Current Research Projects
		Cervical Spine Curvature Study.
		Positron Emission Tomography (PET) Scanning of the Mild Traumatic Brain Injury (MTBI): a Study Correlating Crash Energy.
		Reliability of Event Data Recorders (EDR) in Full Scale Crash Tests.
		Crash Test Dummies: a Multipart Validation Study of Current Anthropometric Test Devices and Human Subject Crash Test Volunteers.
		Human Subjects in Frontal Impact, Full-Scale Crash Tests: Short-Term Follow-up Study.
		Human Subjects in Rear Impact, Full-Scale Crash Tests: Long-Term Follow-up Study.

Croft AC: Treatment paradigm for cervical acceleration/deceleration injuries (whiplash). ACA Journal of Chiropractic, 30(1): 41-45, 1993.

Abstract

Standards of care are the watchwords of the 1990s. With regard to treatment frequency and duration of care, two areas of chief concern are workers’ compensation and personal injury. This paper offers a rational method for determining a reasonable treatment paradigm for cervical acceleration/deceleration trauma based on preliminary data from studies currently underway at the Spine Research Institute of San Diego.

Croft AC, Young DN: Videofluoroscopy: a sampling of chiropractic radiologist's opinions. Topics in Diagnostic Radiology and Advanced Imaging, 2(1): 4-10, 1994.

Abstract

Videofluoroscopy (VF), previously known as cineradiography, has long been a source of polemics in our profession. Researchers in the 1970s concluded that VF was somewhat unreliable due primarily to technical difficulties related to patient positioning and geometric distortion. Due to these criticisms and a concern about inadequate training, the lack of normative data on intersegmental motion, the lack of standardized technique and patient selection protocol, as well as a concern for patient exposure to ionizing radiation, the American Chiropractic College of Radiology (ACCR) adopted a rather restrictive position on VF. More recently the ACCR has modified and relaxed its position in regard to VF, but not all practitioners are aware of these guidelines and few refer patients for VF evaluation. At this institute we have looked into the issue of interinterpreter reliability and we have candidly surveyed the attitudes of several of our most prominent radiologists. In this paper we shall discuss our findings and review salient parts of the most recent (1991) ACCR position on VF.

Key words: Videofluoroscopy.

Croft AC: Proposed classification of cervical acceleration/deceleration (CAD) injuries with a review of prognostic research. Palmer Journal of Research, 1(1): 10-21, 1994

Croft AC: Appropriateness of cervical spine manipulation: a survey of practitioners. Chiropractic Technique 8(4):178-181, 1996.

Abstract

OBJECTIVE To survey chiropractic field practitioners to determine the prevailing practices of cervical spine manipulation in patients known to have or suspected of having herniated or protruded cervical intervertebral discs. Design Postal survey mailed to all licensed chiropractors in the U.S. (n = ~ 50,200). PARTICIPANTS The number of licensed chiropractors responding to the survey was 3,510. MAIN RESULTS The mean age of the respondents was 42 yr (87% men) and the mean number of yr in practice was 13. Less than 2% of the respondents never perform manual manipulation to the cervical spine and 93% of all respondents reported that they would manipulate the spines of patients either known to have or suspected to have cervical disc herniation. Sixty-seven percent would attempt to directly manipulate the involved segment. CONCLUSIONS Although it is not possible to determine whether the respondents to the survey were a representative sample of practicing chiropractors in the United States, the majority reported that they will manipulate the cervical spines of patients who are at least suspected of having herniated cervical intervertebral discs.

Key words: Chiropractic, cervical vertebrae, intervertebral disc.

Sehnert K, Croft AC: Basal metabolic temperature vs. laboratory assessment in posttraumatic hypothyroidism. JMPT 19(1):6-12, 1996.

Abstract

OBJECTIVES To compare standard laboratory analytical methods with measurement of basal metabolic temperature in cases of hypothyroidism arising posttraumatically. SETTING Private medical office. SUBJECTS One hundred and one consecutive status post-whiplash trauma patients. DESIGN All subjects were evaluated with standard laboratory tests (T3RU, T4, FT4I, TSH) for thyroid function. Ninety-four were also evaluated with the newer fluorescence-activated microsphere assay test (FAMA) and basal metabolic temperature (BMT) was measured in all. Correlations were investigated between BMT, age, gender, standard laboratory values and the FAMA test. The differences between low and high BMT vs. normal and abnormal standard laboratory values and the differences between normal and abnormal standard laboratory values vs. normal and elevated FAMA test results were also investigated. RESULTS In 86.4%, the BMTs were below normal. Of this subgroup, 30% had abnormal standard laboratory values. Of the 13% whose BMT was within the normal range, 33% had abnormal standard laboratory values and 66% had increased FAMA titers. Statistically significant correlation was found between BMT and T3RU (p = .05), whereas the correlation between BMT and T4 was somewhat weaker (p = .07). Correlations between BMT and all other laboratory indices failed to reach significance. The laboratory abnormalities observed in this group of subjects were atypical for common types of hypothyroidism. A significant portion of our posttraumatic hypothyroid group (30%) were not identified with either standard laboratory tests or the FAMA test-a group we referred to as lab-normal. CONCLUSIONS Measurement of BMT seems to be a sensitive screening test, in combination with laboratory analysis, for the hypothyroidism seen after whiplash trauma. Whiplash seems to result in a form of hypothyroidism suggesting direct injury to central tissues.

 

Freeman MD, Croft AC, Rossignol AM: "Whiplash-Associated Disorders (WAD)—Redefining Whiplash and its management" by the Quebec Task Force: A critical evaluation. Spine 23(9):1043-1049, 1998.

Abstract

STUDY DESIGN The two publications of the Quebec Task Force on Whiplash-Associated Disorders were evaluated by the authors of this report for methodologic error and bias. OBJECTIVES To determine whether the conclusions and recommendations of the Quebec Task Force on Whiplash-Associated Disorders regarding the natural history and epidemiology of whiplash injuries are valid. SUMMARY OF THE BACKGROUND DATA: In 1995, the Quebec Task Force authored a text (published by the Societe de l'Assurance Automobile du Quebec) and a pullout supplement in Spine entitled "Whiplash-Associated Disorders: Redefining Whiplash and its Management." The Quebec Task Force concluded that whiplash injuries result in "temporary discomfort," are "usually self-limited," and have a "favorable prognosis," and that the "pain [resulting from whiplash injuries] is not harmful." METHODS The authors of the current report reviewed the text and the supplement for methodologic flaws that may have threatened the validity of the conclusions and recommendations of the Quebec Task Force. RESULTS Five distinct and significant categories of methodologic error were found. They were: selection bias, information bias, confusing and unconventional use of terminology, unsupported conclusions and recommendations, and inappropriate generalizations from the Quebec Cohort Study. CONCLUSION The validity of the conclusions and recommendations of the Quebec Task Force regarding the natural course and epidemiology of whiplash injuries is questionable. This lack of validity stems from the presence of bias, the use of unconventional terminology, and conclusions that are not concurrent with the literature the Task Force accepted for review. Although the Task Force set out to redefine whiplash and its management, striving for the desirable goal of clarification of the numerous contentious issues surrounding the injury, its publications instead have confused the subject further.

Croft AC, The Neck Injury Criterion (NIC): Future Considerations. 44th Annual Proceedings of the Association for the Advancement of Automotive Medicine, Chicago, IL, October 1-4, 2000, 519-521.

Freeman MD, Croft AC, Rossignol AM, Weaver DS, Reiser M: A review and methodological critique of the literature refuting whiplash syndrome. Spine 24(1):86-96, 1999.

