Intramuscular and Blood Pressures in Legs Positioned in the Hemilithotomy Position: Clarification of Risk Factors for Well-Leg Acute Compartment Syndrome

Background: Acute compartment syndrome has been widely reported in legs positioned in the lithotomy position for prolonged general surgical, urologic, and gynecologic procedures. The orthopaedic literature also contains reports of this complication in legs positioned on a fracture table in the hemilithotomy position. The purpose of this study was to identify the risk factors for development of acute compartment syndrome resulting from this type of leg positioning. Methods: Eight healthy volunteers were positioned on a fracture table. Intramuscular pressures were continuously measured with a slit catheter in all four compartments of the left leg with the subject supine, in the hemilithotomy position with the calf supported, and in the hemilithotomy position with the heel supported but the calf free. Blood pressure was measured intermittently with use of automated pressure cuffs. Results: Changing from the supine to the calf-supported position significantly increased the intramuscular pressure in the anterior compartment (from 11.6 to 19.4 mm Hg) and in the lateral compartment (from 13.0 to 25.8 mm Hg). Changing from the calf-supported to the heel-supported position significantly decreased intramuscular pressure in the anterior, lateral, and posterior compartments (to 2.8, 3.4, and 1.9 mm Hg, respectively). The mean diastolic blood pressure in the ankle averaged 63.9 mm Hg in the supine position, which significantly decreased to 34.6 mm Hg in the calf-supported position. Changing to the heel-supported position had no significant effect on the diastolic blood pressure in the ankle (mean, 32.8 mm Hg). The mean difference between intramuscular pressure and diastolic blood pressure in the supine position was approximately 50 mm Hg in each of the four compartments. This mean difference significantly decreased to <20 mm Hg in the calf-supported position and then, when the leg was moved into the heel-supported position, significantly increased to approximately 30 mm Hg in all compartments. Conclusions: The combination of increased intramuscular pressure due to external compression from the calf support and decreased perfusion pressure due to the elevated position causes a significant decrease in the difference between the diastolic blood pressure and the intramuscular pressure when the leg is placed in the hemilithotomy position in a well-leg holder on a fracture table. Combined with a prolonged surgical time, this position may cause an acute compartment syndrome of the well leg. Leaving the calf free, instead of using a standard well-leg holder, increases the difference between the diastolic blood pressure and the intramuscular pressure and may decrease the risk of acute compartment syndrome.