Routine - Injury Mechanisms

Guidelines for deciding Injury mechanisms

Review Dates
15 December 2009

Authors

Name Olle Bunketorp

INTACT Partner Sahlgrenska

Introduction

The modified injury mechanism description (InMeDe) is defined by a 5-position code, in which the first and last positions are letters and the second to fourth are integers. This code could be used for most of the entries in the AIS-dictionary, even if this will create some redundancies, as some of the AIS-codes already indicate the type of trauma, i.e. blunt versus penetrating trauma.
The 5-position code represents the following items:

Type of trauma (A – Z)
Proximity of action (local/direct, distant/indirect) (1 – 9)
Character (origin) of action (inertia-related or not) (1 –9)
Joint Injury descriptor (1 – 10)
Type of mechanical action (at the tissue level) (A – Z)

The Joint injury descriptor is used for joint injuries only. The type of mechanical action is used to describe the injury at the “tissue level” or the “microscopic” level, which may be possible only in specific cases.

The type of trauma

The type of trauma describes the type of mechanical, thermal or chemical action, which causes the injury. The values ‘A’ to ‘D’ in the following list represent different types of mechanical action, caused by a contact between the body and a physical structure, which are the most common types in road traffic accidents. The types ‘E’ to ‘G’ represent non-mechanical actions. Blunt trauma means that a penetration into the human body is not present. Penetrating trauma is divided into superficial (limited to the surface area) and deep (not limited to the surface area). Perforating trauma is a specific type of deep penetrating trauma through a greater part of the body, where there is an entrance and an exit wound.

‘A’ Blunt
‘B’ Penetrating, superficial
‘C’ Penetrating, deep
‘D’ Perforating
‘E’ Thermal
‘F’ Chemical
‘G’ Electrical
‘H’ High pressure (explosion)
‘H’ Combination
‘Z’ Unknown

The proximity of action

The proximity of action describes if the injury is located at or very close to the contact surface, or at a distance from the surface.

‘1’ Local/direct (located at the contact surface)
‘2’ Distant/indirect (not located at the contact surface)
‘3’ Combination of local/direct and distant/indirect
‘4’ Other
‘9’ Unknown

A distant/indirect injury can be caused by forces transmitted through the body by rigid or semi-rigid structures on one hand, or by inertia effects on the other. Inertia effects are further specified by the third part of the 5-position code [Character (origin) of action].

"Examples of the proximity of action:"

A knee contact with the dash panel in a frontal impact may cause a fracture of the patella and an injury to the hip joint, like a fracture of the acetabulum or a dislocation. The fracture of the patella should be coded local/direct. The injury to the hip joint should be coded distant/indirect.
The B-pillar in a side impact may cause head injuries to a car occupant [i. e. a vault fracture at the impact point and two contusions of the brain; one beneath the fracture (ipsilateral) and the other on the opposite side of the brain (contralateral, “contre coup” injury)]. The event may also cause a sprain to the cervical spine, even if there is no contact between the B-pillar and the neck. The skull fracture should be coded local/direct, the ipsilateral brain contusion local/direct, the contralateral brain contusion distant/indirect, and the neck sprain distant/indirect.
A spleen or kidney injury (laceration of the capsule and superficial tissue), caused by a direct blow against the side of the trunk where the organ is located, should be coded local/direct.
A spleen or kidney injury (avulsion of the hilus), caused by a great retardation of the trunk of a restrained occupant in a frontal impact, should be coded distant/indirect.

The character (origin) of action

The character (origin) of action specifies if the injury occurred due to forces, transmitted from the impact area to the body parts where the injury is located by inertia effects or not. Non-inertia action is mediated by forces transmitted through structures, between the impact area and the site of injury, without a significant inertia effect (most often due to a movement of rigid or semi-rigid structures - like bones - between the impact point and the site of injury). Inertia action is mediated by a forces acting on a specific part of the body, which cause a change of velocity (acceleration) of another part of the body at a distance from the impact area, without a significant rigid mechanical coupling.

‘1’ Non-inertia effect
‘2’ Inertia effect
‘3’ Combination of non-inertia and inertia effects
‘8’ Not applicable
‘9’ Unknown

Many injuries to visceral organs are caused by a combination of local/direct (external) forces and distant/indirect (internal) forces. Injuries caused by relative organ/body motions, due to contact action should be coded as a combination of non-inertia and inertia effect.

