Designing and validating a staircase to leverage floor mounted force plates

Abstract

Navigating stairs is a challenging task for many patient populations. Unfortunately, assessing lower extremity kinetics is not practical in many laboratories due in part to methodologic constraints. In this study, we designed, fabricated, and calibrated a staircase that accurately measured ground reaction forces applied to the second and fourth step. This implementation met several design criteria that included low-cost, ability to quickly move the staircase in and out of motion capture spaces, stable and safe staircase, and easily modifiable to meet the constraints of different lab layouts. We built the staircase as an outer and inner staircase assembly constructed using a modular aluminum framing system. Once positioned on our force plates that were embedded in the lab floor, we used an instrumented pole to apply known loads to a series of surface locations on the force plates and steps that were resting on top of the force plates. This calibration procedure reduced the center of pressure errors by approximately 50% for the embedded force plates and lower step (step 2) and 3-fold for the higher step (step 4). Next, we demonstrated that these steps can be integrated into a clinical gait analysis workflow. A single healthy-young adult navigated the stairs, the ground reaction forces were transformed into stair reaction forces, and these external loads were used to solve the inverse dynamics problem. This staircase provides other researchers with a new tool to assess stair navigation biomechanics. In this study, we provided the bill of materials, mechanical drawings, and calibration code necessary to modify and implement this staircase paradigm into other lab layouts.