To investigate the annual change of bone mineral density (BMD) around the femoral stem and identified the factors that influence the stress shielding effect in patients who have received extensively porous coated cementless stem.

We reviewed seventy-four patients who were followed up for longer than three years after unilateral primary total hip replacement arthroplasty. The BMD was measured annually using a DEXA QDR 4500® on the proximal femur according at the Gruen zone. We analyzed the relationship between the results and the possible variates of periprosthetic bone remodeling.

In first year after operation, the BMDs of all Gruen zone decreased significantly. From the second year, the BMDs in Gruen zones 1, 2, and 7 were decreased significantly, but those in Gruen zones 3, 5, and 6 were increased. After three years, the BMD showed no significant change. Among the examined variables including sex, patient's age, stem size, and preoperative Singh's index, stem size and age were found to have strong predictive value.

Our findings suggest that periprosthetic BMD decreased in all areas over first postsurgical year. From the third year, the BMD stabilized.