The impact of adherence on sports injury prevention effect estimates in randomised controlled trials: looking beyond the CONSORT statement

J Sci Med Sport. 2011 Jul;14(4):287-92. doi: 10.1016/j.jsams.2011.02.007. Epub 2011 Mar 22.


Objective: To investigate estimated outcome effects of a sports injury prevention intervention when analysed by means of a per protocol (PP) analysis approach.

Design: Randomised controlled trial (RCT) involving 522 athletes who sustained a lateral ankle sprain allocated to either an intervention (received a preventive programme in addition to usual care) or control group who were followed prospectively for one year.

Methods: Secondary analysis of data relating to registered ankle sprain recurrences, exposure and adherence to the allocated intervention using a PP analysis approach.

Results: Twenty-three percent of the RCT intervention group indicated to have fully adhered with the neuromuscular training programme. A per protocol analysis only considering fully adherent athletes and control athletes, showed a Hazard Ratio of 0.18 (95% CI: 0.07-0.43). Significantly fewer recurrent ankle sprains were found in the fully adherent group compared to the group that was not adherent (relative risk = 0.63; 95% CI: 0.43-0.99).

Conclusions: A PP analysis on fully adherent athletes versus control group athletes showed that the established intervention effect was over threefold higher compared to an earlier intention-to-treat based analysis approach. This shows that outcomes of intervention studies are heavily biased by adherence to the allocated intervention.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Ankle Injuries / epidemiology
  • Ankle Injuries / prevention & control*
  • Ankle Injuries / therapy
  • Athletic Injuries / epidemiology
  • Athletic Injuries / prevention & control*
  • Athletic Injuries / therapy
  • Exercise Therapy* / methods
  • Exercise Therapy* / statistics & numerical data
  • Humans
  • Patient Compliance / statistics & numerical data*
  • Proportional Hazards Models
  • Secondary Prevention
  • Sprains and Strains* / epidemiology
  • Sprains and Strains* / prevention & control
  • Sprains and Strains* / therapy
  • Treatment Outcome