"Examples of the character (origin) of action:"

A vehicle is hit from the left side. The driver sustains an anterior dislocation of the humeral head caused by intruding structures of the door. Non-inertia should be coded.
The same driver sustains a cervical neck injury without a head or neck impact. Inertia should be coded.
A spleen or kidney injury (avulsion of the hilus) is caused by a great retardation of the trunk of a restrained occupant in a frontal impact. Inertia should be coded.
A car driver injured in a frontal impact sustains displaced rib fractures and liver lacerations, both on the upper and the lower surfaces the liver. The liver injuries on the upper surface may be caused by the rib fractures and the lacerations on the lower surface by inertia forces. The upper liver injury could be coded as a non-inertia effect and the lower injury as an inertia effect. A combination could also be coded.

The joint injury descriptor

The joint injury descriptor is used for joint injuries only. It defines the mode, by which an exaggerated or non-physiological movement of a joint causes injuries. This part of the code could preferably be used for joints in the extremities, like shoulder, elbow, finger, hip, knee, and ankle. It is not supposed to be used for joints in the vertebral column, even if this would be possible in some cases.

‘1’ Hyperextension
‘2’ Hyperflexion
‘3’ Hypertranslation
‘4’ Hypertorsion (including supination & pronation as sub-classifications)
‘5’ Hyperadduction
‘6’ Hyperabduction
‘7’ Combinations of ‘1’ – ‘6’
‘8’ Not applicable
‘9’ Unknown
‘10’ Joint injury without non-physiological movement

The code ‘10’ is supposed to be used for intra-articular fractures.

"Examples of the joint injury descriptor:"

An unbelted occupant hits the lower leg 5 cm below the knee joint against the dash panel in a frontal impact. A rupture of the posterior crucial ligament is sustained. Hypertranslation should be coded (“Dash-board injury”).
A car occupant hits the shoulder against the B-pillar, when the car is impacted from the side. The humeral head dislocates ventrally. Hypertranslation is coded.
A cyclist falls to the ground and tries to protect himself with a stretched arm. The elbow joint is overstretched, the ventral part of the capsule ruptures, and the Ulna dislocates in the posterior direction relative Humerus. Combination is coded (hyperextension and hypertranslation).
A Monteggia injury (combination of Ulna fracture and dislocation of the Radial head in the elbow joint) should be coded as a hypertranslation, as the joint injury only includes the Radius. The Ulna fracture should be coded separately. The same principle should be used for the Galeazzi injury (a fracture of the Radius and a dislocation of the distal Radio-Ulnar joint).

The type of mechanical action

The type of mechanical action preferably describes the mode, by which a force acts at the tissue (“microscopic”) level. Probably, this part of the code can be used only for specific injuries. In many cases, several modes are active, and if so, the most relevant type of mode should be coded. As this part of the code requires a detailed understanding of the injury process, it might be coded only for some injuries.

‘A’ Compression
‘B’ Tension
‘C’ Shear
‘D’ Bending
‘E’ Twisting
‘F’ Shock wave effect
‘G’ Vacuum effect (contre coup)
‘H’ Combination of mechanical actions
‘Y’ Not applicable
‘Z’ Unknown

The modified injury mechanism description (IMeD) has been discussed and exercised for specific cases (not only from the INTACT project) during four meetings in phase III. Representatives from Autoliv, Volvo Cars, Saab Automobile, and Sahlgrenska Academy have been asked about the usefulness, reliability, and validity of the proposed method. From the beginning, some representatives were sceptical to the method, because of some unclear definitions and difficulties to distinguish between specific items. After the revision was made in the end of phase III a good agreement was achieved and the method was accepted.

"Examples of the type of mechanical action:"

A contusion of the skin caused by a blunt impact without excoriation is coded as compression.
A cut wound is coded as shear.
An avulsion of the brachial plexus in a motorcyclist who hits the shoulder against a pole is coded as tension.
A vertebral burst fracture is coded as compression.
A vertebral wedge fracture is coded as bending.
A posterior vertebral ligament rupture, without a coincident ventral ligament rupture, is coded as bending.
An anterior dislocation of an intervertebral joint (facet joint) is coded as bending.
A cranio-cervical separation is coded as tension.
An excoriation is coded as shear.
A rupture of the medial ligament of the knee in a pedestrian, who is hit by a car bumper at the lateral side of the knee precisely at the tibio-femural joint is coded as bending.
A rupture of the medial ligament of the knee in a pedestrian who is hit by a car bumper at the lateral side of the knee at a distance from the tibio-femural joint is coded as a combination (translation & bending).
A spiral fracture of the tibia in a person, who has rotated the body, when the foot is prevented to rotate during the injurious event, is coded as twisting.
Shock wave effect is only applicable for injuries caused by explosions.
Vacuum effect is only applicable for specific brain injuries.
Degloving injuries are coded as combination.
DAI (axone or white matter injury) in many cases is the result of angular accelerations, causing shear stresses. In that case shear is coded.