Osteoarthritis vs Rheumatoid Arthritis

Introduction

Joint pain is a common presenting symptom in healthcare, and it is often assessed in medical school exams. Two common causes of this are osteoarthritis and rheumatoid arthritis. 

Although both conditions typically present with joint pain, they are very different in their aetiology, diagnosis and management. This article will cover a summary of both osteoarthritis and rheumatoid arthritis and a comparison of the two.

Osteoarthritis

Osteoarthritis is a progressive, degenerative joint disorder. The most common joints affected by osteoarthritis are the knees, followed by the hips and hands.

It is often referred to as a dysfunctional ‘wear and repair’ process within the joint. Over time, continuous ‘wear’ or trauma to the joint causes local inflammation and cartilage thins, leading to exposure of the underlying subchondral bone. This results in progressive loss of joint space and pain.

Risks for osteoarthritis include increasing age, obesity, female sex and joint trauma.

Clinical features

• Joint pain
• Stiffness: typically, worse after activity and at the end of the day
• Limitations in day-to-day activities
• Reduced active and passive range of movement (secondary to pain)
• Tenderness over the joint lines
• Crepitus on movement

Investigations and diagnosis

• Bodyweight and body mass index
• Inflammatory markers (CRP/ESR): typically normal 
• X-ray of affected joints

Interpretation of musculoskeletal X-rays is covered in more detail here.

Diagnosis of osteoarthritis is generally clinical, alongside X-rays. However, it is important to remember that the degree of arthritis visible on an X-ray may not always correlate with the patient’s symptoms.

Management

• Weight loss (if overweight or obese)
• Physiotherapy
• Analgesics in a stepwise approach
• Intra-articular corticosteroid injection
• Joint replacement (arthroplasty) or fusion of the joint (arthrodesis)

Rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic, systemic inflammatory disease characterised by inflammation of the synovial joints, with a predilection for the small joints in the hands. It has a variety of extra-articular features. It is an autoimmune disease in which circulating antibodies damage previously healthy tissue.

The cause of RA remains unknown but is thought to arise due to a combination of genetic (e.g. HLA genes), environmental (e.g. smoking, gut microbiome) and hormonal factors. Risk factors include smoking, obesity, female sex and HLA DR4 and DR1 genes.

Clinical features

• Insidious joint pain, swelling and stiffness over weeks to months
• Symmetrical joint pain and swelling
• Multiple joints affected: usually small joints of hands and feet 
• Fatigue
• Low-grade fever
• Symmetrical small joint polyarthropathy, with prominent hand and foot involvement
• Extra-articular manifestations: rashes, pulmonary nodules, rheumatoid nodules, anaemia, episcleritis, uveitis

Investigations and diagnosis

• Inflammatory markers (ESR/CRP): usually raised but may be normal
• Rheumatoid factor (RF): usually positive in 60-70% of patients but non-specific
• Anti-cyclic citrullinated peptide (anti-CCP): more specific than rheumatoid factor 
• X-ray

Interpretation of musculoskeletal X-rays is covered in more detail here.

The 2020 ACR-EULAR rheumatoid arthritis classification criteria are commonly employed to aid diagnosis. Factors considered in the scoring system include joints affected, serology results, inflammatory markers and duration of symptoms. A score of 6 or more is considered diagnostic.

Management

• Analgesics in a stepwise approach: particularly NSAIDs
• Physiotherapy
• One or more DMARDs, with rapid titration of doses to clinical effect: e.g. methotrexate, sulfasalazine, hydroxychloroquine
• If patients do not respond to DMARDs or are intolerant, and have active disease they are eligible for biologic drugs: e.g. etanercept, infliximab, rituximab
• Corticosteroids can be used at diagnosis or during a disease flare: oral prednisolone or IM depo-medrone

Comparison table

Table 1. A comparison of rheumatoid arthritis and osteoarthritis