Development and mechanical characterisation of an animal model of acute compartment syndrome.

Acute compartment syndrome (ACS) is an orthopaedic emergency that occurs after limb trauma, where increased pressure in muscle compartments disrupts blood flow, risking nerve and muscle damage. Timely diagnosis is essential to avoid permanent harm, but current methods are either invasive, expensive, or subjective. The gold standard remains invasive intracompartmental pressure (IComP) measurement, with other approaches lacking enough evidence to replace it. This study proposes two mechanical tools - mechanical indentation and image-based strain mapping - as simplified methods for ACS assessment. Our work started by establishing a porcine model of ACS, involving intracompartmental gelofusine infusion and pressure measurement in selected muscles of the appendicular skeleton. The IComP could then be adjucted as required from 0 - 40 mmHg (which exceeds the diagnostic threshold of 30 mmHg). With a consistent animal model of ACS, we sought to identify if mechanical methods could measure the internal muscle pressure changes from the surface of the skin. Using a custom-made handheld indenter, we examined the skin overlying muscles during IComP manipulations. Whilst we observed some changes in the mechanical moduli extracted from the indentation force-displacement curves, there was no statistical difference in this method changing pressure. We then used a single-camera digital image correlation (DIC), which showed that as internal pressure increased, corresponding surface skin strains increased. At 30 mmHg the skin reached an average strain of approximately 1.5% although local strains were higher due to an uneven distribution of pressure in the muscle (one reason for the indenter results being so variable). This approach therefore provides a non-invasive diagnostic threshold for ACS in our model and has the potential for clinical use in human patients. STATEMENT OF SIGNIFICANCE: In this study, we established a porcine model of acute compartment syndrome (ACS) to evaluate the mechanical response of skin and muscle under increased intracompartmental pressure (IComP). We developed and tested two non-invasive diagnostic approaches-mechanical indentation and single-camera digital image correlation (DIC)-to assess internal pressure changes from the skin surface. While the indentation method exhibited variability due to uneven pressure distribution, the DIC approach demonstrated a clear relationship between increased IComP and surface strain, identifying a diagnostic threshold of approximately 1.5% strain at 30 mmHg. These findings provide a foundation for the development of non-invasive ACS diagnostic tools that use the mechanical properties of the tissue as a health biomarker (e.g., wearable sensors), offering potential for simplified and cost-effective clinical application.