Abstract
Introduction
Hip resurfacing arthoplasty (HRA) is an alternative to total hip arthroplasty (THA), which has increased in the last years, especially in young patients. A suitable positioning of the resurfacing head is important, mainly because it is strongly related with the neck fracture. The goal of this work was to evaluate the influence of the resurfacing head positioning in the load distribution along the femurs’ structures.
Materials and methods
Using 3D scan technology, the exterior geometry of a composite femur, used to create the FE models, was obtained. Three resurfacing models were used in three different positions in the frontal plane. A model with a positive offset of +5mm (Resurfacing #1), in neutral position (Resurfacing #2), and with a negative offset of −5mm (Resurfacing #3) was developed. A Birmingham® Hip Resurfacing prosthesis was chosen according to the femurs’ head. It was positioned in the femur and acetabulum by an experimented surgeon. The metal on metal contact pair was implemented. Models were aligned with 7° and 9°, considering the position of the anatomical femurs in sagittal and frontal planes. Models were constrained on the wing of the ilium and ischial tuberosity, allowing only vertical and rotational movements on the iliac side. Femurs were constrained on its distal side, allowing only rotational movements.
Results
The most important strains in four different aspects, anterior, posterior, medial and anterior were analyzed. The highest differences occurred on the medial alignment of femurs. Comparing models Resurfacing #1 and Resurfacing #2, the highest displacement increase (11%) comparatively at the neutral position was observed. Besides, comparing models Resurfacing #2 and Resurfacing #3, displacement decrease of 13% (resurfacing #3) in the same region was observed. Thus, one can conclude that: a positive offset increases the strains on the femurs neck; a negative offset decreases the strains on the same region. According to these results, one can state that the risk of neck fracture in resurfacing implants slightly increases as the resurfacing head is positioned with a positive offset. Beyond that region, differences are not relevant.
