Recreated missing leg sensations, connected to the prosthesis sensors, restored leg functional abilities and promoted its cognitive integration.

Systems presenting haptic information have emerged as an important technological advance in assisting individuals with sensory impairments or amputations, where the aim is to enhance sensory perception or provide sensory substitution through tactile feedback. These systems provide information on limb positioning, environmental interactions, and gait events, significantly improving mobility in amputees and their confidence about using such devices. This review summarizes recent progress in haptic feedback systems by providing a comparative analysis of different feedback approaches, evaluating their clinical effectiveness and usability, tactile feedback system design, and user experience, while identifying key gaps in the literature. These insights can contribute to the advancement of more effective, user-centered haptic feedback systems tailored for lower limb prosthetics. The findings are aimed at guiding future research in designing adaptive, intuitive, and clinically viable feedback mechanisms, fostering the widespread implementation of haptic systems in both assistive and rehabilitative applications.

In the past decade, significant focus has been on electromyography (EMG) control of prostheses in transtibial amputees (TTAs). Reliable signal acquisition requires accurate EMG electrode placement. Conventional electrode placement methods are challenging due to altered post-surgical anatomy. This study investigated the application of ultrasound imaging for placement of EMG electrodes in TTAs. Four residual limb muscles, Tibialis Anterior (TA), Peroneus Longus (PL), Gastrocnemius Medial (GM), and Gastrocnemius Lateral (GL), were examined in 9 unilateral TTAs. Ultrasound was used to identify each muscle belly’s thickest part and fiber orientation. A Certified Prosthetist Orthotist (CPO) then performed palpation to identify muscle bellies, blinded to ultrasound findings. Distances between ultrasound- and palpation-identified spots were measured. EMG data were contrasted between methods in terms of root mean square (RMS) amplitude and signal-to-noise ratio (SNR). The results indicated that Ultrasound-guided placement produced slightly higher, though non-significant, signal amplitudes (p = 0.06) and significantly higher SNR (p = 0.04). Moreover, palpation misidentified muscles in four cases. In 72.2% of cases, the distance between ultrasound- and palpation-identified spots was more than 10 mm. The mean distance was the greatest for PL and GL. Relying on palpation to identify PL and TA in TTAs may provide irrelevant EMG due to erroneous placement. Using ultrasound imaging can avoid this and, in addition to accurate muscle identification, may improve signal amplitude and SNR. In conclusion, ultrasound imaging is a valuable tool for enhancing the accuracy of EMG electrode placement in TTAs, which may lead to better prosthetic control outcomes.

This study investigates the structural and functional characteristics of residual muscles in transtibial amputees (TTAs) to improve electromyography (EMG)-based prosthetic control. Using ultrasonography, we measured the thickness of the Tibialis Anterior (TA), Peroneus Longus (PL), Gastrocnemius Medialis (GM), and Lateralis (GL) at rest and during contraction. Surface EMG was employed to assess muscle activation patterns, co-contraction levels, and accuracy in modulating submaximal contractions at 25%, 50%, and 75% of maximum voluntary contraction (MVC). Results revealed that muscle thickness on the amputated side was significantly lower than on the sound side (p < 0.0001), with the TA and PL exhibiting the greatest atrophy. Despite this, all muscles demonstrated significant increases in thickness during contraction (p<0.0001), indicating preserved neuromuscular activity. GL showed the highest percentage increase in thickness (23.7%), followed by PL (20.5%) and GM (15.4%). EMG analysis demonstrated high co-contraction, particularly between TA and PL, which may complicate selective muscle activation for prosthetic control. During dorsiflexion, PL activation was nearly as high as TA, while TA also exhibited unintended activation during eversion, suggesting poor muscle differentiation. During plantarflexion, GM and GL exhibited dominant activation, while the PL showed substantial co-contraction. Accuracy in controlling submaximal contractions was inconsistent, with TA showing the lowest absolute error (0.17), while GM and GL exhibited the highest errors (0.26 and 0.27, respectively). These findings suggest that TTAs retain the ability to activate residual muscles but struggle with selective activation and intensity modulation, emphasizing the need for targeted training and prosthetic control strategies to optimize functional outcomes.

Finding a balance between adaptability for unexpected or non-standard movements and repeatability for cyclic standard movements is a known control challenge for active lower-limb prostheses. This study integrates a volitional electromyography (EMG)-driven musculoskeletal model controller with a finite-state machine impedance controller. During the stance phase, the hybrid controller is activated, and during the swing phase, it functions as a position controller. To provide a seamless transition to the swing phase of the gait, the controller first runs in hybrid mode until it validates that the foot is entirely off the ground. The Gastrocnemius and Tibialis Anterior muscles were modeled using a Hill-type muscle model to function around an ankle joint. The system uses input from ankle sensors and EMG data from antagonist muscle pairs to activate the muscle models. In addition, muscle parameters within the model are optimized using a surrogate-based optimization technique to improve the neuromuscular model controller’s performance and responsiveness. A transtibial amputation participant assessed the hybrid controller online for various activities, including ambulation on level ground, stairs, and ramps, using EMG signals from the residual limb as input. Combined with the impedance controller, the EMG control showed exceptional efficiency and repeatability, particularly for stair ascent, stair descent, and ramp descent. Moreover, according to user feedback, the user felt more involved and capable of using their muscles to control the motion, which improved their overall sensation of stability and control during these activities. The hybrid controller functioned more like an impedance controller during ramp ascents and walking on level terrain.