VALIDATION OF WALL THICKNESS ESTIMATES OBTAINED WITH POLARIZED-LIGHT MICROSCOPY USING MULTIPLE FLUOROCHROME LABELS - CORRELATION WITH EROSION DEPTH ESTIMATES OBTAINED BY LAMELLAR COUNTING

Numerous methods are currently being employed to estimate completed wa ll thickness and final erosion depth. Conflicting estimates of calcula ted bone balance have been obtained from the estimates of wall thickne ss and erosion depth using these various methods. To assess the utilit y of two specific methods to estimate wall thickness (polarized micros copy) and erosion depth (lamellar counts), we conducted a study in nor mal young adult beagle dogs, a model where bone balance should approxi mate 0. Dogs were administered multiple fluorochrome labels in vivo to label actively forming bone pockets. These labels were used to confir m the position of the cement line of the bone structural unit (BSU) in fluorescent light. Parallel measurements of wall thickness were then collected in polarized light. These estimates were compared to estimat es of erosion depth obtained by lamellar counting and bone balance was calculated. Estimates of wall thickness correlated well with estimate s of erosion depth with bone balance not differing significantly from 0. These data suggest that the combination of these two methods is a r easonable approach to obtaining estimates of bone balance at the level of the remodeling unit.