Abstract

The validity of whiplash syndrome has been a source of debate in the medical literature for many years. Some authors have published articles suggesting that whiplash injuries are impossible at certain collision speeds; others have stated that the problem is psychological, or is feigned as a means to obtain secondary financial gain. These articles contradict the majority of the literature, which shows that whiplash injuries and their sequelae are a highly prevalent problem that affects a significant proportion of the population. The authors of the current literature critique reviewed the biomedical and engineering literature relating to whiplash syndrome, searching for articles that refuted the validity of whiplash injuries. Twenty articles containing nine distinct statements refuting the validity of whiplash syndrome were found that fit the inclusion criteria. The methodology described in these articles was evaluated critically to determine if the authors' observations regarding the validity of whiplash syndrome were scientifically sound. The authors of the current critique found that all of the articles contained significant methodologic flaws with regard to their respective authors' statements refuting the validity of whiplash syndrome. The most frequently found flaws were inadequate study size, nonrepresentative study sample, nonrepresentative crash conditions (for crash tests), and inappropriate study design. As a result of the current literature review, it was determined that there is no epidemiologic or scientific basis in the literature for the following statements: whiplash injuries do not lead to chronic pain, rear impact collisions that do not result in vehicle damage are unlikely to cause injury, and whiplash trauma is biomechanically comparable with common movements of daily living.

Harrison DD, Harrison SO, Croft AC, Harrison DE, Troyanovich SJ: Sitting biomechanics, part I: review of the literature. JMPT 22(9):594-609, 1999.

Abstract

OBJECTIVE To develop a new sitting spinal model and an optimal driver's seat by using review of the literature of seated positions of the head. spine, pelvis, and lower extremities. DATA SELECTION Searches included MEDLINE for scientific journals, engineering standards, and textbooks. Key terms included sitting ergonomics, sitting posture, spine model, seat design, sitting lordosis, sitting electromyography, seated vibration, and sitting and biomechanics. DATA SYNTHESIS In part I, papers were selected if (1) they contained a first occurrence of a sitting topic, (2) were reviews of the literature, (3) corrected errors in previous studies, or (4) had improved study designs compared with previous papers. In part II, we separated information pertaining to sitting dynamics and drivers of automobiles from part 1. RESULTS Sitting causes the pelvis to rotate backward and causes reduction in lumbar lordosis, trunk-thigh angle, and knee angle and an increase in muscle effort and disc pressure. Seated posture is affected by seat-back angle, seat-bottom angle and foam density, height above floor, and presence of armrests. CONCLUSION The configuration of the spine, postural position, and weight transfer is different in the 3 types of sitting: anterior, middle, and posterior. Lumbar lordosis is affected by the trunk-thigh angle and the knee angle. Subjects in seats with backrest inclinations of 110 to 130 degrees, with concomitant lumbar support, have the lowest disc pressures and lowest electromyography recordings from spinal muscles. A seat-bottom posterior inclination of 5 degrees and armrests can further reduce lumbar disc pressures and electromyography readings while seated. To reduce forward translated head postures, a seat-back inclination of 110 degrees is preferable over higher inclinations. Work objects, such as video monitors, are optimum at eye level. Forward-tilting, seat-bottom inclines can increase lordosis, but subjects give high comfort ratings to adjustable chairs, which allow changes in position.

Harrison DD, Harrison SO, Croft AC, Harrison DE, Troyanovich SJ: Sitting biomechanics, part II: optimal car driver’s seat and optimal driver’s spinal model. JMPT 23(1):37-47, 2000.

Abstract

BACKGROUND Driving has been associated with signs and symptoms caused by vibrations. Sitting causes the pelvis to rotate backwards and the lumbar lordosis to reduce. Lumbar support and armrests reduce disc pressure and electromyographically recorded values. However, the ideal driver's seat and an optimal seated spinal model have not been described. OBJECTIVE To determine an optimal automobile seat and an ideal spinal model of a driver. DATA SOURCES Information was obtained from peer-reviewed scientific journals and texts, automotive engineering reports, and the National Library of Medicine. CONCLUSION Driving predisposes vehicle operators to low-back pain and degeneration. The optimal seat would have an adjustable seat back incline of 100 degrees from horizontal, a changeable depth of seat back to front edge of seat bottom, adjustable height, an adjustable seat bottom incline, firm (dense) foam in the seat bottom cushion, horizontally and vertically adjustable lumbar support, adjustable bilateral arm rests, adjustable head restraint with lordosis pad, seat shock absorbers to dampen frequencies in the 1 to 20 Hz range, and linear front-back travel of the seat enabling drivers of all sizes to reach the pedals. The lumbar support should be pulsating in depth to reduce static load. The seat back should be damped to reduce rebounding of the torso in rear-end impacts. The optimal driver's spinal model would be the average Harrison model in a 10 degrees posterior inclining seat back angle.

Croft AC, Herring P, Freeman MD, Haneline MT: The neck injury criterion (NIC): future considerations. Accid Anal Prev 34(2)247-255, 2002.

Abstract

The cost of whiplash injuries—both in dollars spent for medical care and disability, and in terms of human suffering—are quite high in westernized nations. This is of particular interest, both from a public health perspective and a general societal one, because the disorder is theoretically preventable: In the very least it can be minimized. This can be achieved with crash prevention strategies and improvements in vehicle safety design—especially with more effective seat back and head restraint systems. Toward the goal of developing a standard for safety research in this area, a neck injury criterion (NIC) was proposed by Boström et al. in 1996. This criterion considers the relative horizontal acceleration and velocity between the bottom (T1) and top (C1) of the cervical spine and has face validity based on current literature. However, the NIC has become almost universally accepted, yet has not been subjected to rigorous scientific investigation or validation in terms of its representativeness in human occupant injury. Such investigation should specifically consider, first, whether the NIC provides an adequate proxy for all potential neck injuries due to whiplash and, secondly, whether the proposed threshold value of 15 m2/s2 is representative of the potential for all types of acute injuries. Based on a review of recent literature, recent human volunteer crash tests by Wheeler et al. and the those of the Spine Research Institute of San Diego, and based on mathematical MADYMO analysis of real world crash pulse data, it appears that the threshold for all acute injury in the general population is likely to require a lowering of the originally proposed NIC value. Moreover, it may be necessary to consider other factors not currently defined with the NIC, such as global neck hyperextension and the negative portion of the NIC curve. The conclusions of this paper should be considered preliminary. Certainly, ongoing work will be necessary to investigate this further and further analysis of more onboard crash data will prove invaluable.

Key words: Neck injury criterion (NIC)/whiplash/motor vehicle crash/cervical acceleration/deceleration injury (CAD).

Freeman MD, Centeno C, Croft AC, Nicodemus CN: Significant spinal injury resulting from low-level accelerations: a comparison with whiplash. International Congress on Whiplash-Associated Disorders, Berne, Switzerland, March 9-10, 1, 2001.

