Rejoovinii
Boosting patient adherence in Knee Electrotherapy
Task completion
82%
SUS Score
94
Area
Research, UX, UI
Rejoovinii is a smart wearable for at-home knee pain management. It pairs a textile-based electronic knee sleeve with a mobile app that delivers controlled electrical pulses to support pain relief and muscle recovery.
Rejoovinii is currently undergoing a Randomised Clinical Trial (RCT) and has started showing encouraging early results. The study focuses on evaluating its efficacy for knee pain while ensuring it can be used safely and consistently by patients in real-world conditions.
Project brief
This project (MR/W029421/1) was funded by the UK Medical Research Council (MRC) to demonstrate the clinical efficacy and real-world value of the device for future NHS adoption.
As the lead designer, I owned the 0→1 design of the companion mobile app with two objectives:
Enable patients to set up and run therapy independently at home
Ensure clean, consistent data capture for clinical analysis
Context: Unpacking the challenge
Knee Osteoarthritis (OA) is a growing challenge in the UK, leading to chronic pain, reduced mobility, and declining quality of life.
1/5 adults over the age 45 affected by Knee OA
Knee OA is projected to reach 8.3 million by 2035 in the UK
There are very few electrotherapy solutions designed specifically for older adults with knee osteoarthritis. However, clinical evidence shows that home-based Transcutaneous Electrical Nerve Stimulation (TENS) therapy can be effective if used consistently.
The problem is that patients rarely stay consistent. Across multiple RCTs and home-based studies reveal,
Adherence to unsupervised home therapy falls below
Common frustrations
People struggle with confusing setup, unclear feedback and lack of confidence.
User signal (paraphrased)
Karen Gillan
Electrotherapy user
My role
As the lead designer, I aligned the team around a clear vision of how patients should move through therapy, how critical steps should behave, and how clinical data should be presented so it remained meaningful, safe, and easy to understand.
Key contributions:
Partnered with engineers and clinical researchers
Led end-to-end UX from discovery to usability testing
Designed interaction behaviour and screen flows
Created the design system foundation for the product
Outcome
Through usability and concept testing, it became clear that early drop-offs were not caused by lack of features, but because patients didn't feel confident or able to use the therapy correctly.
I consciously designed the experience to build confidence at every touchpoint. Once users feel competent, early success follows naturally. And when early success repeats, long-term adherence becomes possible.
Discovery
To design an experience that truly supports long-term adherence, I needed to find the exact moments where confidence breaks down.
Guided by clinical heads, I framed three research questions aligned to the therapy journey, to understand where adherence breaks down:
Where do patients struggle first during therapy setup?
When do they lose confidence in effectiveness?
What motivates or prevents sustained use over time?
Mapping the problem space through evidence
Competitor analysis
Very few electrotherapy apps directly target older adults with knee osteoarthritis in the UK. So I expanded the landscape to understand behavioural patterns, not just product similarity:
Direct competitors: TENS apps for athletes and fitness users
Indirect competitors: Physical exercise and rehab apps for knee pain
Analogous competitors: Game-based therapy tools for low-mobility users
High friction during setup
One-size-fits-all therapy reducing trust
Session logs and outcomes presented without meaningful context
This showed where existing solutions broke down from a patient experience perspective.
Clinical studies review
I reviewed 40+ studies on home-based TENS and NMES. My goal wasn’t to validate the therapy, but to understand patient behaviour around it.
From evidence to patterns: Affinity mapping
I ran an affinity mapping session with the team to synthesise insights from competitor analysis and clinical studies.
We mapped insights along the therapy journey rather than by research source, to reveal behavioural patterns.
Five core themes consistently emerged:
Guidance: Users don’t just need instructions, they need reassurance that they are doing it right, without fear of causing harm.
Feedback: Without clear feedback, users are left guessing whether the therapy worked, which slowly erodes trust.
Customisation: When pain changes but therapy doesn’t adapt, users feel the system does not understand their reality.
Tracking: Data without context doesn’t motivate and it only confuses and disengages the users.
Motivation: Sessions felt repetitive without meaningful reinforcement or perceived progress.
These 5 themes reflected repeated breakdown points at different stages of
therapy use.
From themes to design direction
These five themes surfaced recurring breakdown points across the therapy journey.
This led to three design insights tied to three high-risk stages:
First-time setup, in-session control, and progress interpretation, each critical to building early confidence and sustained use.
I translated each into a focused concept test using targeted wireframes.
Originally, the study was planned with experienced electrotherapy users to reduce usability noise and support cleaner trial data. However, multiple participants dropped out due to illness and scheduling conflicts.
Rather than cancel or delay, I restructured the research approach and proposed concept testing with novice users alongside planned interviews.
User validation through concept testing
After adapting our revised strategy, we did the concept testing approach with new participants who had no prior experience with electrotherapy. My goal was to see if the insights we had from our secondary research held up with a complete novice, ensuring our product would be intuitive for everyone.
