I am truly humbled to be the 2019 recipient of this medal and express my sincere thanks to the Lissner Medal Committee, my nominator, the references who wrote on my behalf, and ASME. Particularly poignant is that I am the first female recipient of the medal since its inception in 1977. The ASME Bioengineering Division has been most progressive in diversity and inclusivity—I was also the first female chair of the Bioengineering Division, from 2008–2009, and the first female conference chair of the division's Summer Bioengineering Conference in 2005 in Vail, CO.
The H. R. Lissner Medal
This medal was named after Professor Herbert Richard Lissner and was established in 1977 as a Bioengineering Division award before being upgraded to an ASME society level award in 1987. It recognizes the recipient for their outstanding career achievements in the field of bioengineering through research, method development, design, teaching, and/or service. Professor Lissner was a pioneer in the field of injury biomechanics. This began in the early 1930s with his receiving degrees in Mechanical Engineering from the University of Illinois at Urbana and then becoming faculty in the new engineering college at Wayne State University. He founded the Biomechanics Research Center there, which is the forerunner of today's Bioengineering Center .
Professor Lissner's interests in injury biomechanics began with a vexing problem of skull fractures and the ensuing brain injury . He collaborated with a neurosurgeon to investigate the relationship of skull fractures to the force/deformation associated with blunt trauma. He developed experimental methods for strain and intracranial pressure, found that the pattern of injuries correlated with areas of high tensile stresses, and, by coupling the theoretical foundations of engineering mechanics with high quality experimental methods, formulated a hypothesis that brain injury was caused by pressure waves. To experimentally record impacts on the cadaver skulls for his research, Professor Lissner ran his experiments into the wee hours of the morning because the oscilloscopes, borrowed from a local company, had to be returned in the morning to support the war effort. That is commitment! These experiments and that of colleagues, with the theoretical underpinnings, led to the Wayne State Tolerance Curve, which predicts the risk of head injury as a relationship between head acceleration and duration of the acceleration. This further impacted (pun intended!) safety standards, equipment, and techniques to minimize the risk of injury, and permitted a retrospective forensic assessment of these injuries.
The roll call of previous Lissner Medalists is a veritable who's who in modern Biomechanics. In naming just a few, many of these giants have been further recognized for their achievements by ASME with awards named in their honor: Professor Fung, recipient in 1978, and the ASME Y. C. Fung Early Career Award established in 1985 (we celebrated his 100th birthday at the 2019 SB3C as well as in La Jolla at UCSD in September 2019); Professor Skalak, recipient in 1985, and the Bioengineering Division's Best Journal of Biomechanical Engineering Paper Award; Professor Mow, recipient in 1987, and the ASME Van C. Mow Medal established in 2004; Professor Nerem, recipient in 1989, and the Robert M. Nerem Education and Mentorship Medal established in 2017; and Professor Woo, recipient in 1991, and the Savio L.-Y. Woo Translational Biomechanics Medal established in 2015. In my beginning years as a budding biomechanist as well as developing in the profession, I was fortunate to have opportunities to speak with and be inspired by so many of the Lissner medalists, all of whom I admire to this day.
The title of this Lissner presentation, “3D Computational Modeling of the Three Legged Stool,” was meant to capture in a humorous way the three pillars of academic life—teaching, scholarship, and service. It is an extremely rewarding while being an extremely challenging career. Each pillar receives a certain amount of load in terms of time and effort that leads to the stresses we experience (Fig. 1). It is rarely balanced and deformation occurs. But with proper preparation, materials, and support, faculty remain below their “yield strength,” even with “fatigue loading,” and our contributions to our field have impact.
My professional journey and three-legged stool was represented by the three sections of a pie chart (Fig. 2).
