terminology and classification of muscle injuries in sport - the munich consensus statement

8/9/2019 Terminology and Classification of Muscle Injuries in Sport - The Munich Consensus Statement

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Terminology and classication of muscle injuriesin sport: The Munich consensus statement

Hans-Wilhelm Mueller-Wohlfahrt,1 Lutz Haensel,1 Kai Mithoefer,2 Jan Ekstrand,3

Bryan English,4 Steven McNally,5 John Orchard,6,7 C Niek van Dijk,8

Gino M Kerkhoffs,9

Patrick Schamasch,10

Dieter Blottner,11

Leif Swaerd,12

Edwin Goedhart,13 Peter Ueblacker1

Supplementary onlineappendices are publishedonline only. To view these lesplease visit the journal online(http://dx.doi.org/10.1136/bjsports-2012-091448)

For numbered afliations seeend of article

Correspondence toDr Peter Ueblacker, Center ofOrthopedics and SportsMedicine, Munich and FootballClub FC Bayern Munich,Dienerstrasse 12, Munich80331, Germany;[email protected]

Accepted 5 September 2012Published Online First18 October 2012

To cite:Mueller-Wohlfahrt H-W, Haensel L,Mithoefer K,et al.Br J

Sports Med2013;47:342350.

ABSTRACTObjective To provide a clear terminology andclassication of muscle injuries in order to facilitateeffective communication among medical practitionersand development of systematic treatment strategies.Methods Thirty native English-speaking scientists andteam doctors of national and rst division professionalsports teams were asked to complete a questionnaireon muscle injuries to evaluate the currently usedterminology of athletic muscle injury. In addition, a

consensus meeting of international sports medicineexperts was established to develop practical andscientic denitions of muscle injuries as well as a newand comprehensive classication system.Results The response rate of the survey was 63%. Theresponses conrmed the marked variability in the use ofthe terminology relating to muscle injury, with the mostobvious inconsistencies for the termstrain. In theconsensus meeting, practical and systematic terms weredened and established. In addition, a newcomprehensive classication system was developed,which differentiates between four types: functionalmuscle disorders (type 1: overexertion-related and type

2: neuromuscular muscle disorders) describing disorderswithout macroscopic evidence ofbre tear andstructuralmuscle injuries (type 3: partial tears and type 4: (sub)total tears/tendinous avulsions) with macroscopicevidence ofbre tear, that is, structural damage.Subclassications are presented for each type.Conclusions A consistent English terminology as wellas a comprehensive classication system for athleticmuscle injuries which is proven in the daily practice arepresented. This will help to improve clarity ofcommunication for diagnostic and therapeutic purposesand can serve as the basis for future comparative studiesto address the continued lack of systematic informationon muscle injuries in the literature.

What are the new things Consensus denitions ofthe terminology which is used in the eld of muscleinjuries as well as a new comprehensive classicationsystem which clearly denes types of athletic muscleinjuries.Level of evidence Expert opinion, Level V.

INTRODUCTIONMuscle injuries are very common in sports. Theyconstitute 31% of all injuries in elite football(soccer),1 their high prevalence is well documentedin the international literature in both football27

and other sports. Thigh muscle injuries present themost common diagnosis in track and eld athletes

(16%),810 but have also been documented in teamsports like rugby (10.4%),11 basketball (17.7%)12

and American football (46%/22% practice/games).13

The fact that a male elite-level soccer team witha squad of 25 players can expect about 15 muscleinjuries each season with a mean absence time of223 days, 148 missed training sessions and 37missed matches demonstrate their high relevancefor the athletes as well as for the clubs.1 The rele-vance of muscle injuries is even more obvious if

the frequency is compared to anterior cruciateligament-ruptures, which occur in the same squadstatistically only 0.4 times per season.14 Eachseason, 37% of players miss training or competitiondue to muscle injuries1 with an average of 90 daysand 15 matches missed per club per season fromhamstring injuries alone.15 Particularly in elite ath-letes, where decisions regarding return to play andplayer availability have signicant nancial or stra-tegic consequences for the player and the team,there is an enormous interest in optimising thediagnostic, therapeutic and rehabilitation processafter muscle injuries, to minimise the absence from

sport and to reduce recurrence rates.However, little information is available in theinternational literature about muscle injury deni-tions and classication systems. Muscle strain pre-sents one of the most frequently used terms todescribe athletic muscle injury, but this term is stillwithout clear denition and used with highvariability.

Athletic muscle injuries present a heterogeneousgroup of muscle disorders which have traditionallybeen difcult to dene and categorise. Sincemuscles exist in many different sizes and shapeswith a complex functional and anatomical organisa-tion,16 development of a universally applicable ter-

minology and classication is challenging. Musclesthat are frequently involved in injuries are oftenbi-articular17 or are those with a more complexarchitecture (eg, adductor longus), undergo eccen-tric contraction and contain primarily fast-twitchtype 2 muscle bres.18 19

In football/soccer, 92% affect the four majormuscle groups of the lower limbs: hamstrings 37%,adductors 23%, quadriceps 19% and calf muscles13%.1 As much as 96% of all muscle injuries infootball/soccer occur in non-contact situations,1

whereas contusions are more frequently encoun-tered in contact sports, like rugby, American foot-

ball and ice hockey.

