Osteoarthritis

Detailed Overview

Once thought to be simple 'wear and tear', OA is now recognized as an active disease process involving defective cartilage repair and low-grade inflammation. Chondrocytes undergo phenotypic changes, producing proteases that degrade the extracellular matrix. As cartilage thins, bone rubs on bone, causing severe pain and functional disability. It is a leading cause of mobility impairment worldwide.

Epidemiology & Demographics

Affects over 32 million adults in the US. Prevalence rises exponentially after age 50. Women are more frequently affected than men, particularly for hand and knee OA.

Etiological Mechanism

A combination of mechanical stress on the joint and biochemical alterations in the articular cartilage and subchondral bone.

Primary Causes

Primary OA is age-related and idiopathic. Secondary OA results from prior joint trauma (e.g., ACL tear), congenital joint malformations (e.g., hip dysplasia), or metabolic disorders (e.g., hemochromatosis).

• Age: The greatest risk factor; cartilage healing capacity diminishes with age.
• Obesity: Increases mechanical load on knees/hips and systemic inflammation via adipokines.
• Joint Injury: History of meniscal or ligamentous tears greatly accelerates OA development.

Mechanical stress and aging alter chondrocyte function. Chondrocytes release matrix metalloproteinases (MMPs) and aggrecanases (ADAMTS) that degrade type II collagen and aggrecan in the extracellular matrix. Cartilage fibrillates and eventually ulcerates. The denuded subchondral bone undergoes sclerosis and microfractures, forming subchondral cysts. At the joint margins, endochondral ossification creates osteophytes. The synovium thickens and produces excess fluid containing inflammatory cytokines (IL-1b, TNF-a).

Characteristic Clinical Presentation

• Joint Pain: Deep, aching pain that worsens with use and weight-bearing, and improves with rest.
• Morning Stiffness: Joint stiffness upon waking that typically resolves within 30 minutes of movement.
• Crepitus: A grinding or popping sensation/sound during joint movement.
• Decreased Range of Motion: Progressive limitation in joint flexibility due to osteophytes and capsular thickening.

Physical Examination Signs

• Heberden's nodes (osteophytes at the distal interphalangeal [DIP] joints) and Bouchard's nodes (proximal interphalangeal [PIP] joints).
• Bony enlargement and varus/valgus deformity of the knee.
• Mild, cool joint effusions without severe warmth or erythema.

• Severe functional limitation: Inability to walk, climb stairs, or perform ADLs, leading to frailty.
• Falls: Increased risk due to joint instability, pain, and muscle weakness.
• Baker's Cyst: Popliteal cyst formation from excess knee synovial fluid, which can rupture and mimic DVT.

Diagnostic Criteria & Guidelines

Primarily a clinical and radiographic diagnosis. American College of Rheumatology criteria for knee OA: Knee pain plus at least 3 of: Age > 50, stiffness < 30 mins, crepitus, bony tenderness, bony enlargement, no palpable warmth. X-rays confirm findings.

Differential Diagnosis

• Rheumatoid Arthritis
• Psoriatic Arthritis
• Gout or Pseudogout (CPPD)
• Avascular Necrosis

Laboratory Tests & Biomarkers

• ESR and CRP: Normal. OA is not a systemic inflammatory disease.
• Rheumatoid Factor (RF) and Anti-CCP: Negative.
• Synovial Fluid Analysis: Non-inflammatory. Clear/yellow, highly viscous, WBC count < 2000 cells/mm3.

Imaging Modalities & Findings

• Weight-bearing X-rays (AP, Lateral, Sunrise views):

• Kellgren-Lawrence Grade 1
  Doubtful joint space narrowing and possible osteophytic lipping.
• Kellgren-Lawrence Grade 2
  Definite osteophytes and possible joint space narrowing.
• Kellgren-Lawrence Grade 4
  Large osteophytes, marked joint space narrowing, severe sclerosis, and definite bony deformity.

Second-Line & Adjunctive Therapy

Intra-articular glucocorticoid injections (e.g., Triamcinolone 40 mg) for acute flares (up to 3-4 times per year). Duloxetine (30-60 mg PO daily) for chronic pain management. Intra-articular hyaluronic acid injections (controversial efficacy).

Surgical & Procedural Management

Total Joint Arthroplasty (e.g., Total Knee Replacement or Total Hip Replacement) is definitively indicated for severe disease refractory to conservative management with unacceptable quality of life.

Recommended Lifestyle Changes

• Participate in low-impact aerobic exercises like swimming, water aerobics, or stationary cycling.
• Use assistive devices (canes) on the side OPPOSITE the affected knee/hip to offload the joint.
• Wear shoes with thick, shock-absorbing soles.

Patient Counseling & Advice

Educate that X-ray severity does not perfectly correlate with pain levels. Advise that paracetamol/acetaminophen is no longer considered first-line due to lack of efficacy. Reassure that appropriate exercise will not 'wear out' the joint faster.

Follow-Up & Monitoring Schedule

Clinical reassessment every 6-12 months for pain control, functional status, and side effects of chronic NSAID use (monitor blood pressure, creatinine, and hemoglobin).

Preventive Strategies

Maintaining an optimal body weight and preventing traumatic joint injuries during sports.

Progressive and irreversible, but the rate of progression varies. Most patients can maintain good quality of life with conservative management and eventual joint replacement.