Development of Fixation Plate and Instrument for Minimally Invasive Surgery in Treatment of Distal Radius Fractures

• Main Authors: Yu Hao Lin, 林昱豪
• Other Authors: M. T. Sun
• Format: Others
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/35962472536763882117

博士 === 長庚大學 === 機械工程學系 === 100 === Fractures of the distal radius are the most common injuries encountered in orthopedics, accounting for approximately 20% of all fractures. The most popular treatment method for unstable distal radius fractures is internal fixation using a metal plate and screw. Although internal fixation is a relatively stable construct that allows early motion, concerns have been raised due to demanding requisite physiological (osteoporosis and fracture configurations) and mechanical problems (internal fixator design and surgical guided instruments), such as minimally invasive surgical (MIS) techniques. The purpose of this study was to design and develop an innovative internal fixator and guided instrument for the MIS surgery. At first, this study was attempted to utilize the FE methods to evaluate the relation of the physiological factor (fractured configuration/fixated type/loading). Secondly, this study determined the relative effects of changes in osteoporosis condition, plate/screw design factors (plate angle/length/width/thickness and screw diameter) and fixation methods (screw number and screw length) on the biomechanical response of dorsal double plating (DDP) fixation at a distal radius fracture to determine the optimal design. The Taguchi method was employed to determine the significance of each design factor in controlling bone/plate/screw stress and distal fragment displacement under axial (100 N), bending (1 N-m) and torsion (1 N-m) loads. The innovative internal fixator and guided instrument was made with stainless steel by the manufacturer with ISO13485 quality management systems and strength evaluated by the experimental test with ASTM-F382, ASTM-F543 standard methods and SAWBONES fatigue tests. The simulated results indicated that postoperative loads with bending and torsion should be avoided as much as possible to decrease the stress values at the bone and fixation plate. The DDP fixation can obtain better mechanical strength to decrease the risk of displacement and stress concentration than that of (Volar plating)VP for different distal extra-articular radius fractures. Simulation results indicated that the order rank to determine the mechanical response was the plate thickness, plate width, screw diameter, and number of screws. Dorsal intermediate (L) plate with 60 mm length, 1.8 mm thickness, 6.0 mm width and 2.8 mm diameter, 20 mm length dual-thread locking screw can be found for optimization. The results of ASTM-F382 testing were show that the mean bending strength was 1.21 ± 0.07 N-m and the fatigue life was 0.45 N-m can pass 1 million loading test. The results of ASTM-F543 testing were show that the mean torsional offset yield strength was 167.1 ± 7 N-cm, the mean maximum insert torque was 14.3 ±1.9 N-cm, the mean maximum remove torque was -14.3 ±1.5 N-cm and the mean maximum pullout strength was 1524.3 ±41 N. The results of SAWBONES fatigue test were show that the average stiffness in 20000 tests cyclic were 425.7 N/mm, 461.1 N/mm and 532.1 N/mm for the 0°, 30° and 60° constructs, respectively. No difference in stiffness was found in the same angled constructs throughout the 20000 cycles of testing (p>0.05). These designs and findings might provide the convenient and efficiency approaches to the MIS surgery.