Mechanisms of Ankle and Knee Joint Injuries in Traffic Accidents

2.7.1. Car-to-Pedestrian Accidents

For many years, the efforts of researchers and car companies have been focused on reducing the degree of trauma in traffic-accident victims (11,29). Changes in bumper

Fig. 22. The pattern of hip dislocation in a frontal collision depends on the initial sitting position of vehicle occupants. See Color Plate III, following page 240.

construction and the distribution of energy on impact over a larger surface have decreased the number of lower-extremity fractures in pedestrians hit by cars. Unfortunately, the redistribution of impact energy paradoxically has increased the risk of injury to joint structures, and ligament injuries have resulted in disability more often than even multisite diaphyseal fractures. By contrast, the low, protruding, and inflexible bumpers in older vehicles frequently caused fractures in the shins; this prevented the knee joint from absorbing the impact energy and, thus, protected it from the effects of trauma. In terms of forensics, however, the changes made in modern vehicles have increased the ability of investigators to reconstruct the accident based on the mechanism of trauma (7,24).

The presence of ankle- or knee-joint injuries indicates that the pedestrian was hit while in an erect position, (27) as such injuries—especially those caused by the compression mechanism and resulting in bone bruises in the central parts of tibial and femoral condyles—occur only when the limb is loaded by body mass. When the victim is run over while in the recumbent position, the injuries are noncharacteristic and usually occur only when the wheel rolls directly over the ankle or knee. Running over of the pedestrian may cause external dislocations of the femoral head outside the acetabulum; such hip-related injuries are not normally observed in victims who were standing erect when hit (7).

When a standing pedestrian is hit by a passenger car, protruding elements of the car hit much lower than the victim's center of gravity, causing the victim's upper body to rotate in the direction opposite that of the speed vector of the car. One or both ankles (depending on whether the victim was standing still or walking when hit) may twist along the rotation axis, causing the body to spread over the hood, in which case the thigh and hip regions are hit first, followed by the trunk and head (4). In this hits caused by small- or medium-sized passenger cars of a trapezoidal or pontoon body, the site of primary impact is usually located in the middle or proximal part of the shins (medium-height victims). Large passenger cars and delivery vans hit at the level of the knee, and trucks with a high bumper may hit the proximal thigh or hip girdle (such a "high" impact is likely to knock the pedestrian down, which increases the risk of a secondary runover). During the first phase of the accident, the victim's body "adjusts" to the shape of the front of the vehicle, and the place of force application determines the type of pathological dislocation that will occur in the joint structures and consequently the mechanism of ankle and knee-joint injuries. On the other hand, injuries to proximal femoral epiphyses (the greater trochanter area) are good markers of an ipsilateral hit while the victim was in the erect position, no matter what the shape of body of the car (7,26).

In contrast to passenger cars, trucks with a high bumper location often cause a reversed complex of injuries in both the knee and ankle joints (the lever principle; compare Fig. 23 and Table 3). Delivery vans, light trucks, sport utility vehicles, pickups, and large passenger cars usually cause a reversed complex of injuries in ankle joints only. Very low hits at the level of distal shin parts resulting in reversed injury complexes in the knee are rare (e.g., they are seen in tall victims and with intensive braking of the vehicles before the accident; particularly those vehicles with low floor and a wedge-shaped body). In short victims, the passenger-car hits resemble the delivery-van hits whereas in children they resemble the truck hits (7,24,26,27).

Therefore, the mechanism of knee-joint injuries should always be considered within the context of every circumstance of the accident and the shape of car body.

Fig. 23. The most common mechanisms of ankle and knee-joint injuries and the mechanisms of shoe-sole scratches in pedestrian hits caused by small passenger cars and trucks with a high bumper location. Compression forces (C); tension forces (T).

Table 3

The Most Common Mechanisms of Ankle- and Knee-Joint Injury in Pedestrians Hit by Vehicles With Various Vehicular Body Shapes

Table 3

The Most Common Mechanisms of Ankle- and Knee-Joint Injury in Pedestrians Hit by Vehicles With Various Vehicular Body Shapes

Joint

Vehicle Type

Impact Height

Mechanisms of Injury According to Hit Direction

Anterior

Posterior

Lateral

Medial

Ankle

Passenger

shin

dorsal flexion

plantar flexion

pronation

supination

Van**

knee

plantar flexion

dorsal flexion

supination

pronation

Truck

thigh

plantar flexion

dorsal flexion

supination

pronation

Knee

Passenger

shin

hyperextension

translocation*

valgus flexion

varus flexion

Van**

knee

hyperextension

-

valgus flexion

varus flexion

Truck

thigh

-

hyperextension

varus flexion

valgus flexion

*isolated injury to the ACL due to anterior translocation of the proximal tibial epiphysis in relation to the femoral condyles.

**also sport utility vehicles, pickups, or large passenger cars (non breaking). ACL, anterior cruciate ligament.

*isolated injury to the ACL due to anterior translocation of the proximal tibial epiphysis in relation to the femoral condyles.

**also sport utility vehicles, pickups, or large passenger cars (non breaking). ACL, anterior cruciate ligament.

Fig. 24. The shoe-sole scratches indicate the impact direction and walking phase of the pedestrian.

However, when the impact direction is explicitly defined (e.g., on the basis of soft-tissue injuries), the findings in knee- and ankle-joint injuries may be used to determine the type of vehicle that was involved, particularly in hit-and-run accidents.

The mechanism of ankle-joint injury often correlates with scratches on the soles of the shoes (28) near the edge of the shoe. When a small passenger car is involved, these scratches are usually found on the side ipsilateral to the side of the vehicle that made contact with the body; when a truck with a high bumper is involved, they are usually found on the side of the shoe that is contralateral to the side of the body that was struck. In some cases, the location of these scratches can be used to determine the walking phase during which the individual was struck (Fig. 24).

