Abstract
Objective The aim of this study was to determine the effect of insertion torque and angulation
on the push-out strength of screws in Atraumatic Rigid Fixation (ARIX) system.
Materials and Methods In vitro mechanical tests of the ARIX system were conducted. Screw plate constructs (n = 120) were tested using five different insertion torques at four different angles
relative to the perpendicular axis of the plate. Before the push-out test, screws
were locked into the plates, and the push-out force of the screw was measured by applying
a load parallel to the screw axis.
Results Implant failure was observed at 0.8 Nm at an insertion angle of 15 degrees, and at
1 Nm at 0 degree, 5 degrees and 10 degrees. Two types of failures were observed: cold
welding and plate deformation. An insertion torque of 0.8 Nm produced a significantly
higher push-out force compared with 0.2 Nm. Non-angled specimens with 0.8 Nm insertion
torque exhibited significantly higher screw push-out forces compared with other tested
specimens and insertion angles. Insertion angle did not affect screw push-out force
at insertion torques of 0, 0.2, 0.4 and 0.6 Nm.
Conclusion The ARIX locking system is much more sensitive to insertion torque than angle. An
effect of insertion angle was observed only at an insertion torque of 0.8 Nm, under
which all angles significantly decreased push-out force relative to zero degrees of
angulation. In addition, low insertion torques can result in screws loosening over
time, while greater insertion torques than 1 Nm can result in screw head stripping
and plate hole deformation.
Keywords
polyaxial locking plate - implant failure - insertion torque - insertion angle - push-out
test
