What is the appropriate evaluation and management for a patient with a twisting injury of the left hip and leg who now has persistent left thigh and quadriceps pain and numbness extending from the knee to the ankle?

Immediate Evaluation and Management

This patient requires urgent plain radiographs of the hip and pelvis as the initial imaging study, followed by advanced imaging (CT or MRI) if radiographs are negative, because the combination of thigh pain, quadriceps weakness, and numbness from knee to ankle after a twisting injury suggests either an occult hip fracture or femoral nerve injury from an iliacus hematoma.

Initial Imaging Approach

Start with plain radiographs (AP view with 15 degrees internal rotation and cross-table lateral view) of the affected hip and pelvis 1. This is the fastest method to detect hip fracture or dislocation and reduces morbidity by enabling rapid diagnosis without moving the patient 1.

If Radiographs Are Negative or Indeterminate

Proceed immediately to CT hip without IV contrast 1. This is critical because:

• CT detects radiographically occult hip fractures in 24.1% of cases with negative initial radiographs 1
• CT has 94% sensitivity and 100% specificity for occult fractures 1
• Speed matters: surgical delays >12 hours significantly increase 30-day mortality risk 1

If CT is also negative but clinical suspicion remains high, obtain MRI hip without contrast 1. MRI is the reference standard for detecting occult fractures and can also identify soft tissue pathology.

Critical Differential Diagnosis

The clinical presentation—thigh pain with quadriceps weakness and numbness extending from knee to ankle—strongly suggests femoral nerve injury, likely from:

Traumatic Iliacus Hematoma

This is a rare but important diagnosis that must not be missed 2, 3. The mechanism fits:

• Twisting injury can cause iliacus muscle bleeding
• Hematoma extends to the lacuna musculorum, compressing the femoral nerve
• Results in quadriceps weakness (inability to extend knee) and numbness in the femoral nerve distribution (anterior thigh and medial leg to ankle)

Key clinical findings to assess:

• Can the patient extend their knee against resistance? (tests quadriceps function)
• Is there numbness on the anterior thigh and medial leg/ankle? (femoral nerve sensory distribution)
• Is there groin/thigh pain that preceded the weakness?

Imaging Strategy for Suspected Femoral Nerve Injury

If initial hip radiographs show no fracture but symptoms persist, obtain MRI of the pelvis/hip to evaluate for iliacus hematoma 2, 3. MRI will show:

• Hematoma in the iliacus muscle
• Extension toward the femoral nerve
• Muscle atrophy if injury is more chronic

Consider EMG and nerve conduction studies if no improvement occurs within 3-6 weeks, to assess the level and severity of nerve injury 4.

Management Algorithm

If Complete Quadriceps Palsy (Cannot Extend Knee at All)

Surgical evacuation of hematoma with femoral nerve neurolysis is required 3. Conservative management fails in complete paralysis, and surgical intervention—even with diagnostic delay—leads to full recovery in most cases 3.

If Partial Weakness Only

Conservative management with:

• Close monitoring for progression
• Physical therapy
• Pain management
• Serial neurological examinations

Most patients with partial injuries recover fully within 60 days 2.

Common Pitfalls to Avoid

1. Don't assume normal radiographs exclude significant pathology: Up to 39% of patients with clinically suspected hip fracture have negative initial radiographs but surgical fractures on advanced imaging 1

2. Don't delay advanced imaging in persistent symptoms: The combination of pain and neurological deficits after trauma warrants urgent cross-sectional imaging even with normal radiographs

3. Don't miss femoral nerve injury: This rare diagnosis (only 39 cases published in 75 years for post-traumatic iliacus hematoma) 3 is easily overlooked but causes significant disability if untreated

4. Don't use frog-leg lateral views acutely: Use cross-table lateral to avoid displacing occult fractures 1

Immediate Next Steps

1. Obtain hip/pelvis radiographs immediately
2. Perform detailed neurological examination focusing on quadriceps strength and femoral nerve sensory distribution
3. If radiographs negative: proceed to CT hip without contrast
4. If neurological deficits present: add MRI pelvis to evaluate for iliacus hematoma
5. Surgical consultation if complete quadriceps paralysis identified

The prognosis for femoral nerve injury is generally favorable with appropriate treatment 4, but timely diagnosis is essential to prevent permanent disability 5.