Abstract
Introduction
Locking compression plate (LCP) fixation is an established method of treatment of distal third tibial fractures. No biomechanical data exists in the literature regarding their use. Additionally no data exists on the biomechanical advantage of locking screw fixation over non-locking screw fixation for these fractures. In this study the axial and torsional stiffness, axial load to failure and fatigue performance of a 3.5 mm LCP medial distal tibia Synthes plate was evaluated for the stabilisation of distal third tibial fractures. Additionally the performance of the plate in uni and bicortical locked mode as well as non-locked mode was evaluated.
Methods
A standardized oblique fracture pattern was created in the tibial metaphysis of 3rd generation composite tibias, 40 mm from the distal end of the tibia (AO 43-A2.3). A 10mm fracture gap was used to model a comminuted metaphyseal fracture. A 3.5 mm medial distal tibia LCP was applied with bi or unicortical locking or bicortical non-locking screws to 5 tibias respectively. All the bio-mechanical tests were performed on a Bose 3510 Electroforce material testing machine.
A ramp to load, loading profile was used to determine the static axial and torsional performance of the construct. Fatigue testing simulated a 6 week gradual weight bearing régime with the load increasing every two weeks by 400N until either 250,000 cycles were completed or the construct failed.
Results
The non-locked plate demonstrated a significantly higher load to failure than both the bicortical and unicortical locked plates, 683N vs. 575N vs. 483N respectively(p<0.01). The non locked plate also demonstrated significantly higher mean axial stiffness than the bicortical locked plate and unicortical locked plate 632±13 N/mm, 337±12N/mm and 266±6 N/mm respectively (p <0.01). The non locked plate demonstrated the highest torsional stiffness followed by the bi and unicortical locking plates 1.16 ±.08 Nmm vs. 0.79 ± .06 Nmm vs.0.40 ± 0.02 Nmm respectively (p < 0.01). The non locked plate demonstrated higher endurance than the bi and unicortical locking plates over a 6 week simulated fatigue cycle with 1.75mm, 2.10mm and 2.3mm residual displacement at 1600N respectively (p < 0.01).
Discussion
This is the first study that has examined the biomechanical properties of the LCP when used for distal third tibial fractures. A review of the literature suggests LCPs outperform dynamic compression plates in osteoporotic bone but demonstrates no clear biomechanical advantage in using a locking construct in non-osteoporotic bone. In our study the non locked construct outperformed the locked constructs in all parameters assessed. We conclude there is no advantage in using a locking construct for distal third tibial fractures in good quality bone.
