A national registry has documented data on more than 1300 cervical
spine injuries resulting from tackle football. Axial loading of
the cervical spine is the primary injury mechanism, an observation
with profound implications regarding implementation of preventative
measures.
Characteristic injury patterns involving the middle (third and fourth)
cervical segment and the more favorable response to prompt reduction
of these injuries are emphasized.
The marked instability and grave prognosis of axial load teardrop
fractures are attributed to the associated sagittal vertebral body
and posterior arch fractures.
Spear tackler’s spine is described and is classified
as an absolute contraindication to participation in collision sports.
Cervical cord neurapraxia, with or without transient quadriplegia,
is neither associated with nor presages permanent neurologic sequelae.
However, there is a considerable risk of recurrence, which can be
predicted on the basis of canal diameter data.
The concept of spinal cord resuscitation is proposed as a means
of obtaining maximum neurologic recovery by reversing the secondary
injury phenomenon that occurs in acute spinal cord trauma.
Athletic trauma to the cervical spine resulting in injury to
the spinal cord is an infrequent but potentially catastrophic event. Recognition
of the problems presented by injury to the cervical spine and spinal
cord led to a series of field, clinical, and basic research studies
conducted over the past twenty-five years. As a result of these
efforts, basic questions have been answered regarding the epidemiology,
prevention, pathomechanics, pathophysiology, and histochemical responses
of reversible and irreversible cervical cord injuries.
The National Football Head and Neck Injury Registry, established
in 1975, has collected data on more than 1300 cervical spine injuries42-44. The criteria for inclusion of
injuries in the Registry were a need for hospitalization for more
than seventy-two hours; a need for an operation; and a fracture,
subluxation, or dislocation resulting in neurologic injury or death.
Data on each injury were collected from the athlete, parents, and
school officials as well as from radiographs and medical reports. When
available, game films or videotapes of the injury were analyzed
to determine the mechanism of injury. The total number of head and
neck injuries from 1971 to 1975 was calculated retrospectively and
compared with the data on injuries from 1959 to 1963 compiled by
Schneider45 in a similar study.
It was found that while both intracranial hemorrhages and deaths
due to intracranial injuries had decreased by 66% and 42%,
respectively, the number of cervical spine fractures, subluxations,
and dislocations had increased by 204% and the number of
cases of permanent cervical quadriplegia had increased by 116% (Fig. 1). The majority
of the cases of permanent cervical quadriplegia that occurred between
1971 and 1975 was determined to have been due to so-called spearing,
or direct compression, when the player made initial contact with
the top of his helmet (Fig. 2).
Axial loading was documented as a mechanism of catastrophic cervical
spine injuries in football players in a review of game films of
actual injuries44. Stop-frame
kinetic analysis, a method that allows estimation of the magnitude
of injury-producing forces, was performed on sixty game films and
videotapes of injuries resulting in permanent quadriplegia. The
orientation of the head, cervical spine, and trunk segment of each
athlete was analyzed to determine the mechanism of injury. Analysis
of these films allowed an accurate determination of the mechanism
of injury in 85% of the cases, and axial loading was determined
to be the mechanism in every instance.
On the basis of these findings, it was concluded that the improved
protective capabilities of modern helmets accounted for the decrease
in head injuries but led to the development of playing techniques
that used the top or crown of the helmet as the initial point of
contact, placing the cervical spine at risk. It was postulated that
execution of headfirst techniques increased the risk of neck injury
by exposing the cervical spine to excessive axial load, a force
to which the cervical spine appears to be particularly susceptible46-48.
In the course of a contact activity, such as tackle football,
the cervical spine is repeatedly exposed to potentially injurious energy
inputs46. Fortunately, most energy
inputs are dissipated by controlled spinal motion through the cervical
paravertebral muscles and the intervertebral discs47. However, the vertebrae, intervertebral
discs, and supporting ligamentous structures can be injured when
contact occurs on the top or crown of the helmet with the head,
neck, and trunk positioned in such a way that forces are transmitted
along the vertical axis of the cervical spine. In this situation,
in which the cervical spine assumes the physical characteristics
of a segmented column, motion is precluded in response to axially directed
impacts, and the forces are directly transmitted to the spinal structures.
