The biomechanical characteristics of anatomic reduction versus medial displacement osteotomy were compared for four-part intertrochanteric fractures experimentally produced in cadaver femurs. Eighteen pairs of femurs were assigned randomly to either the anatomic (A) or the medial displacement (MD) group and instrumented with multiple strain gauges. The femurs in the MD group were tested while intact and following four-part fracture with fixation. The femurs in the A group were first tested intact, followed by a stable two-part fracture with fixation, and then by a four-part fracture with fixation and perfect reduction of the posteromedial fragment (PMF) with a lag screw, partial reduction of the PMF, and with the PMF omitted. All fractures were fixed with a 135 degrees, four-hole, sliding hip screw. The strain distribution in the MD group changed significantly after fracture. The plate tensile strain increased by 360% while the compressive calcar strain decreased 85%. The plate tensile strain in the A group also increased significantly after four-part fracture when the PMF was perfectly reduced (160%), partially reduced (290%), or discarded (275%); the calcar compressive strains for these subgroups decreased approximately 50%. This laboratory study indicates that anatomic reduction of four-part intertrochanteric fractures with the sliding hip screw, regardless of the presence or position of the PMF, provides significantly higher compression across the calcar region and significantly lower tensile strain on the plate than fractures reduced by medial displacement osteotomy. The more physiologic strain distribution and the increased medial load transmission support the use of anatomic reduction for the treatment of unstable intertrochanteric fractures.