Bone and cartilage formation in an experimental model of distraction osteogenesis.

OBJECTIVES: (a) To develop a reliable and reproducible system for distraction osteogenesis in the rat to establish a model for future investigations of bone repair and regeneration. (b) To describe and characterize the histological events in distraction osteogenesis in the rat and to determine whether cartilage development is a normal component of the process. STUDY DESIGN: Species-specific, longitudinal time study. METHODS: Twenty rats underwent production of a middiaphyseal femoral osteotomy and application of a monolateral external fixator specifically designed for distraction. Animals were divided into five groups based on the time and extent of lengthening. RESULTS: During distraction, gap tissue showed collagen bundles and fibroblasts that were oriented longitudinally to the direction of the distraction force. Woven bone appeared to be laid down on these collagen scaffolds, and the newly formed vascular sinuses appeared to be the sites from which bone formation was initiated within the distraction gap. All groups undergoing active distraction showed intramembranous ossification in the distraction gap and endochondral ossification peripherally. However, when distraction was discontinued, endochondral ossification was observed in the gap. CONCLUSION: Distraction produces an environment in the distraction gap that suppresses the formation of cartilage. The formation of cartilage by injured periosteum, however, is obligatory and does not appear to be influenced by distraction. Bone formation within the distraction gap occurs where angiogenesis develops.

Thumb digital neuropathy caused by splinting.

Healthcare professionals are currently faced with a great variety of splints and splinting materials. Choices range from prefabricated products to custom splints made on-site from plaster, orthoplast, or fiberglass. In addition to providing immobilization to maintain a particular posture, a splint must protect important soft tissues. Patients with hand or wrist injuries often receive a prefabricated metal cock-up wrist splint in emergency departments. Complications from splints are not uncommon but are infrequently reported. We report a case in which a metal wrist cock-up splint caused compression of the thumb ulnar digital nerve. Preventive measures for such complication are included.

Effects of diabetes and steroids on fracture healing.

Fracture healing is largely controlled by local regulatory interactions among cells and tissues near the site of injury; however, many systemic hormones including insulin, the glucocorticoids, and the gonadal steroids also can influence the course of tissue repair, particularly in the case of pathologic hormone excess or deficiency. Using well-defined animal models, recent studies have established that deficiencies in insulin and estrogen impair fracture healing, but data from this type of experiment are limited. Still, the similarities between morphogenetic events in fracture healing and those found in normal bone development and remodeling suggest that testable predictions can be made concerning hormonal effects on the progress of fracture healing. One concept that has received some direct experimental support in fracture healing model studies is that systemic hormones exert pleiotropic effects on callus tissue by regulating the expression and activity of local growth factors. Further verification of this and other predicted hormone effects should increase our understanding of the fundamental mechanisms underlying fracture repair, and may aid development of means to improve fracture healing in states of altered endocrine function.