What is the appropriate initial management for an adult patient with left hip and knee pain after a fall, unable to lift the leg, and negative plain radiographs?

Management of Left Hip and Knee Pain After Fall with Inability to Lift Leg and Negative X-rays

This patient requires urgent MRI of the pelvis and affected hip without IV contrast to rule out an occult hip fracture, as inability to lift the leg independently after trauma with negative radiographs represents a high-risk scenario that cannot be safely dismissed. 1

Critical Clinical Context

The inability to actively lift the leg (loss of hip flexion strength) after a fall is a red flag that strongly suggests either:

• An occult proximal femoral fracture (femoral neck, intertrochanteric, or subtrochanteric)
• Severe soft-tissue injury affecting the hip flexors or iliopsoas
• Pelvic fracture affecting muscle attachments

Negative plain radiographs do NOT exclude fracture — at least 10% of proximal femoral fractures are radiographically occult, and up to 38% of patients with hip pain and negative X-rays have fractures elsewhere in the pelvis. 1

Immediate Next Step: Advanced Imaging

MRI Without IV Contrast (Preferred)

MRI of the pelvis and affected hip without contrast is the gold standard next imaging study and should be obtained urgently. 1

• Sensitivity approaches 99-100% for detecting occult proximal femoral fractures, with multiple studies confirming no missed fractures in patients with negative MRI followed clinically for 6+ months. 1
• Detects multiple injury patterns including femoral neck fractures, intertrochanteric fractures with extension not visible on X-ray, pelvic fractures (found in 33-38% of cases), and significant soft-tissue injuries. 1, 2
• Allows confident discharge if negative, reducing unnecessary hospital admissions, while positive findings enable rapid surgical planning and improved outcomes by reducing delay to treatment. 1
• No IV contrast is needed for acute fracture detection; contrast does not improve diagnostic accuracy for this indication. 1

CT Pelvis and Hips (Alternative When MRI Unavailable)

If MRI is not immediately available or contraindicated, noncontrast CT can be performed as a problem-solving modality, but with important limitations. 1

• CT sensitivity is only 86% for occult hip fractures, meaning it will miss approximately 14% of fractures. 3, 4
• A negative CT does NOT exclude fracture and should be followed by MRI if clinical suspicion remains high. 3, 4
• CT is most useful for characterizing fracture morphology once a fracture is suspected or partially visualized. 1
• Some institutions use a cost-effective protocol of CT first, followed by MRI only if CT is negative, which reduces time to diagnosis in the ~50% of cases where CT is positive. 4

Management Pending Imaging

Weight-Bearing Status

• The patient should remain non-weight-bearing or touch-down weight-bearing only on the affected side until fracture is definitively excluded. 1
• Inability to perform straight leg raise is a strong indicator of hip pathology requiring protected weight-bearing.

Pain Control

• Provide adequate analgesia while awaiting imaging, as uncontrolled pain may worsen functional status and delay mobilization if fracture is ultimately excluded.

Admission Consideration

• Consider hospital admission for patients who cannot safely mobilize at home, live alone, or have significant comorbidities, particularly if MRI cannot be obtained within 24 hours. 1

Differential Diagnosis Beyond Fracture

If MRI is negative for fracture, consider:

• Severe muscle or tendon injuries: Iliopsoas strain/tear, rectus femoris avulsion, or quadriceps injury can cause inability to lift the leg. 2
• Soft-tissue abnormalities are found in 65% of MRI studies for suspected occult hip fracture and may include muscle injuries, hematomas, or bursitis. 2
• Knee ligamentous injuries: Given concomitant knee pain, evaluate for ACL, PCL, or collateral ligament injuries if knee MRI is also performed. 5, 6
• Referred pain from lumbar spine: Though less likely with inability to lift leg, consider if hip and knee imaging is unrevealing. 5

Critical Pitfalls to Avoid

• Do not discharge the patient with reassurance based on negative X-rays alone — the combination of trauma, inability to lift leg, and negative radiographs mandates advanced imaging. 1, 7
• Do not rely on CT as definitive — if CT is performed and negative, strong clinical suspicion (inability to lift leg) warrants follow-up MRI. 3, 4
• Do not delay imaging for "conservative trial" — early diagnosis of surgical fractures improves outcomes, and delayed diagnosis increases morbidity. 1
• Do not forget to image the entire pelvis — isolated hip views may miss acetabular, pubic rami, or sacral fractures that refer pain to the hip. 1, 2
• Do not order bone scan — nuclear medicine has been supplanted by MRI and is no longer recommended for acute evaluation. 1

Timeline for Imaging

• MRI should ideally be obtained within 24 hours to facilitate surgical planning if fracture is present or to allow safe discharge if negative. 1
• If using a CT-first protocol, MRI should follow within 24-40 hours if CT is negative. 4