Kinematics of the chest cage and spine during breathing in healthy individuals and in patients with adolescent idiopathic scoliosis

Study Design. The lung function test by a Plethysmograph enabled calculations to be made of the total lung capacity and vital capacity. A Motion Analysis System (Elite, BTS Inc., Milano, Italy) was used to observe and record chest cage and spinal movements and as to correlate lung function with the chest cage and spine kinematics. Objectives. To determine the three-dimensional kinematics and the shape and size changes of the chest cage and thoracic spine motion during deep breathing in healthy and scoliotic individuals. Summary of Background Data. Lateral flexion plus rotation of the involved vertebrae around a vertical axis causing a decrease in lung function is the main disfigurement of scoliosis. Reports show that even after spinal fusion, reduced vital capacity associated with an increased residual volume are detected. Factors such as angle of scoliosis, length of the spinal column involved, and duration of the deformity influence pulmonary function but do not significantly affect its reduction. Mechanical inefficiency during breathing has not been studied. Methods. Three-dimensional kinematics of the chest cage and spine during breathing were studied in 41 scoliotic patients and in 20 healthy individuals. Three-dimensional chest cage motions relative to the spine and thoracic spine motions relative to T12 were calculated. To examine stiffness of the spine, lateral bending angles were calculated. The lung function test, which including spirometry and lung subdivision, also was performed for the scoliotic patients. Results. Significant differences (P < 0.05) were found in the movements of the upper level of the chest cage in anteroposterior and vertical directions, ranging from 16.7 to 28.6 mm in healthy individuals and from 12.1 to 24.2 mm in scoliotic patients. The thoracic spine displayed two-dimensional movements posteriorly and vertically during breathing, whereas less movement was seen in scoliotic patients. In addition, overall the scoliotic spine showed signs of stiffness in lateral bending. Conclusions. The range of movement of the chest cage and spine is more limited in the scoliotic cases. This overall stiffness of the chest cage and the spine may contribute to the mechanical inefficiency and impairment of pulmonary function found in scoliotic patients.