A BIOMECHANICAL STUDY OF THE PELVIS WITH AND WITHOUT FRACTURES AND IMPLANTS: COMBINING COMPUTATIONAL DESIGN AND EXPERIMENTAL TESTING FOR TYPICAL DAILY MOVEMENTS

Doctoral thesis (2023)

This study fulfills the need for a dedicated pelvis testing setup that is widely accepted with physiological relevance. There is limited comparative biomechanical data available for the Supraacetabular ... [more ▼]

This study fulfills the need for a dedicated pelvis testing setup that is widely accepted with physiological relevance. There is limited comparative biomechanical data available for the Supraacetabular External Fixator (SEF) and the Subcutaneous Iliopubic Plate (SIP) used in the treatment of anterior fragility fractures of the pelvis (FFP). Most experimental studies so far have relied on simplified loading and boundary conditions. There has been a growing interest in personalizing motion analysis to develop customized implants that can optimize implant performance and accelerate fractured bone recovery for individual patients. Therefore, the main objective of this study is to develop a biomechanical test bench that can emulate the physiological gait loading of the pelvis, experimentally evaluate the stabilizing effect of the SEF and the SIP in the treatment of FFP, expand the test stand's capability to emulate other common daily movements, investigate the impact of customized musculoskeletal (MS) models, and assess the potential benefits of using personalized 3D metallic printed subcutaneous plates for the treatment of FFP type Ia fractures. The study uses the Computational Experiment Design procedure to design a biomechanical test stand that realistically emulates the pelvis' physiological gait loading. The test stand is designed to iteratively reduce all muscles and joints' contact forces of the pelvis to only four force actuators while still producing a similar stress distribution in the pelvis. The study conducts repeatability and reproducibility tests to ensure the test stand's capabilities. Next, the FFP type Ia is created on a synthetic pelvis for biomechanical testing under gait loading. The osteotomy on the right pelvic ring is then stabilized with the SEF or the nonlocking/locking SIP, and the stability provided by both implants is assessed numerically and experimentally under physiological loading. Motion analysis is conducted to calculate joint and muscle force envelopes for the common daily movement of interest. Stress, strain and displacement of the pelvis under these loads are assessed numerically and then implemented in the biomechanical test stand to emulate each movement following the computational experiment design concept. A metallic 3D-printed SIP is developed to match the anatomical landmarks of the insertion points on the pelvis used in the experiments. This 3D printed plate is assessed numerically and experimentally under physiological load to evaluate its performance compared to conventional plates. Personalization of the MS model is conducted for the pelvis by matching the anatomical landmarks of the pelvis in the generic MS model and the model of the pelvis used in the actual experiments. The developed test stand and the concept of computational experiment design behind it provide guidelines on how to design biomechanical testing equipment with physiological relevance. The boundary conditions and the nature of loading adopted in this study are more realistic regarding physiological relevance compared to the state-of-the-art. The numerically developed biomechanical testing setup of the pelvis in this study is a significant step forward in developing a physiologically relevant pelvis testing setup. [less ▲]

Developing a Biomechanical Testing Setup of the Pelvis, Part I - Computational Design of Experiments

in Journal of Biomechanical Engineering (2023)

Biomechanics of the human pelvis and the associated implants are still a medical and engineering debated topic. Today, no biomechanical testing setup is dedicated to pelvis testing and associated ... [more ▼]

Biomechanics of the human pelvis and the associated implants are still a medical and engineering debated topic. Today, no biomechanical testing setup is dedicated to pelvis testing and associated reconstructive implants with accepted clinical relevance. This paper uses the Computational Experiment Design procedure to numerically design a biomechanical test stand that emulates the pelvis physiological gait loading. The numerically designed test stand reduces the 57 muscles and joints' contact forces iteratively to only four force actuators. Two hip joints' contact forces and two equivalent muscle forces with a maximum magnitude of 2.3 KN are applied in a bilateral reciprocating action. The stress distribution of the numerical model of the developed test stand is very similar to that of the numerical model of the pelvis with all 57 muscles and joint forces. For instance, at the right arcuate line, the state of stress is identical. However, at the location of superior rami, there is a deviation ranging from 2% to 20% between the two models. The boundary conditions and the nature of loading adopted in this study are more realistic regarding the clinical relevance than state-of-the-art. The numerically developed biomechanical testing setup of the pelvis in this numerical study (part I - Computational Design of Experiments) was found to be valid for the experimental testing of the pelvis. The construct of the testing setup and the experimental testing of an intact pelvis under gait loading is discussed in detail in part II - Experimental Testing. [less ▲]

