Knee Fracture

Patients with knee fractures may have a history of the following:

• Direct or indirect trauma with resultant pain and edema
• Patella fracture - Caused by a direct blow, such as a dashboard injury in a motor vehicle accident or a fall on a flexed knee, also caused by forceful quadriceps contraction while the knee is in the semiflexed position (eg, in a stumble or fall)
• Femoral condyle fractures due to axial loading with valgus or varus stress
• Tibial eminence fracture^[1] - Due to a direct blow to the proximal tibia with the knee flexed such as falling off a bicycle, also due to hyperextension with varus or valgus stress, such as in motor vehicle collisions or athletic accidents^[3] (Tibial eminence avulsion fractures occur most often in children aged 8-14 years but can also occur in the skeletally mature patient.^[1] )
• Tibial tubercle fracture - Usually occur with jumping activities such as basketball, diving, gymnastics, and football^[3] , more common in males than in females, more common in adolescents; infrequent in adults
• Tibial plateau fracture - Caused by axial loading with valgus or varus forces, such as in a fall from a height or collision with the bumper of a car, due to the impaction of the femoral condyle into the tibial plateau (In elderly persons and those with osteoporosis, tibial plateau fracture can occur with minor trauma. Patient is generally unable to bear weight. The lateral tibial plateau is fractured more frequently than the medial plateau.) 
   

  maging Studies

  Radiographs

  Obtain anteroposterior, lateral, and oblique radiographs of the knee.^[5] Four views have been shown to be superior to two views in detecting fractures.^[6]
  Oblique views are particularly useful in detecting subtle tibial plateau fractures (internal oblique profiles lateral plateau, external oblique profiles medial plateau). Oblique views also better identify obliquely oriented femoral condyle fractures.
  An axial (or sunrise) view of the patella is useful for detecting vertical patellar fractures, which frequently are missed and nondisplaced. Transverse fractures are most common, followed by comminuted and avulsion-fractures. Adding a sunrise view increases the negative predictive value of radiographs for ruling out patellar fracture.
  A fat-fluid level (lipohemarthrosis) may be identified on a lateral view of the knee; this finding indicates an intra-articular fracture.
  Radiographic evidence of ligamentous injury may be present:
  

  • An avulsion fracture at the site of attachment of the lateral capsular ligament on the lateral tibial condyle (Segond fracture) is a marker for anterior cruciate ligament rupture.^[7]
  • Cortical avulsion fracture of medial tibial plateau (uncommon) is associated with tears of the posterior cruciate ligament and medial meniscus.^[8]

  A patellar spur at the superior portion of the patella is associated with a ruptured quadriceps tendon.^[9]
  Use of the Ottawa rules for obtaining knee radiographs have proven sensitive for fracture and have reduced ED waiting times and costs.^[10] The rules include the following patient findings:^[11]
  

  • Age 55 years or older
  • Tenderness at head of fibula
  • Isolated tenderness of patella
  • Inability to flex knee to 90 degrees
  • Inability to bear weight (4 steps) immediately after injury and in ED

  CT scans and MRIs

  CT scans may be necessary to fully delineate the extent of tibial plateau fractures and other complex knee fractures.
  Compared to CT scans, plain radiography underestimates the amount of articular depression of tibial plateau fractures in most tibial regions. This is significant as the amount of tibial plateau depression is an indicator for operative repair.^[12]
  CT scans are also useful in severely injured patients when obtaining radiographs in all angles is difficult.
  MRIs also are useful and have the added benefit of depicting associated soft-tissue (eg, ligamentous, meniscal) injury.^[13]