The Potential Role of the Cervical Spine in Sports-Related Concussion: Clinical Perspectives and Considerations for Risk Reduction

Abstract

Synopsis:
Sports-related concussion (SRC) occurs due to biomechanical forces to the head or neck that can result in pathophysiological changes in the brain. The musculature of the cervical spine has been identified as one potential factor in reducing SRC risk as well as for underlying sex differences in SRC rates. Recent research has demonstrated that linear and rotational head acceleration, as well as the magnitude of force upon impact, is influenced by cervical spine biomechanics. Increased neck strength and girth are associated with reduced linear and rotational head acceleration during impact. Past work has also shown that overall neck strength and girth are reduced in athletes with SRC. Additionally, differences in cervical spine biomechanics are hypothesized as a critical factor underlying sex differences in SRC rates. Specifically, compared to males, females tend to have less neck strength and girth, which are associated with increased linear and rotational head acceleration. Although our ability to detect SRC has greatly improved, our ability to prevent SRC from occurring and decrease the severity of clinical outcomes postinjury is limited. However, we suggest, along with others, that cervical spine biomechanics may be a modifiable factor in reducing SRC risk. In this commentary, we review the role of the cervical spine in reducing SRC risk, and how this risk differs by sex. We discuss clinical considerations for the examination of the cervical spine and the potential clinical relevance for SRC prevention. Additionally, we provide suggestions for future research examining cervical spine properties as modifiable factors in reducing SRC risk. J Orthop Sports Phys Ther 2019;49(3):202-208. Epub 15 Jan 2019. doi:10.2519/jospt.2019.8582.

Full text

202 | march 2019 | volume 49 | number 3 | journal of orthopaedic & sports physical therapy
[ clinical commentary ]
According to the most recent consensus statement on
concussion in sport, sports-related concussion (SRC) is a
traumatic brain injury that results from biomechanical forces
to the body, including the head and neck.46 These forces induce
pathophysiological changes in the brain, leading to somatic, physical,
cognitive, and emotional symptoms, as well as sleep disturbances.46
The force (g) and duration of an impact
(seconds) influence the magnitude of
an impact25; however, the magnitude of
force associated with SRC is extremely
variable, with no consistent findings
between impact magnitude and clinical
outcomes.26 Musculoskeletal function,
particularly neck strength and activation
of neck muscles, may serve as a key me-
diator of the relationship between impact
magnitude and the resulting transfer of
energy from the head to the brain.7,25,33
Epidemiological studies have demon-
strated higher rates of SRC in female uni-
versity athletes compared to their male
counterparts when competing in com-
parable sports.13,15,17,48 Relative to males,
females also experience more severe
symptoms and longer recovery patterns
post SRC.12,47 Sex dierences in cervical
spine biomechanics are one hypothesis
put forth regarding dierences in SRC
rates and clinical outcomes post SRC in
males and females.12,14,65 This article fo-
cuses on the role that cervical spine bio-
mechanics and function play in SRC risk,
specifically with regard to neck strength,
neck girth, neck strength imbalances,
and cervical spine posture. We address
how these risk factors dier based on sex.
 SYNOPSIS: Sports-related concussion (SRC)
occurs due to biomechanical forces to the head or
neck that can result in pathophysiological changes
in the brain. The musculature of the cervical
spine has been identified as one potential factor
in reducing SRC risk as well as for underlying sex
dierences in SRC rates. Recent research has
demonstrated that linear and rotational head ac-
celeration, as well as the magnitude of force upon
impact, is influenced by cervical spine biomechan-
ics. Increased neck strength and girth are associ-
ated with reduced linear and rotational head accel-
eration during impact. Past work has also shown
that overall neck strength and girth are reduced
in athletes with SRC. Additionally, dierences in
cervical spine biomechanics are hypothesized as
a critical factor underlying sex dierences in SRC
rates. Specifically, compared to males, females
tend to have less neck strength and girth, which
are associated with increased linear and rotational
head acceleration. Although our ability to detect
SRC has greatly improved, our ability to prevent
SRC from occurring and decrease the severity of
clinical outcomes postinjury is limited. However,
we suggest, along with others, that cervical spine
biomechanics may be a modifiable factor in
reducing SRC risk. In this commentary, we review
the role of the cervical spine in reducing SRC risk,
and how this risk diers by sex. We discuss clinical
considerations for the examination of the cervical
spine and the potential clinical relevance for SRC
prevention. Additionally, we provide suggestions
for future research examining cervical spine prop-
erties as modifiable factors in reducing SRC risk.
