Introduction

• Incidence: the carpus is a common site for both congenital and acquired conditions associated with lameness.
• Cause: many potential causes - primary and secondary. Trauma is the most common secondary cause.
• Signs: variable. Some conditions, eg hygroma, cause deformity without lameness.
• Diagnosis: clinical examination and range of ancillary aids including joint anesthesia and radiography.
• Treatment: depends on cause.
• Prognosis: depends on cause.

Pathogenesis

Etiology

• Most common cause of acquired carpal conditions.
• Fractures may be chip   Carpus: fracture - chip  , comminuted   Carpus: fracture - comminuted   or slab   Carpus: fracture - slab   and commonly involved distal radius, radial carpal bone, intermediate and third. Accessory carpal bone less commonly involved   Accessory carpal: fracture  .
• Luxations of the carpal joint are less common than in other joints (pastern, fetlock and hock). The medial collateral ligament is most commonly involved and there may be associated carpal fractures or avulsion fractures.
• Tearing of the medial palmar intercarpal ligament has been described   Carpus: intercarpal ligament (MPICL) - trauma  .
• Traumatic synovitis and capsulitis occur following single or repeated episodes of trauma to the carpal joint. It often progresses to degenerative joint disease   Musculoskeletal: osteoarthritis (joint disease)  .
• Carpal sheath tenosynovitis (carpal tunnel syndrome) and flexor tendinitis can result from irritation or compression of any of the soft tissue structures located within the carpal canal   Carpus: sheath tenosynovitis  .
• Hygroma and synovial hernia   Carpus: hygroma  .
• Hematoma   Hematoma  .
• Synovial fistulas are relatively uncommon.
• Rupture of the extensor carpi radialis tendon   Extensor carpi radialis muscle: rupture  .
• Proximal suspensory desmitis   Suspensory ligament: desmitis - proximal  .
• Synovial ganglia are rare but have been reported in the carpus   Synovial hernia and ganglion  .

Infectious

• Septic arthritis may occur secondary to trauma   Joint: septic arthritis - adult  or via hematogenous spread   Joint: septic arthritis - foal  .
• Accessory carpal bone     .

Multifactorial

• Osteochondrosis is uncommon in the carpal joint   Bone: osteochondrosis  .
• Subchondral bone cysts have been reported in the radial carpal bone   Bone: osteochondrosis  . 
• Osteochondral fragmentation   Carpus: fracture - chip  .
• Osteoarthritis is the most common carpal problem   Musculoskeletal: osteoarthritis (joint disease)                            .

Congenital and perinatal conditions

• Angular limb deformities, carpal valgus and varus   Musculoskeletal: angular deformity  .
• Incomplete ossification and collapse of carpal bones   Musculoskeletal: angular deformity  .
• Rupture of common digital extensor tendon; a rare condition which may occur in association with other defects   Common digital extensor tendon: rupture  .
• Flexural deformity of the carpus   Musculoskeletal: flexural deformity  .

Immune-mediated

• Immune-mediated polysynovitis uncommon, but may involve the carpal joint   Joint: immune-mediated polysynovitis  .

Miscellaneous

• Tumors are extremely rare   Carpus: osteochondroma  .
• Osseous cyst-like lesions do occasionally occur in the carpus   Bone: osseous cyst-like lesions  .

Predisposing factors

• 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.
• Carpal fractures:
  • Poor conformation, especially misalignment of radius, ulna or MC3 results in increased axial compressive forces on one side and tensional forces on the opposite side   Musculoskeletal: conformation  .
  • High motion joint often damaged at high speeds due to over-extension of joint(s)   Carpus: fracture - chip  .
• Poor conformation, eg offset knee (bench knee), back-at-the-knee (calf-knee), carpal varus/valgus             predispose to abnormal joint stresses which can   →   the development of joint pathology.

Pathophysiology

• The carpal joint is the articulation between the carpal bones and the metacarpal bones distally, and the radius and ulna proximally.
• Three distinct joint spaces are recognized: the antebrachiocarpal, the midcarpal and the carpometacarpal joints; with intercarpal joints forming the articulations between the carpal bones in each layer.
• The antebrachiocarpal and midcarpal joints are hinge joints with the vast majority of movement occurring here.
• The carpometacarpal and intercarpal joints are arthrodial, allowing little opening movement.
• See also Joint: synovial pathobiology   Joint: synovial pathobiology  .

Diagnosis

Treatment

Outcomes