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Objectives and questions: Obesity is a widespread disease, affecting more than 600 million individuals worldwide. Body mass index (BMI) serves as an indicator of a patient's nutritional status, with obesity generally defined as BMI > 30. Primary total hip replacement (THR) has become a very successful and safe procedure, alleviating pain and restoring patient mobility, so that it is commonly referred to as the “operation of the century” nowadays. However, outcomes after THR are known to be affected by increased BMI.

The aim of this study was to investigate if BMI changed following THR and to evaluate if this change had an impact on patient-reported outcomes and functional evaluations and radiographic results.

Material and methods: This observational study included 90 patients, median age 67 years (range: 44 to 80), 58 females, who underwent THR. BMI, patient-reported Maudsley Roles and Harris Hip scores were assessed preoperatively and postoperatively up to a minimum of 2-year follow-up. Radiographic evaluation was performed on standard radiographs. Surgery time, blood loss, incision length, hospital stay, and complications were also recorded. All patients received the same uncemented acetabular press-fit cup and the same cementless short metaphyseal femoral stem.

Results: Median follow-up period was 2.6 years (range 2.0 to 2.8). Incision length was 15 ± 2 cm, surgery time 62 ± 7 minutes, preoperative BMI 30.1 ± 4.6 kg/m² (range 25–38), intraoperative blood loss was 380 ml (range 240–730).

Mean BMI was 29.2 ± 2.6 at latest follow-up. Changes in BMI were recorded in 15 patients (17%) with a postoperative decrease by average 7 kg, 21 patients (23%) with a postoperative increase by average 5 kg. The remaining 54 patients (60%) maintained a constant BMI.

HHS increased from 40.1 ± 2.7 preoperatively to 91.2 ± 1.8. Subjective satisfaction evaluation according to Maudsley Roles score was excellent in 73 (81.1%) patients and good in 17 (18.9%), there were no fair or poor scores in any patient. Focusing on patients who sustained a BMI change, no HHS or Maudsley Roles Score change was reported.

Osseointegration was observed by newly formed trabecular meshwork around the cups excepting for asymptomatic radiolucent lines in 3 hips. There were 1 wound hematoma, 1 deep infection, treated with DAIR, 1 dislocation, incruentely reduced.

Discussion and conclusions: THA is a safe procedure, functional, subjective and radiographic results are promising in high BMI patients. The patient improvements in subjective results are similar to normal weight patients.