Scaphotrapeziotrapezoid (STT) Joint Osteoarthritis

Isolated scaphotrapeziotrapezoid (STT) joint osteoarthritis is a fairly common cause of radial sided wrist pain, and it can co-exist with thumb CMC osteoarthritis.
==Anatomy and Biomechanics==
The scaphotrapeziotrapezoid (STT) joint is also known as the triscaphe joint. It is a joint that is shared between the scaphoid, trapezium and trapezoid bones in the wrist.
The biomechanics of STT joint is not completely understood. It is a dome-shaped joint found on the radial side of the wrist. It is involved with thumb movement and transfer of load from the thumb and radial side of the hand to the scaphoid and the radioscaphoid and scaphocapitate joints.
The STT joint may communicate with the rest of the mid-carpal articulation. In patients with inflammatory or osteoarthritis, the midcarpal articulation (including the STT joint) may communicate with the radiocarpal articulation and/or the flexor carpi radialis sheath.
File:Scaphoid.jpg|Scaphoid bone
File:Trapezium.jpg|Trapezium bone
File:Trapezoid.jpg|Trapezoid bone
==Pathology==
STT osteoarthritis changes are more common and more severe on the palmar aspect of the joint.
==Epidemiology==
STT osteoarthritis is commonly seen on x-rays but most cases are not clinically significant. The STT joint is the second most common site for radiographic OA in the wrist. It is reported in 15-59% of wrist radiographs depending on the clinical context, with a higher occurrence (up to 83.3%) in cadaver studies. Radiographic STT osteoarthritis is inversely proportional to scapholunate advanced collapse (SLAC) wrist. It is rare in young patients.
==Clinical Features==
===History===
The clinical symptoms are similar to thumb CMC osteoarthritis. Symptoms include pain at the base of the thumb, distal radial aspect of the wrist, and thenar eminence. There may be pain and/or weakness with pinch and grip.
===Examination===
First ask the patient to extend their thumb to locate the anatomic snuff box. There is tenderness at the distal end of the anatomic snuff box and just radial to the extensor policis longus. 
Then ask the patient supinate their arm and flex their wrist against resistance to identify the flexor carpi radialis tendon. Then ask the patient to relax and feel the scaphoid underneath the tendon, move your finger a little distal to palpate the junction of the scaphoid tuberosity and trapezium.
Tenderness over the STT joint is not associated with radiographic osteoarthritis.
==Imaging==
The following is a classification scheme by White et al. It does not include evaluation of the trapeziotrapezoidal joint.It defines the stage by the highest stage regardless of joint (scaphotrapezial/scaphotrapezoidal) and regardless of the view.
*stage 1 = joint narrowing with or without subcortical sclerosis;
*stage 2 = cyst-like lucencies with or without osteophytes
*stage 3 = complete joint space narrowing or bone-bone apposition without evident space within the cartilage.
==Differential Diagnosis==
==Treatment==
Nonoperative options include bracing/orthotics usually at night, NSAIDs, and STT joint injection
Surgical treatment options include
*Resection of the distal pole of scaphoid with tissue interposition and capsulodesis
*STT joint arthrodesis +/- radial styloidectomy
*Arthroscopic debridement +/- silicone or fascial spacer
*Trapeziectomy with partial proximal trapezoid excision (if combined with thumb CMC OA)
==Videos==
<youtube>https://www.youtube.com/watch?v=LqeOQ5K6V3M</youtube>
==References==
Category:Hand and Wrist Conditions
Category:Osteoarthritis