This document proposes a classification system for rectus femoris (RF) muscle injuries based on anatomical evaluation and a 4-letter initialism to describe the injury's mechanism, location, severity, and recurrence. It emphasizes the importance of clear communication among medical professionals and provides insights from various studies related to RF anatomy and injury prognosis. The system aims to enhance clinical application and facilitate rehabilitation for affected individuals.

1. MLG-R
A Muscle Injuries Classification Proposal

2. Rectus Femoris Anatomy
Proximal MTJ

3. Moraux, A., et al. "An anatomical study of the indirect tendon of the rectus femoris using ultrasonography." European radiology 25.12 (2015): 3614-3619.
Proximal MTJ
• Direct head arises from the anterior
inferior iliac spine (AIIS).
• Indirect head arises from the superior
acetabular ridge and the posterolateral
aspect of the hip joint capsule.
• The two heads form a conjoined tendon
about 2 cm distal to their origin.

4. Hasselman, Carl T., et al. "An explanation for various rectus femoris strain injuries using previously undescribed muscle architecture." The American journal
of sports medicine 23.4 (1995): 493-499.
Note that although this diagram implies purity of each of proximal tendons, there is a 10% overlap
between the tendinous fibers.

5. Tubbs, R. S., et al. "Does a third head of the rectus femoris muscle exist?." FOLIA MORPHOLOGICA-WARSZAWA-ENGLISH EDITION- 65.4 (2006): 377.
Illustration of a right third head (tendon recurrent du droit ant.) of the rectus femoris muscle from [9]
(with permission). Note also the relationship between this head and the gluteus minimus muscle (petit
fessier).

6. Rectus Femoris Anatomy
Distal MTJ

7. Iriuchishima, Takanori, et al. "Anatomical evaluation of the rectus femoris tendon and its related structures." Archives of orthopaedic and trauma surgery
132.11 (2012): 1665-1668.

8. Waligora, Andrew C., Norman A. Johanson, and Bruce Elliot Hirsch. "Clinical anatomy of the quadriceps femoris and extensor apparatus of the knee." Clinical
Orthopaedics and Related Research® 467.12 (2009): 3297-3306.
A schematic is shown of the various
patterns of the layers of the
quadriceps tendon.
(A) A sagittal section of the patella
and its relation to the
quadriceps and patellar
tendons is illustrated.
(B) Bilaminar
(C) Trilaminar
(D) Quadrilaminar patterns of the
quadriceps tendon are shown.
R = Rectus femoris, L = Vastus lateralis, M
= Vastus medialis, I = Vastus intermedius.

9. Classification
• Our classification system for RF
injuries:
• Capable to describe injuries
location and chronology,
• easy clinical application,
• adequate grouping of injuries
with similar functional
impairment, and provide
potential prognostic value,
• to enhance communication
between professionals and
facilitate rehabilitation and
RTP.

10. This evidence-informed and expert consensus-based
classification system based on a 4-letter initialism system

12. Direct Injuries
• Severity depends on the site of impact, the activation status
of the muscles involved (Hayashi 2012).
• Size of direct muscle injuries is not well correlated with
clinical signs and functional impairment (Lee 2012).
• Better evolution with shorter time to recovery in comparison
to indirect injuries (Thorsson 1997).
(Hayashi 2012).

14. Garrett, William E., et al. "The effect of muscle architecture on the biomechanical failure properties of skeletal muscle under passive extension." The
American Journal of Sports Medicine 16.1 (1988): 7-12.
“Our results demonstrate that all four muscle types tested show injury and rupture
at the MTJ whether pulled from proximal or distal attachment, regardless of muscle
structure and rate of strain”

15. Balius, Ramon, et al. "Central aponeurosis tears of the rectus femoris: practical sonographic prognosis." British journal of sports medicine 43.11 (2009): 818-
824.

17. Cross, Thomas M., et al. "Acute quadriceps muscle strains magnetic resonance imaging features and prognosis." The American journal of sports medicine
32.3 (2004): 710-719.
aa

18. Cross, Thomas M., et al. "Acute quadriceps muscle strains magnetic resonance imaging features and prognosis." The American journal of sports medicine
32.3 (2004): 710-719.
Size (%CSA), site and anatomical location (tendon affectation) have
influence on quadriceps muscle injuries prognosis, being the tendon
affectation the most significant predictor of the time loss.

