Summary:The compartment syndrome is a known complication of limb injury. It has been suggested that intramedullary reaming before the insertion of a nail generates unphysiologic pressures in the medulla, resulting in elevated compartment pressures, and thus the unreamed nail is preferable if the specific injury carries the risk of developing an acute compartment syndrome. We examined the effect of intramedullary reaming on compartment pressures in isolation. We investigated intramedullary pressures during intramedullary reaming of the intact ovine tibia and recorded pressures in the anterolateral and deep posterior compartments simultaneously. Muscle blood flow was measured in four anatomically distinct muscle groups (anterior, lateral, deep posterior, and gastrocnemius), by using radiolabeled microspheres —30 min after reaming. Before intramedullary reaming, different positions of the lower limb caused considerable elevations of compartment pressures. During reaming, intramedullary pressure increases >940 mm Hg were recorded, resulting in elevations of compartment pressures. All increases of pressure were transient, and in no case was a persistent increase in compartment pressure observed. There was no decreased blood flow in the soft tissues after reaming. We conclude that intramedullary reaming as such does not lead to the development of an acute compartment syndrome.