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Pathology

Arthritis

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Osteoarthritis

Definition

Mechanically driven but biologically mediated complex degenerative process starting at the tangential zone of articular cartilage of a synovial joint.

Aetiology

  • Primary:
    • Idiopathic
    • Genetic element
    • Mechanical factors
  • Secondary:

Pathology

Primary Events:

  • Altered proteoglycan function
  • Reduced subchondral venous drainage
  • Altered cartilage permeability

Results:

  • Influx of water
  • Reduced stiffness
  • Altered viscoelastic properties
  • Loss of chondrocyte ability to maintain cartilage
  • Fibrillation (fissuring)
  • Loss of hyaline cartilage
  • Subchondral exposure and hypertrophy (sclerosis)
  • Cyst formation
  • Compensatory osteophyte formation

Rheumatoid Arthritis

Epidemiology

  • More common in Caucasians
  • Females: 2:1 compared to males
  • Typically onset around 40 years
  • 1-5% of the population depending on ethnicity

Aetiology

  • Seropositive, autoimmune inflammatory polyarthritis.
  • Characterized by synovitis, periarticular erosions, joint destruction, and systemic manifestations.
  • Rh factor positive in 80%.
  • Primarily affects synovium, leading to secondary joint destruction.

Pathophysiology

  • Inflammatory infiltration of synovium with B cells, T cells, and macrophages.
  • Joint destruction is mechanical (due to inflamed synovium) and chemical (due to inflammatory factors).
  • Positive for HLA DR.

Rheumatoid Factor (RF)

  • Autoantibody that targets the Fc part of IgG.
  • Correlates with the severity of the disease and joint destruction.
  • RF may be raised in other systemic conditions, but has poor positive predictive value.

Clinical Features

  • Inflammation of joints.
  • Symmetric polyarthropathy.
  • Morning pain and stiffness (eases with activity).
  • Extra-articular features:
    • Rheumatoid nodules (30% of patients):
      • Found on extensor aspect of arms.
      • Pathognomonic: Fibrotic capsule surrounding fibrous necrotic center.
      • Non-inflammatory; contains cholesterol crystals on aspiration.
    • Uveitis
    • Cardiac problems
    • Neurologic problems

Imaging Features

  • Periarticular osteopenia.
  • Juxtaarticular erosions.
  • Significant deformity and subluxation due to soft tissue involvement.

Diagnostic Criteria (American College of Rheumatologists)

  • Need to have 4 out of 7 criteria and 3 of the top 4 for at least 6 weeks:
    1. S Symmetric arthritis
    2. H Hand or wrist arthritis for >6 weeks
    3. A Arthritis in at least 3 joints for >6 weeks
    4. M Morning stiffness for 1 hour a day for >6 weeks
    5. P Positive rheumatoid factor
    6. E X-ray changes
    7. R Rheumatoid nodules

Management

  • NSAIDs, prednisolone for acute flare-ups.
  • Disease-modifying agents (DMARDs):
    • Methotrexate
    • Sulfasalazine
    • Hydroxychloroquine (antimalarial)
  • Biologic Response Modulators (BRMs):
    • Etanercept
    • Infliximab
    • Rituximab
  • Surgery:
    • Synovectomy: Good pain relief, especially in knee.
    • Does not alter long-term joint destruction.
    • Arthroplasty: Higher infection rate, poor bone quality, beware of joint instability.

Seronegative Spondyloarthropathy

These are RF-negative arthritidies: 1. Ankylosing Spondylitis (see spine notes) 2. Psoriatic Arthritis 3. Enteropathic Arthritis 4. Reactive Arthritis (Reiter’s syndrome) 5. Juvenile Idiopathic Arthritis

Psoriatic Arthritis

Aetiology

  • Occurs in 20% of patients with psoriasis.
  • 80% have preceding skin manifestations of psoriasis.
  • 50% are HLA B27 positive.

Clinical Features

  • May cause psoriatic spondylitis (uncommon).
  • Predominantly affects hands, especially DIPJ.
  • Dactylitis (sausage digits).
  • Pencil-in-cup deformity of DIPJ.
  • Nail pitting.
  • Distinguished from RA by:
    • RF usually negative.
    • Asymmetric.
    • Absence of rheumatoid nodules.

Management

  • Medical: NSAIDs, DMARDs.
  • Surgical: Joint fusions.

