Triscaphe Arthritis (STT Arthritis)

Triscaphe arthritis is degenerative arthritis of the scaphotrapeziotrapezoid (STT) joint, where the distal pole of the scaphoid meets the trapezium and trapezoid at the radial base of the wrist. It is less common than scapholunate advanced collapse (SLAC) but is the second commonest pattern of degenerative wrist arthritis, and a significant cause of radial-sided wrist pain.

How common. Watson's classic series put isolated triscaphe arthritis at about 26% of degenerative wrists, with SLAC and triscaphe arthritis coexisting in a further 14%. These figures have no stated denominator and come from a single referral practice.

Who. Both sexes are affected, with a slight male predominance in post-traumatic cases and a female predominance in primary osteoarthritis. Presentation is typically at 45-65 years, though post-traumatic cases may present earlier.

The film is not the diagnosis. Radiographic STT arthritis is far commoner than symptomatic STT arthritis, and the two must never be equated. In Rizzo's thumbs followed after trapeziometacarpal arthrodesis, 39 developed radiographic STT change and only 8 were symptomatic: roughly four in five of those arthritic-looking joints never hurt. STT joint-space narrowing is a frequent incidental finding on wrist and thumb radiographs in older patients.

Diagnose it on the patient. The diagnosis rests on focal STT tenderness reproduced clinically and abolished by a diagnostic injection, not on a film. STT arthritis coexists with thumb CMC arthritis often enough that both joints must be examined and, where symptomatic, both treated. No reliable coexistence rate exists, and figures quoted for it are usually derived from studies of the thumb rather than of the wrist.

The joint. The STT joint is a complex three-bone articulation at the radial carpus. The saddle-shaped distal pole of the scaphoid articulates with the trapezium and trapezoid in a reciprocally curved configuration. The surfaces are covered with hyaline cartilage and held by a fibrous capsule reinforced by intrinsic ligaments, the scaphotrapezial and scaphotrapezoid ligaments.

• Trapezium - the radial component, which also articulates with the thumb metacarpal at the CMC joint
• Trapezoid - the ulnar component, and the smallest carpal bone

Its neighbours. The scaphocapitate articulation lies medially and the thumb CMC joint distally. The three joints are distinct but biomechanically interdependent, and the thumb CMC joint is functionally linked to the STT joint.

The scaphoid as a link. The scaphoid bridges the proximal and distal carpal rows. Its distal pole moves with the distal row (trapezium and trapezoid) and its proximal pole with the proximal row (lunate), and it rotates about its waist during wrist motion. The STT joint is a transitional zone between the mobile distal row and the relatively fixed scaphoid.

Where to feel it. The STT joint is palpable 1cm distal and radial to the radial styloid, just proximal to the thumb CMC joint. The CMC joint lies more distally and the scaphoid tubercle more proximally.

The radial artery runs across the STT joint volarly. That matters in choosing an approach, and dorsal approaches are preferred to avoid vascular injury.

How the joint is loaded. The table sets out how wrist position loads the joint. Gripping activities that involve wrist extension substantially increase STT joint reactive forces, which is why push-ups, lifting and forceful gripping make the symptoms worse.

Primary or secondary. Primary, idiopathic osteoarthritis is the most common form. Secondary STT arthritis follows underlying pathology:

• Previous wrist trauma - particularly scaphoid fractures, distal radius fractures involving the radiocarpal joint, and trapezial fractures
• Scaphoid malunion with humpback deformity - post-traumatic arthritis is particularly common here, because the abnormal scaphoid position concentrates load on the distal scaphoid-trapezium articulation
• Scapholunate dissociation - chronic dissociation alters carpal kinematics, increasing STT joint reactive forces and accelerating degeneration; ulnar translation of the carpus is seen in these cases
• Hypermobility of the STT joint
• Thumb CMC arthritis - often coexistent, through shared biomechanical forces
• Generalised osteoarthritis affecting multiple joints
• CPPD

Relationship to SLAC. STT arthritis may be part of the SLAC pattern or occur independently. In SLAC, radioscaphoid arthritis precedes STT involvement, whereas isolated STT arthritis with a normal scapholunate interval is primary osteoarthritis. Always assess the scapholunate gap on the radiographs: normal is less than 3mm.

The degenerative cascade. STT arthritis follows the typical osteoarthritis cascade. Cartilage fibrillation and surface irregularity progress to cartilage loss with exposed subchondral bone, and attempted healing produces subchondral sclerosis, marginal osteophytes and synovial inflammation. In advanced cases the cartilage is lost completely, bone articulates on bone, and cysts and deformity form; loose bodies may develop from fragmented osteophytes.

