What is the most likely diagnosis and appropriate management for lateral hip pain that occurs only when lying supine?

Lateral Hip Pain Only When Lying Flat

The most likely diagnosis is greater trochanteric pain syndrome (GTPS), specifically trochanteric bursitis or gluteus medius/minimus tendinopathy, which characteristically worsens with direct pressure on the lateral hip during supine positioning. 1, 2, 3

Most Likely Diagnosis

Greater trochanteric pain syndrome is the primary consideration for lateral hip pain that occurs specifically when lying flat, as direct pressure on the inflamed trochanteric bursa or damaged gluteal tendons reproduces symptoms. 1, 2, 3

• GTPS affects 10-25% of the general population and is more common in women, patients with obesity, coexisting low back pain, and osteoarthritis. 2, 3
• The condition encompasses trochanteric bursitis, gluteus medius/minimus tendinopathy or tears, and iliotibial band friction. 4, 3
• Pain typically radiates along the lateral thigh to the knee and occasionally below, with point tenderness over the posterolateral greater trochanter. 2, 3
• Gluteus medius tendon tears frequently coexist with bursitis and may present identically, with weakness of hip abduction being a key distinguishing feature. 5, 3

Diagnostic Workup

Begin with plain radiographs of the pelvis and hip as the mandatory first imaging test to exclude alternative causes such as osteoarthritis, fractures, bone tumors, or avulsion injuries. 6, 7, 1

• Obtain anteroposterior pelvis view and frog-leg lateral view of the symptomatic hip. 7
• Radiographic surface irregularities of the greater trochanter >2mm suggest abductor tendon abnormalities, though sensitivity is only 64% and specificity 26%. 1

If radiographs are negative or equivocal, proceed to MRI of the hip without IV contrast (rated 9/9 for appropriateness by the American College of Radiology). 6, 7, 1

• MRI is highly sensitive and specific for detecting trochanteric bursitis, gluteus medius/minimus tendon tears, and other soft tissue pathology. 6, 7, 1
• MRI comprehensively evaluates the gluteal muscles, tendons, and bursa when symptoms persist or surgical intervention is considered. 1
• Distinguishing bursitis from tendinosis on imaging is difficult as both frequently coexist. 1

Ultrasound is a valuable alternative for evaluating specific soft tissue structures and can guide diagnostic/therapeutic injections. 6, 7, 1

• Ultrasound provides real-time visualization and allows simultaneous assessment for gluteal tendon pathology. 1
• However, ultrasound is inferior to MRI for comprehensive evaluation of intra-articular pathology. 7

Management Algorithm

Conservative Treatment (First-Line)

Most cases of GTPS are self-limited and respond to conservative measures within 3-6 months. 2, 3

• Physical therapy with eccentric strengthening of hip abductors is more effective than passive modalities and is the cornerstone of treatment. 1
• Activity modification: avoid prolonged sitting, stair climbing, pivoting, rapid acceleration, forceful hip adduction, and sports requiring quick directional changes. 1
• NSAIDs for pain control during the acute phase. 2
• Cryotherapy: apply ice packs for 10-minute intervals using a wet towel during the first 48-72 hours. 1
• Weight loss in patients with obesity. 2
• Land-based physical therapy is preferred over aquatic therapy. 1

Image-Guided Injection (Second-Line)

If conservative measures fail after 6-8 weeks, perform ultrasound-guided trochanteric bursa injection with local anesthetic and corticosteroid. 1, 2

• Image guidance (ultrasound or fluoroscopy) is mandatory for all trochanteric injections; blind injections achieve proper bursal spread in only 45% of cases. 1
• Ultrasound is the preferred imaging modality for real-time visualization. 1
• Use a mixture of local anesthetic (e.g., lidocaine) and corticosteroid delivered into the trochanteric bursa. 1
• Peritendinous injections are strongly preferred over intratendinous injections to avoid compromising tendon integrity. 1
• Pain relief is typically short-lived with no sustained benefit at two years. 1
• Corticosteroid injections have a low incidence of adverse events at six months. 1

Critical Contraindications

• Avoid corticosteroid injections within three months before planned total hip arthroplasty due to increased infection risk. 1
• Exercise extreme caution in patients with hip prostheses, as adverse reactions to metal debris can mimic trochanteric bursitis. 1
• Limit frequency of repeated corticosteroid injections due to potential adverse effects on bone health and joint integrity. 1

Surgical Referral (Third-Line)

If symptoms persist after 3-6 months of comprehensive conservative treatment (injection, physical therapy, NSAIDs, activity modification), refer for surgical consultation. 1, 5

• Surgical options include repair of gluteus medius/minimus tendon tears or iliotibial band release. 5, 3
• Tendon repair has good outcomes, with all patients pain-free at median 45-month follow-up in one series. 5

Red Flags Requiring Alternative Workup

• In patients <45 years with morning stiffness >30 minutes: obtain MRI of sacroiliac joints and refer to rheumatology to assess for axial spondyloarthropathy. 1
• If pain radiates down the leg with neurologic symptoms: consider lumbar spine pathology and obtain MRI of lumbar spine. 7, 4
• Diagnostic injections can help differentiate hip joint pathology from periarticular sources when diagnosis remains unclear. 6, 7

Common Pitfalls to Avoid

• Failing to obtain both pelvis and hip radiographs may miss important pathology. 7
• Proceeding directly to advanced imaging without plain radiographs is not recommended. 7
• Blind trochanteric bursa injections without image guidance have unacceptably low accuracy. 1
• Intratendinous corticosteroid injection may damage gluteal tendons. 1
• Delaying MRI when symptoms persist beyond 6-8 weeks of conservative treatment may miss surgically correctable gluteal tendon tears. 1, 5