Animal studies have demonstrated the efficacy of the use of bisphosphonates to enhance screw fixation in bone. In this prospective, randomized study of pertrochanteric fractures treated with external fixation, we tested whether systemic administration of bisphosphonates would improve the fixation of hydroxyapatite-coated screws implanted in osteoporotic bone.Sixteen consecutive patients with a pertrochanteric fracture were selected. Inclusion criteria were female gender, an age of at least sixty-five years, and a bone mineral density T-score of less than -2.5 standard deviations. Exclusion criteria included bisphosphonate treatment during the two-year period prior to the fracture. Fractures were fixed with a pertrochanteric fixator and four hydroxyapatite-coated pins. Two pins were implanted in the femoral head (pin positions 1 and 2), and two were placed in the femoral diaphysis (pin positions 3 and 4). The patients were randomized either to therapy with alendronate for a three-month postoperative period (Group A) or to no therapy (Group B). The Group-A patients received an oral dose of 70 mg of alendronate per week. The fixators were removed after three months.All of the fractures healed, and no loss of reduction, nonunion, or delayed union was observed. The combined mean extraction torque (and standard deviation) of the pins implanted at positions 1 and 2 (cancellous bone) was 2558 +/- 1103 N/mm in Group A and 1171 +/- 480 N/mm in Group B (p < 0.0005). The combined mean extraction torque of the pins implanted at positions 3 and 4 (cortical bone) was 4327 +/- 1720 N/mm in Group A and 4075 +/- 1022 N/mm in Group B.These data show that weekly systemic administration of alendronate improves pin fixation in cancellous bone in elderly female patients with osteoporosis. We observed a twofold increase in extraction torque with the pins implanted in cancellous bone. These results support the use of alendronate in the treatment of osteoporotic pertrochanteric fractures to improve screw fixation in the femoral head.