SIMULATION OF THE DIRECTION AND DEPTH OF REAMING WITHOUT NOTCHING IN HIP RESURFACING

Abstract

Hip resurfacing has many advantages such as proximal bone conservation and easy revision including conversion to total hip arthroplasty. The major complication in the hip resurfacing is notching at the lateral cortical bone and fracture of the neck. In this research, we simulated the range of direction of reaming without causing notch.

One left femur model was used for the simulation. The femoral head was fitted by a sphere and the origin of Cartesian coordinate was set at the center of the sphere. The simulation was made by imposing a cylindrical cut to the femoral head in varying direction and location. The existence of notching was decided comparing the maximum distance from reaming axis to neck section contour and the radius of cylindrical cut. If the maximum distance is bigger than the radius of cut, the notching exists and vice versa. We simulated existence of notching by varying inclination(α) from 20 to 70 degrees, anteversion(β) from 0 to 30 degree and depth passing through the head center(d) from 0 to 5mm. The implant used for the simulation was Durom^®, Zimmer^©. We selected the implant size that is close to the fitted sphere of femoral head.

No notching was made for any direction when the depth d was less than 2mm. When the depth was 3mm, notching did not generate in the range of α from 43 degrees to 60 degrees and β from 0 to 25 degrees. When the range of depth was from 4mm to 5mm, notching did not generate in ranges of α from 41 degrees to 60 degrees and β from 0 to 29 degrees. The no-notching angle range had tendency increasing slightly when the depth was increased. The angle between the stem of the implant and the neck shaft axis without notching can be calculated from the angle α. When the depth was from 4mm to 5mm, the corresponding angle between stem of implant and the shaft axis was from 120 degrees to 139 degrees.