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Return to play after hamstring injuries in football (soccer): A worldwide Delphi procedure regarding definition, medical criteria and decision-making

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Abstract

There are three major questions about return to play (RTP) after hamstring injuries: How should RTP be defined? Which medical criteria should support the RTP decision? And who should make the RTP decision? The study aimed to provide a clear RTP definition and medical criteria for RTP and to clarify RTP consultation and responsibilities after hamstring injury. The study used the Delphi procedure. The results of a systematic review were used as a starting point for the Delphi procedure. Fifty-eight experts in the field of hamstring injury management selected by 28 FIFA Medical Centres of Excellence worldwide participated. Each Delphi round consisted of a questionnaire, an analysis and an anonymised feedback report. After four Delphi rounds, with more than 83% response for each round, consensus was achieved that RTP should be defined as 'the moment a player has received criteria-based medical clearance and is mentally ready for full availability for match selection and/or full training'. The experts reached consensus on the following criteria to support the RTP decision: medical staff clearance, absence of pain on palpation, absence of pain during strength and flexibility testing, absence of pain during/after functional testing, similar hamstring flexibility, performance on field testing, and psychological readiness. It was also agreed that RTP decisions should be based on shared decision-making, primarily via consultation with the athlete, sports physician, physiotherapist, fitness trainer and team coach. The consensus regarding aspects of RTP should provide clarity and facilitate the assessment of when RTP is appropriate after hamstring injury, so as to avoid or reduce the risk of injury recurrence because of a premature RTP.
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van der HorstN, etal. Br J Sports Med 2017;51:1583–1591. doi:10.1136/bjsports-2016-097206
ABSTRACT
There are three major questions about return to play
(RTP) after hamstring injuries: How should RTP be
defined? Which medical criteria should support the
RTP decision? And who should make the RTP decision?
The study aimed to provide a clear RTP definition and
medical criteria for RTP and to clarify RTP consultation
and responsibilities after hamstring injury. The study
used the Delphi procedure. The results of a systematic
review were used as a starting point for the Delphi
procedure. Fifty-eight experts in the field of hamstring
injury management selected by 28 FIFA Medical
Centres of Excellence worldwide participated. Each
Delphi round consisted of a questionnaire, an analysis
and an anonymised feedback report. After four Delphi
rounds, with more than 83% response for each round,
consensus was achieved that RTP should be defined as
’the moment a player has received criteria-based medical
clearance and is mentally ready for full availability
for match selection and/or full training’. The experts
reached consensus on the following criteria to support
the RTP decision: medical staff clearance, absence of
pain on palpation, absence of pain during strength and
flexibility testing, absence of pain during/after functional
testing, similar hamstring flexibility, performance on
field testing, and psychological readiness. It was also
agreed that RTP decisions should be based on shared
decision-making, primarily via consultation with the
athlete, sports physician, physiotherapist, fitness trainer
and team coach. The consensus regarding aspects of RTP
should provide clarity and facilitate the assessment of
when RTP is appropriate after hamstring injury, so as to
avoid or reduce the risk of injury recurrence because of a
premature RTP.
INTRODUCTION
Hamstring injuries are the most prevalent muscle
injury in football, and 12%–33% of athletes with
a hamstring injury experience a recurrence within
a year after the initial injury.1–5 The burden of
hamstring injury is high: for the professional player
an average of 18 days and 3 matches missed per
season,5 and for the professional football club an
average of 15 matches and 90 days missed per
season.5 The inability to play because of injury,
but also because of unnecessary prolonged absence
from play during rehabilitation, affects the indi-
vidual player and team performance. Lower injury
burden and higher match availability are signifi-
cantly associated with a higher final league ranking,
points per league match and success in the Union of
European Football Association Champions league
or Europa League.6
Reducing the risk of injury recurrence is a key
priority after the initial hamstring injury. Recurrent
injuries require more extensive rehabilitation than
the primary injury, and previous injury is an undis-
puted risk factor for future injury.3 7–10 Particularly
alarming is the observation that recurrence rates
have not improved over the last 30 years.11–13 High
recurrence rates might be due to inadequate rehabil-
itation and/or premature return to play (RTP).14 15
Of all recurrences, more than half occur within
the first month after RTP.10 16 This has prompted
interest in RTP after hamstring injury.17–21
Unfortunately, different concepts of RTP make
it difficult to analyse and compare various studies
of RTP after hamstring injury.22 23 It is recognised
that diversity in definitions and methodologies
contributes to significant differences in the results
and conclusions obtained from sports injury
research.24–27 Furthermore, in accordance with the
Strategic Assessment of Risk and Risk Tolerance
framework (figure 1), it is commonly agreed that
any RTP decision should be based on an assess-
ment of the risk and the acceptable risk tolerance
threshold.28 29 So far, no studies have specified
how risk should be assessed when clinicians are
faced with the RTP decision after hamstring injury,
although this moment is vital if injury recurrence
is to be prevented. A recent systematic review of
the literature showed that there is great diversity
in how RTP after hamstring injury is defined and
which criteria are used to assess RTP readiness.22
Also, because multiple stakeholders have their own
reasons why RTP should be accelerated or delayed,
it is imperative to provide clarity on who is to
be consulted and who is responsible for the RTP
decision.
The aim of this Delphi procedure was to deter-
mine, based on expert consensus, a clear defini-
tion of and medical criteria for RTP and to clarify
responsibilities for RTP after hamstring injury.
MATERIALS AND METHODS
Study design and setting
This Delphi study was part of the Hamstring Injury
Prevention Strategies project, which includes several
studies focusing on the prevention of hamstring
(re-)injuries. The present Delphi procedure is one of
these studies and aimed to achieve consensus on the
terminology, definition and medical criteria for RTP,
and who should be involved and responsible for the
Return to play after hamstring injuries in football
(soccer): a worldwide Delphi procedure regarding
definition, medical criteria anddecision-making
Nick van der Horst,1 FJG Backx,1 Edwin A Goedhart,2 Bionka MA Huisstede,1 on behalf
of HIPS-Delphi Group
Consensus statement
To cite: van der HorstN,
BackxFJG, GoedhartEA,
etal. Br J Sports Med
2017;51:1583–1591.
1Department of Rehabilitation,
Nursing Science & Sports,
Rudolf Magnus Institute of
Neurosciences, University
Medical Center Utrecht, Utrecht,
The Netherlands
2FIFA Medical Center
Royal Netherlands Football
Association, Zeist, The
Netherlands
Correspondence to
Dr Nick van der Horst,
Department of Rehabilitation,
Nursing Science & Sports,
University Medical Center
Utrecht, Rudolf Magnus
Institute of Neurosciences, P.O.
Box 85500, Utrecht 3508 GA,
The Netherlands;
n. vanderhorst- 3@ umcutrecht. nl
Accepted 10 March 2017
Published Online First
30March2017
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Consensus statement
RTP decision after hamstring injury. The study was carried out
by the Department of Rehabilitation, Physical Therapy Science,
and Sport at the University Medical Centre of Utrecht, the Neth-
erlands. Before the start of this project, a systematic review of
the definition of, and criteria for, RTP after hamstring injury was
performed.22 The results of the systematic review were used as a
starting point for the Delphi procedure.
