Value of micro-CT as an investigative tool for osteochondritis dissecans

Phenotypic characterization of skeletal abnormalities of Osteopotentia mutant mice by micro-CT: a descriptive approach with emphasis on reconstruction techniques

PURPOSE

The novel protein osteopotentia (Opt) has recently been described as an essential regulator of postnatal osteoblast maturation and might possibly be responsible for some of the rarer types of osteogenesis imperfecta. Our aim was the evaluation of micro CT for the qualitative morphological assessment of skeletal abnormalities of Osteopotentia-mutant mice in comparison to radiography and histology.

MATERIALS AND METHODS

Four homozygous mice with insertional mutations in the Opt gene and three wild-type controls were examined ex vivo using radiography and micro-CT. Two of the homozygous animals were evaluated histologically (trichrome reagent). For the micro-CT evaluation three-dimensional (3D) surface reconstructions and two-dimensional (2D) multiplanar reformations (MPRs) were applied.

RESULTS

The Opt-homozygous mice exhibited severe growth. The radiographic examinations showed osteopenia and fractures with hypertrophic callus formation and pseudarthroses of the forelimbs and ribs. Micro-CT confirmed these findings and was able to demonstrate additional fractures especially at smaller bones such as the metacarpals and phalanges. Additional characterization and superior delineation of cortices and fracture fragments was achieved by 2D MPRs. Histological correlation verified several of these imaging findings.

CONCLUSION

Micro-CT is able to screen Opt-mutant mice for osseous pathologies and furthermore characterize these anomalies. The modality seems superior to conventional radiography, but is not able to demonstrate cellular pathology. However, histology is destructive and more time- and material-consuming than micro-CT. Additional information may be gathered by 2D MPRs.

Digital measurements: a different approach to evaluate bone formation. A technical report

In this study a digital measurement technique has been proposed to quantify bone formation on histological images. Two standard parietal defects were created in 30 adult rabbits. The animals were divided into six groups. Four animals of each group were randomly chosen as experimental group in which osteopontin-coated hydroxyapatite (OPN-HA) and hydroxyapatite (HA) were inserted alternatively in created defects. To observe the spontaneous healing process of defects, one animal of each group was used as control animal and these created defects did not receive any implants. The animals were sacrificed after 1, 2, 6, 12, 18 and 30 weeks. The histological sections were magnified (x100) and scanned digitally. The newly formed bone surfaces within the healing area were indicated and quantified by means of Adobe Photoshop 7 software. This measuring technique was found to be reliable and reproducible. The results of this study show no significant differences in bone formation between the OPN-HA and non-coated HA defects, although a significant difference in bone formation was measured at the margins of the defects treated with OPN-HA.