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Difficulty: HardPhysical Examination Findings

A 24-year-old man is evaluated in the emergency department for severe, escalating right lower leg pain. Twelve hours ago, he sustained a closed mid-shaft tibial fracture during a rugby match and was treated with closed reduction and application of a long-leg cast. He now complains of unrelenting pain that is not relieved by multiple doses of intravenous morphine. The resident physician examines the patient and documents: "The right foot is warm with a capillary refill time of less than 2 seconds. Both the dorsalis pedis and posterior tibial pulses are 2+ and symmetric to the contralateral side. Acute compartment syndrome is highly unlikely given the intact distal perfusion." The resident plans to admit the patient for pain control and observation. Which of the following physical examination findings is the most sensitive and reliable early indicator of the condition the resident erroneously excluded?

  1. Exacerbation of deep pain during passive flexion and extension of the toesAnswer
  2. B
    Complete absence of palpable dorsalis pedis and posterior tibial pulses
  3. C
    Loss of two-point discrimination over the first dorsal web space
  4. D
    Presence of erythema, calor, and tense induration of the overlying skin
  5. E
    Reduction in the ankle-brachial index to less than 0.90 on the affected limb

Answer

Exacerbation of deep pain during passive flexion and extension of the toes
Acute compartment syndrome develops when tissue pressure within a closed fascial space rises above capillary perfusion pressure, leading to microvascular compromise and subsequent muscle and nerve ischemia. The earliest and most sensitive physical examination finding is severe pain out of proportion to the apparent injury, which is classically exacerbated by passively stretching the ischemic muscles contained within the affected compartment (e.g., passive plantarflexion/dorsiflexion of the toes). The resident's conclusion is a common and dangerous pitfall; because fascial compartment pressure rarely exceeds systolic blood pressure, major arterial flow continues, meaning distal pulses and capillary refill almost always remain normal during the early, salvageable stages of the syndrome.

Step-by-Step Solution

1
Analyze the clinical vignette
Patient has a recent tibial fracture with cast placement, presenting with pain out of proportion to the injury that is unresponsive to opioids.
This is the classic presentation of acute compartment syndrome, a surgical emergency.
2
Evaluate the resident's physical exam findings and conclusion
The resident ruled out compartment syndrome because distal pulses (dorsalis pedis, posterior tibial) are intact and capillary refill is normal.
This represents a critical misunderstanding of the pathophysiology. Compartment syndrome occurs when interstitial pressure exceeds capillary perfusion pressure (typically around 30 mm Hg), not systolic arterial pressure (120 mm Hg).
3
Identify the most sensitive early clinical sign of compartment syndrome
Pain on passive stretching of the muscles within the affected compartment (e.g., moving the toes to stretch the anterior/deep posterior compartments) is the earliest and most reliable physical examination finding.
Ischemic muscle is highly sensitive to stretch, providing a clinical signal long before large-vessel occlusion (loss of pulses) or irreversible nerve damage (loss of two-point discrimination) occurs.

Key Concept

In acute compartment syndrome, large arterial pulses typically remain intact because compartmental pressures exceed capillary closing pressure but do not reach systolic arterial pressure. Pain on passive stretch is the most sensitive early clinical sign.
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Topics

Physical Examination Findings

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