This protocol is uniquely significant because it's a non-invasive means of assessing intra-compartmental pressures in the leg. This can be important when evaluating an injured extremity, which may be at risk for compartment syndrome, a limb-threatening condition. As intra-compartmental pressures rise, the perfusion of the structures within the compartment decreases, leading to an ischemic insult.
If elevated pressures are not identified and treated quickly, the compartment dies, resulting in permanent disability. The primary advantage of this technique is its non-invasiveness. Currently, the only means by which to measure intra-compartmental pressure is by inserting a large-bore needle equipped with a pressure gauge into the leg compartment.
While reliable, this technique is quite uncomfortable to the patient and is not suitable for performing serial measurements. For someone first trying this technique, I would recommend that they first practice the technique on a volunteer. Learning the amount of pressure to apply and interpreting the ultrasound images can be difficult at first.
To begin this procedure, identify a starting site for the ultrasound probe. Place the probe directly over the anterior compartment, just lateral to the tibial crest and one hand breadth distal to the tibial tubercle. Next, identify the fascia, which is the bright white strip just below the subcutaneous tissue on the ultrasound.
Move the probe until the fascia is seen at the point where it attaches to the tibial crest. Note the geometry of the fascia. With minimal applied, this should be a convex shape.
Once the fascia of the anterior compartment is identified, apply slow and steady pressure to the ultrasound probe until the fascia changes shape from convex to completely flat. Make several attempts, including passing the flattening point to produce a concave shape in an effort to gently hone in on the exact compartment fascia flattening pressure. Once the anterior compartment fascia is perfectly flat, record the pressure sensor measurement.
Repeat the CFFP measurement two more times. Record an average, all three pressures, to define the final CFFP of the injured leg. First, measure and record the CFFP in the contralateral leg in the same manner previously described.
Calculate the delta CFFP by taking the difference between the CFFP of the injured leg from the CFFP of the well leg. In this study, a novel, clinically applicable technique for the non-invasive measurement of intra-compartmental pressures in the leg is demonstrated using an ultrasound coupled with a pressure sensor. This technique has been used to measure 10 consecutive patients with injured legs without evidence of compartment syndrome, and three patients with a clinical diagnosis of compartment syndrome, necessitating decompressive fasciotomies.
The average delta CFFP for patients without compartment syndrome is approximately 10.7 millibar, compared to approximately 157 millibar for patients with compartment syndrome. A single-tailed T-test identified the differences in pressures between the groups as being statistically significant. When performing this technique, it is important to identify the pressure at the exact point when the fascia changes from convex to completely flat.
To best facilitate this, it is helpful to have an assistant available to read the pressure while the person performing the technique maintains their focus on the ultrasound. Once the fascia changes from convex to flat, the person performing the test can call out pressure, signaling the assistant to record the pressure reading. After this diagnostic test is performed, the results can be compared against the gold standard for assessing intra-compartmental pressures, which is needle manometry.
The most commonly used device for this is the Stryker quick pressure monitor set.