Abstract

BACKGROUND The level of force at which significant spinal injury can occur is a topic that has generated much discussion in the literature over the past 30 years. Research pertaining to human injury thresholds is best accomplished with observational study; that is, analysis of real world events. An ideal opportunity for study is presented with amusement park rides; roller coasters in particular, as they deliver a near identical level of acceleration to hundreds of thousands of subjects over a period of years. METHODS Injury incident records kept by the operators of the Rattler Roller coaster for the period 3-28-92 through 10-22-93 (approximately 19 months) were examined for significant spinal injuries that occurred on the ride. Emergency medical response and medical records that pertained to the incident records were also identified and reviewed. RESULTS A total of 39 subjects (out of an estimated 300,000 riders) with significant spinal injuries were found, yielding an injury rate of 13/100,000 exposures. The injuries were as follows; 72% (28 of 39) were single or multilevel cervical disc herniations, 23% were lumbar or thoracolumber disc herniations (9 of 39), and 18% were spinal fractures (seven cases, one cervical and six lumbar). The average Body Mass Index (BMI) was 23.1 (SD=4.4) for the females and 22.6 (SD=3.7) for the males, indicating average height and weight of the subjects. CONCLUSIONS While the injury rate was quite low in the study cohort (one in 7700 riders), it is reasonable to assume that the injury frequency among the self-selected and prepared riders of the roller coaster was lower than that of real world motor vehicle occupants exposed to similar acceleration levels in 3-4 mph rear impact collisions. The present study illustrates the fallacy of determining crash injury potential solely by estimating the level of peak occupant acceleration.

Croft AC, Haneline MT, Freeman MD: Differential occupant kinematics and head linear acceleration between frontal and rear automobile impacts at low speed: evidence for a differential injury risk. International Congress on Whiplash-Associated Disorders, Berne, Switzerland, March 9-10, 28, 2001.

Abstract

BACKGROUND Most epidemiological and clinical studies have highlighted the increased injury risk in rear impact vector crashes vs those of other vectors. However, many other risk factors exist which might potentially confound the observations of these studies. These include gender, age, stature, occupant positioning, and differences between vehicle parameters, such as head restraints, vehicle mass, etc. OBJECTIVE We conducted full scale, human subject crash tests under controlled conditions, using the same vehicles, the same subjects, and the same instrumentation, comparing occupant kinematics in rear vs. frontal crash scenarios. MATERIALS AND METHODS Vehicles and occupants were instrumented with accelerometers and closing speeds and delta Vs were measured. High speed video analysis was performed, and subjective responses to each crash were recorded. RESULTS The frontal vector crash resulted in a relatively simple, monophasic occupant kinematic, whereas the rear vector crash resulted in a more complex, biphasic kinematic. Subjects also rated the rear impact crashes notably less tolerable and more likely to cause injury. CONCLUSIONS Even in the same vehicle and at the same crash speeds, rear impact crash vectors result in comparatively more complex occupant kinematics, which seems to agree with epidemiological and clinical risk assessment data that suggests a greater risk in rear vector crashes vs. those of frontal or side impact vectors.

Key words: whiplash/WAD/cervical spine injury/human subjects testing.

Croft AC, Haneline MT, Freeman MD: Automobile crash reconstruction in low speed rear impact crashes utilizing a momentum, energy, and restitution (MER) method. International Congress on Whiplash-Associated Disorders, Berne, Switzerland, March 9-10, 20, 2001.

Abstract

BACKGROUND AND OBJECTIVE Low speed automobile crash reconstruction is fraught with difficulties. Residual crush, which is used in many reconstruction software programs, is often minimal or non-existent, police reports are rarely available, and witness accounts are generally unreliable. Many modern passenger vehicles can withstand crashes at closing velocities from other passenger vehicles at speeds of up to 15 km/h without sustaining significant damage, and yet the suspected risk threshold for occupants occurs at lower speeds. MATERIALS AND METHODS Using a method reported by Siegmund et al., in which bumper isolator travel is used to estimate energy and restitution values for use in momentum equations, we compared the results obtained mathematically to the actual data obtained from speed traps and accelerometers in two series’ of staged rear impact crash tests, utilizing multiple vehicles at low crash speeds. RESULTS The method was unsatisfactory when one of the two crashed cars had foam bumpers, and tended to yield values for delta V that were either close to the true value or about half, depending on vehicle make. The speed change, however, was never overestimated. When both cars were equipped with isolators, our results were difficult to interpret due to problems with frozen and broken isolators. CONCLUSIONS In real world crash reconstructions, the MER method may provide some guidance in estimating crash speed changes for subject vehicles. However, the method seemed to have only marginal practicality and accuracy. A larger series, with statistical analytical methods will be necessary to definitively determine the utility of this method.

Key words: Automobile crash reconstruction/ crash testing/ low speed crashes.

Centeno C, Freeman MD, Croft AC: A comparison of the functional profile of an international cohort of whiplash injured patients and non-patients: an internet study. International Congress on Whiplash-Associated Disorders, Berne, Switzerland, March 9-10, 2, 2001.

Freeman MD, Nicodemus CN, Croft AC, Centeno C: Significant spinal injury resulting from low-level accelerations: a case series of roller coaster injuries. Cervical Spine Research Society 29th Annual Meeting, Monterey, CA, Nov 29-Dec 1, 2001.

Abstract

STUDY DESIGN A prospective case series of roller coaster ride-induced significant spinal injuries. OBJECTIVES To describe a cohort of significantly injured roller coaster riders and the likely levels of acceleration at which the injuries occurred. These data are compared with contemporary efforts to define a lower limit of acceleration below which no significant spinal injury is likely to occur. METHODS Injury incident records and emergency medical service records for the Rattler Roller Coaster in San Antonio, Texas were evaluated for a 19 month period in 1992-3. Medical records for the more significant injuries were also reviewed and the specific injuries were tabulated, along with the demographics of the cohort. RESULTS There were 932,000 riders of the Rattler roller coaster, estimated to represent between 300,000 and 600,000 individual riders. It is estimated that there were a total of 656 neck and back injuries during the study period, and 39 were considered significant by the study inclusion criteria. Seventy two percent of the injured subjects sustained a cervical disc injury (28 of 39), and 71% of these injuries were at C5-6 (15 HNP, 5 symptomatic disc bulges), while 54% were at C6-7 (11 HNP, 4 symptomatic disc bulges). In the lumbar spine, the most frequent injury was a symptomatic disc bulge (20% of the cohort), followed by vertebral body compression fracture (18%), and L4-5 or L5-S1 HNP (13%). Accelerometry testing of passengers and train cars indicated a peak of 4.5-5g of vertical or axial acceleration and 1.5g of lateral acceleration over approximately 100 msec (0.1 sec) on both. CONCLUSIONS The results of this study suggest that there is no established minimum threshold of significant spine injury, and that the greatest explanation for injury presence following traumatic loading of the spine is individual susceptibility to injury, an unpredictable variable.

Key Words: Cervical spine, disc herniation, whiplash, roller coaster.

Freeman MD, Sapir D, Boutselis A, Gorup J, Tuckman G, Croft AC, Centeno C, Phillips A: Whiplash injury and occult vertebral fracture: a case series of bone SPECT imaging of patients with persisting spine pain following a motor vehicle crash. Cervical Spine Research Society 29th Annual Meeting, Monterey, CA, Nov 29-Dec 1, 2001.

