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Biomechanics - Advanced 3D Technology Laboratory


Current Biomechanics Projects

The Development of VKASS: A Virtual Knee Anatomy and Surgery System

Principal Investigator: Jim Chen
Co-investigators: Jihui Li, Mark Theiss, Craig Cheifetz
Funded by: Inova-GMU Research Grant

Virtual surgery simulators have been widely accepted in resident training of arthroscopic, laparoscopic, and endoscopic surgeries. Research has indicated that these simulators can significantly improve resident skills, reduce the related training cost and improve the quality of healthcare. Currently no full-function surgery simulator is available for orthopedic resident training, although there are more than 100 orthopedic teaching programs around the nation. This simulator may help orthopedic surgeons to improve healthcare by conducting a well-prepared surgical plan in complex cases. In this study, we will develop a virtual knee anatomy and surgery system (VKASS) as a prototype of an orthopedic surgery simulator.

VKASS is composed of the following components:

  1. Three-dimensional (3D) anatomic atlas of human leg for resident training
  2. 3D patient specific anatomic leg model for surgeon’s pre-op planning
  3. Virtual reality and surgery devices
  4. Virtual reality and surgery simulation programs
  5. Surgical skills evaluation tool

Using VKASS, orthopedic residents can learn and practice knee surgeries on virtual knee models that include bones, muscles, tendons, blood vessels, nerves, and fat through force-feedback haptic devices and stereoscopic display. The virtual surgery process can be repeated and modified to achieve the best training outcome. The surgery process can also be evaluated by identifying and tallying the activities and mistakes residents made and providing professional advice and guidance. Orthopedic surgeons can use VKASS as well to plan complex orthopedic cases pre-operatively. VKASS is able to construct a patient specific knee model from the patient’s MRI/CT, and surgeons can use the same platform orthopedic residents used to perform the virtual knee surgery and determine the best procedure and implants for the patient.

Biomechanical Comparison of Two Fixation Techniques in Unstable Intertrochanteric Hip Fractures: Intramedullary Hip Screw vs. Proximal Femoral Locking Plate

Principal Investigator: Jihui Li
Co-investigators: Alireza Malekzadeh, Cary Schwartzbach, Jeff Schulman, Mark Theiss 
Funded by: Synthes Inc.

Unstable intertrochanteric (IT) hip fractures, a common and ever-growing injury in the elderly population, contribute to high health care costs. For these fractures, traditional sliding hip screws have been unsatisfactory in offering stability as intramedullary hip screws (IMHS) have continued to gain favor. Recently, a proximal femoral locking plate (PFLP) was developed for pertrochanteric femoral fractures, but no biomechanical study is available comparing its effectiveness to the IMHS throughout the entire fatigue process.

In this study, a new research scheme combining acoustic emission, motion analysis, and traditional biomechanical methods will be developed to compare the dynamic changes in biomechanical properties of IMHS versus PFLP for unstable IT hip fractures. This will significantly improve our understanding of the mechanism of failure of these fixation methods, help define better usage of each implant, reduce health care costs, and improve the medical care being offered to Virginians treated for unstable IT hip fractures.

Combined Internal and Small Monolateral External Fixation Lapidus Arthrodesis: Finite Element Analysis and Biomechanical Study

Principal Investigator: David Pontell
Co-investigators: Jihui Li
Funded by: Inova Health System & Biomet Inc.

Fusion of the first metatarsal-cuneiform joint (1st MTCJ) is indicated in the treatment of symptomatic, moderate-severe hallux valgus (great toe deformity/rotation with either osteoarthritis or instability of this joint complex). The utility of this procedure to correct high intermetatarsal angles with or without dorsal instability (hypermobility) is well-appreciated. Like other “basal” procedures, however, the extended period of non-weight bearing is a risk factor for potentially-serious complications such as deep vein thrombosis and pulmonary embolus, and compliance is difficult to maintain. These may deter patients and their surgeons from pursuing this valued surgical approach.

