Compartment syndrome, a devastating consequence of limb trauma, is characterised by severe tissue injury and microvascular perfusion deficits. We hypothesised that leucopenia might provide significant protection against microvascular dysfunction and preserve tissue viability. Using our clinically relevant rat model of compartment syndrome, microvascular perfusion and tissue injury were directly visualised by intravital video microscopy in leucopenic animals. We found that while the tissue perfusion was similar in both groups (38.8% (standard error of the mean (sem) 7.1), 36.4% (sem 5.7), 32.0% (sem 1.7), and 30.5% (sem 5.35) continuously-perfused capillaries at 45, 90, 120 and 180 minutes compartment syndrome, respectively versus 39.2% (sem 8.6), 43.5% (sem 8.5), 36.6% (sem 1.4) and 50.8% (sem 4.8) at 45, 90, 120 and 180 minutes compartment syndrome, respectively in leucopenia), compartment syndrome-associated muscle injury was significantly decreased in leucopenic animals (7.0% (sem 2.0), 7.0%, (sem 1.0), 9.0% (sem 1.0) and 5.0% (sem 2.0) at 45, 90, 120 and 180 minutes of compartment syndrome, respectively in leucopenia group versus 18.0% (sem 4.0), 23.0% (sem 4.0), 32.0% (sem 7.0), and 20.0% (sem 5.0) at 45, 90, 120 and 180 minutes of compartment syndrome in control, p = 0.0005). This study demonstrates that the inflammatory process should be considered central to the understanding of the pathogenesis of cellular injury in compartment syndrome.

Cite this article: Bone Joint J 2015;97-B:539–43

Purpose: Recent studies have examined the systemic inflammation that occurs following spinal cord injury (SCI) (Gris et al. 2008). It is believed that this systemic inflammation plays a role in the respiratory, renal and hepatic morbidity of SCI patients, ultimately contributing to mortality post-injury. Evidence of this inflammatory response has been shown as early as two hours post SCI (Gris et al. 2008) Intravital microscopy is a powerful tool for assessing inflammation acutely and in ‘real-time’ (Brock et al. 1999). This tool would be useful for demonstrating the acuteness of a systemic inflammatory response post-SCI, and for assessing the degree of inflammation to different severities of SCI. The liver has been shown to play a particularly important role in the initiation and progression of the early systemic inflammatory response to spinal cord injury (SCI), therefore the purpose was to evaluate hepatic inflammation immediately after SCI. We hypothesized that SCI would cause immediate leukocyte recruitment and that the magnitude of inflammation would increase with increasing severity of cord injury.

Method: Male Wistar rats (200–225g) were randomly assigned to one of the following groups: uninjured, trauma-injured (laminectomy and no cord injury), cord compressed or cord transected. Spinal cord-injured rats were anesthetized by isoflurane, a dorsal laminectomy was performed, and the 4th thoracic spinal segment was injured by a moderately severe clip-compression injury or by a severe complete cord transection injury. Uninjured rats and trauma-injured rats served as controls. At 0.5 and 1.5 h after SCI rats had the left lobe of their livers externalized and visualized using intravital video microscopy.

Results: At 0.5 hours the total number of leukocytes per post-sinusoidal venule was significantly increased after cord compression and cord transection compared to that in uninjured and trauma-injured rats (P< 0.05). Of these leukocytes significantly more were either adherent or rolling along venule walls compared to uninjured and trauma-injured rats (P< 0.05). Of the rolling leukocytes 2–fold more were observed after cord transection compared to cord compression. At 1.5 h the total number of leukocytes per post-sinusoidal venule and the number of adherent leukocytes was significantly increased only after cord transection.

Conclusion: Injury to the spinal cord but not trauma alone causes immediate leukocyte recruitment to the liver within 0.5 h after injury. Also, leukocyte recruitment increases with increasing severity of injury. This is the first study to use intravital microscopy to visualize systemic inflammation in the liver following SCI.

Purpose: Severe compartment syndrome is associated with renal failure, end organ damage, and systemic inflammatory response syndrome (SIRS). Intravital videomicroscopy (IVVM) is a useful tool to study capillary perfusion and inflammation in end organs such as the liver and lungs. In this study, the systemic effect of hindlimb compartment syndrome was studied using hepatic IVVM. The purpose was to measure the effect of increased hindlimb intracompartmental pressure on hepatocyte viability, inflammation, and blood flow in a rodent model.

Method: Ten Wistar rats were randomised into control (C) and Compartment Syndrome (CS) groups. Animals were anaesthetized with 5 % isoflurane. Mean arterial pressure was monitored using a carotid artery catheter. Elevated intracompartmental pressure (EICP) was induced by saline infusion into the anterior compartment of the hind limb and maintained for 2 hours between 30–40mmHg in the CS group. Two hours following fasciotomy, the liver was analyzed using IVVM to quantify capillary perfusion as a measure of microvascular dysfunction. The numbers of adherent and rolling leukocytes in venules and sinusoids were quantified to measure the inflammatory response. Irreversible hepatocyte injury was measured using a fluorescent vital dye which labels the nuclei of severely injured cells.

Results: Hepatocellular injury was significantly higher in the CS group (325±103 PI labeled cells/10-1 mm2) compared to controls (30±12 PI labeled cells/10-1 mm2)(p=0.0087). The number of adherent venular white blood cells (WBC) was significantly higher for the CS group (5±2/hpf) than controls (0.2±0.2)(p=0.0099). Volumetric blood flow was not significantly different between CS and controls.

Conclusion: After only 2 hours of compartment syndrome in this animal model, the number of activated white blood cells increased 25-fold and liver cellular injury increased 10-fold compared to controls. Marked systemic inflammation and hepatocellular damage was detected in response to isolated limb compartment syndrome. Compartment syndrome is a low-flow ischemia/reperfusion injury with a profound inflammatory response. Further research into the severe end-organ damage associated with compartment syndrome is required.