Although there is no specific weight that surgeons consider to be too obese to receive a unicompartmental knee arthroplasty, we use body mass index or BMI as a surrogate to predict the likelihood that a unicompartmental knee arthroplasty will fail. Generally speaking, a BMI of greater than 40 is considered a contraindication to performing a unicompartmental knee arthroplasty; however, some research has used the figure 82 kg to be a cut off for offering this type of surgery to patients.