Under the scholarship “leg,” my foray into computational analyses began when I set out to implement the biphasic theory into finite element analysis (FEA) of articular cartilage behavior. I was a doctoral student in Bioengineering at the University of California at San Diego, under the mentorship of Professor Savio L.-Y. Woo. Only one other group was tackling this problem at the time, Professor Robert Spilker at Rensselaer Polytechnic Institute. Commercial codes were not available. We took a u–p (displacement–pressure) approach in implementing the constitutive, equilibrium, and continuity equations into the matrix equations of the finite element method . Several nonlinearities were incorporated. A few other highlights of this research avenue include using the u–p FEA to investigate the effects of load partitioning at the articular surface between the solid and fluid phases [3–5]. Dramatic changes in maintenance of fluid pressure with spatial position and time with an increased load partitioning to the fluid then reduced the stress in the solid matrix. This influences the repetitive loading the tissue experiences during activities of daily living.
As commercial codes became available, additional modeling complexities could be investigated. In one study, we examined how biomechanical behavior of a simulated repaired articular surface was influenced by different contact conditions and presence of a superficial tangential zone . Material nonlinearities of permeability, bilinear elasticity, and anisotropy were incorporated. Nonlinear contact conditions of two nonconforming surfaces were incorporated. These coupled to illustrate the differences in fluid flow and solid stress resulting from the contact conditions and improved behavior with a quality superficial tangential zone.
The decades of cartilage finite element modeling have seen an explosion of exploration on behavior. These have included multiple layers of complexity, starting with single phase (solid) in the late 1970s/early 1980s to biphasic, poroelastic, triphasic to viscoelastic, poroviscoelastic and fibril-reinforced biphasic, viscoelastic to more nonlinearities. It is a rich history with many conclusions that inform our understanding of the tissue's behavior on a joint surface.
My more recent computational work has been in modeling the 3D behavior of diarthrodial joints, which has been complemented by numerous experimental studies. These computational simulations have created models whereby function is dictated solely by the 3D contacts between articular surfaces, ligamentous restraints, muscle forces, and external perturbations. These models, validated through comparison with published cadaveric and in vivo studies, have been used to predict biomechanical function in healthy, diseased, and reconstructed states, particularly for parameters that cannot be measured in vivo or in vitro.
Model creation begins with a stacked set of computerized tomography (CT) or magnetic resonance imaging images from publicly available sources or custom in-house scans. Through image analysis software, the 3D anatomy of the bones is generated and imported into a computer aided design/simulation software as a bone “part.” Within this modeling environment, ligaments and joint capsule are simulated to connect the bones and muscle forces to designate their action on the bones. Segment weights and body weight are added as well as solid surfaces and loading mechanisms relevant to the particular joint or problem. This modeling approach has been used to investigate conditions on the foot/ankle and hand/wrist, as well as elbow, shoulder, and hip. The purpose is to create tools to investigate complex biomechanical behavior of diarthrodial joints and inform clinical decision-making.
Our foot/ankle modeling (Fig. 3) was used to examine the biomechanical consequences of syndesmotic injury and repair, ankle inversion with ligament tear, as well as arch stability affected by plantar structures [7,8]. Subsequently, more extensive effort was devoted to understand flatfoot deformity, sometimes referred to as adult acquired flatfoot deformity or posterior tibial tendon insufficiency, and its surgical corrective procedures . This is a condition evidenced by clinical exam and weight-bearing radiographs that demonstrate forefoot adduction, arch collapse, and hindfoot valgus. Those with symptomatic adult acquired flatfoot deformity suffer from significant pain and dysfunction of the affected foot, which is then alleviated by surgical intervention if nonsurgical treatments are ineffective. Patients present with varying degrees of deformity, documented by antero-posterior, medio-lateral, and hindfoot angles and distance measures, which has resulted in multiple osteotomy and realignment procedures designed to correct the deformity. We used our foot/ankle modeling approach to investigate the biomechanical outcomes of different surgical procedures. These models contained 20 bones, more than 30 contacting surfaces, more than 144 individual elements representing ligaments and joint capsular structures.
