Perioperative care is a critical part of the elective surgery pathway, but it does not always function as a coordinated system. Too often, patients move through a series of disconnected steps rather than along a single, joined-up pathway.
Patients may be added to surgical waiting lists before their health status, risks, and readiness for surgery have been fully assessed. In many cases, assessment only takes place a few weeks before surgery. This limits the opportunity to optimise health and reduce risk.
This matters because patient condition has a significant impact on outcomes. Frailty and inactivity can increase the risk of surgical complications several-fold, while earlier prehabilitation interventions – such as targeted physical activity – have been shown to reduce this risk substantially. Other important risk factors, such as anaemia, are also frequently identified late in the pathway, despite affecting a significant proportion of surgical patients and increasing both complication risk and treatment complexity.
Key stages of the pathway – such as pre-operative assessment, diagnostic testing, optimisation of health before surgery, theatre scheduling, and discharge planning – often happen at different times and are not well aligned.
This challenge is compounded by an ageing population, with many patients presenting with multiple long-term conditions that increase complexity and risk.
When issues are identified late in the pathway, the consequences can be significant. Operations may be cancelled at short notice, hospital stays may be prolonged, and valuable theatre capacity can be lost. Opportunities to reduce case complexity and improve outcomes are also diminished. These inefficiencies not only impact patient experience but also place additional strain on already stretched resources.
As a result, perioperative care can become a key constraint in the flow of elective care. System performance depends not only on the effectiveness of individual services, but on how well patients, staff, and resources move through the pathway as a whole. Delays or capacity constraints at earlier stages can quickly propagate downstream, leading to underutilised theatres, limited bed availability, and growing waiting lists.
Taken together, these challenges highlight a missed opportunity to intervene earlier in the pathway, when risks can still be reduced and outcomes improved.
Why simulation modelling helps
Simulation modelling is particularly useful for complex systems like perioperative care, where changes in one part of the pathway can affect many others.
By developing a simplified, quantitative representation of the perioperative pathway, it becomes possible to explore how different parts of the system interact and to test the potential impact of changes before they are implemented in practice.
As an initial, high-level proof of concept, The Strategy Unit have developed a model of the elective hip and knee replacement pathway across England in collaboration with clinicians working across perioperative care.
Designed for integrated care boards (ICBs), NHS trusts and system leaders, the model allows users to explore how changes at different stages of the pathway affect overall system performance. A user-friendly interface enables activity projections to be tailored to local populations.
The model helps users understand how interventions at different stages of the pathway influence flow, capacity, and outcomes across the wider system.
What the model explores
A key focus of the modelling is to understand how earlier and more systematic screening of new orthopaedic referrals affects flow through the system.
Early screening aims to identify patients who are not yet ready for surgery and to direct them towards appropriate interventions at an earlier stage. These may include:
- prehabilitation (such as exercise programmes, smoking cessation, or weight management),
- medical optimisation,
- shared decision making about alternative management options where surgery may not be the best course of action.
The model also explores scenarios including:
- Reducing the number of patients entering the surgical pathway through greater use of conservative management,
- Improving early discharge planning to help reduce delays in discharge and increase bed availability and
- Understanding the impact of pathways on throughput and waiting lists
How the model was developed
We developed the model through a series of workshops with clinicians, ICB leads, public health professionals and commissioners.
Together, we mapped the perioperative pathway and built a shared understanding of how patients move through the system, while also exploring how it could be improved. We refined the model iteratively, using feedback from the group to test assumptions and improve how the pathway was represented.
To keep the work focused, we scoped the model to elective hip and knee replacements. This provided a clear and high-volume pathway to work with, while still reflecting many of the wider challenges seen across elective care.
We combined national data with local insight to inform the model. This included theatre activity, waiting list data, conversion rates, and length of stay. Where data was limited, assumptions were developed with input from the workshop group. This helped ensure the model remained grounded in how services operate in practice.
Understanding trade-offs and system flow
The model allows users to test “what if” scenarios in a safe and transparent environment.
Users can explore how changes at different points in the pathway – such as increasing early screening, expanding access to prehabilitation, reducing unnecessary progression to surgery, or improving discharge processes – affect overall flow and system performance. In doing so, the model helps users to better understand trade-offs, anticipate unintended consequences, and identify where interventions can improve both system efficiency and patient outcomes.
This work also shows what a system dynamics project looks like in practice. The value is not only in the model itself, but in the process: bringing people together, developing a shared understanding, and using that to explore potential solutions.
For systems facing similar challenges, this approach provides a practical way to work through complexity and plan change.
Partners and collaboration
This work was funded by University College London, and developed with NHS medical, nursing, public health and service commissioning experts and includes input from the Centre for Perioperative Care, the Royal College of Anaesthetists, the Royal College of Surgeons, GIRFT, NHS England and leads from Integrated Care Boards.
If you would like to find out more about this work or discuss how system dynamics modelling could support your priorities, please get in touch:
The model documentation and source code can be viewed on GitHub, and the Pathway tool can be accessed using the link below.
