STEPFORWARD: A randomised controlled trial and economic evaluation of the impact of a hydraulic self-aligning ankle-foot on quality of life for patients with a below-knee amputation who have limited mobility – Trial overview

Each year, more than 2,000 below-knee amputations are performed in the UK, often as a result of diabetes and/or arterial disease. They mostly occur in patients over 50 years. This patient group is often categorised as having “limited mobility” in the community, or as K2-level prosthesis users, according to the widely used Medicare Functional Classification Levels that inform prescription of prosthetic components, including ankle-feet. Older, below-knee amputees represent the majority (>66%) of lower limb amputees1 and form the most under-researched amputee patient group.

Below-knee amputees with limited mobility almost universally receive a prosthetic limb with a rigid ankle-foot (hereafter simply referred to as foot). Usual care “rigid” feet have limited functionality, designed for level walking and standing. These feet are unable to self-adapt to sloped surfaces, stairs and uneven terrain people encounter in daily environments. Other feet are commercially available on the NHS but seldom prescribed to this patient group because they are more expensive and their clinical and cost-effectiveness have not yet been demonstrated. In 2004, a Cochrane Review found there was insufficient evidence from “high-quality comparative studies for the overall superiority of any individual type of prosthetic ankle-foot mechanism”2.

Our patient public involvement (PPI) work with amputees who have limited mobility revealed their usual care foot is not “fit for purpose” and restricts their daily movement. Consequently, they use their prosthesis less and lead more sedentary lives, exacerbating existing health conditions (including mental) putting them at risk of re-amputation3. This leads to poor quality-of-life and increased healthcare costs for the NHS.

The primary aim of the STEPFORWARD trial is to evaluate the clinical and cost-effectiveness of a flexible foot that uses a hydraulic mechanism to self-align to different surfaces compared to a usual care foot for patients with a below-knee amputation who are categorised as having “limited mobility”.

STEPFORWARDis a pragmatic, parallel, two-arm, randomised controlled trial that will be delivered across 10-12 NHS prosthetics centres in England and Scotland. The anticipated participating sites include Hull, Sheffield, Wirral, Nottingham, Birmingham, Cambridge, Billericay, Portsmouth, Plymouth, London Stanmore and Glasgow. The 4-year study will start in January 2026, with sites expected to open to recruitment in summer 2026 for approximately two years.

We will recruit 266 established prosthesis users with a below-knee amputation who are using a usual care foot and who are categorised as having limited mobility in the community (i.e., K2-level prosthesis users). Participants will be randomised in a 1:1 ratio, stratified by age, prosthetic site and prosthetic experience, to receive a flexible foot (intervention group) or keep their usual care foot (control group). The only difference between the groups will be the foot; all participants will have access to normal care via their prosthetic therapies centre.

We will be using two self-aligning ankle-feet (aka flexible foot) (Avalon-K2, Blatchford, UK and Odyssey-K2, College Park Industries, USA). Both flexible feet use a hydraulic mechanism to automatically adjust to stairs, slopes and uneven surfaces in daily environments, and both belong to the same functional category of foot. They have been designed to meet the complex needs of patients with limited mobility including helping with ground clearance4, reducing falls, and improving prosthetic safety and comfort5.

The primary outcome will be quality-of-life measured with the EQ-5D-5L6 at 12 months (primary endpoint). This patient-reported outcome is preferred by patients who we approached about this study as it is quick and simple and resonates with the domains important to them. It is also routinely used by clinicians, and recommended by the International Society of Prosthetics and Orthotics (ISPO) and the NHS. Secondary outcomes include use of prosthesis (self-reported and with the StepWatch activity monitor (Modus Health, USA) measured over 7 days), functional mobility, mental wellbeing, socket comfort and number of falls. We will undertake an economic evaluation by measuring patients’ use of health resources and costs associated with the hydraulic flexible feet.

During the internal pilot phase, we will interview patients and staff to understand acceptability and practicality of the trial and intervention. We will also explore issues around clinical equipoise and identify strategies to support and improve recruitment. At the end of the trial, we will survey all NHS sites to identify factors that would support or hamper implementation into practice and use our interview findings to develop a plan to support roll out. We will undertake a SWAT focused on the facilitation of recruitment of ethnic minority groups.

This trial is being delivered following the completion of a successful feasibility trial in 2018-20 (NIHR-funded PB-PG-081620029)7. STEPFORWARD will be the first definitive trial investigating prosthetic feet delivered within a clinical NHS setting. We expect STEPFORWARD will provide conclusive evidence for the effectiveness of a self-aligning hydraulic (flexible) foot for improving quality-of-life in below-knee amputees with limited mobility in the community. As such, we will share the results with the NHS clinical commissioning groups for prosthetics to inform prescription policies. We will organise a multidisciplinary stakeholder event for policy-makers, clinicians, service managers, patient groups and charities to translate the findings into practice. We will launch an implementation strategy with prioritisation criteria. Together with our patient advisors, we will develop patient-facing documents about prosthetic feet in different formats (e.g., brochures, videos) and share them via national charities. We will also share our findings with the International Society of Prosthetics and Orthotics and Vascular Society of Great Britian and Ireland.

Patients who fulfil the following criteria could be eligible for STEPFORWARD.