Types of arthritis
The word "arthritis" comes from the Greek arthron (joint) and itis (inflammation) — but not all forms of arthritis involve primary inflammation. The major categories include degenerative, inflammatory/autoimmune, crystal-induced, infectious, and reactive forms.
| Type | Mechanism | Key joints | Age of onset | Prevalence |
|---|---|---|---|---|
| Osteoarthritis (OA) | Cartilage degradation; subchondral bone remodelling; low-grade inflammation | Knees, hips, hands (DIP/PIP), spine, base of thumb | Usually 50+; increases with age | 32.5M Americans; most common form |
| Rheumatoid Arthritis (RA) | Autoimmune synovitis; pannus formation destroys cartilage and bone | Hands (MCP/PIP), wrists, feet — symmetrical; any joint | Peak 30–60; women 3× more than men | 1.3M Americans; ~1% global prevalence |
| Gout | Monosodium urate crystal deposition from hyperuricaemia | Big toe (1st MTP), ankle, knee, wrist — often monoarticular | Men 40s–50s; women post-menopause | 9.2M Americans; most common inflammatory arthritis in men |
| Psoriatic Arthritis (PsA) | Autoimmune; linked to psoriasis; enthesitis and dactylitis | Asymmetric; DIP joints; spine; entheses | 30–50; follows psoriasis by ~10 years | ~30% of psoriasis patients; ~1M Americans |
| Ankylosing Spondylitis (AS) | Autoimmune; sacroiliitis and spinal fusion; HLA-B27 linked | Sacroiliac joints, spine; can affect hips and shoulders | Typically teens to 30s; men 2–3× more | ~0.5% of adults; often underdiagnosed in women |
| Lupus Arthritis | Systemic autoimmune (SLE); immune complex deposition | Small joints of hands, wrists; typically non-erosive | 15–45; women 9× more than men | ~90% of SLE patients have joint involvement |
| Juvenile Idiopathic Arthritis (JIA) | Autoimmune; heterogeneous group of childhood arthritis | Variable by subtype; can affect any joint | Under 16 years | ~300,000 children in the U.S. |
Osteoarthritis in depth
Osteoarthritis is the most common form of arthritis and the most common joint disease overall. For decades it was viewed as simple "wear and tear" — an inevitable consequence of ageing. Modern understanding is more nuanced: OA is a complex metabolic and inflammatory disease involving the entire joint — cartilage, subchondral bone, synovium, ligaments, and periarticular muscles — all driven by a combination of mechanical, inflammatory, and metabolic factors.
How cartilage breaks down
Healthy articular cartilage is a remarkable material — avascular, aneural, and capable of distributing load across joint surfaces with minimal friction. In OA, the balance between cartilage matrix synthesis and degradation shifts in favour of breakdown. Pro-inflammatory cytokines (IL-1β, TNF-α) stimulate chondrocytes to produce matrix metalloproteinases (MMPs) that degrade collagen and proteoglycans. The result is progressive cartilage thinning, surface fibrillation, and eventually full-thickness cartilage loss — exposing bone-on-bone contact.
Risk factors
Non-modifiable
- Age — strongest risk factor
- Female sex (especially post-menopause)
- Genetics — heritability ~60% for hand OA
- Prior joint injury (ACL tear, meniscus)
- Joint malalignment (varus/valgus knee)
- Congenital joint dysplasia
Modifiable
- Obesity — every 1 BMI unit increases knee OA risk ~9%
- Occupational loading (kneeling, squatting)
- Muscle weakness (quadriceps in knee OA)
- Physical inactivity
- Poor proprioception and balance
- Metabolic syndrome (systemic inflammation)
Rheumatoid arthritis in depth
Rheumatoid arthritis is a chronic systemic autoimmune disease that primarily targets the synovial lining of joints. Left untreated, it causes progressive joint destruction, deformity, and significant disability. The disease is driven by a self-perpetuating cycle of immune activation: autoreactive T cells activate B cells to produce autoantibodies (RF, anti-CCP), which form immune complexes that deposit in synovium, triggering macrophage activation and cytokine release (TNF-α, IL-6, IL-1), leading to synovial proliferation (pannus) that literally erodes cartilage and bone.
