Fit-and-fill analysis of trochanteric gamma nail for the Thai proximal femur: a virtual simulation study.

The present study present a three-dimensional virtual simulation method to evaluate the fit-and-fill effect of the insertion of a trochanteric gamma nail (TGN) in 98 Thai dadaveric proximal femora. The circular best fit of the 2-dimensional cross-section of the femoral canal and the nail at 4 levels [d100, d120, d140 and d160] which were located at 100, 120, 140 and 160 mm distal to the tip of the greater trochanter were calculated. The evaluation of each level included, 1) the diameters of the medullary canal, 2) the percentage of area filled by the nail in the unreamed medullary canal, 3) the minimal reamer diameter that required enlargement of the canal to accommodate TGN insertion, 4) the minimal inner cortical reaming thickness that needed to be removed, 5) the percentage of cortical bone area that needed to be removed prior to nail insertion and 6) the deviation of the nail center from the center of the medullary canal. The results showed that at 4 studied locations the diameter of unreamed medullary canal averaged 10.3 to 11.8 mm. The nail cross-section that could fill the medullary canal averaged 86.9-95.1%. The minimal reaming diameter for the medullary canal to accommodate the TGN insertion averaged 11.3 to 12.3 mm. The inner cortical thickness that should be removed averaged 0.6 to 0.8 mm. The cortical bone that needed to be removed averaged 13.6 to 19.3% of the total cortical area. The deviation of the nail center from the canal center averaged 0.3 to 0.8 mm. The present study showed some mismatching of the TGN to that of the Thai proximal femur. Appropriate reaming to prepare the medullary canal should be considered prior to TGN insertion to prevent technical problem. Future re-design of the implant may be considered for Thai patients.