Comparison of Mechanical Properties of Non-ridged Versus Ridged Backslabs in Lower Limb Fractures.

Introduction Lower limb fractures frequently require immobilization with backslabs to promote healing. This study investigates a novel approach involving the incorporation of a single ridge to enhance backslab strength while maintaining cost-effectiveness. Objective The aim of this study was to assess the mechanical performance of ridged backslabs in comparison to traditional non-ridged backslabs, specifically focusing on their load-bearing capacity and cost-effectiveness when used in lower limb fractures. Methods This experimental study, conducted between January 2023 and June 2023, compares three groups of backslabs with varying layers (eight, ten, and twelve) that were fabricated, each consisting of four ridged and four non-ridged specimens. These backslabs, constructed from six-inch plaster of Paris rolls, were 190 cm in length. A three-point bending test was conducted on both groups using a Hounsfield H100KS Universal Testing Machine (Tinius Olsen Ltd., Redhill, UK), with a crosshead speed of 5 mm/min and a span distance of 190 mm between supports. Results Significant differences in mean maximum force endured were observed between the ten-layered and twelve-layered flat and ridged backslabs (p-values: 0.003 and 0.004, respectively). Ten-layered ridged backslabs exhibited a 56 N higher load-bearing capacity, while twelve-layered ridged backslabs withstood 73.9 N more force than their flat counterparts, underscoring the superior strength of ridged lower limb backslabs. Conclusion Ridged backslabs outperformed non-ridged backslabs in terms of strength when subjected to external forces. These findings support the potential adoption of ridged backslabs as a lightweight, cost-effective, and robust alternative for immobilization in lower limb fractures.

A combined experimental and computational study of mechanical properties after balloon kyphoplasty.

Vertebral compression fractures rank among the most frequent injuries to the musculoskeletal system, with more than 1 million fractures per annum worldwide. The past decade has seen a considerable increase in the utilisation of surgical procedures such as balloon kyphoplasty to treat these injuries. While many kyphoplasty studies have examined the risk of damage to adjacent vertebra after treatment, recent case reports have also emerged to indicate the potential for the treated vertebra itself to re-collapse after surgery. The following study presents a combined experimental and computational study of balloon kyphoplasty which aims to establish a methodology capable of evaluating these cases of vertebral re-collapse. Results from both the experimental tests and computational models showed significant increases in strength and stiffness after treatment, by factors ranging from 1.44 to 1.93, respectively. Fatigue tests on treated specimens showed a 37% drop in the rate of stiffness loss compared to the untreated baseline case. Further analysis of the computational models concluded that inhibited PMMA interdigitation at the interface during kyphoplasty could reverse improvements in strength and stiffness that could otherwise be gained by the treatment.

A Multiscale Finite Element Analysis of Balloon Kyphoplasty to Investigate the Risk of Bone-Cement Separation In Vivo.

BACKGROUND: During the past decade there has been a significant increase in the number of vertebral fractures being treated with the balloon kyphoplasty procedure. Although previous investigations have found kyphoplasty to be an effective treatment for reducing patient pain and lowering cement-leakage risk, there have been reports of vertebral recollapse following the procedure. These reports have indicated evidence of in vivo bone-cement separation leading to collapse of the treated vertebra. METHODS: The following study documents a multiscale analysis capable of evaluating the risk of bone-cement interface separation during lying, standing, and walking activities following balloon kyphoplasty. RESULTS: Results from the analysis found that instances of reduced cement interlock could initiate both tensile and shear separation of the interface region at up to 7 times the failure threshold during walking or up to 1.9 times the threshold during some cases for standing. Lying prone offered the best protection from interface failure in all cases, with a minimum safety factor of 2.95. CONCLUSIONS: The results of the multiscale analysis show it is essential for kyphoplasty simulations to take account of the micromechanical behavior of the bone-cement interface to be truly representative of the in vivo situation after the treatment. The results further illustrate the importance of ensuring adequate cement infiltration into the compacted bone periphery during kyphoplasty through a combination of new techniques, tools, and biomaterials in a multifaceted approach to solve this complex challenge.

Strong similarities in the creep and damage behaviour of a synthetic bone model compared to human trabecular bone under compressive cyclic loading.

Understanding the failure modes which instigate vertebral collapse requires the determination of trabecular bone fatigue properties, since many of these fractures are observed clinically without any preceding overload event. Alternatives to biological bone tissue for in-vitro fatigue studies are available in the form of commercially available open cell polyurethane foams. These test surrogates offer particular advantages compared to biological tissue such as a controllable architecture and greater uniformity. The present study provides a critical evaluation of these models as a surrogate to human trabecular bone tissue for the study of vertebral augmentation treatments such as balloon kyphoplasty. The results of this study show that while statistically significant differences were observed for the damage response of the two materials, both share a similar three phase modulus reduction over their life span with complete failure rapidly ensuing at damage levels above 30%. No significant differences were observed for creep accumulation properties, with greater than 50% of creep strains being accumulated during the first quarter of the life span for both materials. A significant power law relationship was identified between damage accumulation rate and cycles to failure for the synthetic bone model along with comparable microarchitectural features and a hierarchical composite structure consistent with biological bone. These findings illustrate that synthetic bone models offer potential as a surrogate for trabecular bone to an extent that warrants a full validation study to define boundaries of use which compliment traditional tests using biological bone.

A parametric finite element analysis of the compacted bone-cement interface following balloon kyphoplasty.

Treating fractures of the spine is a major challenge for the medical community with an estimated 1.4 million fractures per annum worldwide. While a considerable volume of study exists on the biomechanical implications of balloon kyphoplasty, which is used to treat these fractures, the influence of the compacted bone-cement region properties on stress distribution within the vertebral body remains unknown. The following article describes a novel method for modelling this compacted bone-cement region using a geometry-based approach in conjunction with the knowledge of the bone volume fractions for the native and compacted bone regions. Three variables for the compacted region were examined, as follows: (1) compacted thickness, (2) compacted region Young's modulus and (3) friction coefficient. Results from the model indicate that the properties of the compacted bone-cement region can affect stresses in the cortical bone and cement by up to +28% and -40%, respectively. These findings demonstrate the need for further investigation into the effects of the compacted bone-cement interface using computational and experimental methods on multi-segment models.