The treat-to-target revolution
The most important advance in RA management over the past two decades has been the adoption of a treat-to-target (T2T) strategy — setting a clear treatment goal (clinical remission or low disease activity) and adjusting therapy every 3 months until that target is reached. Multiple landmark trials (BeSt, TICORA, CAMERA) demonstrated that T2T significantly reduces joint damage, disability, and cardiovascular risk compared to conventional symptom-driven management. The target is typically DAS28 remission (<2.6) or CDAI remission (<2.8).
Distinguishing features of RA
- Morning stiffness lasting >1 hour — pathognomonic; reflects overnight joint inflammation
- Symmetrical small joint involvement — MCPs, PIPs, wrists; not DIPs (unlike OA)
- Systemic features — fatigue, low-grade fever, weight loss, anaemia of chronic disease
- Extra-articular manifestations — rheumatoid nodules, interstitial lung disease, vasculitis, scleritis, pericarditis
- Autoantibodies — rheumatoid factor (RF) positive in ~70%; anti-CCP antibodies in ~80% (more specific); seronegative RA exists
- Elevated inflammatory markers — CRP, ESR elevated in active disease
Gout in depth
Gout is the most common inflammatory arthritis in men and is caused by the deposition of monosodium urate (MSU) crystals in joints and soft tissues when serum uric acid levels chronically exceed the saturation point (~6.8 mg/dL). When crystals form in a joint, the innate immune system mounts an intense inflammatory response — neutrophils engulf crystals, releasing lysosomal enzymes and activating the NLRP3 inflammasome, producing massive IL-1β release. The result is one of the most acutely painful conditions in medicine.
| Stage | Description | Management |
|---|---|---|
| Asymptomatic hyperuricaemia | Elevated uric acid (>6.8 mg/dL) but no gout symptoms | Lifestyle modification; treat if very high (>9) or with tophi/renal disease |
| Acute gout attack | Sudden severe joint pain, redness, warmth, swelling — peaks 12–24 hours; self-resolves in 7–14 days | Colchicine (first-line); NSAIDs; corticosteroids (oral or intra-articular) |
| Intercritical gout | Symptom-free intervals between attacks; crystal deposits continue to accumulate | Start urate-lowering therapy (ULT) after second attack or with complications |
| Chronic tophaceous gout | Persistent joint inflammation; visible tophi (urate deposits); joint damage and deformity | Aggressive ULT to target uric acid <5 mg/dL; pegloticase for refractory cases |
Gout triggers to know
- Red meat, organ meats (liver, kidney), game meats — high purine content
- Shellfish (prawns, lobster, scallops) and oily fish (anchovies, sardines, herring)
- Alcohol — especially beer (yeast-rich) and spirits; wine in large amounts
- High-fructose corn syrup (sodas, fruit juices) — fructose metabolism generates uric acid
- Dehydration — concentrates uric acid; drink 2–3 litres of water daily
- Thiazide diuretics, low-dose aspirin, ciclosporin — raise uric acid
- Sudden illness, surgery, or starting ULT — mobilises urate crystals
Symptoms and diagnosis
OA vs RA: key distinguishing features
| Feature | Osteoarthritis | Rheumatoid Arthritis |
|---|---|---|
| Morning stiffness | <30 minutes — "gels" briefly | >1 hour — hallmark feature |
| Pain pattern | Worsens with activity, improves with rest | Worse after rest, improves with movement |
| Joint distribution | Asymmetric; weight-bearing joints; DIP, base of thumb | Symmetric; MCP, PIP, wrists, feet; never DIP |
| Swelling type | Hard, bony (Heberden's/Bouchard's nodes) | Soft, boggy, warm synovitis |
| Systemic features | Absent | Fatigue, fever, weight loss, anaemia |
| Blood tests | Normal CRP/ESR; RF and anti-CCP negative | Elevated CRP/ESR; RF and anti-CCP often positive |
| X-ray findings | Joint space narrowing, osteophytes, subchondral sclerosis | Periarticular osteoporosis, erosions, joint space narrowing |
Diagnostic investigations
| Test | What it detects | Used for |
