What is the differential diagnosis (Ddx) and workup for a 45-year-old obese individual with a history of diabetes mellitus (DM) presenting with new onset hip pain, without any history of injury or deformities?

Differential Diagnosis and Workup for Obese 45-Year-Old with Diabetes and New Onset Hip Pain

Begin with anteroposterior (AP) pelvis and frog-leg lateral hip radiographs immediately, as this is the essential first step for all patients with hip pain regardless of age or comorbidities. 1, 2

Critical Differential Diagnoses to Consider

Given this patient's specific risk factors (obesity, diabetes, age 45, no trauma), prioritize these diagnoses:

High-Priority Diagnoses

• Osteonecrosis (avascular necrosis) of the femoral head - diabetes is a significant risk factor, presents with insidious onset hip/groin pain without trauma 1, 3
• Osteoarthritis - obesity and age are major risk factors, typically presents with anterior hip/groin pain exacerbated by activity 1, 4
• Femoroacetabular impingement (FAI) syndrome - can occur in this age group, presents with anterior hip/groin pain 1, 2
• Labral tear - often coexists with FAI or early osteoarthritis, causes anterior hip/groin pain with mechanical symptoms 1, 2, 4
• Diabetic myonecrosis - uncommon but important in poorly controlled diabetics, presents with severe proximal thigh/hip pain, typically unilateral but can be bilateral 5

Secondary Considerations

• Greater trochanteric pain syndrome - if pain is lateral hip, common in obese patients 3, 4
• Referred pain from lumbar spine - must screen for radiculopathy or spinal pathology 1, 3
• Stress fracture - less likely without trauma but consider if pain is acute onset 3

Structured Diagnostic Workup

Step 1: Initial Imaging (Always Required)

Obtain plain radiographs first: AP pelvis view AND frog-leg lateral view of the symptomatic hip. 1, 2, 3

These radiographs will identify:

• Joint space narrowing (osteoarthritis) 1
• Cam or pincer morphology (FAI syndrome) 1, 2
• Femoral head collapse or sclerosis (osteonecrosis) 1, 3
• Acetabular dysplasia (center-edge angle <20-25 degrees) 1
• Fractures or bone tumors 1, 3

Step 2: Physical Examination Priorities

Perform FADIR test (flexion-adduction-internal rotation) - positive test suggests intra-articular pathology such as FAI syndrome or labral tear 1, 2

Assess pain location precisely:

• Anterior hip/groin pain = intra-articular pathology (osteoarthritis, labral tear, FAI, osteonecrosis) 3, 4
• Lateral hip pain = greater trochanteric pain syndrome 3, 4
• Posterior hip pain = lumbar radiculopathy, sacroiliac dysfunction 3, 4

Screen lumbar spine and pelvis - perform straight leg raise, assess for radicular symptoms, palpate sacroiliac joints 1

Step 3: Advanced Imaging (When Radiographs Are Negative/Equivocal)

If radiographs are negative or equivocal, obtain MRI hip without IV contrast (rated 9/9 appropriateness by ACR). 1, 2

MRI without contrast is superior for:

• Osteonecrosis detection - this is critical in diabetic patients, as early osteonecrosis may not show on radiographs 1, 3
• Occult fractures or stress fractures 3, 6
• Bone marrow edema 1
• Diabetic myonecrosis - shows characteristic muscular edema with patchy geographic areas of sparing 5
• Soft tissue pathology (tendinopathy, bursitis) 1

If labral tear or FAI syndrome is strongly suspected clinically, consider MR arthrography - provides superior visualization of labral tears compared to standard MRI 1, 2, 3, 6

Step 4: Diagnostic Injection (For Unclear Cases)

If concurrent low back or pelvic pathology exists and the pain source is unclear, perform image-guided intra-articular hip injection with anesthetic and corticosteroid (rated 8/9 by ACR). 1

This provides both diagnostic confirmation (pain relief confirms intra-articular source) and therapeutic benefit 1

Critical Pitfalls to Avoid

• Never skip plain radiographs - proceeding directly to MRI without radiographs misses important bony pathology and is not cost-effective 1, 2
• Never diagnose based on imaging alone - asymptomatic labral tears and cam morphology are common incidental findings; always correlate with clinical examination 1
• Do not miss osteonecrosis - this is the most critical diagnosis in diabetic patients, as early detection affects prognosis; if radiographs are normal but clinical suspicion is high, MRI is mandatory 1, 3
• Always screen for referred pain - failing to examine the lumbar spine and pelvis leads to missed diagnoses 1
• Obtain BOTH pelvis and hip views - a single hip view misses contralateral comparison and acetabular morphology 1, 2
• Consider diabetic myonecrosis in poorly controlled diabetics - this presents with severe pain and requires MRI for diagnosis, but is treated conservatively with rest and pain management 5

Special Considerations for This Patient

Assess diabetes control - check HbA1c, as poorly controlled diabetes increases risk of osteonecrosis and diabetic myonecrosis 1, 5

Document BMI - obesity (BMI >30) increases risk of osteoarthritis and may affect surgical outcomes if intervention is needed 1

Avoid opioids for chronic hip pain - consensus recommendation against opioid use for symptomatic hip osteoarthritis 1