The STT joint, short for the scaphotrapeziotrapezoid joint, is a small but critical articulation in the wrist where three carpal bones meet: the scaphoid, the trapezium, and the trapezoid. It sits at the base of the thumb side of the wrist and plays a central role in transferring force from the hand into the forearm, stabilizing the wrist during grip and pinch, and allowing the complex range of motion your wrist uses every day. Despite its size, problems here are surprisingly common and can cause persistent pain on the thumb side of the wrist that is easy to misdiagnose.
Where the STT Joint Sits in the Wrist
Your wrist contains eight small carpal bones arranged in two rows. The proximal row (closer to the forearm) includes the scaphoid, lunate, triquetrum, and pisiform. The distal row (closer to the fingers) includes the trapezium, trapezoid, capitate, and hamate. The STT joint is unusual because it bridges both rows. The scaphoid belongs to the proximal row, while the trapezium and trapezoid belong to the distal row. This cross-row position is what makes the joint so important for wrist mechanics: it is one of the key links between the two carpal rows and directly influences how force travels from your hand up through your wrist.
The scaphoid itself is the largest bone in the proximal row and has a distinctive elongated, curved shape. Its distal pole (the end closer to the thumb) forms the top of the STT joint, while its proximal pole articulates with the radius bone of the forearm. The trapezium sits at the base of the thumb and also forms the trapeziometacarpal (TMC) joint, the saddle joint that gives your thumb its exceptional mobility. The trapezoid is a small, wedge-shaped bone tucked between the trapezium and capitate. Together these three bones create a joint space that, while tight, is responsible for a disproportionate share of wrist stability and load transfer.
The Ligaments That Hold It Together
The STT joint is not simply three bones pressed together. It is bound by a complex arrangement of ligaments that control how much the bones can move relative to one another. Detailed anatomical dissections have identified three distinct bands (fascicles) of the scaphotrapezial ligament on the thumb side of the joint. Two of these originate from the scaphoid tuberosity, the bony bump at the base of the scaphoid, and fan out distally in a V-shape. One inserts on the outer aspect of the trapezium, while the other attaches along the trapezial ridge near the tendon sheath of the flexor carpi radialis. A third, deeper fascicle spreads underneath both of these.1The Journal of Hand Surgery. Anatomy of the Scaphotrapezial Ligament Complex and its Implications for Distal Scaphoid Resection
This layered architecture matters because the ligaments do more than prevent the bones from separating. They guide how the scaphoid flexes and extends relative to the distal row during wrist movement, and they distribute compressive loads across the joint surface. When surgeons consider procedures that remove part of the scaphoid or the trapezium, the integrity of this ligament complex becomes a major concern. Disrupting it can destabilize the entire carpal arrangement, a point that comes up repeatedly in the surgical literature.
How the STT Joint Moves
The motion at the STT joint is not a simple hinge. When you flex and extend your wrist or tilt it side to side, the scaphoid rotates relative to the trapezoid in an oblique plane. Researchers using three-dimensional motion tracking have found that the scaphoid-trapezoid motion during both flexion-extension and radial-ulnar deviation follows a pattern best described as an oblique rotation, angled away from the pure front-to-back plane of the wrist.2The Journal of Hand Surgery. The scaphotrapezio-trapezoidal joint. Part 2: A kinematic study In practical terms, the scaphoid does not simply tip forward and backward like a seesaw. It follows a spiraling path that lets the two carpal rows slide past each other smoothly.
This oblique motion explains why the STT joint is so sensitive to small changes in alignment. If arthritis, ligament damage, or a fracture alters the scaphoid’s resting position by even a few degrees, the downstream effects ripple through the wrist. The scaphoid acts as a mechanical link between the rows, and the STT joint is where that linkage is most tightly controlled.
Forces During Grip and Pinch
Even simple hand activities send considerable force through the STT joint. A cadaver study that measured forces during key pinch (the motion you use to turn a key in a lock) found that the loads at the STT joint scaled up sharply with pinch effort. At a pinch force of roughly 1.5 kilograms, the STT joint saw median contact forces of about 2.4 kilograms. At lighter pinches, the loads were lower but still substantial, around 1.2 kilograms at a half-kilogram pinch.3PubMed. Scaphotrapeziotrapezoid joint loading during key pinch grip before and after trapeziometacarpal arthroplasty: a cadaver study So even a gentle gripping task amplifies force at this joint by roughly double, and harder grips push it higher still.
The same study also looked at what happens after surgery to the neighboring trapeziometacarpal joint (the base-of-thumb joint commonly treated for arthritis). After that procedure, the forces at the STT joint did not change significantly. That finding is reassuring for patients who undergo base-of-thumb surgery, but it also underscores that the STT joint carries its own independent load. It is not merely a bystander receiving spillover from the thumb joint; it has its own biomechanical role.
