71 - Sonographic Landmarks for Identification of Foot Compartments in Potential Acute Foot Compartment Syndrome

Poster Board Number: 71
There are separate poster presentation times for odd and even posters.
Odd poster #s – first hour
Even poster #s – second hour

Abstract Body : Introduction and Objective:
Acute compartment syndrome (ACS) can be life-altering and requires surgical intervention. Unlike other areas, foot fascial compartments are not well characterised. Confirmation of ACS requires direct measurement of sustained intra-compartmental pressure (ICP) rises.
Multiple foot compartment models are described, varying in boundaries, contents, and capability. This uncertainty delays diagnosis and treatment. Our study aimed to define landmarks to identify compartments sonographically in an emergency setting, which can guide ICP cannulation into ‘safe’ areas of compartments. The plantar aspect of the six-compartment model by Faymonville and colleagues (2012) was used.

Materials and Methods
Both feet from living participants (n=20) and unembalmed cadavers (n=3) were used for sonography. The most sonographically prominent muscle in each compartment was selected, these are Abductor hallucis (medial), Flexor digitorum brevis (superficial), Quadratus plantae (calcaneal), Abductor digiti minimi (lateral), and Adductor hallucis (adductor).
Measurements were validated through comparison of sonographic devices, and inter- and intra-observer reliability. Both SuperSonic Imagine's Aixplorer with linear probe (SL10-2), and a Samsung Galaxy S2 with Philips Lumify software and linear probe (SL12-4) were used. Muscles were separately imaged by two observers. For five participants, observations were repeated by the primary observer once per week for five weeks.
The CSA at maximum muscle thickness (CSAmax Th) in the lengthwise parasagittal plane was chosen as the easy to locate safe access point and was marked on the skin. This point was standardised to a percentage of foot length (measured from posterior extent of the heel to anterior extent of the second digit).

Results
Comparison of devices and observers showed no significant differences in the proportional location of CSAmax Th for each muscle. The location of CSAmax Th for muscles indicating each compartment was standardised against foot length. CSAmax Th values were then averaged to produce standardised positions of CSAmax Th for each muscle. Positions of CSAmax Th standardised for foot length (mean ± 1SD) for respective compartments are medial 38 ± 2%, superficial 45 ± 3%, calcaneal 42 ± 3%, lateral 31 ± 2%, and adductor 51 ± 3%. The Aixplorer and Samsung tablet performed equally in locating CSAmax Th.
Inter-observer reliability between two observers was assessed with interclass correlation coefficients (ICC). Except for the calcaneal compartment of quadratus plantae (ICC>0.71), inter-observer reliability for identifying CSAmax Th was good (ICC>0.75) or excellent (ICC>0.9). Intra-observer reliability was assessed via two-way ANOVA (p>0.05, not significantly different) with ICC as good (>0.75) or excellent (>0.9).

Conclusions
This study provides proportionally standardised locations of muscles, facilitating accurate sonographic identification of ‘safe’ places for cannulating compartments to monitor ICP in suspected foot ACS.