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Knee injuries – diagnostics, treatment and prevention.



Dansk Sportsmedicin, 2012;4:24-26.
24 Fagligt
Knee injuries – diagnostics,
treatment and prevention
Markus Waldén, MD, PhD & Martin Hägglund, RPT, PhD
Football Research Group & Department of Medical and Health Sciences, Linköping University, Linköping, Sweden
Anterior cruciate ligament (ACL) in-
jury is the knee injury in football that
probably draws the most attention.
Many risk factors for ACL injury are
suggested in the literature, but the
knowledge about potential football-
specic risk factors is limited. Brie-
y, match play is associated with a
considerably higher ACL injury rate
than training, previous ACL injury is
associated with an increased rate of a
future ACL injury, female footballers
are more susceptible to ACL injury
compared to their male counterparts,
and female players also tend to sustain
their ACL injury at younger ages than
males. Fortunately, there is upcoming
evidence that many ACL injuries can
be prevented. In a recent cluster ran-
domised controlled trial in female ado-
lescent football, a coach-led 15-minute
neuromuscular warm-up programme
carried out twice a week during the
season resulted in a 64% reduction in
ACL injury rate.
Football is the most popular sport
worldwide with more than 260 million
active players according to the FIFA
Big Count survey in 2006 (www.fa.
com). The knee injury rate in football
is known to be high and the injury that
probably draws the most attention is
the anterior cruciate ligament (ACL)
injury. However, ACL injury is not a
very common football injury, occurring
to between 0.5 and 6.0% of all female
players and between 0.6 and 8.5% of all
male players annually depending on
the setting (10). This article is a sum-
mary of the lecture on “Knee injuries
– diagnostics, treatment and preven-
tion” held at the Football Symposium
in Copenhagen on September 08, 2012.
The purpose of this short report is to
summarise the current football lite-
rature on ACL injury regarding risk
factors, return to play rates, and injury
prevention with personal reections
from our own research in the Football
Research Group in Linköping, Sweden.
Risk factors
Many risk factors for ACL injury are
proposed in the literature (8), and
they are usually divided into extrinsic
(environmental) and intrinsic (indivi-
dual) factors. These factors can further
be classied as modiable (e.g. body
mass) or non-modiable (e.g. age)
which might be of importance when
targeting injury prevention. A sum-
mary of the most commonly suggested
risk factors are seen in Table 1. Even if
numerous risk factors have been sug-
gested, studies about potential foot-
ball-specic risk factors are few, and
reliable scientic support can only be
found for activity type (extrinsic risk
factor), and previous injury, sex and
age (intrinsic risk factors).
Activity type
Match play is associated with a con-
siderably increased ACL injury rate
compared to training and studies have,
irrespective of sex, reported up to 65
times higher ACL injury rate in match
play than in training (10).
Previous injury
Previous injury is a well-known risk
factor for many different sports inju-
ries, including ACL injury. In a study
on the German female elite league
players with prior ACL injury had a
5-fold increased rate of a future ipsi-
lateral graft tear or contralateral ACL
injury (2).
Female athletes participating in jum-
ping, cutting and pivoting team sports
such as football, handball and basket-
ball are often claimed to have a 4-6
times higher ACL injury rate compared
to their male counterparts (3). The
female-to-male ACL injury rate ratio in
football has recently been reviewed in
two studies (7, 10). According to these
reviews, however, female footballers
are only up to 3 times more suscepti-
ble to ACL injury compared to their
male counterparts. In the rst study,
the pooled female-to-male ACL injury
rate ratio from 5 studies included in a
meta-analysis was 2.67 (7). In the se-
cond study, 13 studies were included
in a structured literature review with
the majority of the studies reporting
a 2- to 3-fold higher ACL injury rates
among females (10). Interestingly, only
one study reported more than a 4 times
higher rate in females and the gender
disparity seems to be more associated
with injury rates during match play
and not during training (10).
ACL injury is rare in pre-pubertal
children, and no difference in ACL
injury rate has been found between
girls and boys up to 12 years-of-age (9).