Watson's classification of STT arthritis parallels his classification of the SLAC wrist, and its practical line falls between Grades II and III. While the radiocarpal and midcarpal joints are preserved (Grades I-II), joint-preserving surgery is possible; once they are involved (Grade III) the disease is pancarpal and salvage is required. The grades run Narrowing, Osteophytes, Pancarpal (NOP).

History. Radial-sided wrist pain, insidious in onset and progressive over months to years. It is activity-related, worse with gripping, pushing, wrist extension and radial deviation, and specific activities aggravate it:

• Push-ups and yoga (the downward dog position)
• Lifting heavy objects
• Tools such as screwdrivers and hammers
• Keyboard use with the wrist extended

Pain may radiate proximally along the radial forearm or distally into the thenar eminence, particularly when thumb CMC arthritis coexists. Rest typically gives partial relief, though night pain may occur in advanced cases, and morning stiffness of 10-30 minutes is common. Clicking or catching may be reported, particularly if loose bodies are present, and the weakness patients describe typically reflects pain inhibition rather than a true motor deficit.

Look. Swelling over the radial wrist is usually mild, and deformity is rare unless the disease is severe. Thenar atrophy suggests median nerve involvement or severe thumb CMC arthritis.

Feel. The key sign is direct tenderness over the STT joint, 1cm distal and radial to the radial styloid. Compare it with the thumb CMC joint and the radial styloid.

Move. Range of motion is usually preserved or mildly reduced, with pain typically at the extremes of extension and radial deviation. Document flexion, extension, radial and ulnar deviation.

Provocative tests.

• STT compression test - axial compression through the thumb metacarpal while the wrist is moved passively from ulnar to radial deviation. Pain localised to the STT joint is highly suggestive; compare with the asymptomatic wrist to separate pathology from normal joint crepitus
• Resisted wrist extension - reproduces the pain
• Scaphoid compression test - positive
• Grind test - positive if the thumb CMC joint is also involved

Strength and nerves. Grip strength is often reduced by 20-40% compared with the other side, and pinch strength may be reduced if the CMC joint is involved. Assess median and radial nerve function; the superficial radial nerve may be tender if compressed by osteophytes.

What it costs the patient. Functional limitation follows pain severity and arthritic stage. Reduced grip affects jar opening, lifting and tool use; bearing weight on the extended wrist becomes difficult for push-ups, yoga and transfers; and keyboard and mouse use (particularly if wrist extension is required) and steering suffer. Patients may compensate by avoiding wrist extension or shifting tasks to the opposite hand.

Check the neighbours. Always examine the thumb CMC joint and check the scapholunate interval for the SLAC association. Radiocarpal arthritis is tender over the radiolunate or radioscaphoid joint. The other causes of radial-sided wrist pain, and the finding that separates each, are compared in the differential diagnosis table later on this page.

Radiographs. Standard PA, lateral and oblique views are the foundation. The PA shows joint space narrowing at the STT articulation, subchondral sclerosis and marginal osteophytes (often dorsal), with subchondral cysts in advanced disease. The STT joint is frequently obscured by bony overlap on a standard PA, and the most useful projections for profiling it are:

• Carpal tunnel (skyline) view - the wrist in maximum dorsiflexion, the beam directed proximally from the palm. It clearly shows joint space narrowing, subchondral change and the relationship between the distal scaphoid and the trapezium-trapezoid, and should be standard when STT arthritis is suspected
• Semi-supinated oblique
• PA in slight ulnar deviation

The lateral assesses overall carpal alignment, the radiocarpal joint and the position of the scaphoid, looking for flexion deformity from SL dissociation or extension from malunion. Scaphoid-specific views (PA with ulnar deviation and slight extension) may reveal a malunion or nonunion that predisposes to STT arthritis. On every film check the scapholunate gap, the radioscaphoid joint space (involvement makes it Grade III) and the thumb CMC joint.

CT gives detailed bone architecture, osteophyte location and size, subchondral cysts and the extent of cartilage loss, inferred from joint space narrowing. It is particularly valuable in planning STT fusion, where it defines bone stock and the optimal fusion position, and in assessing pancarpal disease. Three-dimensional reconstructions help visualise complex deformity.

MRI shows articular cartilage directly on high-resolution sequences, bone marrow oedema (suggesting an active degenerative process), synovitis and soft-tissue pathology such as ganglion cysts. It also assesses the scapholunate ligament for occult dissociation and the rest of the carpus for other pathology. Plain radiographs and CT are usually sufficient for diagnosis and treatment planning.