J Orthop Sports Phys Ther 2019;49(3):202-208.
Epub 15 Jan 2019. doi:10.2519/jospt.2019.8582
 KEY WORDS: head injury, mild traumatic brain
injury, neck
1Department of Rehabilitation and Movement Sciences, School of Health Professions, Rutgers, The State University of New Jersey, Newark, NJ. 2School of Graduate Studies,
Biomedical Sciences, Rutgers, The State University of New Jersey, Newark, NJ. 3Department of Health Informatics, School of Health Professions, Rutgers, The State University of
New Jersey, Newark, NJ. 4Department of Kinesiology and Health, Rutgers, The State University of New Jersey, New Brunswick, NJ. *Represents co-first author, equal contribution
to manuscript. Financial support was provided to Dr Esopenko through the School of Health Professions at Rutgers, The State University of New Jersey. The authors certify that
they have no aliations with or financial involvement in any organization or entity with a direct financial interest in the subject matter or materials discussed in the article.
Address correspondence to Dr Carrie Esopenko, Department of Rehabilitation and Movement Sciences, School of Health Professions, Rutgers, The State University of New Jersey,
65 Bergen Street, Newark, NJ 07107. E-mail: carrie.esopenko@rutgers.edu  Copyright ©2019 Journal of Orthopaedic & Sports Physical Therapy®
MICHAEL STREIFER, DPT1* • ALLISON M. BROWN, PT, PhD1* • TARA PORFIDO, PT, DPT1,2
ELLEN ZAMBO ANDERSON, PT, PhD1,3 • JENNIFER F. BUCKMAN, PhD4 • CARRIE ESOPENKO, PhD1,3
The Potential Role of the Cervical
Spine in Sports-Related Concussion:
Clinical Perspectives and
Considerations for Risk Reduction
Although pathophysiological changes are
typically transient, with symptoms often
resolving within 10 to 14 days in adults,46
a percentage of individuals with SRC ex-
perience persistent symptoms, resulting
in prolonged activity and participation
limitations.44-46 Impacts to the head or
body can result in linear and rotational
head acceleration, which in some cases
can lead to damage to brain tissue.21,25,40,62

journal of orthopaedic & sports physical therapy | volume 49 | number 3 | march 2019 | 203
Additionally, we provide considerations
for clinical examination and clinical rel-
evance to highlight the potential role that
physical therapists, athletic trainers, and
other sports medicine personnel can play
in SRC risk reduction. As there is limited
evidence to support specific recommenda-
tions, the goal of this paper is to highlight
the importance of assessing the cervical
spine with respect to SRC risk, and poten-
tial ways of incorporating these measures
into clinical practice and future research.
