Abstract
Cortical porosity is a useful evaluator of bone since it is sensitive to changes in bone turnover. The aim of this study was to evaluate cortical bone porosity of human vertebrae samples using Scanning Acoustic Microscopy (SAM). Currently the common techniques used to determine bone porosity are histomorphometry or scanning electronmicrosopy images. Both methods require extensive preparation of the bone samples. SAM represents a new technique with the great advantage of minimal sample interference since the bone is imaged in water, or saturated, and requires just one flat surface which is scanned (but not contacted) by the transducer. 46 specimens between the ages of 64–90 years were randomly selected and ground before SAM imaging of was carried out using a 400 MHz transducer. For each sample posterior and anterior sections of the cortical bone were scanned several times, and the porosity measured using Scion image software to process the images. It was possible to image the entire anterior or posterior cortex in a single image with 4 mm spatial resolution. Measured porosity was in the region 5 % – 21 %, and showed a significant increase with age for the female specimens but no age dependence in the male specimens. At low porosity (< 6 %) vertebral compressive strength was uncorrelated with porosity. However, at higher porosities strength was highly correlated with porosity. (As would be expected, strength decreased with increasing porosity). High frequency SAM has potential for future bone characterisation, particularly where it is desirable to correlate local measurements of material properties such as nanohardness or microhardness, with microstructure.
Correspondence should be addressed to Dr Carlos Wigderowitz, Honorary Secretary of BORS, Division of Surgery & Oncology, Section of Orthopaedic & Trauma Surgery, Ninewells Hospital & Medical School Tort Centre, Dundee, DD1 9SY.
