A Novel Non-invasive Method for the Detection of Elevated Intra-compartmental Pressures of the Leg

Summary

An ultrasound probe coupled with a pressure sensor is used to assess the intra-compartmental pressure of the leg by directly measuring the compartment fascia flattening pressure (CFFP). This non-invasive protocol will provide reliable assessment of the pressure inside the anterior muscular compartment of the lower leg.

Abstract

Acute Compartment Syndrome is a devastating consequence of musculoskeletal trauma. Currently the diagnosis is based on clinical signs and symptoms, and while adjuncts such as invasive intra-compartmental pressure measurements are often used to corroborate the physical exam findings, there remains no reliable objective test to aid in the decision to perform a decompressive fasciotomy. In a cadaver model of compartment syndrome, an ultrasound (US) based method has been shown to be a reliable measurement of increased intra-compartmental pressure. An absolute pressure of >100 mbar or a difference of 50 mbar in the CFFP between the legs can be considered pathologic. Using an ultrasound transducer, coupled with a pressure sensor, the pressure needed to flatten the superficial fascia of the anterior compartment of lower legs (Compartment Fascia Flattening Pressure [CFFP]) can be measured. The CFFP of the injured leg is compared to the CFFP of the uninjured leg. This US measured index can then serve as an adjunct to the physical exam in evaluating injured lower extremities and assessing the need for decompressive fasciotomy. The advantages of this protocol include: being a non-invasive method and an easily reproducible technique.

Introduction

The purpose of this novel protocol is to evaluate the intra-compartmental pressure of the leg in a non-invasive way by using an ultrasound transducer coupled with a pressure sensor. Compartment syndrome is a well-known complication in musculoskeletal trauma and is the result of elevated intra-compartmental pressures which compromise the perfusion of tissues leading to irreversible ischemic injury if not intervened upon. Its diagnosis is primarily based on clinical exam. Unfortunately, clinical exam alone has been shown to have poor sensitivity and specificity in the diagnosis of compartment syndrome¹. Invasive intra-compartmental pressure measuring by needle manometry is commonly used in the assessment of compartment syndrome^2,3,4. The disadvantage of needle manometry is that it is an invasive procedure, being quite uncomfortable for the patient and not amenable to serial measurements. Furthermore, invasive intra-compartmental pressure measuring measurement is not routinely performed by some surgeons due to considerable disagreement over the appropriate threshold pressure for diagnosis of ACS and the high (35%) false positive rate and variability of a single invasive measurement^5,6,7.

It has been previously demonstrated in artificial, animal, and human cadaver models that a rise in the intra-compartmental pressure results in a decreased elasticity of the fascia overlying the anterior compartment suggesting a correlation between the intra-compartmental pressure and compliance of the facial compartment as measured by ultrasound^8,9,10. Further work has described using the pressure required to flatten the fascia of the anterior compartment as measured by ultrasound (Compartment Fascia Flattening Pressure [CFFP]) as a surrogate measure of the intra-compartmental pressure¹¹. The anterior compartment fascia can be readily visualized with standard ultrasonography and, with the addition of a pressure sensor to the probe, CFFPs can be easily and reliably measured. This protocol offers a non-invasive diagnostic alternative for evaluating intra-compartmental pressures and can be performed quickly and serially with little to no patient discomfort.

Protocol

This experimental protocol has been reviewed and approved by our hospital’s institutional review board (IRB) and follows all guidelines set forth by our institution’s human research ethics committee.

1. Identify the Fascia of the Anterior Compartment of the Leg

1. Identify a starting site for the ultrasound probe. Place the probe directly over the anterior compartment, just lateral to the tibial crest and one handbreadth distal to the tibial tubercle.
2. Identify the fascia as 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.
3. Note the geometry of the fascia. With minimal pressure applied, this should be a convex shape.

2. Measure the Compartment Fascia Flattening Pressure of the InjuredLeg

1. 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 CFFP.
2. Once the anterior compartment fascia is perfectly flat, record the pressure sensor measurement.
3. Repeat the CFFP measurement 2 more times. Record and average all 3 pressures to define the final CFFP.

3. Calculate the Delta CFFP Compared to the Uninjured (Contralateral) Leg

1. Measure and record the CFFP in the contralateral leg in the same manner described above.
2. Calculate the delta CFFP by taking the difference between the CFFP of the injured leg the well leg.

Results

This technique has been used to measure 10 consecutive patients with injured legs without evidence of compartment syndrome and 3 patients with a clinical diagnosis of compartment syndrome necessitating decompressive fasciotomies. The average delta CFFP for patients without compartment syndrome was 10.7 ± 10.6 mbar compared to 157 ± 51.7 mbar for patients with compartment syndrome and single-tailed t-test identified the differences in pressures between the groups as being statistically significant (P < 0.02)...

Discussion

This article demonstrates a novel, clinically applicable technique for the non-invasive measurement of intra-compartmental pressures in the leg using an ultrasound coupled with a pressure sensor. This technique only requires a hand-held ultrasound and a commercially available pressure sensing transducer. It is quick and easy to perform and is well tolerated by patients. The entire diagnostic procedure can be performed in under 5 min with no additional resources. The calculated delta CFFP may then be used in conjunction w...

Materials

Name	Company	Catalog Number	Comments
Pressure sensor: Venous pressure measurement device	Vein press	VP 2014	A peripheral venous measuring device used in conjuction with an ultrasound to measure peripheral venous pressure.
Ultrasound probe: Vscan Extend R2 Dual Probe DICOM Base Package	GE Healthcare	H8038VP	Any ultrasound probe will be sufficent for this test. Using the narrow tranducer will function best when coupled to the pressure sensor