Title: King-Devick Ocular testing and
impact monitoring provide a relatively simple process for objectively
identifying and managing concussion in sports participants
Running title:
Randwick rugby union concussion study.
Authors: Cohen,
Adrian MB.,BS., King, D., PhD
1. NeckSafe
PO Box 509
Bondi 2026
Australia
Correspondence to:
Dr. Adrian Cohen
NeckSafe
PO Box 509
Bondi 2026
Australia
Keywords: injury, linear, rotational, impact, rugby union, wireless head impact
sensor, cognitive, baseline, King-Devick,
Submitted to: TBA
Abstract: 232 words
Manuscript: 8111 words
References: 71
Tables: 9
ABSTRACT
Background: Concussion in sport is becoming an
increasingly controversial subject, and one where despite considerable advances
in the last few years, a number of questions remained to be answered and a
large degree of subjectivity clouds decision-making.
Purpose: To evaluate and quantify head impacts via a
wireless head impact sensor acceleration for senior amateur rugby union players
during match participation and analyse concussive impacts using the King-Devick
Test of ocular pursuits.
Study Design: Descriptive observational cohort study
Methods: Data on impact magnitude and frequency were
collected with a wireless head impact sensor worn by senior amateur rugby players participating in
the 2015 domestic season of matches. King-Devick Tests were performed
pre-season and after significant impact scores (PLA > 100g, PRA > 10,000
rads/sec/sec). Participants were asked to undergo a one hour baseline assessment
of balance, cognition and have transcranial magnetic stimulation testing
performed. Following concussive episodes or significant head impacts (as
measured by impact sensors), players were re-tested to elicit any differences
and to assist in providing objective criteria for the return to play process.
Results: 20 concussions were recorded in all, of
which only 3 were witnessed (2 players unconscious on the field, one with
balance disturbance resulting in removal from play).
Conclusion: This study defined concussions as either witnessed
or suspected (on the basis of failed performance against baseline pre-season
data from the King-Devick Test in players tested as a result of high impact g
force or rotational forces recorded). Based on the results, a large number of
concussions would have been missed if impact monitoring had not been utilised,
or King-Devick testing routinely implemented after each game and training.
A combination of
regular King-Devick Ocular testing and impact monitoring provides a relatively
simple process for objectively identifying and managing concussion in sports
participants.
INTRODUCTION
Concussion in
sport is becoming an increasingly controversial subject, and one where despite
considerable advances in the last few years, a number of questions remained to
be answered, and a large degree of subjectivity clouds decision-making.
A concussion
typically occurs as a result of a direct impact to the head or from an indirect
impact applied to the body that is transmitted to the head
[i].
This results when the torso is either decelerated or accelerated rapidly
[ii]. Consequently the head sustains a combination
of linear and angular acceleration. Direct impacts with the head (linear
acceleration-deceleration) and inertial loading of the head (rotational
acceleration-deceleration) have been postulated as the two major mechanisms of
head related injuries such as concussion
[iii].
Linear acceleration produces focal injuries while rotational acceleration
produces both focal and diffuse injuries.
There is limited
published research on the forces associated with concussion. The majority of
the data has come from National Football League (NFL) participation
[iv]
by on-field monitoring and using impact reconstruction of concussive impacts.
In laboratory reconstructions it was reported that concussive events occurred
with face mask acceleration impacts of 78G ±18G to 94G ±27G but were greater on
other areas of the head with an average of 107G to 117G
[v].
Using a helmet telemetry system, real-time head acceleration measurements were
recorded for high school football participants with peak linear accelerations
varying from 55.7 to 136.7g for concussive events.
[vi]
This was extended further with the helmet telemetry system monitoring impacts in
collegiate football participants with peak linear accelerations ranging from
60G to 120G for concussive events with the majority of peak accelerations being
above 95G.
[vii] [viii]
On author has
previously studied head impacts in Rugby Union and League footballers using
instrumented mouthguards
[ix] and
skin-mounted sensors
[x].
In this study, we
attempted to provide objective information as to the impact size, rotational
components, frequency and effects from playing rugby, related especially to
concussion events, using an accelerometer attached to the skin of the neck of
player and compare data from this with a number of objective physical (ocular
and balance) as well as cognitive test parameters.
Our definition of
concussion was based on events that were “witnessed”, either players being
rendered unconscious or staggering after impact, or “suspected” based on failed
performance against baseline pre-season data from the King-Devick Test in
players tested as a result of high impact g force or rotational forces recorded
on their impact data.
Following a
presentation to the Randwick District Rugby Union Football Club (RDRUFC) Board
in February 2015, consent was given to undertake a pioneering study into
concussion using the club’s first grade team.
The study aimed to
collect pre and post injury data, and assess the severity of the impact and
resultant diagnosis of concussion using objective testing measures of force
(via impact sensors/accelerometers) as well as physical parameters (ocular and
balance) and cognitive testing.
