Background: Bone mineral density decreases after total knee arthroplasty and is believed to affect prosthetic fixation. Treatment with alendronate has been shown to improve short-term bone mineral density after total knee arthroplasty; however, the long-term effects of this therapy are unknown. The purpose of this study was to evaluate the long-term effects of a six-month course of alendronate on bone mineral density after total knee arthroplasty.

Methods: Sixty patients were randomly assigned to receive either oral alendronate at a dosage of 10 mg/day for six months or no alendronate. The bone mineral density in the distal aspect of the femur and the proximal aspect of the tibia was measured preoperatively and at six, twelve, and thirty-six months after total knee arthroplasty.

Results: Fifty-four patients (twenty-nine in the alendronate group and twenty-five in the control group) completed the study. The alendronate group showed significant increases in bone mineral density in the distal aspect of the femur compared with the controls at six months (+4.8% and —14.2%, respectively; p < 0.01) and twelve months (+1.6% and —11.5%, respectively; p < 0.01). No significant difference in bone mineral density was detected between the groups at thirty-six months (—3.9% and —12.2%, respectively; p = 0.08). Similar trends in bone mineral density changes were also observed in the proximal aspect of the tibia.

Conclusions: A six-month course of alendronate initially increased bone mineral density at six and twelve months after total knee arthroplasty, but no difference was noted after thirty-six months. The effect of alendronate on bone mineral density after total knee arthroplasty may be limited after discontinuation of therapy.

Level of Evidence: Therapeutic Level I. See Instructions to Authors for a complete description of levels of evidence.