Abstract

INTRODUCTION The pathology of chronic whiplash injury continues to be a controversial subject in the literature, with some authors claiming that long term pain following whiplash is a factitious disorder. These claims are made despite a growing canon of research demonstrating the cervical zygapophysis as a primary source of pain in approximately half of all chronic whiplash cases. Other research suggests that the intervertebral disc may be a source of continuing pain, associated with so-called rim lesions and other disc injuries. The pathomechanics of whiplash resulting from a rear impact collision include both segmental hyperextension in the lower cervical spine during the initial rearward movement of the head as well as flexion following the rebound of the head off of the head restraint, suggesting forceful loading of both posterior and anterior elements of the cervical spine. Recent cadaver testing of simulated whiplash has resulted in findings of injuries including fracture of both the vertebral body and elements of the neural arch, leading to the supposition that bony injury can occur with both the extension and flexion phases of whiplash trauma. While plain x-ray with lateral flexion and extension views is the generally recognized standard for evaluating bony injury and instability following whiplash, it is not particularly sensitive for the presence of incomplete cortical disruption such as endplate fractures and subchondral fractures of the facet. In the current investigation, we undertook bone scan and SPECT evaluation of consecutive patients who were referred for significant refractory pain following whiplash trauma based on the hypothesis that there may be a subpopulation of these patients who have continued symptoms resulting from unhealed occult fracture. METHODS Following Institutional Review Board approval of the study protocol, 15 consecutive patients who were referred for orthopedic evaluation of spine pain secondary to a motor vehicle crash (MVC), with symptoms that were un-responsive to conservative means of treatment such as physical therapy, chiropractic, and rehabilitation exercises, were subsequently referred for bone scan and SPECT imaging of their cervical and thoracic spine. The bone scans and SPECT images were read by two radiologists, blinded with regard to each other's findings as well as to the patients' symptom patterns. The results of the bone scan and SPECT imaging were compared to the patients' prior imaging studies (including plain x-ray and MRI) as well as their symptom pattern. Other details regarding patient demographics and the specifics of the MVC were tabulated. RESULTS Of the 15 referrals, one could not obtain insurance coverage for the study and thus did not undergo the diagnostic imaging. Of the remaining 14 subjects who were studied, ten had positive findings on bone scan and/orSPECT (71%). Nine of the ten positive studies closely corresponded with the patient-reported symptoms. The most frequent finding was vertebral endplate fracture, found in six cervical (60%) and three thoracic (30%) vertebrae. There were occult fractures identified in the lateral mass/lamina region of two cervical (20%) and two thoracic (20%) vertebra. A spinous process fracture was identified in the thoracic spine of one (10%) subject. There were ten females and four males in the study, with an average age of 33.3 (SD 9.0). The bone scan and SPECT imaging was performed an average of 18.9 months post-crash (SD 13.5, range 2-47). Pain levels were uniformly high, with average VAS scores of 7.8 (SD 1.1). Seven of the crashes were rear impact (50%), four were side impacts (29%), and three were front end impacts (21%). Nine of the occupants were drivers (64%) and ten were wearing seatbelts (71%). It did not appear that any of the fractures were a result of direct contact with the vehicle interior. None of the subjects had fractures that were detectable on plain film, even after reviewing the SPECT images and re-reading the radiographs. Ten of the subjects had MRI testing prior to the bone scan/SPECT protocol, and of these, six had signs of disc bulging in the cervical spine, four had disc bulges in the thoracic spine, and one had a frank thoracic herniation. One subject had undergone prior cervical discectomy and fusion, but had uptake activity in an area other than the healed fusion. DISCUSSION/CONCLUSION Our results, even though of a limited sample of patients, suggest a possible pathological mechanism at work in chronic whiplash that has not been previously described. While other authors have reported vertebral fractures resulting from whiplash trauma, none that we are aware of have suggested unhealed fractures as a potential source of chronic pain. Lack of specificity of bone scan and SPECT imaging for fracture may be a factor in our series, however, the high correlation of symptoms to findings suggests a traumatic rather than degenerative etiology. Greater subject numbers are needed in order to perform meaningful subgroup analyses relating to gender, age, and injury and crash details as risk factors for occult spinal fracture following whiplash. Our findings may point to more effective methods of dealing with chronic spine pain resulting from motor vehicle crashes.

Haneline MT, Croft AC, Frishberg BM: The association of internal carotid artery dissection and chiropractic manipulation. Neurologist 9(1):35-44, 2003.

ABSTRACT

BACKGROUND In order to determine the relationship between chiropractic manipulative therapy (CMT) and internal carotid artery dissection (ICAD), a Medline literature search was performed for the years 1966 through 2000, using the terms “internal carotid dissection.” Literature that included information concerning causation, and all case studies and series were selected for review. REVIEW SUMMARY In reviewing the few cases of internal carotid dissection proposed to be related to CMT, there were many contributing factors, such as connective tissue aberrations, underlying arteriopathy, or coexistent infection, that obscured any cause and effect relationship. To date there are only 13 reported cases of ICAD temporally related to CMT. Most ICADs appear to occur spontaneously and progress from local symptoms of headache and neck pain to cerebral hemispheric ischemic signs. Approximately one-third of the reported cases were manipulated by practitioners other than chiropractic physicians, and, due to the differential risk related to dissimilarity in training and practice between practitioners who manipulate the spine, it would be inappropriate to compare adverse outcomes between practitioner groups. CONCLUSIONS None of the cases reviewed in the medical literature indicated a clear causal relationship between CMT and ICAD. Reported cases have been exceedingly scarce, and are limited to case studies, which cannot be used to substantiate causation.

Key indexing terms: chiropractic manipulation, internal carotid artery dissection, stroke.

Freeman MD, Croft AC, Rossignol AM: Late whiplash risk factor analysis of a random sample of patients with chronic spine pain. Submitted.

Abstract

OBJECTIVES The current case/control study was designed to determine if there are identifiable risk factors for chronicity following an acute whiplash injury. The responses of 245 randomly selected cases with chronic spine pain resulting from a motor vehicle crash (MVC) were compared with the responses of 116 randomly selected controls with chronic spine pain not attributed to a MVC, but who had a history of acute injury in a MVC and completely recovered. The average time post-injury was 6 years. The groups were subdivided into 187 cases with chronic neck or neck and back pain (neck cases), whose responses were compared with 71 controls with chronic neck or neck and back pain (neck controls). We also compared the responses of 58 cases with chronic back pain (back cases) to 45 controls with chronic back pain (back controls). The subjects were surveyed for individual characteristics, such as gender, height, weight, and age, as well as factors intrinsic to the crash, such as direction of impact, use of head restraints, use of seat belts, position in vehicle, and vehicle damage. Chi square was used to determine if there were significant differences between the groups for any of the variables. FINDINGS Direction of collision was the same for neck cases and neck controls. Back cases were significantly more likely to have been injured in a side impact (p = 0.02). Presence of a head restraint was not found to differ significantly between cases and controls, both neck and back. The presence of a seat belt, when a shoulder restraint was included, was significantly associated with chronicity for neck cases (p = 0.002), while lack of a seat belt was found to have a protective effect (p = 0.003). Seat belt use did not contribute to, or protect for chronicity for back cases. Position of the subject in the vehicle at the time of impact (driver or passenger) was not found to differ between cases and controls for neck or back. The amount of vehicle damage was not a significant factor in developing chronic pain for either neck or back cases. Gender was not found to be a risk factor for chronicity, in either neck or back cases. Female subjects of slight stature were at significantly greater risk for chronic neck and back pain than were their stouter counterparts (p = 0.03). However, body composition was not a risk factor for chronicity among male cases with chronic neck and back pain. Greater age was found to be a significant risk factor for chronic neck pain (p = 0.04), but not for chronic low back pain. CONCLUSIONS Risk variables for chronicity were found to be both extrinsic and intrinsic to the injured occupant. Extrinsic variables were side impacts for chronic low back pain, and the presence of a shoulder restraint for chronic neck pain. Intrinsic risk factors were slight body composition for females for both neck and low back pain, and increased age for chronic neck pain. While the small numbers in this study prompt caution when interpreting our results, they do suggest a direction for future research and potential engineering solutions to the problem of chronic pain following acute whiplash injury.