11 13

The fact that 16% ofmuscle injuries in elite football/soccer are re-injuries

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and associated with 30% longer absence from competition thanthe original injury1 emphasises the critical importance of correctevaluation, diagnosis and therapy of the index muscle disorder.This concerted effort presents a challenging task in light of theexisting inconsistent terminology and classication of muscleinjuries.

Different classication systems are published in the literature(table 1), but there is little consistency within studies and in

daily practice.20

Previous grading systems based upon clinical signs: One of themore widely used muscle injury grading systems was devised byODonoghue. This system utilises a classication that is based oninjury severity related to the amount of tissue damage and asso-ciated functional loss. It categorises muscle injuries into threegrades, ranging from grade 1 with no appreciable tissue tear,grade 2 with tissue damage and reduced strength of the musculo-tendinous unit and grade 3 with complete tear of musculotendi-nous unit and complete loss of function.21 Ryan published aclassication for quadriceps injuries which has been applied forother muscles. In this classication, grade 1 is a tear of a fewmusclebres with an intact fascia. Grade 2 is a tear of a moderatenumber of bres, with the fascia remaining intact. A grade 3injury is a tear of many bres with a partial tear of the fascia anda grade 4 injury is a complete tear of the muscle and the fascia. 22

Previous grading systems based up imaging: Takebayashiet al23 published in 1995 an ultrasound-based three-grade classi-cation system ranging from a grade 1 injury with less than 5%of the muscle involved, grade 2 presenting a partial tear withmore than 5% of the muscle involved and up to grade 3 with acomplete tear. Peetrons24 has recommended a similar grading.The currently most widely used classication is an MRI-basedgraduation dening four grades: grade 0 with no pathologicalndings, grade 1 with a muscle oedema only but without tissuedamage, grade 2 as partial muscle tear and grade 3 with a com-plete muscle tear.25

The limitations of the previous grading systems are a lack ofsubclassications within the grades or types with the conse-quence that injuries with a different aetiology, treatmentpathway and different prognostic relevance are categorised inone group. Some of the grading systems, like the Takebayashiclassication are relative and not consistently measurable. So far,no terminology or grading system (sub)classied disorderswithout macroscopic evidence of structural damage, eventhough a muscle injury study of the Union of European Football

Associations (UEFA) has emphasised their high clinical relevancein professional athletes.26

The objective of our work is to present a more precise den-ition of the English muscle injury terminology to facilitate diag-nostic, therapeutic and scientic communication. In addition, acomprehensive and practical classication system is designed tobetter reect the differentiated spectrum of muscle injuries seenin athletes.

METHODSTo evaluate the extent of the inconsistency and insufciency ofthe existing terminology of muscle injuries in the English litera-ture a questionnaire was sent to 30 native English-speakingsports medicine experts. The recipients of the questionnaireswere invited based on their international scientic reputationand extensive expertise as team doctors of the national or rstdivision sports teams from the Great Britain, Australia the USA,the FIFA, UEFA and International Olympic Committee. Theincluded experts were responsible for covering a variety of dif-ferent sports with high muscle injury rates including football/soccer, rugby, Australian football and cricket. Qualication cri-teria also included long-term experience with sports team cover-age which limited the number of available experts since teamphysicians often tend to change after short periods.

The questionnaire (see online supplementary appendix 1) wasdivided into three categories: rst, the experts were asked toindividually and subjectively describe their denitions of severalcommon terms of muscle injuries and to indicate if the term is a

functional (non-structural) or a structural disorder/injury. In thesecond category, they were asked to associate synonym terms ofmuscle injuries such as strain and tear. In the nal category, theexperts were asked to list given number of muscle injury termsin the order their increasing injury severity.

Following the completion of the survey, the principal authors(H-WM-W, LH and PU) organised a consensus meeting of 15international experts on the basic science of muscle injury as

well as sports medicine specialists involved in the daily care ofpremier professional sports and national teams. The meetingwas endorsed by the International Olympic Committee (IOC)and the UEFA.

A nominal group consensus model approach in which astructured meeting attempts to provide an orderly procedure forobtaining qualitative information from target groups who aremost closely associated with a problem area27 was adopted forcreating a consensus statement on terminology and classicationof muscle disorders and injuries. This model was successfullyapplied before in other consensus statements.28

Table 1 Overview of previous muscle injury classification systems

ODonoghue 1962Ryan 1969 (initially forquadriceps)

Takebayashi 1995, Peetrons 2002(Ultrasound-based) Stoller 2007 (MRI-based)

Grade I No appreciable tissue tearing, no lossof function or strength, only alow-grade inflammatory response

Tear of a few musclefibres, fascia remainingintact

No abnormalities or diffuse bleedingwith/without focal fibre rupture less than5% of the muscle involved

MRI-negative=0% structural damage.Hyperintense oedema with or withouthemorrhage

Grade II Tissue damage, strength of themusculotendinous unit reduced, someresidual function

Tear of a moderatenumber of fibres, fasciaremaining intact

Partial rupture: focal fibre rupture morethan 5% of the muscle involved with/without fascial injury

MRI-positive with tearing up to 50% of themuscle fibres. Possible hyperintense focaldefect and partial retraction of muscle fibres

Grade III Complete tear of musculotendinousunit, complete loss of function

Tear of many fibres withpartial tearing of thefascia

Complete muscle rupture with retraction,fascial injury

Muscle rupture=100% structural damage.Complete tearing with or without muscleretraction

Grade IV X Complete tear of themuscle and fascia of the

muscle

tendon unit

X X

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During the 1-day meeting, the authors performed a detailedreview of the structural and functional anatomy and physiologyof muscle tissue, injury epidemiology and currently existing clas-sication systems of athletic muscle injuries. In addition, theresults of the muscle terminology survey were presented and dis-cussed. Based on the results of the survey muscle injury termin-ology was discussed and dened until a unanimous consensus ofgroup was reached. A new classication system empirically

based on the current knowledge about muscle injuries was dis-cussed, compared with existing classications, reclassied andapproved. After the consensus meeting, iterative draft consensusstatements on the denitions and the classication system wereprepared and circulated to the members. The nal statementwas approved by all coauthors of the consensus paper.