Participation in
this study was voluntary and the research paid for by the charity NeckSafe
[xi].
Ethics approval
was sought and received from Auckland University of Technology (AUT)
[xii]
and Deakin University
[xiii]
with governing body approval through World Rugby (WR) and the Australian Rugby
Union Concussion Advisory Group (CAG). In addition, Rugby insurers Gow Gates
P/L were contacted to confirm that there would be no influence on player
insurance, the Rugby Union Players Association (RUPA) were briefed and each
opposing club was contacted to gain consent for their players to participate in
matches where the sensors were being worn. RDRUFC provided legal indemnity to
the ARU, who in turn provided it to World Rugby.
Players were asked
to complete a pre-competition concussion history questionnaire, a sports
concussion assessment baseline evaluation, undertake a physical examination and
complete a number of computerised cognitive tests: Standardised Concussion
Assessment Test version 3
[xiv]
(SCAT3), King-Devick Test
[xv]
(KD) and Axon Cogstate Test
[xvi].
These questionnaires and tests are used to evaluate players in the event of a
suspected concussion occurring, and are referred to as Baseline Tests.
During the season
additional tests were added, including MyBrainSolutions
[xvii]
cognitive test and associated iPad training exercises.
Balance Testing
was assessed using an IsoBALANCE Forceplate
[xviii]
(including CHOICE and MAZE Cognitive test software).
A research team
from Cornell University under Dr. David Putrino also contributed pioneering
balance software using an Oculus Rift 3D Virtual reality system
[xix].
In addition,
Transcranial Magnetic Stimulation (TMS) testing was introduced as another objective
measure of change in concussion
[xx].
King-Devick OCULAR testing
The King–Devick
Test was developed in 1976 by Alan King and Steven Devick, as an indicator of
saccadic performance as it relates to reading ability. For more than 30 years,
the King–Devick Test has been a proven indicator of oculomotor inefficiencies
regarding eye movements during reading.
The King-Devick
Test is used as an objective remove-from-play sideline concussion screening
test that can be administered in minutes. The test is an accurate and reliable
method for identifying players with head trauma and can help to objectively determine whether
players should be removed from games and when they have returned to their
pre-injury test status they can deemed safe to return to sport or practice
(provided they have no symptoms and are not taking medication).
The K-D Test is a
test of ocular saccades(quick, simultaneous movements of both eyes) that
requires a player to read single digit numbers displayed on a tablet or on an
iPad. The test cards become progressively more difficult to read due to
variability of spacing between the numbers. Both errors in reading and speed of
reading are included in deriving a score. Saccades are quick, simultaneous movements
of both eyes.
After suspected head trauma, the player is
given the test and if the time needed to complete the test is any longer than
the player’s baseline test time, the player should be removed from play and
should be evaluated by a licensed professional.
The K-D Test has
been extensively validated for use as a concussion screening tool. In 2011, researchers from the University of
Pennsylvania Perelman School of Medicine published a study in
Neurology of an investigation of the test as a potential rapid
sideline screening test for concussion in a cohort of 39 boxers and mixed
martial arts (MMA) fighters
[xxi].
A pre-fight K-D test
baseline was determined and a post-fight K-D test was also administered after
bouts. Post-fight K–D time scores were significantly worse (higher) than
pre-fight scores for participants who had sustained head trauma during the
match. Additionally, statistical analysis showed that the K–D test had high
test-retest reliability. The researchers concluded that the King–Devick Test is
an accurate and reliable method for identifying players with head trauma, and
is a strong candidate rapid sideline screening test for concussion.
There have been over 50 peer-reviewed studies
published supporting King-Devick Test as a quick, objective indicator of
suboptimal brain function and correlates with indicators of neurological
conditions such as: concussion, reading disabilities, hypoxia, multiple
sclerosis, Parkinson’s disease, and extreme sleep deprivation.
Validated and promoted by the prestigious
Mayo Clinic, the King-Devick test is fast becoming the standard for assessment
of pre-season, sideline and return-to-play ocular tracking, an essential
component of concussion management.
IMPACT TESTING
Players wore an XPatch impact sensor (accelerometer) fitted behind their
ear from X2 Biosystems
[xxii],
a leading medical tech company based in Seattle, Washington. X2 sensors and
their software are used by National Football League (NFL), Major League
Baseball (MLB), National Hockey League (NHL), Major League Soccer (MLS) in the
US and by Saracens RUFC (UK Rugby) as well as in research initiatives based in
New Zealand
[xxiii].
Each week, the
authors attended the fixture and personally fitted the sensors behind the ears
of players. At the end of the match, these were then collected (sometimes requiring
an hour scouring the ground for ones that had dislodged.
The data was
downloaded overnight and analysed and a top-level report was emailed to coaching
and medical staff highlighting players who had sustained high level impacts and
rotational forces.
