The characteristics of idiopathic hypotonic gait are poorly understood. The purpose of this study was to identify biomechanical parameters that differentiate between children with hypotonia and an age-matched control group. Twelve children with idiopathic hypotonia, aged 6–13 years, participated in the study. Twenty-two children with no known disorders, aged 6–13 years, served as a control group. A 6-camera Vicon MCam and three force plates were used to collect kinematic and kinetic data during gait. Significant differences in the mean kinematic and kinetic values between groups were tested using a MANOVA. No significant group differences were found for any temporal-spatial variables. Significant group differences (P < .05) were found for sagittal ankle angle and moment, sagittal knee angle and moment, and sagittal hip angle. The majority of deviations appear to be related to impairments in the gastrocnemius complex. A greater awareness of gait deviations in this population will increase our understanding of the disorder and aid in treatment planning.

Hypotonia refers to a decreased resistance to passive movement and is a common diagnosis in infants and children. Hypotonia may be caused by peripheral and central nervous system disorders and metabolic, neuromuscular, and connective tissue disorders. Disorders associated with hypotonia include Down syndrome, cerebellar ataxia and muscular dystrophy (MD). In some cases, the underlying cause of hypotonia is unknown and is referred to as idiopathic hypotonia. In conjunction with decreased muscle tone, children with hypotonia may also exhibit decreased strength, joint hypermobility, increased flexibility, delayed acquisition of independent walking and abnormal walking patterns. Despite these serious orthopaedic and motor problems, there are a limited number of studies that provide an objective, three-dimensional analysis of the walking patterns of children with hypotonia. To date, studies of hypotonic gait have tended to focus on children with Down syndrome (DS). DS is typically associated with central hypotonia, in which global or whole body abnormalities in muscle tone are present. Reported deviations in kinematic gait parameters in DS include flat foot contact, reduced sagittal ankle angles, increased stance phase dorsiflexion, increased hip and knee flexion postures, decreased hip extension in terminal swing, increased hip abduction in swing, increased hip adduction in swing, increased pelvic rotations, external foot rotation and longer duration in stance phase. Reported deviations in kinetics included reduced sagittal ankle moments, reduced ankle power, absence of the sagittal knee extensor moment peak and decreased sagittal hip joint moments and hip power. Generalizing the results of DS studies to children with idiopathic hypotonia is problematic for several reasons. First, in conjunction with decreased muscle tone, children with DS typically exhibit ligamentous laxity, hyperflexibility of the joints and orthopaedic problems such as pes planovalgus, hip and patella dislocation and genu valgum. Such disorders could contribute to gait abnormalities and may not be present in children with idiopathic hypotonia. Second, idiopathic hypotonia may stem from central and/or peripheral causes. Depending on the origin of the hypotonia, the gait patterns of children with idiopathic hypotonia may not resemble those of children with Down syndrome, who typically exhibit central hypotonia. This is due to the differential clinical signs between peripheral and central hypotonia related to, among others, weakness, deep tendon reflexes, cognition, antigravity and movements. Research that quantifies the gait patterns of children with idiopathic hypotonia is warranted. Studies examining gait in children with idiopathic hypotonia are needed to increase our understanding of the movement patterns associated with this disorder. Threedimensional gait analysis provides valuable clinical information that cannot be obtained by observational gait analysis alone. For example, measurements of net muscle activity (joint moments and powers) and electromyography data can provide insight on the underlying neuromuscular activity that generates movement. These analyses also provide important information for treatment planning and treatment evaluation (e.g. orthoses, pre- and post-surgery). Currently, little is known about the gait patterns of children with idiopathic hypotonia. Therefore, the purpose of this study was to quantify and assess the gait patterns of children diagnosed with idiopathic hypotonia versus age-matched controls. 

Alpine
Managing Editor
Journal of Orthopedic and trauma.
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