12. A BIODEGRADABLE SCAFFOLD FOR THE TREATMENT OF A DIAPHYSEAL BONE DEFECT OF THE TIBIA

Abstract

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:

1. empty (N=5),

2. iliac crest autograft (N=6), or

3. PLGA/CaP biodegradable scaffold Tissue Regeneration Therapeutics Inc., ON, Canada) (N=7).

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.