Development of nonunions in the rat fibula after removal of periosteal neural mechanoreceptors.

Periosteal proprioceptive nerve receptors may act as mechanoreceptors of long bones during adaptive remodeling after fracture. They may also contribute to the mechanisms of coordinated functional activity of fractured limbs and thus inhibit harmful overloading of fracture callus. The area of proprioceptive nerve receptors around the distal part of the rat fibula was stripped surgically, and a standard fracture of the fibular shaft was produced. Animals failed to unite their fractures and developed mainly atrophic nonunions. Atrophy of ununited fragments was due to osteoclastic bone resorption. Atrophy of the bone fragments was aggravated if the legs were also subjected to sciatic denervation. Sciatic denervation alone, without removal of receptors, did not interfere with the union of fractures. The results indicate that the area of proprioceptive receptors in the rat tibiofibular bone is critical for the healing of fibular fractures. Because the effect on bone healing of receptor removal was not inhibited by sciatic denervation, the effect was not transmitted through spinal pathways of the sciatic nerve. The development of nonunions could not be explained by the surgical trauma alone. Aggravation of fibular atrophy by sectioning of the sciatic nerve suggests that some neural elements are associated with the phenomenon, either directly or indirectly through neuromuscular function.