Study: Obese patients derive similar subjective TKA outcomes as normal-weight patients

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March 2008

SAN FRANCISCO - Although obese patients have an increased risk of complications, they derive the same subjective functional outcomes from total knee arthroplasty as patients of normal body mass index, according to a study presented here at the 54th Annual Meeting of the Orthopaedic Research Society.

"Collectively, these results suggest that, when assessed from that patient's perspective, total knee arthroplasty (TKA) provides similar subjective and functional benefits regardless of BMI," said Matthew D. Driscoll, MD. "This information must be factored into the decision of whether or not to provide knee replacements for obese patients."

Driscoll and colleagues investigated the relationship between obesity and both subjective and functional outcomes of TKA.

"Should we, as objective participants in patient care and policy development, determine that the possibility of increased risks and inferior objective outcomes alone justifies restricting access to joint replacements in these patients? Or must we also consider the outcomes from the perspective of the patients themselves?" he said. "We favor the latter."

Driscoll added, "Our aim was to determine whether increasing BMI (body mass index) has the same detrimental effect on outcomes when viewed from the patient's perspective as it does when viewed from the physician's perspective."

The study included 151 primary TKAs performed by a single surgeon, most of which were posterior stabilizing TKAs involving a variety of implant brands. Of the 151 TKAs, 58% were in patients classified as having normal BMI, 33% as obese and 9% as morbidly obese, Driscoll said.

Follow-up averaged 3.6 years.

Overall, patients' BMI averaged 29.7, ranging from 16 to 53.

Each patient completed a self-administered total knee function questionnaire, which consisted of 55 scaled multiple choice questions.

Investigators found that, postoperatively, range of motion (ROM) averaged 123� among normal-weight patients, 120� among obese patients and 112� among morbidly obese patients.

However, "All patients had sufficient [ROM] to ambulate on slopes," Driscoll said. Also, "All three patient groups reported equal levels of overall satisfaction with their knee function."

Specifically, 83% of obese and morbidly obese patients rated themselves as satisfied compared to 84% of patients in the normal-weight group.

However, "While patients' assessment of functional outcomes appears to be similar regardless of BMI, there were two areas in which obese and morbidly obese patients faired considerably worse than normal-weight patients," Driscoll noted.

"Increased BMI was significantly correlated with increases in perceived swelling and stiffness. Thus, knee replacement in obese patients is not without some subjective complications, even in satisfied and functionally proficient obese patients," he said.

For more information:

• Driscoll MD, Conditt M, Rankin JS, et al. Does TKA benefit obese and non-obese patients equally? Presented at the 54th Annual Meeting of the Orthopaedic Research Society. March 2-5, 2008. San Francisco.