Some providers have begun to advocate small, monolateral external fixation (percutaneous half-pins with external, rigid rails) as a useful adjunct to internal fixation (conventional cancellous bone screws) which may allow safe, early weight-bearing while joint fusion proceeds. However, no peer-reviewed studies have been published to support the efficacious or safe use of this approach. In this study, we will develop finite element analysis (FEA) models of foot-ankle complex with the MTCJ cured by either combined internal and small, monolateral external fixation or internal fixation. The models will be validated by biomechanical testing on cadaveric foot-ankle specimens. FEA is also used to compare the stability of MTCJ fixed by the two methods. A series of biomechanical testing on the cadaveric MTCJ will be performed to evaluate the two methods. Paired t-test will be used to check the significance of the two methods regarding to MTCJ stiffness and strength.

A New Alignment Approach for Total Knee Replacement Surgery

Principal Investigator: Jihui Li
Co-investigators: Edward MacMahon, Mark Theiss 
Funded by: private

The knee arthritis is a major health problem affecting millions of people. Total knee replacement (TKR) surgery has been proved as a successful treatment for knee arthritis. However, compression induced wear on the polyethylene tray have been reported as a major cause of implant failure. Clinical and research evidences showed that the current dominant alignment method, a straight line alignment concept, may be the reason of the unevenly compression distribution between medial and lateral condyles. In this study we investigate four variables that may influence the compression distribution of the replaced knee joint. We plan to set up a new alignment approach based on the relationship among the variables. We hope the new approach can help physicians to better align the implants during TKR surgery.

Acoustic Emissions Testing for Occult Pediatric Fractures and Stress Fractures

Principal Investigator: Kathleen McHale
Co-investigators: Jihui Li, Mark Theiss, Samuel Hawken
Funded by: Inova Health System

Some fractures do not routinely show up on initial X-rays. These common fractures are

  1. Toddlers’ fractures, i.e. occult fractures of the tibia in walking age children
  2. Salter-Harris fractures, i.e. fractures through the physis particularly at the ankle and the wrist
  3. Stress fractures in older children and adults from cyclical loading

Stress fractures of the tibia and of the metatarsals in adults often have normal initial X-rays. Often, X-rays are negative until signs of healing (toddlers’ or S-H fractures) or progression (stress fractures) take place. Diagnostic tools such as bone scans, CT scans, and MRI can be costly, time consuming, and require sedation (MRI). Non-invasive, inexpensive tools have been developed for occult, partial structural failure, i.e. ultrasound and acoustic emissions. Ultrasound (US) is an active acoustic inspection technique in which the sound wave is directed at an area of interest; if it intersects a crack or other discontinuity, a reflected wave is returned. It is performed on an unloaded structure. It has been shown to be good for large diaphyseal long bone fractures in children but is less dependable for juxta-articular and Salter-Harris fractures, lesions of the small bones of the hands and feet, fracture lines less than one millimeter, and for stress fractures. Acoustic emission (AE) is a method of inspection in which a generation of transient elastic waves is produced by a sudden redistribution of stress in a material. When a structure is subjected to an external stimulus, e.g. change in pressure, localized sources trigger the release of energy in the form of stress waves, which propagate to the surface and are recorded by sensors. AE technique enables the nondestructively detection and monitoring loading-induced “microcracks” in real time. The proposed research will investigate the use of AE in the detection and monitoring of occult fractures in children that are not difficult to diagnose by initial plain X-ray. The goal of this research is to develop AE as a diagnostic tool that can be used in the office setting to confirm the presence of a subtle fracture in the pediatric population. Additional benefit will be the minimization of radiation exposure, cost, and time to diagnosis.

Patient Specific 3-D Medical Modeling Can Improve Preoperative Surgical Planning of Complex Spinal Orthopedic Cases

Principal Investigator: Faisal Siddiqui
Co-investigators: Jihui Li, Ali Moshirfar, Joseph White, Ronald Childs
Funded by: Inova Health System

Complex spinal orthopedic cases such as thoracolumbar burst fractures and spinal vertebral body tumors have severe musculoskeletal damages, low satisfactory rate and high healthcare costs. Surgical planning is critical for these surgeries to ensure accurate patient evaluation and proper surgical design. However, the traditional surgical planning (TSP) method that relies on 2D medical images is unable to accurately reveal the anatomic geometry of the complex musculoskeletal damages. As a result, surgical planning is problematic and the clinical outcome is poor.

The objective of this study is to develop a new surgical planning (NSP) method that can help physicians to set up a solid surgical plan for complex spinal orthopedic cases, focusing on thoracolumbar burst fractures and spinal vertebral body tumors. We will propose a sophisticated method that can generate patient-specific 3D medical models of musculoskeletal system based on CT and/or MRI. Physicians can design the surgery and practice it on the models and determine the right surgical approach and implants. Physicians can even bring the models to the operation room as a reference.