Delphi procedure
We used a series of sequential questionnaires or ‘rounds’, inter-
spersed by feedback, to achieve consensus of opinion among
a panel of experts.30 31 This scientific method was originally
developed in the 1950s and has been effectively used in sports
medicine research.32–35 Each Delphi round comprised a ques-
tionnaire, an analysis and a feedback report.
Steering committee
The steering committee that facilitated and guided this
Delphi study consisted of a full professor in sports medicine,
a senior researcher with experience in Delphi procedures, a
team doctor of a national football team and a PhD student.
All members have a clinical (sports medicine, (sports) physical
therapy) and scientific background. The steering committee
was responsible for preparing and analysing the questionnaires
and for reporting the results in anonymised feedback reports.
Expert panel
The FIFA Medical Centres of Excellence (FMCoEs) have a
demonstrable record of leadership in football medicine and
have been accredited through a strict selection process by
FIFA. These centres provide a network of knowledge and
experience in research and clinical management of hamstring
injuries. All FMCoEs (n=40) were invited to select up to
three experts in hamstring injury management to participate
in our Delphi study, adhering to the inclusion criteria as listed
in Box 1. These criteria are commonly used when selecting
experts who participate in a Delphi study.33 36–38 After selec-
tion, the steering committee contacted all experts via email
to provide information about the aim, methods and privacy
statements for the Delphi study.
Procedure
Online surveys were used and adhered to principles of respon-
dent anonymity and feedback between rounds.30 For all Delphi
Figure 1 The Strategic Assessment of Risk and Risk Tolerance (StARRT) framework for RTP decisions.28 RTP, return to play.
Box 1 Experts’ inclusion criteria for participation to the
Delphi study
The selected FIFA Medical Centre of Excellence considers
this expert to be a key person in the field of hamstring injury
management
The expert is a researcher OR medical / health professional
with experience in hamstring injury rehabilitation in a sport
setting
The expert has sufficient knowledge of English language
The expert has an evidence-based attitude
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Box 2 Items* included to start discussion on definition
and criteria for RTP after hamstring 182 injury
Items for discussion on definition of RTP after hamstring
injury
Availability for match selection and/or full training
Clearance by medical staff
A completed game
Full activity
A 100% recovery score on fitness and skill testing
Absence of symptoms on injured leg
Completion of a rehabilitation program
Reaching pre-injury level
Items for discussion on criteria for RTP after hamstring
injury
Medical staff clearance
Absence of pain
Similar hamstring strength
Similar hamstring flexibility
Functional performance
*All items were derived from a systematic review.on definition and
criteria for RTP after hamstring injury.22
Consensus statement
rounds, experts received an invitation via email with a link
to an online questionnaire. Experts were given 6 weeks to
complete the questionnaire, with reminders emailed at 3 and
5 weeks. A structured web-based questionnaire was developed
consisting of three parts: part I for general questions about
RTP consultation and responsibilities, part II for the definition
of RTP and part III for criteria to support the RTP decision
after hamstring injury. During the whole procedure, we used
structured questions, such as ‘Do you feel this item should be a
part of the RTP definition?’ or ‘Do you feel this item should be
a criterion to support the RTP decision after hamstring injury?’
Answer options were ‘yes’, ‘no’ or ‘no opinion’. Experts were
encouraged to provide justification for their answers. Topics
that did not reach consensus were included in the next Delphi
round. For some questions, the steering committee added a
‘note from the steering committee’, based on expert opinion
or the literature.
Cut-off point for consensus
A cut-off score of ≥70% agreement was proposed for consensus
because this cut-off is often used in Delphi procedures.36 37 39
RTP terminology
The expert panel was asked to reach consensus regarding which
term for RTP in sports should be adopted (eg, return to sport,
RTP, return to competition, etc).
Definition of RTP after a hamstring injury
Results from the systematic review22 that we conducted to
inform the Delphi process (Box 2) were used as the starting
point for the Delphi process for the definition of RTP. Experts
were asked which terms should or should not be included in
the RTP definition. Experts were also invited to open-ended
question regarding the definition of RTP after hamstring
injury.
Medical criteria to support the RTP decision after a hamstring
injury
Similar to the definition of RTP, a systematic review of the medical
criteria used to support the RTP decision after hamstring injury
was used as a starting point for this part of the Delphi process.22
Experts were asked which criteria should or should not be used
to support the final RTP decision and to provide any additional
criteria they thought relevant.
RTP responsibilities
The relevant stakeholders in RTP decision-making were initially
identified from the published literature.40 41 Experts were addi-
tionally asked to name other stakeholders involved in RTP
consultation and decision-making.
Data analysis
Data from all Delphi rounds were extracted from the online
survey database to SPSS V.22.0, and anonymously reported
in feedback reports. For questions with a ‘yes/no/no opinion’
answer format, the percentage of answers in each category was
calculated. Qualitative data (ie, expert answers and justifica-
tions) were analysed by content analysis and discussed by the
steering committee. This information and the main arguments
of the experts were summarised and included in a ‘note from the
steering committee’ and added to each question. If consensus was
not reached on a topic, these notes were included in a follow-up
question on a related subject, used to rephrase the original ques-
tion or to compose new questions on this topic.
RESULTS
After four consecutive Delphi rounds, performed between July
2015 and July 2016, full consensus was achieved on three main
content areas. The final consensus is presented in the RTP model
for hamstring injuries in football (figure 2).
Expert panel
Fifty-eight experts were recruited from 28 FMCoEs worldwide
(participating experts are included in the acknowledgements
section). Eleven FMCoEs did not respond to the invitation and
one FMCoE could not participate due to migration. The partici-
pating experts had a range of experiences in clinical practice and
research, including full professor, medical director, lecturer, sports
physician, orthopaedic surgeon, physical therapist, performance
coach, athletic trainer and/or clinical researcher. Most members
had written multiple high-quality international publications, and
had an average of 15.8 (SD ±8.2; range: 3–35) years of practical
experience in the field of hamstring injury management in football.
The response rates in this Delphi procedure were 93% (round 1),
90% (rounds 2 and 3) and 84% (round 4).
Cut-off point for consensus
In Delphi round 1, the expert panel agreed that a cut-off score of
≥70% would be used to define consensus.
RTP terminology
In Delphi round 1, most experts chose either ‘return to play’
or ‘return to competition’ as the term to define RTP. In Delphi
round 2, consensus was reached to adopt return to play—
including its acronym RTP—as the term for return to play in
sports, with the justification being that it is simple, well-known
and adopted worldwide at many levels, including conferences
and publications. It was agreed that ‘return to competition’
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Figure 2 The RTP model for hamstring injuries in football for RTP decision-making, RTP definition and RTP criteria after hamstring injury. GPS, global
positioning system; RTP, return to play.
