Abstract
Background: Repetitive trauma to the hand is a concern for baseball
players. The present study investigated the effects of repetitive trauma and
the prevalence of microvascular pathological changes in the hands of minor
league professional baseball players. In contrast to previous investigators,
we documented the presence of abnormalities in younger, asymptomatic
individuals.
Methods: Thirty-six baseball players on active minor league rosters
underwent a history and physical examination of both hands as well as
additional specialized tests, including Doppler ultrasound, a timed Allen
test, determination of digital brachial pressure indices, and ring sizing of
fingers. Data were compared between gloved hands and throwing hands, hitters
and nonhitters, and players at four different positions (catcher [nine
subjects], outfielder [seven subjects], infielder [five subjects], and pitcher
[fifteen subjects]).
Results: Digital brachial indices in the ring fingers of the gloved
(p < 0.05) and throwing hands (p < 0.02) of catchers were significantly
diminished compared with those in all other players. Doppler testing showed a
significantly greater prevalence of abnormal flow in the ulnar artery at
Guyon's canal when catchers were compared with other position players (p <
0.01). Doppler abnormalities were significantly more common in the gloved hand
compared with the throwing hand (p < 0.05). Seven of nine catchers (and
only catchers) were found to have index finger hypertrophy (average change,
two ring sizes; p < 0.01); the hypertrophy occurred at the proximal phalanx
and the proximal interphalangeal joint of the gloved hand. Catchers had a
significantly higher prevalence of subjective hand symptoms (specifically,
weakness in the gloved hand) compared with pitchers and infielders/outfielders
(44% compared with 7% and 17%, respectively; p < 0.05).
Conclusions: Microvascular changes are present in the hands of
otherwise healthy professional baseball players in all positions, with a
significantly higher prevalence in catchers, prior to the development of
clinically important ischemia. Repetitive trauma resulting from the impact of
the baseball also leads to digital hypertrophy in the index finger of the
gloved hand of catchers. Gloves currently used by professional catchers do not
adequately protect the hand from repetitive trauma.
Level of Evidence: Therapeutic Level IV. See Instructions
to Authors for a complete description of levels of evidence.
Baseball players are repeatedly exposed to hand trauma with each
swing of the bat or impact of the ball into the glove. This exposure has been
documented to lead to ischemia of the hand and digits with symptoms of
paresthesias, cold insensitivity, and
cyanosis1-3.
Modern-era gloves used by professional baseball players have undergone
sequential modifications in order to better protect the catching hand. The
purposes of the present study were (1) to systematically examine the hands of
professional baseball players in order to document the effects of repetitive
trauma and to identify any vascular abnormalities that may be present prior to
the manifestation of clinically important hand symptoms and (2) to evaluate
the specific occupational risk factors (including position, bat type, glove
padding, and exposure time [defined as the number of years of participation in
baseball]) leading to digital ischemia.
From April 2001 to September 2001, thirty-six minor league
professional baseball players underwent a comprehensive evaluation of the
gloved and throwing hands. Informed consent was obtained from each player, and
the study protocol conformed to the ethical guidelines of the 1975 Declaration
of Helsinki as reflected in a prior approval by the Wake Forest University
Baptist Medical Center institutional review committee. Consent also was
obtained from the headquarters of each professional team prior to the
study.
Thirty-six professional baseball players from four teams at the high
"A" level in the Carolina League (based in Greensboro, North
Carolina) participated in the study. All players who played only the catcher
position for the team were included in the study because of the high
prevalence of abnormalities in catchers as reported in previous
studies1,3.
The remaining players were randomly selected on the basis of position so that
infielders, outfielders, and pitchers were represented. In addition, subjects
were stratified as "hitters" and "nonhitters" on the
basis of whether or not they took batting practice or hit in games. On the
teams that were reviewed, no pitchers hit in games or took batting practice;
thus, pitchers were classified as "nonhitters" and were compared
with all other position players (including catchers), who were classified as
"hitters."
History
A detailed medical history that included information on previous hand
injuries and professional sports activity was recorded. Each subject answered
questions related to hand symptoms, including weakness, numbness, tingling,
and pain. Any player who reported any of these symptoms was then asked (1)
whether the symptoms occurred in the throwing hand, in the gloved hand, or
both and (2) whether the symptoms occurred during activity, at rest, or both.
