Bone healing and mineralization, implant corrosion, and trace metals afternickel-titanium shape memory metal intramedullary fixation

Its shape memory effect, superelasticity, and good wear and damping propert ies make the NiTi shape memory alloy a material with fascinating potential for orthopedic surgery. It provides a possibility for making self-locking, self-expanding, and self-compressing implants. Problems, however, may arise because of its high nickel content. The purpose of this work was to determ ine the corrosion of NiTi in vivo and to evaluate the possible deleterious effects of NiTi on osteotomy healing, bone mineralization, and the remodeli ng response. Femoral osteotomies of 40 rats were fixed with either NiTi or stainless steel (StSt) intramedullary nails. The rats were killed at 2, 4, 8, 12, 26, and 60 weeks. Bone healing was examined with radiographs, periph eral quantitative computed tomography, (pQCT) and histologically. The corro sion of the retrieved implants was analyzed by electron microscopy (FESEM). Trace metals from several organs were determined by graphite furnace atomi c absorption spectrometry (GF-AAS) or by inductively coupled plasma-atomic emission spectrometry (ICP-AES). There were more healed bone unions in the NiTi than in the StSt group at early (4 and 8 weeks) time points. Callus si ze was equal between the groups. The total and cortical bone mineral densit ies did not differ between the NiTi and StSt groups. Mineral density in bot h groups was lower in the osteotomy area than in the other areas along the nail. Density in the nail area was lower than in the proximal part of the o perated femur or the contralateral femur. Bone contact to NiTi was close. A peri-implant lamellar bone sheet formed in the metaphyseal area after 8 we eks, indicating good tissue tolerance. The FESEM assessment showed surface corrosion changes to be more evident in the StSt implants. There were no st atistically significant differences in nickel concentration between the NiT i and StSt groups in any of the organs. NiTi appears to be an appropriate m aterial for further intramedullary use because it has good biocompatibility in bone tissue. (C) 1999 John Wiley & Sons, Inc.