Electrotherapy Novices
Electrotherapy Users
Ages
The goal wasn’t to test everything. It was to validate whether improving clarity and confidence at critical stages could measurably change how participants felt about continuing.
1. Designing first-session confidence
Insight:
The first therapy experience is not a learning moment, it’s a trust-building moment.
If confidence breaks during setup, retry probability drops sharply.
What we tested:
Bluetooth pairing and sleeve-wearing setup flow, as secondary research showed this was a common drop-off point during first use.
Shows the patients to power on the garment so it can be detected, then prompts them to grant pairing permission, completing the Bluetooth connection setup.
A step-by-step visual guide showing how to prepare the electrode areas, correctly position and fasten the sleeve before starting therapy.
What we observed
5 out of 8 participants were able to correctly interpret and taught back.
Dense text and technical language slowed first-time users
What this changed in the design
Sequenced setup with visible progress steps (e.g. Step 1 of 4)
Clear paired-device state
Reduced text, prioritising visual instruction over explanation
User signal (paraphrased)
Steps like 1 of 4 would reassure me.
Show a clear paired state.
2 Confidence during therapy: Understanding + control
Insight:
Patients lose confidence when they are unsure what the device is doing or whether they are in control.
What we tested:
The core screens, displaying live session status, pain logging, and intensity adjustment, provide essential transparency and control. This focus is crucial, as secondary research confirms that managing patient uncertainty during therapy prevents early drop-off.
These two screens let the user pick which leg to treat and log their pain levels before and after the session, making it quick to capture consistent data and see changes over time.
What we observed
All participants valued seeing what was happening in real time.
Pain logging as a meaningful feedback.
Some users hesitated when controls felt too dense.
What this changed in the design
Surface simple, visible status cues during the session.
Allow customisation, but keep primary controls minimal and easy.
Position pain logging as part of the therapy loop.
User feedback (paraphrased)
Recording pain score will be brilliant.
I would go for a personalised programme, but I’m open to customisation.
3. Motivation & continuation: Making progress visible
Insight:
Sessions feel repetitive without meaningful reinforcement. Motivation links to seeing change, not just completing sessions.
What we tested:
Screens showing session summaries, pain trends and progress views.
These were chosen as research showed that users disengage when improvement is not made visible.
Shows the user to power on the garment so it can be detected, then prompts them to grant pairing permission, completing the Bluetooth connection setup.
What we observed
Participants cared more about week-on-week patterns than one-off session results.
Rewards were less motivating than seeing actual progress trends.
What this changed in the design
Design the home screen around progress and trend visibility.
Combine summary and trends into one clear narrative of improvement.
Deprioritise gamified rewards in favour of clinical progress feedback.
User feedback (paraphrased)
Often the reward is just relief from pain and seeing the information.
It would be about seeing what patterns arise.
Define
From patterns to persona: Turning struggles into people and stories
I led a workshop to align the team around a common user model.
Linda Theobald: The face of our NHS trial
Linda is a 58-year-old with chronic knee OA and moderate digital confidence. She uses everyday apps but feels anxious around medical technology.
Her biggest barrier is not motivation. It’s confidence. She wants to manage her pain independently, but fears setting things up wrong.
Everything we designed maps back to one question:
Would Linda feel confident completing her first session alone?
Framing the experience: User stories through
Linda’s eyes
With Linda defined, I translated her goals, needs and pain points into user stories.
This helped shift the focus from features to outcomes, and from functionality
to lived experience.
These user stories also became the bridge between research insights, task flows and later design decisions.
Ideation
Linda’s journey revealed three critical moments where confidence typically breaks down. Instead of designing everything at once, I translated these breakdown points into three focused design bets. Each bet targeted a specific moment of user hesitation and confidence loss.
Design bets
A guided session reduces Linda’s first-time anxiety by offering step-by-step setup with clear visual cues, lowering cognitive load at the most fragile moment.
Simple controls with visible feedback reassure Linda that she is using the device correctly and safely, helping her stay in control during the session.
Visible progress and trends give Linda tangible proof of improvement, reinforcing motivation and long-term therapy adherence.
Mapping the solution: Task flows that carry the bets
Using Linda’s goals and the three design bets, I mapped how users would actually move through the product across three critical stages of the therapy experience.
These flows allowed me to structure the product around real user behaviour rather than features or screens.
The Specification
I created a feature specification document to detail user interaction behaviours. This acted as the final source of truth for our engineering team, providing them with a clear, actionable blueprint for development.
With task flows defined, we translated each step into screens and interactions. The next section shows the core flow, the key components, and how each decision ties back to the three insights.
Design
Once the task flows were defined, I used them as a structural blueprint for the interface. Rather than designing screens in isolation, I focused on how each moment would feel across the entire therapy journey. This is where usability, semantics, ergonomics and emotional reassurance converged.
Designing for the patient’s physical and mental context
A therapy session is not just a digital interaction. It happens in a physical, vulnerable and often cognitively loaded context. Linda is wearing a medical garment, managing pain, and using a device that she fears getting wrong. Designing for this meant optimising not just for usability, but for confidence and error prevention.
