STUDY DESIGN: Study of the influence of thoracolumbar spinal surgery through a posterior approach to the intercompartmental pressure of the paraspinal muscles.OBJECTIVE: To create waveforms according to the pressure variations up to 24 hours postoperatively and relate these measurements to independent parameters.SUMMARY OF BACKGROUND DATA: The existence of a paraspinal anatomic compartment and a relevant compartment syndrome has been supported theoretically, proven experimentally, and confirmed in clinical cases. The perioperative variations of the intercompartmental pressures remain largely unknown.METHODS: Five measurements were taken from both paraspinal compartments in each operated patient: preoperatively, intraoperatively, immediately after wound closure, and at 6 and 24 hours postoperatively. The recorded pressures were grouped as normal, elevated, or suggestive of a paraspinal compartment syndrome. Abnormal pressures were correlated with patient-related and operation-related parameters. Forty-two patients participated in the study, 21 male and 21 female patients aged 13 to 83 years (mean age 51 y). Seventy compartments were included in the final analysis.RESULTS: Forty-two compartments developed abnormally elevated pressures postoperatively and in 22 of these, pressures suggestive of a compartment syndrome were recorded. In no case was there a clinical presentation of a true compartment syndrome. Different waveforms were created for the normal and elevated pressures group. In compartments with high measurements, pressures were likely to continue to rise at 6 and 24 hours postoperatively. The body mass index was greater in both the elevated pressures and compartment pressures groups. Procedures lasting >2 hours, extended approaches, and instrumented posterior interbody fusion operations were related with lower postoperative pressures.CONCLUSIONS: A large percentage of patients develop increased paraspinal muscle pressures up to 24 hours after posterior thoracolumbar spine surgery. These increases are related to patient-related and operation-related factors and may not present clinically as a compartment syndrome.