With the neck in a neutral position, the cervical spine is extended
as a result of the normal cervical lordosis. When the neck is flexed
to 30°, the cervical spine becomes straight. When a force is applied
to the vertex, the energy inputs are transmitted along the longitudinal
axis of the cervical spine and are no longer dissipated by the paravertebral
muscles. This results in the cervical spine being compressed between
the abruptly decelerated head and the force of the oncoming trunk48. When the maximum vertical compression
is reached, the cervical spine fails in a flexion mode, with the
occurrence of fracture, subluxation, or facet dislocation (Fig. 3).
In 1976, in response to these data, the National Collegiate Athletic
Association banned "spearing," defined as intentionally
striking an opponent with the crown of the helmet as well as other
tackling techniques in which the helmet is used as the initial point
of contact. Similar rule changes were also enacted at the high-school
level42-44. As a result of these
changes, the rates of fractures, subluxations, and dislocations
of the cervical spine decreased dramatically between 1976 and 1987.
In 1976, the rates of these injuries were 7.72/100,000
and 30.66/100,000 for high-school and college athletes,
respectively; they decreased to 2.31/100,000 and 10.66/100,000,
respectively, by 1987. The number of cervical spine injuries resulting
in quadriplegia also consistently decreased, from a total of thirty-four
cases in 1976 to five cases in 1984 and one case in 1991. In 1976,
the rates of injuries causing quadriplegia were 2.24/100,000
at the high-school level and 10.66/100,000 at the college
level. In 1977, one year following the rule changes, these rates decreased
to 1.30/100,000 and 2.66/100,000, respectively, and,
by 1984, they decreased to 0.40/100,000 and 0/100,000. With
the exception of observed increases in 1989 and 1990, the yearly
incidence of permanent quadriplegia has remained low (Fig. 4).
Numerous biomechanical studies have supported the axial loading
theory49. Mertz et al.50, Hodgson and Thomas51, and Sances et al.52 measured forces to the cervical
spine when axial impulses were applied to helmeted cadaver head-spine-trunk
specimens. The authors were able to produce fractures of the lower cervical
spine when the impulse was applied to the crown of the helmet. Hodgson
and Thomas determined that direct vertex impact imparted a larger
force to the cervical vertebrae than did impact applied farther
forward on the skull. Gosch et al.53 investigated
three different injury modes (hyperflexion, hyperextension, and
axial compression) in anesthetized monkeys and concluded that axial
compression produced cervical spine fractures and dislocations.
Maiman et al.54, Roaf55, and White and Punjabi56 demonstrated that axial loading
of isolated spinal units caused vertebral body fractures in the
lower cervical spine. Roaf55 subjected
spinal units to forces with different directions and magnitudes
and concluded that hyperflexion of the cervical spine was an anatomical
impossibility. In contrast, he was able to produce almost every
variety of spinal injury with a combination of compression and rotation.
Bauze and Ardran57 postulated
that axial loads were responsible for cervical spine dislocations
as well as fractures. They demonstrated failure of the facet joints
and posterior ligaments when axial loads were applied to cadaveric
spines. When the caudad portion of the spine was flexed and fixed
and the cephalad part was extended and free to move forward, vertical
compression produced bilateral dislocation of the facet joints without
fracture. If lateral tilt or axial rotation occurred as well, a
unilateral dislocation was produced. The observed forces were all
less than those required for osseous failure and allowed facet dislocation
without associated osseous injury.
Nightingale et al.58 analyzed
the relationships among head motion, local deformations of the cervical
spine, and injury mechanisms using a cadaver head-and-neck model
impacted in an anatomically neutral position. They observed that
classic concepts of flexion and extension as a mechanism of injury
of the cervical spine do not apply to a vertically impacted head.
They further concluded that straightening of the cervical spine
before injury may be a necessary element of the compressive flexion mechanism.
Analysis of data from the National Football Head and Neck Injury
Registry supports the clinical and laboratory observations that
the axial energy inputs to the straightened cervical spine result
in compressive deformation and subsequent buckling in a flexion
mode with subluxation, dislocation, fracture, or fracture-dislocation
at any level or levels. Clinical entities peculiar to axial loading
of the cervical spine and associated with irreversible cervical
cord lesions have been described.
Schneider and Kahn61 apparently
were the first to define a triangular fracture fragment at the anteroinferior
corner of a cervical vertebral body as a teardrop fracture. Their
description was based solely on analysis of lateral radiographs.
