Changes in bone density after cemented total knee arthroplasty: influence of stem design.
Total knee arthroplasty has shown excellent survivorship in short-term and intermediate-term studies. With longer follow-up, however, aseptic loosening becomes an increasing cause of failure. Dual-energy x-ray absorptiometry scanning has shown that stress shielding occurs from altered mechanical loading. The purpose of this study is to determine if tibial stem design affects 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 Miller-Galante I prosthesis, which has 4 0.5-cm pegs, was compared with the bone quality under a Press-Fit Condylar prosthesis with a single 4-cm stem. Each group was also compared with the unoperated contralateral tibia. Results showed that there is a significantly reduced density of bone in the tibial metaphysis in the cemented stemmed 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 cemented stem reduces proximal stresses and may result in proximal bone resorption. Although the use of a stem provides excellent resistance to lift-off and shear, it comes at a price. The proximal resorption may contribute to the persistence of tibial component loosening as a primary threat to survivorship. This bone loss may complicate revision surgery. Consideration should be given to using shorter tibial stems, less cement, or alternative designs that avoid long-stem fixation.