Free fall traumaS Tan and K Porter

Trauma 2006; 8: 157–167

Intern 王俏慧96-4-3

Introduction

TerminologyFree fall An unimpeded drop from a known point to a known i

mpaction point.

Vertical deceleration Decrease in the speed attained by a falling body, usual

ly at impact.

Autokabalesis the basic components of ‘throw-out-window-self’

(Sims and O’Brien, 1979) the phenomenon of intentional jumping from a height.

Epidemiology Among the causes of trauma deaths in the U.K. and the U.S., falls

rank only second to motor vehicle accidents. all deaths by suicide: in 1961 1.38% rising to 4.4% in 1986

Isbister and Roberts, 1992 In the U.S., approximately 50% of free falls are accidental, about

20% are suicide attempts, another 20% are crime related, and the remainder are from undetermined causes Sex : Men predominate over women (5:1 to 32:1)

intentional falls: the difference is less clear males opted for higher heights in their suicide attempts

Age : the young adult age range (18–41) Season : summer prevailing Alcohol and drug intoxication is commonly implicated Psychiatric illness : in intentional jumpers ;Schihizophrenia, depressi

on

Physical and biomechanicalprinciples

Impact velocityV = √2 gh Discounting the effect of air drag a two-story free fall, 30 feet → 30 mph a six-story fall →53 mph The terminal velocity in the earth’s atmosph

ere, 120 mph, will be reached by a fall from 32 stories

Impact energyKE = 1/2 mv^2KE = ME + PE + heat. KE (kinetic energy) related more to the velocit

y than the mass of the falling body At impact the vast majority of this KE is conver

ted to mechanical energy (ME). Tissue injury occurs as a result of the body abs

orbing the energy (ME) accumulated during the period of free fall.

Impact forceF = mad (deceleration)= gh/s Stopping distance is determined largely by the proper

ties of the impact surface, softer surfaces allow penetration by the fallen body leading to larger stopping distances.

a fall from one story onto concrete, with a stopping distance of ¼ inch → a deceleration of 720 g.

a fall from three stories onto mud with a stopping distance of 8 inches → a deceleration of only 67 g.

Duration of impactt = 2 s/v Longer impact durations allow for greater diss

ipation of mechanical energy over time and theoretically decrease the severity of tissue injury sustained

Distribution of forcesS (The amount of stress)=F/A A body landing feet first will have relatively high stress

es distributed over a small area. The orientation of the body undergoes change throug

hout impact and these changes will also have an effect on how the deceleration forces are distributed through the body.

Parachutists are trained to land with hips and knees flexed, they then further cushion their falls by rolling.

Biomechanical factors Human bodies are composites of many tissues and or

gans with different elasticities, viscosities and resistances to deceleration forces.

In addition, these tissues and organs do not impact in their entirety all at once: each organ and structure has a different deceleration distance depending on its position and moment relative to the body parts making initial and subsequent contacts.

Furthermore the transmission of forces at contact may be in the form of compression, distraction, rotation, shearing or a combination thereof.

Miscellaneous factors wind may alter the body position at impact. rain, snow or frost The physical condition of the victim

Young : the flexible skeleton, relaxed muscle tone, higher proportion of subcutaneous fat and lower body mass

Victims with altered conscious level through drug or alcohol intoxication may have depressed protective mechanisms

Risk of dying

The height of the fall is the most significant determinant

the surface impacted, attitude of the body at impact, location of fall Softer impact surfaces → greater impact durations → dissipat

ing the ME in an urban setting fallers are more likely to strike architectur

al abutments in flight. This potentially enhances survival by modifying the mechanism of injury.

Scalea et al.,1986 Immediate death from free fall is usually a result of m

assive brain damage, thoracic trauma or intra-abdominal bleeding alone or in combination

The risk of dying increased ten fold after falling four storeys as opposed to one storey and 28-fold increases were seen following falls from five storeys

Risser et al., 1996 The risk of dying from a third storey fall was 50%

Lewis et al.,1965 similarly reported 50% overall mortality in suicide jum

pers from three storeys. All jumpers falling six storeys or greater onto a hard surface died in this series. Severe head and facial injuries were the most commonly seen principle causes of death.

