Preferred Imaging Study for Adolescent Hip Pain
Anteroposterior and lateral x-rays of the pelvis are the preferred initial imaging study for this 14-year-old obese boy with intermittent hip pain. 1, 2
Why Pelvis Views Are Essential
The British Journal of Sports Medicine consensus guidelines explicitly recommend anteroposterior (AP) pelvis and lateral femoral head-neck radiographs as the initial diagnostic imaging for hip-related pain in young active adults. 1 The pelvis view is critical because it allows comparison with the contralateral asymptomatic side, which is crucial for accurate diagnosis. 2
Key Clinical Context: Slipped Capital Femoral Epiphysis (SCFE)
This clinical presentation—obese adolescent male with insidious hip pain worsened by activity—is classic for SCFE, one of the most important diagnoses not to miss in this age group. 2 The pelvis view is essential because:
- SCFE can be bilateral in 20-40% of cases, and the pelvis view allows assessment of both hips simultaneously 2
- Subtle slips may only be apparent when comparing the affected side to the normal contralateral hip 2
- The frog-leg lateral view (part of the lateral femoral head-neck imaging) is particularly sensitive for detecting posterior-inferior displacement of the femoral epiphysis 1
Why Not Just Right Hip Views?
Obtaining only right hip radiographs (AP and lateral of the right hip alone) would be inadequate and potentially dangerous because:
- You would miss contralateral hip pathology that may influence treatment decisions 2
- Comparison views are essential for detecting subtle morphological abnormalities 2
- The American College of Radiology emphasizes never relying solely on hip radiographs without including pelvis views 2
Why Not MRI or CT Initially?
MRI and CT are not appropriate first-line imaging for several reasons:
- Plain radiographs serve as an excellent screening tool that guides selection of additional imaging techniques when needed 2, 3
- Imaging should never be used in isolation but combined with symptoms and clinical signs 1, 2
- MRI/MRA or CT are reserved for when three-dimensional morphological assessment is indicated or when radiographs are negative but clinical suspicion remains high 1, 2
- Advanced imaging is particularly useful for evaluating intra-articular structures (labrum, cartilage, ligamentum teres) when conservative treatment has failed or surgery is being considered 1
Practical Imaging Protocol
The recommended views include:
- AP pelvis radiograph with approximately 15 degrees of internal hip rotation 2, 3
- Lateral femoral head-neck view of the affected hip, which can include a Dunn view, frog-leg (Lauenstein) view, or cross-table view 1
Critical Pitfall to Avoid
Never make a diagnosis based on imaging alone—the diagnosis requires integration of symptoms, clinical signs, and imaging findings. 1, 2 Diagnostic imaging has limited ability to confirm the diagnosis of a particular condition as the cause of pain, with only small to moderate shifts in post-test probability. 1