Abstract
Acetabular component malalignment remains the since greatest root cause for revision THA with malposition of at least ½ of all acetabular component placed using conventional methods1. The use of local anatomical landmarks has repeatedly proven to be an unreliable. The reason for this is that the position of local anatomical landmarks varies widely from one patient to another. Another alternative is to simply place acetabular components in a supine position. Unfortunately, cups placed in the supine position under fluoroscopy had the highest incidence of cup malposition in the Callanan study. This is because acetabular anteversion is critically important and pelvic tilt during surgery in the supine position is unknown, uncontrolled, and not correlated with post-operative pelvic tilt.
Image-free surgical navigation can be useful for cup alignment in the absence of pelvic deformity. Image-based surgical navigation can be effective for cup alignment in the presence or absence of pelvic deformity. Unfortunately, while these technologies have been available for a decade, few surgeons employ these technologies. This is likely due to added time, complexity, and expense. Current robotic technology embodies all of these limitations in an even more extreme form.
The HipSextant is a smart mechanical instrument system was developed to quickly and easily achieve accurate cup alignment. The system is image based (CT or MR) and can handle extreme asymmetry and deformity. The instrument 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. Since the planning is provided, the surgeon needs to only review and adjust the plan as desired. Further the system is robust, showing greater accuracy than image-based traditional navigation. Finally, the system takes typically only 3 minutes to use, making it practical for busy practices and hospitals.
