Numerical analysis of gait load distribution in the human pelvis and design of a biomechanical testing device: experimental assessment of two implants for anterior fragility fractures

Doctoral thesis (2019)

The current project research was conducted at the University of Luxembourg in cooperation with orthopaedic surgeons from the Centre Hospitalier de Luxembourg and the Universitätsklinikum des Saarlandes ... [more ▼]

The current project research was conducted at the University of Luxembourg in cooperation with orthopaedic surgeons from the Centre Hospitalier de Luxembourg and the Universitätsklinikum des Saarlandes. The main objective was to investigate the gait load distribution in the human pelvis and the influence of the stiffness of the pubic symphysis and the sacroiliac joints on this force transmission in order to numerically and experimentally assess the stability provided by two reconstruction systems for anterior fragility fractures. To begin with, the global approach consisted in combining inverse dynamics and finite element methods to investigate physiological loadings applied to the pelvis during the gait cycle. Then, an experimental test bench was designed to reproduce those gait conditions on artificial pelvises for biomechanical assessment of different systems used for fragility fractures of the pelvis. At first, muscles forces and joint contact forces from the gait applied to the pelvis were calculated by inverse dynamics with an experimentally validated musculoskeletal model. Implementation in a finite element model including bones and joints of the pelvis highlighted that superior rami experience the highest stresses. Fracture of a superior ramus changed the initial load distribution by increasing the stresses at the inferior ramus and on the posterior structures. Combination of superior and inferior rami fractures on the same side redirected the forces backwards and showed high stresses on the sacral alae where compression fractures are commonly seen clinically. Reconstruction devices showed differences in stability at early stage of healing with benefits provided by the iliopubic subcutaneous plate. No noticeable differences compared to the Supra-Acetabular External Fixator were seen during later healing. Regarding the influence of the joint stiffness on the load distribution in a healthy pelvis, an increase of PS stiffness redirected loads to the anterior pelvis whereas an increase of PS laxity redirected loads to the posterior structures. A fusion of the sacroiliac joints did not show noticeable changes in the normal load distribution. Following the computational investigation, an experimental test bench was designed with numerical engineering tools. The biomechanical setup aimed at reproducing loadings observed during previously studied moments of the gait on artificial pelvises with fused joints. Static loadings and cyclic loadings were performed on artificial pelvises with and without reconstruction devices: first with a superior ramus fracture only and then with superior and inferior rami fractures. The Supra-Acetabular External Fixator and the iliopubic subcutaneous plate did not show any significant stability difference when a superior ramus fracture is considered. When including the inferior ramus fracture on the same side, the iliopubic subcutaneous plate significantly improved the stability of the reconstructed pelvis by reducing IV the displacement of the superior fracture, contrary to the Supra-Acetabular External Fixator that did not show any improvement. For both configurations, no fatigue phenomenon was observed during cyclic loadings simulating four days of walking for a patient (5 000 cycles). There is no conflict of interest related to this work. [less ▲]

Influence of pubic symphysis stiffness on pelvis stress distribution during single leg stance

Poster (2018, July 09)

Design, Repeatability, and Comparison to Literature Data of a New Noninvasive Device Called "Rotameter" to Measure Rotational Knee Laxity

in International Scholarly Research Notices Orthopedics (2015), Volume 2015, Article ID 439095

The present paper deals with the design, the repeatability, and the comparison to literature data of a new measuring device called “Rotameter” to characterize the rotational knee laxity or the tibia ... [more ▼]

The present paper deals with the design, the repeatability, and the comparison to literature data of a new measuring device called “Rotameter” to characterize the rotational knee laxity or the tibia-femoral rotation (TFR). The initial prototype P1 of the Rotameter is shortly introduced and then modified according to trials carried out on a prosthetic leg and on five healthy volunteers, leading therefore to an improved prototype P2. A comparison of results obtained from P1 and P2 with the same male subject shows the enhancements of P2. Intertester and intratester repeatability of this new device were shown and it was observed that rotational laxities of left and right knees are the same for a healthy subject. Moreover, a literature review showed that measurements with P2 presented lower TFR values than other noninvasive devices.The measured TFR versus torque characteristic was quite similar to other invasive devices, which are more difficult to use and harmful to the patient. Hence, our prototype P2 proved to be an easy-to-use and suitable device for quantifying rotational knee laxity. A forthcoming study will validate the Rotameter thanks to an approach based on computed tomography in order to evaluate its precision. [less ▲]