Osteoarthritis of Knee

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.

⭐ 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.

⭐ 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):

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

⭐ 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).
• 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.