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Does Soccer Ball Heading Cause Retinal Bleeding?
William F. Reed, MD;
Kenneth W. Feldman, MD;
Avery H. Weiss, MD;
Alan F. Tencer, PhD
Arch Pediatr Adolesc Med. 2002;156:337-340.
ABSTRACT
Objectives To define forces of youth soccer ball heading (headers) and determine
whether heading causes retinal hemorrhage.
Setting Regional Children's Hospital, youth soccer camp.
Patients Male and female soccer players, 13 to 16 years old, who regularly head
soccer balls.
Measurements Dilated retinal examination, after 2-week header diary, and accelerometer
measurement of heading a lofted soccer ball.
Results Twenty-one youth soccer players, averaging 79 headers in the prior 2
weeks, and 3 players who did not submit header diaries lacked retinal hemorrhage.
Thirty control subjects also lacked retinal hemorrhage. Seven subjects heading
the ball experienced linear cranial accelerations of 3.7 ± 1.3g. Rotational accelerations were negligible.
Conclusions Headers, not associated with globe impact, are unlikely to cause retinal
hemorrhage. Correctly executed headers did not cause significant rotational
acceleration of the head, but incorrectly executed headers might.
INTRODUCTION
SOCCER HAS been reported to cause between 146 000 and 160 000
injuries requiring emergency department care in the United States annually.1 In Orlando, Fla, 13 youths had eye injuries caused
by soccer balls. One had retinal hemorrhage and 5 had retinal edema.2 However, all 10 who had a clear injury history had
sustained direct blunt impact to the globe. Because of these concerns, the
American Academy of Pediatrics Committee on Sports Medicine and Fitness1 has recommended caution with soccer ball heading (headers)
and use of protective eyewear for youth soccer players.
Brief periods of repetitive whiplash, during which the brain is accelerated
in one and then the opposite direction, with or without accompanying impact,
are believed to be the mechanism causing concussion and subdural bleeding
in infants and toddlers with inflicted head injury.3-5
Retinal hemorrhage has been reported to accompany brain injury in 30% to 100%
of these children with inflicted head injury.6
Motor vehicle passenger injuries, which include cranial whiplash, also are
a rare cause of retinal hemorrhage.6 Adult
primate head injury studies of single cranial whiplashes, both with and without
cranial impact, did not establish thresholds for retinal damage.7
The mechanics of soccer ball heading might induce cranial whiplash events
sufficient to cause retinal hemorrhage.
The primary purpose of our study was to determine whether there is a
significant incidence of retinal hemorrhage among adolescents who head the
soccer ball. We chose to study young adolescents because they have the strength
to generate kicked balls of high velocity but might not yet have fully developed
neck muscle strength or header technique. They also still have sufficient
vitreous fibril, firmly adherent to the retina, to allow vitreoretinal traction
to cause retinal bleeding.8 A second purpose
of the study was to determine the forces that are experienced by youths heading
the soccer ball.
SUBJECTS AND METHODS
PLAYER RETINAL EXAMINATIONS
Youth soccer players aged 13 through 16 years who regularly performed
headers were recruited. The players played predominately on upper-skill level
teams. For 2 weeks prior to a dilated retinal examination, they kept a diary
of header frequency and whether these headers were performed during practice
or game conditions. Thirty youths from the same age group coming to the ophthalmology
clinic for evaluations of conditions not known to be predisposed to retinal
disease were used as controls. Players and controls were evaluated from January
1, 1998, through December 31, 2000.
ACCELEROMETER STUDY
Biomechanical testing was conducted while youths headed a soccer ball.
They were highly motivated participants at a summer youth soccer camp conducted
by W. Dean Wurzberger, coach of the University of Washington men's soccer
team. A size 4 soccer ball was lofted to the players from 3 m away by one
of the camp's coaches. The players performed the header from an initial standing
position.
They were fitted with light, inelastic plastic headgear to which accelerometers
were attached (Figure 1). Two uniaxial
accelerometers (PCB Piezoelectronics Inc, Depew, NY) were attached to a circumferential
plastic band near each temporomandibular joint (TMJ), which is close to the
center of gravity of the head in the sagittal plane. One accelerometer of
each array recorded local vertical (Z) and the other measured horizontal (X)
acceleration. Additionally, a triaxial accelerometer was fixed to a sagittal
band of the plastic headgear near the apex of the head so that it formed a
vertical plane with the TMJ accelerometers. Signals were filtered and collected
at a 2-kHz sampling rate by a laptop computer (PowerMac G3; Apple Computer
Co, Cupertino, Calif) with an 8-channel analog/digital converter, PCMCIA card,
and Labview software (National Instruments, Austin, Tex).
