The pattern of strain distribution in the proximal femur changes following total hip arthroplasty (THA) and decreases in bone mineral density (BMD) occur around the stem following cemented and uncemented THA. We herein prospectively examined changes in BMD for 3 years after THA with a cemented Exeter universal stem.
One hundred and sixty five hips from 150 patients who underwent unilateral THA were included as a cohort. Our patients included 20 men (20 hips) and 130 women (145 hips) with a mean age of 63.9 years. BMD was measured 2 weeks postoperatively (baseline) and 3, 6 12, 18, 24, 30, and 36 months (3 years) after surgery using dual-energy X-ray absorptiometry (DEXA) on the lumbar spine and proximal femur of the operated side according to the Gruen zone classification. We quantified longitudinal changes in BMD for more than 3 years after surgery and detected several factors which affected these changes.
In the first year, BMD in the most proximal femur showed a 5.5% reduction at the lateral side (zone 1) and 13% reduction at the medial side (zone 7), with no significant BMD reductions being observed thereafter. BMD reductions at 3 years were the most apparent at the proximal medial part of the femur (zone 7; -10.3%), while BMD ratio change in zone 1 was over the baseline (+2.9%). Especially in zone 7, the BMD ratio decreased with female, decreases in weight, decreases in height, decreases in BMI, and increases in age at the time of surgery.
Bone restoration is expected with a cemented Exeter universal stem. Male patients, a younger age, a high body weight, being tall, and a high BMI were identified as factors associated with the restoration of BMD in proximal femur.