AUSLEGUNG eines BIOMECHANISCHEN TESTSTANDES für das BECKEN einschließlich der MUSKELKRÄFTE des GANGZYKLUS

Scientific Conference (2022, October 28)

Biomechanische Untersuchung zu verschiedenen Verfahren der Stabilisierung von Insuffizienzfrakturen des vorderen Beckenringes

Poster (2022, October 26)

INVESTIGATING THE INFLUENCE OF PERSONALIZED MUSCULOSKELETAL MODELS ON THE CALCULATED STRESSES IN THE PELVIC RING

Poster (2021, September)

This study investigates the influence of personalizing musculoskeletal models (MS) on muscles, contact joints forces and on stresses in the pelvic ring bones during normal gait loading cycle. All ... [more ▼]

This study investigates the influence of personalizing musculoskeletal models (MS) on muscles, contact joints forces and on stresses in the pelvic ring bones during normal gait loading cycle. All calculated forces are utilized to predict stress states in pelvis bones using Finite Element (FE) software. Customized MS models provides more precise muscle and contact forces. Additionally, it enables more automatic coupling between MS and FE environments by data transfer. [less ▲]

Numerical Assessment of two Implants for Pubic Ramus Fracture of human Pelvis applying Normal Gait loading

Poster (2020, October)

Fractures of the anterior pelvic ring reduce patients` mobility and independence and increase mortality. Pelvic instability impairs the load transfer to the lower extremity. Restoring stability has ... [more ▼]

Fractures of the anterior pelvic ring reduce patients` mobility and independence and increase mortality. Pelvic instability impairs the load transfer to the lower extremity. Restoring stability has therefore been a crucial point of research. Most of the reported studies refer to loading on one leg stand without consideration of physiological muscle and contact-joint forces of the common vital daily movements. Our present study considers physiological gait loading of all acting muscles and Hip Joint Contact (HJC) forces of the pelvis. Those muscles and HJC forces were calculated by inverse dynamics for normal gait motion data and applied in Finite Element Analyses (FEA). The biomechanical stability provided to the anterior pelvic ring by two reconstructive techniques was investigated numerically: the iliopubic Subcutaneous Plate (SP) and the Supra-Acetabular External Fixator (SAFE). Numerical biomechanical assessment of two reconstructive devices for pubic ramus fracture. All muscles and HJC forces of normal gait were calculated by means of inverse dynamics software for a healthy patient considering a musculoskeletal model previously validated experimentally. The Finite Element (FE) model was developed for a pelvis with and without superior and/or inferior rami fractures. Furthermore, two FE models for SP and SAFE mounted on the rami fractured pelvis were designed considering fixation bearing at the lumbosacral joint. The calculated forces were implemented on the FE models following the anatomical orientation and attachments/insertions of each muscle. During the two moments of the gait with higher stresses: Left Heel Strike (LHS) and Right Toe-Off (RTO), strains and displacements were recorded and investigated at the fracture location in addition to the implant fixation points. Considering only right superior ramus fracture during LHS and RTO, recorded strains and displacements for both implants showed similar results. However, during RTO, the SAFE showed a slight reduction of strains at the posterior location by 6% compared to SP. When including both superior and inferior right ramus fractures, both devices did not show considerable difference in recorded strains. However, there were significant differences in the displacements between fracture extremities. The SP technique reduced these motions for both LHS and RTO by 40% compared to the gold standard SAFE technique. In cases of superior ramus fracture only, displacements for both reconstructive devices were similar due to the remaining stability provided by the intact inferior ramus. Both devices reduced stresses of the sacrum wing in LHS and RTO with slightly better results for SAFE. In case of superior and inferior pubic ramus fractures, the SP technique reduced the frontal opening of the fractured right pubic bone. The SAFE did not provide any improvements compared to the SP technique. [less ▲]