Definition/Introduction

According to the Centers for Disease Control and Prevention (CDC), motor vehicle collisions (MVC) in 2013 accounted for over 2 million injuries and more than 32,000 deaths annually in the United States (US) [1]. The National Spinal Cord Injury Statistical Center cited the most common cause of spinal cord injuries (SCI) in the US between the years of 2010 and 2013 was MVCs, accounting for 38% of these injuries.  [2][3]

Mechanism of Injury

Mechanism of injury (MOI) specifically refers to the method by which trauma and its associated forces directly or indirectly impacts the human body.  MOI implies a specific transfer of energy from one source (i.e. the environment) to another (i.e. the human body).

These injury patterns assist in the determination of the extent of an injury and fundamental decision-making process regarding trauma triage guidelines.

Energy transfer from the environment can result from a variety of causes. The intensity of the energy transfer will cause damage to the surrounding tissues, organs, muscles, and other body structures when it exceeds the body’s ability to resist such rapid, forceful energy changes.

According to the Law of Conservation of Energy, “Energy can neither be destroyed or created, but it can change form.” This law goes to the essence of trauma. The kinetic or moving energy must be transferred onto the object impacted. So, if a vehicle is traveling at a high rate of speed when it impacts an object, the energy force can be quadrupled. Spinal injuries may be a result of axial loads.[4][5][6]

Issues of Concern

Terminology

• Kinematics: the actual or potential injuries realized by the human body
• Biomechanics: refers to the actual force or impact imparted on the soft tissues and the body
• Mechanism of Injury: the exact cause of the injury and the implied transference of energy from one body to another (i.e. from the environment to the human body)

All of these concepts ultimately impact trauma patients and their ultimate care. These three principles must guide accurate injury assessments. Kinetic and potential states of energy are fundamental physics-related ideologies which play a vital role in this energy potential.

Energy is in a potential state when at rest and an active state when in motion. Once an object or mass become mobile, the kinetic injury is formed.

These principles can apply to a motor vehicle. The vehicle is in a potential state at rest. This vehicle is now traveling along at a certain speed and strikes a tree or immovable object. The vehicle is in motion, and kinetic energy transfer will play a role through an impact sequence.[7][8]

Impact Sequence

The first impact occurs when an immovable object impacts another object (such as a car vs. tree, pole, another parked vehicle, or guard rail), leading to the passengers being launched forward violently.

The second impact happens next when the car comes to an abrupt stop. The body then impacts with the inside of the car the steering wheel, the windshield, the seatbelt or airbag, or the roadway/environment if ejected.

Lastly, the third insult or impact to the body occurs when the internal structures such as organs and tissues collide with the body cavities. For example, the aorta may tear as it propels into the thoracic cavity or ribs may puncture a lung or spleen. Third impact or insults go to the essence of trauma assessment and determination of injuries based on this violent energy transfer.

Mechanism of injury is vital in determining energy potentials and subsequent, patterns of damage based on the extent of those impacts.[4][9]

Impacts/Injury Patterns

• Frontal and near-side collisions lead to the steering wheel or dashboard impacts with front seat passengers.
• Head, neck, chest and abdominal injuries are expectations.
• Suspect pulmonary contusions and rib fractures with front end damage or near side impact. Rib fractures tend to increase with age. 
• Patient weight and body mass index (BMI) have a positive correlation with likelihood of injury. 
• Improperly worn safety belts or unrestrained individuals can add to the risk of a lower extremity, pelvic, and abdominal trauma. 
• T-bone impacts can cause the occupant seated closest to the point of impact a multitude of problems with any intrusion.
• Intrusion crushes the occupant causing another impact, and if that’s not enough, they get a double hit, by contact with the interior of the car and any personal items in the car.
• T-Bone or lateral impacts associated with aortic or organ shear injuries, as well as fractures of the pelvis, neck, clavicle, and skull on the impact side.
• Rear impacts increase the risk of flexion and extension injuries of the neck and chance fractures of the spine.

Scene Assessment of Damage

A study conducted between 2007 and 2009, concluded that emergency medical services personnel do an excellent job of assessing roll over damage, but intrusion, deformity and safety belt use can be difficult to judge on scene unless an experienced investigator is present. On scene, accurate assessments of damages and its correlation with injury potential are vital to the decision making process regarding transfer to an appropriate tertiary care facility or trauma center. An adverse outcome may occur if transfer to a designated trauma center falls outside the “Golden Hour” of trauma. Trauma center designation involves state and local involvement in the designation process and sole triage criteria required.[10]

Trauma Center Designation

The American College of Surgeons (ACS) plays a valuable role in the evaluation and trauma center verification process. Trauma centers range from Level one designation to a level five designation. Trauma center readiness is key to the allocation of resources involved in a successful treatment plan, resuscitative care, and interprofessional of a complex trauma patient. Trauma care often takes on a multifaceted dimension with cultural, social and community ramifications.

Trauma Triage Guidelines/Allocation of Resources 

In conclusion, the mechanism of injury is the key to the successful creation of trauma triage guidelines through predictability of injury patterns and life-saving interventions. Studying injury patterns and population shifts afford us valuable data to assist in the assuage of circumstances leading up to a motor vehicle crash with prevention techniques, treatment changes as well as legislation focused on improving negative outcome potential and car manufacturer safety guidelines related to airbags and safety belts[11]. 

As we go forth into the future, aging populations will represent a challenge in the allocation of resources both financially and medically for hospitals, long-term care facilities, and communities. Prevention, education, and legislation will have lasting ramifications on the healthcare continuum of the polytraumatized patient, finding their basis in research and evidence-based practice and policy changes. Reimbursement and fund allocation considerations will be a part of this decision-making process.[12]

Clinical Significance

Multi-system trauma involvement is clinically significant in that it should carry a high index of suspicion with "t-bone" collisions. Rollover crashes may cause all of these impacts as mentioned above and violent insults to the body. As the roof intrudes into the passenger compartment, head injuries are probable. If ejected, an impact with the windshield, window, and roadway or object on the road further complicate an already complicated patient. High-speed motor vehicle collisions, like those seen on the interstates, have a high probability of multi-system trauma involvement.[13][14]