Dynamic effects of the Nuss procedure on the spine in asymmetric pectus excavatum

Objective: This study aimed to elucidate dynamic effects of the Nuss procedure on the spine in the treatment of patients with pectus excavatum with asymmetric thoraces. Methods: Twenty-five patients with pectus excavatum who underwent the Nuss procedure were categorized into 4 groups by preoperative morphology of the spine and thoracic asymmetry. In group 1 (n = 8), the right side of the thorax was concave and the spine bowed to the right. In group 2 (n = 4), the right side of the thorax was concave and the spine bowed to the left. In group 3 (n = 5), the left side of the thorax was concave and the spine bowed to the right. In group 4 (n = 8), the left side of the thorax was concave and the spine bowed to the left. With computed tomographic data, finite-element models were produced to simulate each patient's thorax. Thereafter, dynamic response patterns of the spine to the Nuss procedure were examined. Validity of these biomechanical findings was verified by referring to clinical outcomes. Results: In group 1 and group 4 models, deformed spines were straightened; in group 2 and group 3 models, spinal bowing increased. These biomechanical findings were compatible with clinical evaluations. Conclusions: Performance of the Nuss procedure for asymmetric pectus excavatum exerts dynamic influence on the spine. Response patterns of the spine are predictable from morphologic relationships between the asymmetric patterns of the anterior thoracic wall and the spine.