Computational characterization of fracture healing under reduced gravity loading conditions

Abstract

ABSTRACT:The literature is deficient with regard to how the localized mechanical environment of skeletal tissue is altered during reduced gravitational loading and how these alterations affect fracture healing. Thus, a finite element model of the ovine hindlimb was created to characterize the local mechanical environment responsible for the inhibited fracture healing observed under experimental simulated hypogravity conditions. Following convergence and verification studies, hydrostatic pressure and strain within a diaphyseal fracture of the metatarsus were evaluated for models under both 1 and 0.25 g loading environments and compared to results of a related in vivo study. Results of the study suggest that reductions in hydrostatic pressure and strain of the healing fracture for animals exposed to reduced gravitational loading conditions contributed to an inhibited healing process, with animals exposed to the simulated hypogravity environment subsequently initiating an intramembranous bone formation process rather than the typical endochondral ossification healing process experienced by animals healing in a 1 g gravitational environment. The literature is deficient with regard to the specific alterations in the localized mechanical environment of skeletal tissue during the reduced gravitational loading characteristic of spaceflight and how these alterations affect fracture healing in Haversian systems. Additionally, investigations that have attempted to link the direct role of these reduced gravitational forces to fracture healing have been limited primarily to rodent studies. [1][2][3][4] The in vivo studies that have been reported have consistently demonstrated that weight-bearing maintains skeletal integrity, and ultimately, accelerates the healing of long bone fractures by promoting rapid callus formation.5 However, the lack of mechanical loading experienced during weightlessness leads to the inhibition of fracture healing. [1][2][3][4] More specifically, these studies have demonstrated decreased chondrogenesis, mechanical strength, callus size, osteoblast activity, and bone formation rates in animals that healed in reduced loading environments as compared to those that healed in a full Earth gravity loading condition.1-4 Despite the limited number of studies directly investigating fracture healing in reduced gravitational loading environments, numerous ground-based studies have examined the effect of fixation rigidity on subsequent fracture healing on Earth. A large number of these studies relied on external fixation devices that allowed predefined amounts of axial movement in order to investigate the magnitude of interfragmentary motion necessary to alter fracture healing in both animal models and human patient cohorts. [6][7][8][9][10][11][12] It has also been demonstrated that rigid fixation has a deleterious impact on the fracture healing cascade while improved fracture healing occurred when axial micromotion is delivered to the fracture site. [13][14][15] While these studies provide valuable insight ab...

Direct electromagnetic coupling for non‐invasive measurements of stability in simulated fracture healing

“…A series of cadaver experiments involved applying the DEC system to a large animal fracture fixation scenario. Our group has extensive in vitro and in vivo experience with this model, and it is well characterized for investigating fracture fixation and healing applications …”

“…A finite element simulation of the bone‐plate experiment described above was developed. The finite element model was adapted from a validated ovine hind limb model previously published by our group . The original model was recreated from computed tomography (CT) image data using AMIRA visualization software (version 5.0, VSG, Burlington, MA).…”

Mechanical comparison of application of locking intramedullary nail to locking compression plate in the ovine metatarsus

“…According to a recent review of 11 in vivo metatarsal defect models in sheep, the models were all able to mimic human conditions due to the vertical weight-bearing cortical bone region and were more easily accessible to surgery in comparison to tibia and femur models ( 15 ). LCP have also been described for use in fracture healing models of the metatarsus in combination with external fixator, which would be impossible in more proximal bones ( 9 , 16 ). Our team recently described the first use of this novel IMN technique in the ovine metatarsus and this mechanical study described herein characterizes the mechanical properties and potential mechanical advantages of utilizing this IMN construct for preclinical fracture models.…”

High throughput computational evaluation of how scaffold architecture, material selection, and loading modality influence the cellular micromechanical environment in tissue engineering strategies

“…In the absence of any feasible experimental methods, one possible tool to predict ECM formation in TE scaffolds is the finite element (FE) method. Cell fates in orthopedic tissues under mechanical loading have been modeled with FE in intervertebral disc 9,37 and bone fracture healing 38 applications. The tissue‐level mechanics of TE scaffolds have also been studied using FE methods 29–31,36 and some of these models have been developed to predict mechano‐regulation of musculoskeletal regeneration 39–41 .…”