Balancing aesthetics and usability for user comfort
Designing for a medical device requires touch targets that are easy to use, especially for patients who may have reduced dexterity. My research found that a major barrier to therapy adherence is the difficulty users have in accurately selecting small targets. Adequate spacing between touch targets is also critical, as it prevents accidental taps on nearby buttons, making the interface reliable and trustworthy.
Touch target design
I designed touch targets with a minimum dimension of 48 pixels, aligning with best practices for usability and accuracy.
Establishing a design grid
The product includes a dedicated Lenovo 7-inch tablet with a display of 1024x600. To ensure the user interface was visually balanced and scalable for this specific screen, I designed the layout using an 8 px baseline grid. This was derived from the greatest common factor of the display dimensions.
All interactive elements, including stepper buttons and pain scale segments, will have a minimum touch target size of 48x48 px, exceeding WCAG recommendations for users with motor impairments.
Spacing for confidence and reliability
The product includes a dedicated Lenovo 7-inch tablet with a display of 1024x600. To ensure the user interface was visually balanced and scalable for this specific screen, I designed the layout using an 8 px baseline grid. This was derived from the greatest common factor of the display dimensions.
Core page layout and interaction
Designing for a medical device requires touch targets that are easy to use, especially for patients who may have reduced dexterity. My research found that a major barrier to therapy adherence is the difficulty users have in accurately selecting small targets. Adequate spacing between touch targets is also critical, as it prevents accidental taps on nearby buttons, making the interface reliable and trustworthy.
From design decisions to testable reality
These design decisions shaped the first working version of the interface. But rather than treating it as a final product, we approached it as a testable hypothesis.
The next step was to validate whether these ideas actually reduced hesitation, improved confidence, and made the therapy experience easier for someone like Linda.
This led into moderated usability sessions and iterative refinement across multiple versions.
In the initial phase of the project, the Rejoovinii interface was designed for a dedicated 7-inch tablet that would ship with the electrotherapy device. This allowed us to design with a fixed screen size, controlled hardware, and stable system behaviour.
However, during technical planning and early prototyping, this approach was no longer feasible due to multiple constraints: Hardware and cost limitations, Firmware reliability, and Post-deployment support risks
Design Direction Change
To reduce technical risk and improve scalability, the product was re-scoped to a mobile-first model, allowing users to install the app on their own smartphones.
The next step was to validate whether these ideas actually reduced hesitation, improved confidence, and made the therapy experience easier for someone like Linda.
This led into moderated usability sessions and iterative refinement across multiple versions.
1. Bluetooth pairing
This is the first real moment of interaction for Linda with the product. It anchors the experience in the physical world and signals “this is real now”.
It sets the emotional tone for can I even do this?
A guided step where the user connects the knee sleeve to
their phone via Bluetooth before starting therapy.
2. Which leg today
This is where Linda emotionally commits to starting a session. It represents the moment she stops observing and starts participating.
Helps the user select the leg being treated, using visual confirmation
to reduce errors and build confidence before setup.
3. Sleeve setup guide
This is the first physical interaction with the product. If the sleeve is worn incorrectly, the therapy feels ineffective, which breaks trust instantly.
This guide reduces that risk by giving simple, visual, step-by-step instructions
at the exact moment Linda needs reassurance.
4. Therapy settings
This is where Linda feels either in control or confused or scared. It visually represents the design relationship between system guidance vs user control.
This screen presents the therapy configuration, showing recommended intensity and
duration while allowing users to adjust settings if needed before starting their session.
5. Post-session summary
This screen presents the therapy configuration, showing recommended intensity and duration while allowing users to adjust settings if needed before starting their session.
This guide reduces that risk by giving simple, visual, step-by-step instructions
at the exact moment Linda needs reassurance.
Putting our bets to the test
Study goal
Evaluate whether the prototype removes setup hesitation, increases confidence during a session, and makes results easy to interpret.
Expereinced Participants
New Participants
Ages
Method
We conducted moderated 1:1 usability sessions with a think-aloud protocol. Each participant was given a short scenario and asked to complete a series of core tasks:
Pair the device via Bluetooth
Select a programme
Set up and wear the sleeve
Start a session and adjust settings
Log post-session pain
Read the session summary and trend view
Key Measures
Task Completion
The percentage of users who completed the critical path without aid.
Errors & Help Requests
Documented user-observed pain points and requests for help.
Time on Task
The time taken for key steps, including pairing and pain logging.
Usability Score
Assessed using the System Usability Scale (SUS) questionnaire.
Constraints
Scheduling delays and participant drop-outs compressed our research window, reducing available time for design and testing before trial deadlines.
Drop-out of experienced electrotherapy users forced us to pivot early testing to novices.
Switching mid-project from a 7-inch tablet to a smartphone required reworking the IA and redesigning screens for the smaller display.