RESULTSMuscle injury surveyNineteen of the 30 questionnaires were returned for evaluation(63%). (Eleven experts did not respond even after repeatedreminders.) Even though, this is a limited number, the responsesdemonstrated a marked variability in the denitions forhyperto-

nus, muscle hardening,muscle strain,muscle tear,bundle/fascicletearandlaceration, with the most obvious inconsistencies for theterm muscle strain (see online supplementary appendix 2).Relatively consistent responses were obtained for pulled muscle(Laymans term) andlaceration.

Marked heterogeneity was also encountered regardingstructuralversus functional (non-structural) muscle injuries. Sixteen percentof expert responders considered strain a functional muscle injury,whereas 0 percent considered teara functional injury (see onlinesupplementary appendix 3). Sixteen percent were undecided toboth terms, 68 percent considered strain and 84 percent tear a

structuralinjury (see online supplementary appendix 3).This conrms that even among sports experts considerable

inconsistency exists in the use of muscle injury terminology and

that there is no clear denition, differentiation and use of func-tional andstructuralmuscle disorders. The results emphasised theneed for a more uniform terminology and classication that reectsboth, thefunctionalandstructuralaspects of muscle injury.

The following consensus statement on terminology and classi-cation of athletic muscle injuries is perhaps best referred to asa position statement based upon wide-ranging experience,observation and opinion made by experts with diverse clinicaland academic backgrounds and expertise on these injuries.

Denitionsrecommended terminologyFunctional muscle disorder

Acute indirect muscle disorder without macroscopic evidence

(in MRI or ultrasound (for limitations see Discussion)) of muscu-lar tear.

Often associated with circumscribed increase of muscle tone(muscle rmness) in varying dimensions and predisposing totears. Based on the aetiology several subcategories of functionalmuscle disorders exist.

Structural muscle injuryAny acute indirect muscle injury with macroscopic evidence(in MRI or ultrasound (for limitations see Discussion)) of

muscle tear.Further denitions reached in the consensus conference are

presented in table 3 together with the classication system.

Denitionsterminology without specic recommendationMuscle injury terms with highly inconsistent answers in thesurvey werestrain,pulled-muscle,hardeningand hypertonus.

Strain is a biomechanical term which is not dened and usedindiscriminately for anatomically and functionally differentmuscle injuries. Thus, the use of this term cannot be recom-mended anymore.

Pulled-muscle is a lay-term for different, not dened types orgrades of muscle injuries and cannot be recommended as a sci-

entic term.Hardening and hypertonus are also not well dened and

should not be used as scientic terminology.

Classication systemThe structure of the comprehensive classication system for ath-letic muscle injuries, which was developed during the consensusmeeting, is demonstrated in table 2.

A clear denition of each type of muscle injury, a differenti-ation according to symptoms, clinical signs, location andimaging is presented in table 3.

DISCUSSION

The main goal of this article is to present a standardised termin-ology as well as a comprehensive classication for athleticmuscle injuries which presents an important step towardsimproved communication and comparability. Moreover, this willfacilitate the development of novel therapies, systematic studyand publication on muscle disorders.

As stated by Jarvinen et al17 current treatment principles forskeletal muscle injury lack a rm scientic basis. The rst treat-ment step is establishment of a precise diagnosis which is crucialfor a reliable prognosis. However, since injury denitions arenot standardised and guidelines are missing, proper assessmentof muscle injury and communication between practitioners areoften difcult to achieve. Resultant miscommunication willaffect progression through rehabilitation and return to play and

can be expected to affect recurrence and complication rate.Studies in Australian Football League players have shown a high

Table 2 Classification of acute muscle disorders and injuries

A. Indirect muscle disorder/injury Functional muscle disorder Type 1: Overexertion-related muscle disorder Type 1A: Fatigue-induced muscle disorderType 1B: Delayed-onset muscle soreness (DOMS)

Type 2: Neuromuscular muscle disorder Type 2A: Spine-related neuromuscular Muscle disorderType 2B: Muscle-related neuromuscular Muscle disorder

Structural muscle injury Type 3: Part ia l muscle tear Type 3A: Minor part ia l muscle tearType 3B: Moderate partial muscle tear

Type 4: (Sub) to tal tear Sub total or co mp lete mu scl e tearTendinous avulsion

B. Direct muscle injury Contusion

Laceration


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recurrence rate of muscle injuries of 30.6%.29 Other studiesdemonstrated recurrence rates of 23% in rugby30 and 16% infootball/soccer.1 One plausible cause for recurrent muscleinjures, which are signicantly more severe than the rstinjury1 30 is the premature return to full activity due to anunderestimated injury. Healing of muscle and other soft tissue is

a gradual process. The connective (immature) tissue scar pro-duced at the injury site is the weakest point of the injured

skeletal muscle,17 with full strength of the injured tissue takingtime to return depending on the size and localisation of theinjury. (Note: mature scar is stiff or even stronger than healthymuscle.) It appears plausible, that athletes may be returning tosport before muscle healing is complete. As Malliaropouloset al10 stated it is therefore crucial to establish valid criteria to

recognise severity and avoid premature return to full activityand the risk of reinjury.