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Figure 1. A 16-year-old girl is fitted with
the accelerometer array for biomechanical testing.
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Raw accelerometer signals were forward and reverse filtered using a
fifth-order Butterworth digital filter implemented in Labview according to
standard protocols (SAE J211; Society of Automotive Engineers, Detroit, Mich)
with a cutoff high-pass frequency of 600 Hz. From the filtered data, the peak
X linear acceleration was determined. Because the TMJ accelerometers were
located at approximately the center of gravity of the head, any difference
in X acceleration between the TMJ and the crown of the head could be divided
by the known distance between the instruments to obtain angular acceleration.
However, angular accelerations were small, as confirmed by videorecording
of each test. The video showed the subjects tensing their neck muscles and
moving the head and torso in unison toward the ball. The linear accelerations
of the left and right accelerometers were averaged, then averaged again for
the 5 test runs conducted on each subject.
HUMAN SUBJECTS
The institutional review board of The Children's Hospital and Regional
Medical Center approved all aspects of the study. These study players received
a $20 reimbursement for their participation in each study phases. Results
were evaluated by simple descriptive statistics.
RESULTS
PLAYER RETINAL EXAMINATIONS
Twenty-one players kept a 2-week header diary and underwent a retinal
examination immediately at the end of that period. Eighteen were adolescent
boys and 3 were adolescent girls. The "U" grouping system roughly reflects
player age in soccer league play. Nine U12, 8 U13, 1 U14, 2 U15, and 1 U16
players participated. Three additional players had retinal examinations but
did not submit diaries (2 U13 and U15 adolescent boys and a U15 adolescent
girl). Thirty control adolescents were also examined.
The soccer players reported a mean of 19 headers per practice session
and 5 per game with a mean of 13 per either game or practice day. The players
reported a sum of 1669 headers in the 2 weeks prior to the eye examinations,
or an average of 79 headers per player. The number of headers per player ranged
from 9 to 362, with a median of 53. Six players had performed more than 100
headers in the 2 weeks before retinal examination. The youngest adolescent
boys performed the most headers. The U12 and U13 adolescent boys averaged
106 headers per player, while the U14 to U16 adolescent boys averaged 33 and
the U12 and U13 adolescent girls 52. No player or control subject had retinal
hemorrhage.
ACCELEROMETER STUDY
Seven adolescents, including six 13-year-old boys and one 16-year-old
girl, participated in the biomechanical study. The lofted ball speed, estimated
from videotapes of the header trials, was 6.7 m/s. The mean peak linear, horizontal
cranial acceleration subsequent to ball impact was 3.7 ± 1.3g (range, 1.7-8.8g). Based on the impact duration
and greatest peak linear acceleration observed, this would result in a Head
Injury Criteria score of 61. Cranial rotational acceleration was negligible.
The tested players used proper heading technique of tensing the neck muscles
and meeting the ball with the upper body as a single unit. Body rotation was
centered at the hips.
COMMENT
A previous photoanalysis9 of a skilled
adult performing headers confirmed that the player's head was fixed in line
with the trunk by tensed neck muscles. The player's head met the ball in essentially
a straight line, and the body's flexion point was at the hip. We observed
a similar technique in adolescents (Figure
2). An improperly executed header uses only rotation of the head
on the neck to meet the ball; the neck muscles are not tensed. In the first
case, the entire mass of the upper body meets the ball, whereas in the latter,
the head mass alone strikes the ball. With correctly performed headers, cranial
acceleration is indirectly related to the ratio of the player's upper body
mass to the ball's mass and deformability and directly related to the ball's
velocity. An adolescent's cranial mass is about 9% of total body weight, while
body mass from the hip to the crown of the head is about 70%. "Light heading"
is first introduced into basic soccer skills training at the U10 level in
Washington State. Children aged 8 to 10 years play with a 240- to 300-g number
3 ball. Through the U13 level, the game is played with a number 4 ball, weighing
330 to 390 g. From the U14 level and up, adolescents play with a number 5
ball, weighing 420 to 480 g. This would result in a head-to-ball mass ratio
of 12 for an average sized 13-year-old boy. If the same player used the entire
upper body to meet the ball, the upper body to ball mass ratio would be 93.
Compared with the header using the head alone, this is nearly an 8-fold shift
of the mass ratio in favor of reduced cranial acceleration. It would then
be predicted that an improperly executed header would be more likely to cause
brain and retinal injury than a properly executed one.
