Disorders of the Carpus in Horses
The carpus involves three articulations: the radiocarpal (antebrachiocarpal), intercarpal (middle carpal), and carpometacarpal joints. Problems are localized to the carpal area based on lameness, swelling, synovial effusion and pain on palpation, and responses to flexion and diagnostic analgesia. Visualization and palpation are important to determine the site of swelling in the carpus (eg, synovial fluid in the joint or tendon sheath or swelling in the subcutaneous space). Light palpation with fingers with the horse standing and with the leg raised is beneficial in determining the specific area of fluid accumulation. Knowledge of the normal anatomic boundaries of the structures is important.
Diagnostic analgesia of the carpal joints is usually done intra-articularly. The antebrachiocarpal and middle carpal joints can be injected easily. The carpometacarpal joint communicates with the middle carpal joint; therefore, local analgesia in the middle carpal joint provides analgesia of the carpometacarpal joint. There is considerable distal palmar outpouching of the carpometacarpal joint; with time, analgesia will diffuse into the area of the proximal suspensory ligament, thus leading to confusing results.
Radiography of the carpus is critical for specific diagnoses and should include flexed lateral as well as skyline views of the distal row of carpal bones (as well as proximal row/distal radius in some horses).