M08.027.001 Osteoarthritis (OA)

Osteoarthritis (OA), also known as degenerative joint disease, is the most prevalent form of arthritis. It’s characterized by the breakdown of articular cartilage, the smooth tissue cushioning the ends of bones within a joint. Unlike other forms of arthritis, inflammation is usually minimal to absent in OA.

Clinical Presentation

Onset: Insidious, often developing gradually over years.

Symptoms:

• Joint stiffness, particularly noticeable upon waking or after prolonged inactivity.
• Deep, aching joint pain that worsens with activity and improves with rest.
• Reduced range of motion in the affected joint.
• Crepitus, a grinding or crackling sensation felt or heard during joint movement.
• Joint effusion (fluid buildup) and swelling in some cases.
• Osteophytes (bone spurs) may develop and compress surrounding nerves, causing pain and weakness.

Imaging Findings:

X-ray reveals:

• Narrowed joint space due to cartilage loss.
• Increased bone density (osteosclerosis) and bone cyst formation.
• Presence of osteophytes (osteophytic lipping) at the joint margins.

Pathogenesis

OA has a complex etiology involving both mechanical and biochemical factors:

• Biomechanical Factors:
  • Aging: Cartilage naturally weakens with age, making it more susceptible to wear and tear.
  • Previous Joint Injury: Trauma can damage cartilage and accelerate its degeneration.
  • Obesity: Excess weight puts significant stress on weight-bearing joints, promoting cartilage breakdown.
• Biochemical Factors:
  • Chondrocyte Injury: Damage to the cells responsible for cartilage production and maintenance.
  • Abnormal Collagen Activity: Altered collagen metabolism weakens the cartilage matrix.

Predisposing Factors:

• Obesity
• Previous joint injury
• Ochronosis (a metabolic disorder)
• Diabetes
• Hemarthrosis (bleeding within a joint)

Joint Involvement

OA primarily affects weight-bearing joints, including:

• Knees
• Hips
• Spine (lower back)

The involvement can be asymmetrical, meaning one side of the joint may be more severely affected than the other.

Pathology Breakdown

• Articular Cartilage: Degenerates and erodes, exposing underlying bone (eburnation).
• Subchondral Bone: Sclerosis (increased density) develops beneath the damaged cartilage.
• Subchondral Bone Cysts: Fluid-filled cavities may form within the subchondral bone.
• Loose Bodies (Joint Mice): Fragments of cartilage and bone break off and float freely within the joint space.
• Osteophytes (Bone Spurs): Bony outgrowths develop at the joint margins in response to inflammation and stress.
• Specific Osteophytes:
  • Heberden nodes: Occur at the distal interphalangeal (DIP) joints of the fingers (closest to the fingertips).
  • Bouchard nodes: Develop at the proximal interphalangeal (PIP) joints of the fingers (middle joints).

Bibliography

• [Insert relevant medical textbook on Rheumatology or Osteoarthritis]
• National Institute of Arthritis and Musculoskeletal and Skin Diseases. Osteoarthritis. https://www.ncbi.nlm.nih.gov/books/NBK482326/pen_spark