# Perspectives and Challenges in Robotic Neurorehabilitation
## 2 An Overview of Robotic Devices for Neurorehabilitation
### Robotic Neurorehabilitation for the Lower Limb
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**End-Effector Name** & **Classification** & **Actuators** & **Actuated DOFs** & **Training Modality** & **Type of Disease** \\ \hline \multirow{4}{*}{Gait Trainer [84]} & \multirow{4}{*}{Footplate-based} & Electric and Mechanical (ropes for controlling COM displacement in vertical and horizontal plane) & Movable footplates allowing for feet movement in the sagittal plane (walking on a flat surface); COM vertical direction; COM horizontal direction & & Stroke [93; 94] *; MS [95]; Parkinson [96]; CP [97] \\ \hline \multirow{4}{*}{Haptic Walker [85]} & \multirow{4}{*}{Footplate-based} & \multirow{4}{*}{Electric} & Freely programmable footplates allowing for feet movements in a 3D space. Simulation of complex movements (climbing) & Passive; Active & - \\ \hline \multirow{2}{*}{G-EO Systems [86]} & \multirow{2}{*}{Footplate-based} & \multirow{2}{*}{Electric} & Freely programmable footplates allowing for foot walking and climbing & Active Assistive & Stroke [86] \\ \hline \multirow{4}{*}{Hunova [91]} & \multirow{4}{*}{Platform-based} & \multirow{2}{*}{Electric} & Ankle Dors,/Plant,; Ankle Active Inv/Evers.; Sagittal plane pelvis rot.; Frontal plane pelvis rot. & Passive; Active & Elderly [88]; work-related \\  & & & & & \\ \cline{1-1} \cline{3-4}  & & & & & \\ \cline{1-1} \cline{3-4}  & & & & & \\ \hline \multirow{4}{*}{Rutgers Ankle [89]} & \multirow{4}{*}{Platform-based} & \multirow{4}{*}{Pneumatic} & Three ankle translations; Ankle Dors,/Plant.; Ankle Active Inv/Evers.; Ankle Internal and External rot. & Passive; Active & Stroke, musculo-skeletal ankle injuries, CP \\ \cline{1-1} \cline{3-4}  & & & & & \\ \cline{1-1} \cline{3-4}  & & & & & \\ \cline{1-1} \cline{3-4}  & & & & & \\ \hline \end{tabular}  
* The review of [PERSON] and [PERSON] compares the effectiveness of randomized studies employing the end-effector Gait Trainer robot or the LokoMat treadmill-based exoskeleton for gait retraining after stroke. ** The review of [PERSON] et al. recapitulates previous studies on robot-assisted ankle rehabilitation with different devices. Among them, the Rutgers ankle has been employed on different patients suffering either from muscolo-skeletal injuries or neurological disease. COM: Center of Mass. Dors. Dorsiflexion; Plant. Plantarflexion; Inv. Inversion; Evers. Evers; Rot. Rotation. Abbreviations for disease under examination—MS: Multiple Sclerosis; CP: Cerebral Palsy; TBI: Traumatic Brain Injury.  
\end{table} 
Table 3: Main features of the most common lower limb end-effector rehabilitation robots. (no crutches or other external supports are required). Treadmill-based exoskeletons have been designed for use in a static configuration inside a rehabilitation structure, while the lightweight overground-walking exoskeletons have been developed to promote functional recovery of locomotion in a natural setting. Moreover, they have also been developed with the intention of using them in continuous contact with the patient, in order to allow, with a long term-perspective, home-based rehabilitation. For further differences between treadmill-based and overground-walking exoskeletons, the reader may refer to a previous review [108]. It is important to note that, among their differences, the overground-walking exoskeletons allow for more adequate control over step initiation than treadmill-based exoskeletons do. The number of DOFs changes depending on the lower limb rehabilitation robot that is considered. Indeed, most of the current systems have two DOFs (per each leg) obtained by the flexion-extension of the knee and hip joints. As an example, the Lokomat, Rewalk, Ekso, and Indego Therapy exoskeletons actuate these two DOFs. Instead, the treadmill-based exoskeleton, ALEX, actuates seven DOFs (three for the trunk, two for the hip flexion/extension and abduction/adduction, one for the knee flexion/extension, and one for the ankle dorsi/plantar flexion).