Cervical Spine Biomechanics
and Function in SRC Risk
Neck Strength and Girth Neck strength
and girth have been described as poten-
tial modifiable risk factors in SRC pre-
vention, with research demonstrating
that lower neck strength and neck girth
are associated with increased head ac-
celeration during impact.5,8,9,20 Whereas
most studies to date have assessed the
relationship between neck strength and
girth on linear rotation and acceleration,
only 1 has prospectively assessed this
relationship with SRC risk. Collins and
colleagues11 found that neck strength val-
ues at baseline were lower in high school
athletes who subsequently sustained an
SRC relative to those who did not, and
further that for every 1-lb (approximately
0.45-kg) increase in neck strength, SRC
risk decreased by 5%.11 The proposed
mechanism by which neck strength de-
creases SRC risk relates to the ability of
the neck to decelerate head movement,
decreasing the transfer of energy to the
brain during impact. A stronger neck can
decrease head acceleration8,27 and is as-
sociated with reduced head velocity, peak
acceleration, and displacement during
impact in human and simulation stud-
ies.9,20,33,70 Sternocleidomastoid (SCM)
muscle strength may be of particular im-
portance in reducing SRC risk, as SCM
strength specifically has been shown to be
predictive of linear and rotational head
acceleration when heading a soccer ball.8
Furthermore, past work suggests that
males have significantly greater neck
strength than females in neck exten-
sion, flexion, and lateral flexion, even
after accounting for dierences in body
mass,10,20,29,66 and that females have
significantly smaller head-neck seg-
ment mass and neck girth compared to
males.5,20 These sex dierences in neck
muscle strength and girth are thought
to contribute to females experiencing
increased head acceleration during im-
pact.9,64 However, it should be noted that
Collins et al11 found that male athletes
who had sustained a concussion, com-
pared to uninjured athletes, had lower
overall baseline neck strength, which was
not significant in female athletes.
Muscle strength imbalances in the
cervical spine may also play an important
role in head acceleration and SRC risk.16,29
Isometric tests demonstrate that cervical
extension strength is generally greater
than flexion strength.49 It has been sug-
gested, however, that when extension and
flexion strength production are similar,
the head and neck may be more protected
during impact.16,29 This suggestion is sup-
ported by research showing that, regard-
less of sex, a flexion-extension strength
ratio close to 1 correlates with lower head
acceleration during impact.16
Cervical Spine Posture Cervical spine
posture may affect the force-generating
capacity of neck muscles, which could in-
fluence SRC risk.29 A common structural
alteration in head positioning is forward
head posture, defined as the external au-
ditory meatus being positioned anterior
to the shoulder joint.37 Forward head pos-
ture alters the normal mechanics of the
neck68 and is generally more common in
females.54 Forward head posture also in-
creases activation of the SCM and upper
trapezius and subsequently inhibits the
deep muscles responsible for segmental
stability and neck proprioception.2,39,42,43
Further, forward head posture is associ-
ated with a decreased flexion-extension
strength ratio,3 which, as mentioned pre-
viously, has an impact on head accelera-
tion forces.16 Thus, forward head posture
may result in increased head acceleration
during impact due to the muscle imbal-
ances noted in this posture.
Potential Clinical Considerations
for SRC Prevention
Neck Strength, Girth, and Endurance To
date, only 1 study has linked greater neck
strength with decreased SRC risk, and no
studies have shown which age- and sex-
specific degree of neck strength is critical
for risk reduction. However, based on the
studies discussed above, it is suggested
that head acceleration during impact is af-
fected by head and neck size/girth as well
as neck strength.8,16 Thus, increasing neck
strength and potentially girth and reduc-
ing neck strength imbalances may, in turn,
reduce SRC risk. Based on this research,
we suggest that clinicians consider per-
forming a thorough cervical spine strength
assessment for athletes who are at risk for
SRC (TABLE). Where normative strength
values exist, clinicians can use these values
to identify reduced strength and potential
areas of focus.8,10,11,50,56,67 Where norma-
tive values do not exist in the literature,
clinicians should still consider collecting
baseline strength and girth values to iden-
tify changes over time or in response to a
specific strengthening protocol.
An examination of standard isomet-
ric cervical spine strength should be con-
sidered in all 3 planes of movement to
quantify flexion/extension, lateral flexion,
and rotation. Additionally, isolated SCM
strength can be measured by isometrical-
ly resisting flexion with the neck rotated
to the contralateral side.30 To measure
cervical spine strength, we recommend
the use of a handheld dynamometer or
other devices that allow for clear quanti-
fication of muscle strength and strength
imbalances (TABLE). If the handheld dy-
namometer is the device of choice, we
further recommend that the handheld
dynamometer be strapped to the table to
optimize stability and minimize inconsis-
tencies in clinician force (FIGURE).19 With
this strength assessment, we recommend
that clinicians also consider assessing the
flexion-extension strength ratio, as a ratio
close to 1 correlates with lower head ac-
celeration during impact.16
Further, clinicians should consider
screening for pain during strength testing,

204 | march 2019 | volume 49 | number 3 | journal of orthopaedic & sports physical therapy
[ clin ical commentary ]
as baseline reports of neck pain have been
correlated with increased SRC risk in
youth athletes.57 The type and severity of
pain may influence the examination val-
ues obtained. We suggest that clinicians
consider addressing patients’ reports of
neck pain or headaches and be cognizant
of pain characteristics (eg, acute versus
chronic, radiating versus localized) when
determining baseline strength values or
prior to implementing a strengthening
protocol.
