A biomechanical comparison of scaphoid screws

The compressive forces generated by various scaphoid screws were measured in the laboratory using a custom designed load washer (transducer) as a means to compare their fixation capabilities. Testing was done using simulated bones fabricated from polystyrene pipette tubing and Pedilen polyurethane foam and paired cadaver scaphoids. The Herbert scaphoid screw was found to have inferior fixation capabilities compared with screws of a more conventional design. However, its size compatibility was the best of all the screws tested. The Heune scaphoid screw demonstrated the best fixation capability, but was found to be too large for routine use. The ASIF cancellous screw (4.0 mm) demonstrated excellent fixation capability, but was believed to have too large a head size for many scaphoids. An optimal screw design is proposed for use in scaphoid fractures based on failure data for various thread sizes and head diameters.