|---|---|---|
| CRP and ESR | Systemic inflammation markers | Distinguishing inflammatory from non-inflammatory arthritis; monitoring disease activity |
| Rheumatoid Factor (RF) | Autoantibody against IgG Fc portion | RA screening (70% sensitivity; not specific — also positive in other conditions) |
| Anti-CCP antibodies | Antibodies to citrullinated peptides | RA (95% specific); positive years before clinical disease; predicts erosive course |
| Serum uric acid | Urate level | Gout assessment and ULT monitoring (target <6 mg/dL; <5 in tophaceous gout) |
| Joint aspiration (arthrocentesis) | Synovial fluid analysis; crystal identification | Gold standard for gout (urate crystals under polarised light); exclude septic arthritis |
| ANA panel | Antinuclear antibodies; anti-dsDNA; complement | Lupus and other connective tissue diseases |
| HLA-B27 | Genetic marker | Ankylosing spondylitis and other spondyloarthropathies |
| X-rays | Bone and joint structural changes | OA (osteophytes, joint space narrowing); RA (erosions); AS (sacroiliitis, bamboo spine) |
| MRI | Soft tissue, cartilage, bone marrow | Early erosions in RA; sacroiliitis in AS; cartilage loss in OA |
| Musculoskeletal ultrasound | Synovitis, tenosynovitis, enthesitis, power Doppler | Detect subclinical RA synovitis; guide joint injections |
Treatment options
OA management is multimodal — no single treatment works alone. The pyramid moves from conservative to interventional.
| Intervention | Evidence | Notes |
|---|---|---|
| Exercise (aerobic + resistance) | Strong — NICE first-line | As effective as NSAIDs for pain; improves function and quality of life; all OA types |
| Weight loss | Strong for knee/hip OA | Every 1 kg lost reduces knee load by 4 kg; 10% weight loss reduces pain ~50% |
| Topical NSAIDs (diclofenac gel) | Strong for hand/knee OA | Effective with minimal systemic side effects; first-line for localised OA |
| Oral NSAIDs (ibuprofen, naproxen, celecoxib) | Strong | Effective but GI/cardiovascular/renal risks limit long-term use; use lowest effective dose |
| Paracetamol/Acetaminophen | Modest — guidelines now downgraded | Minimal benefit beyond placebo in most OA trials; hepatotoxicity limits dose |
| Duloxetine (Cymbalta) | Moderate-strong | SNRI with central pain-modulating effect; useful for central sensitisation component |
| Intra-articular corticosteroids | Moderate — short-term | Rapid pain relief lasting 4–8 weeks; do not repeat >3–4× per year (cartilage effects) |
| Intra-articular hyaluronic acid | Controversial — modest benefit in some | Some guidelines support for knee OA; works best in mild-moderate disease |
| Opioids | Limited; last resort | Poor benefit-risk in chronic OA; tramadol specifically associated with increased falls/fractures in older adults |
RA treatment follows a step-up strategy starting with conventional DMARDs, adding or switching to biologics or targeted synthetic DMARDs (tsDMARDs) if targets are not met within 3–6 months.
| Drug | Class | MOA | Key considerations |
|---|---|---|---|
| Methotrexate (MTX) | csDMARD — anchor drug | Anti-folate; anti-inflammatory; immunomodulatory | First-line for all RA; weekly dosing; folic acid required; monitor LFTs/FBC; teratogenic |
| Hydroxychloroquine (HCQ) | csDMARD | Lysosomal inhibitor; reduces cytokine production | Mild RA; often combined with MTX; annual eye monitoring for retinopathy |
| Sulfasalazine (SSZ) | csDMARD | Anti-inflammatory; immunomodulatory | Moderate RA; part of "triple therapy" (MTX+HCQ+SSZ) |
| Leflunomide | csDMARD | Pyrimidine synthesis inhibitor | Alternative to MTX; similar efficacy; long half-life (washout with cholestyramine) |
| TNF inhibitors | bDMARD | Block TNF-α (key pro-inflammatory cytokine) | Adalimumab, etanercept, infliximab, certolizumab, golimumab; most prescribed biologics; risk of reactivating latent TB — screen before starting |
| Abatacept (Orencia) | bDMARD | T-cell co-stimulation blockade (CTLA4-Ig) | Good for seronegative RA; lower infection risk than TNFi; IV or SC |
