Biomechanical Evaluation of Primary Stiffness of Tibiotalar Arthrodesis with an Intramedullary Compression Nail and Four Other Fixation Devices

Abstract

Background: Many techniques of tibiotalar arthrodesis have been described. Screw fixation is widely used. At our center, intramedullary compression nailing has been successfully used for over 10 years. The question to be answered by this study was whether tibiotalar arthrodesis with a compressed intramedullary nail was superior, in terms of primary stiffness and fusion-site compression, to selected other techniques. Methods: Plane fusion surfaces were machined in third-generation synthetic composite tibiae and the bodies of anatomically correct tali; fixation was with a compressed external fixator (cEF), an uncompressed interlocking nail (uIN), a compressed interlocking nail (cIN), and two different three-screw techniques (ST1 and ST2); three specimens per construct were tested. The compressed contact surface of each construct was measured with pressure-sensitive film and expressed as a percent of the available fusion-site area. Construct stiffness was tested in dorsiflexion/plantar flexion (D/P), varus/valgus (V/V), and internal rotation/external rotation (I/E), analyzing 20 cycles per loading mode. Results: Compressed surface area: cIN 80% ± 10.7; cEF 60% ± 8.6; ST2 59% ± 4.4; ST1 55% ± 6.1; uIN no discernible compression. The greatest primary stiffness in D/P was obtained with the cIN (p < 0.001), followed by ST1. In V/V, ST1 and the cIN had the greatest primary stiffness; the two techniques did not differ significantly. Stabilization with the cEF was significantly better (p < 0.001) than with ST2. In I/E, the cIN produced the greatest primary stiffness (p < 0.001), followed by the two screw techniques, which did not differ significantly between themselves. The uIN had the least primary stiffness in all directions tested. Conclusions: In this biomechanical study, the cIN and ST1 were superior, in terms of primary stiffness in tibiotalar arthrodesis, to the other techniques tested. In D/P and I/E, the cIN construct was signficantly stiffer than the ST1 construct, whose I/E rigidity might, however, be enhanced by a fourth, horizontal screw. Clinical Relevance: Intramedullary compression nailing offers stable tibiotalar arthrodesis fixation with a large bony contact area and may enhance the likelihood of successful tibiotalar arthrodesis.