Introduction and purpose: The failure of a TKP is often due to deficiencies related to alignment, stability or fixation. The purpose of this paper is to determine how loads are distributed when each of two tibial stem models are implanted and to assess those loads densitometrically.

Materials and methods: We analyzed 20 patients with a cemented TKR and divided them into two groups according to whether their tibial stem was cylindrical or cruciform. We studied the evolution of periprosthetic bone density under the internal and external bearings and under the stem. We performed a densitometry after 2 years postop and controls after 3 and 7 years.

Results: In the cylindrical stem group the evolution of mean bone density under the internal bearing after 2 and 3 years was 0.92±0.20 to 0.90±0.19 g/cm2 respectively; mean bone density under the external bearing was 0.97±0.36 to 0.97±0.38 and under the stem it was 1.05±0.25 to 1.08±0.26. In the cruciform group, density under the internal bearing was 0.75±0.08 to 0.71±0.05, under the external one it was 0.89±0.01 to 0.85±0.07 and under the stem it was 1.06±0.06 to 1.04±0.29. In the long term (three patients were lost to follow-up), comparing the cylindrical prostheses to one another, we can say that the evolution under the internal bearing after 2, 3 and 7 years was 0.88, 0.84 and 0.80 g/cm2 respectively; under the external bearing it was 0.79, 0.78 and 0.77 and under the stem it was 0.99, 0.96 and 0.99.

Conclusions: After TKR a progressive loss of bone density is observed. Comparatively, the reduction is greater in the cruciform stem. The internal compartment is the most affected one.