There is evidence that isolated
strengthening of the neck may serve to
protect against SRC31 and reduce func-
tional impairments in the cervical spine.4
Further, isometric neck strengthening
has been shown to reduce neck injury and
SRC risk in sport.31 Thus, we recommend
that clinicians consider implementing a
pre–athletic participation strengthen-
ing program. This strengthening pro-
gram should be targeted to increase neck
strength in an eort to modify the risk
factors associated with SRC. Given the
busy nature of a preseason schedule, cli-
nicians should use their own judgment
when determining the volume and in-
tensity of the exercises.
With regard to neck girth, one can
hypothesize that because increased neck
girth is correlated with lower-head lin-
ear and rotational accelerations during
impact,5,8 interventions to increase neck
girth would create a protective advantage
for reducing SRC risk. Some research has
sought to create reference values for neck
girth10,11; however, given the variety of
anatomical structures that influence neck
circumference (eg, subcutaneous fat and
individual muscle volumes), the best in-
terventions for increasing neck girth are
not clear at this time.
We hypothesize that in addition to an
isometric protocol for superficial cervi-
cal muscles, increasing the endurance
capacity of the deep cervical flexors and
extensors may be important for reducing
TABLE Potential Cervical Spine Examinations
and Clinical Considerations in Reducing SRC Risk
Abbreviation: SRC, sports-related concussion.
Factor of Interest Potential Examinations to Consider Measurements to Consider Clinical Relevance Avenues for Future Research
Neck strength and
girth
Isometric neck strength measures
in all 3 planes of motion to quan-
tify flexion, extension, lateral
flexion, rotation, and flexion in
rotation (sternocleidomastoid)
Isometric strength
measurements with
a handheld dyna-
mometer,5,10,19,67,69 fixed
dynamometer,16,19,50,56 or
handheld tension scale11
Lower neck strength is associated with
increased head linear and rotational
accelerations during impact,5,8,9,20 as well
as increased SRC risk.11 Additionally, every
1-lb (approximately 0.45-kg) increase in
neck strength decreased concussion risk
by 5%11
Development of age- and sex-specific
strength normative values
Relationship between neck strength and
SRC risk, including reducing linear and
rotational head acceleration
Relationship between neck strength and
clinical outcomes post SRC
Neck circumference measurement Circumference measure-
ment above10 or below11
the thyroid cartilage
Lower neck girth is associated with increased
head linear and rotational accelerations
during impact,5,8 as well as increased
SRC risk11
Relationship between girth and SRC risk,
including reducing linear and rotational
head acceleration
Relationship between girth and isometric
neck strength
Neck endurance Neck muscle endurance measures Cervical flexor24,28,34 and
extensor35,58 endurance
tests
As increased activation of the deep cervical
flexors is thought to enhance stability
and posture in the cervical spine22,38 and
possibly play a role in controlling head
accelerations,32,60,71 there is potential for
increases in neck endurance in these
muscles to be associated with decreased
risk of SRC
Relationship between deep muscle endur-
ance and SRC risk
Relationship between deep muscle endur-
ance and clinical outcomes post SRC
Strength imbalances Asymmetry in neck strength
measures across the 3 planes
of motion
Calculation of a strength
imbalance score within
planes of motion16
A flexion-extension ratio that is close to 1
correlates with lower head accelerations
during impact,16 which may allow for more
neck protection16,29
Relationship between neck muscle asym-
metries and SRC risk
Posture Observation for forward head
posture
Craniovertebral angle
measurement55
It is speculated that because forward head
posture is associated with a decreased
flexion-extension strength ratio,3 more
extreme postural impairments may be
associated with SRC risk. Obtaining this
specific measure may be important,
as smaller craniovertebral angles are
associated with forward head posture
impairments72
Relationship between head-neck posture and
