7. THE MOLECULAR MECHANISMS OF COMPARTMENT SYNDROME

Abstract

Purpose: Compartment syndrome is a severe complication of skeletal trauma. Intravital microscopy (IVVM) has demonstrated an inflammatory response to compartment syndrome (CS). The molecular mechanisms underlying this inflammatory response are unknown. The purpose of this study was threefold. First, a broad inflammatory cytokine profile was examined to determine the molecules responsible for white cell recruitment. As well, skeletal muscle expression of white cell adhesion molecules including P-Selectin, E-Selectin, Mac-1 and ICAM-1 were examined to assess the extent of white cell activation in target tissues. Finally, skeletal muscle apoptosis was measured to determine the magnitude of cell death.

Method: Normal and neutropenic rats were randomised to either compartment syndrome or control groups. CS Animals were treated with 45 minutes of elevated intra-compartmental pressure (EICP) of the hindlimb. Fasciotomy was then performed, followed by 60 minutes of reperfusion. Control animals experienced no EICP. Blood was collected from carotid arterial lines used for pressure monitoring. Skeletal muscle tissue samples were collected from the EDL following reperfusion. Blood samples were obtained from carotid arterial lines and skeletal muscle was collected following reperfusion. A Multiplex assay was used to examine serum levels of 24 proinflammatory cytokines/chemokines. Skeletal muscle mRNA levels of P-Selectin, E-Selectin, Mac-1 and ICAM-1 were evaluated using real-time PCR. Finally, skeletal muscle apoptosis was measured by DNA laddering and a caspase-3 assay.

Results: Neutropenic CS animals demonstrated a continuous increase in TNF-alpha levels, peaking at 700+/−350pg/ml by 60 minutes of reperfusion. TNF-alpha values for other groups did not increase. A 104-fold increase in ICAM-1 mRNA levels was observed in neutropenic CS rats while other groups showed no significant increase. There was no significant increase in any group for P-Selectin, E-Selectin, or Mac-1.

Conclusion: This study is the first to attempt to describe the molecular inflammatory response in CS. Neutropenic CS animals demonstrated an upregulation in TNF-alpha and ICAM-1 mRNA levels. This likely represents an attempt to generate an inflammatory response in the neutropenic animals. Additional data at incremental timepoints is necessary to further characterize the molecular mechanisms. However, both TNF-alpha and ICAM-1 appear to be important in the mechanism of inflammatory activation in compartment syndrome.