PURPOSE To biomechanically quantify 2 techniques, compression screw and perpendicular clamp, for generating compression during ulnar shortening osteotomy (USO) in order to promote reliable primary bone healing. METHODS Fourteen fresh-frozen cadaveric human forearms were randomly assigned to 1 of 2 groups. Group I (n = 7) underwent USO according to the traditional AO plate fixation technique using a screw placed eccentrically in an oblong hole to generate compression at the osteotomy site. Group II (n = 7) underwent USO with a commercially available USO plating system using a clamp placed perpendicular to the osteotomy site to generate compression. Both techniques involved a 2-mm resection osteotomy performed with cutting jigs to minimize variability and an interfragmentary lag screw to augment compression. A digital pressure sensor measured contact area at the osteotomy site and average pressure in the observed contact area; these values were used to calculate force across the osteotomy site. Measurements were obtained after the following steps: reduction of osteotomy, compression screw placement (group 1 only), lag screw placement, and final construct with all clamps removed. RESULTS Group II demonstrated significantly greater force than group I, and lag screw placement resulted in significantly increased force independent of fixation technique. The effect of the lag screw on force was maintained after clamp removal. Although technique of fixation did not significantly influence contact area, lag screw placement significantly increased contact area independent of fixation method. However, this effect was not maintained after clamp removal. Average pressure in the observed contact area was not significantly influenced by fixation technique or stage of fixation. CONCLUSIONS Perpendicular clamp compression significantly increased force as compared with traditional compression screw technique, and lag screw placement significantly increased force in both constructs. CLINICAL RELEVANCE Larger compressive forces across the osteotomy may promote primary bone union and decrease the rates of delayed union or nonunion.