Comparison of bone mineral density between porous tantalum and cemented tibial total knee arthroplasty components.

Background: Porous tantalum was recently introduced as a metallic implant material for total knee arthroplasty. Its porosity, low modulus of elasticity, and high frictional characteristics were expected to provide physiologic load transfer and relative preservation of bone stock. However, to our knowledge, the effect of a Trabecular Metal tibial component on bone mineral density has not been reported. The purpose of the present study was to compare the periprosthetic bone mineral density between patients managed with uncemented Trabecular Metal and cemented tibial components.

Methods: Twenty-eight knees receiving a Trabecular Metal tibial component and twenty-eight knees receiving a cemented cobalt-chromium tibial component had dual x-ray absorptiometry scans at two weeks preoperatively and at two weeks and six, twelve, eighteen, and twenty-four months postoperatively, to assess periprosthetic bone mineral density. All of the operations were performed by one surgeon through a medial parapatellar approach.

Results: None of the differences between the two groups in terms of preoperative bone mineral density in the femoral neck, wrist, lumbar spine, or knee were significant. In both groups, the bone mineral density in the tibia decreased postoperatively. However, the postoperative decrease in bone mineral density in the lateral aspect of the tibia was significantly less in knees with Trabecular Metal components than in knees with cemented tibial components at twenty-four months (mean and standard deviation, -6.7% +/- 22.9% compared with -36.8% +/- 24.2%; p = 0.002). At twenty-four months postoperatively, there was no significant difference between the two groups in terms of the Knee Society score, range of motion of the knee, or bone mineral density in the lumbar spine. No prosthetic migration or periprosthetic fracture was detected in either group.

Conclusions: The decrease in bone mineral density of the lateral tibial plateau was less in knees with a Trabecular Metal tibial component following total knee arthroplasty than in knees with a cemented tibial component. Additional research is needed to determine whether long-term clinical benefits are realized with the use of porous tantalum tibial components for total knee arthroplasty.