Table 3 Comprehensive muscle injury classification: type-specific definitions and clinical presentations

Type Classification Definition Symptoms Clinical signs Location Ultrasound/MRI

1A Fatigue-inducedmuscle disorder

Circumscribed longitudinalincrease of muscle tone(muscle firmness) due tooverexertion, change ofplaying surface or change intraining patterns

Aching muscle firmness.Increasing with continuedactivity. Can provoke painat rest. During or afteractivity

Dull, diffuse, tolerable pain ininvolved muscles,circumscribed increase oftone. Athlete reports ofmuscle tightness

Focalinvolvement upto entire lengthof muscle

Negative

1B Delayed-onsetmuscle soreness(DOMS)

More generalised musclepain followingunaccustomed, eccentricdeceleration movements.

Acute inflammative pain.Pain at rest. Hours afteractivity

Oedematous swelling, stiffmuscles. Limited range ofmotion of adjacent joints.Pain on isometric contraction.Therapeutic stretching leadsto relief

Mostly entiremuscle ormuscle group

Negative or oedema only

2A Spine-relatedneuromuscularmuscle disorder

Circumscribed longitudinalincrease of muscle tone(muscle firmness) due tofunctional or structuralspinal/lumbopelvicaldisorder.

Aching muscle firmness.Increasing with continuedactivity. No pain at rest

Circumscribed longitudinalincrease of muscle tone.Discrete oedema betweenmuscle and fascia.Occasional skin sensitivity,defensive reaction on musclestretching. Pressure pain

Muscle bundleor larger musclegroup alongentire length ofmuscle


2B Muscle-relatedneuromuscular

muscle disorder

Circumscribed(spindle-shaped) area of

increased muscle tone(muscle firmness). Mayresult from dysfunctionalneuromuscular control suchas reciprocal inhibition

Aching, graduallyincreasing muscle

firmness and tension.Cramp-like pain

Circumscribed(spindle-shaped) area of

increased muscle tone,oedematous swelling.Therapeutic stretching leadsto relief. Pressure pain

Mostly along theentire length of

the muscle belly


3A Minor partialmuscle tear

Tear with a maximumdiameter of less than musclefascicle/bundle.

Sharp, needle-like orstabbing pain at time ofinjury. Athlete oftenexperiences a snapfollowed by a suddenonset of localised pain

Well-defined localised pain.Probably palpable defect infibre structure within a firmmuscle band. Stretch-inducedpain aggravation

Primarilymuscletendonjunction

Positive for fibredisruption on highresolution MRI*.Intramuscularhaematoma

3B Moderate partialmuscle tear

Tear with a diameter ofgreater than a fascicle/bundle

Stabbing, sharp pain,often noticeable tearingat time of injury. Athleteoften experiences asnapfollowed by a

sudden onset of localisedpain. Possible fall ofathlete

Well-defined localised pain.Palpable defect in musclestructure, often haematoma,fascial injury Stretch-inducedpain aggravation

Primarilymuscletendonjunction

Positive for significantfibre disruption, probablyincluding someretraction. With fascialinjury and intermuscular

haematoma

4 (Sub)total muscletear/tendinousavulsion

Tear involving the subtotal/complete muscle diameter/tendinous injury involvingthe bonetendon junction

Dull pain at time ofinjury. Noticeable tearing.Athlete experiences asnapfollowed by asudden onset of localisedpain. Often fall

Large defect in muscle,haematoma, palpable gap,haematoma, muscleretraction, pain withmovement, loss of function,haematoma

Primarilymuscletendonjunction orBonetendonjunction

Subtotal/completediscontinuity of muscle/tendon. Possible wavytendon morphology andretraction. With fascialinjury and intermuscularhaematoma

Contusion Direct injury Direct muscle trauma,caused by blunt externalforce. Leading to diffuse orcircumscribed haematomawithin the muscle causingpain and loss of motion

Dull pain at time ofinjury, possibly increasingdue to increasinghaematoma. Athleteoften reports definiteexternal mechanism

Dull, diffuse pain,haematoma, pain onmovement, swelling,decreased range of motion,tenderness to palpationdepending on the severity ofimpact. Athlete may be ableto continue sport activityrather than in indirectstructural injury

Any muscle,mostly vastusintermedius andrectus femoris

Diffuse or circumscribedhaematoma in varyingdimensions

*Recommendations for (high-resolution) MRI: high field strength (minimum 1.5 or 3 T), high spatial resolution (use of surface coils), limited field of view (according to clinicalexamination/ultrasound), use of skin marker at centre of injury location and multiplanar slice orientation.


