July 2002

Whiplash Mechanics Update - Low Impact

by Daniel J. Murphy, DC, FACO

             Dan Murphy graduated magna cum laude from Western States Chiropractic College in 1978, and has more than 20 years of practice experience. He received Diplomat status in Chiropractic Orthopedics in 1986. Since 1982, Dr. Murphy has served part-time as undergraduate faculty at Life Chiropractic College West, currently teaching classes to seniors in the management of spinal disorders.

            Dr. Murphy is on the post-graduate faculty of several chiropractic colleges. His post-graduate continuing education classes include “Whiplash and Spinal Trauma” and “Pain Neurology.” Dr. Murphy is the coordinator of a year-long certification program in “Chiropractic Spinal Trauma,” now (2000) in its twelfth year of being offered. This year, the program is being offered through the International Chiropractors Association of California. He has taught more than 700 post-graduate continuing education seminars.

            Dr. Murphy is a contributing author to the book Motor Vehicle Collision Injuries, published by Aspen, 1996; and to the book Pediatric Chiropractic, published by Williams & Wilkins, 1998. He writes a

quarterly column in the Journal of Clinical Chiropractic.

            In 1987, 1991 and 1995 Dr. Murphy received the Post-graduate Educator of the Year award, given by the International Chiropractic Association.

            In 1997, he received The Carl S. Cleveland, Jr., Educator of the Year award, given by the International Chiropractic Association of California.

 

 

Two recent studies add to the understanding of whiplash injury, the prognosis for recovery, and minimum or no vehicle damage collisions, and are reviewed below:

 

Derivation of a clinical decision rule for whiplash associated disorders among individuals involved in rear-end collisions

 

            Accident Analysis & Prevention; Volume 34, Issue 4; July 2002; Pages 531-539, Lisa Hartling, William Pickett and Robert J. Brison

            This is a prospective study that was used to:

            (1) quantify potential risk factors for whiplash associated disorder

following a rear-end motor vehicle collision; and

            (2) develop a simple clinical decision rule for the early identification

of patients at risk for long-term whiplash associated disorder.

            The authors note that whiplash associated disorders (WAD) injuries most frequently occur among occupants that are in rear-end motor vehicle collisions (MVCs).

            The study involved 353 adults involved in rear-end collisions in

Kingston, Ontario, Canada, who were followed up to two years post-collision. This is important, because Ontario has a no-fault insurance program that makes it difficult to receive compensation for pain and suffering.  This minimizes the chances of study error introduced by compensation and litigation.

            This study established that there are three factors associated with probability of suffering from chronic whiplash symptoms.  They are:

            (1)       Increased age (over age 51)

            (2)       Number of initial physical symptoms (3 - 9)

            (3)       Early development of the following symptoms: upper back pain, upper extremity numbness or weakness, or disturbances in vision.

            This study confirmed that a percentage of those injured in a whiplash trauma will suffer from chronic symptoms at six months.  In this study, the percentage was 35.3%.

            The strongest predictors of WAD at six months were age, the number of symptoms experienced early on and the actual individual symptoms. There was a significant trend between the number of symptoms reported early on and increased risk for WAD at six months. The following symptoms were reported at initial interview following MVC:

            • Neck Pain

            • Shoulder Pain

            • Upper Back Pain

            • Lower Back Pain

            • Headaches

            • Neck Stiffness

            • ‑Upper Extremity Numbness or Weakness

            • Dizziness

            • Nausea/Vomiting

            • Vision Disturbances

            • Difficulty Sleeping

            • Fatigue

            • Anxiety

            • Difficulty Concentrating

            • Depression

            Age was a highly significant predictor of WAD at six months. The most important risk factors for WAD at six months in this analysis was age (over age 51).  The presence of age as a risk factor makes sense because both the severity of injury would be greater and recovery from it would be slower with increasing age.

            A simple clinical decision rule that requires asking up to three basic questions of each patient was derived and would have identified 91.5% of persistent whiplash associated disorder cases in this study. These three basic questions were asked at two weeks post-injury used, as follows:

 

   (1)   (A)  Did the collision occur at a location other than an intersection in the city?

                        (B)         Have you experienced upper back pain since the collision?

