| Objective1. To study the method of precisely repair clinical large bone defect by computer-aided design, to observe and evaluate the clinical repair efficiency, and to investigate the value of computer aided surgery in the treatment of clinical large bone defect.2. To study the effect of allograft bone compressive strength when drill holes in it, using three-dimensional finite element analysis method to investigate the most appropriate hole diameter and pitch when not significantly affect the compressive strength of allograft bone, and provide a theoretical basis for drilling hole in allograft bone as much as possible.Method1. Retrospective study of 26 cases of large bone defect which precisely repaired by computer-aided design. According to the principle of reverse engineering, all cases were checked with lamellar CT/MRI scanning, which acquired some two-dimensional data in disease area. Computer-aided simulate the precisely repairation of large bone defect before operation:include the three-dimensional reconstruction of disease area, individual analyze bone defect, computer-aided design individual surgical template and individual prosthesis; simulate the reconstruction by computer. Based on the proposal of computer aided design to accurately operation, and allograft bone with matched shape or allograft bone add personalized prosthetic replacement were used to reconstruct the large bone defect. Clinical observation, imaging and functional evaluation was done after surgery.2. The parameter of tubular bone of normal adult middle femur was measured by Mimics 10.0. Three-dimensional model of tubular bone and flat bone were designed by solidworks 2010. The parameter of hole diameter and pitch were graded design, and simulated to drill holes in tubular bone and flat bone, then evaluated the influence of compressive strength when drill holes in three-dimensional model using three-dimensional finite element analysis method, and evaluate the safe critical value of hole diameter and pitch.Result1. All patients were operated successfully. the length of bone defect was 30-207mm before operation, mean 93.7mm; the length of allograft bone was 30-2.7mm, mean 95.5mm. The following up period was from 3-57 months, mean 28.1 months.2 cases appeared wound infection respectively at 4 months and 14 months after operation; two patients relapsed locally at 1.5 years after operation. The bone healing time was 3-9 months, mean 5 months,3 patients take out the fixation respectively at 12,24 and 26 months after operation. According to evaluation criterion of Enneking, for 16 patients who follow up more than 24 months, the mean function score at 6 months after operation was 21.6, while excellent in 4, good in 11, and fair in 1; at 12 months after operation was 24, while excellent in 7, good in 9; at 24 months after operation was 24.7, while excellent in 9, good in 6, and fair in 1;2. Using general evaluation principle, when not significantly affect the compressive strength of allograft bone, to tubular bone the critical value of hole diameter and pitch were 1.5-3,2.0-4,2.5-5,3.0-6,3.5-7,4.0-7; to flat bone the hole diameter and hole pitch were 1.5-2,2.0-3,2.5-4,3.0-5, 3.5-5,4.0-6. While using safety fact evaluation principle, to tubular bone the safe critical value of hole diameter and pitch were 1.5-4,2.0-5,2.5-7, 3.0-8,3.5-9,4.0-10; to flat bone the safe critical value of hole diameter and pitch were 1.5-4,2.0-5,2.5-5,3.0-6,3.5-7,4.0-9.Conclusion1. Computer aided technology could precisely analyze large bone defect from three dimensional perspective, the individual surgical template and individual prosthesis design by CAD, that ensured the operation successfully based on the proposal of computer aided design. It demonstrates good clinical effect to lager bone defect, is a effective treatment method.2. To drill uniform holes in large bone, and then transplant autogenous bone in holes, could improve the effect of bone formation. We recommend hole diameter and pitch were 2.5mm-7mm,3.0mm-8mm,3.5mm-9mm.
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