A clinical synthesis based on the EULAR 2018 recommendations (Kloppenburg), the ASHT 2023 Delphi consensus (Valdes), the Karanasios 2024 exercise meta-analysis and the consolidated epidemiological data of van der Oest 2021.

How is this condition defined, who is affected and what are the risk factors?

• Female sex : a massive predominance, explained both by hormonal factors (the fall in oestrogen around the menopause, see the dedicated chapter 3), by greater baseline ligament laxity (Spector 1996) and by a different joint morphology (Ladd 2013).⁶,⁷
• Age : a major cumulative factor, with prevalence doubling every ~11 years (van der Oest 2021). Ageing changes the composition of cartilage (loss of proteoglycans, fibrillation) and ligament elasticity.⁴
• Heredity : heritability estimated at 60% for hand osteoarthritis in twin studies (MacGregor 2000, Spector 1996). Higher than for the hip or the knee. Several genetic loci have been identified (FRZB, IL-1, COL2A1).⁸
• Ligament hyperlaxity : laxity of the anterior oblique ligament (the anterior oblique or "beak" ligament), the pillar of anterovolar stability of the TMC, is a major predisposing factor (Ladd 2013).⁷
• Repetitive manual activities : the link between intense manual demand and thumb base osteoarthritis remains debated, the available data being cross-sectional or case-control. Fontana's 2007 case-control study (61 women operated on for TMC osteoarthritis against 120 controls matched for age, PMID 17398355) finds, after adjustment, an excess risk for jobs involving repetitive thumb use and for days without sufficient breaks; no single occupation is established as a cause.
• High BMI : King 2018 (J Hand Surg Am) showed an independent association between BMI > 25 and TMC pain and osteoarthritis, possibly through systemic inflammatory mechanisms (pro-inflammatory cytokines from adipocytes, Sokolove 2013).¹⁰
• Previous trauma : a trapezium fracture, TMC dislocation or a malunited Bennett fracture can precipitate secondary osteoarthritis.

What happens in the body and how does thumb base osteoarthritis progress naturally?

Which questions should you ask to understand the patient and their history?

• Location and quality of the pain 📍: ask the patient to point to the painful area. Thumb base osteoarthritis pain is located precisely at the base of the thumb, on the anteroradial side, over the TMC joint. It is often described as a dull, deep, mechanical pain, sometimes burning.²
• Provocative activities 🔑: a discriminating question. Patients typically report reproducible pain when opening a jar, when turning a key, when wringing out a cloth, or when holding a book or phone for a long time. These movements combine forceful pinch with rotation, the maximum load on the TMC.¹,³
• Time course : onset typically progressive over months to years, with flares (increased, sometimes inflammatory pain) alternating with quieter periods. Sudden onset should suggest another diagnosis (trauma, infection).
• Functional impact : which activities of daily living have become difficult? Use a validated PROM from the first consultation: QuickDASH (11 items, 0-100) or PRWE (Patient-Rated Wrist Evaluation) to quantify objectively.⁴
• History : past trauma to the thumb or wrist? A family history of osteoarthritis (a strong genetic component, heritability ~60%)? Demanding work or hobbies? Hormonal status in women (peri- or post-menopause, hormone replacement therapy)?
• Red flags 🚩: a personal history of cancer (breast, prostate, think bone metastasis), unexplained weight loss, fever, a palpable mass, mechanical night pain not relieved by rest.

Which clinical tests should be done and which other conditions must be ruled out?

• Grind test : the best known. The examiner grasps the patient's thumb and applies axial compression to the first metacarpal while performing circular rotation movements. Positive if it reproduces the familiar pain at the base of the thumb, sometimes with crepitus.⁶
• Traction-shift test (subluxation-relocation) : described by Choa (2014). The examiner applies axial traction to the thumb then attempts a dorsal translation of M1 on the trapezium. Positive if it reproduces pain plus a sense of subluxation.⁷
• Pressure-shear test : lateral compression of the TMC joint in shear. Less studied.
• Adduction-extension test (Merritt 2015): a combination of thumb adduction and extension, sometimes more sensitive than the grind test alone.⁸

