Body Mass Index of 45 Is a Safe Cut-Off for Cementless Total Knee Arthroplasty

It is widely perceived that morbid obesity is associated with unacceptable rates of complication after total knee arthroplasty (TKA), with many surgeons using a body mass index (BMI) of 40 as a cutoff. Also, cemented TKA is widely perceived as the gold standard. However, these two perceptions are not consistently supported by the literature. The aim of this study was to assess the outcomes of two patient groups undergoing cementless TKA in a high-volume unit: one with morbid obesity (BMI 40 to 44.9) and the other nonobese (BMI 20 to 29.9).

This was a retrospective comparative single-center audit looking at 2,674 fully cementless TKAs, all performed with primary components and none having a patellar resurfacing. Of these, 568 were morbidly obese and 2,106 were nonobese. Median follow-up was 7.3 years (range, one to 13). Data were collected via electronic databases and radiology systems.

All-cause revision rates were 0.7% (four of 568) in the morbidly obese and 0.9% (19 of 2,106) in the nonobese (P = 0.801). There were no revisions for noninfective causes in the morbidly obese group. Other key outcomes, such as mortality, venous thromboembolism, and improvement in patient-reported outcomes scores, were also comparable. The reoperation rate for periprosthetic fracture was significantly lower in the morbidly obese (1.1%, [six of 568]) than the nonobese (3.6% [76 of 2,106], P = 0.002). Reoperation rate, excluding periprosthetic fracture, was also significantly lower in the morbidly obese group (1.1% [6 of 568]) than the nonobese (3.0% [63 of 2,106], P = 0.010).

Cementless TKA can be performed safely and with a significantly lower reoperation rate in the morbidly obese as than the nonobese in a high-volume environment. Our numbers, however, were too small to draw conclusions in patients who have a BMI ≥ 45.