Introduction

• Cause: trauma, osteochondrosis, biomechanical wear and tear on a high load, low motion joint; 'ringbone' describes the development of peri-articular new bone which may precede or follow development of osteoarthritis.
• Signs: mainly presents as an insidious, chronic lameness   Musculoskeletal: gait evaluation  , but occasionally there may be a sudden acute onset +/- firm swelling associated with joint and/or attachment of ligaments around the joint     ; pain in response to flexion   Musculoskeletal: manipulative tests  , positive flexion test, worse when turning.
• Diagnosis: palpation, positive response to nerve and intra-articular analgesia   Forelimb: perineural analgesia  , radiography   Forelimb: radiography    Hindlimb: radiography  .
• Treatment: conservative - rest, NSAIDs, intra-articular medication, corrective shoeing; surgery - arthrodesis pastern joint   PIP joint: arthrodesis  .
• Prognosis: depends on degree of osteoarthritic changes but always guarded.
• See Musculoskeletal: osteoarthritis (joint disease)   Musculoskeletal: osteoarthritis (joint disease)  .

Pathogenesis

Etiology

• Trauma:
  • Wear and tear trauma to the joint and associated cartilage. This depends on the type and extent of work, limb and foot conformation, shoeing, size of animal, and age.
  • Articular fractures of the middle   Middle phalanx: fracture  or proximal phalanx   Proximal phalanx: fracture  .
  • Other intra-articular pathology such as osteochondrosis or infection (wounds, penetrations, injections).

Predisposing factors

• Osteochondrosis   Bone: osteochondrosis  .
• Horses that jump and perform dressage may be over represented.

Specific

• Conformation   Musculoskeletal: conformation  .
• Work at high speed with sudden stops and turns in Polo ponies   Polo Pony  and Western-type activities.

Pathophysiology

• High load low motion joint.
• Area of maximal weight bearing is nearly stationary   →   forces concentrated on a small surface area.
• Focal excess weight bearing   →   necrosis of bone and cartilage.
• Secondary joint capsule fibrosis   →   decreased joint movement   →   exacerbates cycle of degenerative joint disease   Musculoskeletal: osteoarthritis (joint disease)  .

Articular ringbone

• Severe degenerative joint disease can lead to excessive osteophytic formation and enthesopathy/periosteal proliferation which used to be termed articular ringbone.
• Further cartilage loss and joint collapse with increasing fibrotic and bony periarticular formation can eventually lead to partial or complete joint ankylosis.

Non-articular ringbone

• Chronic pulling of collateral ligaments, joint capsule attachments, extensor tendon attachments, direct trauma   →   periostitis   →   new bone formation outside of the margins of the joint.
• See Musculoskeletal: osteoarthritis (joint disease)   Musculoskeletal: osteoarthritis (joint disease)  .

Diagnosis

Treatment

Outcomes