Diferencia entre revisiones de «Acute knee injury»

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==Background==
==Background==
 
{{Knee ligaments}}
*Knee injuries are among the most common musculoskeletal complaints in the ED
*Mechanism of injury guides the differential (valgus stress, hyperextension, twisting, direct impact)


==Clinical Features==
==Clinical Features==
*Acute pain, swelling, inability to bear weight
*Immediate large effusion (<2 hours) suggests hemarthrosis → ACL tear, fracture, or peripheral meniscal tear
*Locked knee (inability to fully extend) → meniscal tear with displaced fragment
*Giving way/instability → ligamentous injury
*Patellar apprehension → patellar subluxation/dislocation


===Key Exam Maneuvers===
*Lachman test: Most sensitive for ACL tear (anterior tibial translation at 20-30° flexion)
*Posterior drawer: PCL integrity
*Valgus stress (30°): MCL integrity
*Varus stress (30°): LCL integrity
*McMurray test: Meniscal tear (joint line tenderness is more sensitive)


==Differential Diagnosis==
==Differential Diagnosis==
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==Evaluation==
==Evaluation==
 
{{Ottawa knee rules}}
{{Knee x-rays}}
*X-ray if Ottawa knee rules positive
**Lipohemarthrosis on lateral view (fat-fluid level in suprapatellar bursa) = occult fracture until proven otherwise
*MRI for suspected ligamentous or meniscal injury (usually outpatient)
*Aspiration if large tense effusion causing significant pain: send cell count, culture, crystals


==Management==
==Management==
 
*If x-rays positive (fracture): treat underlying condition, splint, orthopedic consult
*If x-rays negative or not indicated per [[Ottawa knee rules]]:
**Perform full ligamentous exam
**Stable exam: RICE (rest, ice, compression, elevation), crutches if unable to bear weight, NSAIDs
**Unstable exam or unable to evaluate (pain/swelling): knee immobilizer + RICE, weight-bearing as tolerated with crutches


==Disposition==
==Disposition==
 
*Most acute knee injuries are managed as outpatient with orthopedics referral
*'''ED consult/admit:''' [[Knee dislocation]] (check vascular status — popliteal artery injury), open fractures, [[septic arthritis]]
*Urgent orthopedics follow-up (within 1 week) for suspected ACL/meniscal tears, locked knee


==See Also==
==See Also==
 
*[[Knee diagnoses]]
 
*[[Knee dislocation]]
==External Links==
*[[Patellar dislocation]]
 
*[[ACL tear]]


==References==
==References==
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[[Category:Orthopedics]]

Revisión actual - 09:31 22 mar 2026

Background

Knee ligaments

Knee anatomy. Right knee shown from anterio-lateral view.
  • Anterior Cruciate Ligament
    • Limits anterior translation of tibia
    • 75% of all hemarthroses are caused by disruption of ACL
  • Posterior Cruciate Ligament
    • Limits posterior translation of tibia
    • Isolated injuries are rare
  • Medial Collateral Ligament
    • Provide restraint against valgus (outward) stress
  • Lateral Collateral Ligament
    • Provide restraint against varus (inward) stress
  • Knee injuries are among the most common musculoskeletal complaints in the ED
  • Mechanism of injury guides the differential (valgus stress, hyperextension, twisting, direct impact)

Clinical Features

  • Acute pain, swelling, inability to bear weight
  • Immediate large effusion (<2 hours) suggests hemarthrosis → ACL tear, fracture, or peripheral meniscal tear
  • Locked knee (inability to fully extend) → meniscal tear with displaced fragment
  • Giving way/instability → ligamentous injury
  • Patellar apprehension → patellar subluxation/dislocation

Key Exam Maneuvers

  • Lachman test: Most sensitive for ACL tear (anterior tibial translation at 20-30° flexion)
  • Posterior drawer: PCL integrity
  • Valgus stress (30°): MCL integrity
  • Varus stress (30°): LCL integrity
  • McMurray test: Meniscal tear (joint line tenderness is more sensitive)

Differential Diagnosis

Knee diagnoses

Acute knee injury

Nontraumatic/Subacute

Evaluation

Ottawa knee rules

Ottawa knee rules points of tenderness (image of left knee).

X-ray is only required in patients who have an acute injury and one or more of the following:

  • Age >55
  • Isolated tenderness of the patella
  • Tenderness at the fibular head
  • Inability flex to 90 degrees
  • Inability to walk 4 steps BOTH immediately after the injury and in the ED

Knee x-rays

  • Anteroposterior and lateral views
    • Consider sunrise if pain over patella
  • X-ray if Ottawa knee rules positive
    • Lipohemarthrosis on lateral view (fat-fluid level in suprapatellar bursa) = occult fracture until proven otherwise
  • MRI for suspected ligamentous or meniscal injury (usually outpatient)
  • Aspiration if large tense effusion causing significant pain: send cell count, culture, crystals

Management

  • If x-rays positive (fracture): treat underlying condition, splint, orthopedic consult
  • If x-rays negative or not indicated per Ottawa knee rules:
    • Perform full ligamentous exam
    • Stable exam: RICE (rest, ice, compression, elevation), crutches if unable to bear weight, NSAIDs
    • Unstable exam or unable to evaluate (pain/swelling): knee immobilizer + RICE, weight-bearing as tolerated with crutches

Disposition

  • Most acute knee injuries are managed as outpatient with orthopedics referral
  • ED consult/admit: Knee dislocation (check vascular status — popliteal artery injury), open fractures, septic arthritis
  • Urgent orthopedics follow-up (within 1 week) for suspected ACL/meniscal tears, locked knee

See Also

References

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