Single cycle to failure in torsion of three standard and five locking plate constructs

Abstract

SummaryObjectives: The biomechanical properties of standard plates and recently designed locking plates were compared in torsion. We hypothesized that titanium (Ti) constructs would have the greatest deformation, and String of Pearls (SOP) constructs the greatest strength and stiffness.Methods: Dynamic compression plates (DCP), stainless steel (SS) limited contact (LC)-DCP, Ti LC-DCP, locking compression plate (LCP), 10 mm and 11 mm Advanced Locking Plate System (ALPS) 10 and 11, SOP and Fixin plates were applied to a validated bone model simulating a bridging osteosynthesis. Yield torque (strength), yield angle (deformation) and stiffness were compared using one-way ANOVA with post hoc Tukey (p <0.05).Results: The ALPS 11 constructs had significantly greater elastic deformation than all constructs except for the ALPS 10. There were not any differences in strength observed except for the ALPS 10 constructs, which was less than that for the SOP, LCP, DCP and ALPS 11 constructs. No differences in construct torsional stiffness were observed with the SS LCDCP, DCP, LCP and SOP constructs however all had greater stiffness than all remaining constructs. The ALPS 10 construct had lower stiffness than all constructs.Clinical significance: Modulus of elasticity of Ti explains the higher deformation and lower stiffness of these systems, with similar results for the Fixin due to its lower section modulus compared to all other plates. The SOP and standard constructs had surprisingly similar biomechanical properties in torsion. The rationale for selecting these implants for fracture repair likely needs to be based upon their differing biomechanical properties inherent to the diverse implant systems.Presented at the 38th Annual Conference of the Veterinary Orthopedic Society, Snowmass, Colorado, USA March 6, 2011.

In Vitro Biomechanical Comparison of 3.5 String of Pearl Plate Fixation to 3.5 Locking Compression Plate Fixation in a Canine Fracture Gap Model

“…We showed that in a fracture gap model with cadaveric canine bone, the SOP had significantly greater properties in 4‐point bending in static and cyclic testing than the LCP. Our results seem to correlate with the mechanical qualities of the plate itself as previously reported . The SOP plate is anticipated to react in this manner given its greater section modulus compared with the LCP plate but the finding that it is still superior to the LCP when tested on a cadaveric bone construct suggest that in a clinical setting the SOP might be more adequate at resisting bending forces than an LCP system.…”

“…For the torsion single cycle to failure testing, the LCP proved to have significantly greater composite rigidity and significantly less displacement at yield and at failure. This finding disagrees with another study performed by the same group as Blake's, who found no significant difference between the SOP and the LCP in torsion testing, single cycle to failure . In this study the method used for the mechanical testing was very similar to the one we used; however, a different material was used for their construct, which is most likely responsible for the varying results.…”

“…The LCP requires specialized locking head screws in order to be used as a locking system but has combination holes that can accommodate both conventional and locking screws. The mechanical properties of the SOP and LCP have already been tested against other commonly used locking and non‐locking plates . The SOP has shown greater bending stiffness, bending structural stiffness and bending strength than comparable plates in vitro …”

Effect of Screw Type and Distribution on the Torsional Stability of 3.5 mm String of Pearls Locking Plate Constructs

“…While likely true, synthetic bone models offer advantages including reduced variability between specimens, reduced number of samples to establish significant differences between groups and consistent evaluation of the implant independent of the bone/implant interface . Interestingly, our results are comparable to those of an earlier study in which a validated synthetic bone model was used to evaluate the torsional behavior of 3.5 mm SOP constructs . In that study, SOP constructs stabilized with 4 bicortical screws had a unidirectional yield angle of 14.4 ± 3.0° at a torque of 8.7 ± 1.9 Nm.…”

Management of distal femoral diaphyseal fractures with string of pearls locking plate in dogs

“…The contouring was done with help of SOP benders and SOP bending tees to match the topography of lateral aspect of femoral diaphysis and to ensure proper alignment and positioning of the plate to fit to the caudal bow on the bone. The experimental study conducted for design and biomechanical properties of SOP by DeTora and Kraus (2008), Ness (2009) and Cabassu et al (2011) was helpful in the study. SOP locking plate design itself allows maintenance of limited contact with periosteum thus promoting osteogenesis and bone healing in all the cases.…”