Can Bone Healing in Distraction Osteogenesis Be Accelerated by Local Application of IGF-1 and TGF-b1? Anke Bernstein, 1 Hermann O. Mayr, 1,2 Robert Hube 1,2 1 Laboratory of Experimental Orthopedics, Department of Orthopedics, Martin Luther University of Halle-Wittenberg, Halle 06097, Germany 2 Orthopeadic Surgery Munich (OCM), Munich 81369, Germany Received 24 February 2009; revised 13 July 2009; accepted 16 July 2009 Published online 6 October 2009 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jbm.b.31508 Abstract: Because complications of distraction osteogenesis are largely related to the long duration of therapy, increasing efforts were reached to shorten treatment by using osteoconductive replacement materials incorporating bioactive molecules such as IGF-1 and TGF-b1. The controlled release of IGF-1 and TGF-b1 from coated biodegradable poly(D,L-lactide) implants could stimulate fracture healing locally. We investigated the effect of locally applied IGF-1 and TGF-b1 from IGF-1/TGF-b1-enriched polylactide membranes on fracture healing in a sheep model of delayed callus formation. Twenty-eight sheep were used for this study. Callus distraction of 1 mm/day by means of a unilateral fixator was continued for 30 days. At the beginning of the subsequent consolidation phase, either growth factors were applied locally or the defect was packed with cancellous bone, or both. The groups treated with growth factors were compared to a control group. The consolidation phase lasted for 60 days and both tibiae were dissected for histological and histomorphometric analyses. This investigation found a reduced absolute callus area in the lengthening zone in all treatment groups. The two treatment groups that received a membrane coated with growth factors showed distinctly higher relative bone areas than the groups treated with an uncoated membrane or packing of the osteotomy defect with cancellous bone. The differences in bone areas were not statistically significant. Application of the growth factors accelerated bone healing and achieved results comparable with those of established treatment methods (packing with autologous cancellous bone). The best results were achieved with a combination of both methods. ' 2009 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 92B: 215–225, 2010 Keywords: callus distraction; growth factors; histomorphometry; bone healing; osteogenesis INTRODUCTION The sequences and the regulation processes at cellular level during distraction osteogenesis remain to be completely elucidated. The biological processes are characterized by the temporary appearance of periosteal and endosteal callus. The tensile forces between the distracted bone fragments stimulate the osteoblasts. 1 In the distraction gap, the wound (corticotomy) leads to the formation of a hematoma. A typ- ical acute inflammatory reaction occurs, with vasodilation and capillarization. The hematoma is resorbed and replaced by granulation tissue. 2 This tissue consists of fibroblasts, newly formed collagen, and numerous capillaries. In the center of this lengthening segment a growth zone forms. Under the influence of the distraction stimulus, the initially arising resorption and granulation tissue is transformed into longitudinally oriented fibrous connective tissue. 3,4 Within the first few days, capillaries grow into the interfragmen- tary tissue. 5 Osteoblasts gather around these vessels and combine with collagenous fibers and osteoid to form columnar structures extending from the osteotomy line to- ward the center of the lengthening segment. 6,7 This forms a scaffold in which osteogenesis can proceed under the pro- tective covering of a membrane. Osteoblasts are deposited on the mineralized connective tissue matrix, and osteoid forms. The osteoid is further mineralized, and the condi- tions for intramembranous desmoid bone formation are met. 8,9 The maturation processes continue, and the fibrous intermediate zone between the distracted bone ends ossifies. Woven bone forms, bridging the bone ends. This process begins in the consolidation phase, when no longer any ten- sile forces acted on the regenerating callus. 3 A fibrous layer still appeared in the central area between the bone ends. In Correspondence to: A. Bernstein (e-mail: anke.bernstein@medizin.uni-halle.de) ' 2009 Wiley Periodicals, Inc. 215