INFLUENCE OF SIZE AND STABILITY OF THE OSTEOTOMY GAP ON THE SUCCESS OF FRACTURE-HEALING

Flexible fixation of fractures with minimally invasive surgical techni ques has become increasingly popular. Such techniques can lead to rela tively large fracture gaps (larger than 5 mm) and considerable interfr agmentary movements (0.2-5 mm). We investigated the influence of the s ize of the fracture gap, interfragmentary movement, and interfragmenta ry strain on the quality of fracture healing. A simple diaphyseal long -bone fracture was modeled by means of a transverse osteotomy of the r ight metatarsus in sheep. In 42 sheep, the metatarsus was stabilized w ith a custom-made external ring fixator that was adjustable for gap si ze and axial interfragmentary movement. The sheep were randomly divide d into six groups with three different gap sizes (1, 2, or 6 mm) and s mall or large interfragmentary strain (approximately 7 or 31%). The mo vement of the fracture gap was monitored telemetrically by a displacem ent transducer attached to the fixator. After 9 weeks of healing, the explanted metatarsus was evaluated mechanically in a three-point bendi ng test to determine bending stiffness and was radiographed to measure the amount of periosteal callus formation. Increased size of the gap (from 1 to 6 mm) resulted in a significant reduction in the bending st iffness of the healed bones. Larger interfragmentary movements and str ains (31 compared with 7%) stimulated larger callus formation for smal l gaps (1-2 mm) but not for larger gaps (approximately 6 mm). The trea tment of simple diaphyseal fractures with flexible fixation can be imp roved by careful reduction of the fracture; this prevents large interf ragmentary gaps. The experimental fracture model for the metatarsus sh owed that :he healing process was inferior when the gap was larger tha n 2 mm.