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Approach to Acute Knee Pain

Apr 14, 2021 | Knee, Patient Tips

Knee Pain: History

  • Has there been an acute injury?
  • Is a joint effusion present?
  • Is there evidence of osteoarthritis?
  • Are there mechanical symptoms?
  • Is there evidence of systemic disease?
Urgent Considerations:
  • Open fractures
  • Knee dislocations
    • Combination ligament injuries
    • High velocity injury
    • Severe pain and/or swelling
  • Infection
Location of Contact:
  • Blow to the anterior aspect of knee
    • Blow to the hyperextended knee – ACL or posterolateral corner injury
    • Blow to the flexed knee – PCL injury
  • Blow to the lateral aspect of knee (valgus) – MCL injury
  • Blow to the medial aspect of knee (varus injury) – LCL and posterolateral corner injury
  • Non-contact twisting injuries
    • ACL
    • Meniscal tears
    • Patella dislocations
Areas of anaesthesia or strength deficiency:
  • This is relatively uncommon
  • Consider in severe injuries, for example common peroneal nerve dysfunction in varus knee injuries causing a foot drop
  • Compartment syndrome with a knee dislocation due to popliteal artery disruption
Swelling (effusion):
  • Acute effusion
  • ACL tear – usually within 30-60 minutes of injury
  • Meniscal tears – often slightly delayed
  • Chronic effusion
  • Consider underlying osteoarthritis, inflammatory arthritis
  • Infection or tumour less likely but worth considering

Knee Pain: Examination

Physical Examination:
  • Deformity – consider in patellofemoral dislocations, fracture or knee dislocation in high energy injury
  • Skin integrity – exclude open fractures, penetrating knee injury
  • Range of motion – often reduced with swelling and significant intra-articular injuries
    • Consider locked meniscal tear if a block to full extension
  • Ligamentous tests – these are often difficult to perform during the acute phase of injury, and a repeat test when pain and swelling has improved can be helpful
  • ACL – Lachman’s test, anterior drawer, pivot-shift test
  • PCL – posterior drawer
  • Valgus stress – MCL injury
  • Varus stress – LCL or posterolateral corner injury
  • Meniscal injury
    • Patients often have medial or lateral joint line tenderness in association with the side of meniscal tear
    • Can try McMurray’s test – varus or valgus stress with compression and rotation of the medial or lateral side of the knee. Useful test, but can be insensitive.
    • Note – in the case of a locked bucket handle tear of meniscus, full extension cannot usually be achieved. Do not force the knee in to full extension as it can complete / extend the meniscal tear. Suggest MRI scan and prompt referral.

Knee Pain: Imaging


These are often underutilised and still a very useful tool. If the patient is able, request weight bearing films as they give much more information regarding potential degenerative joint disease.

Ottawa knee rules (if patient scores one or more of):

  • Age > 55 years
  • Isolated tenderness of patella (no bone tenderness of knee other than patella)
  • Tenderness of head of fibula
  • Inability to flex to 90 degrees
  • Inability to weight bear both immediately and in the emergency department for 4 steps
MRI scans
  • Younger patients where ligamentous, meniscal or chondral pathology is expected
  • Acute effusions / swelling soon after injury
  • Negative X-rays with persistence of pain
CT scans
  • CT scans can be useful when investigating potential fractures to assess displacement, or for pre-operative planning (e.g. tibial plateau fractures or femoral condyle fractures)
Bone scans
  • Bone scans can help in identifying occult stress fractures, peri-prosthetic infections, tumours
  • Ultrasound imaging around the knee is being used less and less. It has poor ability to diagnose intra-articular pathology such as ACL or other ligament tears, meniscal tears or intra-articular fracture. Ultrasound can be useful when looking at tendon injury (patella tendon or quads tendon), and is also very useful to anatomically guide injections into or around the knee

Knee Pain: Other Tests


This can be utilised if a traumatic effusion is present to reduce the pressure within the knee and increase patient comfort, however commonly nowadays patients are instructed to rest, ice and elevate to achieve a similar result.

Aspiration can be very useful to diagnose:

  • Gout
  •  Pseudogout
  •  Intra-articular sepsis

This is uncommonly utilised as a purely diagnostic tool, since imaging modalities such as MRI are highly sensitive for the diagnosis of intra-articular injury.

Knee Pain: Differential Diagnosis

It can be helpful to group patients by age to address the most common causes of their knee pain.

  • Patellofemoral joint injuries
  • Osteochondritis dissecans
  • Infection – septic arthritis or osteomyelitis
  • Hip pathology – slipped femoral epiphysis (SCFE/SUFE), hip dysplasia, hip infection
  • Fracture
  • ACL, meniscal, or other ligamentous injury
Active adolescent / adult
  • ACL rupture
  • Meniscal injury
  • Other ligament injury
    • MCL, PCL, LCL, posterolateral corner injury
    • Knee dislocation / multi-ligament knee injury
  • Patellofemoral injury
    • Patella dislocation
    • Patella tendon / quadriceps tendon rupture
  • Tendinopathy
    • Patella tendinitis

If you have a patient with a knee problem, please use this form to refer them to Dr Ross Radic.