Osteoarthritis for USMLE Step 3 / COMLEX-USA Level 3
Overview of Osteoarthritis (OA)
- Definition: A chronic, degenerative joint disease characterized by cartilage loss, joint pain, stiffness, and functional impairment, primarily affecting weight-bearing joints.
Pathophysiology
- Cartilage Degradation: Progressive loss of articular cartilage due to mechanical stress, leading to bone exposure.
- Bone Changes: Subchondral bone sclerosis and osteophyte formation contribute to pain and joint dysfunction.
- Inflammation: Local low-grade inflammation is present but less prominent than in inflammatory arthritis.
Risk Factors
- Age: Prevalence increases with advancing age.
- Obesity: A significant risk factor for OA, especially in the knees, due to increased mechanical load.
- Joint Injury/Overuse: Prior trauma, repetitive use, and high-impact activities can predispose to OA development.
- Genetic Factors: Family history of OA and specific genetic mutations can increase susceptibility.
- Gender: Females, particularly postmenopausal women, have a higher incidence of OA.
Symptoms and Signs
- Joint Pain and Stiffness: Pain worsens with activity and improves with rest; morning stiffness typically lasts <30 minutes.
- Decreased Range of Motion: Progressive loss of movement in affected joints.
- Crepitus: A grating sensation felt or heard during joint movement.
- Joint Deformities: Advanced OA may present with bony enlargements like Heberden’s nodes (DIP) and Bouchard’s nodes (PIP).
- Commonly Affected Joints: Knees, hips, hands (DIP, PIP, and thumb base), and spine.
Diagnosis
- Clinical Presentation: Diagnosis based on symptoms, physical examination, and history.
- Radiographic Findings:
- X-ray: Joint space narrowing, osteophytes, subchondral sclerosis, and subchondral cysts are typical.
- Lab Tests: Generally normal; used to rule out other forms of arthritis (e.g., rheumatoid arthritis).
Management
- Non-Pharmacologic Measures:
- Exercise: Low-impact aerobic exercise and muscle strengthening.
- Weight Loss: Reduces load on weight-bearing joints.
- Assistive Devices: Braces, orthotics, and walking aids to reduce joint stress.
- Pharmacologic Therapy:
- Acetaminophen: Initial therapy for mild to moderate pain.
- NSAIDs: For more severe pain or when acetaminophen is ineffective; can be used orally or topically.
- Topical Agents: Topical NSAIDs and capsaicin for localized pain relief.
- Intra-Articular Corticosteroids: For moderate to severe OA flares and refractory symptoms.
- Surgical Options: Joint replacement or arthroplasty for advanced OA unresponsive to conservative measures.
Essential Points
- Progressive Disease: OA symptoms worsen gradually, and early intervention with lifestyle changes can slow progression.
- Multimodal Approach: Combining non-pharmacologic and pharmacologic treatments provides the best symptomatic relief.
- Surgical Intervention: Joint replacement is an option for end-stage disease when pain and functional limitations are not controlled by conservative measures.