Changes in bone density after cemented total knee arthroplasty - Influenceof stem design

Total knee arthroplasty has shown excellent survivorship in short-term and intermediate-term studies. With longer follow-up, however, aseptic loosenin g becomes an increasing cause of failure. Dual-energy x-ray absorptiometry scanning. has shown that stress shielding occurs from altered mechanical lo ading. The purpose of this study is to determine if tibial stem design affe cts bone density in the longterm. Bone densities in the proximal tibia with and without cemented stems were compared at an average of 94 months after surgery. The bone quality under the Milwler-Galante I prosthesis, which has 4 0.5-cm pegs, was compared with the bone quality under a Press-Fit Condyl ar prosthesis with a single 4-cm stem. Each group was also compared with th e unoperated contralateral tibia. Results showed that there is a significan tly reduced density of bone in the tibial metaphysis in the cemented stemme d group but not in the pegged group. There were no changes distally in the diaphyseal bone. This study supports the contention that the use of a cemen ted stern reduces proximal stresses and may result in proximal bone resorpt ion. Although the use of a stem provides excellent resistance to lift-off a nd shear, it comes at a price. The proximal resorption may contribute to th e persistence of tibial component loosening as a primary threat to survivor ship. This bone loss may complicate revision surgery. Consideration should he given to using shorter tibial stems, less cement, or alternative designs that avoid long-stem fixation.