Freeman MD, Croft AC: Late whiplash risk factor analysis of a random sample of patients with chronic spine pain. Submitted.

Abstract

INTRODUCTION/METHODS The current case/control study was designed to determine if there are identifiable risk factors for chronicity following an acute whiplash injury. The responses of 245 randomly selected cases with chronic spine pain resulting from a motor vehicle crash (MVC) were compared with the responses of 116 randomly selected controls with chronic spine pain not attributed to a MVC, but who had a history of acute injury in a MVC and completely recovered. The subjects were surveyed for individual characteristics, such as gender, height, weight, and age, as well as factors intrinsic to the crash, such as direction of impact, use of head restraints, use of seat belts, position in vehicle, and vehicle damage. RESULTS Direction of collision was the same for neck cases and neck controls. Back cases were significantly more likely to have been injured in a side impact (p = 0.02). Presence of a head restraint was not found to differ significantly between cases and controls, both neck and back. The presence of a seat belt, when a shoulder restraint was included, was significantly associated with chronicity for neck cases (p = 0.002), while lack of a seat belt was found to have a protective effect (p = 0.003). Seat belt use did not contribute to, or protect for chronicity for back cases. Position of the subject in the vehicle at the time of impact (driver or passenger) was not found to differ between cases and controls for neck or back. The amount of vehicle damage was not a significant factor in developing chronic pain for either neck or back cases. Gender was not found to be a risk factor for chronicity, in either neck or back cases. Female subjects of slight stature were at significantly greater risk for chronic neck and back pain than were their stouter counterparts (p = 0.03). However, body composition was not a risk factor for chronicity among male cases with chronic neck and back pain. Greater age was found to be a significant risk factor for chronic neck pain (p = 0.04), but not for chronic low back pain. CONCLUSIONS Risk variables for chronicity were found to be both extrinsic and intrinsic to the injured occupant. Extrinsic variables were side impacts for chronic low back pain, and the presence of a shoulder restraint for chronic neck pain. Intrinsic risk factors were slight body composition for females for both neck and low back pain, and increased age for chronic neck pain.

Key Words: Whiplash, neck pain, epidemiology.

Croft AC, Elbridge TR. Human subject rear seat passenger symptoms response to frontal car-to-car low-speed crash tests. J Chiropractic Medicine. 2011;1:141-146.

Abstract

Objective: The purpose of this study was to determine whether healthy adult volunteers report symptoms following exposure to low-speed frontal crashes at low velocities. Methods: Nineteen medically screened, healthy, informed, and willing volunteers (17 men, 2 women; mean age, 37 years) were exposed to low-speed frontal crashes. All volunteers were seated in the rear seat position of the bullet vehicle. Closing velocities ranged from 4.1 to 8.3 mph (mean, 6.7 mph). For the bullet vehicle, the delta V ranged from 1.4 to 3.9 mph with a mean of 2.8 mph. Results: Eighty-eight percent of volunteers attributed symptoms of discomfort to their crash exposure. All reported symptoms were transient, and none required medical treatment. The mean duration was 1 day. Conclusions: Even at relatively low speeds, there is no lower threshold below which it can be reasonably assumed that healthy and prepared volunteer rear seat passengers will not sustain some level of minor injury in a frontal collision. Although the reported mean delta V for injured persons in real-world frontal crashes has been reported to be as high as 8.1 mph, this does not offer any insight into the minimum threshold for such injuries among all at-risk vehicle occupants.

Key Words: Whiplash injuries, Motor vehicles, Chiropractic

Croft AC, Haneline MT, Freeman MD: Differential Occupant Kinematics and Forces Between Frontal and Rear Automobile Impacts at Low Speed: Evidence for a Differential Injury Risk, International Research Council on the Biomechanics of Impact (IRCOBI), International Conference, 2002, September 18-20, Munich, Germany, 365-366.

Abstract

RESEARCH OBJECTIVE Numerous factors are believed influence the risk for injury to the cervical spine in low speed automobile crashes. These include occupant stature, gender, position, age, pre-exiting health status, and awareness of impending crash. Factors extrinsic to the occupant that are thought to influence the risk for injury include seat back characteristics, head restraint geometry, type of restraint system used, crash speed, relative vehicle mass, and the direction of impact. Several studies have indicated that rear impact crashes are associated with greater risk for injury and, in some cases, a worse prognosis. Epidemiological studies have identified many risk factors, but the retrospective study design and wide ranging variables of real life crash scenarios has not allowed careful comparison of specific variables. We sought to answer the question concerning the possible reasons for the disparity in risk between front vector crashes and rear vector crashes using human subject crash testing. MATERIALS AND DATA SOURCES Institutional review board approval was obtained, as was informed consent from all participants. Instrumented human subjects (two males and one female) were placed in instrumented crash test vehicles. Occupant accelerations were recorded for the head, thorax, and lumbar spines. Force and moment analysis were calculated based on head accelerations and the principles of dynamics. Vehicle accelerations, closing velocities, and speed changes were recorded. Volunteers were subjected to three rear impact crashes, two of which were conducted in the unaware mode (subjects had no visual clues as to the time of impact and were distracted with loud music played through ear phones), and one in the aware mode in which the subjects were allowed to brace for the impact. The sequences of crashes—frontal or rear—were staggered among subjects such that two were first struck from the rear and later played the role of the striking driver, while the third subject experienced the reverse sequence, playing first the role of the striking driver and then the role of the struck driver. In this study, all variables were held constant between frontal and rear impact sequences except the relative positions of the two vehicles. Closing velocities and velocity changes were kept as consistent as possible and varied only minutely. Thus, the only variables with this crossover study design were the impact vectors. In addition to collecting accelerometer data, we recorded the entire crash sequence from the lateral view on high speed 16 mm film and high speed video (both at 500 fps). All footage was carefully analyzed for kinematic time histories and correlated with the accelerometer data. After each crash sequence, subjects were asked for their subjective rating of the crash and, after all sequences were complete, they were asked to compare the frontal crashes with the rear. RESULTS For rear impact crash tests, closing velocities ranged from 4.8 km/h to a high of 13.9 km/h, and velocity changes ranged from 2.9 km/h to a high of 10.1 km/h, well within the reported range for possible soft tissue injury. Maximum head linear (x) accelerations in rear crash tests ranged from 2.5 g to 13.3 g (both extremes occurring in the female subject). Maximum head linear (x) accelerations in the frontal crash tests ranged from –1.3 g to –4.5 g. The average head linear (x) accelerations in the frontal crash tests was –2.5 g, whereas the average head linear (x) acceleration in the rear crash tests was 7.0 g—2.8 times higher than that of the frontal crashes. Video analysis revealed several noticeable variations between the crashes. In the rear crashes there were two distinct kinematic phases and two distinct bending moments: an initial rearward phase and extension bending moment and a subsequent frontal phase and forward bending moment. Moreover, shear occurred first in the rearward phase and then in the forward phase. Since the female subject (55.5 kg) had appreciably less body mass than the male subjects, she experienced higher accelerations than the males. As a result, her forward shear effect was more pronounced as was her forward bending moment. However, due to her lesser body mass, she interacted faster with the seat back and head restraint and offered less resistance to their forward motion. This quicker interaction resulted in her earlier and higher amplitude acceleration. In contrast, the males subjects (82 kg and 86 kg) offered greater resistance to the forward moving seat, effectively delaying their forward acceleration. They also caused the seat back to deflect rearward more than the female subject. This increase in their crash duration during this phase resulted in markedly reduced head linear accelerations. However, due to the fact that the head restraints were positioned low relative to their heads (although they were positioned as high as possible) and also due to the male subjects’ greater interaction with the seat backs, the males experienced markedly greater rearward phase extension and bending moments with corresponding less forward phase motion and bending moments. Volunteers rated their subjective experiences in the rear impact crashes as greatly more traumatic or physically unpleasant than in the frontal crashes. Other distinguishing effects are discussed. CONCLUSIONS When holding vehicle mass, crash speeds, occupant variables and their interactions constant, the forces acting on the human neck and cervical spine were nearly three times higher in rear impact crash vectors vs. frontals. The resulting occupant kinematics were more complex in the rear impact crash, which also might explain some of the reported differential injury risk. Additionally, it appears that the mechanism of injury in whiplash may vary with occupant mass. Volunteers’ subjective assessments of the crashes were consistent with these observations. DISCUSSION The findings of this study shed some light on possible reasons for the observed difference in injury risk between frontal and rear impact crash injuries reported in clinical and epidemiological literature and will likely have medicolegal implications as well. The results suggest that more attention should be given to crashworthiness in the rear impact crash vector. LIMITATIONS OF STUDY As in all human subject crash tests, subjects can be made to be unaware, but not necessarily unprepared. Reactions times are likely to be more brisk for volunteers than for real world occupants. The small study size does not allow a high level of confidence in differential forces and resulting kinematics, but the results were always consistent and the differences were large. Differential risk assignment for real world occupants will require a more comprehensive epidemiological review.

