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BMI, Tibiofemoral Alignment Affect Knee Implant Survival

Tibial, femoral malalignment and BMI ≥41kg/m² ups failure of total knee replacement

THURSDAY, Sept. 22 (HealthDay News) -- Proper tibial, femoral, and overall anatomic alignment is important for implant survival after total knee replacement, and a higher body mass index (BMI) increases implant failure rates, according to a study published in the Sept. 7 issue of The Journal of Bone & Joint Surgery.

Merrill A. Ritter, M.D., from St. Francis Hospital in Mooresville, Ind., and colleagues investigated the effect of tibiofemoral, femoral, and tibial component alignment, and BMI on implant survival in 6070 knees of 3992 patients who were followed-up for a minimum of two years after total knee replacements. Failures (revision for any reason other than infection) were evaluated using Cox regression.

The investigators found that failures were most likely (failure rate, 8.7 percent) when tibial component orientation was <90 degrees relative to the tibial axis and the femoral component orientation was ≥8 degrees of valgus. Neutral orientation of tibial and femoral components predicted least likelihood of failure (failure rate, 0.2 percent). Failure rate was 3.2 and 7.8 percent for varus tibial and valgus femoral malalignment, respectively, when varus or valgus malalignment of first implanted component was corrected using a second component to attain neutral tibiofemoral alignment. In patients with BMI of 23 to 26 kg/m² the failure rate in well-aligned knees, varus knees, and valgus knees was 0.7, 1.6, and 1.0 percent, respectively, which increased to 2.6, 2.9, and 7.1 percent, respectively, in patients with a BMI of ≥41 kg/m².

"Attaining neutrality in all three alignments is important in maximizing total knee implant survival," the authors write.

Several authors disclosed financial relationships with the biomedical industry.

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