How to Rule Out Fractures of the Knee and Hip
Start with plain radiographs as the initial imaging study for both knee and hip trauma—this is the standard of care and should be obtained before any advanced imaging. 1
Knee Fracture Evaluation
Initial Imaging Approach
Obtain knee radiographs if any Ottawa Knee Rule criteria are present: 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, 2
Bypass clinical decision rules and obtain radiographs immediately if the patient has: gross deformity, palpable mass, penetrating injury, prosthetic hardware, altered mental status (head injury, intoxication, dementia), neuropathy (paraplegia, diabetes), or unreliable examination 1, 2
Standard Radiographic Views
Minimum two views required: anteroposterior (AP) and lateral views (with knee at 25-30 degrees flexion) 1, 2
Add patellofemoral view if patellar fracture or dislocation is suspected 1
Consider cross-table lateral view with horizontal beam to visualize lipohemarthrosis, which indicates intra-articular fracture 1
If Radiographs Are Negative But Clinical Suspicion Remains High
MRI without contrast is the next appropriate study for suspected occult fractures or internal derangement (meniscal/ligamentous injuries), as it has superior sensitivity for bone marrow contusions, occult fractures, and soft tissue injuries 1, 2
CT may be considered if you specifically need better characterization of suspected occult bony injuries—CT shows 100% sensitivity for tibial plateau fractures versus 83% for radiographs—but MRI remains superior for soft tissue evaluation 1, 2
Do NOT routinely use bone scan, ultrasound, MR arthrography, or MRA as initial or follow-up studies for acute knee trauma 1
Hip Fracture Evaluation
Initial Imaging Approach
Obtain AP pelvis radiograph plus orthogonal views of the symptomatic hip (AP hip with 15 degrees internal rotation and cross-table lateral view) as the initial imaging study 1
Include the pelvis view because patients with proximal femur fractures often have concomitant pelvic fractures (sacrum, pubic rami), and it allows comparison to the contralateral side 1
Clinical Presentation Pearls
Classic presentation: inability to bear weight, groin pain, shortened and externally rotated leg 3, 4
Occult presentation warning: Some patients with hip fractures present with only vague pain in buttocks, knees, thighs, groin, or back, may still be able to walk, and have normal initial radiographs—maintain high suspicion in patients >65 years with nonspecific leg discomfort and difficulty bearing weight 4
If Radiographs Are Negative But Clinical Suspicion Remains High
MRI is the next study of choice for suspected occult hip fracture when radiographs are normal or equivocal 1, 3, 4
MRI should be ordered promptly because delays in diagnosis increase complication rates, length of hospital stay, and short- and long-term mortality 1
Critical Pitfalls to Avoid
Do not miss ipsilateral knee injuries in hip trauma patients: 25% of patients with hip fracture/dislocation have concomitant knee injuries on the same side, and 85% have knee symptoms—always examine the ipsilateral knee thoroughly 5
Do not assume ability to bear weight rules out fracture: Some patients with occult hip fractures can still walk, and negative radiographs do not exclude significant injury 2, 4
Do not skip advanced imaging when clinical suspicion is high: If the patient cannot bear weight after 5-7 days, has significant joint effusion, mechanical symptoms, or joint instability despite negative radiographs, proceed to MRI 2
Do not order MRI as the initial study: Radiographs must come first unless there are specific contraindications—MRI is not routinely used for initial evaluation of acute trauma 1