Arthroscopy enables visualization of the interior surfaces of a joint for diagnostic or surgical purposes. Arthrocentesis is a procedure by which synovial fluid may be removed from a joint for examination. Local anesthetic can be introduced to ascertain whether painful lesions are present in the joint. Intra-articular therapy permits medication to be deposited into the joint. Because this procedure may be painful, a nerve block at a higher level is recommended.
For the distal interphalangeal joint, the needle is inserted lateral to the common or long extensor tendon, which inserts into the extensor process of the distal phalanx. The entry point is just proximal to the coronary band. For the pastern joint (proximal interphalangeal joint), the needle is inserted lateral to the extensor tendon. For the fetlock joint (metacarpophalangeal or metatarsophalangeal joint), the needle is directed downward close to the bone and between it and the interosseous (suspensory) ligament. The joint can also be entered from the dorsal surface in a similar manner to the distal joints; however, the flexor pouch is more capacious than the dorsal one. For the digital synovial sheath (sheath of the deep flexor tendon), the needle is directed downward behind the interosseous ligament.
For the stifle joint, it is advisable to use two sites because in some animals the lateral femorotibial compartment may not communicate with the rest of the joint. The first site is close behind the lateral patellar ligament (lateral femorotibial compartment), and the needle should be directed caudally. The needle is inserted in the second site between the medial and middle patellar ligaments and directed slightly down and toward the large medial lip of the trochlea (femoropatellar and medial femorotibial compartments).