Effect at soft-tissue trauma om the early periosteal response of bone to injury

Objective: To determine whether the periosteal response to skeletal trauma is impaired when muscle is also injured, thereby providing a possible expla nation for why fractures with extensive soft-tissue damage may take longer to heal, Methods: A bone defect was made in the tibia of male Fisher rats, and the p roliferative response, osteoblast concentration, and callus formation that occurred within 7 days were measured in the presence and absence of simulta neously administered model soft-tissue injury (removal of 10% of the anteri or tibialis muscle from a region within 2 to 3 mm of the bone defect), Meas urements were made by using autoradiography, quantitative histology, and mo rphometry. Results: Addition of the muscle injury increased proliferation in the cambi um and in the fibrous periosteum on day 1, but had no effect thereafter; pr oliferation of fibroblasts in the loose connective tissue above the periost eum was not affected. Addition of the muscle injury resulted in increased o steoblast levels 2 to 5 days after injury but had no effect on the amount o f callus produced. Conclusion: The inflammatory milieu created by the muscle injury unexpected ly resulted in an increased periosteal response to skeletal trauma, suggest ing that inflammatory mediators generated in response to wounding of soft t issues are unlikely to account for delayed fracture healing. These findings may indicate that surgical trauma associated with internal fixation by usi ng plates and screws may not be as deleterious to the fracture-healing resp onse as previously thought.