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The presented muscle injury classication is based on anextensive, long-term experience and has been used successfullyin the daily management of athletic muscle injuries. The classi-cation is empirically based and includes some new aspects ofathletic muscle injuries that have not yet been described in theliterature, specically the highly relevant functional muscleinjuries. An advanced muscle injury classication that distin-guishes these injuries as separate clinical entities has great rele-

vance for the successful management of the athlete with muscleinjury and represents the basis for future comparative studiessince scientic data are limited for muscle injury in general.

Diagnosis of muscle injuriesIn accordance with Askling et al31 32 and Jarvinen et al,17 werecommend to start with a precise history of the occurrence, thecircumstances, the symptoms, previous problems, followed by acareful clinical examination with inspection, palpation of theinjured area, comparison to the other side and testing of thefunction of the muscles. Palpation serves to detect (more super-cial and larger) tears, perimuscular oedema and increasedmuscle tone. An early postinjury ultrasound between 2 and 48 hafter the muscle trauma24 provides helpful information aboutany existing disturbance of the muscle structure, particularly ifthere is any haematoma or if clinical examination pointstowards a functional disorder without evidence of structuraldamage. We recommend an MRI for every injury which is suspi-cious forstructural muscle injury. MRI is helpful in determiningwhether oedema is present, in what pattern, and if there is astructural lesion including its approximate size. Furthermore,MRI is helpful in conrming the site of injury and any tendoninvolvement.31 However, it must be pointed out, that MRIalone is not sensitive enough to measure the extent of muscletissue damage accurately. For example, it is not possible to judgefrom the scans where oedema/haemorrhage (seen as high signal)is obscuring muscle tissue that has not been structurally

damaged.Our approach is to include the combination of the currently

best available diagnostic tools to address the current decit ofclinical and scientic information and lack of sensitivity and spe-cicity of the existing diagnostic modalities. Careful combinationof diagnostic modalities including medical history, inspection,clinical examination and imaging will most likely lead to anaccurate diagnosis, which should be denitely mainly based onclinical ndings and medical history not on imaging alone, sincethe technology and sensitivity to detect structural muscle injurycontinues to evolve. For example, the history of a sharp acuteonset of pain, experience of a snap and a well-dened localisedpain with a positive MRI for oedema but indecisive for bre tearstrongly suggest a minor partial muscle tear, below the detectionsensitivity of the MRI. Oedema, or better the increased uidsignal on MRI, would be observed with a localised haematomaand would be consistent with the working diagnosis in this case.The diagnosis of a small tear (structural defect) that is below theMRI detection limit is important in our eyes, since even a smalltear is relevant because it can further disrupt longitudinally, forexample, when the athlete sprints.

Ekstrand et al26 described a signicantly and clinically rele-vant shorter return to sports in MRI negative cases (withoutoedema) compared to MRI grade 1 injuries (with oedema, butwithout bre tearing). Similar ndings are published also byothers.33 However, muscle oedema is a very complex issue andin our opinion too little is known so far. Therefore, we decided

to mention in the classication system that several functionaldisorders present with or without oedema (table 3). This is in

our eyes the best way to handle the currently insufcient data.We think that discussion of the phenomenon of oedema at thispoint is premature but will be a focus of high level studies in thefuture, with more precise imaging and with studies which arebased on a common terminology and classication.

TerminologyAn aspect that may contribute to a high rate of inaccurate diag-

nosis and recurrent injury is that terminology of muscle injuriesis not yet been clearly dened and a high degree of variabilitycontinues to exist between terms frequently used to describemuscle injury. Since it has been documented that variationsin denitions create signicant differences in study results andconclusions,3438 it is critically important to develop astandardisation.

Strain and tearHagglund et al34 dened muscle strain as acute distractioninjury of muscles and tendons. However, this denition israrely used in the literature and in the day-to-day managementof athletic muscle injuries. Our survey demonstrates that theterm strain is used with a high degree of variability betweenpractitioners. Strain is a biomechanical term; thus, we do notrecommend the use of this term. Instead, we propose to use theterm tearfor structural injuries of muscle bres/bundles leadingto loss of continuity and contractile properties. Tear betterreects structural characteristics as opposed to a mechanism ofinjury.

Functional muscle disordersAccording to Fuller et al28 a sports injury is dened as anyphysical complaint sustained by an athlete that results from amatch/competition or training, irrespective of the need formedical attention or time loss from sportive activities. Thatmeans also irrespective of a structural damage. By this den-

ition, functional muscle disorders, irrespective of any structuralmuscle damage, present injuries as well. However, the term dis-order may better differentiate functional disorders from struc-tural injuries. Thus, the term functional muscle disorder wasspecically chosen by the consensus conference.

Functional muscle disorders present a distinct clinical entitysince they result in a functional limitation for the athlete, forexample, painful increase of the muscle tone which can repre-sent a risk factor for structural injury. However, they are notreadily diagnosed with standard diagnostic methods such asMRI since they are without macroscopic evidence of structuraldamage, dened as absence ofbre tear on MRI. They are indir-ect injuries, that is, not caused by external force. A recent UEFAmuscle injury study has demonstrated their relevance in foot-ball/soccer.26 This study included data from a 4-year observationperiod of MRI obtained within 2448 h after injury and demon-strated that the majority of injuries (70%) were without signs ofbre tear. However, these injuries caused more than 50% of theabsence of players in the clubs.26 These ndings are consistentwith the clinical and practical observations of the experiencedmembers of the consensus panel.

