Yes, X-ray This Knee Immediately
A 14-year-old with knee pain and inability to bear weight meets clear criteria for immediate knee radiography, regardless of the absence of acute injury history. 1
Why X-ray is Indicated
The inability to bear weight is a critical red flag that mandates radiographic evaluation in this age group:
The Pittsburgh Decision Rule specifically recommends radiographs for patients under 12 years old OR over 50 years old, OR for any patient who cannot take four weight-bearing steps in the emergency department. 1 Your 14-year-old patient meets the weight-bearing criterion, making X-ray clearly indicated.
The ACR Appropriateness Criteria emphasize that inability to bear weight is one of three key criteria (along with inability to flex to 90° and bony tenderness) that should prompt imaging. 1 Even though this patient falls between the strict age cutoffs of Ottawa (>55 years) and Pittsburgh (<12 years) rules, the inability to bear weight supersedes age considerations.
Patients aged 5-12 years fall outside both Ottawa and Pittsburgh age ranges, and radiographs may be beneficial despite lack of clinical symptoms. 1 At 14 years, your patient is just above this range, but the weight-bearing limitation makes this a moot point.
Critical Differential Considerations in This Age Group
The absence of acute injury does NOT rule out serious pathology requiring immediate identification:
Stress fractures, osteochondritis dissecans, and pathologic fractures (from bone tumors or infections) can all present with insidious onset pain and inability to bear weight in adolescents. 2, 3
Slipped capital femoral epiphysis (SCFE) can present as referred knee pain in this age group and requires urgent orthopedic intervention. This is why you need imaging even without direct knee trauma.
Septic arthritis must be excluded if there is any effusion, fever, or systemic symptoms, as this is an orthopedic emergency. 4, 5
Specific X-ray Views to Order
Order a minimum of two views: anteroposterior (AP) and lateral (with knee at 25-30 degrees flexion). 1, 6
Additional views to consider based on examination findings:
- Patellofemoral view if there is anterior knee pain or patellar tenderness 1, 6
- Cross-table lateral view with horizontal beam to visualize lipohemarthrosis if intra-articular fracture is suspected 1
- Internal and external oblique views for better characterization of suspected fractures 6
What Happens After the X-ray
If X-rays are Negative:
- Conservative management with close follow-up is appropriate IF the patient can bear weight after initial treatment (rest, ice, NSAIDs). 6
- MRI without contrast should be obtained at 5-7 days if symptoms persist, mechanical symptoms develop (locking, catching), or joint instability is present. 6, 5 This evaluates for meniscal tears, ligamentous injuries, osteochondritis dissecans, or occult fractures.
- Consider MRI earlier if there is significant joint effusion or clinical suspicion for internal derangement remains high. 6
If X-rays Show Abnormality:
- Fractures, osteochondritis dissecans lesions, or bone tumors require orthopedic referral. 7
- CT may be needed for better characterization of complex fractures. 6, 7
Common Pitfalls to Avoid
Do NOT skip radiographs based on the absence of acute trauma history. Overuse injuries, stress fractures, and pathologic processes can all present without a specific injury event. 2, 3
Do NOT rely solely on clinical decision rules in adolescents. The Ottawa and Pittsburgh rules were primarily validated in adults and very young children. 1 Physician judgment should supersede guidelines when clinical concern exists.
Do NOT assume this is just "growing pains" or Osgood-Schlatter disease without imaging. While these are common in this age group, inability to bear weight suggests more serious pathology. 2, 3
Do NOT delay imaging to "see if it gets better." The inability to bear weight is an urgent indication for radiographic evaluation to rule out fractures requiring immediate intervention. 1, 8