At the next training
(typically two days after the game), players with high g-force linear were
assessed against the cognitive and physical baselines established earlier in the
season.
In addition
to these linear forces, rotational forces measures in rad/s2 were recorded. It
is hyothesised that these forces may be even more important than direct linear
g-force in the causation of brain injury and concussion
[xxiv].
On the basis
of these results, input was given to the coaching and medical staff on the
concussion status of players which might never otherwise have been known.
RESULTS: IMPACT TESTING
Frequency of head impacts
Over
the duration of the study there were 18,877 impacts to the head greater than 10g (range 10g to 170g) (see Table 1)
recorded over the duration of the study.
The mean number of impacts per player over the
duration of the season of matches was 932 ±623 resulting in a mean of 82 ±69
impacts to the head per player, per match over the duration of the season of
matches. The mean impacts per match were 1,242 ±520 resulting in a mean of 91
±45 impacts to the head per player position, per match. Forwards recorded more
impacts than backs (RR: 1.63 [95% CI: 1.59 to 1.66]; p<0.0001) over the duration of the season of matches.
Magnitude of head impacts
The
impact magnitudes for linear accelerations were skewed to the lower values (Sp=3.27 ±0.02; p<0.0001) with a mean (±SD) linear acceleration of 21 ±14g. Resultant rotational accelerations
were also skewed to the lower values (Sp=2.21
±0.02; p<0.0001) with a mean (±SD)
linear acceleration of 3,107
±3,002 rad/s2.
Location of head impacts
The number of impacts to the areas of the head
varied over the season of matches (see Table 3). The right side of the head
recorded more impacts than the left side of the head (RR: 1.12 [95% CI: 1.09 to
1.14]; p<0.0001) for total impacts
recorded.
Player positions and head impact
characteristics
The
number of head impacts, the number of linear and rotational accelerations, and
the cumulative impact burden per player varied by player position (see Table
2).
In the
forwards, the blind-side flanker recorded a mean of 166 ±56 impacts
per match, and the hooker recorded a median resultant linear acceleration of 18
[13-28]g per match. For rotational
accelerations, the hooker recorded a median of 2,597 [1,388-4,776] rad/s2.
The hooker recorded the highest cumulative linear acceleration burden of 45,883g, and the highest cumulative rotational
acceleration impact burden of 7,174,636 rad/s2. In the backs the
second five-eight recorded a mean of 95 ±60 impacts per match, and the fullback
recorded a median resultant linear acceleration of 19 [13-25]g per match. The centre recorded a
median resultant rotational acceleration of 2,356 [1,329-4,111] rad/s2.
The fullback recorded the highest cumulative linear acceleration burden of
28,717g, and the second five-eight
recorded the highest cumulative rotational acceleration burden of 4,444,897
rad/s2.
The right side of the head recorded more impacts
than the left side of the head for the backs (RR: 1.90 [95% CI: 1.84 to 1.96]; p<0.0001) over the duration of the
match competition season. Forwards recorded more impacts to the left side of
the head (RR: 1.21 [95% CI: 1.17 to 1.25]; p<0.0001)
over the duration of the competition season.
The top left side of the head recorded the highest
median linear accelerations (20 [14-31]g)
for player position and for forwards (24 [17-33]g) while the left side of the head recorded the highest median
linear accelerations for the backs (20 [14-29]g). Linear accelerations were higher on the left than the right
side of the head for impacts recorded to the front (p<0.0001) and the top (p=0.0060)
for player positions.
The top left side of the head recorded the highest
median rotational accelerations (3,130 [1,818-5,896] rad/s2) for
player positions, and this was similar for Forwards (4,081 [2,334-6,126] rad/s2).
Forwards recorded higher rotational accelerations than backs for impacts to the
front left (p=0.0422), back left (p<0.0001), left side (p<0.0001) and the top left (p=0.0388) of the head. There were 79
impacts (1%) above the linear injury risk limit and 2,376 impacts (15%) above
the rotational injury risk limit (see Table 4). Forwards recorded more impacts
in the moderate rotational acceleration (4,600-7,900 rad/s2) range than backs (p=0.0910).
The majority of impacts were in the low impact
severity for linear (98%) and rotational (80%) data acquisition limits. The
calculated mean and median RWE values varied by player position and positional
groups (see Table 5). The calculated RWE varied by the risk function employed.
The values for the RWELinear, RWERotational
and RWECP values for player positions ranged from 0.0001 to 0.2335,
0.0000 to 1.0000 and 0.0001 to 1.0000 respectively.
Two percent (394/18,877) of the RWERotational
values were equal to 1 (100% risk of concussion) and less than 0.4% (7/18,877)
of the RWECP values for the players were equal to 1. None of the RWELinear
values exceeded 0.2335. Forwards recorded higher RWELinear (p<0.0001), RWERotational (p<0.0001) and REWCP (p<0.0001) than backs over the
duration of the match competition season.