To evaluate the efficiency of NSP, both TSP and NSP methods are used in complex spinal thoracolumbar burst fractures and spinal vertebral body tumors. Surgical results in terms of surgical time, estimated blood loss, intraoperative nerve injuries as diagnosed by EMG findings, and the extent of use of spinal implantation devices such as pedicle screws will be collected and analyzed. We anticipate the patient-specific 3D medical models created by the NSP method will help surgeons better understand patient conditions and make the best decision. This new surgical planning method has a great potential to improve the clinical outcomes of complex cases in not only orthopedics, but also other specialties such as heart and vascular, pediatrics, cancer, transplant and others.

Using Acoustic Emission Technique to Diagnose Spinal Osteoporosis and Estimate the Risk of Spinal Compression Fractures

Principal Investigator: Thomas Mazahery 
Co-investigators: Ronald Childs, Mark Theiss, Jihui Li

Osteoporosis is a major health problem and affects millions of people. It can cause spinal compression fractures (SCF) that influence about 40% of women during their life time. However, current diagnostic tool, bone mineral density (BMD), was proved not reliable. As a result, many patients have been treated improperly, either misidentified or incorrectly dosed. In this study we propose an Acoustic Emission (AE) technique to diagnose the spinal osteoporosis and estimate the risk of SCF. To validate this technique, we will simulate flexion/extension on spines of both cadavers and real patients, and monitor the AE microcracks during the tests. Through comparing the properties (number, energy, amplitude and waveform) of the AE microcracks from the two tests and correlating them with micro damages occurred in the vertebrae, we can assess the performance of the AE technique as a tool when diagnosing the spinal osteoporosis and estimating the risk of SCF. The AE technique, if validated, may significantly increase the accuracy of the diagnosis and treatment of millions of patients suffering from spinal osteoporosis and SCF. Improvement in healthcare and cost reduction can be expected.

Completed Biomechanics Projects

Effect of Bone Quality on the Failure of Locked Plate Fixation of Proximal Humerus

Principal Investigator: Jihui Li 
Co-investigators: Robert Hymes, Jeff Schulman, Mark Theiss
Funded by: Inova Faculty Research Grant and Smith & Nephew Inc.

The goal of this study is to understand how bone quality affects the failure of locked plate fixation of humeral fractures. We will develop a sophisticated research tool that combines biomechanical testing, AE technique, computer simulation (finite element analysis) and microscopic observation to test the following hypotheses:

  1. Patients’ average BMD will correlate to the pullout strength of the locked plate fixation. It will also correlate to the stiffness of compression, bending, and torsion, and the screw removal torques.
  2. Cumulative AE microcracks will correlate to the local BMD of each bone-screw interface.
  3. The finite element models of the humeral locked plate fixations developed by standardized procedures will have a 15% or less error in mechanical stiffness compared to that in biomechanical testing.

This research will provide insight into the failure mechanism of locked plate fixation of humeral fractures by quantifying the damages at each bone-screw interface and indicating the weakest point. The improved understanding of the failure mechanism will help physicians to better define the use of the locked plate system, and will help implant manufacturers to optimize their designs. This study will also create computer simulation procedures that could provide better services to Inova patients.

Mechanical Comparison of Different Types of Fixation of Ludloff Metatarsal Osteotomies: A Biomechanical Study

Principal Investigator: Steve Neufeld 
Co-investigators: Jihui Li 
Funded by: Merete Inc. and Synthes Inc.

Hallux Valgus deformities are one of the most common deformities that require surgical correction. Ludloff osteotomy followed with fixation using two screws has been the golden standard of this disease. However, we have experienced cases of failure in non-compliant patients who put early weight on their Ludloff osteotomy, indicating the screws may not provide enough mechanical stability. Recently we developed a locking plate system aimed to improve the mechanical stability of the fixation and realize early weight bearing of the patients taking Ludloof osteotomy. The purpose of this study therefore is to compare the biomechanical properties of Ludloff osteotomies fixed with traditional compression screws and that with a locking plate. The hypothesis is that the locking plate method may provide stronger mechanical stability in a Ludloff osteotomy fixation compared to the compression screws method.

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