Published: May 1, 2013 | Updated: May 2, 2013
By Nancy Walsh , Staff Writer, MedPage Today

Action Points

• This study used knee arthroplasty registries and a population-based control sample from the same geographic region to determine whether knee arthroplasty increases the risk of clinically important weight gain over a 5-year postoperative period.
• Patients undergoing knee arthroplasty were at an increased risk of clinically important weight gain following surgery.

Patients who undergo total knee replacement are at substantial risk for weight gain during the 5 years after the surgery, a large retrospective study showed.

On an adjusted multivariable analysis, recipients of knee arthroplasty were 60% more likely to gain 5% or more of their baseline body weight than matched controls who did not have the procedure (OR 1.6, 95% CI 1.2 to 2.2, P=0.003), according to Daniel L. Riddle, PhD, of Virginia Commonwealth University in Richmond, and colleagues.

And the chance of that “clinically important” weight gain doubled for individuals who had a second arthroplasty during the subsequent 5 years (OR 2.1, 95% CI 1.4 to 3.1, P<0.001), the researchers reported in the May Arthritis Care & Research.

“The logical assumption may be that persons who are overweight or obese prior to surgery are more likely to lose weight following surgery. Because there is less pain and improved mobility, the impediments to increased activity and exercise are eased following surgery, and weight loss would logically follow,” they observed.

However, that hasn’t been the case consistently in previous studies, which have been hampered by short follow-up times and a lack of controls.

To provide a more accurate picture of the weight effects of knee replacement over the long term, Riddle and colleagues analyzed outcome data for 917 patients in the Mayo Clinic arthroplasty registry, matching them with 237 controls from the population-based Rochester Epidemiology Project.

A total of 205 of the 917 Mayo patients had a second lower-limb or hip arthroplasty procedure.

Baseline weight was 89.1 kg (196 lbs) in the arthroplasty group and 76.3 kg (168 lbs) in the control group. Two-thirds were women.

In the 5 years after the index date, controls averaged a mean weight loss of 0.35 kg (0.77 lbs), while those who had just one arthroplasty gained an average of 1.23 kg (2.7 lbs).

Those who had a second arthroplasty had a mean weight gain of 2.62 kg (5.77 lbs).

During the first year after the surgery, 22.1% of patients gained 5% or more of their body weight, compared with 16% of controls.

In the fourth year, 32.3% of surgery patients had that percentage weight gain, as did 22.8% of controls.

On univariate analysis, the odds ratio for clinically important weight gain was 1.7 (95% CI 1.3 to 2.3) after surgery, while the odds ratio after a second arthroplasty rose to 2.3 (95% CI 1.6 to 3.2).

Results were similar on multivariable analysis after adjustment for factors such as age, comorbidities, baseline body mass index, and education level.

Factors that were associated with weight gain were:

• Age below 60, OR 2.7 (95% CI 1.8 to 3.9, P<0.001)
• Age 60 to 69, OR 1.7 (95% CI 1.2 to 2.3, P=0.004)
• Weight loss in 5 years before surgery, OR 1.10 per 1 kg (95% CI 1.07 to 1.13, P<0.001)

The finding that previous weight loss was linked with weight gain after the knee replacement had not previously been reported, the researchers noted.

“Intentional weight loss is known to frequently lead to subsequent weight gain, and we suspect this was the case in our sample,” they acknowledged.

Weight control efforts for patients having the surgery should therefore focus on long-term maintenance, they commented.

They also considered it important that younger patients were likely to gain weight after knee replacement, because people in their 50s and 60s in general tend to put on more weight than those who are older.

Moreover, some authors have predicted that in the near future, most of these surgeries will be done on patients younger than 65.

“Multidisciplinary weight loss/maintenance interventions particularly directed to those [total knee arthroplasty] patients who are younger and have lost considerable weight prior to surgery should be considered,” they wrote.

Limitations of the study included considerable loss to follow-up and the possibility of confounding through factors such as smoking and medications that were not measured.