Thoracic kyphosis affects spinal loads and trunk muscle force

Background and Purpose Patients with increased thoracic curvature often come to physical therapists for management of spinal pain and disorders. Although treatment approaches are aimed at normalizing or minimizing progression of kyphosis, the biomechanical rationales remain unsubstantiated. Subjects Forty-four subjects (mean age [+/- SD] = 62.3 +/- 7.1 years) were dichotornized into high kyphosis and low kyphosis groups. Methods Lateral standing radiographs and photographs were captured and then digitized. These data were input into biomechanical models to, estimate net segmental loading from T2-L5 as well as trunk muscle forces. Results The high kyphosis group demonstrated significantly greater normalized flexion moments and net compression and shear forces. Trunk muscle forces also were significantly greater in the high kyphosis group. A strong relationship existed between thoracic curvature and net segmental loads (r=.85-.93) and between thoracic curvature and muscle forces (r=.70-.82). Discussion and Conclusion This study provides biomechanical evidence that increases in thoracic kyphosis are associated with significantly higher multisegmental spinal loads and trunk muscle forces in upright stance. These factors are likely to accelerate degenerative processes in spinal motion segments and contribute to the development of dysfunction and pain.