Consensus statement
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Table 1 Expert advice on performance on field testing to assess
eligibility for RTP after hamstring injury
Clinical test %* Clinical test %*
Position-specific GPS-targeted
match-specific rehabilitation
82 20 m sprint 57
Repeated sprint ability test 76 Nordic hamstring exercise 55
Single leg bridge 71 Triple hop test 53
Deceleration drills 71 Muscular endurance 45
Acceleration drills 68 YoYo/shuttle run test 43
T-test 63 Speed testing 39
40 m sprint 61 Functional movement screen 35
H-test 58 Single hop test 33
*Percentage of experts stating this test could be suggested for functional
performance assessment. Consensus (eg, ≥70%) was only achieved for the tests
presented in bold letters.
GPS, global positioning system; RTP, return to play.
Consensus statement
should be included in the definition of the generic term ‘return
to play’.
Definition of RTP after a hamstring injury
In the first Delphi round, consensus was reached to include ‘avail-
ability for match selection and/or full training’ and ‘clearance by
medical staff ’ as part of the RTP definition after a hamstring
injury. There was also consensus that ‘a completed game’ should
not be included in the RTP definition because RTP clearance
should be given before a player resumes play and availability to
play a match might be based on non-medical (eg, tactical, team-
based) factors or decisions. The expert panel suggested consid-
ering inclusion of ‘a player’s positive mental attitude (athlete’s
readiness)’ in the definition of RTP after hamstring injury.
In Delphi rounds 2 and 3, there was consensus that ‘full
activity’, ‘a 100% recovery score on fitness and skill testing’,
‘absence of symptoms on injured leg’, ‘completion of a reha-
bilitation programme’ and ‘reaching preinjury level’ should not
be included in the definition of RTP after hamstring injury. The
rationale was that these items are not specific enough and/or
should be considered as criteria for RTP, but not for RTP defini-
tion. In Delphi round 3, consensus was achieved on including ‘a
player’s positive mental attitude (athlete readiness)’ in the defini-
tion of RTP, because mental readiness was considered important
to eliminate anxiety and because a positive mental attitude is
perceived to diminish the risk of reinjury and to improve
performance.
The expert panel reached consensus that RTP should be
defined as ‘the moment a player has received criteria-based
medical clearance and is mentally ready for full availability for
match selection and/or full training’.
Medical criteria to support the RTP decision after a hamstring
injury
After discussion and specification of criteria through all rounds
of this Delphi consensus procedure, the following criteria were
included: medical staff clearance, similar hamstring flexibility
(compared with preinjury data and/or uninjured side, depending
on which data are available or are most reliable for the indi-
vidual player according to the medical staff), performance on
field testing, psychological readiness, and absence of pain on
palpation, strength testing, flexibility testing and/or functional
testing. Additionally, the expert panel stated that specification of
criteria was required. The experts agreed that ‘similar hamstring
flexibility’ could involve a 0%–10% difference between injured
and uninjured leg or compared with preinjury data. The expert
panel reached consensus that hamstring flexibility should be
assessed by means of both the active and the passive straight leg
raise test. The rationale was that the passive straight leg raise
test is considered as the gold standard for hamstring flexibility
measurements in daily practice, and it is important to measure
both the active and passive components.42
With regard to ‘performance on field testing’, the expert panel
mentioned a number of field tests used in clinical practice to
support the RTP decision after hamstring injury (see table 1). In
Delphi round 3, the experts were asked whether they had prac-
tical experience with other field tests of functional performance
and whether they would recommend using these tests to support
the RTP decision after hamstring injury (see table 1). Consensus
was reached that the repeated sprint ability test,43 deceleration
drills, single leg bridge and position-specific global positioning
system (GPS)-targeted match-specific rehabilitation were rele-
vant functional performance tests to support the RTP decision
after hamstring injury. In addition to the consensus achieved on
the inclusion of these tests, the experts frequently commented
that performance on field-testing should involve explosive
movements to mimic football performance.
No consensus was reached for the inclusion or exclusion of
‘similar eccentric hamstring strength’ as a criterion to support the
RTP decision after hamstring injury. The expert panel remained
divided, with two irreconcilable opinions: one group of experts
stated that similar eccentric strength assessment is important as
a criterion for RTP as the eccentric phase is also the contraction
mode in which injury occurs, and strength asymmetries should
be eliminated because they can increase the risk of injury. The
other group of experts stated that strength measurements are not
functional, asymmetries are normal, and that too many factors
influence the measurement of strength, so that reliable measure-
ments are not possible. In Delphi round 4, consensus was
reached to add ‘similar eccentric hamstring strength’ (compared
with preinjury data and/or uninjured side, depending on which
data are available or are most reliable for the individual player
according to the medical staff) as a potential criterion to support
the RTP decision provided that both sides of the argument would
be described in the consensus.
The experts agreed that ‘neuromuscular function’ should
not be included as a criterion for RTP after hamstring injury.
Although the experts stated that neuromuscular function is
always important, specifying the concept and assessment of
neuromuscular function would go beyond the scope of this
Delphi procedure and was therefore not indicated as a criterion.
The exclusion of MRI assessment as a potential criterion for
RTP decision-making after hamstring injury was supported by
recent studies.20 44 Baseline MRI parameters are not predictive of
hamstring reinjury, and MRI is not of additional predictive value
compared with baseline patient history and clinical examination
alone.20 45 Completion of a number of full training sessions was
also excluded as a criterion as ‘availability for full training and
match selection’ was already included in the definition of RTP
after hamstring injury.
RTP responsibilities
In Delphi round 2, consensus was reached that the sports physi-
cian, physiotherapist, fitness trainer and athlete are the primary
stakeholders to be involved in RTP decision-making. There was
discussion about the role of the team coach, who not being medi-
cally qualified might allow an early RTP to improve team perfor-
mance, despite potential medical risks. However, in Delphi
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Consensus statement
round 3, the expert panel reached consensus on the inclusion of
the team coach for RTP consultation because of his/her ability to
assess the sport-specific performance level, his/her role in team
selection and his/her function in the multidisciplinary team staff.
The sports physician (who often acts as the head of the medical
staff) was chosen to be ultimately responsible for the RTP deci-
sion, based on the input provided by the multidisciplinary team
and the athlete.
DISCUSSION
This Delphi study involving 58 experts from 28 FIFA Medical
Centres of Excellence worldwide reached consensus on a clear
definition and medical criteria for RTP after hamstring injury
and who should be consulted about RTP and take ultimate
responsibility for the RTP decision (see figure 2).