In our first examination of flatfoot deformity, we applied loadings to replicate the stance phase of gait with Achilles muscle loading on a healthy lower leg, a simulated flatfoot deformity leg, followed by individual and combination corrective procedures—medial calcaneal osteotomy (MCO), calcaneocuboid distraction arthrodesis (CCDA), and Evans osteotomy (Fig. 4). These computational results predicted the corrections to the angular measures, and potentially overcorrections, that would result in stance loading from the procedures.
Subsequently, we developed pre- and postoperative subject-specific models for patients planning to undergo an MCO [10–12]. An magnetic resonance imaging of each subject's lower leg was used for 3D anatomy capture and tissue assessment. Plane radiographs were taken as well as plantar pressure distribution measured. In addition to Achilles muscle loading, contributions from the flexor hallucis longus, the flexor digitorum longus, the peroneal brevis, and longus muscles were incorporated. The foot/ankle models showed very good to excellent prediction for angular and distance measures between model and patient, both before and after surgery. Patient and model data indicated an offloading of the medial arch postoperatively from the MCO. Some potential concerns predicted by the models were angles, soft tissue strains, and plantar contact loads that may deviate from “normal,” which could be predictors for lateral foot pain while the increased calcaneocuboid contact force may predispose to arthritis, all of which are consequences experienced by some patients.
For these same set of subjects, we asked the question “What if?.” Would combination procedures offer better biomechanical parameters than the MCO alone? To the three procedures originally described, a fourth osteotomy became popular clinically, the Z osteotomy (Fig. 4). From these simulations, it became apparent that each patient may have had better biomechanical (angle and distance) measures from combined procedures—the Evans Osteotomy with or without an MCO, the Z and MCO, or the Z alone . Increased joint contact and lateral plantar forces may still be an issue.
The most recent foot and ankle modeling predictions were in examining Lisfranc injuries, particularly in the first and second tarsometatarsal joints [14,15]. Standing radiographs are often taken when such an injury is suspected to examine joint diastasis (opening). Still, these are particularly challenging to definitively diagnose especially if only soft tissue damage is present. We investigated potential reasons why this might be by contemplating how the foot's placement on the floor and muscle activation might influence the magnitude of joint diastasis. We found that inverting the foot while standing, as if a patient were trying to offload the medial side of the foot, which is the side of the injury, would substantially decrease dorsal diastasis, making it more difficult to detect. The decreased diastasis was compounded even further if muscles were active. This suggests ways in which the diagnosis may be better visualized radiographically.
Our modeling approach was also applied to the hand/wrist. In a similar manner to the foot/ankle, the 3D bony anatomy was created from CT images, the multitude of passive soft tissue structures on both the volar and dorsal sides were implemented, and muscle loadings were simulated for the motions of flexion, extension, radial deviation, and ulnar deviation. The amount of rotation in the wrist under these muscle loadings was measured for four states: the normal, healthy wrist; a radioscapholunate (RSL) fused wrist (for relieving the pain of arthritis in these joints); an RSL fusion plus distal pole of the scaphoid excision (to restore some motion); and an RSL fusion plus distal pole of the scaphoid excision plus triquetral excision (to restore more motion) . The computational model predicted the drastic reduction in movement with the fusion and some motion restoration from distal pole excision but excessive movement present with triquetral excision and thus caution before proceeding with the dual excision. Subsequent studies investigated biomechanical behaviors under proximal row carpectomy and scapholunate dissociation/repair [17,18].
The last computational work discussed was the development of an automated system to provide 3D analysis of important hip measures for diagnosis and pre-operative planning purposes directly the CT scanned pelvis and hip [19–21]. The algorithms developed identify critical bony features—pubic tubercle, ASIS (anterior superior iliac spine), AIIS (anterior inferior iliac spine), and acetabular rim—from the pelvis. On the femur, the femoral head, neck, greater and lesser trochanters, and shaft were automatically identified. On both bones, two parameters then were measured—inclination and version, both of the femoral head and the acetabulum. These measures impact many surgical procedures including total hip arthroplasty, periacetabular osteotomy, and femoral acetabular impingement. With this algorithm development, many other relevant parameters can be deciphered.
