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.
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.
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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Mustonen AO, Koskinen SK, Kiuru MJ. Acute knee trauma: analysis of multidetector computed tomography findings and comparison with conventional radiography. Acta Radiol. Dec 2005;46(8):866-74. [Medline].
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Newton EJ, Love J. Emergency department management of selected orthopedic injuries. Emerg Med Clin North Am. Aug 2007;25(3):763-93, ix-x. [Medline].
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Konstantakos EK, Dalstrom DJ, Nelles ME, Laughlin RT, Prayson MJ. Diagnosis and management of extremity compartment syndromes: an orthopaedic perspective. Am Surg. Dec 2007;73(12):1199-209. [Medline].
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