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.

Background

The position of the hip-joint centre of rotation (HJC) within the pelvis is known to influence functional outcome of total hip replacement (THR). Superior, lateral and posterior relocations of the HJC from anatomical position have been shown to be associated with greater joint reaction forces and a higher incidence of aseptic loosening. In biomechanical models, the maximum force, moment-generating capacity and the range of motion of the major hip muscle groups have been shown to be sensitive to HJC displacement. This clinical study investigated the effect of HJC displacement and acetabular cup inclination angle on functional performance in patients undergoing primary THR.

It is known that excessive varus alignment of the femoral stem in total hip replacement (THR) creates a sub-optimal biomechanical environment which is associated with increased rates of revision surgery and component wear. Little is known regarding the effect of femoral stem alignment on patient functional outcome.