Definition and medical criteria for RTP
The absence of clear and uniform definitions and medical criteria
for RTP has been a methodological issue in studies of different
musculoskeletal domains, such as RTP after anterior cruciate
ligament injury, ankle injury and concussion.46–49 A clear defini-
tion of RTP is needed for consistency when investigating issues
related to RTP, including reinjury risk factors, RTP prognostic
factors and intervention programmes.22 24–27 Differences in the
definition and criteria for RTP after hamstring injury make it
difficult to compare study results and lead to uncertainty about
which findings should be implemented in clinical practice.22 The
2016 consensus statement on return to sport defined RTP as a
continuum comprising three key elements—return to partici-
pation, return to preinjury sport and return to performance.50
This approach complements criteria-based rehabilitation,
and considers the entire rehabilitation and recovery process,
including the phase beyond return to sport where the athlete
returns to his/her desired performance level.50 However, it is
important to differentiate between the return to sport process
and the final RTP decision, where RTP is viewed as an endpoint
(or primary outcome). This Delphi study explicitly focused on
the final RTP decision (when is the player fully available for
match selection and full training) and involved consensus among
experts in the field of prevention and treatment of hamstring
injuries in football. Although not yet studied and validated in
clinical practice, this Delphi study may help clinicians faced with
the problem of when an athlete should RTP after a hamstring
injury. Furthermore, both the definition and criteria can be
used in research, potentially leading to greater uniformity and
promoting comparability of research.
Medical criteria for RTP after hamstring injury
Absence of pain and psychological readiness
Absence of pain on palpation of the hamstrings, during strength
and flexibility testing, and during or after functional perfor-
mance was considered important as pain may indicate incom-
plete tissue healing. Athletes with localised discomfort on
palpation just after RTP following hamstring injury were four
times (AOR: 3.95; 95% CI: 1.38 to 11.37) more likely to sustain
a reinjury than athletes without discomfort on palpation.20
However, pain perception is influenced by tissue damage and
by cognitive factors such as fear of reinjury or fear of pain.51 52
The fear of pain or reinjury generates avoidance behaviour.52 53
In addition, athletes mention fear of reinjury as the main reason
for not returning to sport.54
The relationship between fear of reinjury and unsuccessful
RTP led to the suggestion that psychological readiness be
included in RTP guidelines.55–57 We included psychological
readiness in both the definition and criteria for RTP after
hamstring injury. The expert panel agreed that the psycho-
logical readiness of the player should be considered before
RTP clearance. Studies focusing on other musculoskeletal
injuries previously emphasised the importance of psycholog-
ical readiness assessment as a part of the RTP decision.55–57
For example, the Knee Self-Efficacy Scale is recommended for
the RTP evaluation of patients rehabilitating from an anterior
cruciate ligament injury.58 However, there are no valid tools to
quantify psychological readiness after hamstring injury reha-
bilitation. The potential relationship between psychological
factors and RTP after hamstring injuries remains an important
topic for future research.
Similar hamstring strength and hamstring flexibility
An isometric knee flexion force deficit just after RTP is asso-
ciated with an increased risk of hamstring injury.20 Our expert
panel did not reach consensus regarding whether ‘similar eccen-
tric hamstring strength’ should be a criterion to support the
RTP decision. Although there was consenus that other contrac-
tion modes should not be included as a criterion to support the
RTP decision. Hamstring peak torque, quadriceps peak torque
and conventional concentric hamstring:quadriceps ratios (as
measured with different test speeds and muscle contractions)
are not associated with an increased risk of hamstring reinjury.8
There is also no relationship between concentric hamstring
to opposite hamstring (H:Hopp) ratio and hamstring reinjury.
However, eccentric strength asymmetries are predictive of
hamstring muscle injuries in football players.59 Furthermore,
67% of all football players clinically recovered from hamstring
injuries had at least one hamstring isokinetic testing deficit of
more than 10%.21 Thus elimination of isokinetic strength asym-
metries is not a requirement for RTP, although it is not known
whether isokinetic strength deficits are associated with the risk
of hamstring reinjury.21
From a biomechanical perspective, strength is preferably
measured in a (sub)maximally stretched position, for which a
fair amount of hamstring extensibility is required.60–63 There is
ongoing debate regarding the relationship between hamstring
flexibility and risk of hamstring injury.7 8 Many studies have
not found hamstring flexibility to be a risk factor for hamstring
injury.8 64 However, the H-test (an active hamstring flexibility
test) showed promising results as a complement to clinical exam-
ination.65 Experts in our Delphi study stated that this test seems
promising as it involves an active flexibility component as well
as assessment of insecurity in the athlete. However, there was
no consensus on the inclusion of this test to support the RTP
decision because experts stated there was insufficient evidence to
support the use of the test and because the test lacks functionality.
Performance on field testing
Performance on field testing was considered vital by the
expert panel when assessing RTP readiness, as it mimics the
actual sports requirements. Furthermore, many criteria-based
hamstring injury rehabilitation protocols have suggested
including performance-based criteria, such as a normal week
of training sessions,66 sport-specific scenarios21 and functional
phase training.17 As most hamstring injuries occur in the
latter stages of a match or training, fatigue and its associated
decline in functional performance need to be considered in
addition to field testing.5 67 68 Therefore, one could argue that
both qualitative and quantitative assessments of functional
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Consensus statement
performance should be performed in a fatigued state.14 Future
research should focus on the development of a sport-specific
test battery for RTP after hamstring injury, in which functional
aspects, fatigue, hamstring flexibility, absence of pain and
potentially hamstring strength are assessed in the light of the
RTP decision.
Hamstring RTP decision-making
Owing to the complexity of RTP decision-making, as well as
potential competing interests and different views of various
stakeholders, it is commonly agreed that RTP decisions should
be based on multidisciplinary consultation.23 41 69 Although the
sports physician may be best qualified to synthesise medical
information, step 3 of the Creighton model29 describes some
important RTP decision modifiers (eg, financial interests,
timing in season, internal pressure, etc). Generally, the sports
physician is only responsible for the medical part of the RTP
decision and does not have the final say over these decision
modifiers (such as financial, legal or team-tactical issues).
Hence, the sports physician may have responsibility for the
decision without authority to make it.69 Ultimately, the best
interests of the athlete are decisive, and this covers more
than just the medical risk assessment.28 29 41 Therefore, in our
opinion, different stakeholders with different views should be
involved in the final RTP decision, bearing in mind the best
interests of the athlete.
Strengths and weaknesses of this study
Delphi studies have the advantage of using the knowledge and
expertise of participating experts to reach consensus.30 70 71 This
Delphi study involved a multidisciplinary sample of clinical and
academic experts with extensive experience in hamstring injury
research and rehabilitation. Although there is no scientifically
proven minimally acceptable response rate, a response rate
of 60% has been used as the threshold of acceptability.72 This
Delphi consensus study had an excellent response rate of >83%
for each Delphi round.
The results of Delphi studies should be viewed in the light of
the expert panel’s opinion at any given point in time,70 because
opinions may change in the light of new evidence and paradigm
shifts.73 Therefore, both the definition and criteria for RTP after
hamstring injury should be re-evaluated in the future, based on
new research findings.
