Introduction: To mitigate the shortcomings of traditional nonlocking plates, locking compression
plates (LCP) were devised. Due to their angular stability, LCPs can be placed away
from the bone surface, reducing the need for precise anatomical contouring. While
this provides biological advantages, there are associated mechanical shortcomings.
Few studies exist evaluating the mechanical effect of plate-bone distance (PBD). Furthermore,
these studies used small fracture gap models which do not adequately represent comminution,
the most common pattern seen in small animals. Our hypothesis was that outcome measures
would be significantly larger as PBD increased.
Materials and Methods: Mid-diaphyseal 30 mm gap models were created using a previously validated short-fibre
epoxy bone surrogate. Constructs (n = 4/group) were stabilized with 2.0 mm LCPs at one of three PBD (0, 1, and 3 mm)
and tested nondestructively for 10 cycles. Outcome measures (mean torsional compliance
[TC between 0.3 and 0.7 Nm] and maximum angular deformation [AD] from the 10th cycle)
were statistically compared using a one-way ANOVA (p < 0.05). A post hoc Tukey was used to identify means significantly different from
one another.
Results: The 3 mm offset constructs had the highest (p < 0.0006) TC (43.10 ± 0.74 degrees/Nm) and AD (78.06 ± 0.77 degrees) overall. The
TC was higher in the 1 mm offset constructs (39.58 ± 0.77 degrees/Nm; p = 0.0008) compared with 0 mm (36.37 ± 0.88 degrees/Nm), however, the maximum AD was
not different between these (71.66 ± 0.52 and 68.62 ± 2.5 degrees, respectively; p = 0.05).
Discussion/Conclusion: Larger PBD increased construct compliance, resulting in larger angular deformations.
Clinically, this may represent a higher risk of construct failure in nonreconstructible
fractures. Accordingly, our results suggest that PBD should be minimized when using
2.0 LCPs.
Acknowledgment
Support was provided by DePuy Synthes in the form of plate donations.
