Introduction

• Incidence: the proximal interphalangeal joint is less commonly associated with lameness than more mobile joints such as the carpus or fetlock, or the foot.
• Cause: acute or chronic trauma   →   conditions such as osteoarthritis, luxation or fracture.
• Signs: varies from mild lameness to non-weightbearing. Peri-articular ringbone may be asymptomatic.
• Diagnosis: clinical examination, radiography   Forelimb: radiography    Hindlimb: radiography  and intra-articular anesthesia   Forelimb: joint anesthesia    Hindlimb: joint anesthesia  are often sufficient.
• Treatment: depends on cause.
• Prognosis: depends on cause.

Pathogenesis

Etiology

Trauma

• Acute injury to collateral ligaments, joint capsule, the attachment of the extensor tendon, joint or other soft tissues   PIP joint: osteoarthritis  .
• Luxation or subluxation: uncommon and usually secondary to damage to supporting structures, eg distal sesamoidean ligaments, SDFT branch    PIP joint: luxation  .
• Fractures: may be comminuted, chip (uncommon) or involve the caudal eminence of the middle phalanx   Proximal phalanx: fracture    Middle phalanx: fracture  .
• Wounds to pastern joint.
• Degnerative joint disease (DJD)   Musculoskeletal: osteoarthritis (joint disease)  .
• Osteoarthritis ('high ringbone')   PIP joint: osteoarthritis  ; may also be secondary to articular fractures, infection or osteochondrosis   Bone: osteochondrosis  .

Multifactoral

• Osteochondrosis   Bone: osteochondrosis   +/- osseous fragmentation.
• Subchondral bone cysts   Bone: subchondral cysts  .

Infectious

• Penetrating wounds   →   septic arthritis    Joint: septic arthritis - adult  .
• Occasionally hematogenous spread of infection in foals   →    septic arthritis    Joint: septic arthritis - foal  .

Congenital and perinatal conditions

• Conformational defects/deformities   Musculoskeletal: angular deformity  .

Predisposing factors

• Poor conformation   Musculoskeletal: conformation   may predispose to increasing the stresses placed on the soft tissue structures and cartilage of the joint.
• Septic conditions:
  • Failure of transfer of passive immunity in the foal   Foal: failure of passive transfer (IgG)  , placentitis   Placenta: placentitis  or endometritis   Uterus: endometritis - bacterial  .
  • Poor hygiene.

Pathophysiology

• The proximal interphalangeal (PIP) joint is the articulation between the distal aspect of the proximal phalanx and the proximal aspect of the middle phalanx. 
• Collateral ligaments, abaxial and axial ligaments provide stability to the joint.
• Several ligaments and tendons course over the pastern region, including the superficial digital flexor tendon (SDFT) and deep digital flexor tendon (DDFT).
• Proximity to the ground, paucity of soft tissue cover dorsally and laterally, the degree of flexion occurring at this site and important soft tissue structures (SDFT, DDFT) on its palmar/plantar surface all contribute to this region being vulnerable to injury.
• Depends on the individual joint disease.
• See also Joint: synovial pathobiology   Joint: synovial pathobiology  .

Timecourse

• Acute onset for fractures, luxations and traumatic lesions.
• Chronic and insidious onset for osteoarthritis, bone cysts, DJD.

Diagnosis

Treatment