My faculty journey began in 1991 when I joined Virginia Commonwealth University (VCU) in Richmond, VA. I was fortunate to have a joint appointment with Biomedical Engineering and Orthopedic Surgery, and directed the Orthopedic Research Laboratory. It was a wonderful time to be at VCU as there were many opportunities for professional development. Biomedical Engineering was a graduate program only originally, offering Master of Science degrees within the VCU School of Basic Health Sciences. The program developed a proposal to the State Council on Higher Education in Virginia to award the doctoral degree in Biomedical Engineering which began in 1993. I served as the BME graduate program director from 1993 to 1999. During this time, the School of Basic Health Sciences was merged into the School of Medicine so for a time, BME was a program in the medical school. In 1995, VCU created the School of Engineering and BME became the first department and faculty within this new school. The BME faculty worked to create a new undergraduate curriculum, which established the undergraduate BME degree in 1998. I served as the BME graduate program director again from 2013 to 2017, and associate chair of the department from 2013 to 2019. In addition to many roles for promotion and tenure within the department and college, I represented engineering on the VCU Conflicts of Interest Committee for more than two decades and served on the leadership team for the VCU Faculty Senate.
My joint appointment with the Department of Orthopedic Surgery permitted a direct connection to the clinical needs associated with the health of the musculoskeletal system. We embarked on a paradigm shift for educating our orthopedic residents in basic science research whereby each resident had their own project, which began with hypothesis generation, protocol development, execution of experiments, results and statistical analyses, drawing conclusions, and disseminating in conference presentations and peer archival journal formats. During my years at VCU, more than 125 orthopedic residents, fellows, and medical students performed basic science research in my laboratory. I also directed 32 capstone BME design projects with 62 undergraduate BME majors, 22 M.S. theses, and nine doctoral dissertations.
I was active in professional society work as well. The Bioengineering Division of ASME had many opportunities to serve the profession, which I formally began with the Solids Technical Committee and Bioengineering Division representative to the IMECE (International Mechanical Engineering Congress and Exposition). The division's Summer Bioengineering Conference (SBC) was a rapidly growing and exciting conference to attend as well as program. I was Information chair for the 2003 SBC and conference chair for the 2005 SBC in Vail, CO. I served the BED Executive Committee from 2005 to 2010 during which time I was also the first female chair of the division. ASME honored me with Fellow status in 2007. Additional professional society service came with the Orthopedic Research Society. I was on the Board of Directors from 2009 to 2013, serving as the Treasurer and Director of the Finance Committee. I currently am on the Ethics Committee.
I found another passion in society service, with ABET, the nonprofit organization that accredits college and university programs in applied and natural science, computing, engineering, and engineering technology. This organization is instrumental in ensuring that our educational programs meet rigorous standards, achieve specific metrics, and setup a cycle of continuous improvement. I became a Program Evaluator in 2013 on behalf of the Biomedical Engineering Society (BMES) and am currently a commissioner to the Engineering Accreditation Commission as a BMES representative.
The BMES website  notes that to prepare for a career in biomedical engineering, one must first become a good engineer and acquire a working understanding of the life sciences and BME terminology. Good communication skills are also important to provide vital links to other professionals. This is how I, and many of my colleagues, approach our teaching—using the hallmarks of what makes an engineer, applied to living systems. I enjoyed linking theoretical and computational analyses with experimental foundations to inform and predict. This is important for our field as there is a continued need for translating findings into clinical or societal deliverables.
Biomedical Engineering as a field enjoys more gender parity than almost any other engineering field . This is an exciting aspect of our profession as our society is realizing the importance of diversity—in education, industry, government. And we are committing resources to achieving diversity goals. Important in this regard however is inclusivity—we can have a diverse group of individuals on a task force or committee but if each individual does not strive to include all the others, the diversity achievement misses its mark. We need to be diverse in our inclusivity.
