Arm and leg injuries have been divided into three main types: -
These injuries can occur separately or in any combination. Each however has a different injury mechanism although they can occur within the same impact event.
Skeletal Fractures
Fracture Types And Impact Mechanisms
Skeletal fractures can occur from both direct impact and indirect loading and are caused when the load, whether compression, tension or shear, in a localised part of the bone exceeds the strength of the bone. The severity of the fracture will depend on the energy associated with the impact or loading, and the direction and location of the load in the bone. There are several methods for classifying different types of fracture, and recording the severity of the fracture, which are dependent on the treatment and long-term prognosis. Figure 20 and Table 37 (Appendix 1), shows attempts to summarise the different fracture classifications associated with the loading mechanism and severity level based on the AIS system. There are four main fracture mechanisms: -
Figure 20 Shows Main Types And Locations Of Direct And Indirect Fractures
In the rail vehicle impact environment only direct impact or indirect loading fracture mechanisms will occur. Firstly, direct impact blows as a flailing arm or leg impacts a blunt object. Secondly, indirect loading produced by inertia of the occupants own mass, either as a result of impact, for example femur fracture following knee impact into a seat back in unidirectional seating, or attempting to brace while falling.
The severity of fracture is classified by the type and number of fracture surfaces, which is dependent on the energy of the impact. Non-comminuted or single surface fractures are produced by low energy impacts, typical falling and bracing injuries, while comminuted or multiple surface fractures a rise from high energy impacts such as pedestrian to vehicle impacts. The higher the energy, the higher the number of fracture surfaces, with high velocity bullets literally shattering the bone. In the rail vehicle environment the majority of fractures will be from low energy indirect bracing injuries to medium energy impacts, such as the direct impact of a flailing arm on a rigid blunt object.
In low energy impacts the fracture can occur with no displacement along the fracture surface with a very high probability of a fast recovery, with no surgical intervention or long-term disabilities. With medium and high energy impacts with both non-comminuted and comminuted fractures, displacement along the fracture surface(s) is inevitable requiring moving of the bones to ensure correct setting. With comminuted fractures surgical intervention with the using of pins and plates to correctly locate the parts of the fractured bone is essential, which increases the time of recovery and probability of long-term disability.
Compounding the severity of the actual bone fracture is the amount of soft tissue damage associated with it. Low energy fractures would be associated with only minor lacerations (cuts) and contusions (bruising) with the bone unexposed, and this is classified as a closed fracture. With medium and high energy impacts the fractured portions of the bone are often forced through the muscle and skin and exposed, and so is classified as an open fracture. With the increasing amount of bone exposed there is a corresponding increase in the probability of contamination of the wound, with consequences for increased time of recovery and long-term disfigurement and disability.
The fractures occur both at Diaphysis part of the bone, the hard ‘cortical’ bone, away from the articular or joint surfaces, or at the Epiphysis directly through the articular surface or immediately behind it. Fractures in the Epiphysis tend to be more complicated with much poorer prognosis due to the damage to the load bearing surface and bone growth areas, leading to long-term joint problems and growth abnormalities. These are more difficult to classify in terms of loading mechanisms, but could be more attributed to axial or angled indirect compression loading of the joint from low to high energies. Pylon or longitudinal fracture of the lower tibia is a good example caused by high axial loading of the ankle produced in falling vertically on to a rigid surface (parachuting), or by footwell intrusion in vehicle frontal accidents.
Different types of fracture associated with loading mechanisms and injury severity, in terms of fracture displacement and bone exposure are shown in Appendix 1, Table 37.
There are two major mechanisms, which cause non-skeletal or soft tissue injuries.
Although both are rarely life threatening they can seriously effect the ability of an occupant to egress the rail vehicle and can have long term disabilities.
Severe lacerations are produced by impacts with sharp objects that penetrate the skin and blunt objects that tear the skin. Sharp object lacerations can potentially sever major arteries and veins, which could lead to high blood loss, ligaments and tendons reducing mobility. Long-term disfigurement and disability is another major problem. Broken glass and sharp edges from fractured rail vehicle internal fixtures potentially being the cause of most of these injuries.
Skin tearing from blunt object impacts can expose large areas of flesh with consequent blood loss and with potential long-term disfigurement.
High loads and excessive joint displacements and rotations are produced either from direct impacts, knee dislocation from impact with lower seat backs, or by occupants bracing themselves to avoid impacts, shoulder dislocations during stumbling. These could seriously affect the occupants ability of egress. Full or partial joint dislocation can immediately reduce
the occupants mobility and is often associated with joint cartilage and ligament damage, which has long-term consequences especially in complex joints such as the wrist and ankle. However, these injuries are very difficult to predict and, except for full joint dislocations, may not be apparent immediately after the incident.
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Dr. A.R. Payne |
S. Patel |
© MIRA 2001 |
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Project 427519 |
Version 1.1 |