Effects of body mass index on outcomes of total knee arthroplasty

The aim of this study was to group the patients with total knee arthroplasty(TKA) surgery according to the World Health Organization (WHO) obesity classification and to evaluate the effects of body mass index (BMI) on complication rates, the functional and clinical outcomes of the patients after TKA.

Between 2011 and 2018, 588 patients who underwent TKA by a single surgeon were retrospectively evaluated. According to WHO's classification criteria, 588 patients were divided into 5 groups such as normal (< 25.0 kg/m², n: 138, 23.4%), overweight (25.0-29.9 kg/m² n: 201, 34.1%), class I obese (30.0-34.9 kg/m² n: 124, 21%), class II obese (35-39.9 kg/m² n: 82, 13.9%) and class III obese (> 40 kg/m² n: 43 7.6%). Groups were compared in terms of age, sex, surgical side, follow-up period, case duration, prosthesis infection and aseptic prosthesis loosening rates, Knee Injury and Osteoarthritis Outcome Score (KOOS), Lysholm functional scores and knee flexion degrees.

There was a statistically significant difference between the groups in terms of prosthesis infection or aseptic prosthesis loosening following TKA. The incidence of these complications increased as BMI increased (X2: 20,079, p: 0.01). Postoperative knee flexion degrees, KOOS and Lysholm scores were significantly different between the groups (p: 0.000). As BMI increased, clinical and functional outcomes deteriorated.

Obesity is one of the most important risk factors for prosthesis infection and aseptic prosthesis loosening which can be seen after TKA. High BMI values also adversely affect clinical and functional outcomes after TKA.