Petal Pinch

Project Overview

Petal Pinch is a purpose-built assessment tool designed to bring consistency to thumb opposition tracking between clinical visits. Whether used at home for personal monitoring or reviewed during your next appointment with your OT or PT, the goal was to eliminate subjective reach estimation and provide a structured, tactile method for measuring thumb mobility progress. 

The project resulted in a modular stackable system: individual petals in 1 mm and 10 mm increments that assemble around a central hummingbird component, allowing for precise, repeatable measurement and tangible progress tracking. 

Design Focus

The project was built around two core pillars: tactile feedback and mechanical simplicity: 

• Incremental Petal Stacking: The petal assembly provides measurement in 1 mm and 10 mm increments (4 petals at 10 mm and 10 petals at 1 mm, totaling approximately 50 mm). Each removable petal represents a measurable threshold, making progress visible and tangible between visits.

• Stable Assembly Point: The hummingbird component secures the petals in place, ensuring the measurement configuration remains consistent between sessions and allowing the assembly to be positioned flat, on its side, or held in your other hand.

• Dual-Increment Design: Print petals in alternating colours for visual differentiation. The contrasting pattern makes it easy to count increments and identify your current threshold at a glance.

• Kinesthetic Reference Point: The petals serve as a physical target for pinch contact. This helps establish a repeatable starting configuration for every iteration of the test.

The Assembly System

• The Base & Rod (PLA): The primary structural component. The rod provides the central anchor point for the assembly and can be positioned flat, on its side, or held in your other hand to suit your testing preference.

• The Hummingbird & Petals (PLA): The moving parts. The hummingbird raises and lowers to secure the petals in place. Four petals at 10 mm thickness and ten petals at 1 mm thickness stack to approximately 50 mm total, providing granular progress observation.

Functional Breakthrough

The turning point for this design was recognizing that home-based assessment consistency depends on removing guesswork from the measurement itself. Traditional thumb opposition testing relies on subjective hand positioning and visual estimation. By providing stackable physical increments and a stable assembly point, you can track your own progress tangibly between visits, giving your clinician concrete data to inform treatment decisions.

It's important to note that 3D printing tolerances mean your printed petals may vary slightly from the target thickness. A 1 mm petal may print between 1.05 and 1.14 mm depending on your printer settings, filament, and calibration. This device is designed to give you a consistent way to observe progression rather than clinical-grade precision. What matters is that you're measuring against the same physical reference each time, making improvement visible over weeks and months.

Reflection & Tools

• The priority was simplicity and tactile feedback: stack the petals, position the assembly, and record the data.

• CAD: Plasticity

• 3D Printing: Prusa CORE One

• Slicing: PrusaSlicer

Disclaimer & Safety

Not a Medical Device: Petal Pinch is an experimental ergonomic prototype and assessment aid. It has NOT been evaluated, approved, or endorsed by any medical or regulatory body (such as Health Canada or the FDA).

Consult a Professional: Always ensure that your assessments are reviewed by a qualified healthcare professional. Consult with your OT or PT to ensure this tool is appropriate for your specific needs and rehabilitation goals.

User is the Manufacturer: By downloading these files, the user acknowledges they are the manufacturer of the physical object and assume 100% responsibility for material selection, print settings, and safety testing.

Evolution of the Design