Computer - Assisted Navigation for Acetabular Cup Placement : a Single Image Guiding System

Incorrect angular placement of the acetabular cup in total hip replacement induces femoral head dislocation, osteolysis, and liner wearing. Some computer-assisted navigation systems to aid acetabular cup placement have been developed in the past decade, but these are not used extensively due to their expense. In this study, a novel algorithm to determine the positions of data points in three-dimensional space from a single-plane image was developed. Based on the validation outcomes, the errors between the true coordinates and the computed coordinates were less than 0.1%. This algorithm was employed in the development of an intrasurgical cup navigation system, which we called the CupNav system. The CupNav system consists of four main hardware components: one digital camera, one laptop, one movable trolley cart, and two self-developed assistant guide frames. In-vitro laboratory validation tests indicated that the possible orientation errors induced by the prototype of CupNav system were less than 1.9 degrees in abduction and 1.4 degrees in anteversion. Although the CupNav system for acetabular cup placement is in the early phase of development, it is clear that the minimal hardware requirement (and hence low cost) of this navigation system makes it suitable for the widespread training and evaluation of inexperienced doctors.