Determining the location of hip joint centre: application of a conchoid's shape to the acetabular cartilage surface of magnetic resonance images.

Preoperative planning, or intraoperative navigation of hip surgery, including joint-preserving procedures such as osteotomy or joint-replacing procedures such as total arthroplasty, needs to be performed with a high degree of accuracy to ensure a successful outcome. The ability to precisely localise the hip joint rotation centre may prove to be very useful in this context. The human hip joint has been shown to be a conchoid shape, and therefore the accurate location of the hip joint centre (HJC) cannot be computed simply as the centre of a sphere. This study describes a method for determining the HJC by applying a conchoid shape to the acetabular cartilage surface of magnetic resonance images, in order to increase the accuracy of the HJC location which had previously been calculated by a functional method using reconstructed three-dimensional surface bony models. By approximating a conchoid shape to the acetabulum, it was possible to compensate for HJC calculation errors.