Obesity Affects Knee Implant Survival

While it is known that high BMI (body mass index) can increase a patient’s risk for complications after total knee arthroplasty, researchers from the Mayo Clinic in Rochester, Minnesota, recently took a closer look at implant survival and discovered that rates of reoperation and implant revision or removal after total knee arthroplasty were linked to increased BMI. The study was published in December in The Journal of Bone & Joint Surgery.

Daniel J. Berry, M.D., of the department of orthopedic surgery and biostatistics and health sciences research at the Mayo Clinic in Rochester, and colleagues used data from the clinic’s total joint registry to analyze 16, 136 patients who underwent primary total knee arthroplasty from 1985 to 2012. The mean BMI of these patients was 31.3 kg/m².

According to the results, the higher a patient’s BMI after total knee arthroplasty, the higher the rates of reoperation (p < 0.001) and implant revision or removal (p < 0.001). Patients with a BMI over 35 kg/m² also had a higher risk for infection.

Berry told OTW that the increased risk of infection for patients with high BMI is likely related to three factors:

1. Doing surgery in patients with high BMI is more difficult and surgical times often are longer.
2. The thick adipose tissue layer in patients with high BMI often doesn’t heal as well as muscle tissue and creates a higher infection rate.
3. Patients with high BMI often have medical comorbidities, such as diabetes mellitus and some may also have nutritional protein deficiencies, which put them at higher risk for infection.

“Increased risk of implant revision or removal in high BMI patients is partly driven by increased infection risk (which often leads to implant removal) and partly driven by increased risk of aseptic loosening, ” Berry explained.

“We believe it is important to consider the patient’s entire medical situation when making a decision about if/when to perform a total knee arthroplasty. The potential benefits of surgery need to be weighed against the risks for the individual patient. High BMI is considered a potentially modifiable risk factor for surgery, so for a number of patients optimizing this risk factor ahead of surgery makes sense.”

He added though that “to date there are limited data on how much one reduces risk by weight reduction before surgery for patients that start with a high BMI and lose weight before surgery.”