Determination of the mechanical requirements for a progressive correction system of pectus excavatum in children

Pectus excavatum is the most frequent deformity of the thorax. Many surgical procedures have been used for correcting this chest wall deformity. The Nuss procedure is an instant full correction using a rigid stainless steel bar, but some patients experience acute pain. We propose a new progressive correction technique for the chest deformity using an elastic rod. This method requires the specification of mechanical properties correlated with thorax anthropometric characteristics. We determined the force-displacement correlation for anterior-posterior compression of the thorax for 40 normal male and female subjects between 4 and 16 years of age. The measurement data offer the following conclusions: displacements < 3.1-4 cm in pectus excavatum can be corrected with the Nuss method because the pain level is not acute. Younger children can tolerate an average displacement of 3.22 cm, while older children can tolerate only a shorter displacement, of 2.62 cm. The average required force in order to obtain a displacement of up to 4 cm varies with age between 10.28 kilgram-force (kgf) at a younger age to 13.61 kgf in older children. At a younger age one can achieve larger displacements with a smaller force, but the force required for the same correction grows linearly with age. Displacements > 4 cm must be corrected progressively. The correction of pectus excavatum should be achieved with a progressive correction system (PCs) that must take into account these mechanical parameters.