The Effect of Changes in the Body Mass Index After Total Knee and Hip Arthroplasty on Patient Functional Scores

Introduction High body mass index (BMI) often causes immobility and functional impairment before arthroplasty. Patients expect weight loss post-surgery due to increased mobility, but paradoxically, studies show that weight may not decrease and might even increase postoperatively. This study aims to evaluate if patients lose weight after total knee arthroplasty (TKA) and total hip arthroplasty (THA) and to examine the impact of BMI change on functional scores. Methods We analyzed 459 patients who underwent primary TKA and THA between January 2018 and December 2022, with a two-year follow-up. Patients with incomplete data or bariatric surgery were excluded. Demographic characteristics, BMI, Oxford scores, comorbidities, corticosteroid use, physiotherapy, and surgery type (unilateral or bilateral) were assessed. Results Patients showed a significant increase in BMI postoperatively, especially those with comorbidities and younger age. Throughout the entire follow-up period, the BMI value of the knee group was higher than that of the hip group. Comorbidities significantly influenced BMI increase, while corticosteroid use and physiotherapy follow-up did not. Oxford scores improved postoperatively, but the presence of comorbidities and physiotherapy follow-up negatively impacted score changes. A negative correlation between BMI change and Oxford score change was observed (p = 0.013), indicating that increased BMI is associated with less improvement in functional scores. This correlation was significant for hip arthroplasty patients (p = 0.000), but not for knee arthroplasty patients (p = 0.822). Conclusions BMI changes post-TKA and THA are influenced by various clinical and demographic factors. Increased BMI negatively affects functional outcomes, particularly in hip arthroplasty patients. Comorbidities significantly influenced weight gain, while oral corticosteroid use had no notable effect on BMI. Patients undergoing bilateral procedures experienced lower BMI increases. The hip group gained more weight, but the knee group's BMI remained higher throughout the follow-up. In terms of Oxford scores, comorbidities, corticosteroid use, affected joints, and age did not significantly impact outcomes. Patients under physiotherapist supervision showed smaller score increases. While bilateral procedure patients achieved higher scores, simultaneous bilateral procedures did not lead to greater increases. These findings highlight the importance of weight control and rehabilitation in improving postoperative recovery and quality of life.