Case reveal


  • There is increased mineral opacity in the navicular trabecular bone and enlargement of several synovial invaginations in the distal border.
  • Along the periarticular margins of the proximal and distal interphalangeal joints, mild osteophyte formation is present.
  • The dorsal hoof wall is parallel to the dorsal aspect of the distal phalanx.
  • In the region of the medial articular margin of the distal phalanx, best seen on the dorsoproximal-palmarodistal oblique projections, a small focal region of decreased mineral opacity is surrounded by moderate sclerosis.  There is a focal, concavity in the proximal articular surface of the distal phalanx, seen on the lateral projections.


  • Osseous cyst like lesion, medial articular margin of the distal phalanx., with mild distal interphalangeal arthrosis.
  • Mild navicular bone sclerosis and enlarged synovial invaginations.
  • Mild proximal interphalangeal osteoarthrosis.

A little bit more…

  • Osseous-cyst like lesions- not true bone cyst since they lack an epithelial lining. Most have a fibrous lining and contain fibrous tissue, +/-  synovial gelatinous material. May also be filled with fibrocartilage, occasionally partially mineralised and/or mixed with necrotic bone.
  • True bone cyst reported in horses include aneurysmal and unicameral cysts
  • The phalanges are the second most common location for osseous cyst-like lesions (most common is the medial femoral condyle)
  • Most often adjacent to joints, will sometime communicate with joint.

    subcentral cyst
    Created using
  • Multiple etiologies reported:
    • genetics, nutrition, rapid growth, hormonal changes and mineral imbalances, osteochondrosis, biomechanics and trauma
    • Young horse with bilateral lesions –> likely dvelopmental
    • Older athletic horse –> most likely due to trauma
  • Variable in size (small to large) and shape (dome, conical or spherical in shape).
  • May be surrounded by a thick sclerotic rim.
  • Osseous cyst-like lesions of the distal phalanx are reported to be more common in geldings/stallions. Possibly more common in Thoroughbred horses, although some reports also found a higher occurrence in warmblood horses.
  • Within the distal phalanx, OCLLs have been identified at the following sites:
    • extensor process
    • along the solar surface
    • palmar processes (at the insertion of the collateral ligaments of the distal interphalangeal joint, more commonly medially)
    • insertion of the distal
    • sesamoidean impar ligament attachment
    • within proximal weightbearing surface
  • Perineural analgesia can be used to localize the site of lameness. Intra-articular analgesia may resolve lameness if the lesion communicates with the joint.
  • Radiographic views to consider depending on location of lesion:
    • weightbearing surface, insertion of the DIP joint collateral ligaments or at the insertion of the DSIL
      • –> dorsopalmar or dorsoproximal-palmarodistal oblique views
    • extensor process
      • –> lateromedial views
  • Surgical debridement preferred due to the higher success rate (70–90%)


close up1
Within the DIP, there is a small rounded radiolucency with a thick rim of sclerosis

close up


  • Sherlock, C., and T. Mair. “Osseous cyst‐like lesions/subchondral bone cysts of the phalanges.” Equine Veterinary Education 23.4 (2011): 191-204.
  • Mair, T. S., and C. E. Sherlock. “Osseous cyst‐like lesions in the feet of lame horses: diagnosis by standing low‐field magnetic resonance imaging.” Equine Veterinary Education20.1 (2008): 47-56.
  • Peter, Vanessa G., et al. “Radiographic identification of osseous cyst-like lesions in the distal phalanx in 22 lame thoroughbred horses managed conservatively and their racing performance.” Frontiers in veterinary science 5 (2018): 286.