Croft AC, Haneline MT, Freeman MD: Low speed frontal crashes and low speed rear crashes: is there a differential risk for injury? Proceedings of the 46th Association for the Advancement of Automotive Medicine (AAAM) Annual Scientific Conference, Tempe, Arizona, September 29-October 2, 2002, 79-91.

Abstract

We compared male and female subjects in crash tests in which each subject experienced both frontal and rear impacts. Crash speed and other crash parameters were held constant. We believe this was the first experiment using an independent variable of crash vector and dependent variables of head linear acceleration and volunteer qualitative tolerance. Analysis of data revealed that the rear impact vector crash resulted in 2.8 times greater head linear acceleration than frontal crashes. Rear impact crashes resulted in biphasic, complex kinematics compared to the monophasic, less complex frontal crashes. Rear impact crashes were rated markedly less tolerable. Sex-specific differences are also discussed.

Freeman MD, Croft AC, Centeno C: Fatal head injury cases in a rural Oregon county. Proceedings of the 19th World Congress of the International Traffic Medicine Association, Budapest, Hungary, September 14-17, 2003.

Abstract

OBJECTIVE To describe the epidemiology of fatal crashes in a rural county; in particular those resulting from head injury. METHODS/DATA SOURCES Oregon State Medical Examiner files of all deaths in Clackamas County, Oregon for the years 1990-1999 were reviewed for traffic related fatalities. Data regarding the decedent, the crash, the vehicle(s), and the post-crash response, including extrication and post-mortem evaluation were recorded and analyzed. Data were then compared with referent data collected by the Oregon Department of Transportation (ODOT). RESULTS There were a total of 420 traffic related deaths attributed to Clackamas County for the time period of 1990-1999, with 317 (75%) of the victims having expired in the county and the remainder transported to Multnomah County at time of death (Multnomah County is the nearest location with Level 1 trauma facilities). Of the 317 decedents, 219 (69%) of the decedents were male, and 98 (31%) were female. Males were over-represented in the 61 (19.2%) cases with ejections, 80.3% compared with 19.7% female. There was a correlated disproportionate difference in passive restraint use, with only 26.5% of the males restrained compared with 48.0% of the females.
Head injury was by far the most frequently found major contributor or cause of death, named in 228 (71.9%) cases. Most crashes were frontal or front angled (43.4%), with side impacts (21.1%) and rollovers (18.9%) and finally rear impact (1.8%) listed as the principle direction of force of the crash event that resulted in death. The total number of fatal head injury crashes (FHIC) rose from 31 in 1990 to 45 in 1995, and then decreased every year until 1999, with 22 FHIC cases. The mean age of the vehicles involved in FHIC cases increased during the time period under study; from 8 years old in 1990 gradually increasing to 12 years old in 1999. Alcohol involvement in FHIC cases was 42% in 1990, increasing to a high of 57% in 1992, and then progressively decreasing to 32% in 1999. CONCLUSIONS/DISCUSSION The experience of Clackamas County for fatal crashes in 1990-1999 reflected that of the US as a whole, with decreases in total number of deaths and alcohol involvement. The finding that vehicle age increased over the study period is most likely related to the decreased rate of FHIC in airbag equipped vehicles. Behavioral issues reflected in voluntary restraint use likely played an important role in the difference in the total number of deaths for males versus females. STUDY LIMITATIONS Small sample sizes for the individual years prevented meaningful statistical analysis of year-to-year trends for variables of interest.

Haneline MT, Croft AC: The relationship of chiropractic neck manipulation to internal carotid artery dissection. The Forensic Examiner 12(9,10):38-41, 2003.

Abstract

Literature generated by the medical community contends that chiropractic manipulative therapy (CMT) applied to the cervical spine may be a cause of internal carotid artery dissection (ICAD). We reviewed the literature published in the English language, and were able to locate twelve reports in which the author reported that ICAD occurred following chiropractic manipulation, cervical manipulation, or simply manipulation. A review of the literature is presented concerning ICAD, followed by a critique of the twelve cases as to whether there was convincing substantiation of a connection between CMT and ICAD. We concluded that there were other contributing factors, such as connective tissue aberrations, underlying arteriopathy, or coexistent infection, that obscured a cause and effect relationship. Most ICAD’s occur spontaneously and progress from local symptoms of headache and neck pain to cerebral ischemic signs. ICAD patients may seek CMT during the phase of local symptoms, which then progress to ischemic signs, yet the CMT may have had little or nothing to do with its progression. None of the cases that we reviewed indicated a clear causal relationship between CMT and ICAD. No less than one-third of the cases were not manipulated by chiropractic physicians, and, due to the differential risk related to differences in training and practice, it was not reasonable to consolidate their adverse outcomes with those of chiropractic physicians.

Key words: chiropractic manipulation, internal carotid artery dissection, stroke.

Freeman MD, Croft AC, Rossignol AM, Centeno CJ, Elkins WL: Chronic neck pain and whiplash: A case-control study of the relationship between acute whiplash injuries and chronic neck pain Pain Res Manag 2006 11(2):79-83.

Abstract

The authors undertook a case-control study of chronic neck pain and whiplash injuries in nine states in the United States to determine whether whiplash injuries contributed significantly to the population of individuals with chronic neck and other spine pain. Four hundred nineteen patients and 246 controls were randomly enrolled. Patients were defined as individuals with chronic neck pain, and controls as those with chronic back pain. The two groups were surveyed for cause of chronic pain as well as demographic information. The two groups were compared using an exposure-odds ratio. Forty-five per cent of the patients attributed their pain to a motor vehicle accident. An OR of 4.0 and 2.1 was calculated for men and women, respectively. Based on the results of the present study, it reasonable to infer that a significant proportion of individuals with chronic neck pain in the general population were originally injured in a motor vehicle accident.

Croft AC, Philippens, MMGM: The RID2 biofidelic rear impact dummy: a validation study using human subject in low speed rear impact full scale crash tests. Neck injury criteria (NIC). 2006 SAE World Congress, Technical Paper Series 2006-01-0067, April 3-6, Detroit, MI, 2006.

