Isoforce: A new outrigger system for static progressive orthotic interventions of the proximal interphalangeal joint with constant force transmission—Results of a biomechanical study

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Study Design:

Bench research—biomechanical study.


Static progressive orthotic devices are efficient in treating contractures. However, current outriggers are unable to keep force transmission and the force application angle (FAA) constant.

Purpose of the Study:

To evaluate the biomechanical performance of the Isoforce outrigger, a novel extension orthosis.


A hand model was used to measure the required force at the outrigger and FAA, while simulating resolution of different contracture angles. We also tested feasibility in a small patient series.


The force required with the Isoforce device never exceeded 2.4 N, and the FAA did not change more than 6°. Corresponding figures for the reference devices exceeded 16 N and 20°. The 7 patients testing the Isoforce extension device showed an extension deficit that decreased from 40° at baseline to 25° at 6 weeks. They rated the device as very comfortable to wear.


Isoforce maintains constant force transmission and FAA throughout the full range of motion, promotes the lengthening of contracted structures, and is comfortable to wear.

Level of Evidence:

Not applicable.

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