Changes in bone mineral density of the distal femur after total knee arthroplasty: A 7-year DEXA follow-up comparing results between obese and nonobese patients

Background and purposePeriprosthetic femoral bone mineral density (BMD, g/cm2) decreases after total knee arthroplasty (TKA) as a result of the stress-shielding phenomenon. It is not known whether obesity has an effect on this phenomenon or not. The aim of this study was to assess long-term periprosthetic BMD changes after TKA and compare whether there is a difference between obese and nonobese patients.MethodsA total of 69 TKAs in 61 patients were performed, and BMD measurements of the distal femur were followed up to 7 years postoperatively. The patients were divided into two study groups according to their body mass index, and the groups were compared in relation to BMD and functional outcome.ResultsThe mean of periprosthetic bone loss during the 7-year follow-up varied from 10.3% to 30.6% depending on the region of interest (p < 0.0005). The highest bone-loss rates were detected during the first three postoperative months. A total of 26 patients were categorized as obese with a body mass index value of ≥ 30 kg/m2. The obese patients' total periprosthetic BMD was higher at both baseline (8.6%) and 7 years after operation (p = 0.05) (15.2%).ConclusionPeriprosthetic bone loss around the femoral component continued for up to 7 years postoperatively. The loss of bone density was not associated with any negative clinical outcome in this study, but periprosthetic bone loss was of a smaller quantity in the obese which is probably due to higher weight induced stresses on bone.