Kidney Injuries in Professional
American Football
Implications for Management of an Athlete
With 1 Functioning Kidney
Robert H. Brophy,*† MD, Seth C. Gamradt,† MD, Ronnie P. Barnes,‡ MA, ATC,
ll
†
John W. Powell,§ PhD, Joseph J. DelPizzo, MD, Scott A. Rodeo, MD,
†
and Russell F. Warren, MD
†
‡
From the Hospital for Special Surgery, New York, New York, the New York Giants,
§
East Rutherford, New Jersey, Michigan State University, East Lansing, Michigan,
ll
and New York Presbyterian Hospital–Cornell, New York, New York
Background: The frequency and severity of kidney injuries and their impact on return to play in American football has not been
described in the literature.
Purpose: Our objective is to identify the number of kidney injuries in the National Football League (NFL) and the effect of these
injuries.
Study Design: Case series; Level of evidence, 4.
Methods: All kidney injuries in the NFL from 1986 to 2004 were reviewed, including the type and mechanism of injury, treatment,
and time to return to play. In addition, NFL physicians and athletic trainers were asked if they were aware of any football player
at the professional, collegiate, or high school levels who had lost a kidney and how they would advise a football player with only
1 functioning kidney.
Results: A total of 52 cases of renal injuries were identified, an average of 2.7 cases per season. The rate of kidney injury was
10 times greater during games (0.000055 per exposure) than practices (0.000005 per exposure) (P < .0001). The most common
injury was kidney contusion (42), followed by kidney laceration (6) and kidney stones and dysfunction (2 each). Almost all the
injuries were contact related (49). More than a third of the players required hospitalization for their injury (18), although none
required surgery. All the athletes returned to play. The most days missed were after a kidney laceration (mean, 59.8), followed by
kidney contusion (15.1) and dysfunction (14.0). While 61% of respondents would allow a professional athlete with only 1 kidney
to play, approximately 50% would advise a college athlete with only 1 functioning kidney not to play football, and 60% would
advise a similar high school athlete not to play.
Conclusion: Renal trauma is a rare but potentially debilitating injury in the NFL, with players at greater risk during games. Most
players recover to play, but it may take some time, especially with a kidney laceration. It may be safe for players with only 1 functioning kidney to play in the NFL.
Keywords: renal; single kidney; contact sports
While caring for a professional American football team, the
senior author (R.F.W.) has had experience with a number
of players with kidney disorders. In 1 case, the player suffered a significant kidney laceration and was unable to
play for several months (Figure 1). In another case, a
player was found to have a congenital hydronephrosis,
markedly limiting the function of 1 kidney (Figure 2). In
this case, given the concern over playing with only 1 functional kidney, it would have been helpful to have an idea of
how often players suffer traumatic kidney injury and the
typical sequelae of such an injury.
*Address correspondence to Robert H. Brophy, MD, 14532 South Outer
Forty Drive, Chesterfield, MO 63107 (e-mail: brophyr@wudosis.wustl.edu).
No potential conflict of interest declared.
The American Journal of Sports Medicine, Vol. 36, No. 1
DOI: 10.1177/0363546507308940
© 2008 American Orthopaedic Society for Sports Medicine
85
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Brophy et al
The American Journal of Sports Medicine
Figure 2. Nuclear imaging study of a National Football
League player with congenital hydronephrosis.
led to the development of this study to examine the number
of kidney injuries in the NFL and the effect of these injuries
in order to better understand how to guide the management
of an athlete with only 1 functioning kidney.
MATERIALS AND METHODS
Figure 1. Images of an National Football League player after
severe kidney laceration. A, renal fracture; B, perinephric
hematoma.
