Although the use of three distal bicortical screws in the distal tibial fragment had the greatest acute biomechanical stability compared with two points of distal fixation with or without a medial blocking screw, researchers found no evidence of progressive permanent deformation in any of the fixation methods.
The researchers repaired 21 synthetic tibiae after simulation of a distal tibia metaphyseal fracture with an intramedullary nail and either two bicortical locking screws placed in the two most distal screw holes (IM-L2), three distal bicortical locking screws (IM-L3) or two distal locking screws and a single blocking screw positioned in the sagittal plane on the medial aspect of the nail (IM-L2B). The researchers then tested the specimens under combined cyclic axial and torsional loading for up to 16k cycles.
Results showed all constructs survived 12k cycles without hardware deformation or failure. At the beginning of the test, the researchers found IM-L3 constructs displayed the highest baseline axial stiffness, which was significant compared with the IM-L2 construct; however, no significant differences in baselines axial stiffness was observed between the IM-L3 and IM-L2B constructs.
Compared with the IM-L2 group, the IM-L3 group had smaller relative varus interfragmentary deformation at baseline, according to the researchers. Overall, however, the researchers found no differences in torsional rigidity or relative interfragmentary torsional deformation between groups, as well as no significant difference in the number of cycles to failure, defined as breakage or backout of the distal bicortical screws, fracture of the distal fragment or proximal screw breakage. – by Casey Tingle
Disclosures: Chan received research support from the Foundation of Orthopedic Trauma. Please see the full study for a list of all other authors’ relevant financial disclosures.