Fully threaded headless cannulated screws provide similar biomechanical strength to conventional fixation in 3-dimensionally printed canine medial malleolar fracture models

Abstract

Objective: To compare the failure load of the fully threaded headless cannulated screw (FTHCS) technique with that of fully threaded self-tapping cortical low-profile screw (FTLPS) fixation, 2 Kirschner (K) wires, and figure-of-8 tension band wire (TBW) fixation for stabilizing medial malleolar fractures using a 3-D-printed canine bone model.

Methods: This study was conducted from June 10, 2024, through February 9, 2025. A CT image of the tibia from a 2-year-old 12-kg castrated male Jindo dog was used to create 21 polycarbonate 3-D-printed bone models, and 7 were assigned to each group. The TBW group was stabilized with two 1.2-mm K-wires and figure-of-8 TBW (20 gauge), the FTLPS group was stabilized with a 3.5-mm FTLPS, and the FTHCS group was stabilized with a 3.5-mm FTHCS. Tensile load was applied at 0.2 mm/s using a universal testing machine, and failure load was recorded.

Results: The mean failure load for the TBW, FTLPS, and FTHCS groups was 238.0 ± 38.1 N, 187.3 ± 50.8 N, and 215.5 ± 35.2 N, respectively. There were no statistically significant differences among groups. All screw fixed models failed by fracture of the malleolar fragment.

Conclusions: The FTHCS fixation showed comparable failure loads to conventional fixation methods in this model. While promising, its use may be appropriate only when fragment size and bone quality are sufficient.

Clinical relevance: While failure loads and mechanisms were similar in this model, further investigation into the relative size of the screw to the fragment is necessary to guide the clinical application of this device.

Keywords: 3-D printing; biomechanic; headless cannulated screw; medial malleolar fracture; tension band wire.