Contact sports such as American football are associated
with a number of abdominal injuries, including renal
trauma. Most of the data in the literature comes from the
pediatric population, in which 16% to 30% of renal trauma
has been shown to be sports related.1,6,16 In 1 study reviewing the National Pediatric Trauma Registry recording data
from 50 United States pediatric trauma centers for 1990
to 1999, 42 sports-related traumatic kidney injuries were
reported; 26 (62%) of these resulted from American football.22
Another study reviewed all patients admitted to 1 pediatric
trauma service from 1984 to 2000.13 A total of 193 renal
injuries were recorded; 98 (51%) occurred during recreational
activities including sports. While 27 occurred during bicycling, only 6 were related to team sports, of which 3 injuries
were from American football. Other than 1 reported series of
renal injuries in Australian rules football,11 there are only
isolated case reports of sports-related kidney trauma.4,9,21
There are no published data on the number and consequences of kidney injuries among professional American
football players in the National Football League (NFL). This
We carried out a retrospective review of the injury registry
for the NFL over a 19-year period (1986 to 2004). All cases of
reported kidney disorders were reviewed. The type of injury,
mechanism of injury, setting of injury (game/practice), player
position, player height and weight, treatment, and time to
return to play were recorded. Total athlete-exposures during
the study period were used to calculate the risk for renal
injury in practice compared with during games.
Head physicians and athletic trainers from around the
NFL were then surveyed to determine if they were aware
of a football player who had lost a kidney due to traumatic
kidney injury or suffered loss of kidney function after traumatic kidney injury at the professional, collegiate, or high
school level. The survey also asked how they would advise
a player with a single functioning kidney at the professional, collegiate, or high school levels (Figure 3).
RESULTS
A total of 52 cases of renal injuries were identified from the
NFL database, an average of 2.7 cases per season. The overall rate of injury was 0.000012 per exposure, with a significantly higher rate during games (0.000055 per exposure)
Vol. 36, No. 1, 2008
Kidney Injuries in Professional American Football
87
Are you aware of a football player who has lost a kidney due to traumatic kidney injury at the:
Professional level
No
Yes (please elaborate):_______________________
College level
No
Yes (please elaborate):_______________________
High school level
No
Yes (please elaborate):_______________________
Are you aware of a football player who has suffered loss of kidney function after traumatic kidney
injury at the:
Professional level
No
Yes (please elaborate):_______________________
College level
No
Yes (please elaborate):_______________________
High school level
No
Yes (please elaborate):_______________________
What would you advise a player with a single functioning kidney at the:
Professional level
Don’t play
Play (special padding) Play (normal padding)
College level
Don’t play
Play (special padding) Play (normal padding)
High school level
Don’t play
Play (special padding) Play (normal padding)
Figure 3. Survey questions administered to National Football League team physicians and athletic trainers.
5
Contusion
Laceration
Dysfunction
Stone
Number of injuries
4
3
2
1
0
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
Figure 4. Kidney injuries in the National Football League by year, 1986-2004.
than during practice (0.000005 per exposure) (P < .0001). The
most common injury was kidney contusion (42), followed by
kidney laceration (6), and kidney stones and dysfunction (2
each) (Figure 4). The median recorded height for the injured
players was 6 ft 2 in, median weight was 230.5 lb, and the
median body mass index was 29.2. Almost all the injuries
were contact related (49), most commonly getting tackled
(16) or in a nontackle, nonblocking collision (16). Renal injury
was more likely to occur in a game situation (32) compared
with practice (20). The distribution of injuries by position was
fairly even, with the most injuries occurring among running
backs, wide receivers, and defensive secondary (7 each),
followed closely by offensive line, defensive line, and linebackers (6 each).
88
Brophy et al
Eighteen of the 52 injured players (34%) required hospitalization for their injury, although none of them required
surgery. Players missed the most days after a kidney laceration (mean, 59.8 days; range, 19-111), followed by kidney contusion (mean, 15.1; range, 0-58) and dysfunction
(mean, 14.0; range, 4-24). According to the database, no
player suffered reinjury to the kidney after return to play.
We received a response to our survey from all 31 other
teams in the NFL. One respondent was aware of a professional player who ultimately required a partial nephrectomy.
Two teams were aware of a player who had lost a kidney
while playing football at the college level and one at the high
school level. In terms of advising an athlete with only 1 functioning kidney, 61% of the respondents would allow a professional athlete to play (54% with normal padding, 7% with
special padding). By comparison, 51% of respondents would
advise a college athlete with only 1 functioning kidney not to
play football (5% suggest play with normal padding, 44%
with special padding) and 60% would advise a high school
athlete with this condition not to play (5% allow play with
normal padding, 35% with special padding).