Functional muscle disorders are multifactorial and can begrouped into subgroups reecting their clinical origin includingoverexertional or neuromuscular muscle disorders. This isimportant since the origin of muscle disorder inuences theirtreatment pathway. A spine-related muscle disorder associatedwith a spine problem (eg, spondylolysis), will better respond to

treatment by addressing not only the muscle disorder but alsothe back disorder (ie, including core-performance, injections).


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One could argue, that this presents mainly a back problem, witha secondary muscle disorder. But, this secondary muscular dis-order prevents the athlete from sports participation and willrequire comprehensive treatment that includes the primaryproblem as well in order to facilitate return to sport. Therefore,a broader denition and classication system is suggested by theconsensus panel at this point which is important not onlybecause of the different pathogenesis, but more importantly

because of different therapeutic implications.

Comprehensive classication systemFatigue-induced muscle disorder and delayed onset musclesorenessMuscle fatigue has been shown to predispose to injury. 39 Onestudy has demonstrated that in the hind leg of the rabbit fati-gued muscles absorb less energy in the early stages of stretchwhen compared with non-fatigued muscle.40 Fatigued musclealso demonstrates increased stiffness, which has been shown topredispose to subsequent injury (Wilson AJ and Myers PT,unpublished data, 2005). The importance of warm up prior toactivity and of maintaining exibility was emphasised since adecrease in muscle stiffness is seen with warming up.40 A studyby Witvrouwet al41 found that athletes with an increased tight-ness of the hamstring or quadriceps muscles have a statisticallyhigher risk for a subsequent musculoskeletal lesion.

Delayed onset muscle soreness (DOMS) has to be differen-tiated from fatigue-induced muscle injury.42 DOMS occursseveral hours after unaccustomed deceleration movements whilethe muscle is stretched by external forces (eccentric contrac-tions), whereas fatigue-induced muscle disorder can also occurduring athletic activity. DOMS causes its characteristic acuteinammatory pain (due to local release of inammatory media-tors and secondary biochemical cascade activation) with stiffand weak muscles and pain at rest and resolves spontaneouslyusually within a week. In contrast, fatigue-induced muscle dis-

order leads to aching, circumscribed rmness, dull ache to stab-bing pain and increases with continued activity. It canifunrecognised and untreatedpersist over a longer time andmay cause structural injuries such as partial tears. However, inaccordance with Opar et al39 it has to be stated, that it remainsan area for future research to denitely describe this muscle dis-order and other risk factors for muscle injuries.

Spine-related and muscle-related neuromuscular muscle disordersTwo different types of neuromuscular disorders can be differen-tiated: a spinal or spinal nerve-related (central) and a neuromus-cular endplate-related (peripheral) type. Since muscles act as atarget organ their state of tension is modulated by electricalinformation from the motor component of the correspondingspinal nerve. Thus, an irritation of a spinal nerve root can causean increase of the muscle tone. It is known that back injuries arevery common in elite athletes, particularly at the L4/5 and theL5/S1 level43 and lumbar pathology such as disc prolapse at theL5/S1 level may present with hamstring and/or calf pain andlimitations in exibility, which may result in or mimic a muscleinjury.44 Orchard states that theoretically any pathology relatingto the lumbar spine, the lumbosacral nerve roots or plexus, orthe sciatic nerve could result in hamstring or calf pain.44 Thiscould be transient and range from fully reversible functional dis-turbances to permanent structural changes, which may be con-genital or acquired. Several other studies have supported thisconcept of a back related (or more specically lumbar spine

related) hamstring injury15 33 45

although this is a controversialparadigm to researchers.44 However, this multifactorial type of

injury would logically require variable forms of treatmentbeyond simply treatment of the muscletendon injuries.46 Thus,it is important that assessment of hamstring injury shouldinclude a thorough biomechanical evaluation, especially that ofthe lumbar spine, pelvis and sacrum.15 Lumbar manifestationsare not present in all cases; however, negative structural ndingson the lumbar spine do not exclude nerve root irritation.

Functional lumbar disturbances, like lumbar or iliosacral block-

ing can also cause spine-related muscle disorders.47

The diagno-sis is then established through precise clinical-functionalexamination. The spine-related muscle disorder is usuallyMRI-negative or shows muscle oedema only.44 Many cliniciansalso believe that athletes with lumbar spine pathology have agreater predisposition to hamstring tears,33 44 although this hasnot been prospectively proven. Verrall et al33 showed that foot-ballers with a history of lumbar spine injury had a higher rate ofMRI-negative posterior thigh injury, but not of actual structuralhamstring injury.

We differentiate muscle-related neuromuscular disorders fromthe spine-related ones because of different treatment pathways.Muscle tone is mainly under the control of the gamma loop andactivation of the -motor neurons remains mainly under thecontrol of motor descending pathways. Sensory informationfrom the muscle is carried by ascending pathways to the brain.Ia afferent signals enter the spinal cord on the -motor neuronsof the associated muscle, but branches also stimulate interneur-ons in the spinal cord which act via inhibitory synapses on thealpha motor neurons of antagonistic muscles. Thereby simultan-eous inhibition of the alpha motor neurons to antagonisticmuscles (reciprocal inhibition) occurs to support muscle contrac-tion of agonistic muscle.48 Dysfunction of these neuromuscularcontrol mechanisms can result in signicant impairment ofnormal muscle tone and can cause neuromuscular muscle disor-ders, when inhibition of antagonistic muscles is disturbed andagonistic muscles overcontract to compensate this.48 Increasing

fatigue with a decline in muscle force will increase the activityof the alpha motor neurons of the agonists through Ib disinhib-ition. The rising activity of the alpha motor neurons can lead toan overcontraction of the individual motor units in the targetmuscle resulting in a painful muscle rmness which can preventan athlete from sportive activities.48

For anatomic illustration of the location and extent of func-tional muscle disorders see gure 1.

