Osteoclasts are recruited to the subchondral bone in naturally occurring post-traumatic equine carpal osteoarthritis and may contribute to cartilage degradation.
The role of osteoclasts in osteochondral degeneration in osteoarthritis (OA) has rarely been investigated in spontaneous disease or animal models of OA.


OBJECTIVE
The objectives of the current study were to investigate osteoclast density and location in post-traumatic OA (PTOA) and control specimens from racehorses.


METHODS
Cores were harvested from a site in the equine third carpal bone, that undergoes repetitive, high intensity loading. Histological and immunohistochemical (Cathepsin K and Receptor-activator of Nuclear Factor kappa-β ligand (RANKL)) stained sections were scored (global and subregional) and the osteoclast density calculated. The cartilage histological scores were compared with osteoclast density and RANKL scores.


RESULTS
There was a greater density of osteoclasts in PTOA samples and they were preferentially located in the subchondral bone plate. RANKL scores positively correlated to the scores of cartilage degeneration and the osteoclast density. The relationship between hyaline articular cartilage RANKL score and osteoclast density was stronger than that of the subchondral bone RANKL score suggesting that cartilage RANKL may have a role in recruiting osteoclasts. The RANKL score in the articular calcified cartilage correlated with the number of microcracks also suggesting that osteoclasts recruited by RANKL may contribute to calcified cartilage degeneration in PTOA.


CONCLUSIONS
Our results support the hypothesis that osteoclasts are recruited during the progression of spontaneous equine carpal PTOA by cartilage RANKL, contributing to calcified cartilage microcracks and focal subchondral bone loss.
Comparative Orthopaedic Research Laboratory, Département de sciences cliniques, Faculté de Médecine Vétérinaire, Université de Montréal, 3200 Rue Sicotte, St-Hyacinthe, QC J2S 2M2, Canada. Electronic address: andrea.bertuglia@unito.it.
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Bertuglia
Comparative Orthopaedic Research Laboratory, Département de sciences cliniques, Faculté de Médecine Vétérinaire, Université de Montréal, 3200 Rue Sicotte, St-Hyacinthe, QC J2S 2M2, Canada.
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Lacourt
Département de Pathologie et Microbiologie Vétérinaires, Faculté de Médecine Vétérinaire, Université de Montréal, 3200 Rue Sicotte, St-Hyacinthe, QC J2S 2M2, Canada.
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Girard
Département de Pathologie et Microbiologie Vétérinaires, Faculté de Médecine Vétérinaire, Université de Montréal, 3200 Rue Sicotte, St-Hyacinthe, QC J2S 2M2, Canada.
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Beauchamp
Comparative Orthopaedic Research Laboratory, Département de sciences cliniques, Faculté de Médecine Vétérinaire, Université de Montréal, 3200 Rue Sicotte, St-Hyacinthe, QC J2S 2M2, Canada.
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Richard
Comparative Orthopaedic Research Laboratory, Département de sciences cliniques, Faculté de Médecine Vétérinaire, Université de Montréal, 3200 Rue Sicotte, St-Hyacinthe, QC J2S 2M2, Canada. Electronic address: sheila.laverty@umontreal.ca.
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Laverty
D000818:Animals; D002114:Calcinosis / Q000378:metabolism / Q000473:pathology; D002348:Carpal Bones / Q000378:metabolism / Q000473:pathology*; D050824:Carpal Joints / Q000293:injuries / Q000473:pathology*; D002357:Cartilage Diseases / Q000209:etiology / Q000378:metabolism / Q000473:pathology / Q000662:veterinary; D002358:Cartilage, Articular / Q000378:metabolism / Q000473:pathology; D002452:Cell Count; D002465:Cell Movement / Q000502:physiology; D006734:Horse Diseases / Q000473:pathology*; D006736:Horses; D008297:Male; D010003:Osteoarthritis / Q000209:etiology / Q000378:metabolism / Q000473:pathology* / Q000662:veterinary*; D010010:Osteoclasts / Q000473:pathology* / Q000502:physiology; D053245:RANK Ligand / Q000378:metabolism / Q000502:physiology
D053245:RANK Ligand
Articular cartilage; Osteoclast; Post-traumatic osteoarthritis; RANKL; Racehorses; Subchondral bone