Musculoskeletal System
April 2019

Signalment (JPC #3106281): 6-week-old female mixed breed horse

HISTORY:  This horse had a five day history of lameness of the right rear leg.  Radiographic findings were interpreted as septic arthritis of the right coxofemoral joint.

HISTOPATHOLOGIC DESCRIPTION:  Articular epiphyseal cartilage complex:  A focally extensive approximately 10mm long by 2mm deep area of the epiphyseal cartilage is markedly thickened up to twice the thickness of adjacent unaffected cartilage and extends into the underlying epiphyseal cancellous bone.  At the deep margin large segments of the affected cartilage are pale (loss of matrix proteoglycans) or eosinophilic with loss of cellular detail and large numbers of empty lacunae (necrosis) or lacunae which contain necrotic chondrocytes.  Multifocally, cartilage canals within the affected cartilage are necrotic with absence of normal vascular channels, and with loss of endothelial lining and replacement with scant loose fibrous connective tissue and debris which extends out from vascular channels and replaces chondrous matrix.  At the deep edge of the thickened articular epiphyseal cartilage complex trabeculae contain retained cartilage cores and within this area there are several fragmented displaced bony trabeculae (microfractures) that focally coalesce forming an infraction surrounded by abundant polymerized fibrin and hemorrhage. Focally extensively separating underlying subchondral bone and replacing normal hematopoietic elements are increased numbers of fibroblasts and fibrous connective tissue admixed with fewer lymphocytes and plasma cells. 

MORPHOLOGIC DIAGNOSIS:  Articular epiphyseal cartilage complex:  Chondronecrosis, multifocal, moderate, chronic, with microfractures and infraction of subchondral bone, myelofibrosis and failure of endochondral ossification (osteochondrosis manifesta), mixed breed, equine.

CONDITION:  Osteochondrosis

SYNONYMS:  Dyschondroplasia, osteochondrosis dissecans, osteochondritis dissecans









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