DISCUSSION
Renal trauma is a rare but potentially debilitating injury
in professional American football. As might be expected,
most of the injuries are contact related. It is not surprising
that the athletes face a 10 times greater risk of renal
injury during games as opposed to practice conditions. The
percentage of injuries occurring during practice is higher
than might be expected (~40%), but it results from the
much higher number of player-exposures during practices
(3.77 million over the study period) as opposed to during
games (0.58 million). The players with kidney injuries
were not significantly different from the rest of the league
in terms of height ((NFL median 6 ft 4 in), weight (NFL
median 230 lb), or body mass index (NFL median 29.5)
over the study period. Approximately one third of the
injured players required hospitalization for their injury,
and none of the players in this series required surgery.
While most players were able to get back to playing within
2 to 3 weeks, players who suffered a severe kidney laceration were likely to miss several months of competition. All
the athletes eventually returned to play.
The low rates of surgery and nephrectomy are consistent
with previous reports in the literature.3,5 The series by
Bergqvist et al3 from Sweden reported only 5 cases of surgical
intervention, including 2 nephrectomies, in a series of 59
sports-related kidney injuries. The reported series of kidney
injuries in Australian rules football only reported on patients
who were admitted to the hospital.11 Among their series of 13
patients, 2 required nephrectomy. The padding used in
American football may contribute to the low rate of hospitalization relative to Australian rules football.17 Although
American football players do not typically wear padding
around the kidney, the padding worn on the shoulders and
other areas may dissipate the force when coming into contact
with the trunk and abdomen, perhaps shielding the kidneys.
The American Journal of Sports Medicine
Successful on-field and postgame management of trauma
to the trunk requires, first and foremost, a high degree of suspicion. Because kidney and other intra-abdominal organ
injuries are rare, missed or delayed diagnosis can be a problem. When a player presents with significant trauma to the
abdomen or back, we adhere to the principles described by
Holmes et al.8 After first assessing airway and breathing,
evaluation of hemodynamic status with pulse and blood pressure are mandatory. Hemodynamic compromise from shearing or disruption of major vessels is exceedingly rare but
should be ruled out. Next, physical examination should evaluate the presence or absence of costovertebral tenderness,
flank mass or ecchymosis, transverse process tenderness, and
abdominal rebound tenderness or guarding. The athlete
should be evaluated with a screening urinalysis or dipstick of
the urine. If gross hematuria is present, a significant renal or
bladder injury is suspected and the player should be treated
with foley catheterization and placement of an intravenous
line. The player should then be hospitalized; an emergent urologic consultation and CT scan are warranted.
Because microscopic hematuria is common in football
players (up to 55% of asymptomatic football players15), positive urinalysis does not necessarily indicate significant kidney trauma. Also, it should be noted that the absence of
hematuria does not rule out kidney injury. Santucci and
McAninch18 noted that 4% of 2500 patients with traumatic
renal injury presented without hematuria. Therefore, we
have a low threshold for a complete workup if microscopic
hematuria is present or physical examination is positive for
significant abdominal or flank trauma. This workup should
include a repeat microscopic urinalysis, complete blood
count, electrolytes, glucose, amylase, plain radiographs, and
a CT scan. Plain radiographs are helpful in diagnosing associated rib fractures and transverse process fractures, and a
perinephric hematoma can obscure the psoas shadow.
Computed tomography has largely replaced intravenous
pyelography in managing renal injury.8,10 Computed tomography scans can differentiate between a laceration,
hematoma, or contusion and may detect urinary extravasation. Most important, CT can help determine if an injury
will require surgical intervention.10 If a kidney injury is
diagnosed, appropriate urologic consultation is obtained. As
evidenced by our series of injuries in this report, surgical
intervention for kidney trauma in American football is
rarely necessary; most kidney injuries are managed with
observation, hydration, and analgesics.
