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Weight loss for knee arthritis

Randomised trial
Results
Weight outcomes
Arthritis outcomes
Comment

Knee arthritis is common in older people, and it is as much as anything a mechanical wearing out. We are reasonably sure that exercise early in life is not particularly related to knee arthritis (Bandolier 91), but being overweight may be, because of the extra load excess weight puts on the knee joint, and there is some evidence, from the Framingham study, for instance, that weight loss should reduce arthritic knee symptoms. Until now what has been lacking is a good randomised trial of the effects of weight reduction on patients with knee arthritis. Now we have one [1], we can be more confident that weight reduction is a good thing for people with painful knees.

Randomised trial

The setting was Danish patients who were overweight adults with primary knee osteoarthritis according to standard diagnostic guidelines, with radiological evidence of damage. Overweight was defined as a BMI of over 28 kg/m 2, and for participation they had to express a clear unequivocal motivation for weight loss and no major health problems.

Included patients were randomised to an eight-week programme of either a low energy diet or a control hypo-energetic high protein diet. The low energy diet (3.4 MJ/day) consisted of a nutrition powder dissolved in water and taken six times a day, with weekly nutritional instruction and behaviour therapy. The control diet (5.0 MJ/day) group received a two-hour baseline instructional session with nutritional advice, and recommended foods and diet plans to provide about 5 MJ/day. Randomisation was stratified according to sex, age and BMI. Patients maintained any OA therapy during the trial.

Measurements of weight and body composition were made at baseline and after eight weeks. Symptoms of OA were measured by the WOMAC questionnaire addressing joint pain, stiffness, and limitations of physical functioning, Lequesne index, and health assessment questionnaire.

Results

After initial randomisation there were several withdrawals (about 10% of initial), and results are reported according to completers, since only they had a final value. At baseline the two groups (40 patients in each) were similar, with 90% women, with an average age of about 63 years, average weight of 97 kg, and BMI of 36.

Weight outcomes

The mean weight loss on the low energy diet was 11.1 kg, and on the control diet it was 4.3 kg. Half those on the low energy diet lost more than 10% of initial weight, compared with none on the control diet, while 93% and 25% lost at least 5% (Figure 1). Most of the weight lost was as fat. The number needed to treat with low energy diet for eight weeks to achieve at least a 10% weight reduction was 2.0 (1.5 to 2.9).



Figure 1: Weight loss on low energy and control diets, percent achieving each level of weight loss





Arthritis outcomes

Patients in both groups had improvements in the WOMAC indices (Figure 2). These were better on the low energy diet than control, significantly so for total score and physical functioning. At least 50% reduction in total WOMAC score occurred more frequently in the low energy group than with the control diet. The number needed to treat with low energy diet for eight weeks to achieve at least a 50% reduction in total WOMAC score was 3.4 (2.1 to 8.8).



Figure 2: WOMAC scale outcomes, as percentage decrease from baseline for low energy and control diets





The absolute numbers achieving this degree of improvement was not given, but 30% more patients had this degree of improvement with low energy diet for eight weeks than with control diet. There was a general correlation between weight loss and improvement in symptoms. Lequesne index differences just failed to reach statistical significance, and health assessment results were not given. Adverse events were not mentioned.

Comment

There are those who will not like the idea of a rapid weight loss programme, and the relevance of weight loss is well considered in the paper. But for the purposes of determining how reducing overweight contributes to improving symptoms, it is highly relevant. What is impressive is the degree of improvement. NNTs of 2 for significant weight reduction and 3 for significant improvement in arthritis symptoms make one sit up and take notice, despite the relatively small size of the trial and enhanced recruitment.

These results are probably better than most drug treatments could achieve, especially paracetamol (Bandolier 127), and without the known problems associated with NSAIDs, and similar drugs. Weight loss has other benefits as well, on cardiovascular risk, and possibly cancer risk.

The authors describe a typical patient in their clinic: older woman, significantly overweight, trapped in a negative pattern of continual weight gains and pain, accompanied in turn by decreasing activity and functional capacity. Overturning the negative pattern with rapid weight loss looks like a common sense approach worthy of further study, not just in randomised trials for effect, but rather in implementation of what is already known.

Reference:

  1. R Christensen et al. Weight loss: the treatment of choice for knee osteoarthritis? A randomized trial. Osteoarthritis and Cartilage 2005 13: 20-27.

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