Oxford Arthroplasty Early Change Score (OACS)

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The Oxford Arthroplasty Early Change Score (OACS) is a 14 question Patient Reported Assessment measure used to assess change, recovery pathways and interventions during the first six weeks following surgery.

The Oxford Arthroplasty Early Change Score (OACS) is a 14 question Patient Reported Assessment measure developed by researchers at the Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences and Nuffield Department of Population Health at the University of Oxford. It was designed and developed in accordance with FDA guidelines (2009) and sector best practices.  It is validated for use in the first six weeks following Unicompartmental knee arthroplasty (UKA), Total knee arthroplasty (TKA) and Total hip arthroplasty (THA).

The good measurement properties of the OACS, its relevance to patients, clinicians and other stakeholders, make it the ideal measurements for use in randomised controlled trials that assess the efficiency of different interventions in this patient population.


“As surgeons, once our patients are discharged from our care following surgery, they enter a black hole where we lose sight of how they are progressing with their new hip or knee. The OARs and OACs are the assessment tools by which we can now monitor those patients that were previously invisible to us in the days and weeks immediately following hip or knee replacement surgery.“

– Professor Oliver Pearce, FRCS, Consultant Trauma and Orthopaedics


Lower limb arthroplasty is a commonly performed procedure for symptomatic end-stage arthritis which has not responded to conservative medical treatment.

Each patient’s perspective of the surgical process and early recovery period impacts on their quality of life.

The OACS was devised to gain deeper understanding of the patient perspective on their treatment in the perioperative period and can be used to assess change, recovery pathways and interventions during the first six weeks following surgery.

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Design and development

A five-phased, best practice, iterative approach was used in strict accordance with the Food and Drug Administration (FDA) guidelines: Literature review was followed by Analysis of patient interviews (Phase one), candidate items from Phase One interviews were generated and pilot questionnaire developed and tested in Phase two. Factor analysis with item reduction and final testing of the questionnaire was performed in phase three. Phase Four involved validation testing. The measure was administered to consecutive patients in an independent cohort in combination with a generic heath measure (SF36 v2 Acute).

Prior to testing, a translatability assessment (TA) was performed on the new measure. TA has been recognised as an important part of the questionnaire development process. It provides insight into what extent the items in the questionnaires can be translated into other languages and cultures. This is of particular importance for use in cross cultural trials.

In addition, a concept elaboration document (CED) was created to fully define and clarify question items and the meanings attributed to them. This was developed in combination with the developers and specialist translators, to provide specific detail regarding the explicit line-by-line meaning of items and concepts, providing clarification of each item of the questionnaire.

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Scoring system

A scoring guide is available specifically for OACS and details how to score the change measure across a range of 100, with minus 50 being much worse than before surgery, to 50, being much better than before surgery. Zero indicates no change from self-reported preoperative health status. It also recommends how to treat missing responses.

The scoring system for the sister measure OARS is different and should only be applied to OARS.

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Complementary Measures

The OACS can be used with an early recovery tool, the Oxford Arthroplasty Early Recovery Score (OARS), a Patient Reported Outcome Measure developed under the same guidelines and applicable to the same patient population. The two measures give a snapshot of both patient perceived outcomes at the time taken and also improvement, or change, since the surgery.


The OACS can also be used as an ‘acute’ perioperative measure of recovery in combination with the Oxford Hip and Knee Scores, with their longer term recall periods.

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The development of the OACS was funded in part by Sigma Theta Tau International Honor Society of Nursing.

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Administration Methods

The OACS is to date validated for pen and paper completion. Careful migration to a digital delivery format (for example screen based device) can be authorised. Please contact us for advice.

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