Postpartum Hip Pain + Inability to Lift Leg - Differential Diagnosis

1. Postpartum Lumbosacral Plexopathy (Most likely neurological cause)

• Incidence: ~1 in 2,600 births; many mild cases go unreported
• Mechanism: The lumbosacral trunk is exposed and vulnerable as it crosses the pelvic outlet - it is no longer protected by the psoas muscle at the sacral ala
• Risk factors: Cephalopelvic disproportion, prolonged labor, primigravida, dystocia, instrumental delivery
• Presentation: Hip and buttock pain, weakness of hip flexion and foot dorsiflexion (foot drop), sensory loss over the lateral leg and dorsum of foot
• Key finding: Inability to lift the leg (hip flexion weakness from L2-L4 involvement) + foot drop
• Prognosis: Most are neuropraxic and resolve within 6 weeks (Bradley and Daroff's Neurology in Clinical Practice)

2. Femoral Neuropathy

• Incidence ~2.8 per 100,000 deliveries; 25% bilateral
• Caused by compression of the femoral nerve under the inguinal ligament, particularly with:
  • Prolonged lithotomy position
  • Excessive hip flexion during pushing
  • Large fetus / instrumental delivery
• Presentation: Weakness of hip flexion and knee extension, absent patellar reflex, sensory loss over anterior/medial thigh and medial calf
• "Inability to lift the leg" is a hallmark - the patient cannot climb stairs or rise from sitting

3. Obturator Nerve Injury

• Compressed as the fetal head passes through the obturator canal
• Presentation: Medial thigh pain, weakness of hip adduction, sensory loss on medial thigh
• Less commonly causes frank inability to lift the leg but contributes to hip girdle weakness

4. Pubic Symphysis Diastasis / Osteitis Pubis

• Common in postpartum females from the ligamentous laxity of pregnancy (relaxin effect)
• Presentation: Anterior pelvic pain, "waddling gait," pain radiating to hips and thighs, difficulty lifting the leg due to pain
• On examination: tenderness directly over the pubic symphysis
• Diagnosed with pelvic X-ray or MRI

5. Transient Osteoporosis of the Hip (Postpartum)

• A self-limiting skeletal disorder that classically affects women in the third trimester but is also described postpartum
• Presentation: Disabling hip pain without trauma, no inflammatory signs
• MRI shows bone marrow edema and occasional joint effusion
• Risk of pathologic fracture if not managed
• Treatment: Protected weight bearing, range-of-motion exercises, analgesics; resolves spontaneously within 12 months (Rheumatology, 2022, Elsevier)

6. Avascular Necrosis (Osteonecrosis) of the Femoral Head

• Rare but reported in pregnancy/postpartum even without traditional risk factors (steroids, alcohol)
• Presentation: Progressive hip pain, restricted range of motion
• MRI is the gold standard for early diagnosis; may be confused with transient osteoporosis
• Many cases ultimately require surgical intervention (Rheumatology, 2022, Elsevier)

7. Septic Arthritis of the Hip Joint

• Must be excluded, especially if fever, elevated WBC, or CRP/ESR elevation
• Postpartum women are relatively immunocompromised
• Presentation: Severe hip pain, inability to move the hip in any direction, systemic signs of infection
• Emergency diagnosis - urgent joint aspiration required

8. Lumbar Disc Herniation / Radiculopathy (L2-L4)

• Pregnancy and the mechanical strain of delivery can precipitate or worsen disc herniation
• Presentation: Low back pain radiating to hip/anterior thigh, weakness of hip flexion or knee extension
• Straight-leg raise or reverse SLR may be positive

9. Sacroiliac Joint Dysfunction / Pelvic Girdle Pain

• Very common postpartum due to ligamentous laxity
• Pain in the SI joint region, gluteal area, and posterior hip
• Usually not associated with true muscle weakness but pain-limited movement

Key Distinguishing Features

Recommended Workup

1. Neurological exam - assess hip flexion (iliopsoas L2/L3), knee extension (quadriceps L3/L4), ankle dorsiflexion (L4/L5), reflexes, and sensory distribution
2. Pelvic X-ray - symphysis diastasis, osteopenia
3. MRI hip/pelvis - bone marrow edema (transient osteoporosis/AVN), nerve compression
4. EMG/NCS (after 3-4 weeks from onset) - localizes nerve injury to plexus vs. individual nerve
5. Inflammatory markers (CRP, ESR, WBC) - rule out septic arthritis