Triscaphe Arthritis (STT Arthritis)

Incidence and Demographics

Triscaphe arthritis is less common than scapholunate advanced collapse (SLAC) but is the second most frequent pattern of degenerative wrist arthritis and a significant cause of radial-sided wrist pain. The condition affects both men and women, with a slight male predominance in post-traumatic cases and female predominance in primary osteoarthritis cases. Age of presentation is typically 45-65 years, though post-traumatic cases may present earlier.

Risk Factors and Etiology

STT arthritis may be primary (idiopathic osteoarthritis) or secondary to underlying pathology. Risk factors include previous wrist trauma (particularly scaphoid fractures or distal radius fractures involving the radiocarpal joint), scapholunate dissociation (altered carpal mechanics leading to abnormal STT loading), hypermobility of the STT joint, thumb CMC arthritis (often coexistent due to shared biomechanical forces), and generalized osteoarthritis affecting multiple joints.

Post-traumatic arthritis is particularly common following scaphoid malunion with humpback deformity, where the abnormal scaphoid position concentrates load on the distal scaphoid-trapezium articulation. Chronic scapholunate dissociation alters carpal kinematics, increasing STT joint reactive forces and accelerating degenerative changes.

Associated Conditions

High Yield: STT arthritis commonly coexists with thumb CMC arthritis (30-40% of cases).

STT Joint Anatomy

The scaphotrapeziotrapezoid (STT) joint is a complex three-bone articulation at the radial carpus. The distal pole of the scaphoid articulates with the trapezium and trapezoid in a reciprocally curved saddle-type configuration. The joint surfaces are covered with hyaline articular cartilage and are supported by a fibrous joint capsule reinforced by intrinsic ligaments including the scaphotrapezial ligament and scaphotrapezoid ligament.

The STT joint is distinct from the scaphocapitate articulation medially and the trapezium-first metacarpal (thumb CMC) joint distally, though biomechanically these articulations are interdependent. The STT joint functions as a transitional zone between the mobile distal carpal row (trapezium and trapezoid) and the relatively fixed scaphoid, which serves as a mechanical link between the proximal and distal rows.

Biomechanics and Load Transmission

Watson's classification for STT arthritis parallels his classification for SLAC wrist. Grade I shows joint space narrowing at the STT articulation with minimal subchondral changes and no osteophytes. Grade II demonstrates advanced STT arthritis with subchondral sclerosis, cyst formation, and osteophyte formation, but the radiocarpal joint (particularly radiolunate articulation) and midcarpal joint are preserved. Grade III includes involvement of adjacent joints, particularly the radioscaphoid or capitolunate articulations, indicating pancarpal degenerative disease.

This classification has important treatment implications. Grade I-II STT arthritis with preserved adjacent joints is amenable to joint-preserving surgery (distal scaphoid excision) or STT fusion. Grade III arthritis typically requires proximal row carpectomy or total wrist arthrodesis.

Advanced Imaging

Computed tomography (CT) provides detailed assessment of bone architecture, osteophyte location and size, subchondral cyst formation, and the extent of cartilage loss (inferred from joint space narrowing). CT is particularly valuable for preoperative planning when STT fusion is contemplated, as it defines the quality of bone stock and optimal fusion position. Three-dimensional reconstructions help visualize complex deformity.

Magnetic resonance imaging (MRI) directly visualizes articular cartilage (on high-resolution sequences), bone marrow edema (suggesting active degenerative process), synovitis, and associated soft tissue pathology including ganglion cysts. MRI also assesses the scapholunate ligament (looking for occult dissociation) and the remainder of the carpus for additional pathology. However, plain radiographs and CT are usually sufficient for diagnosis and treatment planning.

Diagnostic Injection

Fluoroscopically guided corticosteroid injection into the STT joint serves both diagnostic and therapeutic purposes. Temporary pain relief following injection confirms the STT joint as the primary pain generator, which is particularly valuable when multiple potential sources exist (thumb CMC arthritis, de Quervain tenosynovitis, radiocarpal arthritis). The injection typically combines a corticosteroid (triamcinolone 40mg or methylprednisolone 40mg) with local anesthetic (lidocaine or bupivacaine).

Response to injection is assessed based on pain relief duration and degree. Complete relief lasting several hours (during local anesthetic effect) followed by gradual return of symptoms over days to weeks confirms STT arthritis. Lack of relief or minimal improvement suggests alternative or additional pain sources requiring further investigation.

Non-Operative Treatment

History

Patients typically present with radial-sided wrist pain that is insidious in onset and progressive over months to years. The pain is activity-related and worse with gripping, pushing, wrist extension, and radial deviation. Specific aggravating activities include push-ups, yoga (downward dog position), lifting heavy objects, using tools (screwdrivers, hammers), and keyboard use with wrist extension. Pain may radiate proximally along the radial forearm or distally into the thenar eminence, particularly when thumb CMC arthritis coexists.