Even if the number of studies that have
reported the average age at injury is
limited, all studies to date have consi-
stently shown that female players are
younger when they sustain their ACL
injury (10). In addition, female late pu-
bertal or early post-pubertal teenagers
seem to be at highest risk (4). Age is
therefore most likely a confounding
factor when calculating female-to-male
ACL injury rate ratios in sports. This
phenomenon is best illustrated by re-
ferring to the example reported in a re-
cent study on the Swedish female and
male elite leagues (11). In that study,
the crude female-to-male ACL injury
rate ratio was 2.6, but after adjusting
for differences in age between the sexes
this ratio was lowered to 2.1, which
thus should be regarded as the “true”
female-to-male ACL injury rate ratio.
In our opinion, the notion that female
athletes participating in jumping, cut-
ting and pivoting team sports have
an up to 6-fold higher ACL injury rate
compared to their male counterparts
should therefore be questioned.
Return to play
In a study on 57 professional/elite
football clubs with 2329 players fol-
lowed over a varying number of sea-
sons from 2001 to 2009, a total of 76
male and female players suffered 78
ACL injuries (11). The majority of the
players with total tears in that study
returned to training within 10 months
after surgery (94%) and participated
in match play within 12 months after
surgery (89%). Up to now, prospective
data for 111 ACL injuries have been
collected between 2001 and 2011 (new
unpublished data). Interestingly, all
57 players with ACL injuries occur-
ring in the so-called UEFA Champions
League study returned to play at the
same level as prior to the injury (100%),
whereas 95% of players in the Swedish
male elite league (Allsvenskan) and
87% in the Swedish female elite league
(Damallsvenskan) returned to football,
respectively. These  gures are thus in
contrast to the average return to sports
rate (at the previous competition level)
after ACL injury that was recently re-
ported to be 63% in a review of 48 in-
dividual studies (1). In our experience,
the underlying reasons to the high
return to play success rates in high-
level football are probably multi-fac-
torial and include  nancial incentives,
referral to experienced high-volume
knee surgeons (“centralised” ACL re-
constructive surgery), use of magnetic
resonance imaging on a routine basis to
obtain an established diagnosis imme-
diately, proper treatment of any associ-
ated joint injuries, and individualised
daily physical therapy by the club phy-
siotherapist and rehabilitation team.
The mean lay-off period was 6.9
months (209 days) to the  rst full
training session without restrictions
(“medical clearance” from club medical
staff) and another month to the  rst
match appearance (245 days). If this
7-8 months lay-off period is the time it
actually takes to come back to the pitch
at the professional/elite level, it is, in
our opinion, unrealistic to expect that
a non-elite youth or amateur player
should be able to return to play after
approximately 6 months, which is the
most commonly recommended rehabi-
litation time advocated by many knee
ACL-injury prevention
Several parallel-group controlled stu-
dies have been conducted in football to
evaluate injury-prevention strategies,
most targeting female adolescents (4).
However, only two non-randomised
studies in adolescent football show sig-
ni cant reduction of acute knee injuries
or non-contact ACL injuries with neu-
romuscular warm-up programmes (5,
6). Importantly, most studies were not
designed to speci cally evaluate pre-
ventive effects on knee or ACL injury
as the primary outcome, and there has
been a lack of high-quality randomised
controlled trials targeting prevention of
these injuries.
26 Fagligt
We therefore conducted a strati ed
cluster randomised controlled trial in
female adolescent football evaluating
a coach-led 15-minute neuromuscular
warm-up programme targeting core
stability, balance, strength and proper
knee alignment (12). The neuromuscu-
lar warm-up programme (Knäkontroll,
SISU Idrottsböcker©, Sweden, 2005)
was intended to be carried out twice a
week throughout the competitive sea-
son in 2009 in the intervention group
clubs, whereas the control group clubs
trained as usual. In total, 309 clubs in
Sweden with female players aged 12-17
years were randomised and 230 clubs
with 4564 players were included for
analysis, making it the largest rando-
mised controlled trial in sports injury
prevention to date. Brie y, 21 players
suffered an ACL injury during the
season and, by intention-to-treat analy-
sis, we found a 64% reduction in ACL
injury rate in the intervention group
(Table 2). No signi cant rate reductions
were seen for the secondary outcomes
acute knee injury and severe knee
injury (Table 2). However, sub-group
analyses of players who carried out the
neuromuscular warm-up programme
at least once a week over the season
(“compliers”) showed signi cant redu-
ctions in all outcomes; ACL injury 83%,
severe knee injury 82%, and any acute
knee injury 47%.
