Body mass index and lower limb diameters in total knee arthroplasty outcomes and surgical planning

Total knee arthroplasty (TKA) is a commonly performed surgery that can successfully treat end-stage osteoarthritis (OA). Obesity is a known risk factor for OA and its progression, but its impact on postoperative satisfaction and implant sizing remains unclear. The current study aimed to assess the association of preoperative body mass index (BMI) and lower limb dimensions with TKA component sizing and patient-reported outcomes.

We retrospectively assessed 108 patients (43 males, 65 females) undergoing primary TKA with a Journey II BCS prosthesis, without patellar resurfacing, between January and November 2023. The mean patient age was 67.4 ±4.1 years, with a mean BMI of 29.3 ±3.9 kg/m². Patients were divided into 2 groups based on BMI: normal weight (< 25; n = 41) and overweight/obese (≥ 25; n = 67). Lower limb widths and component sizes were obtained from postoperative radiographs and protocols. Clinical outcomes were evaluated using the KOOS and WOMAC questionnaires. Statistical analysis was performed to assess correlations between BMI, limb dimensions, implant size, and patient satisfaction.

Significant differences were found between the normal-weight and overweight patients in the diameters of the femoral (15.8 ±2.1 cm vs. 17.3 ±1.9 cm, p = 0.02) and lower leg (14.0 ±1.5 cm vs. 12.5 ±1.2 cm, p = 0.002) areas. However, no significant correlation was found between BMI, limb dimensions, and implant size for the femoral (p = 0.94) and tibial components (p = 0.48). Although patient-reported outcomes were similar between groups, with slightly better results in the normal-weight group, no statistical significance was found.

Body mass index affects lower limb sizes but does not predict implant sizing in TKA. Furthermore, no difference in patient satisfaction postoperatively between BMI categories was observed. The findings indicate that demographic factors may not be adequate to achieve precision in preoperative templating. Instead, surgical planning should be individualized, based on comprehensive anatomical measurements.