Hip disorders such as cartilage degeneration or bone fractures are common pathologies which are often treated with prosthetic surgery. Andrea Calvo-Echenique from the University of Zaragoza, Spain investigated how to prolong the lifespan of hip prostheses, and assessed the best options by comparing different stems and bearing materials. Her goals were to reduce the wear in bearing surfaces, as well as reducing the loosening of the stem, which tends to be caused by a lack of mechanical load in the bone. She received a Mimics innovation Award for the best poster submission in 2015.
Studying the hip joint
Previous works studied the hip joint computationally from two different points of view: inverse dynamic and finite element (FE) analysis. In spite of the availability of reaction and muscle force data during the gait cycle, only quasi‐static analyses were made using FE. Therefore, Andrea and her team simulated a continuous gait cycle and validated it in a healthy hip joint by introducing reaction and muscle forces. This model was modified to introduce different hip prostheses, allowing for a comparison between geometries and bearing materials.
Andrea segmented a healthy hip joint with Materialise Mimics, distinguishing between cortical and cancellous bone and bone marrow based on pixel intensity. She extracted the geometry and then modified it to introduce the hip implant. The muscles, ligaments and articular cartilages were modeled in accordance with an anatomic atlas.
The research process
The team simulated a gait cycle by introducing reaction forces and principal muscle contributions. They analyzed tension and compression stresses in lateral and medial stem surfaces, and found a stress concentration peak in the replacement stem. Also the mechanical loads transmitted to the bone were measured. While the replacement stem did not transmit high loads, PROSIC one maintained a stress distribution that avoided bone resorption and stem loosening. Finally, the team compared contact pressure and shear stresses to different stems and bearing materials. The CVM showed the elevated pressures and shear stresses, and the hydrogel interface reduced the shear stresses because of its low friction coefficient.
Andrea validated a musculoskeletal FE model in a continuous gait cycle. She concluded that a long replacement stem may present a risk of fracture, and could also cause bone resorption and stem loosening. She also noticed that geometry could influence the surface wear as well as the bearing materials. The team concluded that it was good practice to reduce the friction coefficient in order to prolong prosthesis life.
About the author
Andrea Calvo-Echenique is a PhD student at the University of Zaragoza in Spain. She obtained a master’s degree in Biomedical Engineering in 2014. Throughout her master studies, she worked on the computational side of a project developing innovative solutions for hip replacement, based on a hybrid material system. Currently she is working with the Group of Biomaterials in the Aragón Institute of Engineering Research, and doing her thesis on the topic of lumbar spine biomechanics. Her research interest is focused on the intervertebral disc degeneration progress and tissue regeneration after lumbar surgery. Andrea won a Mimics Innovation Award in 2015 for her research on finite element simulations of human gait in healthy and operated hips.