X-Ray Imaging for Left Hip and Knee Pain
Order an AP pelvis radiograph and frog-leg lateral view of the left hip as your initial imaging studies. 1
Initial Radiographic Approach
The American College of Radiology mandates plain radiographs as the first imaging test for hip pain radiating down the leg, specifically requiring both views to avoid missing important pathology. 2, 1 This two-view combination serves as an excellent screening tool to identify:
- Osteoarthritis of the hip joint 1
- Femoroacetabular impingement (FAI) 2
- Acetabular dysplasia 2
- Occult fractures (though MRI is more sensitive) 1
- Bone tumors 1
The complete radiographic evaluation must include both the AP pelvis view (to assess the entire pelvic ring and bilateral hip joints for comparison) and the frog-leg lateral view of the symptomatic left hip (to evaluate the femoral head-neck junction and detect FAI morphology). 1, 3
Why Both Hip AND Knee X-Rays May Be Needed
Given that your patient has both hip and knee pain, you should also consider AP and lateral knee radiographs if clinical examination suggests primary knee pathology. 4 However, hip pathology commonly refers pain to the knee in approximately 20% of cases, making hip imaging the priority. 4, 5
Critical pitfall to avoid: The American College of Radiology warns that proceeding directly to advanced imaging (MRI) without obtaining plain radiographs first is inappropriate and may lead to unnecessary costs and delayed diagnosis. 1
Algorithmic Next Steps Based on Initial X-Ray Results
If radiographs show clear pathology (OA, FAI, fracture):
- Proceed with appropriate treatment based on findings 1
If radiographs are negative, equivocal, or nondiagnostic:
- MRI of the left hip without IV contrast is the next appropriate study (rated 9/9 by ACR) to evaluate for soft tissue pathology including labral tears, tendonitis, muscle tears, or early inflammatory changes that could explain the radiating pain pattern. 2, 1
If diagnosis remains unclear after imaging:
- Image-guided intra-articular hip injection with anesthetic ± corticosteroid (rated 8/9 by ACR) can confirm whether the hip joint is the true pain source—complete pain relief after injection confirms hip origin. 2, 1
Why This Patient's Presentation Suggests Hip Pathology
The pain pattern—worsening with prolonged standing and radiating down the leg below the gluteal region—is classic for hip joint pathology rather than isolated knee disease. 2, 5 Hip disorders frequently present as thigh and knee pain rather than isolated groin pain, making this a common diagnostic pitfall. 2, 5
The stabbing quality and radiation pattern, combined with improvement in sciatic symptoms, suggests the current pain is likely intra-articular hip pathology (labral tear, FAI, early OA) or periarticular pathology (gluteus medius tendinopathy, trochanteric bursitis) rather than nerve-related. 5, 3
What NOT to Order Initially
- Do not order lumbar spine imaging unless radicular symptoms develop, as non-specific low back pain does not require initial spinal imaging. 2
- Do not proceed directly to MRI without plain radiographs first. 1
- Do not order CT, bone scan, or PET imaging for this presentation—these are rated 1/9 (inappropriate) by ACR and provide less diagnostic information while exposing the patient to unnecessary radiation. 1