Thumb-base pain has several potential sources packed into a small anatomical region. The first CMC joint, STT joint and flexor carpi radialis tendon can all produce radial or volar-radial symptoms, but their loading patterns and examination findings differ. The STT joint sits just closer to the wrist, the FCR tendon runs along the palm side beside the trapezium, and the first dorsal compartment, the thumb MCP joint, the superficial radial nerve and the scaphoid are all within a few centimeters.
Each of these structures has a slightly different location, a different provoking load and a different treatment path. Sorting them out is the first step in treating thumb-base pain well.
STT arthritis in a general population
Radiographic STT arthritis
5.3%
of 676 wrists in randomly sampled residents aged 50 to 89
Associated factors
Thumb CMC
radiographic CMC arthritis, female sex and increasing age
PMID 37462591
These are radiographic findings in one Japanese town. They describe joint structure, not which joint is causing a patient’s pain.
The anatomy in a few centimeters
- Thumb CMC joint: between the first metacarpal and the trapezium, at the base of the thumb just beyond the wrist crease. A saddle joint built for mobility.
- STT joint: between the scaphoid, trapezium and trapezoid, slightly closer to the wrist and deeper. STT stands for scaphotrapeziotrapezoid.
- FCR tendon: the flexor carpi radialis tendon runs along the palm side of the wrist on the thumb side, passing through a fibro-osseous tunnel next to the trapezium before attaching at the base of the second metacarpal.
- First dorsal compartment: the APL and EPB tendons over the radial styloid, involved in De Quervain tenosynovitis.
- Thumb MCP joint: the knuckle in the middle of the thumb.
- Superficial radial nerve: a sensory nerve running over the back of the thumb side of the wrist.
- Scaphoid: a carpal bone at the base of the anatomical snuffbox, commonly injured in falls.
The trapezium is the hub. It forms part of both the CMC and STT joints, and the FCR tendon runs right alongside it. That is why pain in this area so often gets labeled "thumb arthritis" without a closer look.
Thumb CMC joint pain
Thumb CMC arthritis typically causes pain at the base of the thumb with pinch, grip and twisting: keys, jars, buttons, wringing and tool use. The examination may find tenderness directly over the joint, pain with CMC compression and rotation, reduced pinch strength and, in more advanced disease, a prominent thumb base.
Joint compression can support CMC involvement when it reproduces the patient's familiar pain, but no single provocative maneuver should be treated as a stand-alone diagnosis.
STT joint pain
STT arthritis can produce pain close to the thumb CMC joint, which is why basal-thumb pain should not automatically be assigned to the first CMC joint. A review described the STT joint as a common location of wrist osteoarthritis that may occur in isolation or together with thumb CMC arthritis or other wrist arthritis patterns (Alder, 2023).
In a cross-sectional study of 676 wrists from randomly sampled residents aged 50 to 89, radiographic STT arthritis was present in 5.3%, and it was associated with radiographic thumb CMC arthritis, female sex and increasing age (Kitamura, 2025).
Clues that point toward the STT joint include:
- Tenderness slightly proximal to the CMC joint, toward the scaphoid, often on the palm side
- Pain with wrist motion and loading, not just thumb pinch
- Radiographic changes between the scaphoid, trapezium and trapezoid, which may need dedicated views to see clearly
The distinction matters because the two joints can coexist, and when surgery is considered, whether arthritis involves the CMC joint alone or both joints affects which procedure is chosen (Alder, 2023).
FCR tendon pain
FCR tendon pain is usually more volar and load-related than classic CMC joint pain and may be reproduced by resisted wrist-flexion loading. An imaging review described the FCR tendon as frequently implicated in radial-sided wrist pain, with disorders including tenosynovitis, tendinopathy, partial or complete tears and compression within the trapezial tunnel (Bouredoucen, 2026).
Clues that point toward the FCR tendon include:
- Pain on the palm side of the wrist near the thumb, along the tendon line
- Pain with resisted wrist flexion and radial deviation
- Tenderness over the tendon as it passes the trapezium
- Sometimes local swelling along the tendon sheath
Arthritic spurs from the STT joint can occasionally irritate the nearby FCR tendon. A 2026 case report described FCR tendon rupture related to STT arthritis with large spurs, which the authors noted is rarely reported (Distor, 2026). It is a reminder that these structures interact, not a common outcome.
Comparing the three
| Feature | Thumb CMC joint | STT joint | FCR tendon |
|---|---|---|---|
| Structure | First metacarpal and trapezium | Scaphoid, trapezium and trapezoid | Tendon of a wrist flexor muscle |
| Location | Base of the thumb | Slightly closer to the wrist, deeper | Palm side of the wrist, thumb side |
| Main provocation | Pinch, grip, CMC compression | Wrist loading and motion | Resisted wrist flexion and radial deviation |
| Problem type | Joint arthritis | Joint arthritis | Tendinopathy or tenosynovitis |
| Helpful imaging | Radiographs | Radiographs, sometimes dedicated views or CT | Ultrasound or MRI |
These patterns overlap, and more than one structure can be involved.
