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Introduction: Scaphoid fractures are common hand fractures and headless screws are favored for internal fixation in order to facilitate fracture stability and compression. Several second generation headless compression screws have been introduced with purported improved biomechanical function.  

Methods: We compared four second generation headless compression screws: Mini-Acutrak2 (Acumed – Hillsboro, OR), Twinfix (Stryker – Mahwah, NJ), Kompressor Mini (Integra – Plainsboro, NJ), HCS 3.0 (Synthes – Paoli, PA), and one first generation Herbert-Whipple (Zimmer – Warsaw, IN) screw. A solid rigid polyurethane foam (0.16 g/cm³) 30mm scaphoid sawbone model with a transverse fracture were used with a torque cell and washer load cell. Five screws of each brand were applied five times each, with pre-drilling and without.

Results: The Mini-Acutrak2 compression and fastening torque gradually increased with each turn until the compression reached a max of 4.63 kg. Compression without pre-drilling was higher (5.00 kgf) but was not significantly different. The Twinfix, unlike the Mini Acutrak2, achieved maximum compression after a quarter turn after unlocking the second stage of the screwdriver, reaching 3.13 kgf. There was a high risk of losing compression beyond a quarter turn. The Kompressor Mini created compression trends similar to the Twinfix, reaching a maximum compression of 2.12 kgf. However, following maximum compression stage, compression was quickly lost.  The HCS 3.0 reached a maximum compression of 1.76 kgf which was not significantly different from the 1.8 kgf achieved without pre-drilling. The Herbet-Whipple generated the least compression force equal to 1.37 kgf and it did not change significantly without pre-drilling (1.03 kgf).

Conclusion:  All second generation headless compression screws achieved greater compression than the first generation Herbert-Whipple screw. The Mini-Acutrak2 generated the maximum compression and showed the most reliability and sustainability. The Twinfix and Kompressor Mini have a rotating head which generates most of their compression. However, both demonstrated loss of compression with increased turns. All screws demonstrated increased fastening torque without pre-drilling.