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the acutely injured knee in ED


  • be aware that a painful knee may be referred pain from an injured hip - see hip pain, or from L5 and S1 nerve roots which may be impinged as part of sciatica - see back pain in the ED
  • knee injuries can be divided into:
    • high energy
      • eg. motor vehicle accident, falls from a height
      • warrant emergent assessment to exclude possible knee dislocation, vascular injury and fractures
    • low energy
      • non-contact sports injury
      • slip and fall
      • very unlikely to have a knee dislocation and vascular emergency, but ACL, meniscal injuries and patellar dislocations are common, while those with osteoporosis are at risk of tibial plateau fractures
    • repetitive / over-use injury
      • Osgood-Schlatter's, patello-femoral pain, bursitis, etc.
  • an important time critical red flag is the possibility of a knee dislocation having occurred (not a patellar dislocation), as this requires urgent investigation to exclude a possible vascular injury to the popliteal vessels.
    • knee dislocation is uncommon and mainly occurs with high energy injuries.
    • most dislocations are clinically evident and require urgent reduction as they may be limb threatening due to vascular injury - see dislocation of the knee joint
    • some spontaneously reduce but there is still potential vascular injury which needs emergent assessment.
    • suggestive features of a spontaneously reduced knee dislocation include:
      • presence of a significant posterolateral corner injury which is suggested by either:
        • fibular styloid fracture on lateral Xray (“arcuate sign”) is pathognomic of posterolateral corner injury and note that this is a different fracture to a fibular head fracture
        • Segond avulsion fracture from the tibial condyle on AP Xray is associated with ACL injury and posterolateral corner injury
        • Medial Segond avulsion fracture from the medial tibial condyle on AP Xray is associated with PCL injury and posterolateral corner injury
        • External Rotation Recurvatum Test:
          • The great toes are held by the examiner as both legs are raised simultaneously. A positive test results in hyperextension, external rotation of the tibia, and apparent tibia vara of the affected limb.
        • the Dial Test:
          • This test is performed with the knee flexed at 30deg and 90deg. The patient may be supine or prone.
          • The thighs are stabilized by an assistant or a strap, while the lower legs are synchronously externally rotated.
          • The amount of external rotation at the tibial tuberosity is compared with the other side. If prone, the external rotation may be measured by the thigh-foot angle. An increase of 10 to 15 degrees is considered a positive test and suggests a significant posterolateral corner injury.

ED Mx of the acutely injured knee

  • is the knee obviously dislocated - this is a serious injury with vascular implications - URGENT Mx as per dislocation of the knee joint.
  • is the patella obviously dislocated
    • older children and young adults frequently present to ED via ambulance with a dislocated patella which is usually clinically obvious, and can be rapidly reduced whilst still on the ambulance trolley while they are sucking on their Penthrane inhaler.
    • plain XRay with skyline views post-reduction to exclude osteochondral fracture
    • Zimmer splint, crutches with follow up by LMO and physiotherapist for vastus medialis exercises, etc.
  • take history, examination as per usual for trauma and for knee injury (see below for DDx, mechanisms, etc)
  • possible open / penetrating injury
    • there should be a low threshold of suspicion for penetrating injuries with wounds near the knee, failure to appropriately manage these may lead to septic arthritis
    • air in the joint on plain Xray makes it highly likely but has a low sensitivity
    • if suspicion, urgent consult with ortho team for consideration of iv antibiotics and exploration +/- washout in theatre that day.
  • acutely locked knee
    • suggests osteochondral fragment or meniscal tear
    • plain Xray and consult with ortho team.
  • acute onset effusion (ie. presumed haemarthrosis) present or high energy injury:
    • if coagulopathy such as Haemophilia, Mx accordingly
    • plain Xrays to exclude fracture, in particular look for:
      • features that may suggest knee dislocation as these patients should be considered for urgent vascular assessment
      • tibial plateau fracture as these require admission +/- CT scan
      • growth plate injuries in children (ie. Salter-Harris fracture distal femur)
      • avulsed fragments which need early surgery
        • children tend to have avulsed tibial spines instead of ACL rupture, and this is particularly common following bicycle accidents
    • no fracture on Xray but haemarthrosis present:
      • if lipohaemarthrosis present
        • this is suggestive of an underlying fracture such as a tibial plateau fracture
        • CT or MRI scan in acute phase
      • if no lipohaemarthrosis
        • it is probable that ACL or meniscal injury is the cause
        • 50% of young adult sports injuries causing haemarthrosis have ACL injury
        • 40-60% ACL injuries are associated with meniscal injuries but only 40% of these meniscal injuries warrant surgery
        • 50% ACL injuries have associated collateral ligt injuries
      • there is usually no need for performing ACL/meniscal diagnostic manouvres in the acute trauma setting, however, if there are concerns there may have been a dislocation of the knee, consider diagnostic manouvres to exclude this.
      • Zimmer splint, weight bear as tolerated, early physiotherapy review, refer for early MRI (within 1 month) and outpatient orthopaedic clinic (ACL injuries do not need early orthopaedic assessment and a 4-6 month time frame may be acceptable)
    • joint aspiration using a 18-20G needle for large traumatic effusions to reduce pressure and pain can be considered but is controversial as the risk of causing a septic arthritis and the likely reaccumulation of fluid must be weighed against the benefits
  • no evidence of haemarthrosis and not a high energy injury:
    • clinical assessment
    • exclude referred pain as cause (eg. sciatica, hip pain - don't miss a slipped femoral epiphysis!)
    • plain Xray as per Ottawa knee rules (see below)
    • be aware that haemarthoses due to ACL/PCL/meniscal injuries may take 24 hours to develop, consider diagnostic manouvres as indicated (eg. anterior drawer test, Lachman and pivot shift test for ACL, and, posterior drawer test and posterior sag test for PCL).
    • outpatient review by LMO / physiotherapist
  • be aware that plain Xrays may miss osteochondral fractures, particularly in younger patients, and tibial plateau fractures can be difficult to see - consider CT scan in older patients.

