Pretest

Patient's symptoms must be reproduced before intracompartmental pressures are measured.4 It is usually recommended that the subject continues to exercise in the days to weeks before testing to maximise the possibility of reproducing typical symptoms.1 Ultimately, it may be necessary to have the subject perform the specific activity that elicits pain, although a variety of exercise protocols, including resisted ankle plantar and dorsiflexion, cycling on an ergometer or treadmill running, have been described.5

Devices

Boody and Wongworawat6 found that the Stryker Intracompartmental Pressure Monitor System was accurate when used to measure in vitro models of known pressure. They compared the three types of needle used (slit catheters, side port needles and straight needles) and found that the slit catheter was most accurate, followed by the side port needle. Straight needles tended to overestimate the pressure. The slits in the slit catheter are thought to minimise tip occlusion and increase the surface area at the catheter–tissue interface.1

Needle positioning

Because intramuscular pressure may be affected by joint angle, measurements should be performed with the knee and ankle in a standardised, relaxed position, for serial recordings.7 A standard angle of needle insertion has not been agreed upon, but insertion at approximately 45° to the skin allows reasonable depth, without excessive discomfort, and is reproducible. Positioning of the catheter is seldom a problem, except in the deep posterior compartment where insertion is ‘blind’.5 Catheter placement into the tibialis posterior is not as reliable due to the relatively inaccessible position of this muscle.8 Wiley et al9 have shown that ultrasound-guided insertion allows for a safe, reliable, reproducible method for catheter tip placement in recording the pressure in tibialis posterior.

Maximum pressure versus rate of return to normal

Some authors suggest that the rate of return to resting pressures following exercise is more accurate than relying on resting or absolute pressures and that maximal exertional pressures seem to demonstrate extreme variability.3 Howard et al10 found that the magnitude of the measured pressure was not useful as a prognostic indicator for patients undergoing fasciotomy, as patients with higher pressures did not necessarily experience greater pain relief postfasciotomy. Use of the slit catheter (the only needle type that remains in situ) allows a progressive monitoring of the peaks of pressure, with time to return to resting levels.

Pedowitz diagnostic criteria (pressure cut-offs)

The normal resting compartment pressure is between 0 and 8 mm Hg.11 Exercise results in an increase in muscle volume of the magnitude of 8–20%,12 13 which results in increased pressure. Following exercise, volume and pressure within a compartment will gradually return to pre-exercise levels, usually within 5 min.4 In a compartment unaffected by CECS, the drop in pressure is almost instantaneous. A prolongation of increased pressure postexercise is felt to be suggestive of CECS, and these pressures may remain abnormally high for 20 min or longer after exercise, before returning to normal.2 Pedowitz et al14 developed ‘modified criteria for the objective diagnosis of chronic compartment syndrome of the leg’. They performed compartment pressure studies on 45 patients who were deemed CECS-positive and 75 patients who were deemed CECS-negative and considered one or more of the following intramuscular pressure criteria to be diagnostic of CECS in the leg:

1. A pre-exercise pressure ≥15 mm Hg

2. A 1-min postexercise pressure ≥30 mm Hg

3. A 5-min postexercise pressure ≥20 mm Hg

4. CECS-negative legs demonstrated the following mean pressure results: resting 7.4 mm Hg; 1-min postexertion 10.7 mm Hg; and 5-min postexertion 8.0 mm Hg.14

Survey of the Australasian College of Sports Physicians

In August 2009, the Fellows and Registrars of the Australasian College of Sports Physicians, who perform intracompartmental pressure testing, were asked to complete a survey, which investigated the current standards of practice. There were 27 respondents. The survey questions are included in the appendix.

Pretest consultation

It was found that 88% of specialists typically perform an initial consultation before the test. In 40% of cases, there was no delay in performing the test, whereas around 50% allowed 1–3 weeks. The authors feel that performing an initial consultation before the test could allow a thorough screening for co-existing causes of exertional leg pain,15 assessment of current investigations, determination of the suitability of the patient to be tested and explanation of the risks of the testing procedure. It can ensure patients will reliably reproduce their symptoms prior to the test, while rehabilitating other causes of exertional leg pain to ensure the symptoms reproduced on the day of testing are due to CECS alone.

Test protocols

Approximately half of respondents will routinely test both limbs. CECS symptoms are bilateral in 75–90% of cases,16 and further research may determine if (in cases of bilateral symptoms) it is possible to investigate one limb only and to be able to safely conclude that a positive result indicates the existence of bilateral CECS.

In 77% of respondents, only the symptomatic compartments were investigated. It is not known whether testing of asymptomatic compartments routinely determines the presence of CECS in these compartments.

Most practitioners surveyed do not adhere to a set exercise protocol, preferring that patients should determine what they need to do, to best reproduce their symptoms, be it, for example, walking at pace, jogging, climbing stairs or treadmill running. Most practitioners surveyed allow for 1–15 min of exertion, and aim for patients to assess their symptoms subjectively as 80% of ‘as bad as it has ever been’. No set standardised leg position is utilised despite the fact that standing pressures typically are 8 mm Hg higher than supine pressures3 and the supine position is reproducible.

Resting pressures

In 48% of respondents, resting pressures are measured as part of their investigation. In none of these is the test stopped if a resting pressure ≥15 mm Hg was found. The authors believe that the pathophysiology of CECS suggests that pain present at rest is not in keeping with CECS.2 Further study may help determine whether measurement of resting pressures is necessary in establishing the diagnosis of CECS.

Pressure protocols

Of greatest concern was the finding that the protocols used for intracompartmental pressure testing had significant variation: 51% adhere strictly to the Pedowitz guidelines (>30 mm Hg at 1 min and >20 mm Hg between 2 and 5 min). The remainder seem at risk of over or underreporting the presence of CECS. Further study and larger sample sizes to determine more accurately normal pressure cut-offs in control groups and a pressure profile in CECS-positive patients may help create better pressure protocols.

Needle type

The majority (77%) of respondents will only use the ‘in–out’ side port needle in their testing.

Needle positioning

Seventy-seven percent have never used ultrasound-guided needle placement, the remainder will rarely use it and none use it routinely. Ultrasound-guided needle placement is thought to be the only accurate way of investigating the deep posterior compartment,8 9 17 and this raises the possibility of inaccurate needle positioning in many of these practitioners. Further study determining ‘blind’ needle insertion position for deep posterior CECS testing may help determine whether ultrasound should be routinely used.

Complications

Despite being invasive, intracompartmental pressure testing seems to be relatively safe. Sixty-three percent of respondents have never had any significant complications despite many years of performing the investigation. However, complications can occur, which can be limb threatening, and should be discussed with the patient before the test. Of the respondents, there was one report of infection, one of significant haematoma, two cases of inadvertent nerve damage (which made full recoveries), two of inadvertent arterial punctures that recovered uneventfully and three cases of significant post-test pain (where a complex regional pain syndrome was suspected in two out of three cases). There were also two reports of the development of acute compartment syndrome needing emergency fasciotomy, both involved in testing the deep posterior compartment.

Survey summary

In summary, no two survey respondents performed intracompartmental pressure testing protocols in the same manner from start to finish. Advice given to patients before the test varies with some clinicians performing investigations with no pretest counselling or determination if the patient can reliably reproduce symptoms. No consensus exists as to how to perform the test, whether it be which compartments are investigated; whether resting pressures are necessary; whether both limbs warrant testing; or how Pedowitz's guidelines are interpreted. While the majority of clinicians seem to perform the investigation in a sensible manner, some techniques could be associated with under or overinterpretation of the tests' outcome.