This document discusses developing a new classification system for muscle injuries. It aims to describe and grade injuries based on several factors: mechanism of injury, clinical prognosis factors, injury location and relation to muscle-tendon junctions (MTJs), imaging description of injury, amount of connective tissue damage, and time of evolution. A coding system is proposed using letters to indicate these different factors, such as mechanism (M), location (L), grade (G) based on percentage of cross-sectional area affected, and whether it is a re-injury (R). The system seeks to classify injuries of similar severity and prognosis but requires further validation through larger studies and collaboration.

1. MLG-R
A Muscle Injuries Classification Purpose
Aspetar and FCB

2. Introduction
•Several grading and classification systems for muscle injuries, for specific muscles, or a specific group of muscles, have been published.

4. Pollock et al, Br J Sports Med-2014

5. Introduction
•The severity of an injury can be determined by
•direct measures (histological assessment),
•or indirectly (imaging, blood test, etc.)..
•..as histological assessment is not possible, injury severity was initially assessed through the symptoms and signs related to the injury; posteriorly with the imaging technics, but forgetting the clinic, injury mechanism, etc. Indeed, no validated classification system exists (Hamilton B).

6. The Purpose
•Our purpose will be based on:
•Mechanism,
•Clinic and imaging prognosis factors,
•Injury imaging description and relation with MTJ,
•Amount of connective tissue damage (indeed of function),
•and evolution in time.
•Through all this data combination, it should be possible:
•To describe muscle injuries.
•….and to classify/grade muscle injuries in groups with similar functional impairment and prognosis?.......

7. The Purpose
•A muscle injury classification purpose should describes and grade the injury; to achieve this, our purpose will be based on:
•Mechanism,
•Clinic and prognosis factors,
•Injury relation with MTJ,
•injury imaging description,
•Amount of connective tissue damage (indeed of function),
•and evolution in time.
•Through all this data combination, it should be possible:
•To describe muscle injuries.
•….and to classify/grade muscle injuries in groups with similar functional impairment and prognosis?........It is still to be seen.

8. Material and Methods
•The authors are experienced sport physicians from Aspetar and FC Barcelona (FCB) medical department, working daily with elite athletes, and with a special interest in muscle injuries. Three consensus meetings were scheduled from September 2102 to July 2013.
•After the last meeting, drafts of the document’s structure, and from the final document, based on the consensus recorded during the meeting were send to authors, this documents circulated to all members for comments. Again, all modifications were send to authors to achieve and agreement, this process was repeated until a total agreement was achieved. This final document has been approved by all authors.
•External experts in imaging give support in this field.

9. Types of Muscle Injury
•Direct injuries are located in the place of the trauma:
•Size is not well correlated with the functional impairment and clinical signs (69);
•They evolve clinically different than indirect injuries, needing less time to recover (107).
•Indirect muscle injuries are located close to a myotendinous junction (MTJ) (5, 26, 40, 41, 54, 61, 62), including the proximal and distal MTJ, or around an intramuscular tendon (2, 26, 39, 50, 74, 101).

10. Connective Tissue Organization
•The extracellular matrix (ECM) is classically formed by three layers (endo-, peri-, and epimysium), but ECM structure and function is under review.

11. Connective Tissue Organization
•ECM is a more complex and interconnected structure (52, 87, 103)…
•“muscle fibres are embedded within a matrix of ECM that forms discrete layers that are mechanically interconnected”(43).
Structure and function of the skeletal muscle extracellular matrix Gillies 2011

12. Connective Tissue Organization
•In this model, force generated by actin-myosin interaction will be transmitted to the ECM and subsequently to the net of connective tissue(43).
•This connective tissue net structure and its role in force generation and transmission, is in our opinion, a key factor in muscle injuries signs, symptoms and prognosis (60).
Structure and function of the skeletal muscle extracellular matrix Gillies 2011

14. Prognostic Factors

15. Based on Clinical Evaluation
•With regard to hamstrings indirect muscular injuries, the mechanism of injury is supposed to be related on:
•the injury location; stretching type more often affect the semimembranosus in its proximal part, muscle or tendon (5, 7);
•and a more cranially palpated injury was related with a longer rehabilitations period (5),
•but conflicting evidence has been published, and this has not been confirmed in other studies (32, 101).
•The time needed to walk pain-free after a hamstring injury, if longer than 24 hours the expected time loss will be more than 3 weeks (112).
•Functional test, like the knee active range of motion (ROM) deficit after a hamstring injury. This ROM deficit has been used to grade the injury severity and the expected recovery time in elite athletes (72, 74), with good reliability (94).

16. Based on Imaging
•When we look for prognostic factors based on imaging in the acute phase, the main part of the studies are:
•MRI based, on hamstrings and rectus femoris injuries;
•and they have tried to find association between different injury measurements and time loss.

17. Based on Imaging
•The MRI parameters associated with the time loss, providing prognostic information due to its relation with the amount of disrupted fibres, the degree of dysfunction and time for recovery are:
•the %CSA,
•the craniocaudal length (CCL),
•and the injury volume (Slavotinek ‘10).
•A smaller time loss in patients with hamstrings injury clinical suspicion but negative MRI has been described (23, 32, 42, 64, 97, 101, 109).
•About rectus femoris injuries, when the central tendon is disrupted the time for recovery is longer (21, 24), also and in US series (10).

