Knee injury (assessment of)

Assessment of knee injury

A detailed history can help narrow down the nature of the injury, including:

• weight bearing - was the limb weight bearing at the time of injury?
  
  
• stress on the joint - was there a varus or valgus stress or rotational force acting through the knee at the time of injury?
  • non-contact twisting injuries
    • twisting injury of extended knee
      • causes include a patellar subluxation or dislocation
        • particularly the case in patients with patella alta where the patella is abnormally high in relation to the femu
          • in this situation the patella is not well engaged in the trochlear groove and is at an increased risk for injury
    • twisting injury of flexed knee
      • causes include a meniscus or ACL tear
        
        
• impact - was there impact with the ground, an opponent or other structure?
  • for example most anterior cruciate ligament tears are non-contact twisting injuries
  • enquire about location of contact:
    • blow to the anterior aspect of knee
      • blow to the hyperextended knee:
        • causes include anterior cruciate ligament (ACL) or posterolateral corner injuries
      • blow to flexed knee (such as in a dashboard injury):
        • causes include posterior cruciate ligament (PCL) injury
    • blow to the lateral aspect of knee (valgus injury)
      • would result in sudden stretching of medial-sided knee structures
        • superficial medial collateral ligament most at risk for injury
    • blow to the medial aspect of knee (varus injury)
      
      • increases stress on the outside of the knee
        • possible posterolateral corner injury
• site of knee pain
  • if medial knee pain
    • if an acute knee injury then consider:
      • medial meniscus injury, articular cartilage injury of medial compartment, or medial collateral ligament (MCL) injury
    • if a chronic injury then causes include:
      • medial compartment arthritis, pes anserine bursitis, and a degenerative medial meniscal tear
  • if lateral knee pain
    • if an acute knee injury then causes include:
      • lateral meniscus tear, lateral compartment articular cartilage injury, or posterolateral corner injury (to include the fibular collateral ligament)
    • if a chronic knee injury then causes include:
      • lateral compartment arthritis, biceps bursitis, and a degenerative lateral meniscus tear
  • if anterior knee pain
    • if an acute injury then causes include:
      • patellar subluxation or dislocation and patellar or trochlear groove chondral injuries
      • patellar tendon rupture should be considered if patient aged of 30 to 45 years old
      • quadriceps rupture is more likely in the age range of 45 to 60 years old
    • if chronic injury then causes include:
      • patellofemoral joint chondromalacia (arthritis) and patellar tendonitis
  • if posterior knee pain
    • if acute injury then causes include:
      • posterior capsule injuries, posterior cruciate ligament injury, or posterior horn meniscal tears
    • if chronic injury then causes include:
      • posterior horn meniscal tears or a Baker's (popliteal) cyst
        
        
• sound and feeling - did the patient feel or hear a 'pop' or 'shift' in the knee?
  • a 'pop' classically occurs with rupture of the anterior cruciate ligament (ACL)
  • a'shift' can occur with ACL rupture or patella dislocation
    
    
• postinjury details - a history of collapse, inability to continue play, or inability to weight bear following the injury raises suspicion of fracture or high grade ligament injury
  
  
• knee swelling - was there swelling and how quickly did this occur?
  • an effusion that develops rapidly within a few hours, most likely indicates an haemarthrosis
    • source of bleeding may be from vessels in a ruptured cruciate ligament or fracture of bone within the joint capsule. In the latter scenario, a lipo-haemarthrosis may be seen on a supine lateral plain radiograph
  • an effusion developing more slowly or the following day is more likely to be a traumatic synovitis associated with meniscal tears and chondral pathology
  • assessment based on age of patient and chronicity of effusion:
    • if an acute effusion
      • if traumatic injury in young patient then most commonly is an anterior cruciate ligament tear, followed by meniscal tears and patellar subluxations
      • if traumatic injury in older patients then the causes include meniscal tears, tibial plateau fractures, aggravations of underlying arthritic processes, or ligament injuries
    • if a chronic effusion
      • in chronic effusions (including those with obvious trauma present) causes include an underlying osteoarthritic process, inflammatory process, infection, or tumour
      • joint warmth or redness may be indicative of an infection or an inflammatory process
        • aspiration of the affected knee may be indicated to evaluate the synovial fluid - may evaluate an effusion in an acute knee to confirm haemarthrosis
      • bloody effusions are usually more consistent with trauma or tumour (pigmented villonodular synovitis)
      • Baker's cyst may indicate swelling elsewhere within the joint and that this fluid has leaked out posteriorly in the knee in the space between the direct arm of the semimembranosus tendon and the medial head of the gastrocnemius tendon
        
