A digital Test for evaluating prosthesis control…

The Box ‘n’ Beans test is a digitized version of the widely used Box ‘n’ Blocks test, which is a quick tool to assess unilateral manual dexterity. It consists of a box with two sections and within 60s, as many blocks as possible should be transferred from one compartment to the other.

User Interface

The Box and Blocks test is a simple but effective tool to measure gross unilateral manual dexterity (Mathiowetz et al., 1985). We developed a digital version of this test, because we saw many advantages for prosthetic research. However, since it could not be a one to one implementation of the real test, because the computer screen is only two-dimensional, we had to think about adding the lost third dimension in another way. During the analogue Box and Blocks test, patients are standing in front of the box and can grab the wooden squares using mainly the joints of the hand and elbow, which would correspond to two DoF (Degrees of Freedom). However, in front of a screen, we lose one DoF, the on associated with elbow flexion and extension. In order to make up for that loss, a change was made to the appearance of the digital Box and Blocks test – the blocks turned into beans.

The beans had the shape of a barbell and could only be grasped when the virtual hand was in a certain position.

Therefore, a forced wrist rotation was the second DoF. If it were only blocks, patients would only need to open and close the virtual hand, but with the barbell or bean shape, they were coerced into actively rotating the virtual hand into a suitable position to grasp the bean.

The digital Box and Beans test can be performed even without a prosthesis and also be used to train prospective myoelectric control. In this paper, it was used to test novel machine learning algorithms with an 8-channel electrode armband, which would otherwise only be possible by reprogramming the prosthesis and manufacturing an individual socket for the patients.



C. Prahm, B. Paaßen, A. Schulz, J. Schoisswohl, O. Aszmann