5.7. Peripheral quantitative computed tomography
5.7.1. Callus morphology
The cross-section of the callus at the osteotomy site appeared to have distinct mineralization zones in pQCT. This callus structure with three layers developed in 12 weeks. The high-density outer zone consisted of periosteal callus. At 26 weeks, it was almost equally thick as the original cortex. The original bone cortex formed the middle layer. The inner high-density layer consisted of the thinner endosteal callus (Figure 5-17B). In the distal metaphyseal area outside the osteotomy zone, a separate peri-implant high-density layer first appeared at 4 weeks and was distinct at 26 weeks and later (Figure 5-17C). There were no morphological changes between the two groups. At 60 weeks, the periosteal callus was thick and well mineralized (Figure 5-17A).
5.7.2. Bone mineral density
The total (BMD) and cortical (CtBMD) bone mineral densities did not differ between the NiTi and StSt groups. Distinct differences were seen in various parts of the femur. Mineral density was clearly lower in the osteotomy area than in the nail area out of the osteotomy, which, in turn, showed lower mineral density values than the proximal operated femur. The proximal femurs had no differences compared to the non-operated femurs of the same rats (Figure 5-18A and B). The mean CtBMD in the osteotomy zone increased slightly from 26 weeks (NiTi = 972 ± 78 mg/ccm, StSt = 982 ± 85 mg/ccm) to 60 weeks (NiTi = 1038 ± 195 mg/ccm, StSt = 1100 ± 62 mg/ccm).
Figure 5-17. pQCT scans of various sites of femur after intramedullary nailing (nail removed). PC = peripheral callus, OBC = original bone cortex, EC = endosteal callus, MBL = mineralized endosteal peri-implant bone layer. The scans refer to the areas in the Figure 5-14A, B and C, respectively. A) Callus area proximal to the osteotomy site. NiTi 60 weeks after implantation. B) Osteotomy site 26 weeks after NiTi implantation. A three-layer structure can be seen. C) Metaphyseal area distal to the osteotomy site 26 weeks after NiTi implantation. A mineralized peri-implant layer has developed.
Figure 5-18. A and B. Mean bone mineral density (BMD) in the different zones of the operated femurs 26 and 60 weeks after operation. A) NiTi group and B) stainless steel group. OZ = osteotomy zone(u), NZ = nail zone proximal and distal from osteotomy (o), PF = proximal area of the operated femur(D). The contralateral intact femur served as control = C (X) .