18. Mechanism
Location
Grade
Re-injury

19. M (Mechanism)
•Describes the mechanism of injury; in indirect injuries describes the injury relation with MTJ and/or if MRI negative.
•When classifying a direct injury we have to codify a Dr .
•When classifying indirect injuries, this letter will describes :
–the injury relation with the muscle MTJs (P for proximal, D for distal),
–if there is MTJ disruption/retraction (gap) or loss of tension (wave), we have to add a superscript, R.
–When classifying indirect injuries with clinical suspicion but negative MRI, we will codify a N.
Mechanism

20. •First letter options:
•If describing a Direct injury Dr
•If describing an Indirect injury
–Located around the proximal MTJ PR (if MTJ disruption/retraction or loss of tension).
–Located around the distal MTJ D
–Clinical suspicion but negative MRI N
Mechanism

21. L (Location)
•Refers to injury location related to muscle anatomy (proximal, middle or distal), the second letter will be a p, m or d (lower case), to avoid confusions with MTJ locations:
•p: proximal
•m: middle
•d: distal
Location

22. •Second letter options:
•If describing a Direct injury Dr-
•If describing an Indirect injury
–Located around the proximal MTJ P-
–Located around the distal MTJ D-
–Clinical suspicion but negative MRI N
Location
Mechanism
p m d
p
m
d

24. G (Grade)
•Will reflect the amount of connective tissue damage. The injury grade will be related to the percentage of the CSA affected by the injury (abnormal intramuscular T2-weighted hyperintensity and architectural distortion), at the injuries location level (MRI between 24-48h from injury
•Grade 1: a structural injury with hyperintensity but without fibre architectural distortion.
•Grade 2: a structural injury with architectural distortion ≤10% of CSA at the injury’s maximal area, in an axial plane of the affected muscle belly.
•Grade 3: a structural injury with architectural distortion 11-25% of CSA
•Grade 4: a structural injury with architectural distortion 26-49% of CSA
•Grade 5: a structural injury with architectural distortion ≥50% of
Grade

25. •Third letter options:
•If describing a Direct injury Dr- - G1
•If describing an Indirect injury
–Located around the proximal MTJ P-
–Located around the distal MTJ D- - G2
–Clinical suspicion but negative MRI N
Location
Mechanism
p m d
p
m
d
Grade

26. R (Re-injury)
•Describes the injury chronology (first episode or a re-injury), and if it is a reinjury:
•R0: No re-injury, R1: First re-injury, R2: Second reinjury…
•A re-injury is defined as “injury of the same type and at the same site as an index injury occurring no more than 2 months after a player’s return to full participation from the index injury (Ekstrand ‘11).
•If during the two months period after the RTP a new injury occur in the same muscle but in a different location, it will also considered a reinjury.
Re-injury

27. •Fourth letter options:
•If describing a Direct injury Dr- - G1
•If describing an Indirect injury
–Located around the proximal MTJ P-
–Located around the distal MTJ D- - G2 - R
–Clinical suspicion but negative MRI N
Location
Mechanism
p
m
d
p m d
Grade
Re-injury

28. Especial Muscles
•Rectus femoris has two proximal MTJ, the direct and indirect tendons, we will codify:
•PD for proximal direct MTJ
•PI for proximal indirect tendon
•P when both MTJ affected.
•If tendon disruption/retraction or loss of tension, we will add a superscript (OPTIONS like before)

29. Discussion
•We have selected the % CSA to grade indirect muscle injuries as a measure to evaluate the structural damage in an objective and reliable way.
•In our opinion because the ECM three-dimensional structure, the important factor is no the length but the percentage of ECM disrupted from the total in the transverse plane.
•We have no data to determinate the different grades, therefore we recommend to record the exact %CSA to determinate grades based on in this data (future).

30. Discussion
•Myofascial, myoaponeurotic, epimysial…The organization and properly use of all this names for communication remains difficult (Kumka ‘12), but necessary, because this inconsistent terminology is a handicap for communication and research.
•Since we describe the injury anatomical location and its relationship with the MTJs, is not necessary to use this terminology avoiding confusions.

31. Discusion
•To incorporate an injury clinical evaluation was one of the goals for the classification purpose, but it is not been done in this first version.
•The pain location, distance to insertion, or time to walk pain free has been evaluated to its introduction; they have not been incorporated due to the published conflicting evidence.

32. Discusion
•To add a letter reflecting the percentage of strength loss compare to the contralateral muscle or a previous test, will be an option in the future, and will help to better analyse injury severity, but more research is needed before.
•Therefore, trough the histological damage quantification (%CSA) we try to evaluate the injury severity as time loss (32, 112), and as an strength impairment reflex (89).

33. Resume
•With an acronym, we offer the possibility to describe the injury type, mechanism of injury, anatomical description, and chronological evolution.
•This new system is useful for describing the injury and communication between/within medical staff, but if it has prognostic value is still unknown.
•This is and invitation, an isolated group has no future, new suggestions, bigger samples, more research and network are necessary to agree in this important point.

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