STT Osteoarthritis Is More Common Than Most People Realize
Arthritis at the STT joint is one of the more frequently overlooked causes of thumb-side wrist pain. In a study that examined wrist radiographs using a dedicated classification system, nearly 60% showed evidence of STT joint osteoarthritis. Most of those cases were early-stage, but the sheer prevalence was striking, roughly double the rate of arthritis found at the radiocarpal joint in the same group.4PubMed Central. Osteoarthritis of the Wrist STT Joint and Radiocarpal Joint
STT arthritis often shows up alongside arthritis at the base of the thumb. Because the symptoms overlap, patients and clinicians may focus on the trapeziometacarpal joint and miss the STT component entirely. The telltale sign of STT arthritis tends to be pain at the anatomical snuffbox, the small depression on the back of the wrist near the base of the thumb, which worsens with gripping, pinching, or twisting motions. Tenderness with direct pressure over the joint is another reliable indicator. Standard wrist X-rays in the right views can usually confirm the diagnosis once the clinician is looking for it.
When STT Problems Lead to Carpal Instability
The STT joint’s role as a bridge between carpal rows means that damage here can unsettle the entire wrist architecture. When severe STT arthritis advances, the scaphoid can shift into an abnormally extended position. A study of radiographic patterns found a clear association between the severity of STT osteoarthritis and the development of a specific instability pattern called DISI (dorsal intercalated segment instability), in which the lunate tilts backward relative to the radius. Interestingly, the scapholunate angle in these patients often remained normal, meaning the instability was driven by changes at the STT level rather than by a torn scapholunate ligament.5PubMed. Radiographic Characteristics of Carpal Instability Associated With Scaphotrapeziotrapezoid Osteoarthritis That distinction matters for treatment planning, because the usual approach to DISI assumes ligament injury and may not be appropriate when the root cause is STT arthritis.
Cadaver experiments have confirmed this vulnerability from a different angle. When researchers removed the trapezium entirely (as is done in certain thumb-base surgeries) or resected the distal pole of the scaphoid, the result was a dissociation between the proximal and distal carpal rows, a form of nondissociative carpal instability.6PubMed. Carpal instability after partial trapeziectomy, total trapeziectomy and the resection of the distal scaphoid pole: a cadaveric study The rows themselves stayed intact internally; they just stopped moving together in a coordinated way. This finding has practical implications for surgeons performing trapeziectomies or distal scaphoid resections, because even a procedure that relieves pain in one joint can compromise the wrist’s overall stability if the STT ligament complex is disrupted.
Conservative Treatment Options
Not every case of STT arthritis needs surgery. For mild to moderate symptoms, the standard first-line approach includes splinting and corticosteroid injections.7PubMed. Treatment of scaphotrapezio-trapezoid arthritis A thumb spica splint or a short wrist splint that immobilizes the base of the thumb can reduce the repetitive loading that aggravates the joint. Corticosteroid injections placed directly into the STT joint space can provide temporary relief, sometimes lasting several months, by reducing local inflammation.
Activity modification is another practical step. Because force at the STT joint ramps up with pinch and grip, avoiding prolonged or repetitive pinching tasks, or using ergonomic tools that distribute force across a wider area of the hand, can reduce symptom flares. Nonsteroidal anti-inflammatory medications help with pain management as well. Many patients with early-stage STT arthritis do well for years with these measures alone, reserving surgery for cases where conservative approaches stop providing adequate relief.
Surgical Options for STT Arthritis
When conservative measures fail, several surgical procedures target the STT joint. The two most common categories are arthrodesis (fusion) and resection arthroplasty (removing part of the joint surface).
STT Arthrodesis (Fusion)
Fusing the scaphoid to the trapezium and trapezoid eliminates the arthritic joint surface and stabilizes the scaphoid. A systematic review pooling data from multiple studies found that after STT fusion, average wrist flexion was about 41 degrees and extension about 50 degrees, with grip strength recovering to roughly 76% of the unaffected hand.8The Journal of Hand Surgery. Scaphotrapeziotrapezoid Arthrodesis: Systematic Review Those numbers represent a meaningful reduction from normal wrist range of motion, but most patients found the trade-off acceptable for pain relief.
Long-term follow-up data confirm that the procedure is durable but not without risk. In one series tracking 58 fused wrists for an average of 10 years, about 10% needed a secondary procedure such as conversion to total wrist fusion, and roughly 7% had problems with the fusion itself not healing (nonunion).9PubMed Central. Scaphotrapeziotrapezoid Arthrodesis: A 10-Year Follow-up Study of Complications in 58 Wrists An earlier series of 30 patients showed that all achieved bony union within about 11 weeks on average, and most returned to their previous activities, though roughly a quarter experienced complications, the most common being arthritis developing at the neighboring radioscaphoid joint over time.10PubMed. Scaphotrapeziotrapezoid fusion: long-term follow-up study Grip strength in that group improved from an average of 18 kilograms of force preoperatively to 27 kilograms afterward.