| Rituximab (Rituxan) | bDMARD | Anti-CD20 (B-cell depletion) | Excellent for seropositive RA; 6-monthly infusions; preferred if lymphoma history; monitor for PML |
| Tocilizumab (Actemra) | bDMARD | IL-6 receptor blockade | Can normalise CRP independently of disease activity (use caution interpreting markers); effective for systemic features; masks fever — important in infection |
| JAK inhibitors | tsDMARD | Block JAK-STAT signalling pathway; oral pills | Tofacitinib (Xeljanz), baricitinib (Olumiant), upadacitinib (Rinvoq); oral convenience; FDA/EMA warnings re: cardiovascular risk, VTE, malignancy in older patients — use with caution |
| Drug | Use | Mechanism | Key notes |
|---|---|---|---|
| Colchicine | Acute attack (first-line); prophylaxis | Inhibits neutrophil migration; blocks NLRP3 inflammasome | Most effective if started within 24 hours; low-dose preferred (1.2 mg then 0.6 mg); GI side effects; interaction with statins and ciclosporin |
| NSAIDs (indomethacin, naproxen) | Acute attack | Inhibit COX-mediated prostaglandin synthesis | Effective; avoid in CKD, peptic ulcer, heart failure; avoid aspirin (raises uric acid at low doses) |
| Corticosteroids (prednisone, IA injection) | Acute attack when colchicine/NSAIDs contraindicated | Broad anti-inflammatory | Oral or intra-articular; useful in CKD, elderly; rebound flare possible |
| Anakinra / Canakinumab | Refractory acute attacks | IL-1β blockade | Canakinumab licensed for gout in Europe; expensive; reserved for frequent attackers intolerant of standard therapy |
| Allopurinol | Long-term urate-lowering therapy (first-line) | Xanthine oxidase inhibitor — reduces uric acid production | Start at 100 mg/day; titrate to target uric acid <6 mg/dL; HLA-B*5801 screening in Asian patients (severe hypersensitivity risk) |
| Febuxostat (Uloric) | ULT — alternative to allopurinol | Selective xanthine oxidase inhibitor | More potent than allopurinol; FDA warning re: cardiovascular mortality — use if allopurinol intolerant; not in history of CVD without careful consideration |
| Pegloticase (Krystexxa) | Refractory tophaceous gout | Recombinant uricase — converts urate to allantoin | Dramatic uric acid reduction; given IV every 2 weeks; risk of infusion reactions and anti-drug antibodies; reserved for severe cases |
Key principle: Always cover ULT initiation with prophylactic colchicine (0.5–0.6 mg daily) for 3–6 months — starting urate-lowering therapy mobilises crystals and can trigger acute attacks if unprotected. The uric acid target is <6 mg/dL for most patients and <5 mg/dL for those with tophi.
Exercise and lifestyle
Exercise is the single most evidence-based non-pharmacological treatment for arthritis — yet it remains the most underutilised. The fear that exercise will "wear out" joints is one of the most damaging myths in arthritis management. In reality, appropriate exercise reduces pain, improves function, delays disability, and improves mental health and cardiovascular risk — without accelerating joint damage.
Evidence-based exercise approaches
- Aerobic exercise: 150 minutes per week of moderate-intensity low-impact activity (swimming, cycling, water aerobics, walking). Swimming and hydrotherapy are particularly well-tolerated in severe disease.
- Resistance training: 2–3 sessions per week. Strengthening quadriceps reduces knee OA pain by reducing joint load. Grip strength exercises help hand OA and RA. Supervised programmes outperform self-directed exercise.
- Tai Chi: Strong evidence for knee OA — comparable to physical therapy for pain and function. Improves balance and reduces fall risk (important with neuropathy from medications).
- Yoga: Moderate evidence for hand OA and RA — improves flexibility, pain, and mental health.
- During flares: Gentle range-of-motion exercises are appropriate; avoid high-impact or resistance training of inflamed joints during acute flares.