Isbister and Roberts, 1992

Victims have survived the initial fall and die after reaching a hospital → this is secondary to uncontrollable haemorrhage and massive CNS injury in the early stages but intermediate and late complications of pulmonary embolus, ARDS, multiple organ failure and sepsis are other causes of mortality.

In terms of the ISS( Injury Severity Score) a clear-cut off between survivors and non-survivors was seen, with all but one patient with a ISS>29 dying and all but one with a ISS<29 surviving

Isbister Roberts, 1992. the high incidence of intoxication with alcohol or illicit

drugsVelmahos, 1997

Pattern of injury

Our understanding of injury pattern and injury severity is based on autopsy studies as well as studies on survivors of free fall.

massive head injury, intra-abdominal injury to solid organs and, to a lesser extent, intrathoracic injury as being the predominant pattern of lethal injury.

The height fallen, the surface impacted and the body position at impact appear to be the predominant determining factors, but the age of the patient, locality of fall and intentionality of the fall also modify the pattern of injury, severity of injury and outcome.

Regional injury

Head injuries Massive head injury is a major cause of immediate death followin

g free fall. The body’s position at impact obviously significantly alters risk

of head injury. Incidence of head injury in feet first landings: 8.3% to 60% A head first position at impact

Skull fractures occur in 60% and nearly all sustain some form of cerebral damage, which is the most common mode of death

Height of fall The presence of skull fracture

Fractures occur to the vault, producing linear and comminuted fractures rather than localized, depressed ones.

Basal fractures usually occur as a result of transmitted force from the spinal column such as in a feet first landing

Contusion and edema the most common finding in fallers with head injury,

Spinal injury ‘jumper’s fracture’

transverse fractures of the upper sacrum resulting from falls from a height and usually associated with suicidal attempts by jumping

The incidence of this fracture in falls patients is most probably low.

awareness of the possibility of such an injury, especially in the presence of perineal neurological deficit

The most common site of spinal injury following a fall : thoraco-lumbar junction By direct impact or by axial loading

The latter transmits flexion forces to the spine, which usually affects the junction between the relatively fixed thoracic spine and the adjacent more mobile lumbar region.

Pure flexion ordinarily results in a simple anterior wedge deformity

Spinal injury Rates of cervical spine involvement in vertical deceler

ation type injuries appear to be somewhat lower, but far from rare. In head-first impacts, these may be burst fractures or flexion

and extension injuries. Hyperflexion is more common in feet-first landings causing ‘

teardrop’ fractures and rupture of the posterior ligaments with or without subluxation.

Notably 85% of these involved the 12th thoracic vertebra.

On classifying type of fracture, compression and burst type fractures predominate

Pelvic injury The pelvis may be directly impacted through horizontal landings

and also when landing on the buttocks. the most frequent impact pattern is the feet first landing. Axial lo

ading is transmitted from the lower limbs, across the hip joint to the pelvis. Acetabular fractures pelvic ring disruption, associated with life-threatening hemorrhage.

Incidence of pelvic injury was second only to head injury in Lewis’ report of high falls.

1/2 were deemed stable (Type A), about 1/3 were stable in the vertical plane (Type B), and 1/3 there was also instability in the vertical plane (Type C).

Associated bladder injuries and sciatic nerve injuries were also recorded.

Thoracic injury Ruptures of the thoracic aorta, pericardium and heart

although common in autopsy series, are uncommon in patients who survive to reach hospital.

Azygous vein laceration as a result of free fall has been reported but again is rare.

landing on the buttocks from a fall gives rise to a higher incidence of intra-thoracic and intra-abdominal injury impact forces cannot be dispersed by the knees and hips flexi

ng, and consequently more force is transmitted to the trunk. Pulmonary injury of differing severity is common

Multiple rib fractures with lung contusion, haemothorax and pneumothorax

Abdominal injuries The liver has been reported as being the most commo

nly injured organ and also the most fatal abdominal injury Lacerations the right lobe

Splenic injuries are caused by a severe degree of violence. Capsular tears and divisions of the lower part of the spleen

renal injury to be relatively rare in free fall patients. the kidneys position and surrounding fat conferred protectio

n. under-diagnosed and under-reported.

