Julia Block

Functional effects of a prosthetic torsion adapter in trans-tibial amputees during unplanned spin and step turns

Background: Shear stress at the stump in trans-tibial amputees induced by turning movements may be reduced with the use of torsion adapters in the prosthesis. Objective: Monitoring the motion and kinetic effects of a regular torsion adapter in comparison to a rigid placebo in unplanned spin and step turns. Study design: Single-blinded placebo-controlled cohort study. Methods: In total, 10 trans-tibial amputees underwent three-dimensional gait analysis in level walking and unplanned spin and step turns with a torsion adapter and with a rigid placebo. Results: Kinetic effects varied among participants. No statistically significant reduction of peak internal and peak external transverse plane moments was found for the torsion adapter in any walking condition. However, transverse plane rotation of the adapter was monitored in all participants. Conclusion: Motion between the socket and the residual limb may be reduced during turns due to transverse plane motion of the torsion adapter and shear stress on the residual limb may be reduced. However, there may be good and bad responders to torsion adapters due to differences in coupling between the residual limb and the socket. Clinical relevance Strong coupling between stump and socket will help the user controlling his prosthesis. Shear stress at the stump may increase in stump–socket interface stiffness and may be the reason for residual limb problems. Torsion adapters therefore may be beneficial for comfort and stump condition in individual cases.

Knee-ankle-foot orthosis with powered knee for support in the elderly

A prototype of a powered knee orthotic device was developed to determine whether fractional external torque and power support to the knee relieves the biomechanical loads and reduces the muscular demand for a subject performing sit-to-stand movements. With this demonstrator, consisting of the subsystems actuation, kinematics, sensors, and control, all relevant sensor data can be acquired and full control is maintained over actuator parameters. A series-elastic actuator based on a direct current motor provides up to 30 Nm torque to the knee via a hinge joint with an additional sliding degree of freedom. For reasons of feasibility under everyday conditions, user intention is monitored by employing a noninvasive, nonsticking muscle activity sensor to replace electromyographic sensors, which require skin preparation. Furthermore, foot plates with force sensors have been developed and included to derive ground reaction forces. The actual knee torque needed to provide the desired support is based on an inverse dynamics model using ground reaction forces signals and leg kinematics. A control algorithm including disturbance feed forward has been implemented. A demonstration experiment with two subjects showed that 23 % of moment support in fact leads to a similar reduction in activation of the main knee extensor muscle.

Integrating strength tests of amputees within the protocol of conventional clinical gait analysis: a novel approach.

Abstract Clinical experience tells us that the lower-limb amputees are one of the patient groups who clearly suffer from a strength deficit in their involved side. However, there is no obvious evidence for the relation between the residual limb strength and walking ability in this population. Correlating the results of the conventional clinical gait analysis (CGA) with strength tests could help to find out how deficits in strength impact the amputees’ gait. In this contribution, a new device for measuring the isometric muscle strength of the hip and the knee was tested for feasibility. Three groups were tested: one group of 11 healthy subjects (29±5 years) to test the repeatability of the device, two unilateral amputees (one transfemoral for 56 years, one transtibial for 65 years), and a reference group of 17 healthy subjects (55±10 years). The new method presents an adequate technique to integrate strength testing within a standard protocol of the CGA. Results showed to be repeatable within sessions [i.e., within-day, intraclass correlation coefficient (ICC)>0.972] and between repeated measurements (i.e., day-to-day, ICC>0.765). The tested amputees showed clear deficits in maximum isometric joint moments in their most distal joint. The first results suggest evidence for a relation between the maximum isometric joint moments and gait deviations in amputees.

Active Knee Orthosis for Supporting the Elderly

1 Dept. of Control Engineering and Mechatronics, TU Darmstadt, Darmstadt, Germany, mgruen@iat.tu-darmstadt.de 2 Measurement and Sensor Technology Lab., Institute for EMK, TU Darmstadt, Darmstadt, Germany 3 Microtechnology and Electromechanical Systems Lab., Institute for EMK, TU Darmstadt, Darmstadt, Germany 4 Dept. of Orthopedics, Trauma Surgery and Paraplegiology, Heidelberg University Clinics, Heidelberg, Germany

Power support by an active knee orthosis during sit to stand

An active knee orthosis has been developed for assisting elderly in challenging ADL-tasks like stair-climbing or sit-tostand (STS). In contrast to approaches of exo-skeletal devices, used in paraplegics without or with marginal motor function of the lower extremity, this orthosis aims to amplify joint moment in elderly with reduced muscle strength. Aim of this study was to test whether the user profits from the supportive function of this device. The support should be visible in reduced EMG-activation during STS when comparing to the situation without support.