Total knee replacement (TKR) is a procedure performed primarily for arthritis with the goal of relieving pain and improving quality of life.1 Some studies have found that patients with a body mass index (BMI) greater than 30 have an increased risk of infection and repeat knee replacement.2 We sought to understand how a patient’s starting BMI affects outcomes after a TKR.
We studied 344,269 patients who had a total knee replacement between January 1, 2017, and July 31, 2023, to determine whether there were differences in rates of failure after a TKR based on the patient’s starting BMI. We considered mechanical failures, infections, embolism, and hemorrhage as failures. Patients with class 3 obesity (BMI over 40) had the highest rate of failure within the first year after their TKR, as seen in Figure 1. Patients with a BMI over 50 were more than twice as likely to have a replacement failure compared to those with a BMI between 18.5 and 35. While the rate of failure was high in the underweight group (BMI under 18.5), it was not statistically significant.
We also evaluated whether a patient’s starting BMI affected recovery time after a TKR surgery. We found that the average number of physical therapy appointments per week does not vary greatly across BMI classes, at around 2.25 sessions per week. The average length of time a patient goes to physical therapy after a TKR also did not vary much between BMI classes, with all classes going for 36.8 to 44.5 days.
