• Chronic intermittent mild right forelimb lameness and “bench knee” confirmation.
• Palpation: moderate middle carpal joint swelling effusion, no heat.
• Positive to carpal flexion.
• Diagnostic anesthesia: 60% improvement with IA middle carpal joint.

• Mild to moderate narrowing and undulating margin of the 2nd metacarpal and 2nd carpal joint Moderate sclerosis of the 2nd carpal bone and proximal aspect of the 2nd metacarpal bone
• Indistinct central linear lucency, 2nd carpal bone, best seen on the DMPLO image.
• Incidental 1st carpal bone present
• Small osseous fragment dorsomedial carpometacarpal joint.

• Suspect compression fracture 2nd carpal bone
• Moderate osteoarthrosis of the 2nd carpal and 2nd metacarpal joint
• Chip fracture, carpometacarpal joint.

• Cyst-like lesion 2nd carpal bone surrounded by marked sclerosis
• Narrowing of the 2nd carpal bone and MCII articulation.
• Linear fissure extending from the cyst-like lesion to the midbody of 2nd carpal bone.

• Severe osteoarthrosis, 2nd carpal and 2nd metacarpal joint. The osseous cyst-like lesion is most likely traumatic in origin and may have lead to an incomplete fracture of the 2nd carpal bone.
• Osseous cyst-like lesions may or may not be associated with lameness. They are often a result of subchondral trauma and sclerosis.

• Multiple full thickness cartilage erosions 2nd carpal bone and apposing MCII.
• Central deep cartilage fissure corresponding to fissure line and cyst-like lesion on imaging.

• Carpometacarpal osteoarthrosis is recognized as a severe clinical syndrome, common in Quarter Horses and Arabians.
• Most common site is MC2/C2 articulation.
• Clinical Presentation: Chronic severe lameness, firm swelling over the MC2/C2 articulation, positive flexion, remission of lameness with IA anesthesia of the middle carpal joint.
• Radiographic features: Proliferative new bone, narrowed joint space, and subchondral lysis.
• Prognosis: Guarded to poor

References

• Panizzi, Luca, et al. “Carpometacarpal Osteoarthritis in Thirty-Three Horses.” Veterinary Surgery, vol. 38, no. 8, 2009, pp. 998–1005.