When drafting this consensus, no limitations regarding
(medical) staff and tools were considered. This makes the
consensus more suitable for a professional setting compared
with an amateur setting due to differences regarding team
staff and (access to) tools such as GPS tracking systems. Teams
with limited access to a comprehensive team staff are advised
to still consider and acknowledge the multifaceted nature of
the RTP decision, as discussed in this manuscript. This Delphi
consensus procedure additionally advised simpler functional
tests if GPS tracking systems and/or speed measurement equip-
ment is unavailable (eg, repeated sprint ability test, decelera-
tion drills, etc), although GPS tracking systems are considered
an important tool for functional assessment by the majority of
our expert panel due to their ability to mimic sport-specific
function.
This study provided medical criteria to assess the health status
of the athlete. This is only the first step in the three-step RTP
assessment after hamstring injury (see figure 1).28 29 In addi-
tion to the health status evaluation, the assessment of tissue
stresses (from type of sport, level of play, etc) and RTP decision
modifiers (timing and season, pressure from the athlete or
external, financial issues, etc) should form a solid basis for RTP
decision-making.28 29
Clinical relevance
Although experts’ opinions are considered a low level of
evidence, we consider this study to be an important first step
in standardising and improving the final RTP decision after
hamstring injury. In addition, the criteria to support the RTP
decision were generated by clinical and academic authorities in
the field of hamstring injury management. These criteria will
help both clinicians and (clinical) researchers to assess the risk of
RTP after hamstring injury.
Future research
There is a need for high-quality prospective research to vali-
date RTP criteria. Considering the multidimensional nature
of hamstring injuries, RTP criteria should not be validated as
univariate factors, but interaction between criteria as well as
the varying weighting of criteria due to time and circumstances
needs to be considered.74 75
CONCLUSION
A panel of 58 international experts reached consensus
regarding RTP terminology, definition, medical criteria,
responsibilities and consultation for RTP after hamstring inju-
ries in football. The results are reported in the RTP model for
hamstring injuries in football. The RTP decision should always
be a multidisciplinary decision. For RTP readiness assessment
of the player after a hamstring injury, emphasis is placed on
pain relief, flexibility assessment, psychological readiness and
functional performance. MRI findings should not be used for
RTP readiness assessment.
Acknowledgements The authors would like to thank FIFA and the FIFA Medical
Centres of Excellence network for their support and cooperation in expert selection
and recruitment.
Collaborators The collaborators of HIPS-Delphi group include: CSA Ahmad (USA);
TEA Andersen (Norway); JP Araujo (Portugal); FE Arroyo (Mexico); CM Askling
(Sweden); PD Batty (UK); BB Bayraktar (Turkey); CB Beckmann (Germany); M Bizzini
(Sweden); M Cohen (Brazil); SPC Connelly (UK); D Constantinou (South Africa);
AS Edwards (UK); J Espregueira-Mendes (Portugal); DJ Exeter (New Zealand); ML
Fulcher (New Zealand); aus der Fünten (Germany); WE Garrett (USA); M Grygorowicz
(Poland); TB Haag (Germany), R Hejna (Poland); JM Houghton (UK); AI Isik
(Turkey); S Kemp (UK); C Kruiswijk (Netherlands); GG Lewin (UK); T Lewis (UK); M
Lichaba (South Africa); N Loureiro (Portugal); RL Loursac (France); NAM Maffiuletti
(Sweden); AM Marles (France); J Mendiguchia (Spain); NM Miyauchi (Japan); HM
Moksnes (Norway); CS Motaung (South Africa); EN Noel (France); GJ O’Driscoll
(UK); TO Okuwaki (Japan); K Peers (Belgium); T Piontek (Poland); R Pruna (Spain);
Ranson CA (UK); YS Saita (Japan); MB Santos (Brazil); CS Schneider (Germany); KS
Schwarzenbrunner (Austria); HJ Silvers (USA); A Stålman (Sweden); EV van den Steen
(Belgium); S Sundelin (Sweden); JL Tol (Qatar); NJ Veldman (Netherlands); R Weiler
(UK); R Whiteley (Qatar); E Witvrouw (Qatar); A Yekdah (Algeria); JE Zachazewski
(USA).
Contributors Four authors have made substantial contributions to this manuscript:
NH, EAG, BMAH and FJGB. They have all participated in the concept and design,
analysis and interpretation of data, and drafting and revising the manuscript. All
authors have read the manuscript and agreed to submission for publication. The
HIPS-Delphi Group, the name of our expert panel, contributed to the full contents
of the consensus. We would therefore like to acknowledge the ’HIPS-Delphi Group’
with authorship as well.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.
© Article author(s) (or their employer(s) unless otherwise stated in the text of the
article) 2017. All rights reserved. No commercial use is permitted unless otherwise
expressly granted.
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1590 van der HorstN, etal. Br J Sports Med 2017;51:1583–1591. doi:10.1136/bjsports-2016-097206
Consensus statement
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criteria and decision-making
procedure regarding definition, medical
football (soccer): a worldwide Delphi
Return to play after hamstring injuries in
Huisstede
Nick van der Horst, FJG Backx, Edwin A Goedhart and Bionka MA
doi: 10.1136/bjsports-2016-097206
30, 2017 2017 51: 1583-1591 originally published online MarchBr J Sports Med
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... Absence of pain was utilized in seven studies as an RTP criterion (Delvaux et al., 2013;Dunlop et al., 2020;Garcia et al., 2022;Taberner et al., 2020Taberner et al., , 2022van der Horst et al., 2017;Zambaldi et al., 2017). Delvaux et al. (2013) used a bespoke questionnaire to interview 37 sports medicine physicians from French and Belgian male professional football clubs about the most important RTP criteria after an HSI. ...
... The definitions of the RTP continuum phases are summarized in Table 3. Similar results were presented by van der Horst et al. (2017) in their Delphi study. Fifty-eight experts from 28 FIFA Medical Centres of Excellence worldwide identified the absence of pain on palpation of the hamstrings, on strength and flexibility testing and on functional performance as important criterion for RTRun. ...
... Hamstring flexibility was utilized in five studies as an RTP criterion (Delvaux et al., 2013;Dunlop et al., 2020;Garcia et al., 2022;van der Horst et al., 2017;Zambaldi et al., 2017). In their survey, Delvaux et al. (2013) reported that Hamstring muscle flexibility represented the fourth most relevant RTP criterion on a list of 12 criteria. ...
Article
Full-text available
The present scoping review aims to describe the available criteria to determine Return-To-Play (RTP), propose methodological considerations and new research questions, and provide information to help practitioners in professional football make informed decisions regarding RTP following a hamstring strain injury (HSI) in professional male football. The following electronic databases were searched: PubMed, MEDLINE, web of science and SPORTDiscus using keywords related to HSI in elite football. All types of studies in English reporting at least one RTP criterion for professional football players who sustained an HSI were included. In total, 19 studies met the inclusion criteria. RTP criteria were divided into three categories: clinical, strength and performance criteria. Clinical criteria were also divided into sub-categories: absence of pain, hamstring flexibility, medical staff clearance, psychological readiness, surgeon's opinion and imaging. Practitioners working in professional male football could benefit from using a combination of criteria in their RTP battery of tests. ARTICLE HISTORY
... То есть данные аппаратных методов визуализации не должны быть определяющими как в отношении вопроса о возобновлении РТД, так и ее безопасности с точки зрения развития рецидивов online first повреждения. Поэтому не должно вызывать удивления, что во всех существующих консенсусах не применялись данные аппаратных методов визуализации о состояния мышечной ткани в качестве критерия возобновления спортсменами РТД [30][31][32]. ...
