Biomechanical comparison of canine femurs implanted with either cemented (CFX) or cementless (with lateral bolt) (BFX+lb) total hip replacement under 4-point bending or torsional loads.

Compare biomechanical properties of femurs implanted with either BioMedtrix biological fixation with interlocking lateral bolt (BFX+lb) or cemented (CFX) stems when subjected to 4-point bending or axial torsional forces. Twelve pairs of normal medium to large cadaveric canine femora were implanted with a BFX + lb ( = 12) and a CFX ( = 12) stem-one in the right and one in the left femora of the pair. Pre- and post-operative radiographs were made. Femora were tested to failure in either 4-point bending ( = 6 pairs) or axial torsion ( = 6 pairs), and stiffness, load or torque at failure, linear or angular displacement, and fracture configuration were noted. Implant position was acceptable in all included femora, but CFX stems were placed in less anteversion than BFX + lb stems in the 4-point bending group (median (range) 5.8 (-1.9-16.3) vs. 15.9 (8.4-27.9) anteversion, respectively ( = 0.04)). CFX implanted femora were more stiff than BFX + lb implanted femora in axial torsion (median (range) 2,387 (1,659-3,068) vs. 1,192 (795-2,150) N*mm/, respectively ( = 0.03)). One of each stem type, from different pairs, did not fail in axial torsion. There was no difference in stiffness or load to failure in 4-point bending, or in fracture configuration for either test, between implant groups. Increased stiffness of CFX implanted femurs under axial torsional forces may not be clinically relevant as both groups withstood expected forces. Based on this acute post-operative model using isolated forces, BFX + lb stems may be a suitable replacement for CFX stems in femurs with normal morphology (stovepipe and champagne flute morphology were not tested).