In oblique pedestrian hits, mixed injury complexes are likely to occur in the region of ankle and knee joints, e.g., during dorsal flexion with the pronation component and during hyperextension with the valgus-flexion component in passenger-car anterolateral hits (24,27). In corner hits (Fig. 25) or sideswipes, rotation may occur within the ankle joint, e.g., a corner of the car may rub against the lateral side of a pedestrian walking along the road, resulting in a pronation-rotation trimalleolar fracture (Fig. 19, part 3).

2.7.2. Car-to-Bicycle Accidents

Ankle- and knee-joint injuries are only slightly less common in cyclists than in pedestrians. This indicates that the pressure exerted on the bicycle pedals by the legs plays a role similar to that of body mass loading in the extremities in pedestrians.

In passenger-car-cyclist hits, the mechanisms involved in ankle-joint injuries (in back and lateral hits) are the same as those in similar pedestrian groups. Injuries to the knee joint are identical to those in pedestrians in lateral hits, only; in front and back hits, passenger cars cause primarily "reversed" injury complexes (Fig. 26). For example, hyperextension of the knee is a typical marker of a back hit in cyclists. Passenger cars usually do not cause knee joint injuries in front hits of cyclists, while almost all such hits cause hyperextension-related injuries in pedestrians (similar to cyclists hit in the front by a truck) (26).

The relations described above may be used to distinguish the means by which a cyclist was hit vs a pedestrian walking with a bike. Bruises in the subcutaneous tissue beneath the medial aspects of the proximal femur (and the scrotal sac in men; Fig. 27) may be used for this purpose, since they are more common in cyclists (due to contact with the saddle) than in pedestrians (26). In oblique passenger car-to-bicycle hits (usually at an angle of <30°) the cyclist's thighs and buttocks rotate the saddle in the direction opposite to the site of impact (Fig. 28), whereas in a perpendicular hit, the saddle rotates towards the striking vehicle (Fig. 29) (30).

2.7.3. Inside-Car Casualties

Injuries to ankle joints and foot bones are common in car occupants and develop most often during front hits primarily as a result of floor intrusion (equally common in drivers and passengers), contact with pedals, and the foot becoming trapped under pedals (in drivers only, and more frequently in the right than in the left leg). The imprints of control pedals on the soles of shoes may be used to determine the circumstances responsible for injuries and to identify the driver. The mechanism of ankle-joint injuries consists of axial loading with simultaneous rapid dorsal flexion, supination, or pronation of the foot (31).

Knee-joint injuries result from contact between the legs and the dashboard. Any of four different mechanisms may be involved (Fig. 30), based on the shape of the passenger compartment, the position of the passenger's seat, and the passenger's height, as well as whether the victim was belted or the occupant's compartment was compressed (32). The determination of the site of contact between the legs and elements of the car's interior makes it easier to find trouser cloth that has rubbed off or melted into plastic dashboard elements. If the occupant's chamber was not compressed and the control panel was not translocated, the presence of dashboard injuries indicates that the victim was not belted on collision.

The most common contact is made between the front surface of a bent knee and the dashboard. This is likely to cause fractures between the patella and acetabulum (Fig. 30, part 1a-f, Fig. 31).

Such injuries are equally common in drivers and car occupants, and the nature of hip injuries may also indicate the position of the victim in his or her seat (compare Subheading 2.6 and Fig. 22).

In nonbelted occupants, the knee is more likely to be hyperextended (Fig. 30, part 4) in the front seat passenger when he is thrown from the car through the windscreen. On

Pull Back Car
Fig. 26. The most common mechanisms of ankle and knee joint injuries in cyclists hit by passenger cars and a truck with a high bumper location.

the other hand, drivers are likely to experience splitting-compression fractures of the tibial plateau as a result of pressure on the femoral condyles when a leg is trapped between the floor and instrument panel (Fig. 30, part 3).

Fig. 27. Bruises in the perineum, scrotal sac (incised), and subcutaneous tissue of the medial surface of the right thigh and right groin in the cyclist caused by contact with the saddle.
Fig. 28. The direction of rotation of the saddle in car-to-bicycle collisions in the left oblique hit (1) and left perpendicular hit (2).
Fig. 29. The direction of knee joint dislocation and rotation of the saddle in car-bicycle collisions in relation to the direction of the impact. See Color Plate IV, following page 240.
Pivot Shift Injury Knee Mri Radiology
Fig. 30. Patterns of dashboard injuries in front collisions in nonbelted occupants.
Fig. 31. The dashboard injury complex: "watch-glass-break"-type fracture of patella, femoral condyles splitting fracture, and acetabulum fracture.

2.7.4. Motorcycle Accidents

From the perspective of a forensic expert, the major difficulty in evaluating motorcycle accidents is to identify the motorcycle driver and passenger rather than to determine the impact direction (which is usually explicitly shown by the motorcycle damage).

The lateral car-to-motorcycle hits are similar to car-to-bicycle hits and may result in similar injuries to joint structures of the lower limbs (both in drivers and passengers). In frontal hits (both in high and low obstacles), the situation of motorcyclists is similar to that of car drivers and the motorcycle passenger is "protected" by the driver's body sustaining no serious lower limb injuries (moving along the driver's back, the passenger is thrown off the motorcycle and sustains some secondary injuries after hitting the road). The driver moving to the front due to inertia often hits the motorcycle elements with his knees sustaining injuries similar to the "dashboard" injuries in car occupants (also similar to the perineum injuries in cyclists). Moreover, the motorcycle driver is more bound than the bicycle rider to his vehicle and frequently sustains lower limb injuries when pressed by the motorcycle after collapsing or rubbing against the road surface (33).

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