OBJECTIVES: To determine whether there are differences in stability between double and triple interlocked intramedullary nails used for the fixation of extraarticular proximal tibial fractures. DESIGN: Randomized in vitro biomechanical-experimental laboratory investigation. SETTING: Biomechanics laboratory of the Clinic for Trauma Surgery at the Johannes Gutenberg-University Mainz. INTERVENTION: A 10-mm defect osteotomy was performed on six paired human tibiae, and the proximal and distal ends were potted in polymethylmethacrylate cement (PMMA). Each pair of bones was randomly stabilized with an intramedullary nail (IM-nail) with two interlocking options (PTN 2s) in one tibia, and with an IM-nail with three interlocking options (PTN 3s) in the corresponding contralateral bone. A biomechanical test of the bone implant construct was then performed with an axial force of 900 N. Displacement of bone fragments was measured and depicted as a force-displacement diagram. MAIN OUTCOME MEASUREMENTS: Biomechanical construction stiffness. RESULTS: The stiffness values for PTN 3s were significantly higher than for PTN 2s. In the group of PTN 2s, two out of six implants failed biomechanically with breakage of one proximal interlocking screw. CONCLUSIONS: Given the parameters of this investigation, triple proximal interlocking provides more stability in nailed proximal tibia fractures than double proximal interlocking. Larger series with clinical follow-up after triple proximal interlocking in tibial nailing should be undertaken to further clarify these questions.
OBJECTIVES: To determine whether there are differences in stability between double and triple interlocked intramedullary nails used for the fixation of extraarticular proximal tibial fractures. DESIGN: Randomized in vitro biomechanical-experimental laboratory investigation. SETTING: Biomechanics laboratory of the Clinic for Trauma Surgery at the Johannes Gutenberg-University Mainz. INTERVENTION: A 10-mm defect osteotomy was performed on six paired human tibiae, and the proximal and distal ends were potted in polymethylmethacrylate cement (PMMA). Each pair of bones was randomly stabilized with an intramedullary nail (IM-nail) with two interlocking options (PTN 2s) in one tibia, and with an IM-nail with three interlocking options (PTN 3s) in the corresponding contralateral bone. A biomechanical test of the bone implant construct was then performed with an axial force of 900 N. Displacement of bone fragments was measured and depicted as a force-displacement diagram. MAIN OUTCOME MEASUREMENTS: Biomechanical construction stiffness. RESULTS: The stiffness values for PTN 3s were significantly higher than for PTN 2s. In the group of PTN 2s, two out of six implants failed biomechanically with breakage of one proximal interlocking screw. CONCLUSIONS: Given the parameters of this investigation, triple proximal interlocking provides more stability in nailed proximal tibia fractures than double proximal interlocking. Larger series with clinical follow-up after triple proximal interlocking in tibial nailing should be undertaken to further clarify these questions.