lower stress of 4.0 MPa occurred at region A2. In the two regions the stresses were the same for the three head sizes. Periacetabular bone was found to be insensitive to the increase of femoral head diameter in cemented THA.