... Ни в одной классификации не оценивались и протоколы лечения, которые применяются в первые часы и дни после получения травмы и которые могут значительно влиять на выраженность болевого синдрома (например, при использовании больших доз анальгетиков). Да и само понятие «регулярная тренировочная деятельность» до сих пор является не строго определенным и не имеет четких критериев, связанных как с необходимой двигательной активности спортсменов, так и с фазой тренировочного цикла и периодом начала участия в соревнованиях [31]. ...
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Full-text available
Introduction Despite the large number of classifications of muscle injuries proposed by different expert groups, there is still no classification that can fully satisfy the requirements of practitioners in terms of predicting the duration of treatment and minimising the risk of recurrence. At the same time, the diversity of classifications may lead to different interpretations of the severity of the same injury with subsequent variability in the choice of rehabilitation protocol and its duration. Aim To analyse the advantages and disadvantages of the most common classifications of muscle injuries in the practice of professionals working with athletes. Materials and methods The Pubmed and Google Scholar databases were searched for articles in English describing classifications of muscle injuries proposed since 2000. The following word combinations were used for the search: ‘classification of muscle injuries’, ‘grading of muscle injuries’, ‘muscle damage’ and ‘muscle injuries’. The study design was a narrative review. Results Eight classifications proposed by different expert groups since 2000 were found. The Munich Consensus and British Athletic Association classifications of muscle injuries and the MLG-R classification can be considered the most commonly used at present, based on various combinations of clinical symptomatology, mechanism of injury and localisation, and magnetic resonance imaging findings. Conclusion There are currently several of the most widely used classifications of muscle injuries, and communities of practice should appreciate this diversity when determining injury severity and predicting treatment time, and use the same classification.
... 1,9 Two Delphi consensus studies on RTP after hamstring injury have suggested several RTP criteria, namely absence of pain, confidence and psychological readiness, functional performance including sprint ability, and full flexibility and hamstring strength. 10,11 In addition to these clinical factors, magnetic resonance imaging (MRI) is used in the management of hamstring injuries. Several studies suggest that MRI might have a potential role in assisting RTP decisions, that is, to predict a time frame for RTP based on injury characteristic and grading system. ...
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Objective To describe 3.0-Tesla (T) magnetic resonance imaging (MRI) findings of hamstring muscles in clinically recovered athletes who were cleared for return to play (RTP). Design Prospective observational study. Setting Hospital. Participants Athletes (amateur and professional) who were cleared for RTP after hamstring injury. Fifty-eight participants were included in the analysis. Independent Variables 3-T MRI at baseline (within 7 days from initial injury) and MRI at RTP (within 10 days of RTP). Main Outcome Measures Injury location, grade of injury (modified Peetrons and British Athletics Muscle Injury Classification/BAMIC), presence and the extent of intramuscular signal abnormality, intramuscular tendon disruption, and thickness. Reinjuries within 1 year of RTP were recorded. Results Magnetic resonance images at RTP showed that 55 (95%) participants had intramuscular increased signal intensity (edema) and 44 (76%) participants had intramuscular abnormal low-signal intensity (suggesting fibrosis) on MRI. There was an overall reduction of injury grades according to the modified Peetrons and BAMIC classification at initial injury to RTP. Three (5%) participants had no abnormal signal intensities (grade 0 or grade 0A) on MRI at RTP. Intramuscular tendon disruption, waviness, and tendon thickening were present at RTP in, respectively, 22 (38%), 15 (26%), and 36 (62%). We recorded 3 (5%) reinjuries. Conclusions At RTP, 3.0-T MRI shows high percentages of MRI abnormalities (edema, fibrosis, and intramuscular tendon disruption and thickening). We conclude that complete normalization of 3.0-T MRI is not expected for RTP decision after a hamstring injury. Its possible association with reinjury risk has to be determined in larger cohorts.
... It is established that full recovery from an ACL injury takes longer than nine months (Read et al., 2020). Criteria, including medical clearance, absence of pain, strength and flexibility testing, functional testing, hamstring flexibility, on-field performance, and psychological readiness, determine a player's readiness to return (Van Der Horst et al., 2017). ...
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Effective management of a soccer team requires informed decision-making that profoundly influences team success, particularly in the dynamic and uncertain environment of the sport. To navigate the complexities, coaches have increasingly adopted data-driven techniques, resulting in an abundance of analyses that can lead to information overload. Therefore, acquiring a comprehensive understanding of existing soccer performance analysis and leveraging relevant insights become crucial. This study encompasses 3263 papers from Scopus published between 1978 and 2022. Our research employs a two-layer bibliometric analysis approach, involving the construction of a broader keyword co-occurrence network and subsequent nested keyword co-occurrence networks to identify and analyze the main research themes and their sub-themes within the field. Through this nested bibliometric approach, we develop a two-layer hierarchical taxonomy comprising seven overarching research themes and 40 corresponding sub-themes, thereby unveiling the intellectual structure of the literature in soccer performance analysis. Furthermore, our methodology allows us to delve deeper into the data collection process, enabling us to measure the proportion of articles effectively included in the keyword co-occurrence network. By employing this nested bibliometric approach, we evaluate the prevalence of multi-thematic papers in the field, revealing a paucity of truly multi-thematic studies. This research contributes to a deeper understanding of the intellectual structure of soccer performance analysis, providing valuable insights for both practitioners and researchers to advance knowledge in the field and foster a more comprehensive comprehension of soccer performance analysis.
... From a rehabilitation perspective, the strength assessment of the HM is crucial for detecting any strength weakness that could potentially increase the risk of HMI ( Van der Horst et al., 2017). For this purpose, current evaluation methods use an isokinetic dynamometer (Croisier et al. 2008(Croisier et al. , 2004, hand-held dynamometer (Lahti et al., 2020) or functional tests such as the single leg hamstring bridge test or force-velocity-power profiling and kinematic analysis during sprinting (Freckleton et al., 2014;Lahti et al., 2020;Bramah et al., 2024). ...
