A biomechanical comparison of intramedullary nail and crossed lag screw fixation for tibiotalocalcaneal arthrodesis

This study compared the mechanical bending and torsional properties of intramedullary nail fixation and lag screw fixation for tibiotalocalcaneal arthrodesis. Seven matched pairs of human cadaver lower extremities were studied, with one hindfoot in each pair stabilized with a 12 mm x 150 mm interlocked intramedullary nail inserted retrograde across the subtalar and ankle joints. The contralateral hindfoot was stabilized with two crossed 6.5 mm cannulated screws inserted across both the ankle and subtalar joints. Specimens were subjected to cantilever bending tests in plantarflexion, dorsiflexion, inversion, and eversion and to torsional tests in internal and external rotation. The intramedullary nail construct was significantly (P < 0.05) stiffer than the crossed lag screw construct in all four bending directions and both rotational directions: plantarflexion (nail, 42.8 N/mm; screws, 16.4 N/mm; P = 0.0003), dorsiflexion (nail, 43.0 N/mm; screws, 10.3 N/mm; P = 0.0005), inversion (nail, 37.7 N/mm; screws, 12.3 N/mm; P = 0.0024), eversion (nail, 35.4 N/mm; screws, 10.8 N/mm; P = 0.0004), internal rotation (nail, 1.29 N-m/degree; screws, 0.82 N-m/degree; P = 0.01), external rotation (nail, 1.35 N-m/degree; screws, 0.44 N-m/degree; P = 0.0001). Intramedullary fixation is biomechanically stiffer than crossed lag screws in all bending and torsional directions tested and therefore this construct may aid in maintaining alignment of the hindfoot during union and may help increase fusion rate through increased stability of the internal fixation.