Evaluation of hollow and full stems implanted in the rabbit tibia: preliminary results

Full and hollow stems were implanted in the right and left tibiae of five rabbits to study the effects of the implant shape on revascularization and remodelling of the bone after 6 months. No significant difference of periosteal and endosteal circumference was observed when the left and right tibiae of each group were compared. Medullary area was, not surprisingly, significantly smaller in the full stem implanted tibiae. The cortical bone area result was significantly higher in the hollow stem group. In hollow stems, vessels were present both inside and outside the implant with connections through the holes of the implant. The observed differences of cortical bone area can be explained in terms of increased vascular spaces inside the cortical bone of full stem implanted tibiae. This supports the hypothesis that hollow implants provide more space for medullary revascularization and are consequently capable of inducing less endosteal remodelling. Cementless prostheses rely for mechanical fixation on a large interface of the implant with bone. Two factors, i.e. revascularization of the medullary canal and stiffness of the stem, can have a relevant effect on the quality of interface. This non-weight-bearing model suggests the relevance of vascular factors.