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Figure 2. A, A 12-year-old boy soccer player
assumes a tensed stance in preparation for ball impact. B, Neck muscles are
tensed and hips flex immediately prior to impact. C, After impact, the neck
muscles remain tensed and hips straightened owing to entire upper body being
used to accelerate the ball.
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Kicked soccer balls have been reported to travel at 7 to 36 m/s.10-13 The
ball speed of our accelerometer study is at the low end of these kicked ball
speeds. Computer simulation has suggested that adults heading a soccer ball
traveling at 10 m/s experience a 19g linear cranial
acceleration and 366 radian/s2 angular acceleration.10
No estimates are reported for children. Schneider and Zernicke10
suggested that the upper limit of adult brain tolerance for rotational cranial
acceleration induced by a headed soccer ball would be 1800 radian/s2. Since injury thresholds are extrapolated from the animal data based
on cranial mass and are lower for larger masses, the injury thresholds for
rotational acceleration in adolescents should be slightly higher than for
adults.7 In primate studies, prevention of
cranial rotation by a cervical collar, which allowed only linear or translational
acceleration, increased the head injury thresholds by 50%.7
Current US Department of Transportation Head Injury Criteria specific to translational
cranial acceleration involve a complex association of the integral of the
cranial acceleration pulse and its time course.14
The greatest translational acceleration we recorded resulted in a Head Injury
Criteria of 61; this is negligible compared with the threshold for brain injury
of a score of 1000 or more.
The current leading proposed mechanism for retinal injuries in rotational
head trauma is that whiplash acceleration forces are translated through the
vitreous body. Vitreous fibrils are attached along the inner retina where
the retinal vessels are located. They are most dense at the posterior pole
and ora serrata retinae.6, 15 As
the vitreous humor moves away from the retina, tension shears the vessels
resulting in retinal bleeding and, at the extreme, retinoschisis. This is
suggested to be a direct result of the acceleration exerted on the globe by
cranial whiplash with or without impact, not an indirect consequence of brain
injury, intracranial hemorrhage, and/or increased intracranial pressure.6 Fibrils connecting the retina to the vitreous humor
degenerate with increasing age.15 However,
young adolescent soccer players still have firm vitreous attachments,8 so they might be at risk for retinal bleeding from
whiplash acceleration forces from heading the soccer ball. The relatively
small number of players who had retinal examinations after 2 weeks of play
leaves an upper statistical possibility of a 12.5% incidence of retinal hemorrhage.16
By intention, our subjects are likely to include the most motivated
and skilled players for their age. We chose them because we assumed they would
perform the most headers of the fastest balls. However, they might not be
representative of the full skill and age range of youth soccer players. Less
skilled players may be more at risk to perform headers improperly. The limited
mobility allowed by the accelerometer wiring and human subject safety considerations
precluded serving maximum velocity soccer balls for heading. The players in
the accelerometer study sustained only modest linear cranial accelerations,
while less skilled players heading vigorously kicked balls would experience
greater linear acceleration and might sustain angular accelerations of the
head on the neck. Although the ball speed in the biomechanical portion of
the study was low, players in the retinal examination portion of the study
probably headed balls of all normal velocities. To study real-life conditions
and ball velocities, high-speed video systems, such as those used in motor
vehicle crash testing, would be required. Even with this equipment, a study
would be difficult as headers during practices and games occur at any location
on the field and distance from the camera. They also would be unlikely to
occur in a plane perpendicular to the player-camera axis. Alternatively, a
device could be designed to serve balls of known velocity to predictable locations.
Either an accelerometer, such as we used, or a high-speed video system could
be used to accurately measure the accelerations sustained by heading these
balls. However, this could create an ethical dilemma as individual soccer
players might head balls of a greater velocity, and greater potential risk,
then they would otherwise encounter in play. Furthermore, this test system
would not duplicate the lack of header anticipation and the effect of fatigue
encountered in actual play. We studied players we expected to be acquiring
adolescent strength and enthusiasm; study of players of other ages and maturity
would be appropriate. The balance between increasing ball mass and velocity
and developing player mass and skill could unpredictably alter the resulting
cranial accelerations.
