CLINICAL ORTHOPAEDICS AND RELATED RESEARCH Number 3555, pp S191-S204 zyx 0 1998 Lippincott Williams zyxw & Wilkins zyxw Bone Regeneration and Fracture Healing zy Experience With Distraction Osteogenesis Model zy Mark Richards, PhD*.**; James A. Goulet, MD*; Jeflrey A. Weiss, PhDf; Nicholas A. Waanders, MD, PhD*; Mitchell B. Schaffleer, PhD$; and Steven A. Goldstein, PhD* The relation between physical forces and the processes of bone regeneration and healing remains incompletely understood. Gaps in understanding of these processes stem in part from models that produce inadequate amounts of new bone for study. Bone created through the use of distraction osteogenesis provides an attractive substrate for the study of mechanical forces and their effects on bone formation because this technique produces large volumes of new bone in a controlled fashion. The optimal mechanical environment in which bone formation occurs clinically has not been fully determined. In laboratory studies, however, the mechanical environment can be manipulated, and resultant changes in bone formation can be measured. To investi- gate how changes in strain environment influ- ence patterns of bone formation, a bilateral New Zealand White rabbit model of bilateral distraction osteogenesis was implemented. When a stiffener was applied to the external From the *Orthopaedic Research Laboratories, Univer- sity of Michigan, MI; **University of Michigan Hospi- tals and Health Center, Ann Arbor, MI; ?Orthopedic Biomechanics Institute, Salt Lake, UT and $Bone and Joint Center, Henry Ford Hospital, Detroit, MI. Supported by NIH (AR-20557), The Orthopaedic Re- search zyxwvutsrq and Education Foundation, and The Whitaker Foundation. Reprint requests to James A. Goulet, MD, University of Michigan Hospitals and Health Center, 1500 East Med- ical Center Drive, Ann Arbor, MI 48109-0328. distractor, computation analyses predicted a sevenfold to eightfold decrease in all strain measures. These reductions in gap strains ap- peared to induce significant decreases in bone volume fraction and mean trabecular thick- ness. When osteotomies were created at a 30" angle to the bony axis to generate more shear within the gap tissue, changes in the distribu- tion of gap strains and resultant new bone ar- chitecture were observed. Specific correla- tions between changes in tissue level strains and the pattern of bone regeneration were seen in both experiments. These results pro- vide direct in vivo evidence that pluripoten- tial gap tissues are sensitive to their physical surroundings. Mechanisms responsible for this sensitivity might include vascularity, stem cell supply, and scaffolding architecture. The process of bone formation in distraction osteogenesis appears to be related to bone for- mation processes associated with more com- mon conditions. The distraction osteogenesis model described suggests a mechanism for bone formation that seems applicable to other more common processes associated with bone formation, including fracture healing and im- paired fracture healing. Distraction osteogenesis has been applied successfully to some of the most challenging conditions in orthopaedic surgery. Although uniform success has not been achieved, the s191