gms | German Medical Science

Objectives: Implant stability is a crucial factor determining the success of rotator cuff repair with bone anchoring devices. Identifying the best surrogate material for biomechanical testing of bone anchoring in human bones using animal sources is challenging because bone quality depends on many factors such as position, depth and structure of bone [1].

Methods: In this ex vivo study, 41 bone biopsies from various species (human, bovine, ovine, porcine) were extracted from the proximal humerus and scanned with a micro computer tomography system at 22µm. Microarchitectural parameters like BV/TV, degree of anisotropy, Trabecular Thickness, Trabecular Separation and Connectivity Density were calculated from the processed images using well established methodologies. Furthermore, these images were converted to large-scale state-of-the-art micro finite element (µFE) models with materials adapted from experimental tests conducted at the tissue level of bone [2]. These numerical models were then used to simulate compression loads in order to provide image-based predictions of apparent stiffness and failure load of the bone biopsies. Additional mechanical uniaxial tests until failure have been performed on each corresponding specimen using a material testing machine to measure apparent bone stiffness and strength to validate the numerical predictions. Statistical analyses like ANOVA and the Kruskal Walis test were conducted to establish a ranking of similarities between each species and human trabecular bone, based on microstructural parameters as well as predicted and measured mechanical properties.

Results and Conclusion: From the results of microCT processing of trabecular microstructural properties alone, it could be seen that porcine bone generally presented the most similarities in microstructural parameters with human bones. Further analysis of the structural mechanical properties of bone using numerical methods, both of which were demonstrated to correlate excellently (R2 for maximum stress and Young's Modulus of 0.97 and 0.87, respectively) have strengthened this observation. In conclusion, these results suggest that, if it is not possible to use human bones to conduct biomechanical tests at the proximal humerus, porcine bones might represent the nearest surrogate from the tested species.