Role of interfragmentary strain in fracture healing: Ovine model of a healing osteotomy

Abstract

It has been hypothesized that the histological pattern of fracture healing is controlled at least in part by the local mechanical strains in the interfragmentary region. To test this "interfragmentary strain hypothesis," we applied cyclic bending deformations to tibial osteotomies in 11 sheep. An instrumented flexible plate spanning a 1-mm osteotomy gap was deformed to create a gradient of tissue elongation from 10% under the plate to 100% at the opposite cortex. The cyclic deformations were applied three times per minute, 24 h per day, for 1-5 weeks. However, as a result of tissue differentiation, the bone-plate complex increased in stiffness with healing time, resulting in a marked reduction of the gap deformation at approximately 4 weeks. Fracture healing was evaluated using vascular injection of India ink and conventional histology. A nonlinear three-dimensional finite element model of the interfragmentary tissue at the initial stage of healing was used to predict the complex tissue strains. The ingrowth of vascularized soft tissue into the interfragmentary gap, as well as the subsequent differentiation of this tissue, occurred earlier and to a greater degree in regions of lower strain. In contrast, the proliferation of callus tissue was greatest at the periosteal and endosteal surfaces of the cortex opposite the plate. Direct comparison of the finite element predictions with the histology demonstrated that the spatial distribution of bone resorption at the fracture fragment ends directly corresponded to the locations of elevated tissue strain and stress. However, there was no consistent numerical relationship between the magnitude of these local peak strains and the corresponding volume of cortical bone resorption over the bone cross section.

Long‐term effects of saw osteotomy versus random fracturing on bone healing and remodeling in a sheep tibia model

“…Cortical remodeling and new bone formation was demonstrated as early as the fourth week. [32][33][34] In contrast to other studies, 35 we were able to demonstrate an ongoing remodeling process in the fracture and osteotomy gap beyond the 26th week.…”

“…Indeed, the movement of the fragments of each tibia was extensive enough to produce a callus at the site of corticotomy and the random type fracture, as well. In agreement with other studies 34 reporting greatest proliferation of callus tissue toward the periosteal and endosteal surface of the cortex opposite the plate, we saw similar tendency in callus formation after week 26. This implies that prolonged instability would more likely be expected at the far plate cortex; namely, at the fracture site, rather than at the near-plate cortex, that is, the osteotomy.…”

The initial phase of fracture healing is specifically sensitive to mechanical conditions

“…This conclusion is, however, often related to the (2003) 6 6 2 4 6 [mm'] 140-bone densty [%] ' mineralized bone area [mmz] connective tissue area [mm'] application of defined movements to stimulate fracture healing [2,6,8,10,33].…”

“…On the other hand, interfragmentary shear movements seem to allow, at least partially, regular bone consolidation [27]. These conclusions are, however, often related to the application of defined movements throughout the healing process [2,6,8,10,33].…”

An Idealised Biphasic Poroelastic Finite Element Model of a Tibial Fracture

“…Therefore biomechanics of bone fracture healing has been examined in many clinical or biological, mathematical or finite element studies (Cheal et al 1991, DiGioia et al 1986, Claes et al 1999, Doblaré et al 2004and Oh et al 2010. Most of the studies model the components of bone fractures as monophasic, homogenous materials, which may not be appropriate considering the large inter fragmentary displacements and high porosity of the reparative tissue.…”