Comparison of fixation methods for scaphoid nonunions: a biomechanical model

The purpose of this study was to analyze the relative bio- mechanical stability of three types of internal ixation with cancellous bone graft in a cadaveric, scaphoid nonunion model. A scaphoid nonunion model was created by remov- ing 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 each were then internally ixed with a pair of parallel 0.045-inch K-wires, Mini-Acutrak screws, or Standard Acutrak screws, respectively for each group. The potted specimens were tested using an Instron(R) 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 of displacement. Results showed that both the Mini-Acutrak screw and the Standard Acutrak screw were statistically stronger and stiffer at 2 mm displacement than the pair of parallel 0.045-inch K-wires. No statistically sig- niicant difference between the Standard and Mini-Acutrak screws was noted at 2 mm displacement. At higher loads (4 mm displacement), the Standard Acutrak became statisti- cally stronger and stiffer than the Mini-Acutrak screw. It was concluded that the Standard Acutrak screw followed by the Mini-Acutrak screw may be a better option than a pair of parallel 0.045-inch K-wires when treating scaphoid nonunions. The screws have increased strength of ixation and stiffness when compared to K-wires. Also, unlike the K wires, the Acutrak screws enhance fracture healing by achieving interfragmentary compression. Even in a cancel- lous bone graft model, interfragmentary compression was achieved and our concern that the bone graft would "spit out" was allayed.