Biomechanical comparison of bone staple fixation methods with suture material for median sternotomy closure using 3D-printed bone models.

AIM: To compare the biomechanical properties of three different sternal closure techniques in a 3D-printed bone model of a sternum from a 30-kg dog. METHODS: Median sternotomy was performed on a total of 90 three-dimensional (3D) copies of a polycarbonate (PC) model of a sternum, generated from the CT images of the sternum of a 30-kg German Shepherd dog. Three different methods were used to repair the sternotomies: polydioxanone suture (group PDS, n = 30), stainless steel bone staples (group SS, n = 30), and nitinol bone staples (group NS, n = 30). Each repair method was tested by applying tensile force in one of three ways (longitudinally, laterally, or torsionally) resulting in a sample size of n = 10 for each repair method-loading combination. In all experiments, the loads at 1-mm and 2-mm gap formation, failure, and the displacement at the failure point were measured. RESULTS: In lateral distraction and longitudinal shear tests, NS and SS staple repairs required application of significantly greater force than PDS across all displacement criteria (1 and 2 mm). NS exhibited significantly greater failure load than PDS. In torsion tests, NS required significantly greater application of force compared to SS or PDS at all displacement criteria (1 and 2 mm) and exhibited a greater failure load than PDS. In terms of displacement at failure point, PDS suture showed more displacement than SS or NS across all experiments (laterally, longitudinally, torsionally). CONCLUSIONS: In this study, bone staples were mechanically superior to PDS suture in median sternotomy closure using 3D-printed bone model in terms of 1-mm, 2-mm displacement loads, and displacement at failure. NS had a higher failure load than PDS under lateral, longitudinal, and torsional distraction. CLINICAL RELEVANCE: These study results imply that bone staples can be considered as an alternative surgical method for median sternotomy closure in dogs.

Determining the Mechanical Properties of Super-Elastic Nitinol Bone Staples Through an Integrated Experimental and Computational Calibration Approach.

Super-elastic bone staples have emerged as a safe and effective alternative for internal fixation. Nevertheless, several biomechanical aspects of super-elastic staples are still unclear and require further exploration. Within this context, this study presents a combined experimental and computational approach to investigate the mechanical characteristics of super-elastic staples. Two commercially available staples with distinct geometry, characterized by two and four legs, respectively, were examined. Experimental four-point bending tests were conducted to evaluate staple performance in terms of generated forces. Subsequently, a finite element-based calibration procedure was developed to capture the unique super-elastic behavior of the staple materials. Finally, a virtual bench testing framework was implemented to separate the effect of geometry from that of the material characteristics on the mechanical properties of the devices, including generated force, strain distribution, and fatigue behavior. The experimental tests indicated differences in the force vs. displacement curves between staples. The material calibration procedure revealed marked differences in the super-elastic properties of the materials employed in staple 1 and staple 2. The results obtained from the virtual bench testing framework have showed that both geometric features and material characteristics had a substantial impact on the mechanical properties of the device, especially on the generated force, whereas their effect on strain distribution and fatigue behavior was comparatively less pronounced. To conclude, this study advances the biomechanical understanding of Nitinol super-elastic staples by separately investigating the impact of geometry and material characteristics on the mechanical properties of two commercially available devices.

Biomechanical comparison of pin and nitinol bone staple fixation to pin and tension band wire fixation for the stabilization of canine olecranon osteotomies.

OBJECTIVE: To compare the initial biomechanical properties of olecranon osteotomies stabilized with intramedullary pins and a Nitinol bone staple to osteotomies stabilized with pin and tension band wire fixation. STUDY DESIGN: Ex vivo mechanical evaluation on cadaveric bones. MATERIAL AND METHODS: Ten pairs of cadaveric forelimbs from skeletally mature Greyhounds with an olecranon osteotomy stabilized with either a pin and Nitinol bone staple or a pin and tension band wire. A single load to failure was applied to each specimen through the triceps tendon. Biomechanical properties were compared based on stiffness, yield load, and maximum load to failure and load at 2 mm of axial displacement. RESULTS: Specimens stabilized with the bone staple were biomechanically superior in all the variables tested. There was significantly greater stiffness (118.0 ± 25.9 N/mm versus 70.1 ± 40.4 N/mm; p = 0.005), yield load (319.0 ± 99.8 N versus 238.0 ± 42.5 N; p = 0.03), maximum load sustained (385.0 ± 99.2 N versus 287.0 ± 37.4 N; p = 0.009), and load at 2 mm of axial displacement (218.0 ± 51.5 N versus 138.0 ± 48.7 N; p = 0.002) in specimens stabilized with pins and a Nitinol bone staple than specimens stabilized with pin and tension band wire fixation. CLINICAL SIGNIFICANCE: The pin and Nitinol bone staple construct provides a biomechanically superior alternative to pin and tension band wire fixation for stabilization of olecranon osteotomies, and its use warrants further clinical investigation.

Assessing the performance characteristics and clinical forces in simulated shape memory bone staple surgical procedure: The significance of SMA material model.

This work is focused on the detailed computer simulation of the key stages involved in a shape memory alloy (SMA) osteosynthesis bone stapling procedure. To this end, a recently developed three-dimensional constitutive SMA material model was characterized from test data of three simple uniaxial-isothermal-tension experiments for powder metallurgically processed nickel-rich NiTi (PM/NiTi-P) material. The calibrated model was subsequently used under the complex, thermomechanical loading conditions involved in the surgical procedure using the body-temperature-activated PM/NiTi-P bone staple. Our aim here is to assess the immediate and post-surgical performance characteristics of the stapling operation using the material model. From this study: (1) it was found that adequate compressive forces were developed by the PM/NiTi-P bone staple, with the tendency of this force to even increase under sustained thermal loading due to the intrinsic "inverse relaxation phenomena" in the SMA material, (2) the simulation results correlated well with those from experimental measurements, (3) the body-temperature-activated PM/NiTi-P staple was proved to be clinically viable, providing a stable clamping force needed for speedy coaptation of the fractured bones, and (4) these realistic assessments crucially depend on the use of suitable and comprehensive SMA material models.