• De Quervain tenosynovitis : stenosing tendinopathy of the first dorsal compartment (APL + EPB). The pain is typically more proximal, at the radial styloid. Positive tests: Finkelstein, WHAT (Goubau 2014). Not to be confused, and coexistence is possible (see the clinical case in chapter 6).⁹
• Carpal tunnel syndrome : compression of the median nerve. Night paraesthesia in the first three digits, a positive Tinel sign at the wrist, a positive Phalen test. Coexistence with thumb base osteoarthritis is frequent in postmenopausal women (Lattanzi 2019).¹⁰
• Intersection syndrome : tendinopathy 4-8 cm proximal to the radial styloid, at the junction of the 1st and 2nd dorsal compartments. Painful palpation plus crepitus.
• Scaphotrapeziotrapezoid (STT) osteoarthritis : can coexist with thumb base osteoarthritis (pantrapezial osteoarthritis, Eaton stage IV). The pain is more distal, at the wrist.
• Scaphoid pathology : fracture (the proximal scaphoid in particular, after a neglected injury), non-union, necrosis. Exquisite tenderness in the anatomical snuffbox.
• Early rheumatoid arthritis : to consider if there is polyarthralgia + morning stiffness > 1 h + symmetrical MCP and PIP involvement + inflammatory signs (CRP, RF, anti-CCP).
• Bone metastasis : a history of cancer (breast, lung, prostate, kidney, melanoma), night bone pain, a mass, a staging work-up is essential.

Should patients with thumb base osteoarthritis be classified, and for what benefit?

What are the specific hormonal and biomechanical mechanisms?

• A fall in proteoglycan synthesis (loss of cartilage elasticity).
• Increased activity of the matrix metalloproteinases (MMP-13 in particular) → accelerated degradation of collagen II.
• Modulation of the local pro-inflammatory cytokines (IL-1β, TNF-α).

What management suits the peri- and postmenopausal woman?

• Information about the hormonal component (without inducing guilt).
• Strategies for joint economy : adapt tools (wide handles, jar openers), modify pinch and twisting movements, break up activities.
• An exercise programme targeting dynamic stability of the thumb (first dorsal interosseous, thumb abductor, opponens), to compensate for the loss of passive stability.⁷

• Carpal tunnel syndrome : frequent coexistence (Florack 1992, Lattanzi 2019). Assess with Phalen + Tinel + night symptoms; management must be joint (a suitable night orthosis + neurodynamics).⁸
• Osteoporosis : postmenopausal women are at risk. A FRAX or bone densitometry can be discussed with the general practitioner; even though osteoarthritis and osteoporosis are distinct entities (and even inversely correlated in some models), they can coexist.
• Early rheumatoid arthritis : to consider if there is polyarthralgia + morning stiffness > 1h + symmetrical MCP and PIP involvement + inflammatory signs (CRP, RF, anti-CCP).
• Fibromyalgia : central sensitisation is frequent in women between 40 and 60 and can amplify the perception of pain.

Where do you start? What is the hierarchy of interventions?

• Therapeutic education and information about the condition.
• Targeted exercises for mobility and strength.
• Orthoses (thumb spica in particular) for the TMC.
• Joint protection and joint economy strategies.
• Topical agents (NSAIDs, capsaicin) before systemic routes.

• An orthosis worn on demand during painful activities (against permanent wear, a recent change).
• Dynamic stability programme (a dynamic stabilisation programme for the thumb).
• Patient education + joint protection techniques.
• Adaptive equipment (wide handles, jar openers, and so on).
• Functional intervention targeted at the activities that matter to the patient.

What is the place of exercise, and is there a superior approach?

• Exercise-based interventions significantly reduce pain against control (weighted MD -21.91 out of 100) in the short term.
• A reduction in functional disability (MD -8.10 out of 100).
• Methodological quality mostly moderate to high, but substantial heterogeneity between protocols.
• Certainty of evidence ranging from very low to moderate depending on the outcome (an important caveat, GRADE).

• First dorsal interosseous (1st DIO): the major dynamic stabiliser of the TMC. Isometric then dynamic strengthening (bands, putty balls).
• Thumb abductor (APL + APB): palmar and radial abduction exercises.
• Opponens pollicis : opposition exercises against progressive resistance.
• Active mobilisation of the TMC through all ranges (pain-free).
• A dynamic stability programme (O'Brien & Giveans) combining proprioception, motor control and functional exercises.⁵

Manual therapies, technologies, injections: what is their real effectiveness?

• Manual therapy added to an exercise programme improves pain and function compared with exercise alone (a moderate effect).
• As an isolated intervention the effect is less clear.
• Considerable heterogeneity in the techniques studied, with no "best technique" established.