Structural injuriesThe most relevant structural athletic muscle injuries, that is,injuries with macroscopic evidence of muscle damage, areindirect injuries, that is, stretch-induced injuries caused by asudden forced lengthening over the viscoelastic limits of musclesoccurring during a powerful contraction (internal force). Theseinjuries are usually located at the muscletendon junction,17 40 49

since these areas present biomechanical weak points. The quad-riceps muscle and the hamstrings are frequently affected sincethey have large intramuscular or central tendons and can getinjured along this interface.50 51 Theoretically, a tear can occuranywhere along the muscletendonbonechain either acutelyor chronically.

Exact knowledge of the muscular macro- and microanatomyis important to understand and correctly dene and classifyindirect structural injuries. The individual muscle bre presentsa microscopic structure with an average diameter of 60 m.52

Thus, an isolated tear of a single muscle bre remains usually

without clinical relevance. Muscle bres are anatomically orga-nised into primary and secondary muscle fascicles/bundles.


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Secondary muscle bundles (eshbres) with a diameter of 25 mm (this diameter can vary according to the training statusaccording to hypertrophy) are visible to the human eye.52

Secondary muscle bundles present structures that can be pal-pated by the experienced examiner, when they are torn.Multiple secondary bundles constitute the muscle (gure 2).

Partial muscle tearsMostindirect structural injuries are partial muscle tears. Clinicalexperience clearly shows that most partial injuries can beassigned to one of two types, either a minor or a moderatepartial muscle tear, which ultimately has consequences fortherapy, respectively for absence time from sports. Thus, indirect

structural injuries should be subclassied. Since previous gradu-ation systems23 24 refer to the complete muscle size, they arerelative and not consistently measurable. In addition to this,there is no differentiation of grade 3 injuries with the conse-quence that many structural injuries with different prognosticconsequences are subsumed as grade 3.

We recommend a classication ofstructural injuries based onanatomical ndings. Taking into account the aforementionedanatomical factors and as a reection of our daily clinical workwith muscle injuries, we differentiate between minor partial tears

with a maximum diameter of less and moderate partial tears witha diameter of greater than a muscle fascicle/bundle (seegure 2).

In addition to the size, it is the participation of the adjacentconnective tissue, the endomysium, the perimysium, the epimy-sium and the fascia that distinguish a minor from a moderatepartial muscle tear. Concomitant injury of the external peri-mysium seems to play a special role: This connective tissuestructure has a somehow intramuscular barrier function in caseof bleeding. It may be the injury to this structure (with optionalinvolvement of the muscle fascia) that differentiates a moderatefrom a minor partial muscle tear.

Drawing a clear differentiation between partial muscle tearsseems difcult because of the heterogeneity of the muscles that

can be structured very differently. Technical capabilities today(MRI and ultrasound) are not precise enough to ultimatelydetermine and prove the effective muscular defect within theinjury zone of haematoma and/or liquid seen in MRI which issomewhat oversensitive at times17 and usually leads to overesti-mation of the actual damage. It will remain the challenge offuture studies to exactly rule out the size which describes thecut-off between a minor and a moderate partial muscle tear.

The great majority of muscle injuries heal without formationof scar tissue. However, greater muscle tears can result in adefective healing with scar formation17 which has to be consid-ered in the diagnosis and prognosis of a muscle injury. Ourexperience is that partial tears of less than a muscle fascicle

usually heal completely while moderate partial tears can resultin a brous scar.

Figure 1 Anatomic illustration of the location and extent offunctionaland structural muscle injuries(eg, hamstrings). (A) Overexertion-relatedmuscle disorders, (B) Neuromuscular muscle disorders, (C) Partial and (sub)total muscle tears (from Thieme Publishers, Stuttgart; planned to be

published. Reproduced with permission.). This gure is only reproduced in colour in the online version.


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(Sub)total muscle tears and tendinous avulsionsComplete muscle tears, with a discontinuity of the wholemuscle are very rare. Subtotal muscle tears and tendinous avul-sions are more frequent. Clinical experience shows that injuriesinvolving more than 50% of the muscle diameter (subtotaltears) usually have a similar healing time compared with com-plete tears.

Tendinous avulsions are included in the classication systemsince they mean biomechanically a total tear of the origin or

insertion of the muscle. The most frequently involved locationsare the proximal rectus femoris, the proximal hamstrings, theproximal adductor longus and the distal semitendinosus.

Intratendinous lesions of the free or intramuscular tendonalso occur. Pure intratendinous lesions are rare. The most fre-quent type is a tear near the muscletendon junction (eg, of theintramuscular tendon of the rectus femoris muscle). Tendinousinjuries are either consistent with the partial (type 3) or (sub)total (type 4) tear in our classication system and can beincluded in that aspect of the classication.

For anatomic illustration of the location and extent ofstruc-turalmuscle injuries see gure 1.

