Abstract
Motor vehicle impacts result in energy being transferred between the involved vehicles and subsequently to occupants within those vehicles. Similarly, when outside of a vehicle, humans constantly encounter energy transfers within their surrounding environment, inducing internal reactions within their bodies. A common method used by biomechanical engineers is to compare the exposure in a particular event to the general exposures during various activities of daily living (ADL). Such comparisons can be in terms of general inertial loading, such as accelerations, or in terms of specific joint loading (i.e., forces and/or moments). Regardless, to be comparable from the biomechanics standpoint, there needs to be sufficient correlation between the duration, magnitude and/or direction of acceleration or load application. An area of forensic science where such comparisons are common is when a biomechanical engineer is assessing an occupant’s exposure to a minor vehicle accident. In many of these events, the accelerations and loading present are found to be well below any published and accepted injury parameters and to be comparable to published exposures to various ADLs. In this study, spinal loading reported in the published literature during spinal manipulation therapy (SMT) is compared to published spinal exposures in minor vehicle accidents.
Extensive research and associated publications regarding both accident reconstruction and biomechanical analyses have studied minor motor vehicle accidents. This current work does not attempt to provide a review of all the volunteer or surrogate studies of occupant exposures available. Instead, this work is the initial phase of a larger study to build on the body of literature that provides quantitative comparisons of human exposures to relatively minor real-world accidents and a wide variety of ADLs, including exposures during the application of common clinical therapies such as SMT.
There is a relative lack of studies that quantify the loads applied to patients or develop within patients during various SMT inputs. However, the studies found that do provide quantification suggest that the spinal loading duration, magnitude and direction are similar to that shown to exist in many minor vehicle accidents. For example, Forand [4] reported that SMT inputs applied forces up to 1,000 Newtons (N) to a particular target site (i.e., disc) within a time duration of about 20 to 170 milliseconds (ms). By contrast, spinal loading durations in minor impacts have been shown in the biomechanics literature [9, 11 and 12] and publicly available testing [18] to have similar durations (50 to 250 ms) with distributed neck forces typically less than 500 N. This study has found that like many other ADLs, the spinal loading present during SMT may be comparable to that present in many minor vehicle impacts due to the similar duration, magnitude and direction of the joint loads.
