The Durability of the Intrascaphoid Compression of Headless Compression Screws: In Vitro Study

Purpose To test a new generation of compression screws: the Acumed Acutrak 2 Mini (AA; Acumed, Hillsboro, OR), the Stryker TwinFix (ST; Stryker, Kalamazoo, MI), and the Synthes 3.0 headless compression screw (SH; Synthes, Solothurn, Switzerland). Methods We used 40 fresh-frozen human scaphoids for this study. Bone density was measured. A K-wire was inserted centrally. A perpendicular osteotomy was created in the middle third (Herbert B2 fracture). A custom-made load sensor was placed between the bone fragments. All screws were implanted according to the manufacturers' instructions. The Synthes 2.0 cortical screw (SC), implanted as a lag screw, was used as a reference. The compression force during each experiment was digitally monitored for 12 hours while the data were acquired. The data were analyzed using analysis of variance with the Bonferroni correction. Results Immediately after screw insertion, ST reached 226 N, followed by AA with 191 N, SH with 137 N, and SC with 72 N. After 12 hours, ST displayed the highest residual compression force, 141 N, followed by AA with 121 N, SH with 78 N, and SC with 32 N. The differences were significant for ST and AA compared to SC. The loss of compression force over 12 hours was 39% for ST, 42% for AA, 49% for SH, and 55% for SC. Conclusions The new generation of headless compression screws, especially ST and AA, provided significantly higher compression forces after 12 hours, as well as the least loss of compression force over time, in comparison to a classic cortical lag screw. Clinical relevance A new generation of headless compression screws, by producing higher compression forces, increase stability at the fracture site and might thereby promote bone healing. (J Hand Surg 2012;37A:1142-1150. Copyright (C) 2012 by the American Society for Surgery of the Hand. All rights reserved.)