            If patients answer yes to both of these questions, they are considered

high risk for WAD at six months.

            If patients answer no to both of these questions, they are asked the following additional question:

   (2)      Do you still experience neck pain (two weeks post-injury)?

            Patients answering no are considered low risk, while those answering yes are considered high risk.

            Those patients answering yes to one of questions (1)(A)(B) above are

asked the following additional question:

   (3)      Do you still experience shoulder pain (2 weeks post-injury)?

            Those responding no are considered low risk, while those answering yes

are considered high risk.

            In this cohort, application of the rule identified 92% of those who experienced persistent WAD symptoms at six months.

            Importantly, symptoms, as opposed to crash and personal characteristics, were the most consistent predictors of persistent WAD.

            In rear-end collisions, there is a low threshold of impact for the occurrence of WAD symptoms, and that the presence or absence of these symptoms is only modestly affected by variations in the crash circumstances.

            Factors that did not increase the probability of chronic WAD at six

months were: Fewer than two symptoms, age 18-30, neck stiffness, shoulder pain, and low back pain.

            The authors clearly show that in this study, the following were not predictive of WAD at six months.  This means that these factors did not increase or reduce the chances of suffering chronic WAD at six months:

            • Position in Vehicle

            • Road Conditions (dry, wet, icy)

            • Prepared for Crash

            • ‑Head Position (straight, looking in rearview mirror, or turned)

            • Seatbelt Use

            • Head Restraint Present

            • ‑The Size of the Vehicle That Hit Yours (bigger, smaller, same)

            • ‑Posted Speed Limit (This means that at low speeds, just as many persons suffered chronic WAD at six months as persons who apparently recovered and did not suffer chronic WAD at six months).

 

KEY POINTS FROM DAN MURPHY

   (1)      In this study of 334 individuals injured in a rear-end MVC, 35%

suffered chronic WAD, while apparently 65% had recovered at 6 months

post-injury.

   (2)      The following initial presenting factors and symptoms are associated with a significant increased probability of suffering chronic WAD at six months post-injury:

            (A)       Three or more symptoms

            (B)       Older than age 51

            (C)       Upper Back pain                               (D)       Upper Extremity Numbness or Weakness

            (E)       Visual Disturbance

            (F)       Nausea and/or Vomiting

   (3)   In rear-end collisions, there is a low thresholds of impact to cause symptoms.

   (4)    Patient symptoms are more important predictors of chronic WAD than are crash characteristics.

   (5)    Patient symptoms are not related to crash characteristics.

   (6)    Older patients sustain greater injury and recover poorly.

 

Delta-V, Spinal Trauma, and the Myth of the Minimal Damage Accident

Journal Of Whiplash & Related Disorders Vol. 1, No, 1, 2002, Scott D. Batterman and Steven C. Batterman

            These authors rigorously analyze the engineering mechanics of a car to car collision when there is little or no crush damage to either vehicle. They show that in a no damage accident, the struck or target vehicle can obtain a delta-v of 10 MPH or greater, which is well into an injury producing range.

            The authors also dispel the myth that a minimal or no damage vehicle to vehicle collision implies that the delta-v of the target vehicle has to be 5 MPH or less.  They note that the literature that refutes whiplash injury in low speed accidents is “scientifically and methodologically flawed which renders many of the literature conclusions invalid.”

            “Many authors, researchers and testifying experts in the fields of accident reconstruction and biomechanics utilize the concept of delta-v to assess the injury producing potential of a crash.”                   “Delta-v is the change in velocity that a vehicle undergoes in an accident, and is intimately related to the vehicle accelerations (decelerations) in a crash.”

            “However, in low to moderate delta-v accidents, with zero or minimal crush damage to the vehicles, delta-v is often erroneously calculated. An incorrect determination of delta-v can then ultimately affect an opinion on injury causation.” These authors present a method to determine vehicle delta-v’s and the impact speed of the striking vehicle in car to car collision where there is little or no vehicle crush damage.

