What clinical assessment is indicated for a patient who slipped and landed on the right knee, initially denied pain and ambulated independently, but now presents with groin pain?

Clinical Assessment for Delayed Groin Pain After Right Knee Trauma

Immediate Priority: Rule Out Hip Fracture

This patient requires urgent plain radiographs of the pelvis and right hip to exclude occult hip fracture, particularly femoral neck fracture, which commonly presents with groin pain and may occur from falls even when the knee appears to be the primary impact site. 1

The delayed onset of groin pain after a fall—even when the patient initially ambulated—is a red flag for hip pathology that was masked by adrenaline or initially minimal displacement. 1

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Structured Clinical Examination

Vascular Assessment

• Check distal pulses (dorsalis pedis and posterior tibial), capillary refill, skin temperature, and color of the right lower extremity to exclude acute limb ischemia or compartment syndrome. 2
• Assess for disproportionate pain relative to examination findings, which may indicate vascular injury or compartment syndrome requiring urgent intervention. 2

Hip-Specific Examination

• Observe leg position at rest—a shortened and externally rotated right lower extremity is pathognomonic for displaced femoral neck fracture. 1
• Palpate the groin for focal bony tenderness over the femoral neck and greater trochanter; tenderness here mandates imaging even if the patient can bear weight. 1
• Test passive hip range of motion—pain with log-roll or any hip motion strongly suggests hip fracture or intra-articular hip pathology. 1
• Assess weight-bearing ability now—inability to bear weight or take four consecutive steps requires immediate imaging of both the knee and hip. 2, 3

Knee Re-Examination

• Palpate for focal bony tenderness at the patella, tibial plateau, and fibular head to reassess for occult knee fracture. 2
• Evaluate for joint effusion—a large effusion that prevents flexion to 90° warrants imaging and possible aspiration to exclude hemarthrosis or septic arthritis. 2
• Check joint stability—assess collateral and cruciate ligaments; instability suggests significant ligamentous injury requiring advanced imaging. 3

Referred Pain Considerations

• Hip pathology commonly refers pain to the knee and groin; conversely, knee trauma can mask concomitant hip injury, especially in elderly or osteoporotic patients. 1, 3
• Lumbar spine pathology can refer pain to the groin and lower extremity; assess for midline tenderness and neurologic deficits if hip and knee imaging are unremarkable. 3

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Imaging Protocol

First-Line Imaging

• Obtain AP pelvis and lateral right hip radiographs immediately to exclude femoral neck fracture, intertrochanteric fracture, or acetabular injury. 1
• Obtain AP and lateral right knee radiographs (minimum two views) to rule out fracture, effusion, or other bony pathology. 2, 3

Indications for Advanced Imaging

If Hip Radiographs Are Negative but Clinical Suspicion Remains High

• MRI of the hip without IV contrast is the next study; it has high sensitivity for occult femoral neck fractures and bone-marrow edema that predict impending fracture. 2
• CT of the pelvis without IV contrast is an alternative if MRI is contraindicated or unavailable; it provides 100% sensitivity for fractures versus 83% for plain films. 3

If Knee Radiographs Are Negative but Symptoms Persist

• MRI of the knee without IV contrast is indicated if there is significant effusion, inability to fully bear weight after 5–7 days, mechanical symptoms (locking, catching), or joint instability. 2, 3
• Do not order MRI as the initial study; plain radiographs must precede MRI to comply with evidence-based practice and exclude fracture. 3

If Vascular Injury Is Suspected

• CTA of the lower extremity with IV contrast is urgent if pulses are absent, there is pallor, paresthesia, or disproportionate pain; vascular injury requires prompt surgical intervention. 2

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Laboratory and Aspiration Considerations

• Perform joint aspiration of the knee if there is a large effusion and concern for septic arthritis (fever, systemic symptoms) or hemarthrosis; use ultrasound or fluoroscopic guidance. 2
• Obtain ESR and CRP if infection is suspected; elevated inflammatory markers increase suspicion for septic arthritis. 2
• Send synovial fluid for cell count, Gram stain, and culture; a positive culture is the reference standard for diagnosing septic arthritis. 2

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Critical Pitfalls to Avoid

• Do not assume the knee is the only injured site simply because it was the point of impact; groin pain after a fall mandates hip imaging regardless of knee findings. 1, 3
• Do not rely on initial ability to ambulate to exclude fracture; adrenaline and minimal displacement can allow weight-bearing initially, with pain developing hours later as displacement progresses. 1
• Do not skip plain radiographs and proceed directly to MRI; radiographs are essential to exclude fracture and guide further management. 2, 3
• Do not delay imaging in elderly patients; femoral neck fractures in older adults are orthopedic emergencies requiring surgical fixation within 24–48 hours to reduce morbidity and mortality. 1
• Do not overlook vascular examination; knee dislocations and proximal tibial fractures carry a 30% risk of vascular injury requiring urgent intervention. 3