Osteoarthritis

 

• Chronic disorder of synovial joints involving cartilage degeneration and irregular regeneration and modelling

 

Cartilage structure

• The superficial layer the fibres are tangential which decreases forces
• The middle zone is vertically aligned which helps transfer load to the joint
• Hyaline cartilage is avascula, aneuronal and alymphatic which means it cant regenerate, when it tries fibrocartilage forms
• Cartilage gets its nutrition from the synovial fluid which is an ultra infiltrate of plasma and hyaluronic acid

 

Epidemiology

• Most common type of arthritis
• Most people over 60 will have some radiological evidence of it – not always symptomatic
• Women over 55 more commonly affected than men
• In those less than 45, men are more commonly affected
• Most commonly affects fingers and large joints of lower limb. The big toe can also be affected
• White>black>japenese>>chinese

 

Aetiology

• Results from an active, sometimes inflammatory process – not inevitable due to age and injury
• Spectrum of disease varies from atrophic disease whereby cartilage distruction occurs without any subcondrial bone response to hypertrophic disease in which there is massive new bone formation at joint margins
• ECM production fails due to focal erosion
• Small tears called fibrillations occur at the articular surface
• Later larger tears form fissures and fragments
• Chondrocytes replicate and undergo physical and enzymatic changes
• Cartilage ulceration exposes underlying bone to stress producing microfracture
• When cartilage is damaged the joint space narrows
• Bone at periphery replicates to form osteophytes
• Subchondrial bone becomes sclerotic
• Areas undergo cystic change due to reabsoption process
• Viscosity of synovial fluid changes, hyaluronic acid production changes and the lubricative effect is lost

 

Pathogenesis

 

Risk factors

• Obesity
• Hereditary – familial tendance to develop nodal and generalised OA
• No particular gene identified but FRLP around collagen type II gene on Chr 12
  gender – polyarticular OA more common in women
• Hypermobility – increased range of joint movement and decreased stability
• Oestoeporosis – reduced risk with OA
• Trauma – meniscal and cruciate ligament tears can cause OA of the knee
• Congenital joint dyplasia – mild acetabular displacemtn can lead to early onset OA
  Joint congruity – e.g. congenital dislocation of the hip a slipped femoral epiphysis
• Occupation

 

Causes of OA

• Primary
  • No known cause
• Secondary
  • Trauma
  • Pre-existing joint damage
  • RA
  • Gout
  • Seronegative spondyloarthropathy
  • Septic arthritis
  • Paget’s disease
  • Avascular necrosis
  • Metabolic diseases
  • Chondrocalcinosis
  • Hereditary haemochromatosis
  • Acromegaly
  • Systemic diseases
  • Haemophilias – recurrent haemarthrosis
  • Haemoglobinopathies e.g. sickle cell
  • Neuropathies

 

Clinical features

• Hip and knee OA is the major form of disability
• Some flare ups are due to inflammation but are not associated with raised inflammatory markers
• Focal synovitis is caused by fragemtns of bone of cartilage
• Radiological OA is usually progressive

 

Symptoms

• Joint pain
• Joint gelling – stiffening and pain after immobility
• Joint instability
• Loss of function

 

Signs

• Antalgic gait (reduction of stance phase of walking)
• Joint tenderness
• Crepitus on movement
• Limitation in range of movement
• Joint instability
• Joint effusion
• Bony swelling
• Wasting of muscles

 

Clinical subsets

 

Localised OA

• Nodal OA distal interphalangeal joints most commonly affected than PIP joints
• Joints of hands are normally affected one at a time over several years
• Inflammation often occurs around the time of menopause
• Inflammatory phase resolves leaving painless boney lesions – Heberden’s nodes (DIP) and Bouchard’s node in the PIP
• PIP OA restricts gripping more than DIP OA
• ‘squared’ hand of OA cuased by boney swelling of the carpometacarpal joint and fixed adduction of the thumb

 

Hip OA

• More common in Caucasion population then black
• Two major subgroups defined by radiological appearance;
• Superior pole hip OA
  • Joint space narrowing and sclerosis predominantly affects the weight bearing upper surface of the femoral head and adjacent acetabulum
  • More common in men
  • Most unilateral
• Medial cartilage loss
  • More common in women
  • Associated with hand involvement
  • Usually bilateral

 

Knee OA

• Prevalence is 40% in those >75
• Commoner in women
• Associated with obesity
• Bilateral
• Strongly associated with polyarticualr OA of the ahnd
• Medial compartment of joint is most commonly affectedand leads to bow legged deformity
• Also retropatellar OA

 

Primary generalised OA

• Less common than OA of the hands but is usually seen in combination
• Other joints affected are;
  • Knee
  • First MTP
  • Hip
  • Intervertebral joints
• Family preponderance
• Onset often sudden and severe

 

Erosive OA

• Rare
• Inflammation of DIPs and PIPs
• Functional outcome is poor
• Radiologically there are marked subchondral cysts
• May develop into RA and not be a true subset of OA

 

Crystal –associated OA

• Most commonly seen with calcium pyrophospahe deposition in the cartilage (chondrocalcinosis)
• Most commonly affects knees and wrists

 

Pain

• Pain not due to damage to cartilage as it is not innervated
• Due to;
  • Osteophytes elevating the periosteum
  • Vascular congestion of subchondrial bone leading to increased intraosteal pressure
  • Synovitis
  • Fatigue of muscles across the joint
  • Joint contracture

 

Investigations

• Bloods – CRP, ESR, rheumatoid and antinuclear antibodies, shouldn’t be any changes
• X-rays
  • Signs on x-ray
    • Subcondrial sclerosis
    • Narrowing of joint space
    • Osteophytes
    • Bone cysts
  • Kallgren and Lawrence  - radiological classification of disease

0-     no features of OA

1-     minute osteophytes

2-     definite osteophytes

3-     moderate joint space narrowing

4-     marked joint space narrowing

• MRI/bone scan correlates poorly with symptoms
• Arthoscopy
• Mostly diagnosis is clinical

 

Treatment

• Physical measures
• Weight loss and exercise
  • Loss of 1lb of weight results in 3-4lb less force across the joint
  • Sport may be protective
• Physiotherapy – cartilage nourished with joint movement

 

Medication

• Analgesics e.g paracetamol, dihydrocodeine
• NSAIDs
• Intra-articular corticosteroid injections or hyaluronic acid
• Glucosamine/chondroitin and possible helpful for early stage (prob with shellfish allergy)

 

Surgery

• Arthroscopic washout
• Osteochondrial graft for small lesions
• Realignment osteotomy of knee and hip
• Arthodesis – fusion of first MCP
• Excision arthroscopy of the first MTP or base of thumb – remove trapezius
• Total hip or knee replacement – arthroplasty