Abstract

Human subjects and the recently developed RID2 rear impact crash test dummy were exposed to a series of full scale, vehicle-to-vehicle crash tests to evaluate the biofidelity of the RID2 anthropometric test dummy on the basis of calculated neck injury criterion (NIC) values. Volunteer subjects, including a 50th percentile male, a 95th percentile male, and a 50th percentile female, were placed in the driver’s seat of a vehicle and subjected to a series of three low speed rear impact crashes each. Both subjects and dummy were fully instrumented and acceleration-time histories were recorded. From this data, velocities of the heads and torsos were integrated and used to calculate the NIC values for both crash test subjects and the RID2. The RID2 dummy is designed to represent a 50th male. The overall performance and biofidelity of the RID2 compared most favorably to the human subject who was, himself, a 50th percentile male. Although the number of tests was small, the biofidelity of the RID2, in the context of the smaller female and larger male, was limited. The overall performance and biofidelity of the RID2 was reasonable when compared to the 50th percentile male volunteer. It is possible that under real world crash conditions, in which the occupant of the target vehicle is exposed to an unexpected impact, that their NIC values might be more comparable to those of the RID2, suggesting that its biofidelity could have been underestimated as a result of the alerted status of the crash test volunteers.

Haneline MT, Croft AC, Frishberg BM: The association of internal carotid artery dissection and chiropractic manipulation. Neurologist 9(1):35-44, 2003.

Abstract

BACKGROUND: To determine the relationship between chiropractic manipulative therapy and internal carotid artery dissection, a MEDLINE literature search was performed for the years 1966 through 2000 using the terms internal carotid dissection. Literature that included information concerning causation of ICAD, as well as all case studies and series, was selected for review. REVIEW SUMMARY: In reviewing the cases of internal carotid dissection potentially related to CMT, there were many confounding factors, such as connective tissue aberrations, underlying arteriopathy, or coexistent infection, that obscured any obvious cause-and-effect relationship. To date there are only 13 reported cases of ICAD temporally related to CMT. Most ICADs seem to occur spontaneously and progress from local symptoms of headache and neck pain to cortical ischemic signs. Approximately one third of the reported cases were manipulated by practitioners other than chiropractic physicians, and because of the differential risk related to major differences in training and practice between practitioners who manipulate the spine, it would be inappropriate to compare adverse outcomes between practitioner groups. CONCLUSIONS: The medical literature does not support a clear causal relationship between CMT and ICAD. Reported cases are exceedingly scarce, and none support clear cause and effect.

Croft AC, Freeman MD: Correlating crash severity with injury risk, injury severity, and long-term symptoms in low velocity motor vehicle collisions. Med Sci Monit 2005 11(10):RA316-321. (Free download at www.medscimonit.com)

Abstract

BACKGROUND: Auto insurers use a variety of techniques to control their losses, and one that has been widely employed since the mid-1990's is the Minor Impact Soft Tissue (MIST) segmentation strategy. MIST protocol dictates that all injury claims resulting from collisions producing US dollars 1000 or less in damage be "segmented", or adjusted for minimal compensation. MATERIAL/METHODS: Multiple databases were searched for studies comparing any of three dependent variables (injury risk, injury severity, or duration of symptoms) with structural damage in motor vehicle crashes of under 40 km/h (25 mph). RESULTS: A limited correlation between crash severity and injury claims was found. We could not determine, however, whether this relationship held across all crash severities. Other studies provided conflicting results with regard to acute injury risk, but both found no statistically significant correlation between crash severity and long-term outcome. CONCLUSIONS: A substantial number of injuries are reported in crashes of little or no property damage. Property damage is an unreliable predictor of injury risk or outcome in low velocity crashes. The MIST protocol for prediction of injury does not appear to be valid.

Freeman MD, Croft AC, Nicodemus CN, Centeno CJ, Elkins WL: Significant spinal injury resulting from low-level accelerations: a case series of roller coaster injuries. Arch Phys Med Rehabil 2005 Nov;86(11):2126-30.

Abstract

OBJECTIVES: To describe a cohort of significantly injured roller coaster riders and the likely levels of acceleration at which the injuries occurred, and to compare these data with contemporary efforts to define a lower limit of acceleration below which no significant spinal injury is likely to occur. DESIGN: A retrospective case series of roller coaster ride-induced significant spinal injuries. SETTING: Injury incident records and emergency medical service records for the Rattler roller coaster in San Antonio, TX, were evaluated for a 19-month period in 1992 and 1993. Medical records for the more significant injuries were also reviewed and the specific injuries were tabulated, along with the demographics of the cohort. PARTICIPANTS: There were 932,000 riders of the Rattler roller coaster, estimated to represent between 300,000 and 600,000 individual riders. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Injury incident reports and medical record review. RESULTS: It is estimated that there were a total of 656 neck and back injuries during the study period, and 39 were considered significant by the study inclusion criteria. Seventy-two percent (28/39) of the injured subjects sustained a cervical disk injury; 71% of these injuries were at C5-6 (15 disk herniations, 5 symptomatic disk bulges) and 54% were at C6-7 (11 disk herniations, 4 symptomatic disk bulges). In the lumbar spine, the most frequent injury was a symptomatic disk bulge (20% of the cohort), followed by vertebral body compression fracture (18%), and L4-5 or L5-S1 disk herniation (13%). Accelerometry testing of passengers and train cars indicated a peak of 4.5 to 5g of vertical or axial acceleration and 1.5g of lateral acceleration over approximately 100ms (0.1s) on both. CONCLUSIONS: The results of this study suggest that there is no established minimum threshold of significant spine injury. The greatest explanation for injury from traumatic loading of the spine is individual susceptibility to injury, an unpredictable variable.

D’Antoni A, Croft AC. Prevalence of herniated intervertebral discs of the cervical spine in asymptomatic subjects using MRI scans: a qualitative systematic review. Journal of Whiplash and Related Disorders 5(1):5-13, 2005.

Abstract

INTRODUCTION. Our objective was to review articles that report the prevalence of cervical disc herniations in asymptomatic subjects using MRIs and conduct a qualitative systematic review. METHODS. A MEDLINE search for articles published between 1974 and 2004 was performed, and five articles were retained in this review. RESULTS. Teresi et al. studied 35 asymptomatic subjects retrospectively and 65 asymptomatic subjects prospectively, and found 20% of subjects 45-54 years, 35% of subjects 55-64 years, and 57% of subjects older than 64 years had cervical disc herniations/bulges. Boden et al. studied 63 asymptomatic subjects and found 10% of subjects less than 40 years and 5% of subjects older than 40 years had disc herniations. Lehto et al. studied 89 asymptomatic subjects and found that each of 2 subjects (one 29 and the other 56 years) had a disc prolapse; the prevalence was 2.2%. Matsumoto et al. studied 497 asymptomatic subjects. They found that 70 of 2480 discs scanned were prolapsed posteriorly (2.8%), and reported that the frequency of these lesions increased after 40 years. Siivola et al. compared 15 asymptomatic and 16 symptomatic subjects after 7 years and found no disc herniations (0%) in the asymptomatic group and 4 disc herniations (25%) in the symptomatic group. CONCLUSIONS. The prevalence of cervical disc herniations in asymptomatic subjects less than 40 years of age is 3% to 10% and increases to 20% in subjects up to 54 years of age. The prevalence increases with age—from 5% to 35% in subjects between 40 and 64 years of age.

