Cookies on this website

We use cookies to ensure that we give you the best experience on our website. If you click 'Accept all cookies' we'll assume that you are happy to receive all cookies and you won't see this message again. If you click 'Reject all non-essential cookies' only necessary cookies providing core functionality such as security, network management, and accessibility will be enabled. Click 'Find out more' for information on how to change your cookie settings.

The ACHE (Arthroplasty Candidacy Help Engine) Tool

The ACHE study involves the development of an evidence based tool to assist GPs deciding which patients are highly likely to benefit from hip or knee joint replacement surgery and which patients are expected to do better under other forms of care.

The tool will combine an established scoring system and a set of evidence based thresholds for treatment.


Our main goal is to deliver better consistency of care and and effective treatment across the NHS in this area.

Applying the ACHE tool would allow selection of patients for surgery who have the capacity to improve whilst protecting patients without such capacity from unnecessary surgical intervention. The tool would be used by GPs to guide referral of patients from Primary to Secondary care, but could also be used in Secondary care to confirm continued candidacy for surgery.


There are two identified problems problems in the patient pathway for hip and
knee replacement:

  • Marked variation in clinical practice within the UK (NHS data);
  • 10-15% of patients are dissatisfied with their surgery, possibly due to intervention being offered at an early stage of the disease, where less benefit is likely. 

These problems have demonstrated a worrying lack of consistency in the way care is delivered.

We propose that a standardised approach to assessment of patients for hip and knee replacement can be achieved by introducing an evidence based clinical tool to identify patients who are candidates for surgery based on their capacity to benefit.

Work packages

Work package 1: Identification of pre-existing assessment tools that could be used to create referral thresholds for hip and knee replacement surgery.

We will initially identify the most suitable clinical score(s) currently available, generating candidate clinical tools for further analysis.

We will then investigate the measurement properties of the candidate tools, identifying their ability to reliably measure an individual patient's capacity to benefit from joint replacement surgery. We will do this by using statistical methods employed on large pre existing databases of clinical information. Through our collaborations we have access to pre and post-operation outcome data on over 190,000 patients.

Work package 2: Creation of the Arthroplasty Candidacy Help Engine (ACHE) tool,
with thresholds for referral based on capacity to benefit and health-economic benefit.

We will use the same datasets and a number of different methods to calculate pre-operation threshold levels (for each potential tool) to identify patients who are a candidate for surgery.

We will also use the same patient datasets to model the effect of using a threshold on the cost-effectiveness of joint replacement. Health Economists within the team will be able to predict whether the threshold level should be changed to improve cost-effectiveness.

Work package 3: We will assess the likely impact, acceptability and feasibility of
introducing the ACHE tool within the NHS, using three different approaches.

We will evaluate the impact of the ACHE tool and its acceptance by patients, GPs, doctors and commissioners. We estimate that the tool will demonstrate its effectiveness by identifying patients who have been appropriately referred, but also a group of patients who would not benefit from surgery and who should not have been referred.

Also in this WP, we will obtain the views of a large number of GPs and patients as to
the acceptability of the ACHE tool.

Finally, we will formally consult with an extended group of stakeholders who are involved in the pathway for hip and knee surgery within the NHS (patients, healthcare professionals and commissioners of services) and present the evidence we have compiled. Group discussion techniques will deliver a consensus view on the acceptability of the ACHE tool and threshold


The Chief Investigator for this project is Professor Andrew Price and, as well as the team at Oxford, involves collaboration with colleagues at the University of Bristol and Peninsula Medical School.

National Institute for Health and Care Research logo

HTA monograph for ACHE

The Arthroplasty Candidacy Help Engine tool to select candidates for hip and knee replacement surgery: development and economic modelling.

See our current trials

Completed trials