Abstract
Introduction
Distal femur fracture is a critical issue in orthopedic trauma, because it is difficult to manage especially in cases with intra-articular fracture. Osteoporosis may cause instability of implant and increase complications. Few studies investigate on the stability of distal femur osteoporotic fracture and the behaviors under cycling. Our hypothesis was that the stiffness of construct would decrease as cycling in osteoporotic bone.
Materials and Methods
Seven cadaver specimens were used in this study. Relative bone density for each specimen was evaluated using CT scanning by three known calibration phantoms scanned simultaneously with the specimen. All cadaver specimens were divided normal (group 1) and osteoporosis (group 2) in accordance with the bone density. The titanium distal femur locking plates with 6 screws placed in distal femur condyle and 4 in shaft. A 10 mm gap with 65 mm proximal to the center of articular surface and a vertical fractural line between intra-articular were created to simulate AO C2 type fracture. Each specimen was cyclically loaded in two-phase at a frequency of 2 Hz. Phase 1 was set at 1000 N for 10000 cycles. In phase 2, the load was set at 2000 N for 10000 cycles. Then, the specimen was loaded up to failure at a rate of 5 mm/min. Stiffness was evaluated from the linear portion of load-displacement curve at 2000 cycle interval.
Results and Discussion
Figure 1 showed the stiffness deterioration during cycling. Group 1 expresses the cadaveric specimen with normal bone density, and group 2 expresses osteoporosis. The stiffness of group 1 (with normal bone density) decreased for 26.2 % after 20000 cycles, however, group 2 (osteoporotic bone) revealed 90.3 % decay in stiffness. The stiffness decay observably when the load increased from 0 to 1000 N and from 1000 to 2000 N. The maximum load for group1 and group 2 were 4883±134 N and 2538 N, respectively. It can be found the normal bone density group showed intact circular hole, however, the osteoporotic bone revealed an oval contour. The subsidence of screws increased the risk of screw loosening and instability. It can be concluded that the bone quality and cyclic loading could be the important factors that affect the stability and failure strength of the construct.
