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 Chapter
1 . Basic and special concepts of biomechanics
Dr. Croft begins with a discussion of the properties of discs, ligaments, muscle and bone, as well as the normal motion of the cervical spine. Soft tissues have viscoelastic material properties which is key to understanding injury mechanisms. He will also touch on the concepts of coupled, intersegmental, and paradoxic motion.
Dr. Croft will explain the now widely adopted cervical acceleration/deceleration (CAD) (or whiplash-associated disorder or WAD) grading system which he developed more than a decade ago. This grading system, which has now been validated in numerous studies, provides the basis for effective intervention and for prognostication.
Dr. Croft will explain the tremendous scope of the current public health problem and the factors contributing to it. He reviews the substantial international literature, including the latest crash data of real world crashes obtained from on-board black boxes. He develops from this analysis—as well as his own published research—a risk estimate for adults and for children, incidence rates, and the prevalence of chronic pain in the U.S. attributable to motor vehicle trauma. With all the confusion and misinformation that exist regarding low speed crashes, amounts of property damage, and relative risk, Dr. Croft is careful to clarify these issues in great detail. For example, and perhaps counter-intuitively, within a specific range of low speed crashes, it is shown that the risk for occupant injury is actually greater when property damage is minimal.
The discussion begins with an introduction of the nomenclature and progresses to a discussion of velocity change (delta V), barrier velocity, and the ways in which velocity, time, and acceleration interact to affect the risk for occupant injury. Dr. Croft then takes attendees on an exploration of our current knowledge based on mathematical models, animal experiments (including the porcine experiments from whence the neck injury criterion (NIC) was proposed), cadaver experiments (where many recent discoveries have been made), dummy experiments (including those of the newest rear impact dummies or RID, which have been tested at the Spine Research Institute of San Diego by Dr. Croft and others), and, finally, the numerous human subject volunteer crash tests. Dr. Croft discusses his several years of crash testing as well as all of the other serious research in that area. As always, his presentation is replete with video footage and illustration to assist in understanding. Also in this section, Dr. Croft will discuss crash vectors other than rear, the important vehicle and subject parameters which modify risk, the dubious practice of estimating injury risk from property damage, the New Car Assessment Program and its unintended effects in low speed crashes, head restraints, seat backs, air bags, and other safety systems and how they modify injury risk and severity. Also discussed will be the general sequence of kinematic events in CAD injury and their relative timing, the head injury criterion (HIC), the neck injury criterion (NIC), and other important injury assessment reference values (IARV).
This section begins with a discussion of soft and hard tissue injuries resulting from whiplash, including data obtained from experimental animal research and surgical and autopsy findings. Fractures (stable and unstable), dislocations, and the broad range of soft tissue lesions, or WAD, will be discussed in the context of mechanism of injury and vector-based occupant kinematics. Dr. Croft has catalogued an immense database of this literature. He will offer an explanation for most of the common components of CAD/WAD including headache, various types of neck and back pain, shoulder and upper extremity pain, lower extremity pain, neurological syndromes, dizziness/lightheadedness, vertigo, visual disturbances, cognitive, and endocrinological disorders, and will additionally explore the common phenomenon of delayed onset of symptomatology.
Common syndromes associated with whiplash include cognitive disorders, usually resulting from mild traumatic brain injury (MTBI), postconcussion syndrome (PCS), thoracic outlet syndrome (TOS), TM joint disorder, carpal tunnel syndrome (CTS), posttraumatic headache, myofascitis, and numerous other less common conditions. Also discussed will be the clinical and diagnostic components of each, again making constant reference to current world literature. Common symptoms of whiplash will be explained and, for those conditions that remain poorly understood, Dr. Croft will discuss the relevant literature and develop and/or describe the best and most current hypotheses. Dr. Croft goes into extensive detail on the subject of MTBI, ranging from the history of our knowledge base to current predictive models, and outlines the range of common symptoms resulting from this all too common, but poorly understood, condition. Headaches are discussed in the context of current classification systems, including that of the International Headache Society. Long-term consequences of MTBI in children and adults is also discussed.
Dr. Croft will discuss the two most common forms of posttraumatic muscle disorder: myofascitis and fibromyalgia, going into detail about their respective diagnostic methods and criteria, such as those of the American College of Rheumatology. He will also provide a historical account of this controversial area, beginning with Virchow in 1852, and ending with the latest research findings.
Neurogenic pain, i.e., the pain that is conducted from peripheral nociceptor to dorsal root ganglion, to spinal cord, and eventually to the somatosensory cortex via the lateral spinothalamic tracts and thalamus, is the type studied and understood by most practitioners. However, few practitioners possess a deep understanding of discogenic, vertebrogenic, and scleragenic pain mechanisms, all of which are critically important in the diagnosis, management, and medicolegal explanation of most CAD cases. Dr. Croft explores the various pain mechanisms associated with CAD injury and its sequelae. He also looks at the epidemiology of chronic pain, sleep disturbance, and depression as an alternate explanation for some CAD symptoms.
For many, this is perhaps the most poorly understood area of this science, despite the magnitude of the current literature that is available. It is also one of the most hotly contested subjects from a forensic standpoint. Yet, in spite of the commonly voiced misconceptions about recovery from CAD, the preponderance of the evidence is clear and unambiguous. Dr. Croft reviews the substantial outcome literature and statistics in detail, and presents not only a thorough meta-analysis of it, but also develops a comprehensive risk analysis methodology found nowhere else. He explores the known risk factors for acute injury, as well as the risk factors for poor outcome—information that provides the physician and the patient with a meaningful guide to management and a scientific basis for clinical expectation. Moreover, Dr. Croft will emphasize the unique qualifications and role of the physician in this comprehensive risk analysis, which typically overshadows simple crash reconstruction or biomechanical analysis in its scope and construct validity. The section concludes with a review of the current literature on litigation neurosis concerning CAD and MTBI.
Spine Research Institute of San Diego, Inc. Voice: (619) 423-9867 or (619) 423-5475 |
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Requisite
and comprehensive biomechanics knowledge for forensic experts
Coronado, CA 92118
| Copyright © 2007 Spine Research Institute of San Diego. |