Dedicated Tibial Tuberosity Fixation Plates Provide Comparable Stiffness to Pin and Figure-of-eight Wire Constructs in Ex Vivo Stabilization of Laterally Transposed Tibial Crests.

OBJECTIVE: The objective of this study is to compare the ex vivo biomechanical properties of four fixation techniques for stabilizing tibial tuberosity transposition (TTT) in dogs. STUDY DESIGN: Sixteen cadaveric tibiae from eight large-breed dogs were assigned to one of four groups. Groups were defined by the method used to stabilize the transposed tibial tuberosity: two parallel pins (PP), headless compression screw (HCS), two pins with a figure-of-eight wire (TPF8W), and rapid luxation plate system (RLPS). Following completion of the tibial crest osteotomy, the crest was transposed 4 mm laterally and stabilized according to the assigned treatment group. All constructs were loaded to failure via a force applied to the patellar ligament. Stiffness, load and displacement at yield, maximum load, and failure, and work to failure as well as the nature of the failure were recorded. RESULTS: There were no significant differences between the TPF8W and RLPS constructs in median stiffness (84.2 vs. 72.8 MPa), load to yield (778.3 vs. 644.6 N), or load to failure (786.0 vs. 691.2 N), respectively. Constructs stabilized with PP and HCS were significantly less stiff (with median of 61.7 and 47.6 MPa, respectively) and failed at lower loads (with median of 558.4 and 422.3 N, respectively). Failure modes differed among groups: pin bending occurred in all PP constructs (4/4), screw stripping in all HCS constructs (4/4), and patellar ligament rupture in all TPF8W constructs (4/4); RPLS constructs failed by either patellar ligament rupture (2/4) or tibial fracture (2/4). CONCLUSION: TPF8W and the RLPS provided similar mechanical resistance to forces acting on the TTT and were superior to methods that did not engage the distal tibial crest.