Mentors and Colleagues
One's professional journey cannot be achieved without the guidance, advice, and support of mentors and colleagues. My engineering mentors formally began with my senior capstone advisor, Professor J. Wallace Grant. I was an engineering science and mechanics (ESM) major at Virginia Tech in Blacksburg and embarked on examining total ankle arthroplasty. That set the stage for studying musculoskeletal biomechanics during my career! Under his influence, I opted to combine my passions for engineering and medicine by pursuing my master's degree in biomedical engineering from Tulane University in New Orleans. There, I was most fortunate to study under Professor Stephen Cowin who was a renowned theoretician and pioneer in bone adaptation and bone structure–properties relationships. It was under his tutelage that the love for cartilage biomechanics and biphasic theory blossomed.
My primary professional mentor is Professor Savio L.-Y. Woo (Fig. 5), my doctoral advisor in Bioengineering at the University of California at San Diego. There, I continued cartilage work, which expanded into experimental studies and developing finite element analysis of tissue behavior. Professor Woo pioneered many experimental treatments of soft tissue structures. He was superb in guiding my path during this graduate work and continues to provide support. He taught me many lessons in research, teaching, mentoring, and life in general. I was also most fortunate that Professor Y. C. Fung was on my doctoral committee—talk about a formidable presence when defending your dissertation!
Professor Woo also introduced me to the wonderful world of conference planning with the First World Congress of Biomechanics in La Jolla, along with Professors Fung, Richard Skalak, and Shu Chien. That experience has come to bear in many subsequent situations. An additional benefit of the congress planning was to meet Professors Louis Soslowsky and Gerard Ateshian who were doctoral students as well at the time. A nearly 30 year friendship thus began.
I am blessed to have the friendship of Professor Bruce Simon and his accomplished wife Pam. I first met Professor Simon at a summer biomechanics conference in the 1980s, and he has provided advice all the years since. I also have two particularly dear friends in our field, Professors Michele Grimm and Rita Patterson. Professor Grimm just finished her NSF program directorship and is now an endowed professor at Michigan State University. Earlier this summer, she received the Theo Pilkington Outstanding Educator Award from the American Society of Engineering Education. Professor Patterson was recipient of the Savio L.-Y. Woo Medal on Translational Biomechanics, which was celebrated at this year's SB3C. She is now Associate Dean for Research at the University of North Texas. For those of you who know us well, Rita and I are both horse enthusiasts. We began our riding adventures at the summer conference in the 1990s and have been doing so ever since. We also have a penchant for BEDRock, along with Professor Naomi Chesler.
The majority of my faculty career was with Biomedical Engineering and Orthopedic Surgery at VCU. The professional relationships established there made the journey most enjoyable. We celebrated substantive achievements in research and orthopedic residency training, with many faculty in the Department of Orthopedic Surgery, particularly Drs. John Cardea (departmental chair), Robert Adelaar (next departmental chair), Wilhelm Zuelzer, William Jiranek, Jonathan Isaacs, and Charles McDowell.
Finally, no academic research laboratory functions effectively without the collaboration of creative and dedicated students. Several doctoral students' achievements were highlighted including Dr. Nilay Mukherjee who was my first doctoral student and focused on extending our articular cartilage modeling work. He is Principal Engineer at Medtronic. Dr. Peter Liacouras began our 3D computational joint modeling work before joining Walter Reed Army Medical Center where he creates custom medical devices for injured military service members. Dr. Joseph Iaquinto solidified our foot/ankle modeling approach and continues foot/ankle research with the Seattle, VA. Dr. Meade Spratley established our multiple patient-specific models before joining the Injury Biomechanics group at the University of Virginia. And my current doctoral student, Nathan Veilleux, is in the finishing stages of his degree finalizing our hip analysis suite. I was also privileged to have amazing masters students, several of whom continued their doctorate with me. Special recognition was given to those whose work was prominently highlighted. John Owen continued our analysis of cartilage FEA and was lab engineer working with me and orthopedic residents. Justin Fisk was an expert with SolidWorks and began our elbow modeling. He is now a Product Development Engineer at DePuy Spine. Alex Smith's flatfoot research received an award at a past SB3C. He is a development engineer with Skeletal Dynamics in Florida. And Tyler Perez just recently defended his degree and presented his Lisfranc foot injury modeling. He moved to Boston to work with a consulting firm for their life sciences division. Ben Majors, Afsar Mir, and E. J. Tremols kept building on our wrist model. They are with medical device companies and the field of technology transfer. And Sean Higgins whose attention to detail and excellence was the foundation for our hip work. He is prominent with a Richmond consulting firm.