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Feller JA. Return to sport following
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2. Faude O, Junge A, Kindermann W,
Dvorak J. Risk factors for injuries in
elite female soccer players. Br J Sports
Med 2006:40:785-790
3. Hewett TE. Neuromuscular and
hormonal factors associated with
knee injuries in female. Strategies for
intervention. Sports Med 2000:29:313-
4. Hägglund M, Waldén M, Atroshi
I. Preventing knee injuries in adole-
scent female football players – design
of a cluster randomized controlled
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skelet Disord 2009:23:10:75
5. Kiani A, Hellquist E, Ahlqvist K,
Gedeborg R, Michaëlsson K. Preven-
tion of soccer-related knee injuries
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Watanabe DS, Knarr JF, Thomas SD,
Grif n LY, Kirkendall DT, Garrett, Jr,
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7. Prodromos CC, Han Y, Rogowski
J, Joyce B, Shi K. A meta-analysis of
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cheli L, Myklebust G, Roos E, Roos
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Curtin M, Apel PJ. Anterior cruciate
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Knee Surg Sports Traumatol Arthrosc
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Correspondence to:
Dr Markus Waldén
Department of Medical
and Health Sciences
Linköping University
581 83 Linköping, Sweden
Tel: + 46 733 920 720
ResearchGate has not been able to resolve any citations for this publication.
Full-text available
To evaluate the effectiveness of neuromuscular training in reducing the rate of acute knee injury in adolescent female football players. Stratified cluster randomised controlled trial with clubs as the unit of randomisation. 230 Swedish football clubs (121 in the intervention group, 109 in the control group) were followed for one season (2009, seven months). 4564 players aged 12-17 years (2479 in the intervention group, 2085 in the control group) completed the study. 15 minute neuromuscular warm-up programme (targeting core stability, balance, and proper knee alignment) to be carried out twice a week throughout the season. The primary outcome was rate of anterior cruciate ligament injury; secondary outcomes were rates of severe knee injury (>4 weeks' absence) and any acute knee injury. Seven players (0.28%) in the intervention group, and 14 (0.67%) in the control group had an anterior cruciate ligament injury. By Cox regression analysis according to intention to treat, a 64% reduction in the rate of anterior cruciate ligament injury was seen in the intervention group (rate ratio 0.36, 95% confidence interval 0.15 to 0.85). The absolute rate difference was -0.07 (95% confidence interval -0.13 to 0.001) per 1000 playing hours in favour of the intervention group. No significant rate reductions were seen for secondary outcomes. A neuromuscular warm-up programme significantly reduced the rate of anterior cruciate ligament injury in adolescent female football players. However, the absolute rate difference did not reach statistical significance, possibly owing to the small number of events. Clinical trials NCT00894595.
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An athlete's intention to return to sport following anterior cruciate ligament (ACL) injury is a major indication for surgical intervention. The purpose of this review was to determine postoperative return-to-sport outcomes after ACL reconstruction surgery. Meta-analysis and systematic review Electronic databases including Medline, Embase, SPORTDiscus and CINAHL were searched from the earliest possible entry to April 2010. Studies were included that reported the number of patients returning to sports participation following ACL reconstruction surgery. The results were presented using the World Health Organization's International Classification of Functioning, Disability and Health as a framework and combined using proportion meta-analyses. Forty-eight studies evaluating 5770 participants at a mean follow-up of 41.5 months were included for review. Overall, 82% of participants had returned to some kind of sports participation, 63% had returned to their preinjury level of participation, and 44% had returned to competitive sport at final follow-up. Approximately 90% of participants achieved normal or nearly normal knee function when assessed postoperatively using impairment-based outcomes such as laxity and strength, and 85% when using activity-based outcomes such as the International Knee Documentation Committee knee evaluation form. Fear of reinjury was the most common reason cited for a postoperative reduction in or cessation of sports participation. The relatively low rate of return to competitive sport despite the high rates of successful outcome in terms of knee impairment-based function suggests that other factors such as psychological factors may be contributing to return-to-sport outcomes.