Players also were questioned about the types of equipment utilized, including
bat type, glove type, and protective padding worn under the glove. Bat type
refers to the shape of the butt of the bat, with type 1 being squared and type
2 being tapered at the end. Many hitters hold the end of the bat in the lower
hand at approximately the level of the hook of the hamate, where the butt of
the bat can impact the hand when the ball is hit. Thus, the different bat
types were considered to be factors that might contribute to hand
injuries.
Physical Examination
Each player underwent a physical examination. All examinations and
specialized tests were performed at rest prior to any daily activity. No
player was tested during or immediately after a practice or a game. No
neurological examination was performed. The hands and wrists of each player
were visually inspected for evidence of repetitive trauma, including changes
in skin color, callosities, ulcers, edema, loss of skin wrinkles, or
deformity. Any finger that demonstrated hypertrophy on visual inspection was
examined with use of a standard ringsizing device used by jewelers and was
compared with the corresponding finger on the contralateral hand. This device
consists of multiple rings that increase incrementally in half-sizes from 8 to
15, with a 1.25-mm difference between successive rings. The assigned size was
determined on the basis of the ability of the examiner to place the smallest
possible ring past the proximal interphalangeal joint to the base of the
webbing of the affected finger.
Specialized Testing
Timed Allen Test
The radial and ulnar arteries on the gloved and nongloved hands were
assessed with the timed Allen test. An examination was labeled as normal if
reperfusion occurred in less than six seconds, as delayed if reperfusion
occurred in six to fifteen seconds, and as abnormal if reperfusion occurred in
more than fifteen
seconds4. Digital
Allen tests were not performed. All assessments were performed by the same
individual (A.M.S.).
Doppler Ultrasound
A handheld 8-MHz Doppler ultrasound device (IMEXDOP CTI+; Nicolet Vascular,
Golden, Colorado) was used to assess the radial and ulnar arteries of both
hands at various points along the path of the artery. The radial artery was
examined from 2 to 4 cm proximal to the wrist crease to the end of the
anatomic snuff box. The ulnar artery was examined from 4 cm proximal to the
wrist crease into the palm, 1 cm distal to the hook of the hamate. The audio
characteristics of the arterial flow were assessed by the examiner and were
recorded as triphasic (normal), biphasic, uniphasic, or absent. The waveform
recorded by the device was examined to confirm either zero, one, two, or three
peaks in order to verify the flow quality.
Digital Brachial Indices
Digital brachial indices were recorded for the index and ring fingers of
the gloved and throwing hands with use of a portable vascular diagnostic
instrument (Life Sciences A-V Recorder; Life Sciences, Greenwich,
Connecticut). This instrument incorporates a manual brachial cuff pressure
gauge, a dual-frequency continuous wave Doppler device, a photoplethysmograph,
and a two-speed thermal strip recorder for noninvasive measurements of
segmental blood pressures. Digital brachial indices were calculated with use
of the values obtained for the tested fingers as the numerator and the
systolic brachial pressure in the tested extremity as the denominator.
Statistical Evaluation
Statistical evaluation of the data was performed using the SAS statistical
software package (SAS Institute, Cary, North Carolina). Analysis of variance
techniques were used to test for differences in continuous outcomes between
pitchers, catchers, and infielders/outfielders. The Fisher exact test was used
to compare categorical outcomes between positions. Spearman correlations were
used to correlate continuous outcomes. The McNemar test was used to compare
categorical outcomes between the throwing and gloved hand on the same
individual. Paired t tests were used to test for differences in continuous
measures within the same person. The level of significance was set at p <
0.05.
Demographic Data
A total of thirty-six male baseball players participated in the
study. The subjects included nine catchers, seven outfielders, five
infielders, and fifteen pitchers. Infielders and outfielders were grouped
together in the analysis as position players. The baseline characteristics of
the subjects are presented in Table
I. There were no differences between the groups with respect to
any baseline characteristic except for the use of pads. Catchers were
significantly more likely to wear protective padding under their glove on the
catching hand compared with all other players (p < 0.0001). All hitters
used wooden bats exclusively. All catchers used a glove of a similar design
(that is, a glove with a single break to allow for one-handed catching).
Hand Symptoms
Overall, eleven (31%) of the thirty-six players reported some type of hand
symptoms (pain, numbness, weakness, or tingling). Catchers were more likely
than any other player to have weakness. Weakness was reported by 44% of
catchers, compared with 7% of pitchers and 17% of infielders/outfielders (p
< 0.05). When catchers were analyzed independently, they had significantly
greater prevalences of weakness and overall symptoms in the gloved hand (44%
and 56%, respectively) compared with the throwing hand (0% and 11%,
respectively) (p < 0.05 for each comparison). Furthermore, only catchers
had symptoms at rest, and there was a trend for catchers to have more pain at
rest in the gloved hand than in the throwing hand, but this trend did not
reach significance (p = 0.08). Therefore, catchers had significantly more hand
symptoms, and these symptoms occurred more frequently in the gloved hand
compared with the throwing hand.
