CORTICAL BONE PERFUSION IN PLATED FRACTURED SHEEP TIBIAE

The limited contact dynamic compression plate and partial contact plat e were designed to decrease contact with cortical bone in an attempt t o decrease cortical ischemia, remodeling, and eventual porosis under t he plate after use of standard dynamic compression plates. This study quantified cortical bone blood flow beneath the plate with these three different designs in a sheep tibia fracture model. In 18 skeletally i mmature sheep, the right tibia was fractured and then was internally f ixed with an interfragmentary screw and a dynamic compression plate, l imited contact dynamic compression plate, or partial contact plate. At 12 weeks, cortical bone perfusion was assessed with laser Doppler flo wmetry in nine areas beneath the plate. The baseline (before fracture) cortical bone cell flux averaged 100 +/- 60 mV. After fracture, this decreased to 60 +/- 48 mV (p < 0.0003); immediately after plating, the perfusion averaged 29 +/- 25 mV (p < 0.01). Cortical bone perfusion t hen increased to 106 +/- 52, 165 +/- 71, and 163 +/- 71 mV at 2, 6, an d 12 weeks after fracture (p < 0.001 for all when compared with values after plating). No significant differences in cortical perfusion were seen between the types of plate. Cortical porosity under the plate wa s assessed with digital density analysis of microradiographs of this r egion. No significant difference was seen between the types of plate i n this analysis or in biomechanical and disulphine blue perfusion anal ysis. Thus, no significant advantage was seen for the new plate design s used in this model. This lack of advantage may be a result of the im mature animals used in the study, the protocol for blood flow measurem ent, the invasive periosteal stripping employed to create the fracture , or all three. However, as advantages with the new plate designs have been seen in other studies, this area warrants further investigation.