Posterior stabilized component increased femoral bone loss after total knee replacement. 5-year follow-up of 47 knees using dual energy X-ray absorptiometry

After total knee replacement (TKR) bone mineral density (BMD) commonly decreases behind the anterior flange of the femoral component, which may increase the risk for supracondylar fracture. Our aim was to evaluate if changes in femoral design and joint area constraint had any effect on the postoperative bone remodeling in the distal femur.

We used dual-energy X-ray absorptiometry in 47 knees up to 5 years after operation with the AMK (DePuy, Johnson&Johnson Leeds, UK) TKR. The knees had been randomly allocated to receive a flat or a concave tibial insert with retention of the posterior cruciate ligament when preoperative deformity was less severe, and either a concave or a posterior-stabilized (PS) insert with resection of the posterior cruciate ligament when deformity was more pronounced.

The most pronounced relative reduction (15–38%) in bone mineral density (BMD) was seen posterior to the anterior flange. There were no significant differences in relative change in BMD between flat and concave inserts. Knees operated with PS inserts had more reduction posterior to the flange than knees with concave inserts in the subgroup with more advanced preoperative deformity (23% and 38% respectively).

Use of posterior stabilized insert may increase the risk of supracondylar fracture compared to concave insert in knees with advanced preoperative deformity.