Trochanteric fractures. Influence of reduction and implant position on impaction and complications. A review of roentgenograms and charts was made of 532 trochanteric fractures treated by the sliding-screw technique. According to Evans' modified classification, 65% of the fractures were unstable. There was no breakage or bending of implants. Twenty (3.8%) reoperations were performed because of technical complications or nonunion. The Singh index revealed more unstable fractures and technical complications in hips with Grades 1-3 than in hips with Grades 4-6. Reoperation was more frequent if the screw tip was within 8 mm from the subchondral line in the superolateral quadrant or in the anteroproximal quadrant than if the screw ended farther from the subchondral line. Fifty-five (10.8%) of the lag screws migrated 2 mm or more. Postoperatively, the neck-shaft angle decreased more in unstable fractures than in stable fractures. The decrease in neck-shaft angle was less when the proximal fragment impinged medially on the shaft fragment. Unstable fractures with this type of reduction also impacted less than hips with anatomic reduction or medial reduction of the shaft fragment. Weight bearing did not significantly influence the degree of impaction. 