Patient Reported Outcome Measures ( PROMs ) at six months have been investigated but have not been vali date d against long-term outcomes .
EBRA can be used to investigate acetabular wear but not femoral migration .
OBJECTIVES High failure rates of metal-on-metal hip arthroplasty implants  have highlighted the need for more careful introduction and monitoring of new implants and for the evaluation of the safety of medical devices .
The National Joint Registry and other regulatory services are unable to detect failing implants at an early enough stage .
We aim ed to identify vali date d surrogate markers of long-term outcome in patients undergoing primary total hip arthroplasty ( THA ) .
IDEAL framework for surgical innovation 2: observational studies in the exploration and assessment stages
The IDEAL framework describes the stages of evaluation for surgical innovations . This paper considers the role of observational studies in the exploration and assessment stages . At the exploration stage , the surgical intervention is usually more widely used , and observational studies should collect prospect i ve data from multiple surgeons , deal with factors such as case mix and learning , and prepare for a definitive evaluation at the next stage of assessment . Although a r and omised controlled trial is preferable , a high quality observational study would be acceptable if a r and omised trial is not feasible or , on rare occasions , deemed unnecessary
Patient Reported Outcome Measures ( PROMs ) at six months have been investigated but have not been vali date d against long-term outcomes .
EBRA can be used to investigate acetabular wear but not femoral migration .
OBJECTIVES High failure rates of metal-on-metal hip arthroplasty implants  have highlighted the need for more careful introduction and monitoring of new implants and for the evaluation of the safety of medical devices .
The National Joint Registry and other regulatory services are unable to detect failing implants at an early enough stage .
We aim ed to identify vali date d surrogate markers of long-term outcome in patients undergoing primary total hip arthroplasty ( THA ) .