The greater prevalence of hand symptoms in catchers occurred despite the
use of protective padding by 89% of these players as compared with 15% of all
others. Eight of the nine catchers used additional padding in the form of a
batting glove worn on the hand under the catcher's mitt. With the numbers
available, there was no correlation between pad use and the prevalence of
symptoms (p = 0.44), indicating that pads did not adequately protect the hand.
In addition, there was no correlation between the prevalence of symptoms and
the number of years in baseball (p = 0.58) or the number of years at the
position (p = 0.49). Among hitters, there was no correlation between bat type
and the prevalence of symptoms (p = 0.71).
Vascular Evaluations
Timed Allen Testing
Timed Allen testing revealed abnormal findings (delayed or absent
reperfusion) in eight subjects (22%) overall, including one catcher, three
pitchers, and four infielders/outfielders. The abnormal findings in the
catcher were present in the gloved hand, whereas the abnormal findings in the
pitchers and the position players tended to be found in either the throwing
hand (three subjects) or the gloved hand (four subjects). The distribution
between radial and ulnar-sided abnormalities was equal. With the numbers
available, there was no significant difference between positions or between
gloved and throwing hands.
Digital Brachial Indices
Digital brachial indices were calculated for the index and ring fingers in
the throwing and gloved hands of all subjects
(Table II). Catchers had
significantly lower digital brachial indices in the ring finger of the
throwing hand (p < 0.02) and the gloved hand (p < 0.05) compared with
all other players. Hitters (catchers and infielders/outfielders) had
significantly lower digital brachial indices in the gloved ring finger
compared with pitchers (p < 0.02). In all players, the gloved hand
corresponded with the lower hand on the bat when hitting. With the numbers
available, no significant differences were found between the throwing hands
and the gloved hands in any group.
Ultrasound
Doppler ultrasound testing revealed abnormal findings (biphasic, uniphasic,
or absent flow) in five catchers, compared with twelve other players. All five
of these catchers had abnormal findings in the gloved hand, and two of them
also showed anomalies in the throwing hand. Compared with all other players,
catchers had a significantly greater prevalence of abnormal Doppler signals in
the ulnar artery at Guyon's canal in the gloved hand (p < 0.01). Four
catchers demonstrated biphasic flow in this region, whereas only one other
player (an infielder) demonstrated abnormal flow in this region. Among
catchers, there was also a significantly higher prevalence of abnormal
ultrasound findings at Guyon's canal when the gloved hand (four of nine) was
compared with the throwing hand (zero of nine) (p < 0.05). With the numbers
available, there were no significant differences at any site along the radial
artery or at any other site along the ulnar artery. There was no correlation
between the findings of any mode of vascular testing and the number of years
in professional baseball, the number of years at the position, or the number
of years of playing overall.
Digital Hypertrophy
Hypertrophy of the index finger was found to occur exclusively in catchers.
In each case, the hypertrophied digits demonstrated enlargement of the soft
tissues overlying the proximal phalanx and the proximal interphalangeal joint.
Seven of the nine catchers demonstrated this finding, compared with none of
the twenty-seven pitchers, infielders, or outfielders. This difference was
highly significant (p < 0.0001). In all seven cases, the larger digit was
found to be the index finger on the gloved hand; this finger was an average of
1.89 ring sizes (approximately 5 mm in diameter) greater than the index finger
on the throwing hand. No digit other than the gloved index finger demonstrated
hypertrophy. The difference in size between the index finger of the gloved
hand and the index finger of the throwing hand was significant (p <
0.01).
Calluses
Calluses were present on the gloved hand of seven catchers (78%), compared
with three pitchers (20%) and three infielders/outfielders (25%). This
difference was significant (p = 0.01). All calluses were present in the palm
just distal to the level of the distal palmar crease, primarily at the base of
the index and long fingers. Furthermore, catchers had significantly more
calluses on the gloved hand (prevalence, 78%) than on the throwing hand
(prevalence, 22%) (p = 0.02). With the numbers available, neither pitchers nor
infielders/outfielders had a significant difference between the gloved hand
and the throwing hand with regard to the presence of calluses (p = 0.18 and
1.0, respectively).
