Bone has a number of different functions in the skeleton including the physical roles of support, protection and sound wave conduction. The mechanical properties, required for these different functions varies and can be achieved by compositional adaption of the bone material, in addition to changes in shape and architecture. A number of previous studies have demonstrated the relationship between mechanical function and mineral to collagen ratio in bones from different species. The aim of this study is to test the hypothesis that the mineral to collagen ratio is higher in bone with a mechanically harder matrix within a species. The red deer The results showed that the hardness (Indentation Distance Increase) was lowest in the metacarpal (8.5µm), followed by the bulla bone (9.4µm) and highest in the antler (14.5µm). Raman spectroscopy showed a mineral:collagen ratio of 1:0.10 (bulla), 1:0.13 (metacarpal) and 1:0.15 (antler) for the different bones. This does not follow the more linear trend previously shown between young's modulus and the mineral:collagen ratio. The location of the mineral appeared to differ between bone types with pQCT revealing locations of concentrated density and banding patterns in antler. Interestingly, Raman spectra showed differences in the amide peaks revealing differences in protein structure. The results reject the hypothesis but also suggest that the organisation of mineral and collagen has an impact on the hardness modulus. We demonstrate that the red deer provides a good model for studying bone specialisation. This work will provide the basis for further investigation into collagen as a controlling factor in mineral deposition.
Osteoarthritis is associated with changes to the matrix composition of subchondral bone. Raman spectroscopy has the potential to detect in vivo the molecular changes in osteoarthritic subchondral bone. The objectives were to determine the levels of mineralisation, carbonate accumulation and bone remodelling in osteoarthritic subchondral bone, which we defined as within 3mm of articular cartilage. This was compared to the proximal-compartment (10mm distal to articular cartilage) and the head-neck junction. Five osteoarthritic (average age: 76 years) and five normal cadaveric femoral heads (average age: 72 years) were scanned using peripheral quantitative computed tomography and then sectioned coronally. Raman spectroscopy was then used to scan the femoral heads. All scans were done in the plane of the longitudinal axis of the diaphysis. Cores were subsequently extracted and sodium dodecyl sulphate polyacrylamide gel electrophoresis performed to determine the levels of homotrimeric collagen. The phosphate-to-amide I ratio, from the Raman spectra, in osteoarthritic subchondral bone was significantly greater than controls (p=0.023). Within osteoarthritic specimens, the phosphate-to-amide I ratio increased proximally. The density in osteoarthritic subchondral bone was 89mg/cm3 higher than controls (p=0.022), and 494mg/cm3 higher than the osteoarthritic proximal-compartment (p<0.001). Moreover, carbonate substitution into the apatite crystals decreased in osteoarthritic specimens. The carbonate-to-amide I ratio was highest in osteoarthritic subchondral bone. Furthermore, the median α1-to-α2-chain ratio in osteoarthritic specimens was 2:1. The changes found in subchondral bone are important in the pathogenesis of osteoarthritis. This study shows that Raman spectroscopy can detect differences between osteoarthritic specimens and controls, further supporting its potential use in diagnosing bone disorders.
Osteoarthritis (OA) is a common, debilitating joint disease involving degeneration of cartilage and bone. It has been suggested that subtle changes in the molecular structure of subchondral bone may precede cartilaginous changes in the osteoarthritic joint. To explore these changes Raman spectroscopy was employed as a diagnostic tool. Raman spectroscopy measures inelastic scattered laser light produced when photons interact with chemical materials. Resultant changes in wavelength form spectra relative to the chemical composition of the given sample: with bone this includes the mineral and matrix components, unlike conventional X-rays. The aim of our study is to explore the hypothesis: Changes in matrix composition of osteoarthritic subchondral bone can be detected with Raman spectroscopy. pQCT and Raman spectroscopy were employed to determine the bone mineral density (BMD) and bone quality, respectively. Ten medial compartment OA and five control (non-OA) tibial plateaus were interrogated and analysis performed to compare OA to control, and medial to lateral compartments. The subchondral bone of the medial OA compartments had higher BMD (p=0.05) and thickness compared to lateral and control samples. Spectral analysis revealed there is no difference between the medial and lateral compartments within either cohort. However, there is a statistically significant (p=0.02) spectral difference between the OA and control specimens. The detection of bone matrix changes in osteoarthritis using Raman spectroscopy contributes to the understanding of the biochemical signature of subchondral bone across diseased and control tibial plateaus. This technique has potential to shed light on the role of bone in osteoarthritis.
