Effects of Ionizing Radiation on Woven Bone

Objectives: Evaluate the effects of ionizing radiation on the newly formed bone microarchitecture, osteocyte network and collagen maturity in the area under bone repair process.
Methods: Ten New Zealand rabbit (3.0-3.5kg) were included. Bone defects (2.3mm) were created on both tibias. After 14 days they were aleatory divided (n=10) into: NoIr (control group, kept free of irradiation) and Ir (irradiated group). In Ir group, animals received single-dose irradiation of 30 Gy on both tibias. Two weeks later, animals were euthanized. Micro-computerized tomography was used to access 3D microarchitecture. Osteocyte network, bone area, and collagen pattern was analyzed following hematoxylin-eosin, Mallory Trichrome and Picrosirius Red staining. Student’s t-test was applied (α=0.05).
Results: Bone surface density (p=0.590), trabecular number (p=0.643), bone mineral density (p=0.353), percent bone volume (p=0.227) and trabecular separation (p=0.651) were the same in both groups. Trabecular thickness in Ir group was lower than in NoIr group (p= 0.028). Histological sections evaluation of bone area showed no statistical difference between NoIr and Ir group. Regarding osteocyte network, lacunae was assessed, counted and measured. Lacuna filled with osteocytes were more numerous (p<0.0001) in NoIr (2.61±0.64) than Ir group (1.97±0.53). Empty lacunae were more present (p<0.003) in Ir group (0.14±0.10) compared to NoIr (0.09±0.10). The mean osteocyte lacunae size revealed higher values (p<0.01) in Ir (15.41±4.41) than non-irradiated animals (12.72±3.73). Collagen analysis showed higher amount (p=0.04) of type I collagen (reddish birefringence) in NoIr group (28.96±5.31) than in Ir group (23.42±4.47). Type III collagen (greenish birefringence) quantification revealed no statistical difference (p=0.17) between NoIr (32,60±6,07) and Ir group (36,09±2,83).
Conclusions: It was shown a delay in bone repair, revealed by thinner trabeculae arrangement, with less osteocytes and more empty lacunae in irradiated woven bone. In addition, smaller osteocyte lacunae size together with greater amount of type I collagen in non-irradiated group also support this fact.