Acute Knee Pain

Aka: Acute Knee Pain, Knee Pain, Anterior Knee Pain

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II. Precautions: Pitfalls

  1. Knee and leg Trauma with commonly missed secondary injuries
    1. Tibial Plateau Fracture (XRay may be non-diagnostic)
    2. Posterior Knee Dislocation
      1. Associated with limb-threatening neurovascular injury
    3. Maisonneuve Fracture
      1. Ankle Fracture with proximal fibular Fracture
  2. Consider referred pain (including Neuropathy or radiculopathy)
    1. Referred Hip Pain in children
      1. Slipped Capital Femoral Epiphysis
      2. Legg-Calve-Perthes Disease
    2. Lumbar Radiculopathy
    3. Sacroiliitis
    4. Proximal Musculoskeletal Injury (e.g. non-displaced Hip Fracture may present with Knee Pain)
  3. Consider malignancy
    1. Osteosarcoma
    2. Chondrosarcoma
    3. Ewing Sarcoma
  4. Consider Monoarthritis
    1. Arthrocentesis is key to exclude Septic Arthritis in Acute Monoarthritis presentations

III. Causes: Fractures and dislocations

  1. Knee Dislocation (Tibial Femoral Dislocation) or Knee Subluxation
  2. Tibial Plateau Fracture
  3. Patella Fracture
  4. Patella Dislocation
  5. Proximal Fibula Fracture

IV. Causes: Adult Knee Pain by frequency

  1. Most common causes of Acute Knee Pain
    1. Knee Osteoarthritis (most common cause in age >45 years, 30%)
    2. Patellofemoral Syndrome (most common cause in age <45 years, 25-40%)
    3. Acute Gouty Arthritis
    4. Trauma
      1. Non-specific strains, sprains and Contusions are most common knee Trauma diagnoses
      2. Anterior Cruciate Ligament Rupture (ACL Rupture, PCL Is less common)
      3. Medial Meniscus Tear (lateral meniscus is less common)
      4. Medial Collateral Ligament Tear of Knee (lateral collateral ligament tear is less common)
      5. Fracture (see above)
  2. Uncommon but important causes of Acute Knee Pain
    1. See Rheumatologic Conditions affecting the Knee
    2. Septic Arthritis (most critical to rule-out)
    3. Rheumatoid Arthritis
    4. Pseudogout
    5. Lyme Disease
    6. Parvovirus B19

V. Causes: Pain by location

  1. Anterior Knee Pain
    1. Patellar Subluxation or instability
    2. Osgood Schlatter or Tibial Apophysitis (adolescents)
    3. Sinding-Larsen-Johansson Syndrome or Distal Patellar Apophysitis (adolescents)
    4. Jumper's Knee (Patellar Tendonitis)
    5. Patellofemoral Syndrome
    6. Chondromalacia Patellae
    7. Prepatellar Bursitis
    8. Patellofemoral Osteoarthritis
    9. Hoffa Disease
      1. Infrapatella fat pad tenderness
    10. Osteochondritis Dissecans
    11. Patella Stress Fracture
  2. Posterior Knee Pain
    1. Baker's Cyst
    2. Posterior Cruciate Ligament Tear
    3. Tear of posterior aspect of meniscus
    4. Gastrocnemius Tear (typically medial gastrocnemius tendon)
    5. Hamstring injury or tenderness
      1. Semimembranosus Tendonitis (posteromedial)
      2. Semitendinosus Tendonitis (posterolateral)
  3. Medial Knee Pain
    1. Medial Collateral Ligament Tear
    2. Medial Meniscus Tear
    3. Osteoarthritis
    4. Pes Anserine Bursitis
    5. Plica Syndrome
    6. Slipped Capital Femoral Epiphysis (referred pain from hip in adolescents)
    7. Medial Tibial Plateau Fracture
    8. Osteochondral or subchondral insufficiency Fracture
  4. Lateral Knee Pain
    1. Iliotibial Band Syndrome (proximal tibial tenderness at IT Band insertion, Gerdy Tubercle)
    2. Lateral Meniscal Tear
    3. Knee Lateral Collateral Ligament Tear
    4. Lateral Tibial Plateau Fracture
    5. Osteochondral or subchondral insufficiency Fracture
    6. Proximal fibular Fracture (e.g. Maisonneuve Fracture)
  5. Diffuse, atraumatic Knee Pain
    1. See Monoarthritis or Polyarthritis
    2. See Rheumatologic Conditions affecting the Knee
    3. Osteoarthritis (especially over age 50 years old)
    4. Septic Joint
    5. Acute Gouty Arthritis
    6. Rheumatoid Arthritis

VI. Causes: Pain by age

  1. See Knee Injury Acute History for injury related causes
  2. Children
    1. Osteochondritis Dissecans
    2. Osgood Schlatter
    3. Jumper's Knee
    4. Patellar Subluxation
  3. Young Adults
    1. Patellofemoral Syndrome
    2. Plica Syndrome
    3. Pes Anserine Bursitis
    4. Rheumatoid Arthritis
    5. Reiter's Syndrome
    6. Septic knee
  4. Older Adults
    1. Knee Osteoarthritis
    2. Gout
    3. Pseudogout
    4. Baker's Cyst

VII. Evaluation

  1. See Knee Injury Acute History
  2. See Knee Examination
  3. Sports Related Trauma
    1. Downhill Skiing Related Knee Injury
    2. Running Injury
    3. Dancer Injury

VIII. Labs

  1. Knee Arthrocentesis Indications
    1. Acute Monoarthritis (exclude Septic Arthritis)

IX. Imaging

  1. See Knee Imaging
  2. Knee XRay Indications (first-line when indicated)
    1. See Ottawa Knee Rules
    2. Evaluate for acute Fracture or Osteoarthritis
  3. Knee Ultrasound Indications
    1. Dynamic tendon evaluation (e.g. Patellar tendon, quadriceps tendon)
    2. Collateral ligament evaluation
    3. Baker Cyst
    4. Neurovascular evaluation
    5. Knee Effusion evaluation (esp. to direct needle aspiration)
  4. Knee CT Indications
    1. Complex or occult Fracture suspected (e.g. Tibial Plateau Fracture, multi-part Patella Fracture)
    2. Posterior Knee Dislocation suspected (CT Angiogram of leg)
  5. Knee MRI Indications (not typically acute)
    1. Occult Fracture not visualized on XRay (CT may also be used)
    2. Suspected significant ligament injury(ACL, PCL, LCL, MCL) or meniscal tear requiring surgery
    3. Suspected Tendon Injury (quadriceps or Patellar tendon)
    4. Mechanical symptoms refractory to trial of physical therapy
    5. Osteochondral Fracture, Osteochondritis Dissecans or avascular necrosis suspected
    6. Malignancy
    7. Osteomyelitis

X. Management

  1. See specific conditions for management
  2. See Knee Osteoarthritis Management
  3. See Patellofemoral Syndrome

XI. References

  1. Spangler and Tollefson (2014) in Herbert 14(6): 9-11
  2. Bunt (2018) Am Fam Physician 98(9): 576-85 [PubMed]
  3. Calmbach (2003) Am Fam Physician 68(5):917-22 [PubMed]
  4. Jackson (2003) Ann Intern Med 139:575-88 [PubMed]
  5. Pendergraph (2026) Am Fam Physician 114(1): 49-62 [PubMed]

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