Kinematics (kn-mtks) n: The science of pure motion, considered without reference to the matter or objects moved or to the force producing or changing the motion. From the Greek, suffix.1
All injury is related to the interaction of the host and a moving object. That object may be commonplace and tangible, such as a moving vehicle or speeding bullet or more subtle as in the case of the moving particles and molecules involved in injury from heat, blasts, and ionizing radiation. Studying kinematics in relation to trauma uses Newtonian mechanics, the basic laws of physics, and the anatomic and material properties of the human body to explain many of the injuries and injury patterns seen in blunt and penetrating trauma. Injury is related to the energy of the injuring element and the interaction between that element and the victim. Although most patients suffer a unique constellation of injuries with each incident, there are quite definable and understandable energy transfer patterns that result in certain predictable and specific injuries. Knowing the details of a traumatic event may lead the treating physician to further diagnostic efforts to uncover occult but predictable injuries.
This chapter has been organized in a stepwise fashion. First, the basic laws of physics and materials that dictate the interaction between the victim and the injuring element are reviewed. This is followed by a more detailed examination of penetrating and blunt trauma with an effort to dispel some of the common myths about these injury mechanisms. Finally, a synopsis of mechanisms specific to organs and body regions is examined. It is hoped that this will offer the reader a better understanding of specific injury patterns, how they occur, and which injuries may result.
The goal of studying kinematics in trauma is to help us understand how injuries occur. Understanding the biomechanics of injury may help us prevent and treat these injuries in order to optimize outcomes. It is tempting to believe in the finiteness of the understanding of physics and biomechanics, the sense that all there is to know is already known; however, ever-improving technology is making the experimental study and computer modeling of such phenomena more effective. Therefore, continual reassessment is critical in order to continue to maintain relevance in an ever-changing world. Nevertheless, much of the basis of current understanding has been laid down by the great minds of the past whose insight and understanding, though it might have come from rather humble or mundane observances, has absolute relevance as we examine biomechanics today.
James Prescott Joule, a 19th century English brewer and amateur physicist seeking to optimize the energy needs of his brewing operations, stumbled upon what is now known as the first law of thermodynamics or the law of conservation of energy. It states that, in a closed system, energy can be neither ...