Biomechanical comparison of distal locking screws for distal tibia fracture intramedullary nailing

Background: Newer generation intramedullary (IM) tibial nails provide several distal interlocking screw options. The objectives were to determine: 1) if the new oblique interlocking option provides superior stability, 2) which screw orientation/ configuration is the most biomechanically stable, and 3) if three distal interlocking screws provide better stability. Methods: A preliminary experiment was performed in torsion, compression, and bending tests with four different screw configurations: (I) one medial-tolateral and one oblique, (II) two medial-to-lateral, (III) one medial-to-lateral and one anterior-to-posterior, and (IV) one medial-to-lateral, one anterior-to-posterior and one oblique in simulated distal metaphyseal fracture tibiae. Twenty-four Synthes EXPERT tibial IM nails were used for six specimens of each screw configuration. Parts I and II, tibial IM nails were locked with 5.0 mm interlocking screws into simulated distal tibiae (PVC and composite analogue tibia). Part III, the two most stable configurations were tested using five pairs of simulated cadaveric distal tibiae metaphyseal fractures. Results: Significant differences were attributable to distal screw orientation for intramedullary nailing of distal tibia fractures. Configurations II and IV were found to be more stable than the other two configurations. No significant difference was detected in construct stability in all modes of testing between Configurations II and IV. Discussion: Configuration I did not provide superior stability for the distal tibia fracture fixation. Configurations II and IV provided equivalent stability. When choosing IM fixation for treatment of distal tibia metaphyseal fractures two medial-to-lateral screws provide the necessary stability for satisfactory fixation. Clinical Relevance: This study indicated an option for operative treatment of distal metaphyseal tibia fracture fixation where preservation of soft tissue and rigid stabilization are needed.