Photoelastic analysis of the proximal femur in deviations of the mechanical axis of the lower limb

SARAH FAKHER FAKHOURI¹; Marcília Valéria Guimarães¹; Cleudmar Amaral Araújo¹; Marcos Massao Shimano²; Daniel Maranho³; José Batista Volpon³

¹ Universidade Federal de Uberândia; ² Universidade Federal do Triângulo Mineiro; ³ Universidade de São Paulo

doi:10.20906/CPS/COB-2015-0214

Resumo

Disorders of the anatomical and mechanical axis of the lower limbs are important because they influence the performance and efficiency of locomotion and, in years to come, may cause arthrosis in the hip, knee and ankle. Pathological deviations of the mechanical axis of the lower limbs deeply alter the stress distributions on the femur and tibia and the hip, knee, and ankle articulations. The purpose of this research was to assess the effects of pathological deviations in different levels of the lower limbs in the distribution of stress in the proximal femur region using photoelasticity of plane transmission. Geometric models of the femurs and tibias were obtained from frontal panoramic X-rays. The X-rays selected were those showing a normal axis and the following pathological deviations: coxa vara, femur varum, geno valgum due to deviation at the extremity of the femur, geno varum due to deviation at the proximal tibia extremity, varum ankle, valgum ankle and varus of the tibial diaphysis. Sixteen photoelastic models were made for all of the experimental groups, where eight were femurs and eight were tibias. The photoelastic analysis was performed on a transmission polariscope. In general, an 8N compressive force was applied to the top of the femoral head through a semi-dome acrylic mould, which represented the acetabulum. The acetabulum mould was positioned in an anatomical manner above the femoral head. The shear stress was calculated in a standardised form, with points localised at 5.0-mm increments over the entire length of the photoelastic model. For most of the types of deviations studied, the results showed that the internal stress was generally higher in the calcar region than in the trochanteric region, followed by the third distal of the femur head. This study allowed for the development of better criteria for the correction of angular deviations and helped identify the deviations that are most harmful to the mechanical axis in terms of the effects on the bone and the articular effort of the lower limbs

Palavras-chave: Alignment; Deviations; Inferior Limbs; Mechanical Axis; Photoelasticity; Stress