Preoperative planning tools for total hip arthroplasty

Preoperative planning of total hip replacement is currently performed by the surgeons superimposing the implant templates printed on a translucent sheet on the anterior-posterior and medial-lateral X-ray projections of the patient femur. Due to the sources of error affecting this method, when the combined femoral neck anteversion and external rotation is greater then 15 degrees, a CT-based method of preoperative planning is recommended. This paper describes a CT-based preoperative planning system for total hip replacement: HIPOP. The system presents some innovative aspects on the user interface combining 2D and 3D representations of the patient anatomy and the prosthesis enhancing usability and friendliness. Moreover a set of quantitative fit and fill indicators has been develop to support the surgeon in his planning activity. Preliminary results on the surgeon learning time and repeatibility of the planning activity show that a surgeon with a basic computer knowledge can conclude his first planning session in 10 to 15 minutes. The surgeon planning repeatibility has shown to be rather high: about 1mm of variability in the position of the stem in the transaxial plane, and about 1 degrees variability on the stem orientation. Lower repeatibility has been found in the position of the prosthetic stem along the z direction. Further investigations need to be carried out to clarify this aspect.