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


METHODS
Nine 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 64Hz. Specimens were tested in a stepwise progression starting with six times ±125N with a frequency of 1Hz for 250cycles each step was performed (1500cycles). The maximum load was then increased to ±250N for another 14 steps or until specimen failure occurred (up to 3500cycles).


RESULTS
Average bone mineral density was 67.4mgHA/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±2.3mm compared to the A3-group with 11.8±2.9mm (t-test, p<0.01). Failure was registered for the HAN after 4571±1134cycles and after 2344±1195cycles 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).


CONCLUSIONS
The 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.


CONCLUSIONS
The data suggest that both implants allow for sufficient primary stability for TTCF in osteoporotic and consequently also in non-osteoporotic bone.


METHODS
Not applicable, experimental basic science study.
Department for Foot and Ankle Surgery Rummelsberg and Nuremberg, Hospital Rummelsberg, Schwarzenbruck, Germany. Electronic address: martinus.richter@sana.de.
Martinus
M
Richter
Department of Trauma, Hand and Reconstructive Surgery, University of Muenster, Muenster, Germany.
Julia
J
Evers
Department of Trauma, Hand and Reconstructive Surgery, University of Muenster, Muenster, Germany.
Dirk
D
Waehnert
Department for Orthopaedics, Duke University, Durham, NC, USA.
Jim K
JK
Deorio
Department for Orthopaedics, Loyola University Chicago, IL, USA.
Michael
M
Pinzur
Department of Trauma, Hand and Reconstructive Surgery, University of Muenster, Muenster, Germany.
Martin
M
Schulze
Department for Foot and Ankle Surgery Rummelsberg and Nuremberg, Hospital Rummelsberg, Schwarzenbruck, Germany.
Stefan
S
Zech
Department of Trauma, Hand and Reconstructive Surgery, University of Muenster, Muenster, Germany.
Sabine
S
Ochman
D000368:Aged; D000369:Aged, 80 and over; D000843:Ankle Joint / Q000503:physiopathology / Q000601:surgery; D001174:Arthrodesis / Q000295:instrumentation*; D001696:Biomechanical Phenomena; D001858:Bone Nails; D002102:Cadaver; D002111:Calcaneus / Q000601:surgery; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D013628:Talus / Q000601:surgery; D013977:Tibia / Q000601:surgery
Ankle and subtalar arthrodesis; Biomechanical testing; Hindfoot arthrodesis; Intramedullary retrograde nail; Stability; Tibiotalocalcaneal arthrodesis