Rest typically provides partial relief, though night pain may occur in advanced cases. Morning stiffness lasting 10-30 minutes is common. Mechanical symptoms such as clicking or catching may be reported, particularly if loose bodies are present. Weakness is often described but typically reflects pain inhibition rather than true motor deficit.

Physical Examination

Inspection: Look for thenar atrophy (suggests median nerve involvement or severe thumb CMC arthritis), swelling over radial wrist (usually mild), and deformity (rare unless severe)

Palpation: Direct tenderness over STT joint (1cm distal and radial to radial styloid, just proximal to thumb CMC joint); compare to CMC joint and radial styloid

Range of Motion: Usually preserved or mildly reduced; document flexion, extension, radial deviation, ulnar deviation; pain typically at extremes of extension and radial deviation

Provocative Tests: STT compression test (axial load on thumb while moving wrist in radial/ulnar deviation), resisted wrist extension (reproduces pain), grind test (if CMC also involved)

Strength: Grip strength often reduced 20-40% compared to contralateral side; pinch strength may be reduced if CMC involved

Neurovascular: Assess median and radial nerve function; superficial radial nerve may be tender if compressed by osteophytes

The STT compression test is performed by applying axial compression through the thumb metacarpal while passively moving the wrist from ulnar to radial deviation. Pain with this maneuver, particularly localized to the STT joint, is highly suggestive of STT arthritis. Comparison with the contralateral asymptomatic wrist helps differentiate pathologic findings from normal joint crepitus.

Functional Impact

Functional limitations correlate with pain severity and arthritic stage. Common difficulties include reduced grip strength affecting jar opening, lifting, and tool use, inability to bear weight on extended wrist (affecting push-ups, yoga, transfers), keyboard and mouse use (particularly if wrist extension is required), and steering wheel manipulation. Patients may develop compensatory strategies such as avoiding wrist extension or shifting tasks to the opposite hand.

Radiographic Evaluation

Standard wrist radiographs including posteroanterior (PA), lateral, and oblique views form the foundation of imaging assessment. The PA view demonstrates joint space narrowing at the STT articulation, subchondral sclerosis, and marginal osteophytes. However, the STT joint is often better visualized on specialized views.

The carpal tunnel (skyline) view, the semi-supinated oblique, and a PA view in slight ulnar deviation are the most useful projections for profiling the STT joint, which is frequently obscured by bony overlap on a standard PA radiograph. The carpal tunnel view is obtained with the wrist in maximum dorsiflexion, with the X-ray beam directed proximally from the palm. This view profiles the STT joint and clearly demonstrates joint space narrowing, subchondral changes, and the relationship between the distal scaphoid and the trapezium-trapezoid. This view should be standard in the assessment of radial wrist pain when STT arthritis is suspected.

The lateral radiograph assesses overall carpal alignment, scaphoid position (looking for flexion deformity from SL dissociation or extension from malunion), and the radiocarpal joint. Scaphoid-specific views (PA with ulnar deviation and slight extension) may reveal scaphoid pathology such as malunion or nonunion that predisposes to STT arthritis.

Radiographic Classification

Initial management of STT arthritis is conservative, particularly for Grade I disease and mild Grade II. Activity modification involves avoiding or limiting provocative positions and activities, particularly wrist extension with loading, forceful gripping, and repetitive radial deviation. Patients are educated to modify technique (using neutral wrist position for lifting, avoiding push-up exercises, adjusting keyboard ergonomics).

Non-steroidal anti-inflammatory drugs (NSAIDs) provide symptomatic relief and may reduce synovitis. Topical NSAIDs (diclofenac gel) may be preferred for patients with gastrointestinal concerns or those on anticoagulation. Acetaminophen is an alternative for pain control without anti-inflammatory effects.

Splinting with a wrist extension restriction orthosis (limiting wrist extension to 20-30 degrees) reduces STT joint loading and may provide symptom relief during activities. Custom thermoplastic splints fabricated by hand therapists or off-the-shelf wrist braces may be used. Splints are typically worn during aggravating activities rather than continuously to avoid stiffness and muscle deconditioning.

Corticosteroid injection provides temporary relief in 60-80% of patients, with duration of benefit ranging from weeks to months. Repeat injections may be performed, though prolonged corticosteroid use risks cartilage damage and is generally limited to 2-3 injections per year. Hyaluronic acid (viscosupplementation) has been described for STT arthritis but lacks robust evidence supporting its efficacy.

