Which matters more for preventing knee replacements: reducing overactivity or combating inactivity?

Maintaining baseline Physical Activity Scale for the Elderly (PASE) scores resulted in a knee replacement surgery incidence ratio of 4.71% over 96 months.

• The baseline maintenance scenario served as the reference condition for comparing all hypothetical PA interventions.
• Incidence ratio was 4.71% (95% CI: 4.37% to 5.05%).
• The follow-up period was 96 months.
• Data were drawn from the Osteoarthritis Initiative on US adults with symptomatic knee OA or at risk for knee OA.

Reducing PASE scores to 200 only for those with scores above 242 decreased the knee replacement incidence ratio to 2.98%.

• This intervention targeted only individuals with baseline PASE scores greater than 242, reducing their scores to 200.
• The resulting incidence ratio was 2.98% (95% CI: 2.39% to 3.57%).
• This represented a substantial reduction compared to the baseline maintenance incidence ratio of 4.71%.
• This finding suggests that reducing excessive physical activity to an optimal level provides meaningful benefit.

Increasing PASE scores by 10% and 20% among those with low baseline scores further reduced the risk of knee replacement surgery.

• The benefit of increasing PA was observed specifically among individuals with low baseline PASE scores.
• Moderate increases of 10% and 20% in PASE scores were associated with additional reductions in knee replacement risk.
• Larger increases of 30% to 50% diminished the additional benefit, suggesting a threshold or ceiling effect.
• These results indicate a non-linear relationship between PA level and knee replacement risk.

Seven hypothetical daily PA treatment regimens were developed and evaluated using a doubly robust targeted minimum loss-based estimator.

• Daily PA was measured using the Physical Activity Scale for the Elderly (PASE) score.
• The study used a targeted learning approach (doubly robust targeted minimum loss-based estimator) to estimate effects of PA interventions.
• The analytical framework allowed comparison of multiple hypothetical PA regimens against a baseline maintenance scenario.
• The outcome measure was incidence of knee replacement surgery over a 96-month follow-up period.

Tailoring daily physical activity to an optimal level, especially by reducing excessive PA, was identified as most beneficial for preventing knee replacement in older adults.

• The study concluded that reducing overactivity (bringing high PASE scores down to an optimal level) produced a greater reduction in knee replacement incidence than increasing activity among inactive individuals.
• The optimal PASE score threshold identified for reduction was 242, with a target of 200.
• The findings applied to older adults with symptomatic knee OA or at risk for knee OA.
• Results suggest that both overactivity and inactivity are relevant, but reducing overactivity had a comparatively larger impact on knee replacement incidence.