J Shoulder Elbow Surg (2013) 22, 1154-1159
www.elsevier.com/locate/ymse
SHOULDER
Scapular dysfunction in high school baseball players
sustaining throwing-related upper extremity injury:
a prospective study
Joseph B. Myers, PhD, ATCa,*, Sakiko Oyama, PhD, ATCb,
Elizabeth E. Hibberd, MA, ATCa
a
Sports Medicine Research Laboratories, Department of Exercise and Sport Science, University of North Carolina,
Chapel Hill, NC, USA
b
Department of Health and Kinesiology, University of Texas, San Antonio, TX, USA
Hypothesis and background: Though commonly suggested as an injury risk factor, scapular dysfunction
has not been established as a prospective cause of throwing-related upper extremity injury in baseball
players. The purpose is to determine whether scapular dysfunction identified during preseason screening
is predictive of increased risk of throwing-related shoulder and elbow injuries in high school baseball
players.
Materials and methods: The presence or absence of scapular dysfunction was obtained prospectively
during preseason screenings in 246 high school baseball players over the 2010 and 2011 seasons. Exposure
and injury surveillance data were then obtained weekly over the course of each season to determine
whether scapular dysfunction was predictive of subsequent throwing-related upper extremities sustained.
Results: There were 12 throwing-related upper extremity injuries sustained in the 246 participants,
yielding an injury rate of 1.0 per 1,000 athlete exposures. There were no significant differences in injury
rates between the participants with normal scapular function versus subtle scapular dysfunction (P ¼ .62),
normal scapular function versus obvious scapular dysfunction (P ¼ .26), or subtle versus obvious scapular
dysfunction (P ¼ .45).
Conclusion: This study showed that scapular dysfunction identified during preseason screenings is not
associated with subsequent throwing-related upper extremity injury.
Level of evidence: Level I, Prospective Design, Prognosis Study.
Ó 2013 Journal of Shoulder and Elbow Surgery Board of Trustees.
Keywords: Baseball; shoulder; elbow; scapula; throwing; clinical assessment
The Institutional Review Board at the University of North Carolina
at Chapel Hill approved this study (No. 09-1268). The protocol is entitled
‘‘Identification of Physical Characteristics Associated With Upper Extremity Injuries in High School Baseball Players: A Prospective Study.’’
*Reprint requests: Joseph B. Myers, PhD, ATC, Department of Exercise and Sport Science, University of North Carolina at Chapel Hill,
CB 8700 Fetzer Hall, Chapel Hill, NC 27599-8700, USA.
E-mail address: joemyers@email.unc.edu (J.B. Myers).
Throwing-related upper extremity injuries, which
comprise more than half of all injuries occurring in baseball, affect a large number of competitive baseball
players,5,10,16,17,20,21,23,26,28,31 resulting in significant time
loss from participation.23 Epidemiologic studies show that
approximately 20% and 70% of baseball players have
shoulder and elbow pain, respectively,6,9-11,16,17,20,21,26,30
1058-2746/$ - see front matter Ó 2013 Journal of Shoulder and Elbow Surgery Board of Trustees.
http://dx.doi.org/10.1016/j.jse.2012.12.029
Scapular dysfunction injury risk in baseball
with many of these injuries occurring in high school–aged
players.4,7,20,26,28,30-32 The shoulder and elbow not only are
the most frequently injured body parts but also result in the
longest time loss when injured.23
Although there are various proposed intrinsic and extrinsic factors suggested as risk factors for throwing-related
upper extremity injury, scapular dysfunction has been repeatedly suggested to be a contributing factor.3,13,14 Scapular
dysfunction, often termed scapular dyskinesis,13,14,36 is an
alteration in position and motion of the scapula during
shoulder girdle motion. Scapular dysfunction is believed to
be problematic in baseball players because of the integral
role that the scapula plays in shoulder movement. The
resulting dysfunctional scapular movement affects the upper
extremity kinetic chain and can lead to overuse injuries by
altering the stress pattern on the structures surrounding the
shoulder and elbow joint. However, whether the scapular
dysfunction is linked to increased risk of throwing-related
upper extremity injuries has not been shown.
