Comparison of fixation methods for scaphoid nonunions: a biomechanical model
Anand Panchal1, Erik Kubiak2, Mitchell Keshner2, Eric Fulkerson2
1Department of Orthopedic Surgery, Grandview Hospital Medical Center
2Department of Orthopedic Surgery, The New York University Hospital for Joint Diseases
Keywords: Biomechanics; bone screws; cadaver; fracture fixation, internal/methods; scaphoid bone/injuries; stress, mechanical.
Objectives: The purpose of this study was to analyze the relative biomechanical stability of three types of internal fixation with cancellous bone graft in a cadaveric, scaphoid nonunion model. Materials and methods: A scaphoid nonunion model was created by removing a volar wedge of bone from the waist of the scaphoid in 18 fresh frozen human cadavers. Cancellous sawbone graft was inserted into the osteotomy site and three groups of six cadavers were randomized for internal fixation with a pair of parallel, 0.045-inch K-wires, a Mini Acutrak screw, or a Standard Acutrak screw, respectively. The potted specimens were tested using an Instron Tensile Testing machine by applying force to the distal pole of the scaphoid. The load and stiffness were calculated at 2-mm and 4-mm displacements.
Results: Both the Mini and Standard Acutrak screws were statistically stronger and stiffer at 2-mm displacement than the pair of parallel K-wires. No statistically significant difference was noted between the Standard and Mini screws at 2-mm displacement. At higher loads (4-mm displacement), the Standard Acutrak screw exhibited significantly greater strength and stiffness than the Mini Acutrak screw.
Conclusion: Due to increased strength of fixation and stiffness, and with an additional advantage of interfragmentary compression, the Standard Acutrak screw followed by the Mini Acutrak screw may be a better option than a pair of parallel K-wires in the treatment of scaphoid nonunions.