Indications for Surgery

Surgical treatment is considered when conservative measures fail to provide adequate symptom control, pain significantly limits function or quality of life, patients wish to return to activities incompatible with conservative management, or there is documented radiographic progression despite conservative treatment. The duration of conservative treatment varies but typically 3-6 months of appropriate therapy is recommended before proceeding to surgery.

Distal Scaphoid Excision

Distal scaphoid excision with tendon interposition arthroplasty is the most common procedure for isolated STT arthritis (Grade I-II). The technique involves a radial-sided approach between the first and second dorsal compartments or a volar-radial approach. The distal 2-4mm of the scaphoid is excised using an osteotome or oscillating saw, removing all arthritic bone and osteophytes while preserving the scapholunate ligament attachment proximally.

Interposition arthroplasty using a rolled portion of flexor carpi radialis (FCR) tendon, capsule, or allograft is performed to prevent bone-to-bone contact between the proximal scaphoid and trapezium. The interposition material is secured with suture or anchor. Some surgeons perform simple excision without interposition with comparable results.

Postoperative immobilization in a thumb spica splint for 2 weeks is followed by progressive range of motion exercises. Full activity is typically allowed at 6-8 weeks. Outcomes are generally good with 80-85% patient satisfaction and relief of pain. Complications include persistent pain (10-15%), scaphoid instability (rare), and progressive radiocarpal arthritis (long-term concern).

STT Arthrodesis

STT fusion is preferred for younger, higher-demand patients who wish to maintain grip strength and are willing to accept some motion loss. The procedure involves exposure of the STT joint, removal of articular cartilage from all three surfaces (scaphoid, trapezium, trapezoid), positioning the bones in optimal alignment (slight scaphoid extension to prevent flexion collapse), and fixation with headless compression screws, plates, or K-wires.

Bone graft (usually iliac crest autograft or allograft) is placed in the fusion site to promote union. Immobilization in a thumb spica cast for 6-8 weeks is required, followed by protected motion until fusion is confirmed radiographically (typically 10-14 weeks). Fusion rates are 85-95% with modern techniques and rigid fixation.

Outcomes after STT fusion include excellent pain relief in 85-90% of patients, maintenance of grip strength close to pre-disease levels, and wrist motion loss of approximately 10-15 degrees in flexion-extension arc and 10 degrees in radial-ulnar deviation. Complications include nonunion (5-15%), hardware prominence or irritation, and progression to radiocarpal arthritis (long-term concern due to altered carpal kinematics).

Proximal Row Carpectomy

Proximal row carpectomy (PRC) is indicated for Grade III STT arthritis with pancarpal involvement, provided the lunate fossa of the radius and the head of the capitate have preserved articular cartilage. The procedure involves complete excision of the scaphoid, lunate, and triquetrum through a dorsal approach. The capitate articulates directly with the lunate fossa, creating a new radiocarpal articulation.

PRC provides reliable pain relief (80-85% satisfaction) and preserves functional wrist motion (typically 50-60% of normal flexion-extension arc). Grip strength recovers to 70-80% of the contralateral side. The procedure is advantageous as a salvage option because it does not burn bridges for future reconstruction (total wrist arthrodesis remains possible if PRC fails). Long-term concerns include progressive capitate-lunate fossa arthritis, though this is typically slow in onset.

Total Wrist Arthrodesis

Total wrist arthrodesis is reserved for Grade III arthritis with extensive cartilage loss that precludes PRC, failed prior motion-preserving surgery, or patients with low functional demands who prioritize pain relief and stable support over motion. The procedure fuses the radius to the second and third metacarpals in neutral to slight extension (10-15 degrees) and neutral radial-ulnar deviation.

Fixation options include dorsal plates (most common), intramedullary rods, or combinations. Bone graft promotes fusion, which is achieved in greater than 95% of cases. Pain relief is excellent and predictable. The primary disadvantage is complete loss of wrist motion, which impacts activities of daily living. However, most patients adapt well, particularly if unilateral involvement allows the opposite hand to perform two-handed tasks.

Surgical Considerations

Persistent Pain after Excision: May indicate incomplete excision, scaphoid instability, or unrecognized radiocarpal arthritis; reassess with CT and consider revision or salvage

Nonunion after STT Fusion: Occurs in 5-15%; may be asymptomatic or painful; symptomatic nonunion requires revision with bone graft and rigid fixation

Hardware Prominence: Common with dorsal plates and screws; remove hardware if symptomatic after fusion consolidation

Progressive Radiocarpal Arthritis: Long-term concern after both excision and fusion; monitor with serial radiographs; PRC or arthrodesis if develops

Superficial Radial Nerve Injury: Risk with radial approaches; protect nerve branches, avoid retractor pressure; dysesthesias usually temporary

Early complications include wound healing problems (infection, dehiscence), hematoma formation, and superficial radial nerve injury (numbness or painful neuroma over radial thumb and dorsal hand). Hardware-related complications include screw prominence, plate irritation, and hardware failure. Complex regional pain syndrome (CRPS) is rare but devastating when it occurs (less than 2% incidence).