Diagnostic injection. A fluoroscopically guided corticosteroid injection into the STT joint is both diagnostic and therapeutic. It is particularly valuable when several pain sources compete: thumb CMC arthritis, de Quervain tenosynovitis, radiocarpal arthritis. The injection typically combines triamcinolone 40mg or methylprednisolone 40mg with lidocaine or bupivacaine.

Reading the response. Complete relief lasting several hours, while the local anaesthetic acts, followed by a gradual return of symptoms over days to weeks confirms the STT joint as the primary pain generator. No relief, or minimal improvement, suggests an alternative or additional source that needs further investigation.

Conservative treatment comes first, particularly for Grade I and mild Grade II disease.

• Activity modification - avoid or limit loaded wrist extension, forceful gripping and repetitive radial deviation. Patients learn to lift with the wrist in neutral, avoid push-ups and adjust their keyboard ergonomics
• NSAIDs - symptomatic relief, and they may reduce synovitis. Topical diclofenac gel may be preferred for patients with gastrointestinal concerns or on anticoagulation; paracetamol controls pain without an anti-inflammatory effect
• Splinting - activity-specific, in a neutral position or as a wrist extension restriction orthosis limiting extension to 20-30 degrees, which reduces STT loading and may relieve symptoms. Custom thermoplastic splints from a hand therapist or off-the-shelf braces may be used, worn during aggravating activities rather than continuously to avoid stiffness and muscle deconditioning
• Corticosteroid injection - temporary relief in 60-80%, lasting weeks to months. Injections may be repeated, but prolonged use risks cartilage damage and is generally limited to 2-3 a year
• Hyaluronic acid (viscosupplementation) has been described but lacks robust evidence of efficacy

When to operate. Surgery is considered when conservative measures fail to control symptoms, pain significantly limits function or quality of life, the patient wishes to return to activities incompatible with conservative management, or radiographs document progression despite it. The duration varies, but typically 3-6 months of appropriate conservative treatment is recommended first.

Choosing the operation. The grade decides whether the joint can be preserved; the patient's demands decide between the two joint-preserving operations.

Distal scaphoid excision with tendon interposition is the most common procedure for isolated Grade I-II disease. It preserves wrist motion, and it accepts a DISI pattern in over half of wrists, discussed with the technique below.

STT fusion is preferred for younger, higher-demand patients who wish to maintain grip strength and will accept some loss of motion. It gives reliable pain relief and keeps grip close to pre-disease levels, and fusion rates are 85-95% with modern techniques and rigid fixation.

Be careful with the motion figures. Watson's original description, carded in the Evidence Base, claims the fusion retains about 80% of the flexion-extension arc and 66% of radial-ulnar deviation. On a normal arc that is a loss of roughly 25-30 degrees of flexion-extension and 15-20 degrees of radial-ulnar deviation, not the 10-15 degrees often quoted. Watson's figures are the most optimistic in the literature: they come from the originator of the procedure, with no comparison group and no stated denominator, and subsequent series generally report greater loss. Counsel the patient with the larger number.

Proximal row carpectomy is indicated for Grade III disease with pancarpal involvement, provided the lunate fossa of the radius and the head of the capitate have preserved cartilage. It is a reliable salvage: grip recovers to 70-80% of the other side, and it does not burn bridges, because total wrist arthrodesis remains possible if it fails. Progressive capitate-lunate fossa arthritis is the long-term concern, though typically slow in onset.

Total wrist arthrodesis is reserved for Grade III arthritis with cartilage loss extensive enough to preclude PRC, for failed motion-preserving surgery, and for patients with low functional demands who put pain relief and stable support before motion. Fusion is achieved in more than 95% and pain relief is excellent and predictable. The price is complete loss of wrist motion, which affects activities of daily living, though most patients adapt well, particularly when unilateral involvement leaves the opposite hand to manage two-handed tasks.

Distal scaphoid excision

Approach. Dorsoradial, between the first and second dorsal compartments, or volar-radial through the FCR sheath. Protect the branches of the superficial radial nerve.

