Abstract:

BACKGROUND: The double-rod of bridge-link type combined internal fixation system belongs to eccentric fixation, which may lead to the weakening of longitudinal fixation and the decrease of transverse anti-torsion after operation.

OBJECTIVE: To compare the biomechanical characteristics of bridge-link type combined internal fixation system with mixed-rod and double-rod in the treatment of femoral and tibial fractures.

METHODS: Twenty human long bone diaphysis models were made by 40 short polyformaldehyde materials. Of these, 10 were fixed by mixed-rod, and the rest with bridge-link type combined internal fixation system. Axial compression tests and radial torsion tests were carried out (five models were selected from each group). The changes of axial compression forces and displacements and transverse torque and angle were observed. The maximum load was recorded when the curve had a break point or in a horizontal state, and then the yield load was calculated.

RESULTS AND CONCLUSION: (1) When the axial compression load was ≤ 2 000 N, and with same displacement, the axial compression yield load in the mixed-rod group was larger than that in the bridge-link type combined internal fixation system group. When the axial compression load was > 2 000 N, and with the same displacement, the axial compression yield load in the bridge-link type combined internal fixation system group was larger than that in the mixed-rod group. The maximum axial compression yield load in the bridge-link type combined internal fixation system group was larger than that in the mixed-rod group [(2 420.60±5.67), (2 721.40±5.80) N, t=-82.885, P=0]. (2) When the radial torsional yield load was ≤ 50 N•m, and with the same angle, the torque in the mixed-rod group was less than that in the bridge-link type combined internal fixation system group. When the radial torsional yield load was > 50 N•m, and with the same angle, the torsion in the mixed-rod group was greater than that in the bridge-link type combined internal fixation system group. The maximum radial torsional yield load in the mixed-rod group was larger than that in the bridge-link type combined internal fixation system group [(101.85±2.97), (85.41±2.82) N•m, t=8.985, P=0]. (3) These results indicate that the mixed-rod and of bridge-link type combined internal fixation system can be used to fix the fractures strongly, but the mixed-rod is more stable and reliable, thus it is easier to promote fracture healing. The fracture end is easy to create slight movement after the fracture is fixed with transverse mixed-rod, which is in accordance with elastic fixation. The maximum anti-torsion and anti-fatigue performance is better than the double-rod, which prevents from breakage.

Key words: bridge-link type combined internal fixation system, double-rod, mixed-rod, biomechanics, femoral and tibial fractures, yield load, axial compression