Anatomical Overview & Clinical Localization:
Three Primary Articulations: Includes the radiocarpal (antebrachiocarpal), intercarpal (middle carpal), and carpometacarpal joints.
Joint Communication: The carpometacarpal joint communicates with the middle carpal joint; therefore, injecting the latter provides analgesia for both.
Indicators of Problems: Issues are localized to this region through lameness, swelling, synovial effusion, pain on flexion, and diagnostic analgesia.
Swelling Identification: Palpation and visualization are used to determine if fluid is in the joint, the tendon sheath, or the subcutaneous space.
Diagnostic Methodologies:
Diagnostic Analgesia: Usually administered intra-articularly; clinicians must note that analgesia can diffuse into the proximal suspensory ligament over time, potentially causing diagnostic confusion.
Radiography: Critical for specific diagnoses; standard views should include flexed lateral and skyline views of the carpal bones.
Advanced Visualization: Arthroscopic examination is used to diagnose internal damage like ligament tears or to guide surgical repairs.
Osteochondral (Chip) Fractures:
Etiology: Common in racehorses, primarily caused by trauma during fast exercise.
Location: Typically occur on the dorsal aspect of the joint.
Treatment: Arthroscopic fragment removal is the treatment of choice.
Definition: Fractures extending from one articular surface to another.
Common Site: Frontal slab fracture of the radial facet of the third carpal bone.
Treatment: Lag screw fixation with arthroscopic guidance (for fractures > 10 mm) or fragment removal.
Accessory Carpal Bone Fractures:
Signs: Acute and severe lameness with possible carpal sheath effusion.
Treatment: Typically managed conservatively, though articular fragmented pieces may be surgically removed.
Osteoarthritis (OA) of the Carpus:
Radiocarpal/Middle Carpal OA: Characterized by chronic joint capsule thickening and decreased range of motion; common in retired Thoroughbred broodmares.
Carpometacarpal Joint OA:
Affected Breeds: Spontaneous occurrence mainly in Arabians and Quarter Horses.
Signs: Firm swelling over the medial aspect of the distal carpus and minimal initial lameness.
Radiographic Features: Periarticular new bone proliferation over the proximal second or third metacarpal bones.
General Management: Chondroprotectants, NSAIDs, exercise modification, and intra-articular medication.
Soft Tissue and Developmental Disorders:
Definition: A subcutaneous, usually aseptic swelling over the dorsal carpus resulting from trauma.
Nature: Generally a cosmetic blemish that does not cause lameness.
Treatment: Early stages involve drainage, steroid injections, and bandaging; infected tissue requires surgical resection.
Intercarpal Ligament Injuries: Most commonly involve the medial palmar intercarpal ligament; identified by synovitis unresponsive to standard therapy.
Subchondral Bone Damage: Often precedes slab fractures in racehorses; diagnosed via skyline-view radiographs showing lysis and sclerosis.
Exostoses and Osteochondromas: Arise on the caudal distal radius metaphysis; can cause carpal sheath tenosynovitis and are treated via tenoscopy.