Purpose of Study: Current knowledge links the biological cascade of fracture healing to the fracture muscle envelope and to the preservation of stable, perpetual axial micromovements. The active biological compounds in the initiation of osteoneogenesis are cytokines. The current study correlates the latter by their molecular weight to their osteoneogenetic activity.
Materials and Methods: Under GA and strict aseptic conditions, experimental fractures were produced in the mid-diaphysis of the left tibia in 60 adults Wistar rats. They were stabilized by an intramedullary no 20 needle. They were split into for equal groups:
Group A: Fractures were left to heal spontaneously. This was the control group.
Groups B,C,D: Using meticulous dissection, a sterile nitrocellulose membrane was wrapped around the fracture between the periosteum and muscle envelope.
The membranes pore sizes were: 3.5 kDa in group G; 12–14 kDa in group C; and 50 kDa in group D. The rats were euthanized at weeks 2, 5, 10 by an overdose of pentobarbital. Fracture healing was assessed by radiographies, histologic examinations and immunohistochemical localization of bone specific genes [IGF-1, IGF-1 receptor, cartilage proteoglycans, type II collagen, osteocalcin].
Results: In group A, callus formation was present at 2 weeks and progressed to full fracture healing by 5 weeks. In group B, no callus was detectable even at 10 weeks. In group C, most rats did not develop any callus, while a few started to develop calluses at 10 weeks. In group D, callus development was comparable to group A.
A good correlation was found between the radiological and morphological results.
Immunohistochemical localization of gene expression revealed a high level of PCNA [proliferating cellular nuclear antigen] with high local levels of IGF-1, and high levels of type II collagen as well as osteocalcin. In group B, this level of activity was very mild and did not reach bone healing level. In groups A and D, the results were comparable. They developed both medullary and periosteal callus, the former being persistently absent in groups B and C.
Conclusions: Extensive direct contact between fractured bone and it’s muscle envelope is essential for the biological sequence of new bone formation, i.e. fracture healing. Preventing the diffusion of cytokines with a molecular weight higher than 14 kDa from muscle to fractured bone effectively interrupts the biological cascade of osteoneogenesis.
