Bone mineral and migratory patterns in uncemented total knee arthroplasties: a randomized 5-year follow-up study of 38 knees.

We measured the amount of bone mineral in the medial tibial condyle 1 week postoperatively, after 1 year and after 4-5 years in 38 arthrotic knees randomized to a Freeman-Samuelson hydroxyapatite-coated (FS HA) or a Miller-Galante II (MG II) total knee arthroplasty. Clinically excellent results were recorded in both groups after 5 years. At the last follow-up, the overall decrease in bone mineral was 26%, as measured by triple-energy X-ray absorptiometry. The decrease was larger in FS HA knees than in MG II knees after 4-5 years, indicating stress-shielding of the proximal tibia. Radiostereometry at 1 and 5 years showed smaller maximum total point motion, maximum subsidence and varus or valgus tilt in the FS HA group. There was a tendency towards a reversed relationship between subsidence and change in bone mineral after 1 year, but not after 4-5 years. Distal fixation of the stem in the Freeman-Samuelson hydroxyapatite-coated (FS HA) components might explain the more pronounced loss of bone mineral in the medial tibial condyle.