Knee Fracture Workup

Updated: Oct 17, 2015
  • Author: Mark Steele, MD; Chief Editor: Trevor John Mills, MD, MPH  more...
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Workup

Imaging 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.

Computed tomography can be a useful diagnostic modality in preoperative planning for tibial plateau fractures. Tibial plateau fracture maps in one study showed recurrent patterns of fracture lines, revealing 4 major fracture characteristics: the lateral split fragment, found in 75%; the posteromedial fragment, seen in 43%; the tibial tubercle fragment, seen in 16%; and a zone of comminution that included the tibial spine and frequently extended to the lateral condyle, seen in 28%. [12]

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. [13]

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. [14]

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Procedures

Arthrocentesis may be of diagnostic and therapeutic benefit for tense effusions. Presence of blood and glistening fat globules indicates lipohemarthrosis, which is pathognomonic for intraarticular knee fracture.

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