Different fixation hardware has been tried. Kirschner wires (thin metal pins) are the most commonly used method, but compression staples represent a newer alternative. A case series using compression staples found that all patients achieved complete bone union within four months and had improvement in radial-sided wrist pain, though grip strength decreased postoperatively rather than improving.11PubMed Central. The Use of Compression Staples for Scaphotrapeziotrapezoid Arthrodesis in the Treatment of Scaphotrapeziotrapezoid Arthritis That conflict with the broader fusion data is worth noting: results can vary depending on patient selection, fixation method, and what motivated the surgery.
Distal Scaphoid Resection
An alternative to fusion is removing a small portion of the distal end of the scaphoid, eliminating the arthritic surface without locking the bones together. This can be done arthroscopically, a minimally invasive technique using a camera and small instruments through tiny incisions. Arthroscopic distal scaphoid resection has shown fewer complications than the equivalent open procedure while still effectively relieving pain from STT arthritis.12PubMed Central. Arthroscopic Distal Scaphoid Resection for Scapho-Trapezium-Trapezoid Arthritis The appeal is a shorter recovery and less surgical trauma, though the long-term stability implications of removing part of the scaphoid remain a concern given the instability data from cadaver studies described earlier.
How surgeons choose between fusion and resection often depends on the patient’s age, activity level, degree of arthritis, and whether neighboring joints are also affected. A younger, more active patient might benefit from the structural stability of a fusion despite its motion trade-offs, while an older patient seeking faster recovery and less invasive surgery might be better served by resection. There is no one-size-fits-all answer, and the field continues to debate optimal indications for each approach.
Why STT Arthritis Gets Missed
Part of the reason STT problems fly under the radar is location. The pain pattern mimics several other wrist conditions. Scaphoid fractures, de Quervain’s tenosynovitis (inflammation of the tendons on the thumb side of the wrist), and base-of-thumb arthritis all produce discomfort in overlapping areas. An X-ray taken primarily to evaluate the thumb or the radiocarpal joint may not show the STT joint clearly unless the right views are obtained. A “scaphoid view” or an oblique projection tends to reveal STT narrowing and bone spurs much better than a standard posteroanterior wrist film.
Clinical examination helps narrow it down. Pressing directly over the STT joint while the patient makes a fist or pinches usually reproduces the pain in a way that other conditions do not. Grinding the scaphoid against the trapezium with the thumb in opposition is another provocative test. If these tests are positive and X-rays show joint-space narrowing or osteophytes at the STT joint, the diagnosis is fairly straightforward. The issue is that many practitioners do not think to check for it, especially when the base-of-thumb joint looks arthritic on the same X-ray and seems like the obvious culprit.
The STT Joint After Thumb-Base Surgery
Because the trapezium participates in both the STT joint and the trapeziometacarpal joint at the base of the thumb, surgery for thumb-base arthritis inevitably affects the STT joint to some degree. Trapeziectomy, one of the most common procedures for severe thumb-base arthritis, involves removing the trapezium entirely. As the cadaver data showed, that removal destabilizes the connection between the carpal rows. In practice, many patients compensate well because the remaining soft tissues scar down and provide some stability over time. But a subset develops persistent wrist pain or weakness that is attributable to STT-related instability rather than recurrence of their original thumb problem.
Patients considering thumb-base surgery should be aware that pre-existing STT arthritis can influence outcomes. If the STT joint is already arthritic before a trapeziectomy, removing the trapezium may not fully resolve the thumb-side wrist pain because the scaphoid-trapezoid interface remains a source of discomfort. Some surgeons address both problems simultaneously, for example by performing a hemitrapeziectomy (removing only part of the trapezium) combined with treatment of the STT surface, though evidence on the best combined approach is still limited.
A Rare Anatomical Curiosity
In extremely rare cases, the scaphoid and trapezium are naturally fused from birth, a condition called osseous scaphotrapezial coalition. Unlike surgical fusion, this congenital variant typically causes no pain or functional limitation and is usually discovered by accident on an X-ray taken for another reason.13PubMed Central. Osseous Scaphotrapezial Coalition Carpal coalitions within a single row are occasionally seen, but a coalition crossing the proximal and distal rows, as this one does, has traditionally been thought to result from an injury or a congenital syndrome. The existence of isolated, symptom-free scaphotrapezial coalition challenges that assumption and suggests the fusion can occur as a standalone developmental variant.
From a clinical standpoint, the main risk of this variant is misinterpretation. A radiologist unfamiliar with it might mistake the fused bones for an old fracture with callus formation, or a pathological process. Recognizing it as a benign developmental anomaly avoids unnecessary workups. For the patient, it is little more than a conversation starter at the orthopedic office: their wrist essentially performed its own “arthrodesis” in the womb, decades before any surgeon could propose the idea.