Muscle contusionsIn contrast toindirectinjuries (caused by internal forces), lacera-tions or contusions are caused by external forces,5 3 5 4 like adirect blow from an opponents knee. Thus, muscle contusionsare classied as acute direct muscle injuries (tables 2 and 3).Contusion injuries are common in athletes and present acomplex injury that includes dened blunt trauma of the muscu-lar tissue and associated haematoma.5 3 5 4 The severity of theinjury depends on the contact force, the contraction state of theaffected muscle at the moment of injury and other factors.Contusions can be graded into mild, moderate and severe.55

The most frequently injured muscles are the exposed rectusfemoris and the intermediate vastus, lying next to the bone,with limited space for movement when exposed to a direct

blunt blow. Contusion injury can lead to either diffuse or cir-cumscribed bleeding that displaces or compresses muscle bres

causing pain and loss of motion. It happens that muscle bresare torn off by the impact, but typically muscle bres are nottorn by longitudinal distraction. Therefore, contusions are notnecessarily accompanied by a structural damage of muscletissue. For this reason athletes, even with more severe contu-sions, can often continue playing for a long time, whereas evena smallerindirect structural injury forces the player often to stopat once. However, contusions can also lead to severe complica-tions like acute compartment syndrome, active bleeding or large

haematomas.

CONCLUSIONThis consensus statement aims to standardise the denitions andterms of muscle disorders and injuries and proposes a practicaland comprehensive classication. Functional muscle disordersare differentiated from structural injuries. The use of the term

strainif used undifferentiatedis no longer recommended,since it is a biomechanical term, not well dened and used indis-criminately for anatomically and functionally different muscleinjuries. Instead of this, we propose to use the term tear for

structural injuries, graded into (minor and moderate) partial and(sub)total tears, used only for muscle injuries with macroscopicevidence of muscle damage (structural injuries). While this clas-

sication is most applicable to lower limb muscle injuries, it canbe translated also to the upper limb.

Scientic data supporting the presented classication system,which is based on clinical experience, are still missing. We hopethat our work will stimulate researchbased on the suggested ter-minology and classicationto prospectively evaluate the prog-nostic and therapeutic implications of the new classication and tospecify each subclassication. It also remains denitely the chal-lenge of future studies to exactly rule out the size which describesthe cut-off between a minor and a moderate partial muscle tear.

Author afliations1MW Center of Orthopedics and Sports Medicine, Munich and Football Club FCBayern Munich, Munich, Germany2Harvard Vanguard Medical Associates, Harvard Medical School, US SoccerFederation, Boston, Massachusetts, USA

Figure 2 Anatomic illustration of theextent of a minor and moderate partialmuscle tear in relation to theanatomical structures. Please note,that this is a graphical illustration,there are variations in extent. (FromThieme Publishers, Stuttgart; plannedto be published. Reproduced with

permission.). This

gure is onlyreproduced in colour in the onlineversion.


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3UEFA Injury Study Group, Medical Committee UEFA, University of Linkping,Linkping, Sweden4Football Club Chelsea, London, UK5Football Club Manchester United, Manchester, UK6School of Public Health, University of Sydney, Sydney, Australia7Australian Cricket team and Sydney Roosters Rugby League team, School of PublicHealth, University of Sydney, Australia8Orthopedic Department Academic Medical Centre, Amsterdam, The Netherlands9Department of Orthopedic Surgery and Orthopedic Research Center, AcademicMedical Center, Amsterdam, The Netherlands10International Olympic Committee, Lausanne, Switzerland11Department of Vegetative Anatomy, Charit University of Berlin, Berlin, Germany12University of Gothenborg and National Football Team Sweden, Gothenburg,Sweden13Football Club Ajax Amsterdam, Amsterdam, The Netherlands

Contributors H-WM-W: member of Conference, senior author ofnal statement,responsible for the overall content; LH: member of Conference, senior co-author ofnal statement; KM: member of Conference, co-author ofnal statement; JE:member of Conference, co-author ofnal statement; BE: member of Conference,co-author ofnal statement; SM: member of Conference, co-author ofnalstatement; JO: member of Conference, co-author ofnal statement; NvD: member ofConference, co-author ofnal statement; GMK: member of Conference, co-author ofnal statement; PS: member of Conference, co-author ofnal statement; DB:member of Conference, co-author ofnal statement; LS: member of Conference,co-author ofnal statement; EG: member of Conference, co-author ofnal

statement; PU: member of Conference, executive and corresponding author,responsible for the overall content.

Funding The Consensus Conference was supported by grants from FC BayernMunich, Adidas and Audi.

Competing interests None.

Provenance and peer review Not commissioned; externally peer reviewed.

Open Access This is an Open Access article distributed in accordance with theCreative Commons Attribution Non Commercial (CC BY-NC 3.0) license, whichpermits others to distribute, remix, adapt, build upon this work non-commercially,and license their derivative works on different terms, provided the original work isproperly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/3.0/

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doi: 10.1136/bjsports-2012-09144818, 2012

2013 47: 342-350 originally published online OctoberBr J Sports Med

Hans-Wilhelm Mueller-Wohlfahrt, Lutz Haensel, Kai Mithoefer, et al.statementinjuries in sport: The Munich consensusTerminology and classification of muscle

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terminology and classification of muscle injuries in sport - the munich consensus statement

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