• A moderate to large effect on pain and a small to moderate one on function in the medium term (3-12 months).
• No clear effect in the short term (< 3 months); the orthosis does not act immediately.
• Quality of evidence low to moderate.
• No clear superiority of a rigid over a soft orthosis, or of custom over prefabricated (the Arazpour 2020 meta-analysis confirms the absence of a significant difference).

• LLLT (low-level laser therapy) : limited evidence, with older meta-analyses (Brosseau 2000) showing major heterogeneity. No strong recommendation.
• Therapeutic ultrasound : a possible short-term effect but not durable, low quality of evidence.
• Extracorporeal shockwave therapy (ESWT) : emerging data, but low methodological quality and strong heterogeneity. A recent case report (PMC12832892) describes an isolated case of benefit with focused ESWT, preliminary data only.
• TENS : a non-specific option for pain modulation, low level of evidence but high safety.

Beyond the physical: how do you educate the patient and address psychological factors?

• Mechanism : "your pain comes from instability and shear, not from irreversible 'wear'; it can be actively compensated for."
• A realistic natural history : thumb base osteoarthritis is chronic but often stable or improving symptomatically with well-conducted treatment (Becker 2015); it is not an inevitable decline.
• Joint economy : concrete techniques for reducing pinch and twisting loads (adapted tools, modified movements, breaking tasks up).
• Orthosis : use on demand, not permanently. For activities at risk (prolonged gardening, a long car journey, intense manual tasks).
• Exercises : regularity > intensity. A short home programme (15-20 min) repeated 3-5 times a week.

• Pain catastrophising (PCS, Pain Catastrophizing Scale): "my hand will end up paralysed", "nothing will work". It increases the perception of pain and hinders engagement in treatment.
• Kinesiophobia (TSK, Tampa Scale for Kinesiophobia): fear of making things worse by moving. It limits adherence to exercise.
• Low self-efficacy : a sense of being unable to manage the condition. A direct target of therapeutic education and motivational interviewing.
• Associated depression or anxiety : to screen for (PHQ-9, GAD-7), with collaboration with the general practitioner if significant.

How is the patient made an active participant in their own recovery through self-management?

• An initial 60-minute session (or 2 × 30 min) on the condition, its mechanism, its natural history and the levers for action.
• Summary sheets (on paper or digital) covering the exercises, the joint economy techniques and the warning signs.
• A telephone follow-up or a short consultation at 4-6 weeks to adjust and reinforce.
• Ideally a group module (4-6 patients) to encourage peer learning and normalise the experience.

• Widen tool handles (ergonomic cutlery, foam handles, wide-ring scissors, mechanical or electric jar openers).
• Spread the loads over larger joints (carry a bag on the shoulder rather than in the hand, use two hands).
• Avoid prolonged forceful pinch with twisting (keys, manual screwdrivers; prefer power tools).
• Break up activities that are long and repetitive (gardening, sewing, housework) into sessions of 20-30 min with breaks.
• Adapt the smartphone : two-handed use, a tablet stand, voice dictation.

• It improves adherence (the orthosis is experienced as a tool, not a constraint).
• It avoids functional dependence and deconditioning of the intrinsic muscles.
• It allows periodisation (a stronger orthosis in phases of intense activity, a lighter one in routine).

• A short programme (15-20 minutes maximum), 3-5 times a week.
• Target: 1st DIO (first dorsal interosseous), thumb abductor, opponens, TMC dynamic stability.
• Gradual progression: isometric → dynamic → functional.
• Use simple equipment (foam ball, band, putty, marbles), available at home.
• A smartphone app or a paper diary for follow-up.

When and how should a safe return to manual and sporting activities be planned?

1. Phase 1, controlling pain and inflammation : VAS pain < 4/10 at rest and during activities of daily living. Able to do the basic exercises without significant post-session pain (≤ 24 h).
2. Phase 2, recovering the functional prerequisites : full, pain-free ranges. Strength in lateral pinch (key pinch) on the Jamar dynamometer > 80% of the healthy side. Tip pinch strength > 80% of the healthy side.
3. Phase 3, gradual reintroduction of the specific movements : start with lighter versions of the target movement. For a gardener: light pruning before brush-cutting; for a golfer: putting then short approaches before the full swing; for a climber: easy routes with large holds before pinch holds. An orthosis on demand is possible during this phase.
4. Phase 4, increasing volume and intensity : a pragmatic rule of at most 10-20% increase a week, with careful monitoring of the 24 h after the activity. Transient pain ≤ 2/10 is tolerated, provided it returns to baseline within 24 h.