1. Expose the STT joint through a capsulotomy and identify the distal scaphoid articular surface
2. Excise the distal 2-4mm of the scaphoid with an osteotome or oscillating saw
3. Remove all arthritic bone and every osteophyte, so that nothing is left to impinge
4. Preserve the scapholunate ligament attachment proximally
5. Interpose a rolled slip of flexor carpi radialis tendon, capsule or allograft, secured with suture or an anchor, to prevent bone-to-bone contact between the proximal scaphoid and the trapezium. Some surgeons perform simple excision without interposition, with comparable results
6. Close capsule and skin

How much to take. Only the arthritic distal pole: enough to clear the STT articular surface and osteophytes, leaving the proximal two-thirds of the scaphoid and, critically, its scapholunate ligament attachment intact.

Why over-resection destabilises. The distal scaphoid is normally buttressed against the trapezium-trapezoid, which resists scaphoid flexion. Resecting the distal pole removes that support, so the scaphoid tends to extend and the proximal row rotates into a DISI (dorsal intercalated segment instability) pattern; the carpal-instability topic covers the general mechanism. Taking too much, or violating the SL attachment, exaggerates this and risks a symptomatic instability.

Does the DISI matter? In Garcia-Elias's series a DISI appeared in most wrists after distal-pole resection yet caused no further joint deterioration at short-to-medium follow-up, so a mild radiographic DISI is generally accepted. Whether it accelerates radiocarpal arthritis over decades is unresolved, which is why the resection is kept minimal and the SL attachment preserved.

STT fusion

Approach. Dorsal, protecting the ECRL and the superficial radial nerve.

1. Remove the articular cartilage from all three surfaces: scaphoid, trapezium and trapezoid
2. Position the scaphoid in slight extension relative to the lunate to prevent flexion collapse, matching the contralateral scapholunate angle if possible. Excessive flexion increases radiocarpal load
3. Pack bone graft into the fusion site to promote union, usually iliac crest autograft or allograft; Watson's original description found a local donor site sufficient, without iliac crest harvest
4. Fix with headless compression screws (the most common choice; Herbert or Acutrak, for example), a dorsal plate, or K-wires, which are less stable and carry a higher nonunion rate

Radial styloid impingement. Once the scaphoid is fused to the trapezium-trapezoid in extension, it no longer flexes out of the way during radial deviation. The extended distal scaphoid and the fused trapezium then abut the radial styloid, producing radial-sided pain on radial deviation, a common cause of persistent pain despite a solid fusion.

• Prevention - many surgeons perform a limited radial styloidectomy of about 3-4mm at the time of STT fusion to create clearance. Over-resection is avoided because the radioscaphocapitate ligament origin sits on the styloid, and taking too much risks ulnar translation of the carpus
• Late presentation - if radial-deviation pain develops after a united fusion, image for styloid abutment; a delayed radial styloidectomy is the usual remedy. Distinguish this mechanical impingement from progressive radiocarpal arthritis, which is managed differently (PRC or total wrist fusion)

Proximal row carpectomy

Through a dorsal approach between the third and fourth extensor compartments, the scaphoid, lunate and triquetrum are removed completely. The cartilage of the capitate head is assessed and must be intact. The capitate then articulates directly with the lunate fossa as a new radiocarpal joint, and the capsule is closed over it.

Total wrist arthrodesis

The radius is fused to the second and third metacarpals in neutral to slight extension (10-15 degrees) and neutral radial-ulnar deviation. Dorsal plates are the most common fixation, with intramedullary rods or combinations as alternatives, and bone graft promotes fusion.

After distal scaphoid excision. Persistent pain affects 10-15%. Scaphoid instability is rare, and follows over-resection.

After STT fusion.

• Nonunion in 5-15% - it may be asymptomatic or painful. Smoking, inadequate fixation and poor bone stock are the risk factors, and a symptomatic nonunion is revised with rigid fixation and bone graft
• Persistent pain in 5-10%
• Hardware prominence or irritation - common with dorsal plates and screws; remove symptomatic hardware once the fusion has consolidated
• Radial styloid impingement, and the loss of motion counselled for above

After any operation. Radial approaches risk the superficial radial nerve, giving numbness or a painful neuroma over the radial thumb and dorsal hand; protect its branches and avoid retractor pressure, and the dysaesthesias are usually temporary. Early problems include wound infection or dehiscence and haematoma, and hardware may fail. Complex regional pain syndrome is rare, less than 2%, but devastating. Thumb CMC arthritis may become symptomatic or progress after STT surgery if it is not addressed at the same time.

Persistent pain. Pain that continues after excision may mean incomplete excision, scaphoid instability or unrecognised radiocarpal arthritis. Re-evaluate the diagnosis for a missed CMC arthritis or radiocarpal disease, obtain a CT for residual osteophytes or impingement, use a diagnostic injection to identify the source, and consider revision or salvage (PRC or arthrodesis).

