Osteoarthritis for USMLE Step 1 / COMLEX-USA Level 1
Overview of Osteoarthritis (OA)
- Definition: OA is a degenerative joint disorder characterized by the breakdown of joint cartilage and subsequent bone changes, leading to pain, stiffness, and functional limitation.
Pathophysiology
- Cartilage Degeneration: Due to mechanical wear and biochemical factors, the articular cartilage gradually wears down.
- Subchondral Bone Changes: Sclerosis and formation of osteophytes (bone spurs) occur, contributing to joint space narrowing.
- Minimal Inflammation: Unlike inflammatory arthritis, OA features minimal synovial inflammation.
Risk Factors
- Age: Incidence increases with age.
- Gender: Females have a higher prevalence, particularly after menopause.
- Obesity: Increases stress on weight-bearing joints, accelerating OA.
- Joint Injury/Overuse: Previous trauma, occupational overuse, or high-impact sports can predispose to OA.
- Genetic Predisposition: Family history and genetic factors play a role, particularly in hand and hip OA.
Symptoms and Signs
- Joint Pain: Worsens with activity and improves with rest; asymmetrical joint involvement.
- Morning Stiffness: Brief, typically <30 minutes, improving with movement.
- Crepitus and Joint Swelling: A sensation of grating or cracking within the joint during movement.
- Commonly Affected Joints: Knees, hips, hands (distal and proximal interphalangeal joints), 1st carpometacarpal joint, and spine.
Diagnosis
- Clinical Presentation: Symptoms and physical findings are often sufficient for diagnosis.
- Imaging:
- X-ray Findings: Joint space narrowing, osteophyte formation, subchondral sclerosis, and subchondral cysts are characteristic.
- Laboratory Tests: Typically normal, used to exclude other forms of arthritis.
Management
- Lifestyle Modifications: Weight loss, exercise (especially low-impact), and joint protection strategies.
- Pain Management:
- Acetaminophen: Often first-line for mild pain.
- NSAIDs: For moderate to severe pain, oral or topical.
- Topical Treatments: Capsaicin or topical NSAIDs for localized relief.
- Intra-Articular Injections: Corticosteroids or hyaluronic acid for temporary symptom relief in advanced cases.
- Surgical Interventions: Reserved for severe cases; options include joint replacement and other surgical corrections.
Essential Points
- Gradual Onset: Symptoms develop slowly over time, often starting with pain after use.
- Imaging Features: X-ray is the primary tool showing osteophytes, joint space narrowing, and subchondral changes.
- Management Approach: Focus on non-pharmacologic interventions and pain control, with surgery as a last resort for advanced OA.