The occurrence of vascular injury in association with
repetitive-impact hand trauma during high-level sports activities has been
well established. Ischemia due to ulnar artery insufficiency has been
documented in many sports involving the use of a racket or club, such as
tennis5,
golf6,
badminton7, and
hockey8.
Anatomically, this ischemia is thought to result from the repetitive impact of
the racket or club into the ulnar artery against the hook of the hamate as the
artery passes distal and superficial to the transverse carpal
ligament9,10.
Similar findings have been noted in patients who use the hand as a striking
device, as in
handball11, and
applause-induced ischemia has even been noted in fans who watch these
sports12. The
current study documents pathological changes in the hands of a representative
sample of young, professional baseball players who had not previously reported
symptoms and had not yet sought treatment.
Professional baseball players may be exposed to more repetitive hand trauma
than other athletes are, with trauma being sustained with each catch of a ball
or swing of a bat. Players take batting practice daily, often hitting hundreds
of balls in one session. The impact to the hypothenar area of the hand in
baseball players is known to occur as the handle of the bat drives into the
hamate with each swing, occasionally leading to fractures of that
bone13. The
decrease in the digital brachial indices in the ring fingers of hitters as
compared with pitchers (who take little, if any, batting practice) may be
related to this phenomenon. The ring finger and the corresponding metacarpal
are the common area of impact from the end of the bat. However, the type of
bat (that is, tapered or squared end) had no effect on digital brachial
indices and likely is not a risk factor for hand injuries related to
hitting.
Catchers sustain hand trauma as a result of the repetitive impact of the
pitched ball into the mitt and as a result of foul balls that strike the
ungloved hand. This may explain the diminished digital brachial indices in the
throwing hand of catchers in addition to the changes observed in the gloved
hand. Catchers may receive 150 pitches per game at speeds well over 90 mph
(145 km/hr). Catchers also must catch warm-up pitches from pitchers before
entry into the game and also must catch practice pitches from pitchers who are
not competing in the game that day. This could easily add up to >300
impacts to the gloved hand of the catcher per day. Pitchers and position
players are subjected to far fewer impacts per game. In addition, noncatchers
tend to receive the ball in the webbing of the glove, away from the hand
itself. The current design of catcher's mitts ensures that the majority of the
pitches are caught at the base of the webbing in a location that corresponds
anatomically with the index metacarpal head. This location is an area where
digital nerves and vessels are relatively vulnerable, which may explain the
high prevalence of symptoms, hypertrophy, and vascular changes in the index
finger of the gloved hand of catchers in the current study. However, catchers
also had significant abnormalities on the ulnar side of the hand (decreased
ring finger digital brachial indices and a higher prevalence of Doppler
anomalies at Guyon's canal), which may represent global hand trauma associated
with the impact of the ball being distributed by the glove to the entire
hand.
Previous evaluations of competitive baseball players have detailed impaired
circulation in the index finger as indicated by symptoms of hypersensitivity
and cold
intolerance3, a
positive digital Allen
test1, and Doppler
flow abnormalities. Catchers were more likely than other players to exhibit
abnormalities1-3
and to seek treatment for their
symptoms2. Also,
correlations were found between accumulated playing time and digital
symptoms3. In
addition, each of the previous studies stressed the need for improvements in
protective equipment, especially with regard to glove
technology1-3.
The current study confirms many of these points, specifically with regard to
hypertrophy of the index finger of the gloved hand as well as flow
abnormalities in the gloved hand. Despite the recommendations for improvements
in glove technology in those previous studies, current gloves apparently are
still inadequate for the protection of catchers.
The present report expands the findings of previous studies by confirming
the presence of microvascular changes in the hands of relatively young,
otherwise healthy players from all positions prior to onset of clinically
evident digital ischemia. None of the players in the present study had sought
the care of a physician or trainer because of symptoms of pain, weakness,
numbness, or tingling. However, many of the catchers were wearing a thin
batting glove or additional foam padding under their catcher's glove for
additional protection because of symptoms that they had experienced. No
players had sought or required treatment for hand ischemia or had been limited
in their activity.
Despite well-padded mitts and the use of additional padding, the catchers
in the present study continued to demonstrate changes in the gloved index
finger, including significant Doppler ultrasound abnormalities and thickening.