Enteropathic Arthritis

  • Occurs in individuals with inflammatory bowel disease (IBD), especially Crohn’s disease.
  • Affects lower limbs, but also spine.
  • Spondylitis similar to ankylosing spondylitis.
  • Severity of arthritis correlates with severity of gut inflammation.
  • Extra-articular features include uveitis, pyoderma gangrenosum, etc.

Management

  • Mainly medical: Manage gut inflammation (e.g., sulfasalazine), which helps arthritis.

Juvenile Idiopathic Arthritis (Juvenile Rheumatoid Arthritis)

Epidemiology

  • Affects individuals under 16 years of age.

Aetiology

  • Similar to rheumatoid arthritis, an inflammatory polyarticular disease with systemic manifestations.
  • Rh factor is rarely positive, but if positive, indicates more aggressive disease.

Clinical Features

  • Classic difference in hand from RA:
    • Wrist is ulnar deviated.
    • Fingers are radially deviated at MCPJ.
  • 3 Subtypes:
    1. Systemic (Still's disease):
      • Worst long-term prognosis.
      • Lymphadenopathy, polyarthritis, hepatosplenomegaly, anemia, rash, fever (20% of JRA).
    2. Oligoarticular (Paucarticular):
      • Most common type.
      • Affects <5 joints.
      • More in girls.
      • Good rate of remission (70%).
    3. Polyarticular:
      • Affects >5 joints.
      • More in girls.
      • Reasonable rate of remission (60%).

Management

  • Steroids, DMARDs.
  • Joint aspirations, synovectomy.
  • Osteotomy, fusion, and arthroplasty as necessary, even in young patients.

Reactive Arthritis (Reiter’s Syndrome)

Aetiology

  • Occurs secondary to a genitourinary tract infection (Chlamydia, Shigella, Salmonella, Campylobacter).

Clinical Features

  • Usually affects the knee.
  • Enthesitis and spondylitis can occur.
  • Extra-articular manifestations:
    • Severe conjunctivitis.
    • Urethritis (burning on urination).
    • "Can't see, can't pee, can't climb a tree".

Management

  • Supportive therapy (condition is self-limiting over 18 months).

Other Conditions

Gout

  • Disorder of purine (nucleic acid) metabolism leading to intra-articular accumulation of uric acid crystals, causing pain, inflammation, and arthrosis.

Epidemiology

  • 80% of cases occur in men.
  • Most common in older adults.

Aetiology

  • Uric acid crystal deposition in synovium.

Clinical Features

  • Acutely painful, swollen joint(s).
  • Often mono-articular (thumb IPJ, big toe IPJ commonly affected).
  • Ankle is often the first large joint to be affected.
  • Flare-ups caused by metabolic activity:
    • Alcohol
    • Excessive purine intake (oily fish)
    • Thiazide diuretics
  • Serum urate may be normal.
  • Aspiration reveals negatively birefringent crystals.

Imaging Features

  • Periarticular erosions.
  • Cliff edge sign: Sharp overhanging edge at peripheral margin of bone.

Management

  • Remove inciting event.
  • Acute flare-ups: NSAIDs, colchicine.
  • Long-term prevention: Allopurinol.

Pyrophosphate Arthropathy

  • Calcium pyrophosphate crystals deposited in joints causing pain, mimicking septic arthritis.
  • X-ray may show chondrocalcinosis.
  • Commonly affects wrist and knee.
  • Aspiration reveals positively birefringent pyrophosphate crystals.

Scleroderma

  • Systemic disease causing systemic sclerosis.
  • Main orthopedic manifestation in hands:
    • Erosion of distal phalanx tufts.
    • Calcification of soft tissues.
    • DIPJ & PIPJ contractures.
    • Raynaud’s phenomenon: Ulceration of skin.

Management

  • Sympathectomy.
  • Limited amputations.
  • DIPJ, PIPJ fusions.

Related FRCS revision notes

CartilageAvascular Necrosis of the HipNonunionShoulder ArthritisDiabetic foot (Pathology)Charcot

Linked from

← Pathology← Cartilage← Ankle arthritis← Ankle arthritis← First CMC Joint Osteoarthritis← Glucosamine and chondroitin← Irritable Hip and Septic Arthritis← Septic arthritis

Written/reviewed by Kishore Puthezhath

Professor of Orthopaedics and Consultant Paediatric Orthopaedic Surgeon

FRCS (Tr & Orth) revision resource

Reviewed: September 2026

Core revision references: Miller's Review of Orthopaedics; Campbell's Operative Orthopaedics; Orthobullets. Current specialty guidelines are linked within individual notes where applicable.