Evaluating the role of weight loss in symptomatic knee osteoarthritis: an audit

Key points

1. 01The more weight people lost, the greater the improvement in knee pain and function, a clear dose-response pattern.
2. 02Starting body mass index did not change the benefit, all BMI groups lost a similar percentage of weight (7.3 percent to 7.9 percent) and improved by a similar amount.
3. 03Even as little as 2.5 percent weight loss produced a clinically meaningful improvement in pain across all BMI categories.
4. 04People with worse baseline knee pain improved far more, roughly double the benefit, while those with mild pain (KOOS over 75) saw little meaningful change.
5. 05This is a retrospective audit of one program with only 18 weeks of follow-up, so long-term durability is unknown.

How it was conducted

Design

Retrospective observational audit of routinely collected program database, January 2014 to July 2022

Participants

Privately insured patients with BMI of 28 or higher and a knee osteoarthritis diagnosis in the Osteoarthritis Healthy Weight For Life program; 9004 enrolled, 6360 with complete data analysed

Intervention

Remotely delivered 18-week community program combining weight loss, self-directed exercise and muscle strengthening, and healthcare support

Groups

Patients grouped by baseline BMI (overweight, obese class 1, 2, 3) and by baseline KOOS pain (mild, moderate, severe, extreme)

Primary outcome

Change in Knee Injury and Osteoarthritis Outcome Score (KOOS) pain and function from baseline to completion

Analysis

ANOVA and two-way ANCOVA adjusting for age and gender, with Tukey post hoc testing and Bonferroni corrections

What they found

• Mean weight loss in the total cohort was 7.7 percent, with men losing 8.13 percent and women 7.57 percent.
• Mean weight loss was consistent across all baseline BMI categories (mean 7.73 percent, range 7.3 percent to 7.9 percent).
• Mean KOOS pain change was 14 points and mean KOOS function change was 14 points in the full cohort, with no significant difference between BMI groups (pain P=0.71, 95 percent CI 13 to 14; function P=0.15, 95 percent CI 13 to 15).
• KOOS pain improvement rose with baseline pain severity: mild 4 points (SD 10), moderate 13 points (SD 13), severe 20 points (SD 17), extreme 27 points (SD 22), all P<0.01.
• KOOS function improvement also rose with baseline pain severity: mild 6 points (SD 11), moderate 14 points (SD 14), severe 18 points (SD 18), extreme 23 points (SD 22), all P<0.01.
• Only patients with a baseline KOOS pain score below 75 achieved a meaningful improvement; the mild group (KOOS over 75) fell significantly below the minimum 8-point change.
• A statistically significant trend of increasing KOOS pain change was seen with greater percentage weight loss, with no significant differences between BMI ranges at each weight loss bracket.
• The dropout rate was 12 percent (1044 of 9004 did not complete the program).

Limitations

• Retrospective observational audit of a single program with no control group, so improvements cannot be firmly attributed to weight loss alone rather than the accompanying exercise and psychosocial support.
• Follow-up was only 18 weeks, so it is unknown whether benefits are sustained; a cited 18-month RCT found pain improvements that did not differ from controls.
• Only program completers with complete data were analysed, introducing potential selection bias, and only privately insured patients were included, limiting generalisability.
• Outcomes relied on self-reported KOOS scores, which are subjective; two authors have financial ties to the company delivering the program.

Why it matters

For patients

If you are overweight and have painful knee osteoarthritis, even a modest weight loss of around 2.5 percent may ease your pain, and the more you lose the better, especially if your pain is severe.

For clinicians

Weight loss programs benefit overweight knee osteoarthritis patients regardless of starting BMI, and those with the most severe pain (baseline KOOS below 75) have the most to gain.

For readers

This is the largest cohort in its field to date, but it is an uncontrolled, short-term, industry-linked audit, so treat the dose-response signal as supportive rather than definitive.