Biomechanical comparison of stability of tibiotalocalcaneal arthrodesis with two different intramedullary retrograde nails

BackgroundThe aim of the study was to compare the initial construct stability of two retrograde intramedullary nail systems for tibiotalocalcaneal arthrodesis (TTCF) (A3, Small Bone Innovations; HAN, Synthes) in a biomechanical cadaver study.MethodsNine pairs of human cadaver bones were instrumented with two different retrograde nail systems. One tibia from each pair was randomized to either rod. The bone mineral density was determined via tomography to ensure the characteristics in each pair of tibiae were similar. All tests were performed in load-control. Displacements and forces were acquired by the sensors of the machine at a rate of 64 Hz. Specimens were tested in a stepwise progression starting with six times ±125N with a frequency of 1 Hz for 250 cycles each step was performed (1500 cycles). The maximum load was then increased to ±250N for another 14 steps or until specimen failure occurred (up to 3500 cycles).ResultsAverage bone mineral density was 67.4 mgHA/ccm and did not differ significantly between groups (t-test, p = .28). Under cyclic loading, the range of motion (dorsiflexion/plantarflexion) at 250N was significantly lower for the HAN-group with 7.2 ± 2.3 mm compared to the A3-group with 11.8 ± 2.9 mm (t-test, p < 0.01). Failure was registered for the HAN after 4571 ± 1134 cycles and after 2344 ± 1195 cycles for the A3 (t-test, p = .031). Bone mineral density significantly correlated with the number of cycles to failure in both groups (Spearman-Rho, r > .69, p < 0.01).ConclusionsThe high specimen age and low bone density simulates an osteoporotic bone situation. The HAN with only lateral distal bend but two calcaneal locking screws showed higher stability (higher number of cycles to failure and lower motion such as dorsiflexion/plantarflexion during cyclic loading) than the A3 with additional distal dorsal bend but only one calcaneal locking screw. Both constructs showed sufficient stability compared with earlier data from a similar test model.Clinical relevanceThe data suggest that both implants allow for sufficient primary stability for TTCF in osteoporotic and consequently also in non-osteoporotic bone.Level of evidenceNot applicable, experimental basic science study.