Temporal variation in fixation stiffness affects healing by differential cartilage formation in a XXXX osteotomy model.

@entity1 @entity174 @entity245 @entity79 @entity1442 @entity35 @entity2472
BACKGROUND: Dynamization involves a reduction in fixation construct stiffness during @entity79 , allowing increased interfragmentary movement of the @entity174 through physiologic weightbearing and @entity2472 . Within some optimal range, interfragmentary movement stimulates healing, but this range likely varies across stages of @entity79 . QUESTIONS/PURPOSES: How does the time of dynamization affect the cartilage formation, bony bridging, and bone resorption in a @entity35 @entity174 -healing model? METHODS: Unilateral external fixators, stabilizing a 1-mm gap, were dynamized at 1 (D1 group, n = 10), 3 (D3 group, n = 11), or 4 (D4 group, n = 11) weeks postoperatively. Continuously 5 weeks stiff (S group, n = 10) and flexible (F group, n = 11) fixation were included for comparison. After 5 weeks, healing was evaluated by histomorphometric methods. RESULTS: @entity1442 , indicated by less cartilage and a greater rate of bony bridging, was observed in the S group compared to the D1 or F group. In contrast, the D3 and D4 groups had less cartilage and more bridging compared to the S group. Also, the S group had less cortical resorption than the F and D1 groups. CONCLUSIONS: These data suggest late dynamization at the onset of bony bridging led to enhanced healing, whereas dynamization at the early stage of cartilage differentiation @entity245 . CLINICAL RELEVANCE: Although our observations from this small-animal study cannot be directly transferred to @entity1 , these data suggest, once bony bridging begins, dynamization may stimulate @entity79 and accelerate remodeling.
