Do metal implants for total hip arthroplasty affect bioelectrical impedance analysis? A retrospective study

BACKGROUND: Evaluation of body composition after total hip arthroplasty (THA) is essential because it can be used to evaluate muscle and functional recovery. Muscle volume and degeneration are evaluated using computed tomography (CT). However, CT evaluation of muscle volume has several limitations, such as radiation exposure and high medical cost. Bioelectrical impedance analysis (BIA) has gained attention for resolving these limitations of CT. BIA takes advantage of the microelectric current; thus, metal implants may affect the results. Therefore, this study aimed to elucidate the effects of metal implants on BIA after THA. METHODS: Two groups of patients were assessed (Group 1: 70 patients who underwent unilateral THA and BIA; Group 2: 35 patients who underwent THA and BIA before and after THA). Electric impedance (resistance and reactance) of the operated and non-operated lower limbs was compared in Group 1. The pre- and post-operative impedances of the torso and operated ipsilateral limbs were compared in Group 2. RESULTS: Regarding electric impedance in Group 1, no significant differences were observed in electrical resistance and reactance between the operated and non-operated lower limbs. Concerning electric impedance in Group 2, postoperative electric resistance of the torso was significantly lower than that preoperatively. However, no significant difference was seen in electric resistance and reactance of the operated ipsilateral limbs preoperatively and postoperatively. CONCLUSIONS: Electrical resistance and reactance of the limbs did not change significantly after THA. BIA is useful for measuring body composition after THA.