Evaluation of the effects of holes of various sizes on fracture rates in sheep femurs

Defects in long bones are known to lead to increased risk of pathologic fracture. Holes weaken bones and increase the risk of fracture during bending, especially on exposure to torsional forces. Here, we investigated the effect of holes of varying numbers and sizes drilled into sheep femur bones on the resistance of the bone to torsional forces. Ninety-six fresh sheep femur bones were allocated to 8 groups, which were further subdivided into 4 groups of 3 bones each. In each group, 1 to 4 holes ranging from 2 to 5.5 mm were drilled into the femurs, and the bones were subjected to a rotation test. Forces that caused fractures and the force curves were measured and recorded. The effect of the number and size of the holes drilled in the femurs on the occurrence of fractures was compared using two-way analysis of variance, and Tukey's multiple comparison test was used for multiple comparisons. P < 0.05 was considered statistically significant. We found that the resistance of a bone to torsional forces decreased significantly with increase in the number and size of the drilled holes (P < 0.001). The rate of fractures increased as the number and sizes of the holes increased. The resistance of the bones to torsional forces decreased as the number of holes increased. We showed that the size of a defect in a bone is extremely important for torsional resistance and is, in fact, more important than the number of defects.