What to Write on a Knee X-ray Requisition
The clinical indication on a knee X-ray order should include the mechanism of injury or symptom onset, specific clinical findings (focal tenderness, effusion, inability to bear weight), and the suspected diagnosis or clinical question you need answered 1.
Essential Components for the Requisition
For Acute Trauma/Injury
When ordering knee radiographs for acute trauma, your clinical indication should document:
- Mechanism of injury: Specify "fall," "acute twisting injury," "direct blow," or "motor vehicle accident" 1
- Key clinical findings that justify imaging per Ottawa or Pittsburgh rules 1:
- Focal tenderness (specify location: patella, fibular head, joint line)
- Joint effusion (if palpable)
- Inability to bear weight or walk 4 steps
- Limited range of motion (inability to flex to 90°)
- Patient age if >55 years (Ottawa) or >50 or <12 years (Pittsburgh)
- Suspected pathology: "rule out fracture," "evaluate for patellar dislocation," "assess for tibial plateau fracture"
Example: "45yo male, fall on flexed knee 2 hours ago, focal tenderness over lateral joint line, unable to bear weight, rule out fracture"
For Chronic Knee Pain
For non-traumatic knee pain, document 2:
- Duration of symptoms: "chronic knee pain x 6 months"
- Primary symptom: pain, mechanical symptoms (locking, catching), instability
- Clinical findings: effusion, crepitus, limited motion
- Suspected diagnosis: "evaluate for osteoarthritis," "assess for loose bodies," "rule out osteochondritis dissecans"
Example: "62yo female, progressive medial knee pain x 8 months, crepitus on exam, evaluate for osteoarthritis"
Why This Matters
The ACR Appropriateness Criteria emphasize that radiographs should be the initial imaging modality when Ottawa or Pittsburgh rule criteria are met 1. However, providing adequate clinical information serves multiple purposes:
- Guides the radiologist's interpretation: Knowing the mechanism helps identify subtle fracture patterns or specific injury patterns (Segond fracture with twisting injury, patellar dislocation with direct trauma) 1
- Justifies the examination: Documentation of clinical decision rule criteria (Ottawa/Pittsburgh) supports medical necessity 1
- Determines appropriate views: Suspected patellar pathology warrants patellofemoral (sunrise) views; suspected tibial plateau fracture may need oblique views 1
- Prevents unnecessary advanced imaging: Approximately 20% of patients with chronic knee pain undergo MRI without recent radiographs, which is inappropriate 2
Common Pitfalls to Avoid
Don't write vague indications like "knee pain" or "evaluate knee." This provides no clinical context and may result in:
- Inadequate or inappropriate imaging views
- Missed diagnoses due to lack of clinical correlation
- Difficulty justifying medical necessity
Don't omit mechanism of injury in trauma cases. The radiologist needs to know if this was high-energy trauma (motor vehicle accident, knee dislocation requiring vascular assessment) versus low-energy injury 1.
Don't forget to mention inability to bear weight or focal tenderness when present—these are key Ottawa rule criteria that justify the examination and guide interpretation 1.
Standard Views to Request
For most knee radiographs, request 1, 2:
- Anteroposterior (AP) view: minimum requirement
- Lateral view: obtained at 25-30° flexion, essential for detecting effusion/lipohemarthrosis
- Additional views as indicated:
- Patellofemoral (sunrise) view for suspected patellar fracture or dislocation
- Oblique views for complex fractures
- Weight-bearing views for chronic pain/osteoarthritis assessment
The minimum acceptable study is two views (AP and lateral) for acute trauma evaluation 1.