Abstract
The etiology of bone refractures after screw removal can be attributed to residual drill hole defects. This biomechanical study compared the torsional strength of bones containing various sized cortical drill defects in a tibia model.
Bicortical drill hole defects of 3 mm, 4 mm, and 5 mm diameters were tested in 26 composite tibias versus intact controls without a drill defect. Each tibia was secured in alignment with the rotational axis of a materials testing system and the proximal end rotated internally at a rate of 1 deg./s until mechanical failure.
All defect test groups were significantly lower (P < 0.01) in torque-to-failure than the intact group (82.80 ± 3.70 Nm). The 4 mm drill hole group was characterized by a significantly lower (P = 0.021) torque-to-failure (51.00 ± 3.27 Nm) when compared to the 3 mm drill hole (59.00 ± 5.48 Nm) group, but not different than the 5 mm hole group (55.71 ± 5.71 Nm). All bones failed through spiral fractures, bones with defects also exhibited posterior butterfly fragments.
All the tested drill hole sizes in this study significantly reduced the torque-to-failure from intact by a range of 28.4% to 38.4%, in agreement with previous similar studies. The 5 mm drill hole represented a 22.7% diameter defect, the 4 mm drill hole a 18.2% diameter defect, and the 3 mm drill hole a 13.6% diameter defect. Clinicians should be cognizant of this diminution of long bone strength after a residual bone defect in their creation and management of patient rehabilitation programs.
•Residual drill holes in composite tibia significantly reduce torque-to-failure from intact.•A 28.4% to 38.4% reduction in tibia strength was observed.•Clinicians should consider long bone strength when creating and managing residual bone defects.