In addition, a majority of the work on scapular dysfunction to date has used sophisticated laboratory equipment
(electromagnetic tracking devices primarily) to measure
scapular motion. Yet, visual assessment of scapular motion
is performed as part of clinical practice during preseason
screening and injury evaluations, to identify the presence
of scapular dysfunction. Currently, there are several published descriptions of clinically based visual scapular
assessment methodology,15,22,25,29 with the scapular dyskinesis test (SDT) described by McClure and associates22,33
appearing to have the highest level of both reliability22 and
validity.22,33 If the scapular dysfunction identified with the
SDT is associated with increased risk of injuries, this test
could be used as a screening tool to identify baseball
players who are at risk of throwing-related shoulder or
elbow injuries. Therefore, the purpose of this study is to
determine whether scapular dysfunction detected during
preseason screening is associated with increased risk of
throwing-related shoulder and elbow injuries in high school
baseball players.
Materials and methods
Procedures
All participants in this study were varsity-level, male baseball
players who participated at 1 of 17 high schools from across the
state of North Carolina during the 2010 or 2011 spring baseball
season. Before participation, a parent or guardian consented to
his or her son’s study participation by providing a signature on
a university institutional review board–approved parental consent
form. In addition, university-approved consent/assent was obtained on the day of testing from each participant. All consenting
players on a team participated in the study regardless of playing
position.
All testing was conducted at each team’s high school facility
(athletic training room, gymnasium, or classroom), allowing for an
1155
entire team to be screened during 1 testing session. All testing
sessions were conducted from mid January to mid February, to
capture the desired data before the beginning of the spring baseball season (spring season starts the second week in February
in the state of North Carolina). Each participant started the testing
session by completing a participation history survey developed
by use of Teleform document scanning and recognition software
(Autonomy Cardiff, Vista, CA, USA). The survey captured
a history of the amount of baseball participation during the
player’s entire career, current and past playing positions, and
throwing-related upper extremity injury history. Each player then
underwent a clinical-based scapular dysfunction assessment.
Then, over the course of the season, each participant’s game and
practice exposure and injury were captured weekly with the aid
of the certified athletic trainer, over the course of the entire spring
season.
Scapular dysfunction assessment
The SDT described in studies by McClure and associates22,33 was
used to assess scapular dysfunction. The SDT has been shown to
be both reliable and valid when compared with electromagnetic
tracking methodology.22,33 Each participant was asked to remove
his shirt and stand 2 to 3 meters away from a tripod-mounted
video camera (Sony MiniDV Handycam Camcorder [model
DCR-HC62]; Sony Corporation of America, San Diego, CA,
USA). The camera was positioned to obtain a posterior view of the
participant’s torso and arms (Fig. 1). Each participant was given 2
handheld weights whose mass was dependent on his body mass.
For participants weighing less than 68.1 kg, 1.4-kg (3-lb) handheld
weights were used, whereas for those with a mass greater than
68.1 kg, 2.3-kg (5-lb) weights were provided. Each participant
was instructed on how to perform bilateral shoulder flexion and
abduction raises and provided an opportunity to practice. Once the
participant successfully demonstrated the task, video recording
was initiated and each participant was instructed to perform 5
bilateral shoulder flexion repetitions immediately followed by 5
abduction repetitions. All repetitions were performed at a speed of
3 seconds for elevation and 3 seconds to descend. All videos were
saved for later analysis.
After completion of data collection, 2 certified athletic trainers
with extensive clinical experience (working with overhead athletes
for >5 years) and PhD-level training in upper extremity biomechanical/neuromuscular research (video analysis, electromagnetic
tracking, electromyography, and diagnostic ultrasound) independently graded each participant’s video using the operational
definitions of normal scapular function, subtle dysfunction, and
obvious dysfunction.22,33 When there was disagreement between
the 2 observers, the videos were reviewed together and discussed
and a consensus was obtained.
