Purpose: The purpose of this study was to relate the extent of reaming to bone formation occurring around a critical sized defect in the tibia.

Method: Eleven canines were allocated into 2 groups: empty (N=5) or iliac crest autograft (N=6). All tibiae were reamed to 7.0 mm and fixed with a 6.5 mm statically locked intramedullary nail after creation of an 8.0 mm diaphyseal defect. The extent of reaming of the canal was dependent on the cross-sectional area of the tibia as all tibiae were reamed to 7.0 mm. Fluorescent markers were given at different times: calcein green (6 weeks), xylenol orange (9 weeks), and tetracycline (11 and 14 weeks). Animals were sacrificed at 15 weeks and perfused with a barium compound. Radiography, Micro CT, brightfield microscopy and fluorescent microscopy were used for analysis.

Results: Bone and vasculature volume within the defect were reported as a percentage of the total volume of the defect. Linear regression analysis of percent bone volume (dependent variable) and canal area (independent variable) provided a Pearson correlation coefficient of 0.925 (p=0.025) for the empty group and 0.244 (p=0.641) for the autograft group. Linear regression analysis of percent vasculature volume (dependent variable) and canal area (independent variable) provided a Pearson correlation coefficient of 0.784 (p=0.117) for the empty group and −0.146 (p=0.783) for the autograft group. Bone formation at osteotomy sites was defined as the distance from the original osteotomy site to the tip of newly formed bone. Linear regression analysis of bone formation at the osteotomy sites (dependent variable) and canal area (independent variable) provided a Pearson correlation coefficient of 0.132 (p=0.832) for the empty group and −0.937 (p=0.006) for the autograft group. Bone formation rates were reported as the distance between the fluorescent labels. Bone formation rate was less within the endosteum, cortex and periosteum with extensive reaming in empty samples.

Conclusion: Our results suggest that the acute management of tibia fractures with bone defects should involve limited reaming. This does not apply when the defect is autografted. Limited reaming may be defined by the cross-sectional area of the tibia in ratio to that of the reamer.

Purpose: The aim of our study was to evaluate bone formation and angiogenesis produced within a biodegradable poly-D, L-lactide-co-glycolide acid/calcium phosphate (PLGA/CaP) scaffold when used to treat a diaphyseal tibia defect and compare this to an iliac crest autograft or an empty defect.

Method: An 8.0 mm diaphyseal defect was created in a canine tibia model. All tibiae were reamed to 7.0 mm and fixed with a 6.5 mm statically locked intramedullary nail. Eighteen canines were allotted into three treatment groups:

empty (N=5),

Fluorescent markers were given at different times: calcein green (six weeks), xylenol orange (nine weeks), and tetracycline (11 and 14 weeks). Animals were sacrificed at 15 weeks and perfused with a barium compound. Radiography, Micro CT, and brightfield and fluorescent microscopy were used for analysis.

Results: Micro CT and brightfield images of scaffold samples displayed multiple vessels (10 to 100μm) within the scaffold. The bone volume and vasculature volume (measured with Micro CT) within the tibial defect site were reported as a percentage of the total volume of the defect site. The percent bone volume within the defect site was not different between treatment groups (p=0.112). There was greater percent vasculature volume in the scaffold group than the autograft group (p< 0.001). Bone formation at the osteotomy sites was defined as the distance from the original osteotomy site to the tip of newly formed bone. Osteotomy bone formation was significantly greater in the scaffold group than the autograft group (p=0.015). Osteotomy sites associated with greater angiogenesis displayed greater bone formation. Bone formation rates were reported as the distance between the fluorescent bone labels. Autograft samples had the greatest bone formation rates within the periosteum. Autograft and scaffold samples had the greatest rate of bone formation within the cortex.

Conclusion: Our canine tibial defect model provides a satisfactory facsimile of the traumatic tibia fracture with associated bone loss. The PLGA/CaP biodegradable scaffold we have employed promotes angiogenesis within a defect and could be used in conjunction with autografting.