linear and rotational head acceleration
Relationship between head-neck posture and
severity of clinical outcomes post SRC

journal of orthopaedic & sports physical therapy | volume 49 | number 3 | march 2019 | 205
SRC risk. Deep cervical flexor activation
is thought to enhance stability and im-
prove posture in the cervical spine,22,38
and when activated properly can help to
decrease reliance on superficial muscles
for controlled movement of the cervical
spine.23 Additionally, research has sug-
gested that some of the deep muscles of
the neck may play a role in decreasing
head accelerations.32,60,71 Although the
majority of studies have assessed cervi-
cal flexor endurance, reliable measures
for both cervical flexor endurance1,24,28,34
and cervical extensor endurance35,58 ex-
ist. Normative data have been developed
for the cervical flexor endurance test18,36
and can be utilized for reference values;
we are not aware of normative values for
neck extensor endurance. While we rec-
ommend that cervical spine assessment
and strengthening protocols be per-
formed for both sexes, we believe they are
of particular importance for the female
athlete, given the previously mentioned
sex dierences in neck muscle strength.
Cervical Spine Posture A thorough
postural assessment should be consid-
ered as part of an athlete’s examination.
Forward head posture can be observed
clinically from the sagittal direction
with the athlete in a standing or sitting
position. Measuring the craniovertebral
angle with a goniometer may further as-
sist with quantifying forward head pos-
ture.55 Smaller craniovertebral angles
have been significantly associated with
forward head posture impairments.72 In-
tervening on postural impairments often
implies correcting forward head posture
and normalizing associated muscular im-
balances. When the postural assessment
is complemented by the strength assess-
ment, an individualized intervention plan
can be put into place to correct postural
imbalances. This plan will vary based
on the athlete’s individual presentation;
however, there are some general practices
for reducing forward head posture that
are supported by the literature. Exercises
combining cervical retraction and axial
extension are commonly prescribed to
restore muscle balances in individuals
with forward head posture.41 We also
recommend taking note of the muscles
that are commonly affected by forward
head posture, including the SCM,54 upper
trapezius,6 levator scapulae,6 and suboc-
cipital muscles.6
Questions for Future Research
Most studies to date have examined
linear and rotational head acceleration
in laboratory situations or have related
neck strength to a past history of con-
cussion. Given the relationship between
greater neck strength and girth and re-
duced head acceleration and rotational
forces, coupled with work of Collins et al11
demonstrating that overall neck strength
is lower in those who experience SRC,
the evidence is strong enough to war-
rant future prospective, highly powered
studies that further examine the role of
neck strength as a preventative measure
for SRC, as well as a potential interven-
tion for SRC-related symptoms. That is,
studies should include measurements of
cervical spine characteristics in athletes
before SRCs occur to determine wheth-
er those with increased neck strength
and girth, less neck muscle asymmetry,
greater endurance, and neutral align-
ment of the head and neck experience
fewer SRCs. Furthermore, cervical spine
characteristics may impact clinical out-
comes post SRC by reducing the number
of symptoms, symptom severity, and re-
covery timelines. Thus, it is important
to collect data on these variables and
understand their relationship to clinical
outcomes.
Furthermore, although the magni-
tude of acceleration and rotation forces
on impact may be a proxy for expected
SRC risk due to the range of force magni-
tudes that result in concussive injuries,25
the amount of force required to cause
an SRC is not known. Nor do we know
whether these forces have direct eects
on clinical outcome measures post injury
(eg, symptoms, symptom severity, and re-
covery timelines) or on the severity of po-
tential brain tissue damage post impact.
