Mechanics of Hip Dysplasia Reduction in Infants With the Pavlik Harness Using Patient-Specific Geometry

Abstract

A physics-based computational model of neonatal Developmental Dysplasia of the Hip (DDH) following treatment with the Pavlik Harness was developed to obtain muscle force contribution in order to elucidate biomechanical factors influencing the reduction of dislocated hips. Clinical observation indicates that reduction occurs in deep sleep and involves passive muscle action. Consequently, a set of five (5) adductor muscles, namely, the Adductor Brevis, Adductor Longus, Adductor Magnus, Pectineus, and Gracilis were identified as mediators of reduction using the Pavlik Harness. A Fung-type model was used to characterize the hyperelastic stress-strain muscle response. Four grades (1–4) of dislocation as specified by the International Hip Dysplasia Institute (IHDI) were considered. A three-dimensional model of the pelvis-femur-lower limb assembly of a representative 10 week-old female was generated based on CT scans of a 6-month and 14-year old female as well as the visible human project with the aid of anthropomorphic scaling of anatomical landmarks. The muscle model was calibrated to achieve equilibrium at 90° flexion and 80° abduction. The hip was computationally dislocated according to the grade under investigation, the femur was restrained to move in an envelope consistent with Pavlik Harness restraints, and the dynamic response under passive muscle action and under the effect of gravity was resolved using the ADAMS solver in Solidworks. Results of the current model with an anteversion angle of 50° show successful reduction IHDI Grades 1–3, while IHDI Grade 4 failed to reduce with the Pavlik Harness. These results are consistent with a previous study based on a simplified anatomically-consistent synthetic model and clinical reports of very low success of the Pavlik Harness for Grade 4. However, our model indicates that it is possible to achieve reduction of Grade 4 dislocation by hyperflexion. This finding is consistent with clinical procedures that utilize hyperflexion to help achieve reduction for patients with severe levels of DDH for whom the Pavlik Harness fails.

Developmental dysplasia of the hip: A computational biomechanical model of the path of least energy for closed reduction

“…Details of the computation model are in previous publications. [13][14][15][16][17] A collision detection algorithm was used to determine the location of the femoral head center coordinates while the femoral head is in contact with the pelvic surface as it travels from an original start point (computational dislocation) towards the center of the acetabulum. Femur orientation angles (flexion, abduction, and hip rotation angles) were independently varied for each femoral head location.…”

“…pathogenpathogenSeveral constraints were considered. First, the femoral head was modeled as spherical 14,17 and always in contact with the pelvic surface at a distance "d," which is the femoral head radius ¼ 7 mm. The distance formula was used to compute the coordinates (x,y,z) of the femoral head center.…”

A comprehensive review on Kenaf seeds and leaves for medicine

“…Flour of kenaf seeds has been utilized in industry of food for making cakes, bread, noodles and other meals (Zwawi et al, 2014) [77] . Whitten leaves of kenaf are eaten within ten days of seeding, due to their high protein approximately 34%, and are tasty.…”