Croft AC: Human subjects exposed to very low velocity frontal collisions. Journal of Biomechanics 39 (Supplement 1) S146, 2006.

Abstract

STUDY DESIGN: Experimental study subjecting passengers to frontal collisions with speed changes of under 4 mph and utilizing post-test structured interviews immediately after and 4 weeks after impact to quantify subjects’ clinical responses. OBJECTIVES: To determine whether healthy adult volunteers report symptoms following exposure to low speed frontal crashes at speeds below those hypothesized to represent a threshold for injury risk and whether experimental frontal crashes can be conducted safely at the levels studied. SUMMARY OF BACKGROUND DATA: Recent studies have shown that neither speed change (delta V) nor structural damage are strong correlates of injury risk. No standards currently exist for the level at which frontal crash tests can be safely conducted with human volunteer passengers.
MATERIALS AND METHODS: 17 medically screened volunteers (15 males, 2 females; mean age 37 years) were exposed to low speed frontal crashes. Closing velocities ranged from 6.6 km/h to 13.4 km/h (mean 10.8 km/h). The delta V ranged from 2.3 km/h to 6.3 km/h with a mean of 4.5 km/h. RESULTS: 88% of the volunteers attributed symptoms of discomfort to their crash exposure. All reported symptoms were transient and none required medical treatment. All were characterized as either minimal or slight in severity and none had a duration exceeding one week. The mean duration was 1 day. CONCLUSIONS: Even at relatively low speeds, healthy and aware rear seat passengers can sustain some level of minor injury in a frontal collision. While the reported mean delta V for injured persons in real world frontal crashes has been reported to be 13.0 km/h, this does not offer any insight into the minimum threshold for such injuries among all at-risk vehicle occupants. The results of the current testing indicate that even medically screened volunteers can sustain some degree of injury in frontal collisions with a speed change of less than 6.4 km/h. It is incumbent upon researchers conducting such testing that they inform prospective volunteers that some degree of minor injury and resulting short-term symptoms are possible, and this fact must be carefully considered by Institutional Review Boards that are asked to approve human subject crash testing.

Croft AC: Biomechanical and kinematic differences between rear impact and frontal impact automobile crashes at low velocities. Journal of Biomechanics 39 (Supplement 1) S145, 2006.

Abstract

BACKGROUND Numerous factors are believed to influence the risk for injury to the cervical spine in low speed automobile crashes. Several studies have indicated that rear impact crashes are associated with greater risk for injury and, perhaps, a worse prognosis. We sought to answer the question concerning the possible reasons for the disparity in risk between front vector crashes and rear vector crashes using human subject crash testing. MATERIALS AND METHODS Instrumented human subjects were placed in instrumented crash test vehicles. Occupant accelerations were recorded. Force and moment analysis were calculated. Vehicle acceleration and speed metrics were recorded. Volunteers were subjected to three rear impact crashes, two of which were conducted in the unaware mode, and one in the aware mode in which the subjects were allowed to brace for the impact. All variables were held constant between frontal and rear impact sequences except the relative roles of the two vehicles (e.g., striking or struck). Thus, the only variables with this crossover study design were the impact vectors. RESULTS Volunteers rated their subjective experiences in the rear impact crashes as markedly more traumatic or physically unpleasant than in the frontal crashes. When holding vehicle mass, crash speeds, occupant variables and their interactions constant, the acceleration of the subjects’ heads was nearly three times higher in rear impact crash vectors vs. frontals. The resulting occupant kinematics were more complex in the rear impact crash. Additionally, it appears that the mechanism of injury in whiplash may vary with occupant mass. CONCLUSIONS The results suggest that more attention should be given to crashworthiness in the rear impact crash vector. The small study size does not allow a high level of confidence in regards to our findings of differential forces and resulting kinematics, but our results were always consistent and the observed differences were quite large. To our knowledge, this is the first study to look specifically at differential effects of rear vs. frontal crashes at low speeds, holding all other variables constant.

Croft AC, D’Antoni AV, Terzulli SL: Update on the antibacterial resistance crisis. Med Sci Monit, 2007 13(6): RA103-118. (Free download at www.medscimonit.com)

Abstract

This nation--and in fact the world--is currently facing a crisis in the form of a growing antibacterial drug resistance. In the 60 or so years since the discovery of penicillin, physicians and pharmaceutical companies have been constantly challenged to stay a step ahead of the bacteria that constantly adapt to the drugs used to control them. These magic bullets were at one time expected to eliminate the concern over infectious disease and have been relied upon heavily. But their effectiveness has been steadily waning in recent years as, more and more, strains of bacteria emerge that are resistant to multiple drugs and, in some cases, have become nearly "panresistant." Nosocomial infections with these resistant strains were once confined to hospitals but new community-acquired infections are an ominous portent. Meanwhile, perhaps equally as distressing, many pharmaceutical companies are discontinuing efforts to develop new antimicrobial drugs for a variety of reasons and few new agents are currently in the pipeline. The selective pressure triggering these bacterial mutations are complex, but they can be shared by healthcare workers, hospitals, long-term care facilities, the agriculture industry, and even healthcare consumers themselves. In this paper, these topics are discussed, in turn, and the paper concludes with an apologia for change that can and should be equally shared by these stakeholders.

Croft AC, Philippens MMGM: The RID2 biofidelic rear impact dummy: A pilot study using human subjects in low speed rear impact full scale crash tests. Accid Anal Prev 39:340-346, 2007.

Abstract

STUDY DESIGN: Human subjects and the recently developed RID2 rear impact crash test dummy were exposed to a series of full scale, vehicle-to-vehicle crash tests. OBJECTIVE: To evaluate the biofidelity of the RID2 anthropometric test dummy on the basis of calculated neck injury criterion (NIC) values by comparing these values to those obtained from human subjects exposed in the very same crashes. SUMMARY OF BACKGROUND DATA: The widely used and familiar hybrid III dummy has been said to lack biofidelity in the special application of low speed rear impact crashes. Several attempts have been made to modify this dummy with only marginal success. Two completely new dummies have been developed; the BioRID and the RID2. Neither have been tested under real world crash boundary conditions in side-by-side comparisons with live human subjects. METHODS: Volunteer subjects, including a 50th percentile male, a 95th percentile male, and a 50th percentile female, were placed in the driver's seat of a vehicle and subjected to a series of three low speed rear impact crashes each. The RID2 dummy, which is modeled after a 50th percentile male, was placed in the passenger seat in each case. Both subjects and dummy were fully instrumented and acceleration-time histories were recorded. From this data, velocities of the heads and torsos were determined and both were used to calculate the NIC values for both crash test subjects and the RID2. RESULTS: The RID2 demonstrated generally higher head accelerations and NIC values than those of the human subjects. Most of the observed variations might be explained on the basis of differing head restraint geometry, posture, and body size. The RID2 NIC values compared most favorably with those of the 50th percentile male subject. For the whole group, the correlations between RID2 and human subjects did not reach statistical significance. CONCLUSIONS: The small number of test subjects and crash tests limited the statistical power of this pilot study, and the correlation between the RID2 and human subject NIC values were not statistically significant. The overall qualitative performance and biofidelity of the RID2 was reasonable when compared with the male human 50th percentile subject. Its overall higher ranges of head acceleration and calculated NIC values compared to all of the human subjects were generally consistent. This condition could likely be improved by increasing the stiffness of the RID2 neck. Biofidelic validation of the RID2 will require ongoing testing using a larger number of human subjects and varying boundary conditions. The results of this pilot study, while encouraging, should be considered preliminary.

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