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Anterior cruciate ligament (ACL) injury causes long lay-off time and is often complicated with subsequent new knee injury and osteoarthritis. Female gender is associated with an increased ACL injury risk, but few studies have adjusted for gender-related differences in age although female players are often younger when sustaining their ACL injury. The objective of this three-cohort study was to describe ACL injury characteristics in teams from the Swedish men's and women's first leagues and from several European men's professional first leagues. Over a varying number of seasons from 2001 to 2009, 57 clubs (2,329 players) were followed prospectively and during this period 78 ACL injuries occurred (five partial). Mean age at ACL injury was lower in women compared to men (20.6 ± 2.2 vs. 25.2 ± 4.5 years, P = 0.0002). Using a Cox regression, the female-to-male hazard ratio (HR) was 2.6 (95% CI 1.4-4.6) in all three cohorts studied and 2.6 (95% CI 1.3-5.3) in the Swedish cohorts; adjusted for age, the HR was reduced to 2.4 (95% CI 1.3-4.2) and 2.1 (95% CI 1.0-4.2), respectively. Match play was associated with a higher ACL injury risk with a match-to-training ratio of 20.8 (95% CI 12.4-34.8) and 45 ACL injuries (58%) occurred due to non-contact mechanisms. Hamstrings grafts were used more often in Sweden than in Europe (67 vs. 34%, P = 0.028), and there were no differences in time to return to play after ACL reconstruction between the cohorts or different grafts. In conclusion, this study showed that the ACL injury incidence in female elite footballers was more than doubled compared to their male counterparts, but also that they were significantly younger at ACL injury than males. These findings suggest that future preventive research primarily should address the young female football player.
Full-text available
Football (soccer), the most popular sport worldwide, is associated with a high injury risk, and the knee joint is often affected. Several studies have found female players to be more susceptible to knee injury, anterior cruciate ligament (ACL) injury in particular, compared to their male counterparts. There is, however, some controversy regarding the magnitude of this risk increase and a few studies have found no differences. The influence of age and activity type on gender-related differences in injury risk is only scarcely investigated. In this paper, the literature reporting gender-specific ACL injury risk in football is reviewed. A literature search yielded 33 relevant articles that were included for review. These show that female players have a 2-3 times higher ACL injury risk compared to their male counterparts. Females also tend to sustain their ACL injury at a younger age than males, and a limiting factor in the existing literature is that age is not adjusted for in comparisons of ACL injury risk between genders. Furthermore, the risk increase in females is primarily evident during match play, but type of exposure is also rarely adjusted for. Finally, the studies included in this review share important methodological limitations that are discussed as a starting point for future research in the field.
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Knee injuries end many careers among female soccer players. The number of injuries can be anticipated to increase because of the increasing popularity of the sport worldwide and the higher incidence of knee injuries among young females compared with males. In a community-based intervention trial performed from February 1 through October 31, 2007, we sought to reduce the number of knee injuries among female soccer players aged 13 to 19 years (N = 1506), representing 97 teams from 2 Swedish counties. A physical exercise program designed exclusively for female soccer players was combined with education of athletes, parents, and coaches to increase awareness of injury risk. The training program aimed to improve motor skills, body control, and muscle activation. New acute knee injuries, diagnosed by the physician, were the main outcome measure. Three knee injuries occurred in the intervention group and 13 occurred in the control group, corresponding to incidence rates of 0.04 and 0.20, respectively, per 1000 player hours. The preventive program was associated with a 77% reduction in knee injury incidence (crude rate ratio, 0.23; 95% confidence interval, 0.04-0.83). The noncontact knee injury incidence rate was 90% lower in the intervention group (crude rate ratio, 0.10; 95% confidence interval, 0.00-0.70). Adjustment for potential confounders strengthened the estimates. Forty-five of the 48 intervention teams (94%) reported a high adherence of at least 75%. The incidence of knee injuries among young female soccer players can be reduced by implementation of a multifaceted, soccer-specific physical exercise program including education of individual players.
Full-text available
Knee injuries in football are common regardless of age, gender or playing level, but adolescent females seem to have the highest risk. The consequences after severe knee injury, for example anterior cruciate ligament (ACL) injury, are well-known, but less is known about knee injury prevention. We have designed a cluster randomized controlled trial (RCT) to evaluate the effect of a warm-up program aimed at preventing acute knee injury in adolescent female football. In this cluster randomized trial 516 teams (309 clusters) in eight regional football districts in Sweden with female players aged 13-17 years were randomized into an intervention group (260 teams) or a control group (256 teams). The teams in the intervention group were instructed to do a structured warm-up program at two training sessions per week throughout the 2009 competitive season (April to October) and those in the control group were informed to train and play as usual. Sixty-eight sports physical therapists are assigned to the clubs to assist both groups in data collection and to examine the players' acute knee injuries during the study period. Three different forms are used in the trial: (1) baseline player data form collected at the start of the trial, (2) computer-based registration form collected every month, on which one of the coaches/team leaders documents individual player exposure, and (3) injury report form on which the study therapists report acute knee injuries resulting in time loss from training or match play. The primary outcome is the incidence of ACL injury and the secondary outcomes are the incidence of any acute knee injury (except contusion) and incidence of severe knee injury (defined as injury resulting in absence of more than 4 weeks). Outcome measures are assessed after the end of the 2009 season. Prevention of knee injury is beneficial for players, clubs, insurance companies, and society. If the warm-up program is proven to be effective in reducing the incidence of knee injury, it can have a major impact by reducing the future knee injury burden in female football as well as the negative long-term disabilities associated with knee injury. NCT00894595.
