Fragmenting densely mineralised acellular protrusions from articular calcified cartilage: a role in osteoarthritis?

Fragmenting densely mineralised acellular protrusions from articular calcified cartilage: a role in osteoarthritis? A. Boyde a, G.R. Davis a, D. Mills a, T. Zikmund a, V.L. Adams b, L.R. Ranganath b, N. Jeffery b, J.A. Gallagher b a Dental Physical Sciences, Oral Growth and Development, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London, UK b Department of Musculoskeletal Biology, Institute of Ageing and Chronic Disease, University of Liverpool, Liverpool, UK Objectives High density mineralised protrusions (HDMP) from the tidemark mineralising front into hyaline articular cartilage (HAC) were first discovered in Thoroughbred racehorse fetlock joints and later in Icelandic horse hock joints. If these fragment, they could make a significant contribution to joint destruction in osteoarthritis. We looked for them in human material. Methods Whole femoral heads removed at operation for joint replacement or from dissection room cadavers were studied by MRI DESS at 0.23mm resolution and 26 micron resolution high contrast x-ray microtomography (XMT), then sectioned and embedded in PMMA, and block faces polished and the blocks re-imaged with 6 micron resolution XMT. Tissue mineralisation density was imaged qualitatively by backscattered electron SEM (BSE SEM) at 20kV using uncoated samples at 50Pa chamber pressure to achieve charge neutralisation. HAC histology was studied by BSE SEM after staining block faces with ammonium triiodide solution. Block surfaces were sequentially repolished and restained. Results Figure: 3D rendering of 6 micron voxel resolution XMT data set showing HDMP complex projecting above subchondral bone plate. Human femoral head removed at arthroplasty. We found examples of HDMP in HAC in human hips. Their 3D shapes are complex and may show cutting blade forms. Their mineral content (a) exceeds that of articular calcified cartilage (ACC), otherwise the densest tissue in the joint and (b) is not uniform. The mineral phase morphology frequently shows the agglomeration of many fine particles into larger concretions. Cracks within them are frequent. Dense fragments may be found within damaged HAC. Conclusions HDMP arise via the extrusion of an uncharacterised matrix into clefts in HAC. Little evidence of their existence remains after tissue has been decalcified with usual histological protocols. Their formation may be an extension of a normal but poorly recognised crack self-healing mechanism found in bone and ACC. They are surrounded by HAC, are dense and brittle and show innumerable fault lines within them. We provide evidence that they break in vivo by being able to find matching fragments in HAC. We conclude that these hard and sharp particles contribute to the shredding destruction of HAC. The osteoarthritis research community should be aware of their existence so that the frequency and possible clinical significance can be assessed in the future. Larger HDMP can be detected with the best MRI imaging

‘The MSK Grand National: What we have learnt about the musculoskeletal system from studying racehorses’.

Bone Research Society Annual Meeting Liverpool 13-15 April 2023 Programme Page 6 [Joint meeting with 50th ECTS Congress] www.boneresearchsociety.org Invited Lecture IL1 Friday 14th April 2023 ‘The MSK Grand National: What we have learnt about the musculoskeletal system from studying racehorses’. Alan Boyde, London U.K. I reviewed studies I have conducted over many years and jointly with many colleagues concerning calcified tissues in horses from: Scanning electron microscopy of primary membrane bone. Boyde A, Hobdell MH. Z Zellforsch Mikrosk Anat. 1969;99(1):98-108. doi: 10.1007/BF00338800. Through: Coronal cementogenesis in the horse. Jones SJ, Boyde A. Archs Oral Biol. 1974 Aug;19(8):605-14. doi: 10.1016/0003-9969(74)90128-9. To: The Bone Cartilage Interface and Osteoarthritis. Boyde A. Calcif Tissue Int. 2021 Sep;109(3):303-328. doi: 10.1007/s00223-021-00866-9. The PowerPoint slides are condensed into a PDF available on the QMRO site which I have also made available in the format of a 2024 and 2025 Calendar

Clinically available scanning techniques are a potential detection tool for high density mineralised protrusions (HDMP) in human knees joints.

Abstract from Bone Research Society Annual Meeting 29 June- 1 July 2016, LiverpoolClinically available scanning techniques are a potential detection tool for high density mineralised protrusions (HDMP) in human knees joints. Neil Thomas1, Nathan Jeffery1, Briony Dillon1, Valerie Adams1, Lakshminarayan Ranganath1, Rob van ‘t Hof1, Alan Boyde2, James Gallagher1 1University of Liverpool, Liverpool, UK 2Queen Mary University of London, London E1 4NS, UK High density mineralised protrusions (HDMPs) from the mineralising front into Hyaline articular cartilage (HAC), originally discovered in horses have been confirmed in human hip joints. Thought to be naturally occurring, these phenomena possess mineral concentrations greater than any healthy joint structure and have the potential to fragment. Thus, their presence would likely influence the biomechanical performance of surrounding tissues and they have been associated with osteoarthritis (OA). Incidence, location and morphology of HDMPs in human knees were assessed by two methodologies: In-vivo: MRI data of patients with Alkaptonuria (n=36; age=19–67) were acquired sagitally (in-plane resolution=0.58mm) and potential protrusions were assigned a confidence value (1–5; 1=least confidence), representing potential for misinterpretation. Ex-vivo: Knees (n=11) from 8 cadavers (age=74–97) were imaged isotropically (resolution=0.26mm) by dual echo steady state MRI. Size and location of potential protrusions were recorded. Knees were assessed for OA using the Kellgren-Lawrence (KL) scale. All knees had signs of OA (KL score ≥1). A total of 216 potential HDMPs were identified across both studies (in-vivo=180; ex-vivo=36), with ≥1 reported in 10 out of 11 cadaveric subjects and in all patients. Ninety-two percent of those noted in-vivo had a confidence score ≥3, indicating a low likelihood of misinterpretation. Distribution as variable, with potential protrusions noted in all areas of the joint. They were observed in isolation and in small clusters. The ratio of femoral to tibial protrusions in-vivo was 4.6:1 compared with 1.77:1, ex-vivo. The percentage of protrusions found in regions central to articulation was 50 in-vivo and 75 ex-vivo. The mean width and depth of protrusions within HAC were 1.67mm and 1.72mm. However, morphology varied considerably. Regions central to articulation typically experience the greatest stress within the knee. It is likely that the many HDMPs observed here would be subjected to fragmentation, at the detriment of surrounding HAC. This may account for clustering and is suggestive of a role in progression of arthropathy. Morphological variability may be indicative of different pathophysiological forms and stages. Crucially, these data suggest radiologic detection of HDMPs is possible with clinical technology. Moreover, it should be considered as a biomarker for predicting joint destruction. P040 page 117-118 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