The effect of load obliquity on the strength of locking and nonlocking constructs in synthetic osteoporotic bone

Biomechanical Performance of Charcot-Specific Implants

Over the past 2 decades, an increased number of diabetic Charcot neuroarthropathy reconstructions have been performed. Despite advances in implant technology, arthrodesis complication rates remain high. This study examined the biomechanical properties (4-point bending, cantilever bending, and thread pullout resistance) of intramedullary implants designed for midfoot reconstruction. Large implants included A1 (7.4 mm cannulated stainless steel beam), B1 (6.5 mm solid titanium bolt), and C1 (7.0 mm cannulated titanium beam). Smaller implants included A2 (5.4 mm cannulated stainless steel beam) and C2 (5.0 mm solid titanium bolt). Four-point bending testing compared flexural properties of the body of the implants. Cantilever-bending testing was performed with the maximum bending moment being applied off the main thread of the implant to assess the thread portion. Thread pullout strength was tested by fixing the implants to a Sawbone block on a platform, and the distal portion of the implant in a clamp connected to loading actuator. Implant A1 demonstrated higher stiffness, force to failure, and fatigue compared to implants B1 and C1 (p < .05). Pullout strength of implant A1 was higher than implant B1 (p < .05). Thread fatigue strength of implant A1 was higher than implant C1 (p < .05). Implant A2 demonstrated higher stiffness, force to failure, tip fatigue strength, and thread pullout strength compared to implant C2 (p < .05), while implant C2 demonstrated higher body fatigue failure than implant A2 (p < .05). Alteration of beam/bolt parameters influences the biomechanical performance of implants used in Charcot reconstruction. Greater stiffness resists deformation, providing improved stability. Greater static failure load and fatigue limit improves the implant's ability to withstand higher and repetitive loads before failing This study should stimulate further clinical research to determine if these biomechanical properties translate into reduced implant failure rates and improved clinical outcomes in patients with diabetic Charcot neuroarthropathy.

The Effect of Pitch Variation and Diameter Variation on Screw Pullout

Introduction: There are many screw and thread designs commercially available to surgeons for bone fixation. There is a paucity of literature on comparative mechanical properties of various screw and thread designs including variable pitch screws, and tapered screws. This purpose of this study was to test whether varying a screws thread pitch and/or tapering a screws core diameter alters the mechanical performance of screws. Methods: A mechanical pullout test was performed on 4 different screw designs, including a variable pitch screw, a constant pitch screw, and variations of these in a straight and tapered screw design. Three-dimensional printing technology was used to manufacture the metal screws in order to control for as many variables as possible. Results: The pullout strength of the constant pitch screws (304.9 ± 25.3 N, P < .001) was significantly greater than the variable pitch screws (259.7 ± 23.4 N). The pullout strength was also significantly greater for screws with a tapered diameter (305.4 ± 24.1 N) than a constant diameter (259.1 ± 23.5N, P < .001). Tapered diameter variable pitch screws had the largest stiffness overall, which was statistically significant against all other groups (P ⩽ .001). Conclusion: The pullout strength is significantly greater for screws with a tapered diameter than a constant diameter and greater for screws with a constant pitch than for a variable pitch. Results of stiffness testing is mixed depending on the screw taper. The clinical significance of this study is that it provides data on the effects that thread design and tapering have on the pullout strength of screws. Levels of Evidence: Level V: Mechanical study.