Laura Peeters

The trunk in spinal musclar atrophy | 95 5 BACKGROUND Spinal muscular atrophy (SMA) is characterized by progressive degeneration of motor neurons in the spinal cord, leading to muscle weakness and atrophy [1]. As a result patients experience limitations in performing daily activities independently [2, 3]. Patients are categorized based on maximum acquired milestones and disease onset, but clinically it is more a gradual scale of functional abilities [4, 5]. The natural course of children with SMA is characterized not only by weakness of upper and lower extremity muscles, but also by (severe) weakness in the trunk leading to scoliosis at young age [4]. However, the natural course is now changing due to effective treatment with Spinraza [6]. When performing seated activities, the trunk plays an indispensable role as it interacts with upper extremity (UE) movement as part of the kinematic chain and it provides a stable base for UE movements [7-10]. Only a few studies describe trunk function in patients with SMA. Trunk muscle force and axial function seems to be less for patients with SMA type 2 compared to type 3 [4, 11]. But literature contradicts whether axial function decreases with age. Vuillerot, et al. [5] found only a decline in axial motor function for SMA type 2 patients based on the Motor Function Measure dimension 2, whereas Wadman, et al. [11] found a decline in motor function for all SMA types based on the Hammersmith Functional Motor Score. Both measures are not solely based on axial function (i.e. upper or lower extremity function also influences the score), which might explain differences in findings. It is remarkable that so little research has been done concerning trunk function although scoliosis secondary to muscle weakness is a major problem in childhood for patients with SMA [4]. Therefore, the aim of this study was to investigate trunk function and its relation with upper extremity movements when performing seated upper extremity tasks in patients with SMA types 2 and 3. We hypothesized that maximum trunk torques and maximum active range of movement are reduced in patients with SMA (types 2 and 3) compared to healthy controls, while trunk movements and muscle activity levels when performing daily tasks are increased to compensate for reduced upper extremity function and trunk muscle strength. METHODS Participants Seventeen people with SMA and fifteen healthy controls (HC) participated in this study. Participants were included if they were older than 6 years, able to bring their