Osteoarthritis of Knee

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Definition & Risk Factors - Knee's Creaky Saga

  • Definition: Degenerative joint disease of the knee involving progressive loss of articular cartilage, osteophyte formation, subchondral sclerosis, and synovial inflammation.
  • Primary Risk Factors:
    • Age (> 50 years): Most significant non-modifiable.
    • Female sex (especially post-menopausal).
    • Genetic factors.
  • Secondary Risk Factors:
    • Obesity (BMI > 30).
    • Previous knee injury (e.g., meniscectomy, ACL tear).
    • Occupational stress (repetitive kneeling, squatting, heavy lifting).
    • Joint malalignment (genu varum/valgum).

⭐ Obesity (BMI > 30) is the most significant modifiable risk factor for knee osteoarthritis, increasing load and inflammation.

Pathophysiology - Cartilage Calamity

  • Triggers: Mechanical stress, aging, genetics.
  • Chondrocyte Role: Dysregulation → ↑Catabolic enzymes (MMPs, ADAMTS), ↓Anabolic factors.
    • Pro-inflammatory cytokines (IL-1, TNF-α) amplify damage.
  • ECM Failure:
    • Proteoglycan loss → ↓hydration, ↓resilience.
    • Collagen II network breakdown → fibrillation, erosion.
  • Bone Response: Subchondral sclerosis, osteophytes.
  • Synovitis: Contributes to pain and progression.

Stages of Knee Osteoarthritis

⭐ MMP-13 (Collagenase-3) is a key enzyme responsible for Type II collagen degradation in OA.

Clinical Features & Diagnosis - Groans & Grades

  • Symptoms: Insidious pain (worse with activity, relieved by rest), morning stiffness < 30 min, "gelling" after inactivity, crepitus, joint swelling (cool effusion/bony).
  • Signs: Restricted ROM, tenderness, bony enlargement, deformities (varus > valgus).
    • Antalgic gait.
  • Diagnosis: Primarily clinical.
    • X-ray (weight-bearing): Confirms.
      • Kellgren-Lawrence (KL) Grades (0-4).
      • Key findings: Joint space narrowing (JSN), osteophytes, subchondral sclerosis & cysts. 📌 Mnemonic: LOSS. Knee Osteoarthritis X-ray with Kellgren-Lawrence Grades

⭐ Morning stiffness < 30 minutes is a key differentiator from inflammatory arthritis (e.g., Rheumatoid Arthritis).

Imaging - X-Ray Exposé

  • Key Views: Weight-bearing Anteroposterior (AP), Lateral, and Skyline (patellofemoral).

  • 📌 LOSS Mnemonic for X-ray findings:

    • Loss of joint space (esp. medial compartment)
    • Osteophytes (marginal)
    • Subchondral sclerosis
    • Subchondral cysts
  • Kellgren-Lawrence (K-L) Grading (Grades 0-4):

    GradeDescription
    0Normal
    1Doubtful joint space narrowing (JSN), possible osteophytes
    2Definite osteophytes, possible JSN
    3Moderate osteophytes, definite JSN, sclerosis, possible deformity
    4Large osteophytes, severe JSN, marked sclerosis, definite deformity

Kellgren-Lawrence Grading of Knee Osteoarthritis

⭐ Weight-bearing AP X-rays are crucial for accurately assessing joint space narrowing, a hallmark of knee OA progression.

Management - Joint Relief Roadmap

  • Goals: Pain relief, improve function, improve quality of life.
  • Stepwise Approach:
  • Conservative Pillars:
    • Lifestyle: Weight reduction (5-10% if overweight).
    • Physiotherapy: Quadriceps strengthening, ROM exercises, low-impact aerobics.
    • Aids: Cane (contralateral), valgus knee brace (for medial compartment OA). Valgus knee brace for medial compartment OA
  • Pharmacotherapy Ladder:
    • 1st line: Paracetamol (up to 1g QID, max 4g/day).
    • 2nd line: Topical NSAIDs. If ineffective, oral NSAIDs (lowest dose; +PPI if GI risk).
    • Intra-articular: Corticosteroids (short-term, max 3-4/year), Hyaluronic acid.
  • Surgical Intervention (End-stage):

    ⭐ High Tibial Osteotomy (HTO) for active patients <60 years with medial unicompartmental OA and varus deformity, aiming to delay TKA.

High‑Yield Points - ⚡ Biggest Takeaways

  • Knee is the most common large joint affected by Osteoarthritis (OA).
  • Primary OA is idiopathic; Secondary OA results from trauma or pre-existing joint disease.
  • Medial compartment involvement is most common, often leading to genu varum.
  • Radiographic hallmarks: Joint space narrowing (JSN), osteophytes, subchondral sclerosis, and cysts.
  • Key symptoms: Activity-related pain, morning stiffness <30 minutes, crepitus, and decreased range of motion.
  • Conservative management: Weight reduction, exercise, NSAIDs; Total Knee Replacement (TKR) for end-stage disease.

Practice Questions: Osteoarthritis of Knee

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