Other nearby causes
- De Quervain tenosynovitis: tendon pain over the radial styloid, on the back of the thumb side of the wrist, provoked by thumb and wrist tendon loading. See thumb CMC arthritis vs De Quervain's.
- Thumb MCP joint: pain or instability at the middle knuckle of the thumb, sometimes after a sprain, is anatomically separate from the CMC joint and needs its own assessment.
- Superficial radial nerve: burning, tingling, numbness or skin sensitivity over the back of the thumb points toward nerve irritation. Sensory symptoms are not arthritis.
- Scaphoid or other carpal injury: focal radial wrist pain after a fall onto an outstretched hand, especially with snuffbox tenderness, needs imaging. A suspected fracture is not routed into shockwave or routine arthritis care.
- Ganglion: a lump on the palm side of the wrist near the FCR or on the back of the wrist can cause local pain.
How the examination separates them
The exam works through location and load:
- Palpation of the CMC joint, STT region, FCR tendon path, radial styloid, MCP joint and snuffbox
- Key pinch, tip pinch and grip, noting which reproduces the familiar pain
- CMC compression and rotation
- Resisted wrist flexion and radial deviation for the FCR
- Resisted thumb extension and abduction for the first dorsal compartment
- Wrist motion and loading for the STT joint
- MCP stability testing
- Sensation and nerve provocation for the superficial radial nerve
The goal is to find the structure that reproduces the patient's familiar pain, then confirm with imaging when it would change the plan.
Daily tasks as clues
The tasks that hurt can narrow things down. Turning a key, opening a jar or pinching a zipper loads the CMC joint most. Pushing up from a chair with the wrist extended or carrying weight through the wrist loads the STT region. Repetitive wrist flexion against resistance, such as lifting with the palm up, gardening with a trowel or some racquet strokes, loads the FCR tendon. Tasks are never diagnostic on their own, but they guide where the exam looks first.
Imaging choices
Radiographs are the usual first test for CMC and STT arthritis, though the STT joint can be harder to see on standard views. Ultrasound is useful for tendon problems such as FCR tenosynovitis and De Quervain's, and for ganglia. MRI is reserved for unclear cases, suspected occult fracture, or deeper structural questions.
Imaging severity and symptom severity are not interchangeable. Radiographic arthritis in one joint does not prove that joint is producing the pain, especially when two neighboring joints both show changes.
Why the distinction matters for treatment
Symptomatic thumb CMC arthritis has the most developed conservative evidence base of these conditions, with hand exercise, multimodal care and splinting supported by network meta-analyses, and small direct randomized evidence for focused shockwave therapy. That evidence is reviewed in shockwave therapy for thumb CMC osteoarthritis.
Those results should not be transferred automatically to STT arthritis or FCR tendinopathy. STT arthritis is usually managed initially with activity modification, bracing, anti-inflammatory medication, therapy and injection, with surgery for refractory cases (Alder, 2023). FCR tendinopathy is managed as a tendon problem, with load modification and progressive loading, and injection or surgery considered for persistent cases.
A splint chosen for CMC arthritis may not suit a wrist-level STT problem, and exercise aimed at pinch capacity is not the same as a wrist-flexor loading program.
When to seek prompt assessment
Pain after a fall with bone tenderness, a sudden thumb injury with instability, marked swelling or deformity, a hot, red joint or progressive numbness should be assessed promptly.
How Novo approaches thumb-base pain
We localize the pain to the CMC joint, STT region, FCR tendon or nearby structures, test the loads that reproduce it, screen for nerve and bone causes, and use radiographs or ultrasound when they change the plan. See how we approach thumb CMC arthritis and thumb-base pain.
References
- Alder KD, Feroe AG, Karim KE. Management of scaphotrapeziotrapezoid osteoarthritis: a critical analysis review. JBJS Reviews. 2023;11(10):e23.00093. PMID 38096476. (link)
- Kitamura Y, Kato H, Hayashi M, Ikegami S, Isobe F, Takahashi J. Prevalence and associated factors for primary osteoarthritis of the scaphotrapeziotrapezoid, radiocarpal, and distal radioulnar joints in the Japanese general elderly population. Journal of Hand Surgery (American Volume). 2025;50(1):103.e1-103.e10. PMID 37462591. (link)
- Bouredoucen H. Anatomy, variants, and multimodality imaging of flexor carpi radialis tendon pathology and post-therapeutic evaluation. European Journal of Radiology. 2026;204:113175. PMID 42696839. (link)
- Distor MG, Muramatsu K, Genuino KA, Morita Y. Flexor carpi radialis tendon rupture from scapho-trapezio-trapezoid osteoarthritis: a case report and review of literature. Journal of Hand Surgery (Asian-Pacific Volume). 2026;31(4):445-449. PMID 42290073. (link)
- Shapiro LM, McQuillan TJ, Kerkhof FD, Ladd A. Radiographic progression of thumb CMC osteoarthritis: a systematic review. Journal of Hand Surgery Global Online. 2020;2(6):343-348. PMID 35415524. (link)
