Hamstring MRI SCAN

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Original article

Ekstrand J, Healy JC, Waldn M,et al. Br J Sports Med(2011). doi:10.1136/bjsports-2011-090155 1 of 6

ABSTRACTBackground Hamstring injury is the single most com-mon injury in professional football. MRI is commonlyused to confirm the diagnosis and provide a prognosis oflay-off time.Objective To evaluate the use of MRI as a prognostictool for lay-off af ter hamstring injuries in professionalfootball players and to study the association betweenMRI findings and injury circumstances.Methods Prospective cohort study where 23 Europeanprofessional teams, were followed between 2007 and2011. Team medical staffs recorded individual player expo-sure and time-loss injuries. Radiological grading was per-formed using a modified Peetrons classification into fourgrades where grades 2 and 3 represent fibre disruption.Results In total, 516 hamstring injuries occurred and58% of these were examined by MRI. Thirteen per centwere grade 0 injuries, 57% grade 1, 27% of grade 2 and3% of grade 3. Grade 0 and 1 injuries accounted for 56%(2141/3830 days) of the total lay-off. The lay-off timediffered between all four radiological grades of injury(83, 1710, 2211 and 7360 days, p


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Ekstrand J, Healy JC, Waldn M,et al. Br J Sports Med(2011). doi:10.1136/b jspor ts-2011-0901552 of 6

disorders such as total and partial muscle ruptures, as well asfunctional disorders such as fatigue-induced, spine-related orneuromuscular muscle disorders were included while contu-sions, haematomas, tendon ruptures and chronic tendinopa-thies were excluded.

Data collectionPlayer baseline data were collected once yearly at the start of

the season. Individual player exposure in train ing and matcheswas registered by the clubs on a standard exposure form to besent to the study group on a monthly basis. The team medi-cal staffs recorded injuries on a standard injury form that wassent to the study group each month. The injury form providedinformation about the diagnosis, nature and circumstancesof injury occurrence. All injuries resulting in a player beingunable to fully participate in training or match play (ie, time-loss injuries) were recorded, and the player was consideredinjured until the team medical staff allowed full participationin training and availability for match selection. All injurieswere followed until the final day of rehabilitation.

MRIFrom the 23 teams involved in the UCL study, 15 (65%) agreedto participate in a discussion about MRI of thigh muscleinjuries. A questionnaire was sent to these clubs in February2007, and agreement was reached concerning the use of MRIfor inclusion in this study. For the purpose of this study, theclubs were instructed to perform the initial MRI examinationwithin 2448 h of the injury event. The MRI machine shouldnot be older than 5 years and have a field strength of at least 1.5T. The minimum MR sequences should include axial and coro-nal planes using T1, T2 with fat saturation, and/or Short TauInversion Recovery (STIR) sequences. An MRI Thigh InjuryReport Form was created with information about date of imag-

ing, name of radiologist evaluating the images, MR sequencesused, muscles involved and severity of injury. If more thanone muscle was injured, the muscle with the most extensivepathology was denoted as the primary muscle involved, andassessment criteria were taken for that par ticular muscle.

For severity classification, a modification of Peetrons classi-fication27was used with the following grading system: grade0 negative MRI without any visible pathology, grade 1 oedemabut no architectural distortion, grade 2 architectural disruption

indicating part ial tear and grade 3 total muscle or tendon rup-ture. All radiologists used the same standard evaluation pro-tocol. Nine of the teams used PACSMail (www.sybermedica.com) to send their MRIs for online review by two independentradiologists ( J.H. and J.L) who were unaware of clinical detailsother than the suggested hamstring injury. Copies of scansand associated reports from the nine teams using PACSMailwere then sent electronically to the UEFA injury surveillance

study group. The other six teams had the paper-based MRIforms filled in by the consultant radiologist for the club andthese were sent to the study group by mail.

AnalysesAnalysis of variance with Bonferroni post hoc test was usedfor between-group comparisons of lay-off time. Associationbetween categorical variables was measured with Pearsons2 test or Fishers exact test. Bonferroni correction was usedfor multiple pairwise comparisons. The significance level wasset at p


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(439 days) for grades 1, 2 and 3, respectively. The lay-off timefrom football differed significantly between the four grades ofinjury (83, 1710, 2211 and 7360 days for grades 0, 1, 2 and3 respectively, p


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by MRI or US or with a combination of these examinations.As always, the clinical examination is the base for diagnosis,but at the professional level different sorts of imaging are fre-quently used to enhance the quality of the diagnosis in orderto better prognosticate healing time and lay-off from football.MRI has been the preferred modality in recent years and hasoffered a highly detailed imaging analysis of the extent ofinjury.16 1820 28

Most hamstring injuries have no signs of muscle fibredisruptionTwo of three hamstring injuries were grade 0 or 1 injuries,showing no signs of muscle fibre disruption on MRI. Still,these injuries caused more than half of the absence days. Thismeans that from a clubs perspective, these injuries representa significant problem due to their high incidence, even if mosthamstring injuries have a favourable prognosis and are effec-tively handled conservatively.24 Surgical repair is normallyreserved for total ruptures, such as avulsion injuries, but theseinjuries are rarely seen in football, representing only a few percent of all hamstring injuries as shown in this study.

