A New Fastener With Improved Bone-To-Implant Interface Shows Superior Torque Stripping Resistance Compared With the Standard Buttress Screw

Abstract

Objective: The conventional AO buttress screw used for fracture fixation relies on a historic buttress thread design, which is prone to stripping at the bone–implant interface. We hypothesized that a new Bone-Screw-Fastener with an innovative interlocking thread design demonstrates increased resistance to torque stripping forces compared with the buttress screw, without compromising pullout strength. Methods: A biomechanical model was established in 6 matched pairs of adult human cadaveric tibiae to test torque resistance between the 3.5 mm Bone-Screw-Fastener and the 3.5 mm cortical AO buttress screw until failure. Uniaxial pullout testing of both screw types was performed as an internal control experiment. Results: The 3.5 mm Bone-Screw-Fastener had a significantly increased resistance to torque failure compared with the standard 3.5 mm AO buttress screw (P = 0.0145). In contrast to the buttress screws, none of the Bone-Screw-Fasteners stripped from the bone but rather failed at the screwdriver–implant interface in terms of a metal-on-metal failure. The internal control experiments revealed no significant difference in axial pullout strength between the 2 implants (P = 0.47). Conclusions: These data demonstrate the superiority of the new Bone-Screw-Fastener over the conventional AO buttress screw regarding protection from torque stripping forces. In addition, the new thread design that interlocks to the bone does not sacrifice axial pullout resistance conveyed by the buttress screw. Future controlled trials will have to validate the in vivo relevance of these findings in a clinical setting.

Influence of interlocking thread screws to repair simulated adult canine humeral condylar fractures

“…The proposed advantages of the interlocking thread design include improved resistance to multidirectional forces and improved resistance to stripping 22 . This hypothesis is supported by a recent study that demonstrated that ITS has higher torque stripping resistance than BTS 42 . Further studies are required to determine how the increased temperature and work generated during drilling and screw insertion impacts the ITS performance in a clinical setting.…”

“…22 This hypothesis is supported by a recent study that demonstrated that ITS has higher torque stripping resistance than BTS. 42 Further studies are required to determine how the increased temperature and work generated during drilling and screw insertion impacts the ITS performance in a clinical setting.…”

Development and initial validation of a novel thread design for nonlocking cancellous screws

“…However, studies suggest that the typical buttress thread cannot adequately resist multiaxial forces and is prone to stripping at the bone-screw interface. 11,12 Nonetheless, the optimal thread design for a nonlocking cancellous screw remains unclear.…”

“…Since then, the buttress thread has become the standard for bone screws, with most medical device companies manufacturing buttress‐threaded nonlocking cancellous screws. However, studies suggest that the typical buttress thread cannot adequately resist multiaxial forces and is prone to stripping at the bone–screw interface 11,12 . Nonetheless, the optimal thread design for a nonlocking cancellous screw remains unclear.…”

Fixation stability comparison of bone screws based on thread design: buttress thread, triangle thread, and square thread

“…Improving the fixation strength of bone screws is a feasible way to reduce the failure rate [8]. Screw thread is the determinant component that governs the initial screw stability of fixation, therefore, it is extremely important to choose the right thread profile for the bone screw [9][10][11]. Bone screws are derived from industrial screws with various thread designs for different purposes [12].…”