Our biomechanical study demonstrates only linear cranial acceleration
with headers; we can surmise that greater forces than those of lofted balls
would be required to cause significant rotational acceleration of the player's
head. These results and the direct retinal examinations are reassuring that
headers are unlikely, barring globe impact, to cause retinal injury in youth.
| What This Study Adds
Although eye injuries occur in soccer due to direct globe impact, it
was unknown whether headers indirectly cause retinal hemorrhage. Players performing
headers were prospectively evaluated. Headers could not be documented to cause
retinal hemorrhage. Forces of youth soccer headers were evaluated. The relatively
low-velocity balls studied did not cause rotational cranial acceleration.
The accelerations we observed are unlikely to cause eye or brain injury.
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AUTHOR INFORMATION
Accepted for publication October 18, 2001.
The project was funded, in part, by the Harborview Injury Prevention
Research Center grant R49/CCR002570 from the Centers for Disease Control and
Prevention, Atlanta, Ga.
This study was conducted as Dr Reed's Independent Study in Medical Science
medical student thesis at the University of Washington School of Medicine.
We thank the Puget Sound youth soccer teams and their players, W. Dean
Wurzberger, University of Washington men's soccer coach, and the ophthalmology
residents at The Children's Hospital and Regional Medical Center.
Corresponding author: Kenneth W. Feldman, MD, 2101 E Yesler Way,
Seattle, WA 98122 (e-mail: kfeldman{at}u.washington.edu).
From the School of Medicine (Drs Reed, Feldman, Weiss, and Tencer),
Departments of Pediatrics (Dr Feldman), Ophthalmology (Dr Weiss), Orthopedics
(Dr Tencer), and Sports Medicine (Dr Tencer), University of Washington, The
Children's Hospital and Regional Medical Center (Drs Feldman and Weiss), and
the Harborview Injury Prevention Center (Dr Tencer), Seattle, and the Sacred
Heart Hospital, Internal Medicine Residency Program (Dr Reed), Spokane, Wash.
REFERENCES
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1. Injuries in youth soccer: a subject review: American Academy of Pediatrics
Committee on Sports Medicine and Fitness. Pediatrics. 2000;105:659-661.
FREE FULL TEXT
2. Orlando RG. Soccer-related eye injuries in children and adolescents. Physician Sports Med. 1988;16:103-106.
3. Duhaime AC, Gennarelli TA, Thibault LE, Bruce DA, Margulies SS, Wiser R. The shaken baby syndrome: a clinical, pathological, and biomechanical
study. J Neurosurg. 1987;66:409-415.
ISI
| PUBMED
4. Alexander R, Sato Y, Smith W, Bennett T. Incidence of impact trauma with cranial injuries ascribed to shaking. AJDC. 1990;144:724-726.
5. Alexander R. Head trauma: forensic pediatric approaches. Paper presented at: San Diego Conference on Responding to Child Maltreatment;
January 30, 1997; San Diego, Calif.
6. Levin AV. Retinal hemorrhages and child abuse. Recent Adv Paediatr. 2000;18:151-219.
7. Ommaya AK, Hirsch AE. Tolerances for cerebral concussion from head impact and whiplash in
primates. J Biomech. 1971;4:13-21.
FULL TEXT
|
ISI
| PUBMED
8. Sebag J. Age-related differences in the human vitreoretinal interface. Arch Ophthalmol. 1991;109:966-971.
ABSTRACT
9. Mawdsley H. A biomechanical analysis of headers. Momentum. 1978;3:30-40.
10. Schneider K, Zernicke RF. Computer simulation of head impact: estimation of head injury risk
during soccer heading. Int J Sports Biomech. 1988;4:358-371.
11. Anzil F. The football player's jumping abilities and head playing. International Congress on Sports Medicine Applied to Football. Rome, Italy: 1979:643-652.
12. Burslem I, Lees A. Quantification of impact accelerations of the head during the heading
of a football. In: Reilly T, Lees A, Davids K, Murphy WJ, eds. Science and Football. London, England: E & FN Spon; 1988:243-248.
13. Townsend M. Is heading the ball a dangerous activity? In: Reilly T, Lees A, Davids K, Murphy WJ, eds. Science and Football. London, England: E & FN Spon; 1988:237-242.
14. Margulis SS, Thibault LE. A proposed tolerance criteria for diffuse axonal injury in man. J Biomech. 1992;25:917-923.
FULL TEXT
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ISI
| PUBMED
15. Hogan MJ. The vitreous, its structure, and relation to the ciliary body and retina. Invest Ophthalmol. 1963;2:418-444.
PUBMED
16. Harley JA. If nothing goes wrong, is everything all right? interpreting zero numbers. JAMA. 1983;249:1743-1745.
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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES
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No Evidence That Soccer Ball Heading Leads to Retinal Bleeding in Adolescents
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