Osteoarthritis (OA)

Aetiology:

• Early in the development of OA, the surface of the cartilage becomes fibrillated and fissured as the collagen matrix breaks down
• These changes lead to focal erosion of cartilage
• Cartilage ulceration exposes underlying bone to increased stress (producing microfractures and cysts)
• The bone attempts repair but produces abnormal sclerotic subchondral bone and overgrowths at the joint margins (called osteophytes)

The term primary OA is sometimes used when there is no obvious predisposing factor

Causes of secondary OA:

Pre-existing joint damage:

• RA
• Gout
• Seronegative spondarthritis
• Septic arthritis
• Paget’s disease

Metabolic disease:

• Acromegaly
• Hereditary haemochromatosis
• Chondrocalcinosis

Systemic diseases:

• Haemophilia (recurrent haemarthrosis)
• Sickle-cell disease

Mechanical factors:

• Trauma (e.g. meniscal/cruciate tears)
• Joint dysplasia
• Joint hypermobility

Risk factors:

• Obesity
• Sex (females > males)
• Family history
• sport

Symptoms:

• Joint pain
• Evening stiffness
• Joint instability
• Loss of function

Signs:

• Crepitus on movement
• Limitation of range of movement
• Joint instability
• Joint effusion
• Bony swelling
• Wasting of muscles

Most commonly affected sites:

In decreasing order of prevalence:

• DIPs
• 1^st metacarpophalangeal
• 1^st metatarsophalangeal
• Cervical and lumbar spine
• Hip
• Knee

Clinical subsets:

There are 5 main subsets:

• Nodal OA
• Erosive OA
• Generalized OA
• Large-joint OA
• Crystal-associated OA

Nodal OA:

• The joints are usually affected one at a time over several years
• DIPs being most often involved
• Onset may be painful and associated with:
• Tenderness
• Swelling
• Inflammation
• Impairment of hand function

• The inflammatory phase settles after some months or years, leaving painless bony swellings posterolaterally with Heberden’s nodes (DIPs) and Bouchard’s nodes (PIPs) along with stiffness and deformity

Large-joint OA:

This affects the hips and the knees independently

The hips:

• Superior-pole hip arthritis:
• Most common in men
• Affects the weight-bearing upper surface of the femoral head and adjacent acetabulum
• Unilateral at presentation but may become bilateral

• Medial cartilage loss:
• Most common in women
• Associated with hand involvement
• Usually bilateral

The knees:

• Generally bilateral
• Strongly associated with polyarticular OA of the hand
• Medial compartment is most commonly affected

Investigation in OA:

X-rays:

• Characteristic changes (see below) only apparent when the damage is advanced

MRI:

• Can demonstrate early cartilage changes

Arthroscopy:

• Can reveal early fissuring and surface erosion of the cartilage

X-ray changes in OA:

• Osteophytes
• Joint space narrowing
• Bony cysts
• Subarticular sclerosis

Treatment – physical measures:

• Weight loss
• Exercise
• Hydrotherapy

Treatment – medical:

• Short courses of analgesics
• Intra-articular corticosteroid injections provide short-term improvement when there is a painful joint effusion

Surgery:

Total replacement arthroplasty:

• Complication rate ~1%