Biomechanical comparison of plate fixation with oblique screws

The aim of this study is to evaluate; plate fixation with screws perpendicular in two plane as in conventional technique, oblique in one plane and angled in two planes, does change the strength of the fixation to bending forces. And is there any correlation between elevated strength and deformity resistance. As the study method; 2,5-3,5 year old sheep rear leg tibias are fixed with the help of a custom made guide to a six hole DCP. Fixation in Group 1: With screws perpendicular in two planes. In Group 2: 20 degree to the shaft axis and perpendicular in the transverse plane. In Group 3: 20 degree to the shaft axis and 7 degree in the transverse plane. We tested these Groups fixation strength with gap-close bending (A) and side bending (B) forces in tree point bending fashion. We statistically analyzed the maximum moment force and deformation at the time of the failure. After the experiments; mean maximum moment force was A1:51.90 Nm, A2:67.47 Nm, A3:82.05 Nm, B1:34.64 Nm, B2:49.91 Nm, B3:49.29 Nm. In gap-close bending tests p value was < 0.05 between Group 1 and the other groups. Between Group 2 and 3 p=0.053. In site bending tests p value was < 0.05 between Group 1 and the other two but not significant between 2 and 3. When two of the bending tests evaluated together p value was significant in only between Group 1 and 3 (p=0.006).The deformity at the time of the maximum moment was not significantly different between any Groups. In consequence, oblique screw placement in two plane increases the strength of the platescrew fixation under bending forces. But there is no degrease of the deformity with elevated strength of the fixation. KEY WORDS: Biomechanics; Fractures; Internal fixation; Plate osteosythesis; Osteoporosis.