Ju Mizuno,1 Toru Takahashi2 1Department of Anesthesiology and Pain Medicine, Juntendo University Faculty of Medicine, Bunkyo-ku, Tokyo, 2Faculty of Health and Welfare Science, Okayama Prefectural University, Soja-shi, Okayama, Japan Background: Well-leg compartment syndrome (WLCS) is one of the catastrophic complications related to prolonged surgical procedures performed in the lithotomy position, using a knee-crutch-type leg holder (KCLH) system, to support the popliteal fossae and calf regions. Obesity has been implicated as a risk factor in the lithotomy position-related WLCS during surgery. In the present study, we investigated the relationship between the external pressure (EP) applied to the calf region using a KCLH system in the lithotomy position and selected physical characteristics. Methods: Twenty-one young, healthy volunteers (21.4±0.5 years of age, eleven males and ten females) participated in this study. The KCLH system used was Knee Crutch®. We assessed four types of EPs applied to the calf region: box pressure, peak box pressure, contact pressure, and peak contact pressure, using pressure-distribution measurement system (BIG-MAT®). Relationships between these four EPs to the calf regions of both lower legs and a series of physical characteristics (sex, height, weight, and body mass index [BMI]) were analyzed. Results: All four EPs applied to the bilateral calf regions were higher in males than in females. For all subjects, significant positive correlations were observed between all four EPs and height, weight, and BMI. Conclusion: EP applied to the calf region is higher in males than in females when the subject is supported by a KCLH system in the lithotomy position. In addition, EP increases with the increase in height, weight, and BMI. Therefore, male sex, height, weight, and BMI may contribute to the risk of inducing WLCS. Keywords: well-leg compartment syndrome, pressure-distribution measurement system, peak contact pressure, physical characteristics, obesity