A biomechanical study on variation of compressive force along the Acutrak 2 screw

Acutrak 2 screws are commonly used for scaphoid fracture fixation. To our knowledge, the variation in compressive force along the screw has not been investigated before. The objectives of our study were to measure variance in compression along the length of the standard Acutrak 2 screw, to identify the region of the screw which produces the greatest compression and to discuss the clinical relevance of this to the placement of the screw for scaphoid fractures.

A laboratory model was set up to test the compressive force at 2mm intervals along the screw, using solid polyurethane foam (Sawbone) blocks of varying width. The Acutrak 2 screws were introduced in the standard method. Forces were measured using a custom-made load cell washer introduced between the Sawbone blocks and were plotted as a graph along the whole length of the screw.

Maximum compression was at the mid-point of the screw. Overall compressive forces were higher in the proximal half of the screw by 19% when compared with the distal half. Minimum compression was seen at 4mm or less from either end of the screw.

There is variation in compression along the length of the standard Acutrak 2 screw and the maximum compression was obtained at the mid-point of the screw. From this study, we would recommend when using an Acutrak 2 screw for internal fixation of scaphoid fractures, to attain maximum compressive force, place the fracture at the mid-point of the Acutrak screw. If this is not possible, then place the fracture towards the proximal half of the screw.