However, the throwing hand showed significantly fewer abnormalities,
indicating that a one-handed catching technique is beneficial to, or
protective of, the throwing hand. Modern catcher's gloves employ less padding
than gloves used prior to the 1960s. This feature allows the glove to be
manipulated solely with the gloved hand, thereby eliminating the need for a
two-handed catching technique. This results in a quicker catch and release of
the ball when the catcher is throwing out base runners who are attempting to
steal, but it offers less protective padding for the hand. These advantages
may be offset by a greater exposure of the gloved hand, leading to a higher
prevalence of microvascular trauma. In the current study, all catchers
utilized a similar type of glove (that is, a glove with a single-break,
one-handed design), and therefore no association between glove type and hand
abnormalities can be made. However, the data suggest that any improvements in
glove design that have been made in recent years do not adequately protect the
hand from trauma.
Allen testing showed a relatively high rate of abnormalities. In the
current study, 22% of subjects showed delayed or absent refill. This rate is
higher than those reported in previous studies of asymptomatic subjects, which
showed rates of abnormal refill ranging from
5.5%14 to
9%4. The current
study also showed no differences between player positions with regard to the
results of Allen testing. This finding may have been related to the relatively
small sample size. In future studies, the use of digital Allen testing may
better demonstrate vascular abnormalities. While there were no differences
between positions, the overall high rate of abnormalities may have been
related to repetitive hand trauma associated with playing baseball at any
position.
Symptoms such as weakness, tingling, or pain that occur in the digits
during games are likely the result of neurological trauma as opposed to acute
ischemia. Impact to the digital nerve at the level of the metacarpal head is
likely to occur during catching of the ball. It is still not clear whether
resting symptoms are neurological or vascular in nature. Future studies might
benefit from objective measures of vascular and neurological function,
including digital Allen testing, nerve-conduction-velocity testing, digital
temperature and oxygenation readings, and measurement of two-point
discrimination before and during games.
The finger hypertrophy observed in catchers is probably multifactorial. As
with any tissue that is subjected to repetitive trauma, there is a potential
for injury to vessels, nerves, and soft tissue, leading to local tissue
inflammation and edema. However, we postulate that the microvascular trauma is
the most likely source of future problems. These observations and conclusions
are supported by our review of the literature and the findings of the present
study, specifically the decreased digital brachial indices and the Doppler
ultrasound abnormalities. We suspect that at least some of the current players
will demonstrate progressive decline in microvascular indices, eventually
leading to symptomatic digital ischemia.
Previous
studies2,3
on symptomatic players who presented for the treatment of digital ischemia
included relatively older players who had played for a longer period of time.
Furthermore, abnormalities were associated with accumulated exposure
time3. In the
current study, there was no correlation between the length of playing time and
the prevalence of either hand symptoms or vascular abnormalities. This finding
may be explained by the fact that there was very little variability in the
length of playing time between subjects in our study. The majority of the
patients were similar in age and had similar accumulated amounts of playing
time compared with those in previous studies, which included players from the
little league level to the advanced major league
level3. Thus,
additional studies that evaluate both younger, minor-league players and
veteran, major-league players might be necessary in order to show a
correlation between abnormalities and accumulated playing time.
The weaknesses of the current study include the small sample size; the
absence of an age-related, nonparticipating control group for comparison; the
absence of long-term follow-up; and the lack of digital Allen testing. The
small study population obviously decreased the power of the analysis as many
of the observations were made between smaller subgroups. Also, without a
control group, it is difficult to compare the current study group with the
general population except in the area of Allen testing, which showed a higher
prevalence of abnormalities as compared with the findings of previous
reports4,14.
However, the prevalence of vascular abnormalities and hand symptoms was
clearly greater in catchers than in other players. It certainly would be
beneficial to follow the subjects with use of repeated objective vascular
testing in the future as well as to administer objective symptom
questionnaires, to perform neurological testing (i.e., two-point
discrimination testing), and to test players before and after activity.
While none of the players in the present study were limited in their
required duties as professional baseball players, the long-term effect of
repetitive microvascular trauma may lead to digital ischemia. Additional
studies of glove design are necessary in order to make appropriate
modifications to the gloves that protect the hands of professional baseball
players. Long-term, longitudinal studies of baseball players would be helpful
for predicting the risk of digital ischemia and determining the natural
history of this process in catchers.
The authors did not receive grants or outside funding in support of their
research or preparation of this manuscript. They did not receive payments or
other benefits or a commitment or agreement to provide such benefits from a
commercial entity. No commercial entity paid or directed, or agreed to pay or
direct, any benefits to any research fund, foundation, educational
institution, or other charitable or nonprofit organization with which the
authors are affiliated or associated.
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