Findings
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There is increased mineral opacity in the navicular trabecular bone and enlargement of several synovial invaginations in the distal border.
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Along the periarticular margins of the proximal and distal interphalangeal joints, mild osteophyte formation is present.
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The dorsal hoof wall is parallel to the dorsal aspect of the distal phalanx.
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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.
Diagnosis
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Osseous cyst like lesion, medial articular margin of the distal phalanx., with mild distal interphalangeal arthrosis.
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Mild navicular bone sclerosis and enlarged synovial invaginations.
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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.
- 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
- weightbearing surface, insertion of the DIP joint collateral ligaments or at the insertion of the DSIL
- Surgical debridement preferred due to the higher success rate (70–90%)
References
- 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.