Thus, prospective studies are needed that
examine for relationships between cervi-
cal spine characteristics, such as neck
strength and endurance, neck girth, and
posture, as well as biomechanical factors
thought to increase SRC risk, such as
head acceleration and rotation. Baseline
biomechanical measures are likely to be
of particular importance in contact and
collision sports, where SRC risk is great-
er, and have the potential to provide ad-
ditional information about SRC risk and
clinical outcomes. Given what is known
about dierences in head acceleration
and rotational forces between males and
females, coupled with observations that
female athletes incur more SRCs and
experience a greater number of symp-
toms and severity, as well as prolonged
recovery time, it is important that studies
are adequately powered to examine sex
dierences.
In addition, it is imperative to develop
sex-specific norms for neck strength that
are associated with reduced risk of SRC.
Normative data on isometric strength
for cervical flexion, extension, sidebend-
ing, and rotation have been published
for males and females,50,56 with females
having weaker necks compared to males,
even when accounting for body weight,
body mass index, height, and neck
length.50,56,67 However, it is not known
whether there are specific strength val-
ues in male and female athletes that may
be associated with fewer SRCs and, more
FIGURE. In the supine position, the athlete is
performing isometric cervical flexion at midrange
cervical flexion. The clinician is able to quantify
the athlete’s strength by using the handheld
dynamometer, which is strapped to the table to
optimize stability and minimize inconsistencies in
clinician force.

206 | march 2019 | volume 49 | number 3 | journal of orthopaedic & sports physical therapy
[ clin ical commentary ]
importantly, fewer clinical symptoms,
reduced symptom severity, and reduced
recovery time.
Additionally, the influence of innate
anatomical variations of the cervical spine
between males and females warrants fur-
ther investigation.61 Specifically, females
tend to have increased ligamentous lax-
it y,51,52,59 smaller vertebral body width,63
and less consistent vertebral coupling,63
which have been suggested to decrease
dynamic stability of the cervical spine.61
These geometric dierences between
male and female necks,67 along with fac-
tors such as the ratio of muscle strength
around the cervical spine, also warrant
further investigation with respect to
their roles in SRC risk or prevention. If
sex-specific strength targets and muscle
strength balance goals can be identified,
then preactivity training programs can be
designed to meet those targets.
Finally, future research examining the
relationship between cervical spine char-
acteristics and SRC risk should consider
sport-specific factors and level of compe-
tition. That is, greater neck strength and
girth, reduced muscle asymmetries, and
neutral alignment of the head and neck
may be of greater importance for athletes
participating in high-impact sports asso-
ciated with greater magnitude of impacts
to the head and body. Athletes participat-
ing in sports with no, or limited, contact
may not need to incorporate these proto-
cols in pre–athletic participation assess-
ments. Nonetheless, we believe it is still
important to collect normative values and
understand dierences in cervical spine
characteristics in athletes who compete
in collision, contact, limited-contact, and
noncontact sports.
CONCLUSION
Significant advancements have
been made in the diagnosis and
management of SRC, yet we are still
falling short in preventing and reducing
the risk of these injuries. As such, an im-
portant focus moving forward is to deter-
mine ways to prevent SRCs and reduce
the severity of their impact when they do
occur. Neck strength, girth, and cervical
spine posture have been identified as po-
tential factors that may reduce SRC risk
by decreasing linear and rotational head
acceleration and the magnitude of force
upon impact. Further, it is speculated
that biomechanical dierences in the
cervical spine between males and females
may impact sex dierences in SRC rates.
Thus, we suggest that it is important to
focus on the biomechanical properties
of the cervical spine, as these properties
may represent a modifiable factor in re-
ducing SRC risk.
Clinically, it is important to com-
prehensively assess the cervical spine,
including strength, girth, and postural
assessments, prior to engagement in
sport, and particularly in those for whom
there is a high risk of impact, to deter-
mine who would benefit from preactivity
cervical spine interventions. Established
normative values and baseline measure-
ments would help in implementing in-
tervention and preventative measures.
In addition, future research that focuses
on how cervical spine biomechanics in-
fluence SRC risk, sex dierences in SRC
rates, and whether reductions in head
acceleration and rotation forces directly
impact SRC outcomes is needed. 
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