Introduction: Three dimensional preoperative planning for each patient has been done in our institution. Anatomical designs of prosthesis are necessary to realize primary stability. The purpose of this study is to visualize the area which concerns about initial stability and load transfer post-operatively.

Methods: A preoperative three-dimensional planning based on CT-scan data was performed. Two different contour prostheses (Versys and Revelation) were studied for each patient.

Distance from central axis of the stem to inside wall of the femoral cortex (A) and distance from central axis of the stem to the surface of the stem (B) were measured. We defined B/A as cortex-stem ratio and mapped it on the surface of the stem like contour lines.

Results: Cortex-stem ratio of Versys stem of proximal femur indicated over 90% at medial, but no more than 70% at anterior, posterior and lateral. In a circumference of distal stem, that ratio was high. On the contrary, cortex-stem ratio of Revelation represented 90~100% at medial and lateral,85~95% at anterior portion.

Discussion: High rate region of cortex-stem ratio represent a great difference between Versys stem and Revelation stem. These region participate in primary fixation and lord transport to femoral cortex. Preoperative three-dimensional mapping is useful technique to better understand the relative position between the stem and the femur, to evaluate which regions were concerned in initial stability after operation and lord transfer later. The visualized result can also suggest the surgeons where and how to prepare the canal efficiently for each design of the stems.