Late complications include persistent pain despite surgery (10-15% after excision, 5-10% after fusion), nonunion after STT fusion (5-15%), scaphoid instability after excessive distal scaphoid excision, and progressive radiocarpal or midcarpal arthritis (long-term concern after both excision and fusion due to altered kinematics). Thumb CMC arthritis may become symptomatic or progress after STT surgery if not addressed concurrently.

Outcomes and Prognosis

Patient satisfaction after surgical treatment for STT arthritis is generally good, with 75-85% reporting significant improvement. Pain relief is achieved in 80-90% of patients, though complete pain resolution is uncommon. Functional outcomes include return to work in 85-90% of patients (3-4 months for excision, 4-6 months for fusion), return to recreational activities in 70-80%, and grip strength recovery to 75-90% of contralateral side.

Factors predicting better outcomes include isolated STT arthritis without pancarpal involvement (Grade I-II), absence of workers' compensation or litigation, realistic patient expectations, and good compliance with postoperative rehabilitation. Factors predicting poorer outcomes include Grade III arthritis with radiocarpal involvement, concurrent thumb CMC arthritis not addressed, smoking (affects fusion healing), and secondary gain issues.

STT fusion reliably relieves pain and preserves grip, but it fixes the scaphoid in slight extension - and the surgical and complications sections describe altered radiocarpal loading without naming the specific mechanism that produces radial-sided pain after an otherwise-united fusion.

• The mechanism. 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 impingement pain on radial deviation - a common cause of persistent pain despite a solid fusion.
• Prevention: prophylactic radial styloidectomy. Many surgeons perform a limited radial styloidectomy (about 3-4mm) at the time of STT fusion to create clearance and prevent styloid-scaphoid/trapezial abutment. Over-resection is avoided because the radioscaphocapitate ligament origin sits on the styloid, and taking too much risks ulnar translation of the carpus.
• When it presents late. 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).

The exam warning says "do not over-resect the distal scaphoid" and the Garcia-Elias evidence card records a DISI malalignment in most wrists after resection, but the body never quantifies the safe resection or explains why over-resection destabilises the carpus.

• How much. Remove only the arthritic distal pole - about 2-4mm - 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 distal support, so the scaphoid tends to extend/dorsiflex and the proximal row rotates into a DISI (dorsal intercalated segment instability) pattern (see the carpal-instability topic for 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 pattern 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.

• 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 association between STT arthritis and thumb CMC arthritis is particularly important clinically, as both conditions cause radial-sided hand pain and may require concurrent treatment. Careful examination and imaging of both joints is essential to avoid missing combined pathology and incomplete symptom resolution after treating only one joint.

Triscaphe (STT) arthritis affects the scaphotrapeziotrapezoid joint and accounts for 10-15% of degenerative wrist arthritis, presenting with radial-sided wrist pain worse with gripping and wrist extension. It commonly coexists with thumb CMC arthritis (30-40% of cases) and may be associated with scapholunate dissociation. Clinical examination reveals tenderness 1cm distal and radial to the radial styloid, with pain on resisted wrist extension. Conservative management includes activity modification and corticosteroid injection (50-60% temporary relief), while surgical options include distal scaphoid excision for isolated STT, STT fusion for high-demand patients, or proximal row carpectomy for pancarpal involvement.

During wrist motion, the scaphoid rotates about its waist, with the distal pole moving relative to the trapezium and trapezoid. With wrist extension and radial deviation, the STT joint experiences maximum compressive loading. Gripping activities that involve wrist extension substantially increase STT joint reactive forces. These biomechanical factors explain why activities such as push-ups, lifting, and forceful gripping exacerbate symptoms in STT arthritis.

Degenerative Cascade

The pathologic process in STT arthritis follows the typical osteoarthritis cascade. Initial cartilage fibrillation and surface irregularity progress to cartilage loss with exposure of subchondral bone. Attempted healing responses include subchondral sclerosis, marginal osteophyte formation, and synovial inflammation. In advanced cases, complete cartilage loss occurs with bone-on-bone articulation, cyst formation, and deformity. Loose bodies may develop from osteophyte fragmentation.

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.

This topic provides comprehensive coverage of triscaphe (STT) arthritis aligned with FRACS examination requirements, emphasizing clinical diagnosis, radiographic assessment, and evidence-based surgical treatment options tailored to disease severity and patient functional demands.