Fracture healing in mice under controlled rigid and flexible conditions using an adjustable external fixator

Abstract

Mice are increasingly used to investigate mechanobiology in fracture healing. The need exists for standardized models allowing for adjustment of the mechanical conditions in the fracture gap. We introduced such a model using rigid and flexible external fixators with considerably different stiffness (axial stiffnesses of 18.1 and 0.82 N/mm, respectively). Both fixators were used to stabilize a 0.5 mm osteotomy gap in the femur of C57BL/6 mice (each n = 8). Three-point bending tests, CT, and histomorphometry demonstrated a different healing pattern after 21 days. Both fixations induced callus formation with a mixture of intramembranous and enchondral ossification. Under flexible conditions, the bending stiffness of the callus was significantly reduced, and a larger but qualitatively inferior callus with a significantly lower fraction of bone but a higher fraction of cartilage and soft tissue was formed. Monitoring of the animal movement and the ground reaction forces demonstrated physiological loading with no significant differences between the groups, suggesting that the differences in healing were not based on a different loading behavior. In summary, flexible external fracture fixation of the mouse femur led to delayed fracture healing in comparison to a more rigid situation.

The Interaction of BMP2‐Induced Defect Healing in Rat and Fixator Stiffness Modulates Matrix Alignment and Contraction

“…Previous studies demonstrated a prolonged cartilage phase and larger amounts of bone tissue associated with a larger bony callus in the context of unstable fixation 48, 49. Here we showed that this association can still be observed in the context of BMP2 treatment.…”

Partial weight bearing of the tibia

“…10 or 20 kg [1,2]. The rationale for partial loading schemes is to improve the biological process of fracture healing: While certain forces are required for fracture healing, excessive movement is known to delay the healing process compared to a more rigid situation [4]. Axial forces are necessary for the healing process [5].…”

Desenvolvimento e desempenho de um fixador flexível na consolidação de fraturas diafisárias transversais provocadas iatrogênicamente na tíbia de carneiros

“…O mesmo não ocorreu quando se utilizou um fixador externo rígido e outro flexível dinamizado pelo afrouxamento das conexões para reduzir osteotomias de fêmures de ratos. Neste estudo, as osteotomias reduzidas com fixador rígido consolidaram mais rapidamente do que as reduzidas com o fixador flexível (RÖNTGEN et al, 2010), possivelmente devido ao afrouxamento excessivo do fixador, mesmo quantificando-o previamente. Acreditase que, no decorrer do pós-operatório, o afrouxamento possa aumentar, o que não aconteceria com uma haste de flexibilidade pré-determinada.…”