Rationale and Objectives
To evaluate cone beam computed tomography (CBCT) for monitoring of tibial bone defect healing in comparison to histopathological findings.
Materials and Methods
Circumscribed tibial bone defects were created in 16 mini-pigs and imaging of the tibia was performed on day 42 using a modern CBCT scanner with flat panel detector (PaX-Duo3D, Vatech, Korea). The extent of osseous consolidation including remaining calcium phosphate granules was measured quantitatively by a CBCT volumetry tool using commercially available software (Osirix Imaging software, Pixmeo, Geneva, Switzerland). Volumes of the entire defect (including all pixels), areas of osseous consolidation (density values >2350) and nonmineralized areas (density values <2350) of the defect were determined. The extent of bone regeneration was determined and correlated with the histomorphometrical reference standard. Independently, a visual semiquantitative CBCT-score was applied (4-point scale) to assess bone defect healing.
Results
The extent of osseous consolidation in CBCT volumetry ranged from 14% to 92% (mean, 63.4 ± 17.6%). There was a significant positive correlation between histologically visible newly formed bone and the extent of bone regeneration on CBCT volumetry ( r = 0.74–0.79, P < .001). The visual score matched with the volumetric results in 75% of the cases.
Conclusion
CBCT volumetry allows for reliable, noninvasive quantitative monitoring of bone defect healing and correlates significantly with histological findings. CBCT is a promising technique for imaging of peripheral bones suggesting further evaluation in clinical trials.
Cone beam computed tomography (CBCT) is based on a cone-shaped x-ray beam centered on a two-dimensional detector. The tube-detector system performs a 360° rotation around the object leading to multiple two-dimensional images. Using a modification of the original cone beam algorithm, images are reconstructed to a three-dimensional dataset . CBCT techniques have been previously employed in radiotherapy and fluoroscopic systems to obtain cross-sectional images. Dedicated CBCT scanners for the oral and maxillofacial (OMF) region were introduced about a decade ago independently by Mozzo and Arai . Interest in this imaging technique has increased over the past few years. For example, CBCT is a widely accepted low radiation dose imaging modality for preoperative planning of dental implants providing precise anatomical information . The radiation exposure of a typical dental examination with CBCT is reported to be only one third compared to multidetector CT (MDCT) . However, other body regions than the OMF region have barely been examined by CBCT so far.
In fractures of the extremities, exact monitoring of the osseous healing process is relevant because impaired or delayed healing can occur in 5%–10% . An exact analysis of bone healing provides important information for further treatment because defects in fracture healing might be detected at an early state, allowing for an optimized administration of additional growth factors or spongiosa to support the healing process . Various methods have been used to assess bone healing (eg, conventional radiography, high-resolution CT, micro-CT, magnetic resonance imaging) . A good correlation of CT and magnetic resonance imaging in detecting fracture union and nonunion of vertebral bodies after spinal injury has been reported . Conventional radiography (CR) is generally used as the primary imaging modality, but its value for objective quantification of bone healing has been reported to be limited . Based on only two imaging dimensions, overlapping structures (eg, bones, cast material) might lead to a missing of persistent fractures and a reduced ability to assess the extent of fracture healing and stability by CR. The use of CT overcomes the problem of overlapping structures. Direct imaging of bone bridging and callus formation has become possible . However, CT causes elevated radiation exposure to the patient compared to CR.
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Materials and methods
Animal Model
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Histopathological Analysis
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CBCT
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Quantitative CBCT Volumetry
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Semiquantitative Scoring
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Statistical Evaluation
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Results
Histopathological Analysis
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Table 1
Analysis of 16 Tibia Bone Defects in an Animal Model: Visual Scoring, Measurements of CBCT Volumetry and Histopathological Data
Tibia Number CBCT CBCT Volumetry CBCT Volumetry Histopathology Histopathology Visual Score Entire Defect (cm 3 ) Defect Consolidation (%) Cortical Bone Healing (%) Central Bone Healing (%) 1 3 1.94 66.7 37.5 33.3 2 3 0.80 69.5 32.6 26.5 3 3 0.63 62.8 31.1 25.6 4 1 1.54 13.9 25.4 21.4 5 1 0.87 55.1 28.4 22.0 6 3 1.48 50.9 29.7 23.9 7 3 1.64 56.0 33.2 27.8 8 3 0.99 47.1 41.1 33.7 9 3 1.12 75.3 41.9 42.0 10 4 1.61 64.7 34.9 28.7 11 3 0.64 64.2 31.2 28.5 12 4 1.00 91.6 49.3 43.2 13 3 1.74 67.0 35.0 33.8 14 4 1.15 79.6 43.9 43.0 15 4 1.52 68.2 36.4 36.3 16 4 1.20 81.8 37.3 39.6 Mean 3.06 1.24 63.40 35.55 31.83 SD 0.93 0.41 17.55 6.23 7.39
CBCT, cone beam computed tomography.
The measured volume of the entire defect is markedly smaller than the surgically aspired dimension of the defect. Reasons from the site of defect creation (e.g. variable lateral defect dept) as well as CBCT volumetry (e.g. variable cortical and trabecular borders) are probably responsible for this discrepancy.
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CBCT Volumetry
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Semiquantitative Scoring
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Correlation of Histopathology and CBCT Volumetry
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Comparison between CBCT Volumetry and the Semiquantitative Scoring
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Discussion
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Conclusion
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