• Pain persisting > 48h after an activity.
• Measurable loss of strength on the dynamometer.
• A new or worsening visible or palpable subluxation.
• A sense of instability or giving way during movements usually under control.

• Rapid worsening over a few weeks despite well-conducted rehabilitation.
• New inflammatory signs (redness, heat, swelling).
• New red flags (see chapter 2: cancer, fever, night pain).
• Failure after 3-6 months of well-conducted conservative management in a patient with high functional demand → a surgical discussion becomes possible.

• Setting SMART goals (Specific, Measurable, Achievable, Realistic, Time-bound) with the patient.
• Motivational interviewing (Miller & Rollnick): explore ambivalence, reinforce intrinsic motivation.
• Use of technology : smartphone apps for tracking exercises, notifications, gamification.
• Follow-up at decreasing intervals: weekly at first, then twice-monthly, then monthly, then "on demand" plus an annual check-up.
• Including a relative in the process (partner, adult child), social support being a major predictor of adherence.

Analysis of a "classic" case: from assessment to conservative resolution

• An initial standardised assessment including: joint ranges (TMC, MCP, IP), grip and pinch strength (Jamar, B&L), the shoulder sign, VAS pain, function (a specific questionnaire).
• Plus a rehabilitation programme that is structured:
  • Strengthening the dynamic stabilisers (first dorsal interosseous, thumb abductor, opponens).
  • Proprioception and motor control exercises for the thumb.
  • Pain-free active mobilisation.
  • Education about joint protection and joint economy.
  • An orthosis according to clinical severity.

The diagnostic challenge: when thumb base osteoarthritis coexists with another condition

• Mechanical pain at the base of the thumb on pinch (typical of thumb base osteoarthritis).
• Night paraesthesia in the first three digits waking the patient, relieved by shaking the hand (typical of CTS).
• Recent clumsiness (dropping objects).

• For the thumb base osteoarthritis: an orthosis on demand + stabiliser exercises + education.
• For the CTS: a night wrist orthosis (neutral wrist) + median neurodynamic techniques + education about movements at risk.
• If that is not enough, a carpal injection (by a doctor); if it fails or if there are significant motor signs, carpal tunnel release surgery.

Study of a complex case: conservative failure and innovative options

• Intra-operative identification of the articular branches to the TMC (a branch of the superficial radial nerve, the lateral cutaneous branch of the forearm).
• A diagnostic test by nerve block with lidocaine: immediate relief of the pinch pain → confirmation that the pain is articular.
• Selective division under local anaesthesia.

When and to which other health professionals should the patient be referred?

• Pain catastrophising (PCS), "my hand will end up paralysed".
• Kinesiophobia (TSK), fear of making things worse by moving.
• Low self-efficacy, a sense of being unable to manage.
• Significant depression or anxiety (PHQ-9, GAD-7).

• General practitioner : coordination, blood tests (CRP, RF, anti-CCP, vitamin D, calcium), imaging requests, management of comorbidities.
• Rheumatologist : if an inflammatory condition is suspected, in generalised digital osteoarthritis, on conservative failure, to discuss an intra-articular injection.
• Hand surgeon : if well-conducted conservative treatment fails (3-6 months) in a patient with high demand, to discuss trapeziectomy ± LRTI or an alternative (Cochrane Wajon 2017).
• Psychologist or pain physician : significant yellow flags, severe resistant chronic pain.
• Occupational therapist : making a custom orthosis, adapting the home or workstation.

How do you measure outcomes and overcome the barriers to implementation?

1. A lack of time in often short consultations, linked to funding models that reward volume over quality.
2. A lack of skills in critically appraising papers, searching for evidence and integrating it into clinical reasoning.
3. Lack of organisational support : limited access to databases, no clinical mentoring, professional isolation.⁵
4. Tension between standardisation and personalisation : evidence-based practice must adapt to the unique patient without drifting into "recipe physiotherapy".

• Individual: continuing education (DPC), subscribing to clinical syntheses (Physio Learning, BMJ EBM, JOSPT Perspectives), peer groups.
• Organisational: building PROMs into the patient software (ideally self-completed by the patient on a tablet in the waiting room), time set aside for training, structured clinical mentoring, "Friday journal clubs".
• Cultural: creating a practice culture that values intellectual curiosity, case discussion and epistemic humility ("I do not know, let us check").