Clinical CT for August 2016
by Adam Blumenberg MD
A 75 year-old woman with a history of left femur ORIF and hypertension was “clipped” on the left knee by a turning car as she was crossing the street. She is dressed in religious garb with a head scarf and long sleeves. She has been unable to bear weight since, and has a slowly expanding knee effusion. Distal pulses are intact. A CT of her knee just superior to the patella is shown.
- Please describe this image.This is a transverse CT slice through the distal femur. There is a circular radio-dense structure in the marrow space, likely an intramedullary nail. There is also an effusion in the suprapatellar bursa (continuous with joint space) with a fluid-fluid level.
- What is the significance of the radiographic findings? How does the patient’s history influence your interpretation of this image?The patient is an elderly woman with a history of femur fracture and her clothing lowers her exposure to sunlight thereby increasing her risk of hypovitaminosis D and subsequent risk of osteoporosis. The patient’s risk factors for fracture include female sex, elderly, low exposure to vitamin D, prior fracture with an implanted device, and mechanism (struck by a vehicle). She has a traumatic knee effusion and is unable to bear weight. The layered joint effusion may represent either a hemarthrosis with the cellular components settling away from the serum, much like hematocrit effect. The fluid-fluid level may also indicate a lipohemarthrosis. The presence of fat in the joint space would imply disruption of bony cortex because the bone marrow would be the source of fat.
- What similar radiographic finding is highly specific for fracture?A double fluid-fluid level would imply presence of fat, serum, and cellular layers and is highly specific for fracture.
- What is the next step in management?Assess the density of each fluid layer in Hounsfield units. Then, closely scrutinize the entirety of the CT image for a fracture.
- What is the patient’s disposition?Further review of the images reveals a non-displaced tibial plateau fracture. Place the patient in knee immobilization with non-weight bearing status and have the patient follow up closely with orthopedics as an outpatient.
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