Abstract
Acetabular component malalignment remains the single greatest root cause for revision THA with malposition of at least half of all acetabular components placed using conventional methods. These studies repeatedly document that the concept of using local anatomical landmarks has no scientific basis over a breadth of presenting pathology. Traditional navigation and robotics can potentially lead to improved component placement but these technologies have not gained widespread use due to the increase in time of use, complexity, and cost of these systems. Robotic systems have also proven to be potentially hazardous and inaccurate in routine clinical use. The alternative of placing the cup in the supine position, even with the use of arthroscopy, has been proven to have an incidence of inaccuracy equal or greater than that in the lateral position.
A smart mechanical instrument system was developed to quickly and easily achieve accurate cup alignment (HipXpert System, Surgical Planning Associates, Boston, MA). The system is based on a low dose, low cost CT study and a customised patient-specific surgery plan. The laterally-based system docks on a patient-specific basis with 3 legs: one through the incision behind the posterior rim, one percutaneously on the lateral side of the ASIS, and a third percutaneously on the surface of the ilium. A direction indicator on the top of the instrument points in the desired cup orientation. The anteriorly-based system also docks on a patient-specific basis with one leg on the anterior ischium and one leg on each ASIS, either to skin or to bone.
The lateral system has been proven to be robust, with repeated studies showing accurate cup placement in 100% of cases and an independent study showing accurate cup placement in 98% of cases for both anteversion and inclination. This compares to a recent study of robotic methods that 88% of inclination and 84% for anteversion.
Smart mechanical navigation of cup placement offers the optimum combination of accuracy, speed, and simplicity for solving the ubiquitous problem of acetabular component malorientation.
