Knee Osteoarthritis

Aka: Knee Osteoarthritis, Knee Degenerative Joint Disease, Knee DJD

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II. Risk Factors

  1. Femal gender
  2. Older age
    1. Affects one third of those over age 65 years
  3. Obesity (Body Mass Index >30 mg/kg)
  4. Occupation
    1. Prolonged squatting or kneeling
    2. Lifting more than 25 kg regularly
    3. Walking more than 2 miles per day
  5. History of comorbid inflammatory joint disease
    1. Septic Knee Joint
    2. Gouty Arthritis
    3. Rheumatoid Arthritis
  6. Previous Knee Injury (e.g. Meniscal tear)

III. Symptoms: General

  1. Less than 30 minutes of morning knee stiffness resolving with activity
  2. Chronic progressive Knee Pain
  3. Mild Joint Swelling
  4. Crepitation on knee range of motion
  5. Provocative
    1. Standing or weight bearing
    2. Stair climbing
  6. Palliative
    1. Rest
  7. Findings suggestive of advanced cases
    1. Instability symptoms
    2. Genu Valgum (knock knee)
    3. Genu Varum (bow leg)
      1. More common due to medial meniscus more often affected

IV. Signs

  1. Mild Knee Effusion
  2. Minimal synovial thickening
  3. Atrophy of Muscles surrounding knee
  4. Restricted knee range of motion (active and passive)

V. Differential Diagnosis

  1. See Knee Pain
  2. Other Arthritis
    1. Gouty Arthritis
    2. Rheumatoid Arthritis
    3. Pseudogout
    4. Septic Arthritis
  3. Injury
    1. Meniscal tear
    2. Collateral Ligament Tear of Knee
    3. Iliotibial Band Syndrome
    4. Pes Anserine Bursitis
    5. Prepatellar Bursitis

VI. Diagnosis

  1. Clinical criteria
    1. Age over 50 years
    2. Bony enlargement
    3. Bony tenderness
    4. Crepitation
    5. No palpable warmth
    6. Stiffness less than 30 minutes
  2. Lab criteria
    1. Erythrocyte Sedimentation Rate (ESR) <40 mm/h
    2. Rheumatoid Factor <1:40
    3. Synovial Fluid clear, viscous with white count <2000 per uL
  3. Imaging criteria
    1. Osteophytes present
  4. Interpretation
    1. Knee Pain and 3 clinical criteria
      1. Test Sensitivity: 95%
      2. Test Specificity: 69%
    2. Knee Pain and either lab criteria or 5 clinical criteria
      1. Test Sensitivity: 92%
      2. Test Specificity: 75%
    3. Knee Pain and osteophytes on xray and either lab criteria or 5 clinical criteria
      1. Test Sensitivity: 91%
      2. Test Specificity: 86%
  5. References
    1. Altman (1986) Arthritis Rheum 33:1039-49 [PubMed]
    2. Wu (2005) Semin Arthritis Rheum 35(3): 197-201 [PubMed]

VII. Labs

  1. Synovial Fluid examination
    1. Indication: Nontraumatic monarticular effusion
    2. Findings
      1. White Blood Cells <200 per mm3 (<2000 in a flare)
      2. Fluid color is clear and minimally turbid
  2. Rheumatologic evaluation
    1. See Osteoarthritis

VIII. Radiology: Knee XRay

  1. See Knee XRay in Osteoarthritis

IX. Management

  1. See Knee Osteoarthritis Management
  2. See Osteoarthritis

X. Management: Referral Indications

  1. Systemic Rheumatic disease
  2. Significant functional deterioration
  3. Septic Arthritis or Osteomyelitis
  4. Primary malignancy or metastases
  5. Safety concerns (e.g. recurrent falls)
  6. Pain and Disability refractory to conservative care

XI. References

  1. Coggon (2000) Arthritis Rheum 43:1443-9 [PubMed]
  2. (1997) Postgrad Med 102(5): 167-79 [PubMed]
  3. Ringdahl (2011) Am fam Physician 83(11): 1287-92 [PubMed]

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