| Internal fixation using plates plays an important role in the treatment of the long bone fractures. In conventional plating, the screw functions as an anchor, its axial force being exploited to press the undersurface of the plate against the bone. This results in a large frictional force at the bone-plate interface when the bone is loaded, thus achieving motionless rigid transmission of forces between the plate and the bone surface. However, this contact cause severe disturbance of bone blood supply beneath the plate, result in bone necrosis and remolding, osteoporosis is inevitable. Regional vascular damage not only slows the healing of fracture, but also increases the chance of bone infection. The concept of fracture treatment has changed dramatically in recent years, which transformed from emphasizing mechanical stability of fracture fixation into biological internal fixation. While traditional internal fixation technique is reform, the design of the plate is also improved. The concept of limited contact plate and point contact plate was introduced. Point Contact-Fixator (PC-Fix) , which is still on clinical trail, represents the new development of internal fixation implants. Because it cannot produce dynamic compression between fracture fragments, PC-Fix cannot replace traditional compression plate in some circumstances.Aims directly at the shortcomings of point contact plates and conventional plates, we have developed a Point Contact-Dynamic Compression Plate (PC-DCP). PC-DCP, which consisted of two parts, Dynamic Compression Plate (DCP) and Point Contact Nut (PC NUT), use bi-cortical screws to fix fractures.Fracture stability was enhanced through PC NUT conical tips piercing intocortical bone beneath the plate. Compression was produced through screw tip sliding in plate screw hole. The plate touches the underlying bone only by a few points, so there is a Imm-space between the plate and bone. In order to provide theoretical and experimental basis for future clinical application, the biomechanical and biological characteristics and animal experiments of the PC-DCP were studied using traditional DCP as a control.Firstly, the biomechanical characters of PC-DCP were studied in vitro. Results showed: (1) PC-DCP can effectively compress the fragments of the fracture; (2) The torsion and bending rigidity of PC-DCP bone constructs resembled that of DCP; (3) The stress shielding rate of PC-DCP was 36%, which showed no significant difference between that of DCP. The stress shielding in the cortical bone beneath the plate played an important role. (4) Fractures Compression fixed by both of the PC-DCP and the DCP can greatly decreased the strains on the plate and increased stress conduction between fragments. All above data revealed that there are similar biochemical characteristics between the PC-DCP and the DCP.Secondly, the regional microcirculation in cortical bone, bone structure, bone geometry and biomechanical characteristics of the tibia was compared between the PC-DCP group and DCP group using goat intact tibia as subjects. Results showed: (1) Blood circulation in cortical bone beneath the plate in the DCP group decreased dramatically at Id post operation, ischemia is obvious even 6w post operation, it was normal after 12w. The circulation of cortical bone under plate in the PC-DCP group at 1 d post operation was superior to that of DCP, only little ischemia region was found around the screw holes and the PC NUT tips. After 2 weeks, the circulation was normal and kept high level until 12w. No difference of blood circulation in the opposite cortical bone of the plate was founded between the PC-DCP and DCP; (2) There was obvious osteoporosis in cortical bone beneath the plate in the DCP group and noobvious osteoporosis was observed in the PC-DCP group. At 24w, the underlying bone absorbing took place in both of PC-DCP and DCP. Results suggested: compared with DCP, the PC-DCP can protect the regional blood circulation and prevent the temporary osteoporosis caused by the disturbance o...
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