Injury surveillance
Over the course of the 2010 and 2011 seasons, the exposures and
injuries sustained by each participant were tracked with the aid of
the certified athletic trainer employed at each high school. During
each week of the season, the athletic trainer received a Web link
by E-mail from the study coordinator for an online injury
surveillance survey. Each week, the athletic trainer reported
practice and game exposures, where an athlete exposure was
1156
J.B. Myers et al.
Table I
Participant characteristics (N ¼ 246 participants)
Data
Age (mean SD) (y)
Height (mean SD) (cm)
Mass (mean SD) (kg)
Length of baseball participation
(mean SD) (y)
Primary or secondary position
of pitcher
16.4
179.7
76.3
10.5
1.1
7.4
12.5
2.7
91 (37.0% of participants)
Results
Figure 1
Assessment of scapular dysfunction using SDT.
defined as full participation in a practice session or a game. When
a participant missed an exposure or had a limited exposure,
additional information was obtained, including the reason for the
missed exposure (because of either injury or another reason).
When an injury was listed as the reason for a missed or limited
exposure, the survey would obtain injury-specific data including
diagnosis (made by the athletic trainer and/or physician), injury
mechanism, and exposure loss/modification. This study focused
on throwing-related upper extremity injuries, which was defined
as a shoulder or elbow injury that resulted from the act of
throwing/pitching and resulted in at least 1 missed or limited
exposure. All injury and exposure data were verified at the end of
the baseball season with the help of each high school’s athletic
trainer (injury data) and coach (attendance, practice, and game
participation).
Statistical analyses
Initially, agreement between the 2 independent raters of scapular
dysfunction (normal, subtle, and obvious) was determined using
calculation of weighted and maximum k scores. The injury rates
for the participants with normal scapular function, subtle scapular
dysfunction, and obvious scapular dysfunction were calculated as
the number of injuries reported divided by the number of exposures and were reported per 1,000 athlete exposures. The injury
rates among groups were compared by use of Poisson regression
with a generalized estimating equation and natural log of the total
number of exposures (practices and games) as an offset, as well as
an estimation of rate ratios.
In this study, 248 varsity-level players from 17 high schools
initially were evaluated. Two athletes were subsequently
excluded from this study because they were dismissed from
the team early in the season, leaving 246 athletes included
in the analysis. Complete demographics appear in Table I.
To establish the agreement between the independent
raters of scapular dysfunction in this study, weighted k
scores were calculated. Agreement between independent
raters was considered good (0.60-0.80),1 yielding a weighted
k score of 0.730 (maximum k, 0.885).
Over the course of the 2 seasons, 12 throwing-related
upper extremity injuries were sustained and reported.
A description of these injuries appears in Table II. The
injury rates (with accompanying exposures) in the participants with normal scapular function, subtle scapular
dysfunction, and obvious scapular dysfunction are presented in Table III. There were no significant differences in the
injury rates between the participants with normal scapular
function versus subtle scapular dysfunction (0.71; 95%
confidence interval [CI], 0.19-2.70; c2 ¼ 0.25; P ¼ .62),
normal scapular function versus obvious scapular
dysfunction (0.30; 95% CI, 0.04-2.40; c2 ¼ 1.29; P ¼ .26),
or subtle versus obvious scapular dysfunction (0.42; 95%
CI, 0.04-4.04; c2 ¼ 0.56; P ¼ .45).
Discussion
Given the importance that clinicians and researchers place
on scapular function (and dysfunction) as it relates to injury
in baseball players (and all overhead athletes), the purpose
of this study was to prospectively examine whether scapular dysfunction identified during preseason screenings is
a risk factor for throwing-related shoulder and elbow
injuries in baseball players. It was hypothesized that those
individuals who exhibited scapular dysfunction during
preseason screening would be more at risk of sustaining
a throwing-related upper extremity injury during the
season. That hypothesis was rejected in this study. Participants in this study with subtle or obvious scapular
dysfunction were not at a significantly greater risk of
sustaining a throwing-related shoulder or elbow injury.
