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Saturday, Nov 28, 2009 - Room 1 (3F Conference room 301)

Keynote 1
Professor Guoan Li, Orthopedic Surgery/Bioengineering, Harvard Medical School, Boston, MA, USA
Professor Guoan Li obtained his PhD in Mechanical Engineering in 1993 from the Johns Hopkins University, Baltimore, USA. After working at The Johns Hopkins Medical School and University of Pittsburgh Medical Center, he is a Professor at the Orthopedic Surgery/Bioengineering in Harvard Medical School from 2008. He has been carrying out orthopaedic biomechanics studies on the musculoskeletal system.

Dual Fluoroscopic Analysis of the Function, Dysfunction, and Treatment of Joints in the Human Body

Guoan LI / Department of Orthopaedic Surgery / Harvard Medical School
Samuel K. Van de VELDE / Department of Orthopaedic Surgery / Harvard Medical School
Thomas J. GILL / Department of Orthopaedic Surgery / Harvard Medical School
Harry E. RUBASH / Department of Orthopaedic Surgery / Harvard Medical School

Current orthopaedic practice is to a large extent based on the widely accepted assumption that abnormal joint kinematics, with consequent abnormal loading within the joint, initiate detrimental processes such as posttraumatic osteoarthritis and polyethylene component failure. The biomechanics of the various musculoskeletal articulations are therefore studied so that treatment protocols could be developed that create optimal joint environments. However, the measurement of the in-vivo function, dysfunction, and treatment of joints in the human body with an acceptable accuracy and precision is technically challenging. This paper reviews our work of the past decade during which we developed a non-invasive imaging technique for the measurement of the human joint system under in-vivo loading conditions. The technique combines a dual fluoroscopic setup with magnetic resonance imaging, in which the fluoroscopic system captures the in-vivo joint motion whereas the magnetic resonance images record and recreate the anatomic structures of the joint. We further present the results from a series of papers demonstrating the feasibility of the technique to study: 1) the normal biomechanics of joints including the knee, ankle, shoulder, and spine, evolving from static to dynamic loading; 2) the extent of mechanical alterations in the joint following musculoskeletal pathologies such as cruciate ligament deficiency; and 3) the efficacy of current orthopaedic interventions to recreate optimal joint biomechanics. These results have created an in-vivo database of the normal, diseased, and surgically treated articular function, and have affected variables from graft tensioning, location of graft fixation, to total knee and shoulder arthroplasty component design. Furthermore, the mere need for access to a standard magnetic resonance scanner and a set of fluoroscopes has now placed the in-vivo analysis of the various musculoskeletal joints within reach of virtually every researcher or physician working in a routine clinical setting.

Keywords : Biomechanics, Orthopaedics

Sunday, Nov 29, 2009 - Room 1 (3F Conference room 301)

Keynote 2
Associate Professor Yoon Hyuk Kim, Department of Mechanical Engineering, Kyunghee University, Korea
Professor Yoon Hyuk Kim obtained his PhD in Mechanical Engineering in 2000 from the KAIST, Korea. From 2000 to 2002, he was a Post-Doc Research Fellow at the Johns Hopkins Orthopaedic Surgery Biomechanics Laboratory. He is an Associate Professor at the Department of Mechanical Engineering in Kyunghee University from 2004. He has been carrying out computational biomechanics studies on the musculoskeletal system.

Virtual Biomechanical Test of Cervical and Lumbar Artificial Discs Using Finite Element Analysis

Yoon Hyuk KIM/Department of Mechanical Engineering, Kyung Hee University/Korea
Kyungsoo KIM/Department of Mathematics, Kyonggi University/Korea

Even though spinal fusion has been used as one of the common surgical techniques to treat some spinal disorders such as degenerative disc or disc herniation in the spine, high stiffness in the fusion segment could generate clinical complications in the adjacent spinal segment. As an alternative treatment technique, the total disc replacement using artificial discs has recently been proposed to preserve motion at the surgical level in spine surgery. In this study, we investigated the biomechanical performance for two artificial discs for the cervical spine and three artificial discs for the lumbar spine using finite element analysis.
Three dimensional finite element models for C2-C7 and L1-S were developed based on CT images and previous anatomical literatures. The finite element models for two types of cervical artificial discs (semi-constrained and un-constrained), and three types of lumbar artificial discs (semi-constrained and metal on polyethylene core type, semi-constrained and metal on metal type, and un-constrained and metal on polyethylene core type) were developed. The cervical and lumbar artificial discs were inserted at C5-C6 and L4-L5 segments, respectively. Based on the conventional surgical techniques, some parts of ligaments and intervertebral disc at the surgical level were removed to insert artificial discs. In the case of cervical spine, bottom of C7 was constrained in all directions and 1.5 Nm of flexion and extension were applied on the superior plane of C2 with 50 N of compressive load along follower load direction. In the case of lumbar spine, bottom of sacrum was constrained in all directions and 5 Nm of flexion and extension moments were applied on the superior plate of L1 with 400 N of compressive load along follower load direction. In both flexion and extension, the artificial discs showed higher rotation ratio at the surgical level, but lower rotations at the adjacent levels than those in the intact model regardless of the cervical and lumbar artificial discs. There was no big difference of the intersegmental rotations among the artificial discs. In extension, the facet joint contact forces at the surgical level were 34 to 36 N in the cervical spine and 140 to 160 N in the lumbar spine whereas those in the intact model were 17 N and 60 N, respectively.
From the results of this study, we virtually investigated the biomechanical performance of two cervical and three lumbar artificial discs. The relative rotation at the surgical level would be increases at the early outcome after total disk replacement. Also all types of artificial disc model have higher risk of facet joint arthrosis. The results suggested that more careful care must be taken to choose surgical technique of total disc replacement surgery. Moreover, the evaluation technology can provide a useful tool for not only the decision of the surgical options in total disc replacement but also the development of new artificial discs.

Keywords : Artificial disc, Cervical spine, Lumbar spine, Finite element analysis, Biomechanics

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