[A comparative study of effects on bone healing and remodelling between embracing fixator and bone]

The authors made their own design of sawteeth-arm embracing internal fixator (SEIF) with NiTi shape memory alloy and used for fractured femoral shaft of dogs in comparison with 316L stainless steel plate-screw system. A transverse osteotomy on both sides of femoral diaphyses was performed in 15 adult dogs. One side was plated with bone plate and the other with SEIF. Five animals in each group were killed at 4, 8, 12 weeks after operation and observed under roentgen rays examination, light microscopy and transmission electron microscopy. The results showed that the fracture healing and the course of callus remodelling were similar in these two groups, but the cortical bone remodelling underneath the fixater near osteotomized area was significantly different. Eight-week post-implantation, osteocytes entered into degenerative phase were observed in cortical bone underneath SEIF, and 12-week after operation, the numbers of degenerative osteocytes increased remarkably. While in the case of bone plate, 4-week post-implantation, osteocytes entered into degenerative phase, and 8-week afterwards autolysis occurred in most of the degenerative osteocyles. In other words, the changes of osteocytes phase in bone plate side appeared earlier and more vigorous than that in the SEIF side. The authors are of the opinion that the elastic modulus of NiTi shape memory alloy is lower, the stress-shielding effect in the bone underneath SEIF is less, the axial compression stress of fracture line is kept larger and the contact of SEIF with the bone is not so close that is beneficial to the recovery of blood supply and bone remodelling.