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Injury claims from an insurance company specializing in soccer coverage were reviewed for a 5-year period. A total of 8215 injury claims (3340 females, 4875 males) were divided into three categories: (1) all injury, (2) knee injury, and (3) ACL injury. Knee injuries accounted for 22% of all injuries (30% female, 16% male). ACL injury claims represented 31% of total knee injury claims (37% female, 24% males). The youngest ACL injury was age 5. The ratio of knee injury/all injury increased with age. Compared with males, females demonstrated a higher ratio of knee injury/all injury and a higher ratio of ACL injury/all injury. This study demonstrates that ACL injury occurs in skeletally immature soccer players and that females appear to have an increased risk of ACL injury and knee injury compared with males, even in the skeletally immature. Future research related to ACL injury in females will need to consider skeletally immature patients.
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Among female athletes it has not been established whether a neuromuscular and proprioceptive sports-specific training program will consistently reduce the incidence of anterior cruciate ligament injuries. To determine whether a neuromuscular and proprioceptive performance program was effective in decreasing the incidence of anterior cruciate ligament injury within a select population of competitive female youth soccer players. Cohort study; Level of evidence, 2. In 2000, 1041 female subjects from 52 teams received a sports-specific training intervention in a prospective non-randomized trial. The control group consisted of the remaining 1905 female soccer players from 95 teams participating in the same league who were age and skill matched. In the 2001 season, 844 female athletes from 45 teams were enrolled in the study, with 1913 female athletes (from 112 teams) serving as the age- and skill-matched controls. All subjects were female soccer players between the ages of 14 and 18 and participated in either their traditional warm-up or a sports-specific training intervention before athletic activity over a 2-year period. The intervention consisted of education, stretching, strengthening, plyometrics, and sports-specific agility drills designed to replace the traditional warm-up. During the 2000 season, there was an 88% decrease in anterior cruciate ligament injury in the enrolled subjects compared to the control group. In year 2, during the 2001 season, there was a 74% reduction in anterior cruciate ligament tears in the intervention group compared to the age- and skill-matched controls. Using a neuromuscular training program may have a direct benefit in decreasing the number of anterior cruciate ligament injuries in female soccer players.
Full-text available
To describe risk factors for injuries in elite female soccer. A total of 143 female soccer players from the German national league participated in the study. Baseline information on player characteristics--for example, anthropometric measurements and playing position--and medical history were recorded at the start of the study. During one outdoor season, injuries and training and match exposure times were prospectively documented for each player. The risk of a new anterior cruciate ligament (ACL) rupture was significantly increased in players with a previous rupture (odds ratio (OR) = 5.24, p = 0.01). This was not the case for ankle sprain (OR = 1.39) or knee sprain (OR = 1.50). In addition, no significantly increased risk of new sprains or ACL ruptures was found when the injured leg was the unit of analysis. Injury incidence was considerably higher in defenders (9.4 injuries per 1000 hours exposure) and strikers (8.4/1000 hours) than goalkeepers (4.8/1000 hours) and midfielders (4.6/1000 hours). Ten per cent of all players (n = 14) sustained more than three injuries. Most of these were defenders (n = 8) or strikers (n = 4). Significantly more injuries occurred to the dominant leg (105 v 71, p = 0.01); this was particularly true for contact injuries (52 v 29, p = 0.01). Injury risk should be assessed on an individual basis. Therefore it seems appropriate to individualise preventive training programmes, as is recommended for other training content. Evaluating the existing rules of soccer and their appropriate application may also help to decrease injury risk, particularly in contact situations.