Scapular dysfunction injury risk in baseball
Table II
1157
Injuries reported
No. of participants
Throwing-related arm injuries reported
Shoulder injury
Elbow injury
Specific injuries reported
1. Elbow: flexor mass strain
2. Shoulder: rotator cuff strain
3. Elbow: flexor mass strain
4. Shoulder: rotator cuff strain
5. Shoulder: posterior impingement
6. Shoulder: posterior impingement
7. Shoulder: biceps tendinosis
8. Elbow: medial epicondylitis
9. Shoulder: posterior impingement
10. Shoulder: posterior impingement
11. Shoulder: deltoid strain
12. Shoulder: deltoid strain
First/second position
Missed exp
Limited exp
Catcher/pitcher
First base/pitcher
Shortstop/pitcher
Shortstop/pitcher
Catcher/shortstop
Outfield/pitcher
Pitcher/shortstop
Pitcher/first base
Pitcher/outfield
Outfield/none
Pitcher/none
Outfield/none
0
0
5
5
0
15
1
10
6
0
0
1
5
2
15
1
3
0
9
0
4
1
13
0
12 (4.9%)
9 (3.7%)
3 (1.2%)
First/second position, Primary and secondary positions of player injured; Limited exp, number of exposures for which participation had to be modified
because of injury; Missed exp, number of missed exposures because of injury.
Scapular dysfunction has been linked to various
throwing injuries in a cross-sectional study.18 However,
a limitation of a cross-sectional study is that it is unable to
determine whether the scapular dysfunction predisposed the
athlete to injury or whether the injury resulted in alteration
of scapular movement. Therefore, this study aimed to
identify scapular dysfunction before the injury occurred. Of
the 246 participants, 122 were identified as either having
subtle or obvious scapular dysfunction, yet only 4 of those
individuals went on to sustain an injury. Individuals who
were identified as having normal scapular motion patterns
sustained the remaining 8 injuries. This observation indicates that use of the SDT as a preseason season risk
assessment tool might be limited.
There are several possible interpretations for our observation that showed an absence of a link between preseason
scapular dysfunction and development of injury over the
course of the season. First, alteration in scapular movement
may not necessarily be related to injuries. Although many
studies have identified scapular dysfunction after the injury or
complaints of pain, no study has shown that the presentation of
scapular dysfunction precedes pain or injury. An adaptation in
scapular position and orientation at rest27 and during shoulder
elevation24 has been shown in healthy uninjured overhead
athletes. In our study, all 122 participants who showed either
subtle or obvious dysfunction were asymptomatic at the time
of testing. These studies support the interpretation that altered
scapular movement may not predispose throwers to injuries
but that scapular dysfunction reported in the literature to be
present after injury results from the injury.
The second interpretation of this study observation is that
1-time preseason screening of scapular dysfunction cannot
detect potential changes in scapular movement occurring
during a season that may have led to injuries. As previously
stated, all of these measurements were taken at the start
of the season, before injuries occurred. No additional measurements were taken after the season or after an injury was
sustained. Previous work has shown that scapular movement
patterns can change over the course of the season.34,35
Potentially, players who sustained an injury may have adapted from their preseason ‘‘normal’’ scapular movement
pattern over the course of the season, putting additional
stress on the soft tissues about the shoulder and elbow,
contributing to injury. However, this could not be determined
in our study. Future work should include not only a prospective preseason screening data collection session but also
subsequent follow-up later in the season or after injury.
A third interpretation of this study is that other factors
besides scapular dysfunction had a larger influence on
injury development. Scapular dysfunction is one of many
potential risk factors for injuries. Although we hypothesized that scapular dysfunction may be a risk factor for
injury, we recognize that throwing-related upper extremity
injuries result from a multitude of factors, with scapular
dysfunction being only one of many potential contributors.