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Aim The Royal Dutch Society for Physical Therapy (KNGF) instructed a multidisciplinary group of Dutch anterior cruciate ligament (ACL) experts to develop an evidence statement for rehabilitation after ACL reconstruction. Design Clinical practice guideline underpinned by systematic review and expert consensus. Data sources A multidisciplinary working group and steering group systematically reviewed the literature and wrote the guideline. MEDLINE and the Cochrane Library were searched for meta-analyses, systematic reviews, randomised controlled trials and prospective cohort studies published between January 1990 and June 2015. Eligibility criteria for selecting studies Included literature must have addressed 1 of 9 predetermined clinical topics: (1) preoperative predictors for postoperative outcome, (2) effectiveness of physical therapy, (3) open and closed kinetic chain quadriceps exercises, (4) strength and neuromuscular training, (5) electrostimulation and electromyographic feedback, (6) cryotherapy, (7) measurements of functional performance, (8) return to play and (9) risk for reinjury. Ninety studies were included as the basis for the evidence statement. Rehabilitation after ACL injury should include a prehabilitation phase and 3 criterion-based postoperative phases: (1) impairment-based, (2) sport-specific training and (3) return to play. A battery of strength and hop tests, quality of movement and psychological tests should be used to guide progression from one rehabilitation stage to the next. Postoperative rehabilitation should continue for 9–12 months. To assess readiness to return to play and the risk for reinjury, a test battery, including strength tests, hop tests and measurement of movement quality, should be used.
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Injury prediction is one of the most challenging issues in sports and a key component for injury prevention. Sports injuries aetiology investigations have assumed a reductionist view in which a phenomenon has been simplified into units and analysed as the sum of its basic parts and causality has been seen in a linear and unidirectional way. This reductionist approach relies on correlation and regression analyses and, despite the vast effort to predict sports injuries, it has been limited in its ability to successfully identify predictive factors. The majority of human health conditions are complex. In this sense, the multifactorial complex nature of sports injuries arises not from the linear interaction between isolated and predictive factors, but from the complex interaction among a web of determinants. Thus, the aim of this conceptual paper was to propose a complex system model for sports injuries and to demonstrate how the implementation of complex system thinking may allow us to better address the complex nature of the sports injuries aetiology. According to this model, we should identify features that are hallmarks of complex systems, such as the pattern of relationships (interactions) among determinants, the regularities (profiles) that simultaneously characterise and constrain the phenomenon and the emerging pattern that arises from the complex web of determinants. In sports practice, this emerging pattern may be related to injury occurrence or adaptation. This novel view of preventive intervention relies on the identification of regularities or risk profile, moving from risk factors to risk pattern recognition.
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Deciding when to return to sport after injury is complex and multifactorial-an exercise in risk management. Return to sport decisions are made every day by clinicians, athletes and coaches, ideally in a collaborative way. The purpose of this consensus statement was to present and synthesise current evidence to make recommendations for return to sport decision-making, clinical practice and future research directions related to returning athletes to sport. A half day meeting was held in Bern, Switzerland, after the First World Congress in Sports Physical Therapy. 17 expert clinicians participated. 4 main sections were initially agreed upon, then participants elected to join 1 of the 4 groups-each group focused on 1 section of the consensus statement. Participants in each group discussed and summarised the key issues for their section before the 17-member group met again for discussion to reach consensus on the content of the 4 sections. Return to sport is not a decision taken in isolation at the end of the recovery and rehabilitation process. Instead, return to sport should be viewed as a continuum, paralleled with recovery and rehabilitation. Biopsychosocial models may help the clinician make sense of individual factors that may influence the athlete's return to sport, and the Strategic Assessment of Risk and Risk Tolerance framework may help decision-makers synthesise information to make an optimal return to sport decision. Research evidence to support return to sport decisions in clinical practice is scarce. Future research should focus on a standardised approach to defining, measuring and reporting return to sport outcomes, and identifying valuable prognostic factors for returning to sport.
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Background: Despite relatively high reinjury rates after acute hamstring injuries, there is a lack of detailed knowledge about where and when hamstring reinjuries occur, and studies including imaging-confirmed reinjuries are scarce. Purpose: To investigate the location, radiological severity, and timing of reinjuries on magnetic resonance imaging (MRI) compared with the index injury. Study design: Case series; Level of evidence, 4. Methods: A MRI scan was obtained ≤5 days after an acute hamstring index injury in 180 athletes, and time to return to sport (RTS) was registered. Athletes with an MRI-confirmed reinjury in the same leg ≤365 days after RTS were included. Categorical grading and standardized MRI parameters of the index injury and reinjury were scored by a single radiologist (with excellent intraobserver reliability). To determine the location of the reinjury, axial and coronal views of the index injury and reinjury were directly compared on proton density-weighted fat-suppressed images. Results: In the 19 athletes included with reinjury, 79% of these reinjuries occurred in the same location within the muscle as the index injury. The median time to RTS after the index injury was 19 days (range, 5-37 days; interquartile range [IQR], 15 days). The median time between the index injury and reinjury was 60 days (range, 20-316 days; IQR, 131 days) and the median time between RTS after the index injury and the reinjury was 24 days (range, 4-311 days; IQR, 140 days). More than 50% of reinjuries occurred within 25 days (4 weeks) after RTS from the index injury and 50% occurred within 50 days after the index injury. All reinjuries with more severe radiological grading occurred in the same location as the index injury. Conclusion: The majority of the hamstring reinjuries occurred in the same location as the index injury, early after RTS and with a radiologically greater extent, suggesting incomplete biological and/or functional healing of the index injury. Specific exercise programs focusing on reinjury prevention initiated after RTS from the index injury are highly recommended.
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Background More than half of the recurrent hamstring injuries occur within the first month after return-to-play (RTP). Although there are numerous studies on RTP, comparisons are hampered by the numerous definitions of RTP used. Moreover, there is no consensus on the criteria used to determine when a person can start playing again. These criteria need to be critically evaluated, in an attempt to reduce recurrence rates and optimize RTP. Objective To carry out a systematic review of the literature on (1) definitions of RTP used in hamstring research and (2) criteria for RTP after hamstring injuries. Study DesignSystematic review. Methods Seven databases (PubMed, EMBASE/MEDLINE, CINAHL, PEDro, Cochrane, SPORTDiscus, Scopus) were searched for articles that provided a definition of, or criteria for, RTP after hamstring injury. There were no limitations on the methodological design or quality of articles. Content analysis was used to record and analyze definitions and criteria for RTP after hamstring injury. ResultsTwenty-five papers fulfilled inclusion criteria, of which 13 provided a definition of RTP and 23 described criteria to support the RTP decision. “Reaching the athlete’s pre-injury level” and “being able to perform full sport activities” were the primary content categories used to define RTP. “Absence of pain”, “similar strength”, “similar flexibility”, “medical staff clearance”, and “functional performance” were core themes to describe criteria to support the RTP decision after hamstring injury. Conclusion Only half of the included studies provided some definition of RTP after hamstring injury, of which reaching the athlete’s pre-injury level and being able to perform full sport activities were the most important. A wide variety of criteria are used to support the RTP decision, none of which have been validated. More research is needed to reach a consensus on the definition of RTP and to provide validated RTP criteria to facilitate hamstring injury management and reduce hamstring injury recurrence.PROSPERO systematic review registration number: CRD42015016510.
