The scaphotrapeziotrapezoid joint (STT joint, triscaphe joint) is the articulation between the distal pole of the scaphoid and the proximal surfaces of the trapezium and trapezoid. It is a tripartite synovial joint bound by the palmar and dorsal scaphotrapezial and scaphotrapezoid ligaments. The STT joint typically does not communicate with the radiocarpal or midcarpal joint cavities and is an isolated compartment injected separately during wrist arthrography.
The STT joint is a common site of primary wrist osteoarthritis and is the second most common site after the thumb CMC joint in the radial column. STT arthrosis produces pain at the radial wrist reproduced by axial loading of the scaphoid tuberosity and ulnar deviation. Arthroscopic debridement or limited STT arthrodesis is performed for advanced arthrosis. The distal scaphoid pole is the site most frequently resected during partial wrist fusion procedures. STT arthrography using a separate injection approach to this compartment is important for diagnosis.
Primary or post-traumatic arthrosis of the scaphotrapeziotrapezoid joint produces radial-sided wrist pain worsened by pinch and radial deviation, with tenderness at the distal scaphoid tuberosity and characteristic sclerosis and joint space narrowing on radiograph, managed with splinting, injection, or STT fusion.
Scapholunate ligament disruption alters the STT joint mechanics, causing the distal scaphoid to be pulled by the trapezium into flexion while the proximal scaphoid dorsiflexes with the lunate, producing the DISI deformity with secondary STT overloading and arthrosis.
