Objectives: Effects of the UK Department of Health’s national Enhanced Recovery After Surgery (ERAS) Programme on outcomes after primary hip replacement.

Design: Natural experimental study using interrupted time-series to assess the changes in trends before, during, and after ERAS implementation (April 2009 to March 2011).

Setting: Surgeries in the UK National Joint Registry were linked with Hospital Episode Statistics containing inpatient episodes from NHS trusts in England and patient-reported outcome measures.

Participants: Patients aged ≥18 years from 2008 to 2016.

Main outcome measures: Regression coefficients of monthly means of length of hospital stay, bed day cost, change in Oxford hip scores (OHS) 6 months post-surgery, complications 6 months post-surgery, and revision rates 5 years post-surgery.

Results: 438,921 primary hip replacements were identified. Hospital stays shortened from 5.6 days in April 2008 to 3.6 in December 2016. There were also improvements in bed day costs (£7573 in April 2008 to £5239 in December 2016), positive change in self-reported OHS from baseline to 6 months post-surgery (17.7 points in April 2008 to 22.9 points in December 2016), complication rates (4.1 % in April 2008 to 1.7 % March 2016), and 5-year revision rates (5.9 per 1000 implant-years (95% CI: 4.8 to 7.2) in April 2008 to 2.9 (95% CI: 2.2 to 3.9) in December 2011). The positive trends in all outcomes started before ERAS was implemented and continued during and after the programme.

Conclusions: Patient outcomes after hip replacement have improved over the last decade. A national ERAS programme maintained this improvement but did not alter the existing rate of change.