Equivocal Compartment Pressure After a Tibial Shaft Fracture
A 32-year-old man is 8 hours after a closed tibial shaft fracture from a motorcycle crash. He has a long leg backslab, a morphine PCA, and escalating pain. He describes pain as 9/10 despite 15 mg of morphine in the last hour, worse with passive dorsiflexion of the toes, and the anterior compartment is tense. Sensation is reduced in the first web space, and the dorsalis pedis pulse is present. Compartment pressure in the anterior compartment is 32 mmHg, and his diastolic blood pressure is 70 mmHg. He is otherwise stable, with no head injury, and is not anticoagulated. CT angiography shows no vascular injury. The limb is warm, with capillary refill of 3 seconds, and he has passed urine normally. The registrar suggests repeating the pressure in 2 hours.
1. How do you interpret the compartment pressure, and what is your decision?
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Use the delta pressure, the diastolic pressure minus the compartment pressure, rather than the absolute pressure alone. Here the delta is 70 − 32 = 38 mmHg. The commonly used threshold for fasciotomy is a delta pressure below 30 mmHg, so this value sits above the threshold. That does not, by itself, rule out compartment syndrome.
The clinical picture is concerning: pain out of proportion, pain on passive stretch, a tense compartment, and reduced sensation in the first web space, which is deep peroneal nerve territory. These are the earliest and most reliable signs. The pressure is a single measurement taken with a technique that carries a recognized error of a few mmHg, and the trend matters more than the number.
My decision would be to treat on clinical grounds unless the examination improves. Remove the backslab and any circumferential dressing down to skin, keep the limb at heart level rather than elevated, ensure adequate analgesia, and reassess within 30 minutes. If the pain and tension persist, proceed to four-compartment fasciotomy. If they improve markedly, repeat the pressure and continue close monitoring with hourly documented examinations.
2. The registrar wants to repeat the pressure in 2 hours. How do you respond?
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Repeating the pressure is reasonable only if the clinical findings are equivocal and the limb is being continuously observed by someone competent to act on the result. In this patient the findings are not equivocal: he has pain on passive stretch, a tense compartment, and a sensory deficit, all of which are clinical signs of compartment syndrome. Waiting 2 hours risks irreversible muscle and nerve necrosis - ischemic tolerance is roughly 4–6 hours for muscle, and the clock starts at the time of injury, not at the time of diagnosis.
If the team is genuinely uncertain, the safer path is to monitor in a high-dependency setting with hourly documented examinations and pressures, not to defer the decision to a timed repeat. Also confirm that the diastolic pressure is accurate; a hypotensive patient has a lower delta pressure for the same compartment pressure. In this patient the diastolic is 70, so the delta is 38; if his diastolic fell to 55, the delta would be 23 and the indication would be unambiguous.
Do not wait for the pulse to disappear - that is a late sign. The presence of a palpable dorsalis pedis pulse does not exclude compartment syndrome.
3. What if the pressure were 22 mmHg with a diastolic of 70? Would you still do a fasciotomy?
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A delta pressure of 48 mmHg with a reassuring examination would argue against fasciotomy. The number alone should not drive surgery. But the reason for the low reading matters: a single low value can be falsely reassuring if the needle is in a superficial or incorrect compartment, if the limb is not at the level of the heart, or if the pressure is taken after the backslab has already been split. Re-examine and, if the clinical picture remains concerning, repeat the measurement in the most symptomatic compartment and consider measuring all four compartments.
If the examination normalizes and the pressure remains low, continue observation with hourly checks, a split cast, and adequate analgesia. Document the trajectory so the next clinician can see whether things are improving or deteriorating. If pain and tension recur, or if there is any new sensory or motor deficit, proceed to fasciotomy regardless of the number.
The corollary is that a high pressure with a normal examination should prompt repeat measurement and clinical review, not automatic surgery. Clinical judgment and the trend take precedence over a single reading.