Non-locked and locked small fragment straight plates have a similar behavior in buttressing the posteromedial shear tibial plateau fragment: a biomechanical analysis of three different fixations.

Purpose: The aim of this study is to compare the biomechanical behavior of three different fixation constructions currently used for buttressing the posteromedial shearing tibial plateau fragment. Our hypothesis is that non-locked implants provide sufficient comparable stability in posteromedial tibial plateau fractures as locked implants.
Methods: Fifteen left synthetic tibiae from a single manufacturing batch were used to create a posteromedial shear tibial plateau fracture. The fracture was buttressed with three different posteriorly placed five-hole straight small-fragment plate. Five models were fixed with a one-third tubular plate (TTP), five models with a dynamic compression plate (DCP), and five models with a locking compression plate (LCP). All groups were tested to vertical subsidence (Stage 1). In the same experiment (Stage 2), TTP and DCP groups were tested until catastrophic failure. Force versus displacement curves were obtained in the two stages of the experiment.
Results: Stage 1 - There was no significant difference in stiffness (p = 0.89), subsidence up to 2 mm (p = 0.38), and energy (p = 0.36) among the three fixation constructions. Stage 2 - Yield load revealed significantly less yield strength for the TTP group as compared with the DCP group (p = 0.048). However, there was no significant difference in maximum load to failure among the TTP and DCP fixation constructions (p = 0.16).
Conclusion: Placement of either a locked or non-locked small fragment straight plate to buttress the posteromedial shear tibial plateau fragment has a similar biomechanical behavior. When the implant is positioned to buttress the shearing fragment it maximizes biomechanical stiffness.