        
• clicking, locking and instability
  • painful clicking can occur with meniscal tears or chondral pathology
  • true locking indicates a mechanical block to extension by a displaced meniscal fragment or loose body
    • a meniscal tear will often cause loss of the end range of movement
    • a loose body can cause locking in variable degrees of flexion
  • a knee that functions well in the anterior-posterior axis but gives way with rotational movements (often painlessly) suggests ACL deficiency
  • a knee that feels unstable descending stairs or walking downhill suggests posterior cruciate ligament (PCL) deficiency or patellofemoral pathology
  • note that 'giving way' can also occur secondary to pain related muscle inhibition
    
    
• any previous injuries?
  • may have symptoms secondary to either a previous injury or previous surgery
  • need to ascertain if any changes in the swelling or motion, when compared to the contralateral normal knee, are acute or chronic
  • if previous ligament injuries, with or without surgery then there is an increased risk for re-injuring structures and causing other secondary injuries
  • if previous medniscal repair then high risk of developing arthritis of the same compartment - could lead to pain and swelling with activities

Physical Examination

This can be difficult in the acute setting and may need to be repeated several days after the injury.

Examination involves assessment of weight bearing, inspection, palpation for tenderness and effusion, assessment of range of movement and muscle strength, and special tests to exclude specific injury including:

• ACL rupture - Lachman and pivot shift tests
  
  
• PCL injury - posterior draw test and posterior sag
  
  
• collateral ligament injury - varus and valgus stress tests
  
  
• meniscal injury - McMurray test
  
  
• patella dislocation - patella apprehension test

Investigation

In the acute setting, examination of the knee is difficult and history and investigations are the most useful means of ascertaining a diagnosis.

A plain radiograph series of the knee consists of four views:

• weight bearing anterior-posterior, lateral, intercondylar and patellofemoral, and is the ideal first investigation in the setting of an acute knee injury
• look for fractures of the femoral condyles, tibial plateau and avulsion injuries
• in the hyper-acute setting, only two views are generally obtained - anterior posterior and lateral
• according to the Ottawa knee rules a knee x-ray series is indicated for people who have sustained a knee injury and demonstrate any of the following:
  • age 55 years or older
  • isolated tenderness of patella (no bone tenderness of knee other than patella)
  • tenderness of head of fibula
  • inability to flex to 90°
  • inability to bear weight, both immediately and in the emergency department, for 4 steps
• in some cases a computerised tomography (CT) scan may helpful, particularly to detect occult or intra-articular fractures before surgery

MRI - the best investigation to assess ligamentous injuries; are useful for determining a diagnosis when there is doubt

• are particularly useful for diagnosis of acute injuries, where bleeding and oedema are noted by increased signal uptake on the MRI scans

Aspiration - may be used to discriminate a haemarthrosis from synovitis

CT scans

• most commonly used to assess for significant bony pathology - best investigation for fractures if X-rays are equivocal
  • in investigation of acute knee injury includes assessment of fractures, tumours, and post-surgical assessments where an MRI may not be possible (patients with pacemakers, significant metal around the knee)

Reference:

• 1) Scotney B. Sports knee injuries - assessment and management. Aust Fam Physician. 2010 Jan-Feb;39(1-2):30-4. Sudden Onset Knee Pain Common Injuries