When do you use X-ray (X-radiation) or ultrasound of the leg?

When to Use X-ray or Ultrasound of the Leg

X-ray should be the first-line imaging modality for acute leg trauma, while ultrasound is preferred for soft tissue pathologies, dynamic assessments, and in radiation-sensitive populations. 1

Indications for X-ray of the Leg

Acute Trauma

• X-ray is the mainstay of initial imaging for acute leg trauma when Ottawa rules are positive (pain in specific areas with inability to bear weight) 1
• Standard radiographic protocols should include three views: anteroposterior, lateral, and mortise views 1
• Weight-bearing radiographs are preferred when possible, particularly for suspected fracture instability or Lisfranc injuries 1

Specific Clinical Scenarios Requiring X-ray

• Suspected fractures in patients with diabetes mellitus and neuropathy (Ottawa rules should not be applied) 1
• Suspected Charcot neuro-osteoarthropathy in diabetic patients (bilateral plain X-rays if possible) 1
• Patients on long-term bisphosphonate treatment (3-5 years) with thigh or groin pain 1
• Significant trauma such as motor vehicle accidents 1
• Penetrating trauma with concern for foreign bodies 1
• Suspected fractures in regions not covered by Ottawa rules (e.g., toes, metatarsal heads) 1

Indications for Ultrasound of the Leg

Primary Indications

• Evaluation of soft tissue pathologies (tendons, ligaments, muscles) 2
• Assessment of soft tissue foreign bodies 2
• Evaluation of peripheral nerves 2
• Conditions requiring dynamic imaging for diagnosis 2
• Examination of soft tissues adjacent to metal hardware 2
• Screening tool in radiation-sensitive patients (children, pregnant patients) 3

Secondary Indications (After Initial X-ray)

• Follow-up of known fractures 3
• Monitoring treatment of knee osteoarthritis (effusion, Baker's cyst) 4
• Assessment of bone density in patients with diabetic polyneuropathy 5
• Detection of osteophytes and erosions in inflammatory and non-inflammatory joint diseases 6

Clinical Decision Algorithm

1. For acute trauma:

   • Apply Ottawa rules if no exclusionary criteria exist 1
   • If Ottawa rules positive → X-ray 1
   • If Ottawa rules negative → no imaging needed 1

2. For suspected diabetic foot complications:

   • For suspected Charcot neuro-osteoarthropathy → X-ray first 1
   • If X-ray normal but clinical suspicion remains → MRI (if available) 1
   • If MRI unavailable or contraindicated → consider nuclear imaging, CT, or SPECT-CT 1

3. For soft tissue pathology:

   • Ultrasound as first-line imaging 2
   • For suspected foreign bodies → ultrasound preferred 2

Common Pitfalls and Caveats

• Ottawa rules should not be applied in patients with: penetrating trauma, pregnancy, skin wounds, altered sensorium, neurologic abnormalities, or underlying bone disease 1
• Normal X-rays do not exclude fractures in early Charcot neuro-osteoarthropathy; more advanced imaging may be needed 1
• Ultrasound has limitations in detecting deep bone abnormalities and is highly operator-dependent 2, 3
• Weight-bearing X-rays are preferred when possible as they may detect dynamic abnormalities not apparent on non-weight-bearing images 1
• For patients on long-term bisphosphonates with negative initial X-rays but persistent symptoms, MRI is recommended as the next step 1