Osteoarthritis for USMLE Step 2 / COMLEX-USA Level 2
Overview of Osteoarthritis (OA)
- Definition: OA is a degenerative joint disease characterized by the breakdown of cartilage and formation of bone spurs, leading to pain, stiffness, and decreased mobility.
Pathophysiology
- Cartilage Degeneration: Loss of articular cartilage due to mechanical wear and tear.
- Subchondral Bone Changes: Sclerosis and bone spur (osteophyte) formation occur as the cartilage wears away.
- Inflammation: Low-grade, secondary inflammation contributes to the progression of joint damage, but it is not the primary driver as in rheumatoid arthritis.
Risk Factors
- Age: Risk increases with age.
- Joint Trauma or Overuse: Previous injuries, repetitive use, or chronic joint stress predispose to OA.
- Obesity: Increases mechanical stress on weight-bearing joints.
- Genetics: Family history plays a role, particularly in hand and hip OA.
- Gender: Women are more prone to OA, especially post-menopause.
Symptoms and Signs
- Joint Pain and Stiffness: Worsens with activity and improves with rest; typically asymmetrical.
- Morning Stiffness: Short duration (<30 minutes), improves with movement.
- Crepitus: Cracking or grating sensation in the joint during movement.
- Joint Deformity and Limited Range of Motion: Advanced disease can lead to visible deformities.
- Commonly Affected Joints: Knees, hips, hands (DIP and PIP joints, and 1st carpometacarpal joint), and spine.
Diagnosis
- Clinical Presentation: Diagnosis is primarily clinical based on characteristic symptoms and physical examination.
- Imaging:
- X-rays: Show joint space narrowing, osteophytes, subchondral sclerosis, and subchondral cysts.
- Lab Tests: Typically normal; used to rule out other causes of arthritis like rheumatoid arthritis.
Management
- Non-Pharmacologic: Weight management, physical therapy, activity modification, and supportive devices (e.g., braces, canes).
- Pharmacologic:
- Acetaminophen: First-line for pain management.
- NSAIDs: For moderate to severe pain or when acetaminophen is ineffective.
- Topical Agents: NSAIDs and capsaicin cream.
- Intra-Articular Injections: Corticosteroids or hyaluronic acid for symptom relief in advanced cases.
- Surgical: Joint replacement or other procedures for severe, refractory OA.
Essential Points
- Pain and Functional Loss: Pain with activity and short-duration morning stiffness are hallmark features.
- First-Line Management: Lifestyle modifications, physical therapy, and acetaminophen are first-line treatments.
- Joint Replacement: Considered for patients with severe OA who do not respond to medical management.