            Although the authors use the well-known EDCRASH computer program, they caution that the EDCRASH program is flawed in zero or minimal crush damage collisions, and a “100% error in the vehicle delta-v’s can occur.” Their analysis shows that the vehicle delta in zero or minimal crush damage collisions can be 10 MPH or greater, “which is well into an injury producing range.” They state that “the analysis emphasizes that in low speed accidents, which are essentially elastic in nature with little or no energy dissipated by crush, neglecting the vehicle restitution phase of the collision results in serious underestimates to the vehicle delta-v and the injury producing potential of the accident.”

            These authors “dispel the myth that a minimal or no damage vehicle to vehicle collision implies that the delta-v of the target vehicle has to be 5 MPH or less,” stating “this is a totally incorrect assertion sometimes promulgated by accident reconstruction and biomechanics experts who are unfamiliar with the proper analysis of a zero damage, elastic collision where energy is conserved and no permanent crush  occurs.”

            The authors review the actual collisions of a 3500 pound bullet vehicle impacting the rear bumper of a stationary 2500 pound target vehicle in two different tests. In the first test, the impact speed of the bullet vehicle is 4 MPH and 9 MPH, resulting in a delta-v of the target vehicle of 5 MPH and 11 MPH. In both tests there was no permanent damage to the bumper system of either vehicle, i.e., “the collisions were elastic and are representative of vehicle responses in a zero or minimal damage accident.”

            The authors note that an elastic collision means that there is no

permanent damage sustained by either vehicle although the bumper systems do compress and then rebound during the restitution phase.  They note that there are three major flaws in the EDCRASH computer program, the most serious being the delta-v’s derived are not the total delta-v’s of the vehicle in the crash because EDCRASH does not consider the elastic rebound phase of the vehicles that follows bumper deformation. This oversight is critical in evaluating the delta-v’s of zero or minimal crush damage collisions.

            The authors use a lot of math and examples to show that actual

delta-v’s from zero or minimal crush damage collisions are typically

double those calculated by the EDCRASH program.  This often puts these zero or minimal crush damage collisions into the injury producing range. The authors “emphasize that neglecting the elasticity of the bumper systems and the restitution phase of the crash will result in a very serious underestimation of delta-v” of the struck vehicle “in a low speed collision.” They state that “If a reconstructionist or biomechanician accepted the EDCRASH results for delta-v a 100% error will occur.” “It is critical in the analysis of low to moderate delta-v accidents to include the elastic restitution phase of the crash in order to properly calculate the total vehicle delta-v’s.”

            The authors note that depending on the weight ratio of the vehicles and the bumper design, in a no damage collision, the struck vehicle’s delta-v’s “can be in excess of 10 MPH without any permanent crush damage to either vehicle.” They state that “It is totally incorrect, and a myth, if a reconstructionist or biornechmician concludes that no damage means that the delta-v must be less than five MPH.”

 

KEY POINTS FROM DAN MURPHY

            (1)       The apparent standard used to assess the injury producing potential of a crash is the concept of delta-v.

            (2)       The delta-v is often assessed by using the EDCRASH computer system.

            (3)       However, the EDCRASH program is flawed in zero or minimal crush damage collisions.

            (4)       Specifically, the well-known EDCRASH computer program can

underestimate  the delta-v by 100%, meaning that the actual delta v was

twice that assessed by the computer program.

            (5)       This underestimate of the actual delta-v means that the delta-v is often well into an injury producing range, even though it was a zero or minimal crush damage collisions.

            (6)       The vehicle delta-v in zero or minimal crush damage collisions can be 10 MPH or greater, which is well into an injury producing range.

            (7)       The basic flaw in the EDCRASH assessment is that zero or minimal crush damage collisions are elastic (meaning no damage to either

vehicle) resulting in little or no energy dissipated by crush, even though the bumper systems do compress and then rebound during the restitution phase.

            (8)       Neglecting the elasticity of the bumper systems results in a very

serious underestimation of delta-v of the struck vehicle in a low speed collision.

            (9)       Many accident reconstruction and biomechanics experts are unfamiliar with the proper analysis of a zero damage elastic collision where energy is conserved and no permanent crush occurs.

            (10)     Vehicle damage cannot be properly assessed by looking at vehicle

photographs, but requires careful vehicle inspections and measurements.

            (11)     Literature that proclaims that one cannot sustain whiplash injury

in low speed accidents is scientifically and methodologically flawed and invalid.