Radiological grading relates to lay-offThe ability to predict lay-off is very important for the injuredplayer as well as the coaching staff.18Another main finding ofthis study is therefore that radiological grades are highly associ-ated with lay-off time from football. It seems logical that radio-logical severity is correlated to clinical severity, thus indicatingthat an MRI examination done 2448 h after a hamstring injurycould provide information about what absence to be expected.Several studies from Australian Rules football1619 2123 haveshown the possibility to use MRI to prognosticate lay-off timeafter hamstring injury. Schneider-Kolsky et al19compared MRI(with radiologists blinded to clinical data) and clinical assess-ment of acute hamstring injuries and found both methods to beuseful as a predictor for the duration of rehabilitation required.

However, muscle injuries are a heterogeneous group and theneed for classification and subgrouping of muscle injuries have

been emphasised.4 10Ekstrand et al4have recently shown thatmore than 90% of all muscle injuries in male elite footballersaffect four muscle groups (hamstrings, quadriceps, adduc-tors and calf muscles), but injuries to dif ferent muscle groupsbehave differently. If the aim is to prognosticate absence dueto injuries, a further subgrouping into severity grades is nec-essary since the absence differs significantly between differ-ent radiological grades. As suggested by Gibbs et al18 in theirstudies of hamstring injuries in Australian Rules football,further subgrouping into injury type, intramuscular location

and dimension of pathology might be of additional value inprognosticating absence. In this ongoing study, these qualitiesare measured, but (due to the necessity of subgrouping intomuscle groups and grades) the numbers of each subgroup arestill smal l and further data are needed for safer statements.

The importance of imaging has increased, as not all causesof posterior thigh pain are the result of a hamstring musclefibre strain.15 24 We found 27 (13%) grade 0 injuries with amean absence of 8 days. Several studies have demonstratedthat a negative MRI finding in the context of clinically sus-pected hamstring strain is associated with shorter recoverytime.1619 21 23As such, these clinically diagnosed hamstringinjuries with a negative MRI appear to have a good prognosis.

The actual cause of posterior thigh injury where MRI showsno pathology is unclear. It is possible that these injuries arebelow the sensitivity of MRI detection and are subtle muscleinjuries.29Another explanation is that such athletes may havean alternative diagnosis such as back-related problem, neuraltension or muscle spasm.10 16

The majority of hamstring strains affect the biceps femorismuscleIn our 180 injuries with pathology on MRI, we found that84% affected the BF, 11% the SM and 5% the ST. Our findingsare consistent with previous studies by Koulouris et al,16whoanalysed MRIs of 31 hamstring injuries in Australian football

players and found 84% injuries to the BF, 10% to the SM and6% to the ST.

Table 2 Associations between radiological grades and clinical severity, lay-off time, muscles involved,etiology and recurrence

Total Grade 0 Grade 1 Grade 2 Grade 3

Injuries 207 27 (13%) 118 (57%) 56 (27%) 6 (3%)

Clinical severity

Minimal 5 (2%) 1 (4%) 4 (3%) 0 0

Mild 29 (14%) 12 (44%) 13 (11%) 4 (7%) 0

Moderate 143 (69%) 14 (52%) 89 (75%) 38 (68%) 2 (33%) Severe 30 (15%) 0 12 (10%) 14 (25%) 4 (67%)

Lay-off time (days)* 1917 83 1710 2211 7360

Muscles involved

Biceps femoris 150 (84%) 101 (86%) 45 (81%) 5 (83%)

Semimembranosus 20 (11%) 12 (10%) 8 (14%) 1 (17%)

Semitendinosus 9 (5%) 5 (4%) 3 (5%) 0

Aetiology

Trauma 130 (64%) 8 (31%) 79 (69%) 39 (70%) 4 (67%)

Overuse 72 (36%) 18 (69%) 35 (31%) 17 (30%) 2 (33%)

Recurrence 34 (16%) 2 (7%) 20 (17%) 12 (21%) 0

Radiological grades were classified according to Peetrons27: grade 0 negative MRI without any visible patholog y, grade 1

oedema but no architectural distortion, grade 2 architectural disruption indicating partial tear and grade 3 total muscle or

tendon rupture. Clinical severity was classified according to the football consensus26: minimal (causing absence of 13 days),

mild (absence 47 days), moderate (absence 828 days) and severe (absence>28 days).*Values are meanSD.

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In accordance with the findings of Slavotinek et al21 inAustralian Rules football, we found no relation between thespecific muscle involved and lay-off time.