Dietary approaches
| Approach | Evidence for arthritis | Practical guidance |
|---|---|---|
| Mediterranean diet | Best evidence for inflammatory arthritis (RA, PsA); modest benefit for OA via weight | Olive oil, fish (omega-3), vegetables, legumes, whole grains; limit red meat and processed foods |
| Omega-3 fatty acids | Moderate for RA — reduces joint swelling and morning stiffness; may reduce NSAID need | 2–3 portions oily fish/week; or fish oil supplement 2–3g EPA+DHA daily |
| Weight loss (all diets) | Strong for OA; beneficial for gout, metabolic arthritis | 5–10% body weight reduction produces meaningful pain reduction in knee OA |
| Low-purine diet (gout) | Moderate — reduces uric acid ~1 mg/dL typically | Avoid organ meats, shellfish, high-fructose drinks, alcohol; increase dairy, cherries, coffee |
| Gluten-free diet | Insufficient evidence for arthritis without coeliac disease | Not routinely recommended; coeliac disease does increase RA risk — screen if suspected |
When surgery is needed
Surgery is considered when conservative measures have been exhausted and quality of life remains severely impaired. Modern orthopaedic surgery for arthritis produces excellent outcomes in appropriately selected patients.
- Total knee replacement (TKR): One of the most successful elective surgical procedures — 90% of patients report significant pain relief and functional improvement. Implants last 15–20+ years in most patients. Annual volume: ~800,000 in the U.S.
- Total hip replacement (THR): Similarly excellent outcomes for end-stage hip OA or RA. Minimally invasive anterior approach allows faster recovery. Typically returns to normal activities within 6–12 weeks.
- Partial knee replacement (unicompartmental): For isolated medial or lateral compartment OA — smaller operation, faster recovery; not suitable for inflammatory arthritis or multi-compartment disease.
- Hand surgery: Synovectomy, joint fusion (arthrodesis), or small joint replacement for severe RA hand deformity; trapeziectomy for base-of-thumb OA.
- Arthroscopy: Limited evidence for OA — lavage and debridement not supported by RCT evidence for knee OA. Still used for specific indications (meniscal tears, loose bodies).
- Osteotomy: Realigns the knee or hip to shift load away from damaged compartment — suitable for younger patients with localized OA to delay joint replacement.
With modern biologic therapy, many RA patients no longer develop the joint destruction requiring surgery. However, if significant damage has occurred prior to biologic era or in inadequately treated disease, joint replacement is highly effective. Biologics are typically paused peri-operatively to reduce infection risk — coordinate with your rheumatologist before any surgery.
Frequently asked questions
Osteoarthritis (OA) is a degenerative joint disease caused by cartilage breakdown — primarily affecting weight-bearing joints (knees, hips, spine) in older adults. Pain worsens with activity and improves with rest. Rheumatoid arthritis (RA) is an autoimmune disease where the immune system attacks the joint lining — affecting any joint, typically symmetrically (both hands, both wrists), often with morning stiffness lasting over an hour, systemic fatigue, and elevated inflammatory markers in the blood. RA can cause joint erosion and deformity if untreated; modern biologics have transformed its prognosis.
No form of arthritis is currently curable, but all are manageable. OA can be effectively controlled with exercise, weight management, and targeted pain relief. RA can achieve sustained remission with modern DMARDs and biologics — many patients live full, active lives with minimal joint damage when treated early and aggressively under the treat-to-target strategy. Gout is uniquely controllable — effective urate-lowering therapy that keeps uric acid below the crystallisation threshold can eliminate attacks entirely and dissolve tophi over time.
For gout: purine-rich foods (red meat, organ meats, shellfish), alcohol (especially beer and spirits), and high-fructose corn syrup significantly raise uric acid and trigger attacks. For RA and other inflammatory arthritis: ultra-processed foods and omega-6-heavy seed oils promote systemic inflammation. An anti-inflammatory Mediterranean-style diet shows modest benefit for inflammatory arthritis symptoms. The evidence for specific food triggers in OA beyond body weight is limited — focus on overall dietary quality and weight management rather than eliminating individual foods.
Yes — exercise is one of the most evidence-based treatments for all forms of arthritis. The fear that exercise will "wear out" joints is not supported by evidence. Appropriate low-impact exercise (swimming, cycling, walking, water aerobics) reduces pain, improves joint function, strengthens surrounding muscles, and improves mood and cardiovascular health — without accelerating joint damage. The key is choosing appropriate activities and exercising within comfortable range. "Motion is lotion" for arthritic joints. Rest during acute flares is appropriate, but prolonged inactivity significantly worsens long-term arthritis outcomes.
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