Abstract
The cyclic axial dynamisation of a stabilised fracture is intended to promote callus formation and bone healing. Most studies focused on biomechanical properties or the quantity of new bone formation. Far less is known about the quality of newly formed callus tissues, such as tissue distribution and arrangement within the callus. The aim of this current study was to investigate the effect of cyclic, axial dynamisation on the quantity and quality of callus in an established delayed fracture healing model. In 41 sheep transverse osteotomies with a gap size of 3 mm were stabilised with a unilateral external fixator. In 32 of these, fracture ends were axially stimulated with displacement amplitudes of 0.8 mm, 0.4 mm, 0.2 mm, or 0.0 mm, respectively, for six weeks. In the remaining 9 sheep of the control group, an additional external fixator was mounted to achieve almost total rigidity. Animal material originating from a past animal experiment was reanalysed in this study. Histological thin-ground sections were histomorphometrically analysed regarding the histological structure and composition of the defect region. A slight tendency towards an increase in size of total callus area, area of new bone (nB.Ar), and cartilage (Cg.Ar) was detected with increasing displacement amplitudes compared to the control group. At the anterior callus side nB.Ar and Cg.Ar were significantly larger than at the posterior side in all groups independent of treatment. Regarding the quality of callus, areas of very compact bone were predominant in the treatment groups whereas in the control group a slight shift to more porous bone was observed. No difference of callus compactness was observed between the anterior and the posterior side. The established method to assess the local compactness of callus areas is a useful tool to quantitatively determine the spatial distribution of new bone tissue within the callus. The application of this method in combination with biomechanical testing might reveal interesting relations between tissue distribution and bone strength that, with traditional histomorphometry, cannot be identified.
Highlights
In clinics, most biomechanical and patient-related factors effecting fracture healing are unmodifiable such as the type of fracture, severity of soft tissue injury, blood supply, and patients’ age and pre-existing diseases [1]
The use of external fixators for fracture stabilisation allows for the individual adjustment of the mechanical environment which is mainly composed of fracture end stability and mechanical stress applied through weight bearing during the fracture healing process [2]
A recent μCT study of Tufekci et al [19] demonstrated that 1 mm compressive interfragmentary movement (IFM), that were applied within the first 3 weeks, result in significantly increased bone volume compared to osteotomy gaps that were completely isolated from functional loading and IFM
Summary
Most biomechanical and patient-related factors effecting fracture healing are unmodifiable such as the type of (comminuted) fracture, severity of soft tissue injury, blood supply, and patients’ age and pre-existing (inflammatory) diseases [1]. What can be adapted is the rigidity of fracture stabilisation. The use of external fixators for fracture stabilisation allows for the individual adjustment of the mechanical environment which is mainly composed of fracture end stability and mechanical stress applied through weight bearing during the fracture healing process [2]. Rigid devices reduce interfragmentary movement (IFM) and mechanical stress on fracture ends, whereas flexible devices. The principal idea to mechanically stimulate fractured bone in order to enhance healing is based on Wolff ’s decisive conclusion on the Mechanotransduction of bone [4]. The external mechanical stimulation of a stabilised fracture site is intended to promote bone healing by simulating loads that naturally occur in healthy bone underweight bearing, for instance. The force, frequency, timing, and duration of externally applied mechanical stimulation via so-termed micromovements can be varied
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