Running/sprinting most common mechanismIt is well established that hamstring muscle injuries are com-mon in sports characterised by high-velocity sprinting15 3032or multidirectional acceleration.32 Similar to the study by

Woods et al,15our study shows that the majority of hamstringinjuries occurred during running or sprinting. Eccentric over-loading at the end of the swing phase has been suggested as apossible mechanism behind hamstring injuries.30 3234Fatiguemight be another important factor; it has previously beenshown that muscle injuries occur more frequently towards theend of each half.3 4 35In a laboratory study of male professionalfootball players, Grieg et al36 showed that the eccentric ham-strings strength decreased over time and, in particular, afterthe half-time interval. Fatigue might also alter the neuromus-cular activity in the hamstrings, as shown by Pinniger et al.37

Re-injuries only to biceps femoris

Recurrent hamstring muscle injuries are common and pre-vious injury is an important risk factor for new hamstringinjury.15 23 3841 In football, recurrence rates of 1225% haspreviously been reported,11 15 but these studies have limita-tions such as small material, no exposure data or differentdefinitions of a re-injury. In this study, re-injuries constituted16% of all hamstring injuries with no significant difference ininjury rates between different radiological grades. However,30 re-injuries occurred to the BF muscle and none of them toST or SM, a finding that needs to be further explored. Previousstudies of re-injuries in general have shown that re-injuriescause longer absence than non-re-injuries.3 4 13 In this study,however, no difference was found in lay-off time between re-injury and index injury, possibly indicating that top-level clubsin Europe have greater medical support, providing more indi-vidualised rehabilitation for injured players.4One could alsospeculate whether the frequently used radiological examina-tions for diagnostics and return-to-play decisions could help toreduce the re-injury rate.4

Strengths and limitationsAn obvious strength of this study is its design, with a homo-geneous group of male professional footballers followed pro-spectively with a standardised methodology that complieswith the international consensus agreements on proceduresfor epidemiological studies of football injuries.25 26 Further,the number of players included and number of MRI exami-nations are substantially larger compared with previous stud-ies evaluating the association between hamstring injuries andMRI findings.1619 2123

A limitation is that muscle injury const itute a heterogeneousgroup including all types of muscle injuries, structural (par-tial or total ruptures) as well as functional (fatigue induced,spine-related or neuromuscular muscle disorders, etc).4 10Furthermore, the material includes muscle injuries of differentseverities, of different extramuscular and intramuscular loca-tions and of different sizes.4 10Next, MRIs were examined byseveral radiologists from dif ferent countries. Even if an agree-ment about how and when the MRIs should be executed andeven if a standard MRI form was used, the inter-observer reli-

ability between the different radiologists is unknown. Ourstudy population was limited to male professional football

players and might therefore not necessarily reflect the injurycharacteristics of a more general population or other levels ofplay. Although the use of imaging is frequently used to planand assist rehabilitation of professional football players, analgorithm that integrates clinical and imaging information intoa management plan remains to be established and tested.20

As a conclusion, this study shows that MRI can be helpfulin verifying the diagnosis of a hamstring injury and also toprognosticate lay-off time. Radiological grading is associatedwith lay-off times after injury. Seventy per cent of hamstringinjuries seen in professional football show no signs of fibredisruption on MRI (radiological grade 0 or 1 injuries), but stillcause the majority of absence days.

Acknowledgements The authors wish to thank the participating clubs, medicalstaffs and players. A special thanks to the contact persons in clubs that have sentus MRIs by PACSMail: Edwin Goedhart (AFC Ajax), Markus Braun (BV BorussiaDortmund), David Wales (Arsenal F C), Alex Nieper (Chelsea FC), FrancescoBenazzo, Franco Combi and Giorgio Panico, (FC Internazionale Milano), NelsonPuga (FC Porto), Cees-Rein van den Hoogenband and Luc van Agt (PSV Eindhoven),Paco Biosca and Viktor Kirilenko (Shakhtar Donetsk). The statistical advice of HenrikMagnusson (Msc) is also gratefully acknowledged.

Funding UEFA, Swedish Centre for Research in sport and Praktiker tjnst AB.

Competing interests None.

Patient consent Obtained.

Ethics approval UEFA Football Division and UEFA Medical Committee.

Provenance and peer review Not commissioned; externally peer reviewed.

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What is already known on this topic?

Hamstring injury is the most common injury in profes-sional football.

Most of the hamstring injuries occur to biceps femoris.

What this study adds

MRI can be helpful in verifying the diagnosis of a ham-string injury and also to prognosticate lay-off time.

Radiological grading is associated with lay-off times

after injury. Seventy per cent of hamstring injuries seen in profes-

sional football show no signs of fibre disruption on MRI,

but still cause the majority of absence days.



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doi: 10.1136/bjsports-2011-090155published online December 5, 2011Br J Sports Med

Jan Ekstrand, Jeremiah C Healy, Markus Waldn, et al.return to playfootball: the correlation of MRI findings withHamstring muscle injuries in professional

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