# Cable-Driven Exoskeleton for Ankle Rehabilitation in Children with Cerebral Palsy
## 1 Introduction  
Cerebral palsy (CP) is a non-progressive neurological disorder originating from damage to the upper motor neurons of the central nervous system (CNS). It is the most prevalent neuromotor condition in newborns, with an incidence of 2-2.5 per 1000 live births [1]. Although the primary brain injury is non-degenerative, its symptoms often lead to a range of secondary impairments, including spasticity, movement dysfunctions, cognitive deficits, language disorders, or epilepsy [2]. Notably, the loss of ambulatory ability is strongly associated with a decline in both health status and overall quality of life [3]. In addition to its health consequences, CP imposes a substantial economic burden on both healthcare systems and families. Costs increase markedly with the severity of the condition, underscoring the need for effective therapeutic interventions [4]. Neurodevelopmental treatments remain a cornerstone of CP management to reduce quality of life. These focus on muscle tone, reflex activity, abnormal movement patterns, postural control, and perceptual-cognitive functions [1]. Among these, physiotherapy is the most widely adopted approach due to its demonstrated efficacy in improving functional outcomes [3]. In recent years, the use of exoskeletons has emerged as a promising complement to conventional therapies in the treatment of CP [5]. The use of these robotic devices in combination with physiotherapy has proven to have great benefits, as opposed to the isolated use of physiotherapy or surgery, which in the long run can lead to problems in maintaining patients' muscle strength over a prolonged period of time [6]. Exoskeletons enable repetitive, task-specific training aimed at enhancing neuroplasticity. Active functional training has been shown to improve both motor skills and muscular strength in children with CP [7]. Furthermore, these devices support passive movements and promote autonomous exploration of the environment, contributing to both physical and cognitive development. This form of intervention--commonly referred to as robot-assisted therapy--relies on medical robotic devices to deliver targeted physical rehabilitation [8; 9]. Rigid exoskeletons represent the traditional approach in assistive robotics. These devices are designed to provide full or partial body weight support, making them suitable for patients with severe mobility impairments who cannot stand or walk independently. By employing structured, predefined movement trajectories, they facilitate controlled gait patterns that closely resemble natural human walking. Their rigid structure ensures stability and controlled joint moments, enabling children with motor impairments to engage in independent ambulation while maintaining biomechanical alignment and safety [10; 11]. One of the leading examples of a rigid exoskeleton is ATLAS 2030 (Marsi Bionics, Spain) [12; 13], an advanced pediatric exoskeleton designed for gait rehabilitation in children with CP. It features 8 actuated degrees of freedom (DOFs), with four per leg allowing for hip, knee, and ankle rotations in the sagittal plane, along with hip rotation in the frontal plane. It has an adjustable stiffness mechanism, which minimizes impact forces, enhances user safety, and efficiently stores and releases energy through passive elastic elements. Additionally, the exoskeleton's geometry can be customized to match the child's body dimensions, with adjustable joint limits, ensuring a more personalized and effective rehabilitation process [12]. ATLAS 2030 has been shown to significantly improve gross motor function, range of motion (ROM), and spasticity reduction when integrated into conventional therapy. It has emerged as a promising tool for facilitating greater mobility, independence, and overall quality of life in children with motor impairments [13]. Currently, the most studied exoskeleton for gait rehabilitation is Lokomat (Hocoma, Norwell, MA, USA ).