Cutting directions of bone with biomaterials in situ does influence the outcome of histomorphometrical quantifications

Ten commercially pure titanium implants were inserted in the tibia of ten mature New Zealand white rabbits for a healing period of 3 months. Cut and ground sections were performed on transversely and longitudinally cut tibia bone with implants in situ. Each implant with surrounding bone was processed by (a) dividing it into two parts by cutting transversely through the tibia and then (b) cutting one of the implant halves longitudinally through the tibia. In both cases 10 microns sections were made. Computerized histomorphometrical calculations of the bone-to-metal contact and the bone area in the threads were performed and comparisons of the differently cut sections were made for the same implant. Larger amounts of bone-to-metal contact and bone area in the threads were observed in the longitudinally cut samples in comparison to transversely cut ones. A strong statistically significant difference was obtained when comparing the transversely with the longitudinally cut samples with respect to bony contacts in the cortical region, demonstrating 25% more bone-to-metal contact lengths in the longitudinal cutting direction of the tibia. Quantitative histomorphometrical comparisons should, therefore, be performed on samples that are cut in the same direction.