Comprehensive Testing Strategies for Anatomical and Mechanical Characterization of Layered Tissue Structures of Musculoskeletal Extremities

Ahmet Erdemir, PhD, Tammy M. Owings, DEng, Tyler Schimmoeller, BS, Erica Neumann, MS, Tara Nagle, MS, Robb Colbrunn, DEng

Cleveland Clinic, Cleveland, OH

Background. Musculoskeletal extremities of the human body are protected by layers of skin, fat, and muscle tissue. Simulation of the mechanical response of this layered-tissue structure has important implications in healthcare, ranging from an understanding of protective capacity to evaluation of haptic response. In regard to the latter, anatomical and mechanical properties of these tissue layers dictate the aggregate response on the extremity surface, which is necessary to reproduce in surgical simulations. In military, extremities are major sites of combat related injury and preparation of surgeons to accommodate the large variety of tissue response will likely require high fidelity simulations supported with comprehensive data. Such data, however, are scarce.

Objectives. The goal of this document is to summarize our experimental studies that have been aimed to acquire anatomical and mechanical data from multi-layer tissue structures of lower and upper extremities. In vivo and in vitro testing strategies are described where comprehensive data sets capture the variety of the general population and the detail of individual subjects and specimens.

Methods. In vivo testing utilizes an instrumented ultrasound for measurement of skin, fat, and muscle thickness in the upper and lower legs and arms at 48 regions (right side; 4 circumferential x 3 longitudinal x 4 segments). At eight locations (right side; central regions of upper and lower legs and arms, anteriorly and posteriorly) indentation response is characterized by using the ultrasound probe as an indenter and measuring probe forces along with tissue thickness changes. Demographics and anthropometric data (3 circumferences and 1 length for each segment) on study participants are also acquired. In vitro testing repeats the procedures of in vivo study, this time on cadaver legs and arms. In addition, computed tomography and magnetic resonance imaging of specimens provide detailed anatomy of the extremities. An added benefit of in vitro experimentation is the possibility to extract tissue samples (skin, fat, and muscle) from central regions of the specimens and conduct tissue mechanical testing for specimen-specific identification of tissue mechanical properties. In follow-up in vitro testing, surgical acts are performed on central regions of upper legs to characterize surgical tool forces during probing, cutting and dissection using instrumented scalpel, retractor, and forceps. Three-dimensional strains on the surface of the skin are also measured during a subset of these trials. All the procedures were approved by the Cleveland Clinic IRB and the Human Research Protection Office of the U.S. Army.

Results. In vivo testing was performed on 100 subjects (50 males and 50 females) and data were publicly disseminated. In vitro characterization using instrumented ultrasound has been completed for a total of 16 segments (legs and arms procured from 8 donors). In vitro testing for tissue mechanical characterization and for quantification of surgical tool forces are at final stages of preparation. The operating procedures have been fine tuned and mock testing is being performed to streamline experimentation.

Discussion. Comprehensive testing by leveraging in vivo and in vitro approaches provides foundational data on anatomy and mechanics of layered tissue structures in order to build high fidelity computational models. Given the diversity of the information to represent general population and its detail to assure subject-/specimen-specificity, it will be possible to capture realism in virtual reality systems for research and clinical training.

Acknowledgments. Contributions by Andrew K. Cho, John E. Jelovsek, Joy P. Ku, Mark Lobosky, Benjamin Landis, Mike Wong to experiment design, instrumentation, and dissemination are appreciated. This study has been supported by USAMRMC (W81XWH-15-1-0232). The views, opinions and/or findings contained in this document are those of the authors and do not necessarily reflect the views of the funding agency. Ultrasound imaging system and probes were loaned by Siemens Medical Solutions USA, Inc. See project site for more information; https://simtk.org/projects/multis.

2017-01-16T17:56:02.279145585