Progressive radiocarpal or midcarpal arthritis is a long-term concern after both excision and fusion, because altered carpal kinematics may accelerate degeneration. Monitor with serial radiographs; if it becomes symptomatic, the answer is PRC or total wrist arthrodesis.

Confirming fusion. Look for bridging bone and trabeculae crossing the fusion site, and obtain a CT if union is uncertain on plain films.

Hand therapy covers oedema control (elevation and compression), scar management, progressive range of motion in flexion-extension and radial-ulnar deviation, grip and pinch strengthening, and return-to-work counselling. Heavy manual labour may require 3-4 months, and workers' compensation cases may have a prolonged recovery.

Results. Satisfaction after surgery is generally good, with 75-85% reporting significant improvement. Pain relief is achieved in 80-90%, though complete resolution is uncommon; 85-90% return to work and 70-80% to recreational activities, and grip recovers to 75-90% of the contralateral side.

Who does well. Outcomes are better with isolated Grade I-II disease, realistic expectations, good compliance with rehabilitation and, for fusion, not smoking. They are poorer with Grade III radiocarpal involvement, a concurrent thumb CMC arthritis left unaddressed, smoking (which affects fusion healing), workers' compensation or litigation, and secondary gain.

Related pages: SLAC Wrist is the other half of Watson's periscaphoid classification and the pattern this one is defined against - together they account for the great majority of degenerative wrists, and the two coexist in a substantial minority; Scapholunate Dissociation drives the altered carpal kinematics that load the STT joint and is the precursor to SLAC, while Carpal Instability: DISI and VISI explains the dorsal intercalated segment instability that follows distal scaphoid excision and the opposite scaphoid dorsiflexion Crosby described in untreated STT arthrosis; Thumb CMC Arthritis is the coexisting diagnosis that must be examined and injected separately before either joint is operated on, since treating the wrong one is the commonest cause of incomplete relief; Proximal Row Carpectomy and Four-Corner Fusion are the salvage procedures for pancarpal disease, with Total Wrist Arthroplasty and Wrist Arthroplasty covering the motion-preserving alternative to total wrist fusion; Scaphoid Nonunion and Scaphoid Fractures cover the humpback malunion that concentrates load distally and causes post-traumatic STT degeneration; De Quervain Tenosynovitis is the principal soft-tissue differential for radial wrist pain; and Kienbock's Disease completes the differential for degenerative carpal pain with altered load transfer.

• Excision versus arthrodesis for isolated Grade I-II disease. No randomised data exist. Distal scaphoid excision preserves motion with faster recovery but induces a DISI carpal malalignment; STT fusion gives stronger, more predictable grip but loses arc and carries a real nonunion risk. Selection remains demand- and surgeon-dependent.

• Does distal scaphoid excision matter long-term? Garcia-Elias showed a DISI pattern develops in most wrists after distal pole resection, yet without measurable further deterioration at short-to-medium follow-up. Whether this malalignment accelerates radiocarpal arthritis over decades is unresolved, so over-resection is avoided and the proximal scaphoid-SL attachment is preserved.

• Interposition or not? Both interposition (FCR slip, capsule, allograft) and simple excision are described with broadly comparable outcomes; some series report greater retained motion without interposition. Interposition is not clearly superior.

• Open versus arthroscopic STT fusion / excision. Arthroscopic techniques may reduce stiffness from extra-articular adhesions but the evidence is small-series and operator-dependent; open surgery remains the default for most surgeons.

• Role of the diagnostic injection. Universally recommended yet variably predictive - relief confirms the STT joint as a pain source but does not guarantee complete relief after surgery, especially when CMC arthritis coexists.

• PRC versus four-corner-type salvage for Grade III. When pancarpal disease is present, the choice between proximal row carpectomy and a midcarpal-fusion-based salvage hinges on the integrity of the capitate head and lunate fossa rather than on STT pathology itself.

The literature on STT arthritis treatment demonstrates that surgical outcomes are generally favorable for appropriately selected patients. Distal scaphoid excision and STT arthrodesis are both well-supported for isolated STT arthritis - excision preserving motion and arthrodesis maximising grip in higher-demand patients - while proximal row carpectomy serves as an excellent salvage for pancarpal arthritis when the capitate head and lunate fossa are preserved. Hand therapy is integral to both conservative and postoperative care, and any coexisting thumb carpometacarpal arthritis should be assessed and treated on its own merits to avoid incomplete symptom relief.