What could be the cause of severe hip pain in a patient with a normal hip X-ray?

Severe Hip Pain with Normal X-ray: Diagnostic Approach

MRI of the pelvis and affected hip without IV contrast is the next imaging study of choice, as it approaches 100% sensitivity for detecting radiographically occult fractures, soft tissue injuries, labral tears, and other intra-articular pathology that commonly cause severe hip pain despite normal radiographs. 1

Most Likely Causes

Occult Fractures (Most Critical to Rule Out)

• Radiographically occult proximal femoral fractures are the most urgent diagnosis to exclude, as they require prompt surgical intervention to prevent complications 1
• MRI demonstrates 99-100% sensitivity for detecting these fractures, with studies showing no missed fractures in patients with negative MRI followed clinically for 6+ months 1
• Seemingly isolated greater trochanter fractures on radiographs frequently have intertrochanteric extension visible only on MRI 1
• Sacral insufficiency fractures can radiate pain to the hip/groin region and are commonly missed on radiographs due to overlying soft tissue, bowel gas, and sacral curvature 1

Intra-articular Pathology

• Labral tears are a common cause of hip pain in younger and middle-aged adults with normal radiographs 1, 2
• Femoroacetabular impingement (FAI) frequently coexists with labral and chondral damage 1
• Chondral injuries and ligamentum teres tears may not be visible on plain films 1
• MRI detects these conditions with high accuracy, though MR arthrography is superior if labral pathology is specifically suspected 3, 4

Extra-articular Soft Tissue Causes

• Greater trochanteric pain syndrome (gluteus medius tendinopathy/tear, bursitis) is the most common cause of lateral hip pain 2
• Iliopsoas tendinopathy or "internal snapping hip" causes anterior hip pain 5
• Muscle/tendon tears and bursitis are well-visualized on MRI 3

Referred Pain Sources

• Lumbar radiculopathy (particularly L3-L4) can present as hip pain with dermatomal sensory changes 6
• Sacroiliac joint dysfunction and piriformis syndrome cause posterior hip pain 2, 4
• Consider lumbar spine imaging if clinical examination suggests nerve root compression 3

Diagnostic Algorithm

Step 1: Obtain MRI Hip Without IV Contrast

• This single study evaluates both proximal femoral fractures (including pelvis/sacrum) and soft tissue pathology with near-perfect sensitivity 1, 3
• Coronal STIR and T1 sequences provide 99% sensitivity for fracture detection 1
• Comprehensive evaluation includes labral, chondral, tendon, and muscle pathology 1

Step 2: Consider Diagnostic Injection if MRI is Equivocal

• Image-guided intra-articular hip injection with anesthetic confirms whether pain originates from the hip joint itself versus surrounding structures (rated 8/9 appropriateness) 3
• This provides both diagnostic information and therapeutic benefit 3

Step 3: Additional Imaging Based on Clinical Suspicion

• Lumbar spine MRI if symptoms suggest radiculopathy (dermatomal sensory loss, radiating leg pain, negative hip-specific tests) 6
• MR arthrography if labral tear or FAI is strongly suspected after initial MRI 1, 3
• Ultrasound can supplement evaluation for specific superficial structures like trochanteric bursitis, though it's inferior for comprehensive assessment 3

Critical Pitfalls to Avoid

• Never assume normal radiographs exclude fracture: Radiographs have low sensitivity for occult hip fractures, particularly in older/osteoporotic patients 1
• Do not proceed directly to bone scan or CT: These modalities are NOT appropriate (rated 1/9) as they miss soft tissue pathology and provide less diagnostic information than MRI 3
• Do not delay MRI if pain persists or worsens: Occult femoral neck fractures require urgent diagnosis within 2-3 days to prevent displacement and need for emergency surgery 3
• Avoid relying solely on imaging: 38% of patients with acute hip pain and negative radiographs have extrafemoral trauma (pelvis fractures), emphasizing the need for comprehensive MRI including the pelvis 1
• Do not use peripheral nerve blocks for diagnosis: These are experimental/investigational with insufficient evidence 3
• Remember that incidental MRI findings are common in asymptomatic individuals: Diagnosis should never be made on imaging alone without correlating clinical examination 1

What NOT to Do

• Nuclear medicine bone scan is NOT appropriate (lacks specificity, time-consuming, often requires supplemental imaging anyway) 1, 3
• CT without contrast is NOT appropriate for initial evaluation of severe hip pain with normal radiographs 3
• PET imaging is NOT appropriate for this clinical scenario 3
• Contrast-enhanced MRI is unnecessary for fracture detection or most soft tissue pathology 1