Biomechanics of leg deformity treatment

J. Culik (1), I. Marik (2), E.P. Cerny (3)

(1) Czech Technical University of Prague, Faculty of Biomechanical Engineering, Sitna, Kladno, Czech Republic;
(2) Ambulant Centre for Locomotor Defects, Prague, Czech Rep.;
(3) Ortotika s.r.o., Prague, Czech Republic

Abstract
At pre-school age, there is a possibility to treat severe varosity and/or valgosity of legs by orthoses. The three points force effect of the orthosis partially corrects the pathologic defect of the leg. If the orthosis is intermittently used for a long time the correction is permanent. Step by step correction of bone deformities are based on remodelling of growth epiphyses and bones that are caused by orthotic bending pre-stressing. According to Hüter-Volkmann’s law, the oblique loading regulates the growth of epiphyseal plates of long bone into the direction of the pressure result and the bone remodelling process is started: it means that the bone grows at the tensile part of growth epiphyses more quickly than at pressure one and gradually eliminates the varosity and/or valgosity defect. The knowledge of stress values for starting of the bone remodelling process is principal for clinical praxis. The values of pre-stressing cannot be increased by starting the remodelling process from the ethical point of view but it can be judged on its starting according to the success of the treatment. The aim of this article is to study the bone, ligament stress state and deformations of successful treatment. Method and calculation algorithm of stress state and deformation that are necessary for the starting of the remodelling process at the knee region were verified on a group of eight patients that were fitted by orthoses with bending pre-stressing. The space models of the knee, femur and tibia were composed with the help of X-ray, CT and MRI scan. The calculation algorithm was implemented on a PC and the program can be easily applied at clinical praxis.

Keywords: Varosity, Valgosity, Stress State, Ligament Forces, Biomechanics of Leg Deformities