Biomechanics of internal fixation in Hoffa fractures – A comparison of four different constructs

Abstract

ObjectiveCompare the biomechanical effectiveness of four different bone-implant constructs in preventing fracture displacement under axial loading. MethodsTwenty artificial femora had a standardized coronally oriented fracture of the lateral femoral condyle, representing a Hoffa fracture classified as a Letenneur type I. Four different fixation constructs were applied to the synthetic bones for biomechanical testing. The constructs consisted of a posterolateral (PL) buttressing locking plate in conjunction with two cannulated lag screws inserted from posterior to anterior (PA) – Group 1; Two cannulated screws inserted from anterior to posterior (AP) without plating– Group 2; A posterolateral (PL) buttressing locking plate in isolation – Group 3; and a combination of two lag screws from anterior to posterior (AP) in addition to a horizontal one-third tubular locking plate – Group 4. An axial load was applied to the fracture site with a constant displacement speed of 20 mm/min, and the test was interrupted when a secondary displacement was detected determining a fixation failure. We recorded the maximum applied force and the maximum fracture displacement values. ResultsGroup 1 demonstrated the highest overall bone-implant axial stiffness with the lowest secondary displacement under loading. Groups 3 and 4 showed equivalent mechanical behavior. Group 2 presented the lowest mechanical stiffness to axial loading. The combination of the one-third tubular locking plate with anterior-to-posterior lag screws (Group 4) resulted in 302 % increase in fixation stiffness when compared to anterior-to-posterior lag screws only (Group 2). ConclusionsThis study confirms the mechanical superiority of having a plate applied parallel to the main fracture plane in the setting of coronally oriented femoral condyle fractures. The addition of a horizontal plate, perpendicular to the main fracture plane, significantly increased the resistance to shearing forces at the fracture site when compared to constructs adopting just cannulated screws. Level of evidenceBiomechanical study