who should have plain Xrays?

Ottawa knee rules

  • 99% sensitive for radiologic apparent fractures
  • Xray those who have acute injury with knee pain and EITHER:
    • age > 55 years
    • isolated tenderness of the patella (and no other bony tenderness of the knee)
    • tenderness at the head of the fibula
    • inability to flex the knee 90deg
    • inability to weight bear immediately and in the ED for four steps regardless of limp (ie. unable to transfer weight onto that knee at least 2 times)

DDx of knee injuries

  • referred pain from hip
    • eg. Slipped femoral epiphysis - check for hip pain on int/ext. rotation of hip.
  • patellar dislocation
    • may have been spontaneously reduced prior to presentation
    • +/- osteochondral avulsion fragment - do skyline views post-reduction.
  • over-use injuries:
    • patello-femoral pain
    • Osgood-Schlatter's osteochonditis of the tibial tuberosity in adolescents\
  • medial meniscal injury
    • +/- locked knee
    • tenderness at medial joint line and often anterior-medially
    • pain on hyperextension
  • lateral meniscal injury
  • anterior cruciate injury (ACL)
    • mainly in sports active 14-29 year olds; women at higher risk than men.
    • 10% are isolated ACL injuries
    • ACL composed of two bundles: anteromed and posterolat
    • immediate swelling of the knee after injury with no evidence of fracture on XR is highly suggestive of ACL injury
    • possible Xray signs:
      • Segond fracture
      • tibial spine avulsion fracture
    • MRI is only 85% sensitive
    • best non-invasive test may be a Lachmann test performed once acute swelling and pain have settled (eg. day 10 or later)
      • better than anterior drawer test or pivot-shift test
  • posterior cruciate injury (PCL)
    • +/- medial Segond fracture
  • collateral ligament strain or rupture
    • tenderness at insertion of ligament rather than at joint line as occurs with meniscal injuries
    • instability on testing if ruptured
  • posterolateral corner injury
    • isolated injuries said to account for 1.6% acute knee ligament injuries
    • mechanism: blow to the anteromedial knee, hyperextension, or varus forces (sports, falls or motor vehicle accidents)
    • +/- fibular styloid fracture +/- Segond fracture +/- medial Segond fracture
    • +/- ACL or PCL injury
    • +/- common peroneal nerve injury
    • +/- knee dislocation - major risk to popliteal vessels
  • fractures
    • fibular head fracture
    • fibular neck fracture +/- ankle injury
    • intrarticular femoral condyle fracture - intercondylar or condylar
    • supracondylar femoral fractures
    • growth plate injuries distal femoral physeus
    • patellar fractures
    • tibial plateau fracture
      • fall from height or lateral or medial blunt trauma to knee (eg. pedestrians, cyclists hit by car bumper)
      • can be very subtle and easily missed - consider CT or MRI scan, esp. if lipohaemarthrosis or unable to walk with normal Xray
      • consider CT angioangram to assess popliteal artery in major injuries
      • lateral condyle is much more commonly fractured than medial, and may be accompanied by ACL and MCL injuries
      • Schatzker system of classification
      • > 5 degrees angulation or depressed fragments of greater than 2 mm will generally require ORIF
      • ensure non-weight bear and early orthopaedics!
      • 8% of all fractures in the elderly and may occur with even minimal trauma
    • proximal tibial fractures
      • risk of delayed (> 6 months) angulation in paediatric age group - need longer term follow up
  • penetrating injuries
    • may be occult - eg. sewing needles may become embedded in joint space without historical account
  • traumatic bursitis
  • ruptured Baker's cyst
  • gonyalgia paresthetica
    • pain from the infrapatellar branch of saphenous nerve
    • causes numbness and pain on inframedial aspect of knee and is often bilateral due to compression of the nerve by the knees

mechanism of injury


  • tibial plateau fracture if side impact

front seat motor vehicle dashboard injury

  • penetrating anterior knee injury / quads tendon injury
  • patellar fracture
  • PCL injury if dashboard hits upper tibia


