Age and mechanical stability influence fracture callus microstructure
MedWire News: Both age and fracture fixation stability influence fracture callus formation during bone healing, study findings indicate.
However, varying fixator configurations in older individuals did not alter the dominant effect of age on callus tissue mineralization, unlike in their younger counterparts. Therefore, age-associated influences appeared independent of stability, say researchers.
Using three-dimensional in vitro micro-computed tomography (µCT) derived metrics, two-dimensional in vivo radiography, and histology, Georg Duda (Charité-Universitätsmedizin Berlin, Germany), and colleagues investigated the influence of age and varying fixation stability on callus size, geometry, microstructure, composition, remodeling, and vascularity.
They divided 48 female Sprague-Dawley rats with a 1.5-mm osteotomy gap in the femora into four groups defined by variation of fixator stabilities (rigid vs semirigid) and age (12 vs 52 weeks): young rigid; young semi-rigid; old rigid; and old semi-rigid.
The researchers report that semi-rigid fixations resulted in a larger callus cross-sectional area compared with rigid ones.
In vitro µCT analysis at 6 weeks postmortem showed callus bridging scores in younger animals were superior to those in their older counterparts. Younger animals also showed significantly larger callus strut thickness, lower perforation in struts, and higher mineralization of callus struts.
Callus mineralization was reduced in young animals with semi-rigid fixation compared with rigid fixation, but remained unaffected by stability in the older group.
While stability had an influence, age showed no influence on callus size and geometry of callus. With no differences observed in relative osteoid areas in the callus region of interest, old as well as semi-rigid fixated animals showed a higher osteoclast count.
In addition, blood vessel density was reduced in animals with semi-rigid fixation.
"In conclusion, in vivo monitoring indicated delayed callus maturation in aged individuals," write Duda and co-authors in the journal Bone.
They explain that callus bridging and callus competence (microstructure and mineralization) were impaired in individuals with an advanced age, which matched with increased bone resorption due to higher osteoclast numbers.
"This study illustrates the dominating role of osteoclastic activity in age-related impaired healing, while demonstrating the optimization of fixation parameters such as stiffness appeared to be less effective in influencing healing in aged individuals," say the researchers.
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By Laura Dean