Imaging Guidelines for Knee and Hip Trauma

Initial Imaging Approach

The American College of Radiology recommends starting with plain radiographs as the initial imaging study for both knee and hip trauma, which is the standard of care and should be obtained before any advanced imaging 1, 2
Obtain knee radiographs if any Ottawa Knee Rule criteria are present, such as age >55 years, focal tenderness at the patella or fibular head, inability to bear weight for 4 steps immediately after injury, or inability to flex the knee to 90 degrees 1, 3
Obtain AP pelvis radiograph plus orthogonal views of the symptomatic hip as the initial imaging study for hip trauma 2

The American College of Radiology recommends a minimum of two views, anteroposterior (AP) and lateral views (with knee at 25-30 degrees flexion), for standard radiographic views of the knee 1, 3
Add patellofemoral view if patellar fracture or dislocation is suspected 1, 4
Consider cross-table lateral view with horizontal beam to visualize lipohemarthrosis, which indicates intra-articular fracture 4, 5
MRI without contrast is the next appropriate study for suspected occult fractures or internal derangement (meniscal/ligamentous injuries) when radiographs are negative but clinical suspicion remains high 1, 6

Include the pelvis view in initial imaging because patients with proximal femur fractures often have concomitant pelvic fractures (sacrum, pubic rami) 2
MRI is the next study of choice for suspected occult hip fracture when radiographs are normal or equivocal 2
MRI should be ordered promptly because delays in diagnosis increase complication rates, length of hospital stay, and short- and long-term mortality 2

CT may be considered if better characterization of suspected occult bony injuries is needed, but MRI remains superior for soft tissue evaluation 4, 6
Do not routinely use bone scan, ultrasound, MR arthrography, or MRA as initial or follow-up studies for acute knee trauma 1, 4, 6
Do not order MRI as the initial study, radiographs must come first unless there are specific contraindications 1, 7, 5, 6

The American College of Radiology suggests that inability to perform straight leg raise against gravity, palpable defect in the patella, severe focal patellar tenderness, large knee effusion, and inability to bear weight are indicative of patellar fracture, and immediate immobilization of the knee in full extension is recommended pending definitive imaging 8, 9
Focal bony tenderness directly over the patella meets Ottawa Knee Rule criteria and indicates the need for imaging, according to the American College of Radiology 8
A large hemarthrosis/effusion develops rapidly after patellar fracture, causing visible swelling and a tense, ballotable patella, as noted by the American College of Radiology 8
Inability to bear weight for 4 steps immediately after injury is an Ottawa Knee Rule criterion that mandates imaging, as stated by the American College of Radiology 8
Inability to flex the knee to 90 degrees due to pain suggests significant bony or soft tissue injury, according to the American College of Radiology 8

Non-weight-bearing status should be maintained until fracture is excluded or surgical consultation obtained, as recommended by the American College of Radiology 8

Arrange urgent transport for definitive imaging, including standard radiographs with AP, lateral, and patellofemoral views, as soon as feasible, as suggested by the American College of Radiology 9
Document clinical findings thoroughly, including specific Ottawa Knee Rule criteria present, to justify imaging when the patient reaches the appropriate facility, according to the American College of Radiology 8