Those other factors that have been identified in prospective
studies (which were not examined in this study) include
patterns of flexibility,32,38 humeral geometry,37 strength
patterns,12 and actual game/participation factors.6,20,21 It is
possible that the effects of scapular dysfunction on injury
were overshadowed by these other factors.
An additional reason that no association was present
might be that there were a low number of throwing-related
injuries observed in our study. Compared with the literature, our entire sample group (246 participants) had a lower
incidence of injury of 1.0 per 1,000 athlete exposures. The
incidence of shoulder and elbow injuries in baseball players
reported in the literature is 1.39 to 5.83 per 1,000 exposures.2,7-9,19-21,23,26,28,30 The differences in injury rates
across the literature may stem from potential disparities in
1158
Table III
SDT
Normal
Subtle
Obvious
Overall
J.B. Myers et al.
Exposure and injury risk analyses
No. of participants
124
69
53
246
No. of injuries
8
3
1
12
No. of athlete exposures
Injury rate (1,000 athlete exposures)
Practice
Game
Total
4,270
2,294
1,714
8,278
1,916
953
862
3,731
6,186
3,247
2,576
12,009
how injury was defined. In this study, we used a conservative definition of injury (ie, a missed exposure) to eliminate
the typical upper extremity aches and pains that are common in high school overhead sports participants. Perhaps
this injury definition may have resulted in failure to capture
some injuries that throwers were able to play through,
which resulted in a lower estimate of injury risks. In addition, most of the epidemiology work to date has focused on
older players (collegiate and professional level) who play
the pitching position. Our study included not only pitchers
(who have a higher risk of injury) but also all position
players who are of high school age. The result might have
been decreased injury incidence.
A limitation that must be acknowledged is that this study
only used 1 method of assessing scapular dysfunction (the
SDT described by McClure and associates22,33). Yet, there
are other methods published that may better identify injury
risk.15,22,25,29 This is an area for future research. We opted
for the methods described by McClure and associates because of the higher level of reliability and validity established for their scapular assessment.
1.29
0.92
0.39
1.00
Conclusions
Though commonly suggested as an injury risk factor for
throwing-related shoulder and elbow injury in baseball
players, scapular dysfunction (as measured with a clinical screening tool before the start of the season) could
not be established as a prospective risk factor in this
study. This study showed that scapular dysfunction is
commonly seen in high school baseball players.
Acknowledgments
We acknowledge both Amber Sauls and Casey Shutt for
their contribution to data collection and data reduction.
We also acknowledge the certified athletic trainers at the
participating high schools for the contribution they made
to the injury surveillance portion of this study.
Clinical significance
Disclaimer
The results of this study provide some valuable information
that can be applied clinically. First, this study showed that
scapular dysfunction identified during screenings is not
associated with subsequent injury. This would suggest that
its use as a preseason season risk assessment tool might be
limited. However, our observation does not necessarily
refute the previous studies linking scapular movement to
injury, because scapular dysfunction that developed during
the season, which was not examined in this study, may have
led to injuries. Periodic screening of scapular motion and
close monitoring of shoulder and elbow symptoms during
a season may be necessary to determine whether the
alteration in scapular movement is associated with injury
development. However, the assessment of scapular dysfunction can be administered with reliability. We established
good reliability in this study, supporting previous literature
showing its reliability and validity. Thus, it appears to be
a good tool for identifying atypical scapular movement
patterns. So, although the tool might not identify risk before
injury, it may reliably identify scapular dysfunction as part
of a clinical examination for scapular dysfunction that may
be present when injury occurs.
The authors, their immediate families, and any research
foundations with which they are affiliated have not
received any financial payments or other benefits from
any commercial entity related to the subject of this
article.
The project described was supported by grant No.
R03AR055262 from the National Institute of Arthritis and
Musculoskeletal and Skin Diseases/National Institutes of
Health. Its contents are solely the responsibility of the
authors and do not necessarily represent the official views
of the National Institute of Arthritis and Musculoskeletal
and Skin Diseases or National Institutes of Health.
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