Knee Osteoarthritis

**Knee osteoarthritis** is a progressive degenerative disease affecting the cartilage and surrounding tissues of the knee joint. While often called "wear and tear arthritis," modern understanding shows it's more complex — involving inflammation, mechanical stress, and biological changes throughout the entire joint. **Joint Components Affected:** - **Articular cartilage**: Smooth surface covering bone ends; progressively wears away - **Subchondral bone**: Bone beneath cartilage; develops sclerosis (hardening) and cysts - **Synovium**: Joint lining; can become inflamed (synovitis) - **Meniscus**: Cartilage cushions; degenerative tears common in OA - **Ligaments and tendons**: Become stiffer and more vulnerable - **Joint capsule**: Thickens and contracts **Three Compartments of the Knee:** - **Medial (inner) compartment**: Most commonly affected — varus deformity ("bow legs") - **Lateral (outer) compartment**: Less common — valgus deformity ("knock knees") - **Patellofemoral compartment**: Anterior knee pain; common with maltracking **Stages of Progression (Kellgren-Lawrence):** - **Grade 0**: Normal — no features - **Grade 1**: Doubtful — possible osteophyte formation - **Grade 2**: Mild — definite osteophytes, possible joint space narrowing - **Grade 3**: Moderate — multiple osteophytes, definite joint space narrowing, sclerosis - **Grade 4**: Severe — large osteophytes, severe joint space narrowing, bone deformity **Primary vs Secondary OA:** **Primary (Idiopathic) OA:** - No identifiable cause - Most common type - Related to age, genetics, mechanical factors - Develops gradually over decades **Secondary OA:** - Identifiable underlying cause - Develops earlier (younger age) - Common causes: prior knee injury (ACL tear, meniscus tear, fracture), inflammatory arthritis, obesity, occupational overuse **Why "Wear and Tear" Is Outdated:** Modern research shows OA is not just mechanical wear — it involves: - Active inflammatory processes - Bone remodeling - Changes in cartilage cell biology - Immune system involvement - Crystal deposition This is why simply resting doesn't prevent progression — and why modern treatments target multiple mechanisms.

## Root Causes **Knee OA is multifactorial — combining mechanical, biological, and genetic factors:** **Mechanical Factors:** - **Joint loading**: Excessive forces over time damage cartilage - **Malalignment**: Varus or valgus increases compartmental loading - **Joint instability**: Previous ligament injuries (especially ACL) create abnormal mechanics - **Occupational kneeling/squatting**: Carpet layers, miners, gardeners - **Body weight**: Each pound = 4 lb on knee during walking, 7 lb during squatting **Biological Factors:** - **Aging cartilage**: Reduced cellular activity, water content decline - **Inflammation**: Low-grade chronic inflammation drives progression - **Hormonal changes**: Post-menopausal women have accelerated OA - **Bone remodeling**: Subchondral bone changes affect cartilage health **Genetic Factors:** - **Family history doubles risk** - **Specific gene variants** identified in research - **Genetic predisposition** to inflammation and cartilage breakdown **Risk Factors:** *Modifiable:* - **Obesity**: BMI >30 increases knee OA risk 4-5x - **Previous knee injury**: ACL tear, meniscus tear, fracture (3-5x higher risk) - **Muscle weakness**: Quadriceps weakness predicts and exacerbates OA - **Occupational overuse**: Repetitive heavy loading - **Sports participation**: Cumulative effects, especially with injury *Non-Modifiable:* - **Age >50**: Single most important factor - **Female sex**: After menopause - **Genetics**: Family history - **Anatomic factors**: Joint shape, alignment - **Race/ethnicity**: Some populations have higher rates

## Treatment Approach: Stepped Care **Knee OA treatment follows a stepped approach — start conservative, escalate as needed.** **Step 1: Education and Lifestyle Modification (Foundation)** *Weight Loss (CRITICAL if Overweight):* - **5% weight loss reduces knee pain by 18%**; 10% reduces pain by 50% - Most powerful non-surgical intervention - Each pound lost = 4 lb less knee load - Combined diet + exercise programs most effective *Exercise (Essential):* - **Quadriceps strengthening**: Strongest evidence - **Hip strengthening**: Gluteus medius/maximus - **Aerobic exercise**: 30 min, 5x weekly (walking, swimming, cycling) - **Tai chi**: Improves balance and reduces pain - **Aquatic exercise**: Excellent for severe OA (water buoyancy) - **AVOID**: High-impact activities like running on hard surfaces in advanced OA *Activity Modification:* - Substitute high-impact for low-impact activities - Use proper supportive footwear - Walking aids (cane in opposite hand) for severe cases **Step 2: Topical and Oral Medications** *First-Line:* - **Topical NSAIDs** (diclofenac gel) — fewer side effects than oral - **Acetaminophen** — limited efficacy but few side effects - **Capsaicin cream** — moderate evidence *Oral NSAIDs:* - **Most effective oral medication** for OA pain - Use lowest effective dose, shortest duration - GI, cardiovascular, renal risks (especially in elderly) - Selective COX-2 inhibitors (celecoxib) — fewer GI side effects *Other:* - **Duloxetine** (Cymbalta) — for patients with chronic pain - **Tramadol** — limited use due to dependency concerns - **AVOID long-term opioids** — significant risks, limited efficacy **Step 3: Injections** *Corticosteroid Injection:* - **Provides 4-8 weeks of pain relief** - Useful for acute flares - Limit to 3-4 per year (concerns about cartilage damage) *Hyaluronic Acid (Viscosupplementation):* - Modest evidence for short-term pain relief - Effects last 3-6 months - More effective in mild-moderate OA *Platelet-Rich Plasma (PRP):* - Emerging evidence — may be superior to HA in some studies - Not yet first-line; some insurance coverage limited - Best for early-mid OA in younger patients **Step 4: Bracing and Devices** - **Unloader brace** for unicompartmental OA — shifts load to healthy compartment - **Patellar tracking braces** for patellofemoral OA - **Cane in opposite hand** reduces affected knee load by 25% **Step 5: Surgical Treatment** *Arthroscopic Surgery:* - **Modern evidence shows minimal benefit** for OA - Multiple landmark studies (Sihvonen et al, Moseley et al) show no benefit over sham surgery - Generally NOT recommended for OA-related symptoms - Exception: mechanical symptoms from large meniscus tears *Osteotomy (Bone Realignment):* - For young patients with isolated medial or lateral compartment OA - Realigns the leg to shift load to healthy compartment - Delays joint replacement by 5-15 years *Partial Knee Replacement:* - For unicompartmental OA only - Less invasive than total knee replacement - Faster recovery - 90%+ implant survival at 10 years *Total Knee Replacement (Arthroplasty):* - **Gold standard for end-stage OA** - Modern procedure with 90-95% good-to-excellent outcomes at 5 years - 90% implant survival at 15-20 years - 700,000+ performed annually in US - Recovery: 3-6 months for full activity - Indication: severe pain limiting quality of life despite conservative care **What Doesn't Work (Despite Marketing):** - **Glucosamine and chondroitin**: Most rigorous studies show no benefit beyond placebo - **Stem cell injections**: Insufficient evidence; expensive; experimental - **Magnetic therapy**: No evidence - **Most "joint health" supplements**: Limited evidence ## The 4 Pillars of Effective OA Management 1. **Weight management** (if overweight) 2. **Exercise therapy** (quadriceps + aerobic) 3. **Education and self-management** 4. **Pain management** (topical/oral medications, judicious injections) When these fail to maintain quality of life, **total knee replacement** is highly successful for end-stage disease.