In the blink of an eye a routine trip to the grocery store, taking the kids to school, or going to work can turn into a deadly situation. Each day thousands of lives are changed by motor vehicle accidents (MVA).
The death rate per miles driven is on the decrease thanks in part to the development of an Emergency Medical Service (EMS) system. This system provides on site stabilization and supportive transportation to emergency equipped hospitals. Many people who would have died during an accident are now being cared for and safely transported by ambulance or helicopter lifelines. The odds of surviving an automobile accident have never been better.
In addition, the development of safer cars and improved safety systems adds to the increased likelihood of crash survival. To meet consumer demands, new car manufacturers have gone to great extremes to redesign automobiles to save lives. Without a doubt the multi-billion dollar investment by the government and private industry has paid off in lives spared.
Safer designs and efficient EMS systems have also changed society. Car accident victims who may not have previously survived are now living with soft tissue injuries. Clinicians are expected to correctly diagnose and treat these conditions and help restore a pain free quality of life. This quality must try to mimic the pre-accident condition of the survivors. In essence, issues change from purely medical to medico-legal.
The diagnosis and treatment of soft tissue trauma as a result of MVAs is an area in which all clinicians find common ground. Injury mechanism and injury patterns are consistent with the involved type of tissues. In other words, tissues respond according to the energy transmitted and their physiological make up rather than the educational degree of the treating clinician. It’s imperative that clinicians of all disciplines understand these common patterns and predictable human tissue responses to better serve injured patients and improve communication with third parties.
Thresholds for Soft Tissue Injuries
There are no set thresholds for human hard or soft tissues under which injuries never exist or above which injuries always exist. While parameters can be estimated, all injuries to individuals are anecdotal and individual responses will vary greatly according to numerous factors. According to a study by Seigmeund, et al.1 peak head acceleration varied almost 100 percent with the same subject, same seats, same vehicles, and same vehicular Delta V (5 mph Delta V) impact. As a result, it is impossible to determine individual injury potential strictly by estimating the impact velocities of the involved vehicles. The cost of car repair or amount of damage to the components of automobiles cannot be used to determine individual human response. While logic would dictate that there is more injury potential to the occupants at a 90 mph closing speed as compared to a 10 mph closing speed, the personal occupant injury response must be measured as it is found. In fact, each automobile collision categorically consists of three separate collisions.
Collision I — Vehicle to Vehicle
Determining closing speed estimates and injury potential to vehicles can be fairly accurate. A forensic engineer may be able to measure, objectively demonstrate damage, and draw conclusions regarding vehicle impact velocity. Still one must be careful when correlating data extracted from a controlled crash test to a non-staged automobile accident. Slight alterations in impact velocity, angle of impact, and a myriad of other variables leads to wide variations in vehicle damage, forces generated, and even cost of repair. Individual crash tests are considered entities unto themselves and often cannot be accurately compared. The effects of Collision I cannot be used to predict the effects of Collisions II and III.
Collision II — Occupant to Vehicle
The resulting motion of the occupants can only be demonstrated in strict test conditions utilizing high-speed film and carefully located cameras and sensors. Occupant reaction and motion are often not accurately reproducible even under the strictest of conditions and results vary greatly from occupant to occupant even within the same crash test. There has never been a published study that accurately demonstrates human motion in automobile collisions outside of strictly controlled tests under artificial conditions. Data gathered from staged crash tests indicates approximate guidelines only, not definitive answers, and should never be used to predict or determine individual injuries.
Collision III — Human Body Parts
This collision is the most overlooked aspect of automobile accidents but is the most important in actual injuries. This aspect of the collision and the resulting damage is determined much the same way as I and II. While the first two collisions are measured by forensic engineers and computerized devices, medical personnel measure the third collision. In the same manner as forensic engineers, the clinicians measure, objectify, and draw conclusions from human tissue, which they are trained to diagnose and treat. Their job is much the same as the crash test engineers only they are trained to interpret human tissue instead of man-made materials. Just as medical personnel cannot draw conclusions about the amount of damage to a car using human tissue damage or the cost and time to repair (heal), forensic engineers, insurance adjustors, or attorneys cannot draw conclusions regarding human tissue trauma based upon damage or the cost of repair to automobile components such as bumpers. On the other hand, clinicians cannot look at individual injuries and make generalizations about other accidents or even about injuries to other occupants involved in the same accident. Injury patterns to humans do exist in the same manner as injury patterns (damage) to automobiles but general assumptions to predict human injury or lack thereof cannot be assumed.
Factors Which May Influence Individual Injuries
Occupant position at time of impact is one of the most critical aspects determining human injury potential. Small variations of occupant positioning can result in large increases of impact forces transmitted to the injured areas.2
The position in which crash test dummies are seated is not often the position in which humans feel comfortable while driving. Humans change positions almost constantly when seated for periods of time to help distribute loads. Factors that influence injury potential to a given area can change almost instantly. Individual vulnerability at the precise moment of energy transfer during impact (.1-.2 sec.) is immeasurable in mathematical terms and can only be ascertained after the fact by symptomatic complaints and clinical assessment.