What else is next? For me it is coming full circle (Fig. 6).
Family, the Future, and the Final Analysis
One's life is complete only with family. My parents Nancy and Richard Wayne—my mother was a nurse and my father an analytical chemist. Their support and encouragement stirred me to pursue engineering when it was not common for girls to do so. Their regular conversations about medicine directed me to biomedical engineering. We were a family of four, with my older sister Karen (Fig. 7). Later years saw marriages and births, with my brother-in-law Steven Berzak, my niece Dr. Laura Hopkins and nephew, Bryan Berzak, their spouses and children.
Last but not least is my dearest and closest friend and confidante for 38 years, my husband Dr. Forrest E. Sloan (Fig. 8). We have two beautiful and talented daughters, Stephanie and Nancy, who are pursuing their passions in music and engineering, and now a son-in-law Andrew Barth who is a pilot with the Air Force. They have taught me more than they know—how to appreciate, how to balance, how to be humble, and how to love unconditionally.
As I think back on my professional career thus far, there are several guiding principles to share with our junior colleagues. First, become part of a research team, and lead a team, of multidisciplinary researchers that enable learning about different dimensions of the same problem, and thus solve larger problems. Become engaged with clinicians to understand the pressing issues and translate research findings into improved healthcare delivery. Second, take advantage of networking opportunities within your institution, at professional conferences, community groups. Get to know leaders, organizers, developers, and their professional paths and hear their advice. Participate in workshops, seminars, etc., that help you grow in leadership, teaching, or any aspect of your career that you would like to improve, from your university, company, professional society. Do not be afraid of constructive feedback and learn from it. Third, be passionate about all three pillars of academic life. Research is exciting (and frustrating too!), bringing many rewards and accolades; service opportunities abound. So, while we devote different levels of effort to each, we should also relish our time in the classroom. It is here that we have a large impact on dozens of students at one time. We have the opportunity to excite them about the topics, to help them see the relevance of the material to the field, to practice applying knowledge to unseen problems, and to bring research discoveries into context. While this principle may seem relevant only to academicians, there are many opportunities for those in other sectors to engage students. The fourth is aligned with the third. I adopted a “puzzle” analogy when contemplating our responsibility to students, and by extension, their families and society. This evolved from a gift I gave my daughter years ago—her picture on puzzle pieces, which required assembling for her face to come into view. Students arrive in college as an amorphous shape, full of colors from their life thus far. The curriculum we assemble and how we teach, along with other college experiences, are all pieces of the puzzle, required to bring the new engineer into clearer view. One that could go on to designing the next medical device we, or one of our family members, might need. We are responsible for providing the training to make them competent at the end of their curricular path. Fifth, embolden students to take charge of their learning. While the curriculum and other experiences bring the new engineer into view, the picture is still somewhat fuzzy. The students need to be the masters of their learning, as they will have great responsibilities going forward. And finally, strive for balance in your professional and personal life. Make time for family, friends, and self as a regular habit and grow these relationships. Exercise. Read books. Contribute to your community.
In closing, I leave you with a few thoughts, which are recapped from a poem attributed, at least in part, to Mother Teresa and her Missionaries of Charity in Calcutta, India, “In the Final Analysis.” My sincerest appreciation and heartfelt thanks for this tremendous honor!