Abstract
Background
Obesity has been shown to be an independent risk factor for aseptic loosening of the tibia and smaller implant size has been correlated with increased risk of failure of tibial components in obese patients [1,2]. Many surgeons have noted that obese patients, especially females, not uncommonly will have small implant sizes. As such, we hypothesized that obesity was not directly correlated with total knee arthroplasty (TKA) implant sizes. The purpose of this study was to determine if increasing body mass index (BMI), height, and/or weight is associated with implant size in primary TKA.
Methods
The institutional registry of a single academic center was reviewed to identify all primary TKAs performed between 2005 and 2016. Those without minimum 2-year follow-up or with incomplete implant data were excluded. The different manufacturer's implant designs were categorized based on anteroposterior and mediolateral dimensions of the femoral and tibial component sizes and cross sectional area was determined. BMI was categorized by the World Health Organization (WHO) obesity scale (Class I: BMI 30 to <35, Class II: BMI 35 to <40, Class III: BMI 40 kg/m2 or greater). Patient demographics including sex, height, weight, and BMI were analyzed to evaluate correlations with implant size using Pearson correlation coefficients.
Results
There were 8,107 TKA included in the analysis with a mean age of 67.3 ± 9.5 years and mean BMI of 30.4 ± 6.3 kg/m2. There was a significantly higher proportion of females (63%) in the total cohort as well as in the Obese I, II, and III categories. BMI had no significant association with implant size in the femur or tibia; however, weight had a moderate association with implant size (ρ=0.39–0.48, p<0.001). Increasing height had the strongest correlation with increasing implant size of both the femoral and tibial components (ρ=0.63–0.77, p<0.001).
Conclusion
Implant size was correlated with increasing height and weight, but not BMI in this cohort. Therefore, short patients who suffer from obesity, will most likely have smaller component sizes that may necessitate adjuvant fixation techniques (i.e. tibial or femoral stem). In addition, these findings may be useful in predicting TKA implant size based on a patient's height and weight.
For figures, tables, or references, please contact authors directly.
