Equis ISSN 2398-2977

Stifle: femorotibial subchondral bone cyst

Contributor(s): Stephen Adams, Patrick Colahan, Graham Munroe, Chris Whitton




  • Subchondral cystic lesions occur at various sties. For the basis of this description true bone cysts are considered to occur only in the distal medial femoral condyle of the femorotibial joint.
  • Cysts at this site have a consistent pathological structure with a true fibrous cyst lining. Subchondral cystic lesions at other sites are classified as osseous cyst-like lesions.
  • Unknown for certain.
  • Various hypotheses.
  • May be primary lesions or can occur secondary to anything that causes an articular cartilage and/or subchondral bone defect, eg osteochondrosis   Bone: osteochondrosis  , trauma.


  • Subchondral cystic lesions in the distal weight-bearing aspect of the medial condyle have been produced by creating full-thickness articular cartilage plus subchondral bone defects and then exercising horses.

Hypothesis I: osteochondrosis as initiating factor

  • Defective cartilage (osteochondrosis   Bone: osteochondrosis  )   →   cracks, due to degenerative process or mechanical trauma   →   synovial fluid flows to subchondral bone   →   mechanical factors, including weightbearing, causes bone resorption   →   subchondral cystic lesion.
  • The lining of the cyst contains active inflammatory enzymes which can cause bone resorption   →    increase in size over time.
  • Bone response to contain the lesion   →   subchondral bone sclerosis.

Hypothesis II: trauma as initiating factor

  • Joint trauma   →   subchondral ischemia and necrosis and/or synovial fluid forced under cartilage and against damaged subchondral bone.
  • Weightbearing   →   bone resorption and cystic lesions beneath articular surface.

Causes of pain

  • Subchondral - increased pressure due to accumulated inflammatory material and synovial fluid, particularly during weightbearing.
  • Synovial - osteochondrosis   →   synovitis   →   joint effusion.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Bodo G et al (2004) Autologous osteochondral grafting (Mosaic arthroplasty) for treatment of subchondral cystic lesions in the equine stifle and fetlock joints. Vet Surg 33 (6), 588 PubMed.
  • Kold S E & Killingbeck J M (1998) The use of autogenous cancellous bone graft for the treatment of subchondral bone cysts in the distal phalanges, three cases. Equine Vet Educ 10 (6), 307- 312 Wiley Online Library.
  • McIlwraith C W (1998) Subchondral bone cysts in the horse, etiology, diagnosis and treatment options. Equine Vet Educ 10 (6), 313- 317 (Overview of bone cysts and personal experience of author with treatment options) VetMedResource.
  • Kold S E & Hickman J (1984) Results of treatment of subchondral bone cysts in the medial condyle of the equine femur with an autogenous cancellous bone graft. Equine Vet J 16, 414-418 PubMed.

Other sources of information

  • Nixon A J (2003) Update on Management of Subchondral Bone Cysts. In: Proc ACVS Conference 2003.
  • Ross M W & Dyson S J (2003) Eds. Diangosis and Management of Lameness in the Horse. Elsevier Science, USA.