Early mechanical stimulation only permits timely bone healing in sheep

Abstract

Bone fracture healing is sensitive to the fixation stability. However, it is unclear which phases of healing are mechano-sensitive and if mechanical stimulation is required throughout repair. In this study, a novel bone defect model, which isolates an experimental fracture from functional loading, was applied in sheep to investigate if stimulation limited to the early proliferative phase is sufficient for bone healing. An active fixator controlled motion in the fracture. Animals of the control group were unstimulated. In the physiological-like group, 1 mm axial compressive movements were applied between day 5 and 21, thereafter the movements were decreased in weekly increments and stopped after 6 weeks. In the early stimulatory group, the movements were stopped after 3 weeks. The experimental fractures were evaluated with mechanical and micro-computed tomography methods after 9 weeks healing. The callus strength of the stimulated fractures (physiological-like and early stimulatory) was greater than the unstimulated control group. The control group was characterized by minimal external callus formation and a lack of bone bridging at 9 weeks. In contrast, the stimulated groups exhibited advanced healing with solid bone formation across the defect. This was confirmed quantitatively by a lower bone volume in the control group compared to the stimulated groups.The novel experimental model permits the application of a well-defined load history to an experimental bone fracture. The poor healing observed in the control group is consistent with under-stimulation. This study has shown early mechanical stimulation only is sufficient for a timely healing outcome. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1790-1796, 2018.

The Effect of External Fixator Configurations on the Dynamic Compression Load: An Experimental and Numerical Study

“…Actually, the success of bone remodelling depends on adequate blood supply and on the gradual increase of mechanical stability [39,40], the localized modification of one condition has different effects than a global modification of both conditions. Moreover, in the physiological-like group [38], the active fixator applied 1 mm axial compressive IFMs, commencing on the fifth post-operative day, and, after three weeks, the movements were decreased in 0.25 mm increments until week six, when the applied movements were stopped [38]. This decrease of IFM does not seems related to the physiological loading on bone healing phases.…”

“…In this case, the load passing to the callus was higher, and thereby increased the interfragmentary movement. On the contrary, in the work of Tufekci et al [38] the dual unilateral fixation was maintained in all healing weeks and the dynamization was performed in the mobile fragment by a DC motor. The first main difference between these two studies is associated with the rate of change of movement in the fracture.…”

“…Even though there are differences between the numerical and experimental models, namely concerning the clearance and the continuity of connections between the free clamp and Schanz screws, and of all components connected to the locked clamp, it is worth noting that both models confirm that the fixator configuration has a significant effect on the percentage of load passing to the callus. Moreover, disagreements between recent studies on whether mechanical stimulation is required during consolidation and remodelling healing stages [37,38] could also be related to differences between the external fixator configurations in the several studies. In fact, Claes et al [37] performed an elastic dynamization by decreasing the stiffness of the fixation and assuming that, within the dynamization weeks, the load bearing on the operated leg does not changed considerably.…”

“…Moreover, it would require considerable resources to validate an experimental and/or numerical model that were able to predict important parameters. Nevertheless, because the generality of studies concerning the fracture healing process has been focus on the compression load [28,35,38,41,42] and the main goal of this work was to investigate the viability of the LRS fixator in the dynamic compression mode on different configurations, we were interested in relative rather than absolute results. Another limitation of this work is associated with the use of a nylon bar instead of a realistic geometry of the tibia.…”

Individualized cyclic mechanical loading improves callus properties during the remodelling phase of fracture healing in mice as assessed from time-lapsed in vivo imaging

“…Compared to control animals, in which bone resorption still increased during this early remodelling period (week 3-4), loaded animals showed significantly lower bone resorption rates in all callus VOIs (DC, DP, FP) in this first week of loading, indicating a strong mechano-responsiveness of the fracture callus during this healing period. Most of the previous studies either assessed the loading effects only after a longer loading period of minimum 2 weeks 27,28 or they did not see significant loading-mediated effects on the fracture callus after shorter treatment periods 8,10,26 . So far only one study by Leung et al 29 was able to detect a loading-mediated improvement of fracture healing (larger callus diameter) after a short loading period of 1…”