  • ACL:
    • non-contact deceleration injury, or hyperextension injury
    • rarely can continue playing
  • PCL:
    • direct blow to upper tibia with knee flexed (dashboard, bikes, baseball runner colliding with catcher, fall onto flexed knee with ankle in plantarflexion), or in association with MCL or LCL injury
    • may be able to return to play
  • MCL - valgus stress injury
  • LCL - varus stress injury
  • meniscal tear - twisting the knee with foot locked on the ground
  • Segond fracture (avulsion fracture of lateral tibial plateau):
    • knee flexion with excessive internal rotation and varus stress
  • patellofemoral pain - over-use injury, particularly women under 45 years age
  • Osgood-Schlatter's - over-use injury, particularly adolescent males
  • iliotibial band syndrome - excessive running, particularly on uneven ground or with worn shoes, or with varus alignment of the knee

clinical findings


  • rapid swelling usually within 2-4 hours of injury
  • ACL injury is the most common cause
  • meniscal injury
  • collateral ligt injury
  • osteochondral fracture (fracture is particularly likely if there is a lipohaemarthrosis on lateral Xray)
  • patellar dislocation
  • Haemophilia and other blood clotting disorders

synovial effusion

medial joint line tenderness

  • medial meniscal tear - usually pain increases on extension and may cause knee to lock
  • 2nd and 3rd degree medial collateral ligt injuries - usually pain or laxity on stressing
  • medial tibial plateau fracture
  • osteoarthritis

tenderness below medial joint line

  • anserine bursitis (located 6cm below the joint line at insertion of vastus medialis muscle)
  • low grade medial collateral ligt injuries
  • busritis of the bursa associated with medial collateral ligt (pain not increased on stressing ligt)

anterior knee pain

  • quadriceps injury
  • patello-femoral injury
  • medial meniscal tear (antero-medial pain)
  • prepatellar bursitis (usually obvious swelling “housemaid's knee”)
  • patellar tendinopathy (eg. jumpers with pain at inferior pole patella)
  • Osgood-Schlatter's - localised to tibial tuberosity

lateral joint line knee pain

  • lateral meniscal injury
  • lateral collateral ligt injury
  • osteoarthritis

lateral femoral condyle pain

  • iliotibial band syndrome

lateral knee pain below the joint line

  • tibial plateau fracture
  • fibular head/neck fractures
  • postero-lateral corner injury

popliteal pain

  • may accompany any of the above patterns if associated with an effusion
  • most commonly due to a large effusion as flexion forces fluid posteriorly, over time if pressure persists, a Baker's cyst may form
  • ruptured Baker's cyst

+ve Lachman’s test

  • an adaption of the more commonly known Anterior Draw Test and assesses the integrity of the ACL
  • is performed in 20°-30° of knee flexion rather than 80° which helps to isolate the effect of the ACL
  • patient needs to be able to relax completely which is often not possible in an acute injury so the test may need to be repeated once the initial swelling and pain has subsided
  • one hand of the examiner secures and stabilizes the distal femur while the other hand secures and stabilizes the proximal tibia
  • a gentle anterior force is then applied to the proximal tibia
  • anterior movement should be minimal, usually 0-3 mm with a hard, firm stop or end point provided by the intact ACL

+ve McMurry’s test

  • a test for damage/tears to the meniscus
  • performed with the patient in supine position with the knee to be tested fully flexed. The sole of the foot is held with one hand and the medial or lateral aspect of the tibio-fibular joint is palpated with the other depending of whether the medial or lateral meniscus is being tested.
  • to test the medial meniscus, the postero-medial aspect of the knee is palpated while extending the knee and externally rotating the tibia. A valgus (outward angulation of the distal tibia) stress is also applied
  • to test the lateral meniscus, the postero-lateral joint line is palpated while extending the knee, internally rotating the tibia and applying a varus (inward angulation of the distal tibia) stress.
  • in either case a positive test occurs when either pain is felt by the patient or if a ‘click’ is felt by the subject or examiner

posterior draw test

  • assesses the integrity of the posterior collateral ligament (PCL)
  • The knee is flexed to approximately 80° to relax the hamstrings.
  • with the foot in neutral rotation and stabilized, a firm but gentle posterior force is applied to the proximal tibia.
  • in a patient with a PCL rupture, a posterior force results in posterior subluxation of the tibia on the femur.

30° Valgus stress test

  • assesses medial stability of the knee
  • the medial collateral ligament (MCL) is one of the most commonly injured ligaments in the knee. It is composed of several components including the superficial medial collateral ligament, the deep medial collateral ligament and the posterior oblique ligament. The proximal division of the superficial medial collateral ligament is important to valgus stability, while the distal division of the superficial medial collateral ligament is important for external rotation stability.
  • the valgus stress test at 30° determines if there is a medial knee injury present and is primarily testing the superficial medial collateral ligament which is the largest and most important structure on the medial aspect of the knee.
  • the knee is flexed between 20° - 30° and the examiner’s fingers are placed directly over the joint line. A valgus stress is then applied to the knee by pushing the patient's foot or ankle laterally. The knee joint should be assessed for medial gapping/ joint opening.
trauma_knee.txt · Last modified: 2015/12/31 04:42 by

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