THE USE OF COMPUTERISED RANGE OF MOTION SIMULATIONS TO DEMONSTRATE THE NEED FOR IMPROVED ACCURACY IN ACETABULAR CUP PLACEMENT IN TOTAL HIP ARTHROPASTY

Abstract

HipNav, a validated CT-based computer simulation software program, was used to calculate prosthetic and native hip ROM using collision detection. High resolution CT scans and CAD models of THA implants were used to create the simulations. Point cloud graphs were developed to graphically represent three-dimensional hip ROM graphs for all combinations of potential motion within maximal ROM parameters based on ligamentous restraints. A total of 27 normal hips were selected from a group of computer assisted total hip patients having surgery on the opposite side. The hips were then segmented and hip motion simulated inside the accepted limits of 50 degrees abduction, 30 degrees of adduction, 45 degrees internal and external rotation, 120 degrees of flexion and 40 degrees of extension

Point cloud graphs of the normal hips provided the baseline for minimal acceptable available motion. Recent literature indicates that acetabular cup placement is quite variable using traditional methods. One thousand five hundred different acetabular component positions (abduction from 30–60 degrees and 0–50 degrees of anteversion) were analyzed based on this data and their corresponding point cloud graphs were overlaid and compared to the native hip point cloud graph. The femoral component was set at 15 degrees of anteversion.

When simulating a THA with a 28mm femoral head and non-augmented liner, regardless of acetabular component positioning, native hip ROM could not be duplicated. Further, many positions inside two standard deviations of reported cup placement accuracy had substantial impingement. This technique provides a graphical tool that will help evaluate THA range of motion and clearly demonstrates how implantation accuracy affects hip ROM and impingement.