Reverse Dynamization Accelerates Regenerate Bone Formation and Remodeling in a Goat Distraction Osteogenesis Model
Authors: Bafor Anirejuoritse , Iobst Christopher , Samchukov Mikhail , Cherkashin Alexander , Singh Satbir , Aguilar Leonardo , Glatt Vaida 
Published: August 2023

Update
This article was updated on December 20, 2023, because of previous errors, which were discovered after the preliminary version of the article was posted online. Figure 4 has been replaced with a figure that presents different p values. Also, on page 1943, the text that had read: “Quantitative microCT confirmed that the total volume of the regenerate in the RD group was much smaller compared with the SF (p = 0.06) and DF (p = 0.007) groups, although it was significantly smaller only compared with the DF group (Fig. 4-A). The total volume of the intact bone (contralateral tibia) was significantly smaller in the RD group compared with the other groups, but the RD group had values closest to those for the intact tibia. Similarly, the RD group had less bone volume compared with the SF and DF groups, and this value was significantly different from the DF group (p = 0.034; Fig. 4-B). Of the 3 groups, the RD group had vBMD that was the closest to that of intact bone. It also had significantly higher vBMD compared with the SF and DF groups (p < 0.0001 for both; Fig. 4-C).
The results of torsional testing (Fig. 4-D) confirmed that the regenerate bone formed under conditions of RD was significantly stronger than that formed under SF or DF (p < 0.001 versus SF group, and p = 0.0493 versus DF group).”
now reads: “Quantitative microCT confirmed that the total volume of the regenerate in the RD group was significantly smaller compared with the SF and DF groups (p < 0.01 for both groups; Fig. 4-A). The total volume of the intact bone (contralateral tibia) was significantly smaller compared with the SF and DF groups (p < 0.0001 for both). The RD group had values closest to those for the intact tibia, and this difference was not significant (Fig. 4-A). Similarly, the RD group had less bone volume compared with the SF and DF groups, and this value was significantly different from the DF group (p < 0.01; Fig. 4-B). Of the 3 groups, the RD group had vBMD that was the closest to that of intact bone, but the intact bone was significantly different compared with all of the other groups (p < 0.0001 for all groups). The RD group had significantly higher vBMD compared with the SF and DF groups (p = 0.042 and p = 0.046, respectively; Fig. 4-C).
The results of torsional testing (Fig. 4-D) confirmed that the regenerate bone formed under conditions of RD was significantly stronger than that formed under SF or DF (p < 0.0001 versus SF group, and p = 0.0493 versus DF group). The intact group was significantly different compared with the SF group (p < 0.0001).”

Background:
The concept of reverse dynamization involves modifying the mechanical environment surrounding a fracture to influence the healing response. Initially, less rigid stabilization is performed to allow micromotion, encouraging cartilaginous callus formation. This is followed by a conversion to more rigid fixation to prevent the disruption of neovascularization, thereby accelerating bone healing and remodeling. The effect of reverse dynamization in distraction osteogenesis has not been studied, to our knowledge. The aim of this study was to determine whether reverse dynamization can accelerate the formation and maturation of regenerate bone in a goat distraction osteogenesis model.

Methods:
Midshaft tibial osteotomies were created in 18 goats and stabilized using circular external fixation. After a 5-day latency period, 4 weeks of limb distraction began to obtain a 2-cm gap; this was followed by 8 weeks of regenerate consolidation. The goats were divided into 3 groups: static (rigid) fixation (SF, n = 6); dynamic fixation (DF, n = 6), consisting of continuous micromotion using dynamizers; and reverse dynamization (RD, n = 6), consisting of initial micromotion during the distraction period using dynamizers followed by rigid fixation during the consolidation period. Healing was assessed using radiographs, micro-computed tomography, histological analysis, and mechanical testing.

Results:
Radiographic evaluation showed earlier regenerate formation in the DF and RD groups compared with the SF group. After the distraction and consolidation periods were completed, the regenerate formed under the conditions of RD had less trabeculation, higher bone mineral density, and smaller total and bone volumes, and were stronger in torsion compared with the SF and DF groups. This appearance is characteristic of advanced remodeling, returning closest to the values of intact bone. The DF group also had evidence of an interzone (radiolucent fibrous zone) at the end of the consolidation period.

Conclusions:
Application of the reverse dynamization regimen during distraction osteogenesis accelerated formation, maturation, and remodeling of regenerate bone.

Clinical Relevance:
The findings of this study have important implications in the clinical setting, as reverse dynamization may lead to shorter treatment times and potentially lower prevalence of complications for patients needing distraction osteogenesis.