Man Ther. 1999 Aug; 4(3): 157-62.

Comparison of ribcage and posteroanterior thoracic spine stiffness: an investigation of the normal response.

Edmondston SJ, Allison GT, Althorpe BM, McConnell DR, Samuel KK.

Curtin University of Technology, Perth, Western Australia.

Evaluation of the movement response to posteroanterior (PA) loads applied to the spinous processes is a recognized part of the physical examination of the thoracic spine. During this clinical procedure the thoracic spine is supported by the ribcage which may contribute to the movement response. However, the contribution of ribcage stiffness to the PA stiffness of the thoracic spine has not been established. The purpose of this study was to measure the PA stiffness of the thoracic spine and compare this to the stiffness of the ribcage under anteroposterior load. Using force-displacement analysis, this study measured the PA stiffness of the thoracic spine at T4, T7 and T10 in 20 asymptomatic individuals, and compared this to the ribcage stiffness measured through sternal compression. The mean PA stiffness at T7 (10.7 N/mm) was significantly greater than at T4 (9.1 N/mm, P < 0.001), and there was a non-significant increase between T7 and T10 (11.4 N/mm, P = 0.08). The stiffness of the ribcage measured via sternal compression (7.6 N/mm) was significantly lower than the thoracic PA stiffness at all levels (P < 0.01). A significant proportion (33%) of the thoracic spine PA stiffness was accounted for by the stiffness of the ribcage (P < 0.01). In young, asymptomatic subjects, the PA stiffness of the thoracic spine is significantly greater than the stiffness of the ribcage. This suggests that the response to PA load application in the thoracic spine can be attributed to factors relating to the spine as well as the ribcage. Defining consistent patterns of PA stiffness in the thoracic spine may assist in the interpretation of clinical measurements of patients with mechanical dysfunction of the thoracic spine.