Neovascularization across a gap defect in a rabbit tibial cortex was monitored using the optical bone chamber implant (BCI). Cortical bone growing by apposition as trabeculae was observed weekly as it penetrated a slit into a tissue space in vivo and in situ. Each rabbit was viewed weekly with an intravital microscope from 3 to 8 weeks postimplantation. The constant field of view was the slit-gap tissue space, which was 100 microns thick and 2 mm in diameter. Vessels were imaged with epi-illuminated fluorescence microscopy as they carried FITC-dextran 70 that had been injected into an aural vein. Observations were videotaped and photographed. Videotape frames were analyzed with a digital image processing system to obtain measures of vessel length per unit volume (L/V) of fibroblastic granular tissue and trabeculae, caliber C, and flow velocity u, all as functions of time. Observations supported the conclusions that (1) neovascularization precedes neo-osteogenesis, (2) major vessels tend to align with the tibial axis, (3) bone apposition-generated destruction of fibrous granular tissue vessels stimulates fibrous granular tissue angiogenesis, which keeps its L/V constant, (4) L/V in trabeculae increases with time, and (5) blood supply (Q) and nutrient exchange in healing trabeculae are not positively correlated. Thus, O2 supply to the trabeculum cannot be predicted from Q alone because the nutrient exchange area is not constant. It was noted that an increase in the potential nutrient exchange area occurred in both fibrous granular tissue and osseous vessels and the volume fraction of blood decreased in the fibrous granular tissue and remained constant in the trabeculae.

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Neo-osteogenesis of cortical bone trabecular was observed as they regenerated into a bone chamber implant by appositional growth. Measures of change in bone area were obtained from 13 rabbits each week starting the third and ending the eighth week postimplantation. Observations were made using intravital microscopy and were analyzed using digital image processing. Images were computer-captured video frames equivalent to 78 (6 x 13) separate observations. They were measured by tracing the trabecular outlines with a digitizing crosshair each week and comparing changes in area as a percent of the circular field-of-view ("slit-gap") filled. Data supported the hypothesis that trabecular regeneration week 3 to week 8 followed the logistic growth curve regression: A% 100%/1 + 9.47e-0.7747(t-3) where A% is the percent of slit-gap area covered by bone and t is time, at a very high significance level. Nevertheless, a highly significant linear regression fit the data. Statistical analysis showed that the regression line could be fit to bone area measurements from weeks 3 to 8 (W3-W8) postimplantation, giving a constant neo-osteogenesis rate of 7.42 +/- 0.67 X 10(4) microns 2/day and a decreasing linear neo-osteogenesis rate from 73 microns/day at W4 to 21 microns/day at W8; the latter is based on a circle-segment approximation of trabeculum shape. This range approximated a bridge between ranges for cortical gap defect healing and porous ingrowth healing reported by other workers and supported the hypothesis that the BCI control model was a cross between gap healing and porous ingrowth.

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