Dislocation following total hip replacement surgery (THR) remains a significant clinical problem. Malposition of the acetabular component increases the occurrence of impingement, reduces the " safe " range of motion and increases the risk of dislocation. Not fully understanding the interaction between pelvic orientation and final acetabular cup alignment may be one of the main contributing factors in the continued significant incidence of dislocations following total hip replacement. There has been little clinical research to examine the effects of patient positioning and pelvic motion on the alignment of the acetabular implant during total hip replacement surgery. Until now, no tools were capable of accurately measuring these variables during the actual procedure. As part of a broader program in medical robotics and computer assisted surgery, we have developed several enabling technologies that provide surgeons with a new class of image guided measurement tools and assist devices. These surgical navigation tools provide position and alignment information never before available intraoperatively. Our Hip Navigation system (HipNav) continuously and precisely measures and tracks pelvic location and relative implant alignment. HipNav technology is used to gauge current clinical practice and provide intraoperative feedback to surgeons in order to improve the precision and accuracy of acetabular alignment during THR. These tools were successfully introduced into the clinical practice of surgery with results showing that: a) there exist unpredictable and large variations of the initial position of patients' pelvii on the OR table as well as significant pelvic movement during surgery and during intraoperative range of motion testing; b) current mechanical acetabular alignment guides do not account for these variations, and result in variable and in some cases unacceptable acetabular alignment; and c) press fitting oversized acetabular components influences the final cup orientation.

There has been little clinical research to examine the effects of patient positioning and pelvic motion on the alignment of the acetabular implant during total hip replacement surgery. Until now, no tools were capable of accurately measuring these variables during the actual procedure. As part of a broader program in medical robotics and computer assisted surgery, a clinical system has been developed that includes several enabling technologies. The hip navigation system (HipNav) continuously and precisely measures pelvic location and tracks relative implant alignment intraoperatively. HipNav technology is used to gauge current clinical practice and provide intraoperative feedback to surgeons with the goal of improving the precision and accuracy of acetabular alignment during total hip replacement. This system provides surgeons with a new class of image guided measurement tools and assist devices. These tools successfully were introduced into the clinical practice of surgery with results showing the following: (1) There exist unpredictable and large variations in the initial position of patients' pelves on the operating room table and significant pelvic movement during surgery and during intraoperative range of motion testing; (2) current mechanical acetabular alignment guides do not account for these variations, and result in variable and in the majority of cases unacceptable acetabular alignment; and (3) press fitting oversized acetabular components influences the final cup orientation.

During the past year our group has been developing HipNav, a system which helps surgeons determine optimal, patient-specific acetabular implant placement and accurately achieve the desired implant placement during surgery. HipNav includes three components: a pre-operative planner, a range of motion simulator, and an intra-operative tracking and guidance system. The goals of the current HipNav system are to: 1) reduce dislocations following total hip replacement surgery due to acetabular malposition; 2) determine and potentially increase the “safe” range of motion; 3) reduce wear debris resulting from impingement of the implant's femoral neck with the acetabular rim; and 4) track in real-time the position of the pelvis and acetabulum during surgery.