Issue: July 2012
Perspective from Matthew J. Kraay, MD
July 03, 2012
3 min read

Primary TKA found effective in patients with BMI greater than 50

At mid-term follow-up, investigators noted a higher mortality rate among the ‘super obese’ patients.

Issue: July 2012
Perspective from Matthew J. Kraay, MD
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SAN FRANCISCO — Researchers from London, Ontario, found total knee arthroplasty efficacious in patients with body mass indices equal to or greater than 50, but remained cautious about the safety of the procedure in the group due to higher risks of complications and revisions.

“We found similar improved results when compared to nonobese or class 1 obese [patients] in regards to SF-12, WOMAC, Knee Society scores, blood loss, length of stay and re-admission rates,” Robin Martin, MD, said during his presentation at the American Academy of Orthopaedic Surgeons 2012 Annual Meeting. “Is it safe? Maybe. We found similar complication rates except for a significantly higher mortality rate reaching 11%, an increased delayed wound healing problem and a trend for higher infection rates, surgical complications and revision rates.”

Martin and colleagues identified 4,104 primary total knee arthroplasties (TKAs) performed at their institution during a 10-year period and stratified patients into the following body mass index (BMI) groups based on categories defined by the World Health Organization and noted in the current literature: normal weight (BMI of 20 to 24.9); class 1 obese (BMI of 30 to 34.9); and super obese (BMI =50).

The investigators identified 47 super obese patients (75 TKAs, group 1) and matched them with both normal (group 2) and class 1 obese patients (group 3) for factors including gender, age, side of surgery, time since surgery, prior TKA in the contralateral limb, use of posterior stabilizing implants, patella resurfacing and preoperative SF-12 mental component summary score (MCS). Overall, patients had a mean clinical and radiographic follow-up of 6.5 years. Mean time since surgery was 8.9 years.

Patients in the super obese group had an average age of 60 years and most were women. Of the super obese patients, 75% had bilateral TKAs, most received posterior stabilizing implants and almost all underwent patella resurfacing. In addition, 27% of the group had type 2 diabetes, 84% had an ASA grade of 3 or 4, 27% had sleep apnea and 20% had a history of ischemic heart disease.

Comparing the super obese group with the normal weight and class 1 group, researchers found no significant differences between the groups for operative and tourniquet times, blood loss based on 72-hour postoperative hematocrit and hemoglobin levels, length of hospital stay, re-admissions, and rates of superficial infection, deep venous thrombosis, pulmonary embolism, hematoma and knee stiffness. Although super obese patients had higher rates of surgical complications (6.3% vs. 1.3% for group 2; 4% for group 3), deep infection (4% vs. 1.3% for group 2; 2.7% for group 3), transfer to a rehabilitation center (13.3 % vs. 4% for group 2; 8% for group 3) and revision surgery (9.3% vs. 6.7% for group 2; 5.3% for group 3), these differences were not statistically significant. However, significantly more patients in the super obese group had a delay in wound healing beyond 3 postoperative weeks (10.7% vs. 1.3% for group 2; 2.7% for group 3) and showed a higher mortality rate at 8.9 postoperative years (10.6% vs. 0% for group 2; 1.3 % for group 3).

“Super obese patients had lower preoperative SF-12 physical summary scores,” Martin said. “Following TKA, they had a higher improvement in these scores compared to normal weight [patients] and similar [scores] compared to the class 1 obese [group]. Similar results were found for the WOMAC scores.” In addition, he noted that patients in the super obese group had lower preoperative Knee Society scores, but showed similar improvement compared to the other groups. – by Gina Brockenbrough, MA

  • Martin R, Somerville L, McCalden RW, et al. Is primary total knee arthroplasty safe and efficacious in the super obese patient (BMI =50)? Paper #8. Presented at the American Academy of Orthopaedic Surgeons 2012 Annual Meeting. Feb. 7-11. San Francisco.
For more information:
  • Robin Martin, MD, can be reached at Orthopaedic Surgery Department, Geneva University Hospital, rue Gabrielle-Perret-Gentil 4, 1211 Genève, Switzerland; email:
  • Martin has no relevant financial disclosures.