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Friday, March 17, 2000

Computer simulation of THR has many benefits

The use of a computer program for planning and simulation of total hip replacement (THR) surgery has many benefits, say investigators who presented scientific exhibit 26. Precise preoperative planning can help surgeons to better prepare for the surgery and avoid complications associated with reduced range of motion and unexpected leg length change, the investigators said.

The planning is based on CT images obtained preoperatively. The proper size, position and orientation of implant components are selected within the CT scan image. To aid in the placement of implants, the orientation and size of the native acetabulum and femoral head and neck are measured and used as a guideline for initial automatic placement of components. The placement of components is expressed in anatomic reference systems automatically extracted for each bone.

To predict postoperative range of motion, both prosthetic and bone impingement are interactively simulated for leg motion paths that are typically used to test for anterior and posterior instability. Leg length change is continually updated and displayed, as well as the percentage of the cup area in contact with bone. This allows the surgeon to interactively modify both implant selection and orientation until an optimal selection is found for any individual patient. An animation of the patient's range of motion is displayed to visually communicate this information to the surgeon.

The planner has been used routinely as a part of an image-guided THR procedure in a clinical trial. More than 100 cases have been planned using this software. After the preparation of a bone surface model by a technician and the setup of the planner, it takes the surgeon is on average between 5 and 10 minutes for planning and simulation using this approach. The surgeon is presented with an increased amount of information to aid precise preoperative planning, yet the information is presented in a user-friendly fashion.

Another benefit of the planner is the simulation of leg length and offset change, allowing the surgeon to optimally plan the surgery for any individual. Although the planner can be used independently of the surgical procedure, and can serve as an excellent teaching tool, the full benefit is achieved when it is coupled with an image-guided surgical system, which permits precise execution of the surgical plan.

The researchers, all of the Center for Orthopaedic Research, University of Pittsburgh Medical Center Shadyside, Pittsburgh, Pa. are Branislav Jaramaz, PhD, research scientist and co-director; Anthony M. DiGioia III, MD, director; and Constantinos Nikou, MS, research programmer.

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