They did not describe findings on anteroposterior radiographs or
mention the possibility of a sagittal vertebral body fracture or
a posterior arch fracture. Schneider and Kahndid
not distinguish between an isolated fracture of the anteroinferior
corner and one associated with a sagittal fracture of the vertebral
body. They concluded that the teardrop fracture was caused by acute
flexion of the cervical spine and resulted in a severe neurologic
deficit. Acute flexion and teardrop39 have been accepted as the terms
describing vertebral body fractures with a fracture fragment at
the anteroinferior corner. Others have described these fractures
as burst or compression fractures or have used the terms flexion
teardrop and burst interchangeably62,63.
Inherent in the descriptive terminology of these injuries is confusion
regarding the mechanism of injury. These fractures have been attributed
to flexion, hyperflexion, hyperflexion with compression, axial loading,
hyperextension, and a combination of hyperextension and hyperflexion.
Woodford64 reported that the sagittal
fracture occurs with burst fractures caused by an axial force but
not with flexion teardrop fractures and stated that the two fractures
can be differentiated on the basis of the mechanism of injury. Allen
et al.1 observed that vertical
compression fractures with an anterior fracture fragment can be
differentiated from fractures at the anteroinferior corner caused
by compression flexion. Lee et al.65 reported
that forceful flexion produces the triangular fracture at the anteroinferior
corner and strong axial load compression produces the sagittal fracture.
Because of the inconsistency with regard to terminology and mechanism
of injury, the neurologic sequelae of each of the fracture patterns
had not been clarified.
Data on fifty-five patients with fifty-eight teardrop fractures included
in the National Football Head and Neck Injury Registry were analyzed66. Nine fractures were at the fourth
cervical level; forty-three, at the fifth cervical level; and six,
at the sixth cervical level. Axial compression was determined to
be the mechanism responsible for fifty-one of the fifty-five injuries.
Radiographically, patients were divided into two groups according
to the fracture pattern. Six had an isolated fracture of the anteroinferior
corner of the vertebral body, and the other forty-nine had, in addition,
a sagittal fracture of the vertebral body; that is, they had a three-part,
two-plane fracture pattern through the lamina (Fig. 5). Forty-five
patients in the series were permanently quadriplegic, and ten had
transient neurologic symptoms. Five of the six patients with an
isolated fracture of the anteroinferior corner had no serious neurologic
sequelae. One patient with fractures of the posterior elements of
the subjacent vertebra was quadriplegic. Of the forty-nine patients
with a documented three-part, two-plane injury, forty-four (90%)
were quadriplegic.
The terms flexion teardrop, acute flexion teardrop, and burst
fracture are incomplete descriptors of a comminuted fracture
of the cervical vertebral body, and they inaccurately explain the mechanism
of injury. The anteroinferior corner (teardrop) fracture has two
patterns; it can be an isolated fracture, which is usually not associated
with permanent neurologic sequelae, and it can be a three-part,
two-plane fracture that includes a sagittal fracture of the vertebral
body and a fracture of the posterior neural arch, which is usually
associated with permanent neurologic sequelae. The mechanism of
both fracture patterns is axial loading. When either type of lesion
is suspected, an anteroposterior radiograph, in addition to a lateral radiograph,
is essential in the initial screening process to determine the presence
of a sagittal vertebral fracture or a fracture of the posterior
neural arch. Computed tomography may then better define the anatomy.
Spear tackler’s spine is a clinical entity that constitutes
an absolute contraindication to participation in tackle football and
other collision activities that expose the cervical spine to axial
energy inputs. A subset of football players were identified who
demonstrated developmental narrowing of the cervical canal (a canal-vertebral
body ratio of <0.8), straightening or reversal of the normal
cervical lordosis, and post-traumatic radiographic abnormalities
and who had been seen employing spear-tackling techniques on videotape.
Fifteen patients who met these criteria were identified between
1987 and 199067. Eleven had complete
neurologic recovery: four of them had a transient episode of cervical
cord neurapraxia and seven had a brachial plexus root radiculopathy,
all of which resolved. The other four patients had a permanent neurologic
deficit: two had quadriplegia; one, incomplete hemiplegia; and one,
residual long-tract signs. Three of these four patients had acute fracture-dislocation
of the cervical spine. Permanent neurologic injury occurred as the
result of axial loading of a persistently straightened cervical
spine due to head-impact playing techniques. On the basis of these
observations, it was concluded that individuals with the aforementioned
characteristics of spear tackler’s spine should be precluded
from participation in tackle football and other collision activities, such
as rugby and ice hockey, that expose the cervical spine to axially
directed energy inputs.