Novel systems for the application of isolated tensile, compressive, and shearing stimulation of distraction callus tissue

Abstract

BackgroundDistraction osteogenesis is a procedure widely used for the correction of large bone defects. However, a high complication rate persists, likely due to insufficient stability during maturation. Numerical fracture healing models predict bone regeneration under different mechanical conditions allowing fixation stiffness optimization. However, most models apply a linear elastic material law inappropriate for the transient stresses/strains present during limb lengthening or segment transport. They are also often validated using in vivo osteotomy models lacking precise mechanical regulation due to the unavoidable stimulation of secondary interfragmentary motion during ambulation under finitely stiff fixation. Therefore, in order to create a robust numerical model of distraction osteogenesis, it is necessary to both characterize the new tissue’s viscoelasticity during distraction and determine the influence of strictly isolated stimulation in each loading mode (tension, compression, and shear) to account for potential differences in mechanical and histological response.AimTwo electromechanical fixators with integrated load cells were designed to precisely perform and monitor in vivo lateral distraction and isolated stimulation in sheep tibiae using a mobile, hydroxyapatite-coated titanium plate. The novel surgical procedure circumvents osteotomy, eliminating the undesirable and unquantifiable mechanical stimulation during ambulation.MethodsAfter a 10-day post-surgery latency period, two 0.275 mm distraction steps were performed daily for 10 days. The load cell collected data before, during, and after each distraction step and was terminated after no less than one minute from the time of distraction. A 7-day consolidation period separated the distraction phase and 18-day stimulation phase. Stimulation was carried out in isolated tension, compression, or shear while recording force/time data. Each stimulation session consisted of 120 cycles with a magnitude of either 0.1 mm or 0.6 mm in the tension and compression groups and 1.0 mm in the shear group. The animals were euthanized after a 3-day holding period following stimulation.ResultsOur initial results show that the tissue progressively stiffens and maintains an increasingly large residual traction. The force curves during compressive stimulation show a progressive drift from compression toward tension. We hypothesize that this behavior may be due to the preferential flow of fluid outward from the tissue and a greater resistance to reabsorption during the plate’s return to the starting position.

Can implants move in bone? A longitudinal in vivo micro‐CT analysis of implants under constant forces in rat vertebrae

“…In this context it has to be noted that remains unclear whether the new bone formation is linked to the inflammatory process which occurs within hours after implant insertion (Bielemann, Marcello‐Machado, Bel Cury, & Faot, ; Bosshardt et al, ; Insua, Monje, Wang, & Miron, ). As this inflammatory process provokes bone remodeling (Ma et al, ), the movement of the implant might have induced a distraction of the newly formed woven bone (Meyers, Schulke, Ignatius, & Claes, , ). However, further research is needed to investigate the associated molecular patterns and also potential relationships to early implant failures.…”

Intramembranous bone formation after callus distraction is augmented by increasing axial compressive strain

“…In an animal experiment employing sheep, a distraction device ( Fig 1 ) incorporating a mobile hydroxyapatite-coated titanium plate (CelGen AG, Zug, Switzerland) was mounted to the right tibia [ 8 ]. Postoperatively, the animals were subjected to a combined protocol of lateral callus distraction and subsequent cyclic, compressive stimulation of the regenerate tissue through movement of the titanium plate ( Fig 2A ).…”

The mode of interfragmentary movement affects bone formation and revascularization after callus distraction

“…A custom-designed system, which allowed a protocol of lateral callus distraction and subsequent cyclic compressive, tensile, or shearing stimulation of the regenerate tissue [ 12 ] was applied in an ovine model to the anteromedial tibial surface of the right hind leg.…”

“… A modified system was used for shear movements described in detail in a previous publication [ 12 ]. …”

“…To study the effect of isolated IFM directions on bone formation and revascularization during the maturation process, novel callus distraction devices were developed. This allows the isolated application of compressive, tensile, and shearing movement [ 12 ] after callus distraction. The hypothesis of this study is that the direction of IFM after callus distraction affects the bone formation and revascularization during the maturation process of the newly formed bone.…”