What are the types of osteoarthritis (OA)?

Types of Osteoarthritis

Osteoarthritis (OA) can be classified into several distinct types based on anatomical location, etiology, and clinical presentation, each requiring different assessment and management approaches. 1

Main Classification Types

Based on Anatomical Location

• Hand OA: Includes three recognized subsets with different risk factors, associations and outcomes 1:

  • Interphalangeal joint (IPJ) OA: Affects distal and proximal interphalangeal joints, often with Heberden's or Bouchard's nodes 1
  • Thumb base OA: Affects the first carpometacarpal joint, commonly occurring in isolation 1
  • Erosive OA: Targets interphalangeal joints with radiographic subchondral erosion, often with more severe outcomes 1

• Knee OA: Most common large joint affected, leading to disability in approximately 10% of people over 55 years 1

  • Tibiofemoral OA: Affects the main knee joint compartment 1
  • Patellofemoral OA: Affects the joint between kneecap and femur 1

• Hip OA: Major contributor to global disability, often requiring joint replacement in advanced stages 1

Based on Etiology

• Primary (Idiopathic) OA: Develops without obvious causative mechanism, but can be further classified into 2:

  • Type I OA: Genetically determined 2
  • Type II OA: Estrogen hormone dependent, often related to menopause 2
  • Type III OA: Aging related 2

• Secondary OA: Occurs due to identifiable predisposing factors 3, 4:

  • Post-traumatic OA: Follows joint injury, particularly common in knee joints 1
  • Inflammatory OA: Associated with underlying inflammatory conditions 5
  • Metabolic OA: Related to metabolic disorders 5

Based on Structural Involvement

• Ligament-related OA: Initial pathology in ligamentous structures 4
• Cartilage-related OA: Primary degeneration begins in articular cartilage 4
• Bone-related OA: Initial changes in subchondral bone 4
• Meniscal-related OA: Begins with meniscal damage (particularly in knee) 4
• Synovial-related OA: Initial pathology in synovial tissue 4
• Mixed pattern/multifocal OA: Involves multiple structures simultaneously 4

Clinical Presentation

• Pain characteristics: Typically worsens with activity, improves with rest, morning stiffness lasting less than 30 minutes 6
• Functional limitations: Difficulty with purposeful movement, particularly weight-bearing activities, decreased mobility and walking distance 6
• Physical findings: Limited range of motion, muscle weakness (particularly quadriceps in knee OA) 6

Generalized vs. Focal OA

• Generalized OA: Affects multiple joint sites, with strong association between hand OA and development of knee/hip OA (OR = 2.1) 1
• Focal OA: Limited to a single joint or joint group 1

Erosive vs. Non-Erosive OA

• Erosive OA: Characterized by 1:

  • Abrupt onset with marked pain and functional impairment
  • Inflammatory symptoms (stiffness, soft tissue swelling, erythema)
  • Radiographic subchondral erosion progressing to bone/cartilage attrition
  • Mildly elevated C-reactive protein levels
  • Worse long-term functional outcomes than non-erosive OA

• Non-erosive OA: More gradual onset, less inflammatory features, better functional prognosis 1

Clinical Implications

• Comorbidity burden: 59-87% of OA patients have at least one other chronic condition, particularly cardiometabolic disorders 7
• Functional impact: OA causes significant disability comparable to rheumatoid arthritis in many cases 6
• Economic burden: Substantial costs due to healthcare utilization and lost productivity 7

Diagnostic Considerations

• Plain radiographs: Gold standard for morphological assessment, showing joint space narrowing, osteophytes, subchondral sclerosis and cysts 1
• Differential diagnosis: Must distinguish from other arthropathies including psoriatic arthritis, rheumatoid arthritis, gout, and hemochromatosis 1

Management Approach

• Core treatments: Education, structured exercise, and weight loss for all OA types 1
• Pharmacological options: Topical NSAIDs as first-line treatment, oral NSAIDs and intra-articular injections for persistent pain 1
• Joint-specific interventions: Hand orthoses for first carpometacarpal joint OA, knee bracing for tibiofemoral and patellofemoral OA 1

Understanding the specific type of OA is crucial for appropriate management and prognostication, as different subtypes may respond differently to various interventions and have distinct natural histories.