Punch shear test for quantitative evaluation of bone defect repair in Wistar rat tibia.

INTRODUCTION Bone healing is a complex process influenced by biological and mechanical factors that restores the injured bone's load bearing function. Qualitative methods are usually employed to assess this repair process. This study presents a method of quantitative evaluation of bone repair in circular defects produced in the medial proximal metaphysis of the tibia of rats by means of punch shear tests (PST). OBJECTIVE To describe and test a mechanical punch shear test designed to quantify over time the regeneration of bone defects produced in Wistar rats' tibiae. MATERIAL AND METHODS In seven experimental groups, 3.2 mm in diameter and 1.5 mm deep defects were drilled on the medial surface of both proximal tibial metaphyses of the animals, just below the joint surfaces. The animals of an additional group were maintained with intact tibiae. After one, two, three, four, six, eight and 12 weeks of follow-up, the animals were sacrificed and the tibiae removed. After removing the soft tissue, the tibial proximal metaphyses were embedded in epoxy resin and cut with a diamond cutting blade, in order to obtain bone slices with equal thickness. The PST were carried out in a universal testing machine and the maximum shear forces were measured. RESULTS The forces increased as a function of the follow-up time in the period of one to three weeks (p <0.001); from this follow-up time on, there were no statistical significant differences between the groups, including the intact tibiae. CONCLUSION The test method proved to be suitable to quantitatively assess bone regeneration in monocortical defects produced in the proximal metaphysis of rat tibia within one and three weeks after defect production.