Recommendation for return to play after a kidney injury
ranges from 2 to 6 weeks.8,20 It was clear in our series that
most NFL players with renal contusion were able to return
to play after approximately 2 weeks. Players with kidney lacerations, however, missed an average of 8 weeks of competition, and some missed the rest of the season. A follow-up
urinalysis should be performed before return to play to rule
out persistent hematuria. We recommend that physical
examination, urinalysis, and laboratory evaluation normalize before returning to play to eliminate the risk of a second
hit to a vulnerable, incompletely healed kidney. Also, patients
with more severe renal trauma should be reexamined periodically with a urinalysis, blood pressure, and imaging (CT or
Vol. 36, No. 1, 2008
Kidney Injuries in Professional American Football
TABLE 1
Grading of Renal Trauma
Grade
Type
Description
I
Minor
Contusion: microscopic or gross hematuria
with normal urological studies or
Hematoma: subcapsular, nonexpanding
without parenchymal laceration
Laceration <10 mm parenchymal depth of
renal cortex with nonexpanding
perirenal hematoma confined to renal
retroperitoneum
Laceration >10 mm parenchymal depth of
renal cortex without collecting-system
rupture or urinary extravasation
Laceration extending through the renal
cortex, medulla, and collecting system or
Main renal artery or vein injury with
contained hemorrhage
Completely shattered kidney or
Avulsion of renal hilum that devascularizes
kidney
II
III
IV
V
Major
intravenous pyelography) to rule out late hydronephrosis or
kidney dysfunction20 such as hypertension.
Because traumatic kidney injuries are rare and unlikely
to result in nephrectomy, our data suggest that it is very
unlikely for athletes with only 1 functioning kidney to lose
their kidney while playing in the NFL. A solitary kidney is
either congenital or acquired. The incidence of unilateral
renal agenesis is estimated to be 1 in 500 to 1800 people,2
and this condition is often discovered incidentally. An
acquired solitary kidney results from disease or trauma. In
the case of trauma, the other kidney is likely to be functional. However, if 1 kidney is lost due to disease, the
remaining kidney may be impaired. Athletes with a solitary kidney that is ectopic, multicystic, or functionally
impaired or obstructed should avoid contact sports.12
The existing literature on the topic of sports participation with a healthy, functioning, solitary kidney has been
inconclusive. Generally, the risk of losing a kidney from
sports-related trauma is thought to be very low.2 One study
reported that 54% of the members of the American Medical
Society of Sports Medicine would allow full sports participation in collision or contact sports at the high school or
college level after discussing the possible risks.2 While this
is very similar to the percentage of respondents in our survey who would allow athletes with only 1 kidney to play
professional football, it is higher than the percentage of
respondents in our survey who would allow such athletes
to play at the collegiate or high school level.
A recent study reported that in a survey of the American
Society of Pediatric Nephrology, 62% of respondents would
not allow participation in contact/collision sports for patients
with a single, normal kidney.7 Eighty-six percent of the
respondents who would not allow participation in contact/
collision sports identified American football as the primary
activity to avoid. However, after reviewing the evidence in
89
the literature, this same study concluded that kidney
injury from sports is very rare and that restricting contact/
collision sport participation in patients with a single, normal kidney is unwarranted. The findings in our study support that conclusion.
An inherent weakness of this study is the methodology
used to classify kidney injuries in the NFL database. The
injuries are classified as laceration versus contusion at the
discretion of the team physician and athletic trainer. In
the medical literature, renal injuries are typically classified by the American Association for the Surgery of
Trauma Grading System (AASTGS) (Table 1), with grade I
to III injuries usually considered minor and grade IV and
V injuries considered major.14,19 We suspect that kidney
contusion is consistent with grade I to III injuries while
kidney laceration correlates to grade IV and V injuries, but
with the current methods we cannot confirm this relationship. In the future, more stringent classification of kidney
injuries consistent with the AASTGS is advisable for the
NFL injury database and should be considered by any
other database or study of traumatic kidney injuries.
In summary, traumatic kidney injury is a rare occurrence in professional American football. Athletes are at
much greater risk for these injuries during games than
during practices. Most injured athletes recover to play but
it may take some time, especially with a kidney laceration
(grade IV and V injury). Athletes with only 1 functioning
kidney are unlikely to lose their kidney playing in the
NFL. It is not certain that this conclusion can be applied to
athletes playing American football at the collegiate and high
school level. Nevertheless, this study provides insight into the
consequences of traumatic kidney injuries in American football and how to manage kidney injuries in these athletes.
ACKNOWLEDGMENT
The authors acknowledge the work of the NFL athletic
trainers in maintaining the NFL database for the past 27
years.
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