Reluctance to perform total knee arthroplasty (TKA) in obese patients may be unwarranted, at least when it comes to functional outcomes, according to multiple studies presented in March at the annual meeting of the American Academy of Orthopaedic Surgeons (AAOS).

Several speakers noted a growing hesitancy among some surgeons to perform TKA in obese patients along with a similar reluctance among some insurance companies to cover such procedures. But the presented research, while confirming that obesity is associated with longer lengths of stay and related costs, nonetheless suggests that functional gains in obese patients rival those of their nonobese counterparts and that complication rates are similar.

Researchers from the National University Health System in Singapore prospectively analyzed 301 consecutive TKA patients, 77 of whom had a body mass index (BMI) of 30 kg/m2 or higher and were categorized as obese. Complication rates, including rates of deep venous thrombosis, were similar between groups. Preoperative scores on the Western Ontario McMaster University Osteoarthritis Index (WOMAC) were significantly lower in the obese group than in the nonobese group, but two years after surgery the WOMAC scores for the two groups were not significantly different.

“Obese patients actually had a greater absolute improvement,” said researcher Bernard Lau, MBBS, who presented his group’s findings at the AAOS meeting.

Looking at 395 patients nine years after TKA, investigators from the UK found that Knee Society outcome score increases from baseline were significantly lower in obese patients than nonobese patients, but that the improvement in the obese patients was still considerable—even in highly obese patients (BMI of 35 or higher). Knee Society knee scores improved by 49.9 points in the 51 highly obese patients, 52 points in the 143 mildly obese patients (BMI between 30 and 35), and 55.8 points in the 201 nonobese patients. Knee Society functional scores also improved in all groups, but began to deteriorate between five and nine years
after TKA.

Complication rates were similar in all groups. However, in the October 2006 issue of the Journal of Bone and Joint Surgery (British), the same researchers  reported a complication rate of 32% in patients with a BMI higher than 40.

“We are very reluctant to offer knee replacement to patients with a BMI over 40, but we don’t think there’s any reason to withhold it from patients with a BMI between 35 and 40,” said Robert A. Clayton, MB, ChB, a consultant orthopedic surgeon at Queen Margaret Hospital in Dunfermline, Scotland, UK, who presented the nine-year study results at the AAOS meeting. Those findings were also published in the Journal of Bone and Joint Surgery (British) in 2012.

In a study of 8129 TKA patients, researchers from the Mayo Clinic in Rochester, MN, also found that obesity was not associated with increased complication rates. However, they did find that obesity was associated with significantly longer hospital stays and significantly higher costs. Even after adjustment for comorbidities, every 10-unit increase in BMI over 25 was associated with an additional $541 in hospitalization costs and an additional $504 in 90-day costs.

“We’re not saying we shouldn’t operate on these folks just because it’s more expensive, but it’s something we need to consider and possibly push for increased reimbursement in those cases,” said study author David G. Lewallen, MD, a professor of orthopedics at the Mayo Clinic.

Sources:

Collins R, Walmsley P, Amin A, et al. Does obesity influence clinical outcomes at nine years following total knee arthroplasty? Presented at the Annual Meeting of the American Academy of Orthopaedic Surgeons, Chicago, March 2013.

Collins RA, Walmsley PJ, Amin AK, et al. Does obesity influence clinical outcome at nine years following total knee replacement? J Bone Joint Surg Br 2012;94(10):1351-1355.

Amin AK, Clayton RA, Patton JT, et al. Total knee replacement in morbidly obese patients. Results of a prospective, matched study. J Bone Joint Surg Br 2006;88(10):1321-1326.

Maradit-Kremers H, Kremers WK, Naessens J, Lewallen DG. The effect of obesity on direct medical costs in total knee arthroplasty. Presented at the Annual Meeting of the American Academy of Orthopaedic Surgeons, Chicago, March 2013.