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Context: Hamstring acute muscle injuries are prevalent in several sports including AFL football (Australian Football League), sprinting and soccer, and are often associated with prolonged time away from sport. Evidence acquisition: In response to this, research into prevention and management of hamstring injury has increased, but epidemiological data shows no decline in injury and re-injury rates, suggesting that rehabilitation programs and return to play (RTP) criteria have to be improved. There continues to be a lack of consensus regarding how to assess performance, recovery and readiness to RTP, following hamstring strain injury. Results: The aim of this paper was to propose rehabilitation protocol for hamstring muscle injuries based on current basic science and research knowledge regarding injury demographics and management options. Conclusions: Criteria-based (subjective and objective) progression through the rehabilitation program will be outlined along with exercises for each phase, from initial injury to RTP.
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“QUICK—GET AN MRI SO WE KNOW WHEN HE WILL BE BACK READY TO PLAY” In the elite athlete setting, MRI has gradually gained a magical reputation: it is the crystal ball that answers all the questions of the injured athlete, coaching and medical staff. Without imaging the injury, there is no peace of mind within the team. There is no doubt that the evolution of imaging techniques can support the management of the injured athlete, but we argue that the current available data suggests that it is almost useless for predicting return to play (RTP) following hamstring injury. IF YOU THINK A GRADE II INJURY WILL TAKE 4 WEEKS, IT WILL TAKE 4 WEEKS IRRESPECTIVE OF WHEN THE PLAYER WAS READY In a recently published systematic review of the literature, we concluded that there is no strong evidence for any MRI finding that can guide sports physicians and radiologists in predicting prognosis for the time to RTP after an acute hamstring injury.1 This conclusion is mainly based on two limitations in the current literature: 1. Multiple studies on hamstring injuries found correlations between different MRI measures and the time to RTP. Unfortunately, these are limited to univariate analyses on correlations between MRI parameters and RTP. None of the studies analysed the additional value of MRI to clinical evaluation in multivariate models. No study has established if the addition of MRI helps predict RTP. 2. There is a considerable risk of bias in most of the studies on this topic, as the clinicians are not blinded to the MRI as they treat their players. WHY IS BLINDING CRUCIAL TO PREVENT BIAS? “All my MRI Grade I hamstring injuries take 3 weeks because I let all my MRI grade I hamstring injuries go back after 3 weeks” When studying prognostic factors, the outcome measure should be independent of the prognostic factor of interest to prevent biased results.2 For daily practice, this implies that the RTP decision-maker is unaware and blinded to the potential prognostic factors such as baseline MRI results. SELF-FULFILLING PROPHECY: BREAKING BAD AND THE OBSERVER EFFECT The lead character in the TV series Breaking Bad went by the pseudonym of ‘Heisenberg’—an oblique reference to the Quantum Mechanics’ Uncertainty Principle and the strange phenomenon that observing some particles changes the properties of these particles. We feel that observing hamstring injury on MRI changes the way the observer behaves (but not the hamstring injury). Take the example of an ‘MRI negative injury’. The knowledge that there is no sign of injury seen on MRI will likely affect judgements of the injured athlete and the medical staff involved, and result in a faster progression through rehabilitation and RTP than in MRI positive injuries. It is a selffulfilling prophecy that, without blinding for the MRI findings, the factor ‘MRI negative injury’ will most likely be associated with a shorter time to RTP. To the best of our knowledge, of the 12 studies documenting RTP after hamstring injury where MRI was available, only 2 had the clinicians blinded to theMRI.3 4 CLINICAL RELEVANCE: ‘BYE, BYE MRI’? In clinical practice, the diagnostic work up generally consists of history, physical examination and, possibly, additional imaging. We argue that the prognostic value of an investigation is only of clinical relevance when it provides additional prognostic value after clinical evaluation. As none of the studies included in the systematic review analysed both clinical and MRI findings, it is unknown whether the MRI findings provide such additional prognostic information. Recent data clearly show that MRI did not provide additional prognostic information.5 “I AGREE THAT MRI MIGHT NOT BE USEFUL IN A RESEARCH SETTING, BUT FOR MY ELITE-ATHLETES IT IS INDISPENSABLE” In clinical practice, we are interested in providing an RTP prognosis for an individual injured athlete. Although our knowledge has significantly improved at a group level, the current available research cannot satisfactorily predict the time to RTP for the individual athlete. We will illustrate this with an example using the MRI grading system, which is the most commonly used prognostic MRI factor. In the largest series and landmark paper on the prognostic value of MRI, Hallen and Ekstrand found that, in professional football players, MRI grading was significantly correlated with injury time.6 This study reported, for each injury grade (in days ±SD): grade I, 18±19; grade II, 24 ±13; grade III, 60±57. By applying these results to an individual professional football player with a grade II hamstring injury, we can estimate that there is a 95% chance that he returns to play somewhere between 0 and 50 days (mean: 24 days±2 times the SD of 13 days). The athlete, coaching staff and press will justly argue that these estimations of the injury time are a long way from being satisfactory. STATISTICS ON THE TABLE There are many different factors determining RTP in hamstring injuries, and anatomical severity, as measured by the MRI, is only one of the factors. But the current available data show that MRI does not substantially contribute to the answer of the athletes’ most important and simple question after they are injured: ‘When can I return to play?’. Is it therefore the right moment to say ‘bye–bye MRI’ to the device as a prognostic tool for predicting RTP after hamstring injuries in the individual athlete? We tend to answer yes, but we encourage you to surprise us with unbiased and blinded data.
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Background There are limited data on hamstring injury rates over time in football. Aim To analyse time trends in hamstring injury rates in male professional footballers over 13 consecutive seasons and to distinguish the relative contribution of training and match injuries. Methods 36 clubs from 12 European countries were followed between 2001 and 2014. Team medical staff recorded individual player exposure and time-loss injuries. Injuries per 1000 h were compared as a rate ratio (RR) with 95% CI. Injury burden was the number of lay off days per 1000 h. Seasonal trend for injury was analysed using linear regression. Results A total of 1614 hamstring injuries were recorded; 22% of players sustained at least one hamstring injury during a season. The overall hamstring injury rate over the 13-year period was 1.20 injuries per 1000 h; the match injury rate (4.77) being 9 times higher than the training injury rate (0.51; RR 9.4; 95% CI 8.5 to 10.4). The time-trend analysis showed an annual average 2.3% year on year increase in the total hamstring injury rate over the 13-year period (R2=0.431, b=0.023, 95% CI 0.006 to 0.041, p=0.015). This increase over time was most pronounced for training injuries—these increased by 4.0% per year (R2=0.450, b=0.040, 95% CI 0.011 to 0.070, p=0.012). The average hamstring injury burden was 19.7 days per 1000 h (annual average increase 4.1%) (R2=0.437, b=0.041, 95% CI 0.010 to 0.072, p=0.014). Conclusions Training-related hamstring injury rates have increased substantially since 2001 but match-related injury rates have remained stable. The challenge is for clubs to reduce training-related hamstring injury rates without impairing match performance.