A novel protocol to measure the kinematics of torque adapters and torsional cells used in prosthetics with the support of a specific “clamp-cluster”

INTRODUCTION A torque adapter (TA) is a 1 degree-of freedom (DoF) torsion spring, with adjustable stiffness (e.g. 4R85, Otto-Bock, DE). For transtibial amputees’ prostheses, one or more TAs can be included between the socket and the foot to reduce the torsional stresses at the stump-socket interface or to ease the execution of specific every-day life activities, such as turning while walking and housekeeping, or sports activities, like golf swing. A “Torsion Control Cell” (TCC Ossur, IS) is an evolution of a torque adapter, thou with a reduced rotational range (<±20°), which functionally adds a damper to the torsion spring, for the absorption of longitudinal loads. How many TAs to include in the prosthesis, how stiff each one should be, whether to combine a TCC and a TA or not, remain questions of debate and answering a time-consuming activity in the standard practice: for CPOs it is, in fact, almost impossible to understand at “naked eye”, when each TA/TCC starts/stops turning and how much it is turning. This is particularly critical in professional golfing, as the actual timing and range of motion can influence the overall swing performance. Quantitative motion analysis can be of support to address these issues. However, at present none of the protocols available in the literature is: 1) reported with all the mathematical details required for its implementation [1,3] or, 2) takes into account the a-priori knowledge about the DoFs of TA/TCC, required to ensure accurate measurements [2], or 3) it is suitable to analyze the behavior of a single TA or TCC in a series. The aim of this work was to describe such a missing protocol for transtibial amputees, following the guideline described in [4]. In what follows, the most generic case of a TCC will be considered.