Abstract
The pathomechanisms of curve progression in adolescent idiopathic scoliosis (AIS) remain poorly understood and biomechanical data are limited. A deeper insight into spinal loading could provide valuable information toward the improvement of current treatment strategies. This work therefore aimed at using subject-specific musculoskeletal full-body models of patients with AIS to predict segmental compressive forces around the curve apex and to investigate how these forces are affected by simulated load carrying. Models were created based on spatially calibrated biplanar radiographic images from 24 patients with mild to moderate AIS and validated by comparing predictions of paravertebral muscle activity with reported values from in vivo studies. Spinal compressive forces were predicted during unloaded upright standing as well as standing with external loads of 10, 15, and 20% of body weight (BW) applied to the scapulae to simulate carrying a backpack in the regular way on the back as well as in front of the body and over the shoulder on the concave and convex sides of the scoliotic curve. The predicted muscle activities around the curve apex were higher on the convex side for the erector spinae (ES) and multifidi (MF) muscles, which was comparable to the EMG-based in vivo measurements from the literature. In terms of spinal loading, the implementation of spinal deformity resulted in a 10% increase of compressive force at the curve apex during unloaded upright standing. Apical compressive forces further increased by 50–62% for a simulated 10% BW load and by 77–94% and 103–128% for 15% and 20% BW loads, respectively. Moreover, load-dependent compressive force increases were the lowest in the regular backpack and the highest in the frontpack and convex conditions, with concave side-carrying forces in between. The predictions indicated increased segmental compressive forces during unloaded upright standing, which could be ascribed to the scoliotic deformation. When carrying loads, compressive forces further increased depending on the carrying mode and the weight of the load. These results can be used as a basis for further studies investigating segmental loading in AIS patients during functional activities. Models can thereby be created using the same approach as proposed in this study.
Highlights
Adolescent idiopathic scoliosis (AIS) is a complex threedimensional deformity of the spine, which affects as many as 4 out of 100 adolescents and occurs in early puberty (Cheng et al, 2015)
The evaluation of muscle geometry indicated that the implementation of spinal deformity resulted in side-to-side asymmetries, which agreed with reports in the literature
The validation studies showed higher convex erector spinae (ES) and MF muscle activity around the curve apex, which was comparable to the EMG-based in vivo measurements from the literature
Summary
Adolescent idiopathic scoliosis (AIS) is a complex threedimensional deformity of the spine, which affects as many as 4 out of 100 adolescents and occurs in early puberty (Cheng et al, 2015). Once the diagnosis of AIS is made, adolescents are generally treated conservatively using scoliosis-specific exercises (SSEs) and other forms of physiotherapy in order to minimize curve progression (Romano et al, 2012). In about one fourth of the patients treated with exercises and braces, the progression of deformation cannot be contained and surgical intervention is required (Dolan and Weinstein, 2007). Since the pathomechanics of the AIS spine are not well understood, SSE protocols that affect spinal loading in a targeted, and scientifically sound manner cannot be developed. The literature currently lacks any studies reporting on spinal loading during functional activities or exercises in AIS patients
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