Synovial fluid is withdrawn from the radiocarpal joint. To help identify the extensor pollicis longus tendon, the patient should actively extend the wrist and thumb. To puncture the joint, the wrist is flexed and ulnar-deviated about 20 to 30°. Traction is applied to the hand. Needle entry occurs just distal to the Lister tubercle, ulnar to the extensor pollicis longus tendon.