Abdominal injuries Hollow viscus injuries appear to be present in similar

proportions as solid organ injuries a shearing of the viscus at the junction between its fixed and

mobile portions. lacerations may occur at the junction between the terminal il

eum and the caecum, in the sigmoid colon, and at the duodenojejunal flexure

Retroperitoneal hemorrhage was identified by Scalea and associates as the most likely source of ongoing blood loss in patients surviving long enough to present to hospital. The vascular injuries were attributed to pelvic and vertebral fr

acture.

Extremity injury Lower limb injuries are consistently reported as the co

mmonest injuries found in all patients who fall from a height. the feet first landing the path of force transmission from impact, axially through th

e bony skeleton. metaphyseal and epiphyseal injuries of the distal joints (foot,

subtalar and ankle joints) The os calcis consistently is reported as the single bone most

commonly fractured (18–64%) more common following lower (one to two storey) than higher (3

storey) falls. a significant association between os calcis and thoracolumbar fr

actures

Extremity injury Upper limb injuries are commonly described following

free fall impact (24.8–38%) metaphyseal and epiphyseal regions of the distal jo

ints (wrist and elbow) are predominantly involved. Fractures of the diaphyseal areas and the proximal

joints (shoulder and humerus) are relatively rarer.

Jumpers and fallers There does not appear to be any specific injury that is

pathoneumonic of either intentional or accidental fall. Jumper

‘suicidal jumper’s fracture’ to describe transverse fractures of the sacrum

Roy-Camille et al. (1985) A high ratio of lower limb fractures and a small number of hea

d injuries are typical for patients landing on their feet tend to try and break their falls using their dominant (usually

right) side. ( based on injuries )

Jumpers and fallers Fallers

a lower incidence of feet first landings in fallers the body tends to land as predicted by its center of gravity in t

he upper torso The height of fall, striking architectural abutments, wi

nd conditions and alcohol or drug intoxication may all modify the final impact. the difference in orientation seen with low and high falls, sug

gesting a greater variation in impact position with higher falls. It was Teh et al.’s (2003) experience that jumpers ten

ded to suffer falls from greater heights than did fallers. Thus, a higher incidence of head injuries could be the product of the height of fall.

Predicting the severity of injury The height of a fall has been shown to be a strong pre

dictor of mortality.

a threshold height of 20 feet as the cut-off above which major trauma is considered a clinically important risk. However, the height of fall is a poor predictor of injury severity

Factors such as age and mechanism of fall obviously have significant bearing on outcome

Summary

Free fall trauma represents a distinct form of blunt trauma.

The distance of fall, impact surface, body orientation at impact, victim’s age and depressed protective mechanisms are important factors to be considered in our analysis.

The distance of a fall is perhaps the strongest single predictor of mortality with falls from three storeys carrying a 50% risk of death and those from five storeys or more rarely being compatible with survival.

Massive head injury, intra-abdominal solid viscus injury and, to a lesser extent, intra-thoracic injury are the predominant lethal injuries.

A threshold of 20 feet is commonly cited in triage as the level at which major trauma needs to be considered.

Musculoskeletal injuries, lower extremities injury in feet first landings.

os calcis fracture and Spinal injury, thoraco-lumbar junction

spinal injuries are commonly unstable, burst or compression type configurations and carry a high incidence of neurological injury

Ruptures of the aorta, pericardium and heart as well as major hepatic and splenic injuries are common sequelae following massive decelerations. However, such injuries are usually not survivable.

haemodynamic instability in a free fall survivor the possibility of retroperitoneal haemorrhage especially from vertebral or pelvic fracture should always be borne in mind.

The distinction between so called ‘jumpers and fallers’

Thanks to your attention!