20. Mechanism Location Grade Reinjury
Name the muscle and ...

21. M (Mechanism)
• Describes the mechanism of injury:
• Direct injuries T
• Indirect injuries I
» Negative MRI injuries N
Mechanism

22. L (Location)
• Is a letter regarding the anatomical location:
• P, M or D For injuries located at the proximal, middle or
distal anatomical third of the muscle belly.
• We also describe the injury relation with the proximal
or distal MTJ adding a subindex P or D.
» For MRI negative injuries we will describe pain location.
Location

23. Kerr, R. M. MRI Web Clinic—May 2014.
• For the proximal MTJ
we describes if the
injury locates
• conjoined tendon P
• at the direct P1
• indirect P2

29. R (Re-injury)
• Describes the injury chronology (first episode or a re-injury):
• R0: First episode,
• R1: First re-injury, R2: Second re-injury… and so on.
• A re-injury (R) is defined as an injury of the same type and location as the
index injury occurring during the first 2 months after return to full
competition (Ekstrand 2011).
• Injuries affecting the same MTJ, its intramuscular tendon or fibers
associated with it (even in a different location), will also be considered a
re-injury.

30. Examples Direct RF Injuries

31. Kerr, R. M. MRI Web Clinic—May 2014.
Code T-D-G-R.
Code T-P-G-R.
Code T-M-G-R.

32. Examples Indirect RF Injuries
with Negative MRI

33. Kerr, R. M. MRI Web Clinic—May 2014.
Code N-D-0-R.
Code N-P-0-R.
Code N-M-0-R.

34. Examples of Indirect RF Injuries
Around the Proximal MTJ

35. Kerr, R. M. MRI Web Clinic—May 2014.
Code I-PP-G-R.
Code I-P1-G-R.
Code I-M2-G-R.
Code I-M2-GR-R.
Brukner 2015
Brukner 2015

36. Examples Indirect RF Injuries
Around the Distal MTJ

37. Kerr, R. M. MRI Web Clinic—May 2014.
Code I-MD-G-R.
Code I-DD-G-R.
Balius R
Balius R

38. Kassarjian 2014

39. Hasselman, Carl T., et al. "An explanation for various rectus femoris strain injuries using previously undescribed muscle architecture." The American journal
of sports medicine 23.4 (1995): 493-499.
Schematic representation of the pathophysiology in strain injury involving the deep intramuscular tendon of the indirect
head.
A note the normal pattern of fibers arising from the deep intramuscular tendon of the indirect head.
B acutely, muscle fibers tear from the tendon and retract distally, with hemorrhage into the space created.
C chronically, this area organizes into a fibrous encasement of the deep tendon with muscle fibers attaching to the scar
and serous fluid envelops the tendon and its encasement. The tendon remains intact throughout this injury site.
Kerr, R. M. MRI Web Clinic—May 2014.

40. Kerr, R. M. MRI Web Clinic—May 2014.
Code I-DD-G-R.

41. Kerr, R. M. MRI Web Clinic—May 2014.
Code I-DD-GR-R.

42. Mechanism of injury (M) Locations of injury (L) Grading of severity (G)
Number of muscle re-
injuries (R)
RF direct injuries
T (direct) P Injury located in the proximal third of the muscle belly
0-3
0 1st episode
1 1st re-injury
2 2nd re-injury, and so on.
M Injury located in the middle third of the muscle belly
D Injury located in the distal third of the muscle belly
RF indirect injuries
I (indirect) P Injury located in the proximal third of the muscle belly. The second
letter is a subindex p or d to describe the injury relation with the
proximal or distal MTJ respectively.
0-3
0 1st episode
1 1st re-injury
2 2nd re-injury, and so on.
M Injury located in the middle third of the muscle belly, plus the
corresponding subindex.
D Injury located in the distal third of the muscle belly, plus the
corresponding subindex.
Negative MRI injuries (location is pain related)
N N p proximal third injury
0-3
0 1st episode
1 1st re-injury
2 2nd re-injury, and so on.
N m middle third injury
N d distal third injury

43. Practice and Research Gaps
• With a 4-letter initialism system we can
describe the injury anatomical location
and relation with ECM.
• Easy to use, and avoid confusing
terminology.
• Allows communication among medical
staff.
• Flexible structure allowing to
incorporate new knowledge in the
future.