Tidal dynamics in the structure of the bone–cartilage interface.

Abstract from Bone Research Society Abstracts, Annual Meeting, Liverpool, UK, 29 June – 1 July 2016.Tidal dynamics in the structure of the bone–cartilage interface Alan Boyde Biophysics OGD, Queen Mary University of London, London E1 4NS, UK Background: Normal joint function is dependent on the maintenance of interfaces between hyaline articular cartilage (HAC) and articular calcified cartilage (ACC) and ACC and bone. Regulation of the ACC mineralising front and processes that influence ACC resorption and replacement by bone are not well understood. Mechanical overload is a risk factor for osteoarthritis (OA) although mechanisms linking trauma and OA are poorly characterised. Material: The osteochondral junction in man, mouse, rat, rabbit, elephant, and horse. Tissue processing: Embedding in PMMA to maintain integrity of hard and soft tissue junctions: avoidance of demineralisation and microtomy: micromilling or polishing of block surfaces: removal of mineralised tissue to leave a plastic cast of the soft tissue/cell space (Figure 1): or maceration of unembedded tissue to remove all cells and non-mineralised matrices (Figure 2). Microscopy: 2D, 2.5D, or 3D backscattered electron scanning electron microscopy: confocal scanning light microscopy: embed in iodinated resin: stain with triiodide solution: dry staining with elemental iodine vapour: x-ray microradiography: x-ray microtomography: nano-indentation. Findings: Equine exercise/training experiments establish that the regulation of the rate and density of calcification of ACC occurs at the mineralising front and is influenced by exercise and position in the joint, indicating that loading conditions affect ACC parameters. Exercise inhibits vascular invasion of ACC. Extension of cutting cones through ACC decreases the attachment of HAC to bone and is a major feature in human ageing. Responses of bone to overload exercise in large mammals involve a repair mechanism whereby microcracks are sealed by the intrusion of very dense, acellular, mineralised matrix: this may extend into HAC from the ACC mineralising front. The resulting high density mineralised protrusions have been shown in several human and equine joints, and may even occupy full thickness HAC. This hard, dense material may fragment, migrate within the HAC and eventually enter the joint space as an abrasive. FIGURE 1: Dynamic resorptive and formative activity of cutting cones in the subchondral region can be inferred from study of resin casts of soft tissue space. PMMA cast of palmar condyle of 2-year-old Thoroughbred racehorse. FIGURE 2: Sodium hypochlorite bleach macerated human osteoarthritic patella showing a high density mineralised protrusion from the ACC mineralising front. IS4 page 186-188 Bone Research Society Annual Meeting 29 June- 1 July 2016 Liverpool DOI: 10.3389/978-2-88919-974-7 ISBN: 978-2-88919-974-7 Published in Frontiers in Endocrinolog