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📋 Condition Guide2024-01-17

Knee Osteoarthritis: Causes, Symptoms, and Comprehensive Treatment

Knee osteoarthritis is the most common joint disease worldwide. Learn how cartilage wears down, what symptoms to expect, how severity is diagnosed, and the full range of treatments from lifestyle changes to knee replacement.

Educational content only. This article is not medical advice. Always consult a qualified orthopedic surgeon or physician for diagnosis and treatment.

What Is Knee Osteoarthritis?

Knee osteoarthritis (OA) is a degenerative joint disease characterized by the progressive breakdown of articular cartilage — the smooth, protective coating on the ends of the bones inside the knee. As cartilage erodes, the protective joint space narrows, bone rubs on bone, bone spurs (osteophytes) form, and the knee becomes painful, swollen, and functionally limited.

Knee OA affects over 30 million Americans and is one of the leading causes of disability in the world. It is the most common reason for total knee replacement surgery.

Anatomy of the Knee

The knee is the largest joint in the body. Three bony surfaces come together:

  • Medial compartment: Between the inner surfaces of the femur and tibia
  • Lateral compartment: Between the outer surfaces
  • Patellofemoral compartment: Between the kneecap (patella) and the front of the femur

OA most commonly affects the medial compartment first (accounting for medial knee pain with walking), but can involve all three compartments.

Causes and Risk Factors

Non-modifiable:

  • Age: Most patients with symptomatic knee OA are over 50
  • Female sex: Women have 2x the prevalence after menopause
  • Genetics: 40–65% of OA risk is heritable
  • Prior joint injury: ACL tear, meniscus tear, fracture — "post-traumatic OA"
  • Knee alignment: Varus (bowlegged) or valgus (knock-kneed) deformity concentrates load on one compartment

Modifiable:

  • Obesity: The single most important modifiable risk factor — each pound of weight loss reduces knee joint force by 4 pounds
  • Physical inactivity
  • Repetitive heavy loading occupations

Grading (Kellgren-Lawrence Scale)

Grade X-Ray Finding
0 Normal
1 Doubtful narrowing, possible osteophytes
2 Definite osteophytes, possible narrowing
3 Moderate narrowing, multiple osteophytes, sclerosis
4 Severe narrowing with bone-on-bone contact

Symptoms

  • Medial (inner) knee pain worsening with activity — walking, stairs, squatting
  • Morning stiffness lasting less than 30 minutes
  • Stiffness after prolonged sitting ("gelling")
  • Crepitus — grinding, creaking, or crackling sensation with movement
  • Swelling: Bony enlargement and/or synovial effusion (fluid in the joint)
  • Reduced range of motion — difficulty fully bending or straightening the knee
  • Night pain in advanced disease
  • Deformity: Progressive varus (bowing) or valgus (knock-knee) angulation

Diagnosis

  • Standing X-rays: Weight-bearing AP, lateral, and sunrise views — joint space narrowing, osteophytes, alignment assessment
  • MRI: Characterizes cartilage loss, meniscal pathology, bone marrow edema (not routinely needed for straightforward OA)

Treatment

Lifestyle and Conservative (First-Line)

Weight Loss: The most impactful intervention. Every 10 lbs lost reduces knee OA pain by meaningful margins and slows progression. A 10% body weight loss achieves greater symptom relief than most medications.

Exercise: Counterintuitively, exercise improves knee OA symptoms by strengthening the muscles that support and protect the knee, and by stimulating joint fluid circulation. Best tolerated: swimming, cycling, walking, aquatic therapy.

Physical Therapy:

  • Quadriceps strengthening (primary focus)
  • Hip abductor strengthening
  • Gait training and cane use

Medications:

  • Acetaminophen: Safe for chronic use
  • Topical NSAIDs (diclofenac gel): Excellent option with minimal systemic side effects
  • Oral NSAIDs (ibuprofen, naproxen, celecoxib): More potent but GI and cardiovascular risks with chronic use
  • Duloxetine: FDA-approved for knee OA; beneficial for centralized pain

Injections:

  • Corticosteroid injection: Rapid, temporary relief (weeks to months); can be repeated
  • Hyaluronic acid (viscosupplementation): Series of injections; benefit is modest and controversial per AAOS guidelines
  • PRP (platelet-rich plasma): Emerging evidence suggests benefit; not yet a standard of care

Braces:

  • Unloader knee brace: For medial compartment OA — shifts load to the lateral compartment; can be dramatically effective for appropriately selected patients
  • Neoprene knee sleeve: Warmth and proprioceptive feedback

Surgical Treatment

For severe, end-stage knee OA:

  • Total knee replacement (TKA): Most common; replaces all three compartments
  • Partial knee replacement (unicompartmental): Replaces only the affected compartment; faster recovery, more natural feel, but less durable
  • High tibial osteotomy (HTO): For younger patients with medial OA and varus malalignment; realigns the leg to offload the damaged compartment

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