JPC SYSTEMIC PATHOLOGY
Musculoskeletal System
April 2019
M-M21

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

GENERAL DISCUSSION:

PATHOGENESIS:

TYPICAL CLINICAL FINDINGS:

TYPICAL GROSS FINDINGS:

TYPICAL LIGHT MICROSCOPIC FINDINGS:

DIFFERENTIAL DIAGNOSIS:

COMPARATIVE PATHOLOGY:

REFERENCES:

  1. Borst LB, Suyemoto MM, Sarsour AH, Harris MC, Martin MP, Strickland JD, Oviedo EO, Barnes HJ. Pathogenesis of enterococcal spondylitis caused by enterococcus cecorum in broiler chickens. Vet Pathol. 2017 Jan;54(1):61-73.
  2. Craig LE, Dittmer K, Thompson KG. Bones and joints. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. St. Louis, MO; Elsevier: 2016; 132-135.
  3. Craig LE, Reed A. Age-associated cartilage degeneration of the canine humeral head.  Vet Pathol. 2013;50(2): 264-268.
  4. Etterlin PE, Ekman S, Strand R, Olstad K, Ley CJ. Osteochondrosis, synovial fossae, and articular indentations in the talus and distal tibia of growing domestic pigs and wild boars. Vet Pathol. 2017 May;54(3):445-456.
  5. Janes JG, Garrett KS, McQuerry KJ, Waddell S, Voor MJ, Reed SM, Williams NM, MacLeod JN. Cervical Vertebral Lesions in Equine Stenotic Myelopathy. Vet Pathol. 2015 Sep;52(5):919-927.
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  7. McInnes EF, McKeag S. A brief review of infrequent spontaneous findings, peculiar anatomic microscopic features, and potential artifacts in Göttengen minipigs. Toxicol Pathol. 2016;44(3)385-45.
  8. Olson EJ, Carlson CS. Bones, joints, tendons, and ligaments. In: McGavin MD, Zachary JF, eds. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier; 2017:975-979.
  9. Olstad K, Ekman S, Carlson CS. An update on the pathogenesis of osteochondrosis. Vet Pathol. 2015; 52(5):782-802.
  10. Olstad K, Østevik L, Carlson CS, Ekman, S. Osteochondrosis can lead to the formation of pseudocysts and true cysts in the subchondral bone of horses. Vet Pathol.2015; 52(5):862-72.
  11. Olstad K, Ytrehus B, Ekman S, Carlson CS, Dolvik NI. Early lesions of osteochondrosis in the distal femur of foals. Vet Pathol. 2011; 48(6): 1165-1175.
  12. Wormstrand B, Østevik L, Ekman S, Olstad K. Septic arthritis/osteomyelitis may lead to osteochondrosis-like lesions in foals. Vet Pathol. 2018 Sep;55(5):693-702.
  13. Ytrehus B, Carlson CS, Ekman S. Etiology and pathogenesis of osteochondrosis. Vet Pathol. 44; 2007: 429-448.


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