Muscle injuries of the rectus femoris muscle. MR update

Review
Muscle injuries of the rectus femoris muscle. MR update
C.A. Mariluisa,*, J. Cupitob and F. Mamoneb
a
b
Magnetic Resonance Imaging Department, DIM Centros de Diagnóstico, Ramos Mejía, Buenos Aires, Argentina
Orthopedics Department, DIM Centros de Diagnóstico, Ramos Mejía, Buenos Aires, Argentina
Abstract
The tear of the anterior rectus femoris is the most frequent injury of the quadriceps muscle group, and one of the
most common causes of lower limb muscle lesions (after the injury of the hamstring muscle group). As its anatomy is
complex, and symptoms may be unclear, imaging and in particular, Magnetic Resonance Imaging (MRI) provides precise
information on the type of tear, topography, extent, and severity.
This article presents a detailed description of the anatomy of the RF and a selective study by MRI, with specific technical
inputs to optimise this study method. The current concepts of tendinous, myotendinous, and the infrequent myofascial
muscle-tendon tears are also addressed, providing key data that must be considered in MRI reports and which are of
paramount importance for the orthopedist.
© 2015 Sociedad Argentina de Radiología. Published by Elsevier España, S.L.U. This
is an open access article under the CC BY-NC-ND license (http://creativecommons.org/
licenses/by-nc-nd/4.0/).
Keywords: Magnetic Resonance; Recturs femoris; Soft tissue injuries.
Introduction
Injury of the quadriceps muscle group is very common in the
general population and even more common in athletes, generally due to hyperextension of the hip with knee flexion (in
activities which involve kicking, running, martial arts, etc.). It
is the most common cause of muscle tear in the lower limbs,
second only to the injury of the hamstring muscle group1,2.
The quadriceps muscle group consists of four muscles: the
rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM)
and vastus intermedius (VI). Of the four muscles that comprise this group, the RF is the only one that crosses two joints;
therefore, in addition to being part of the group of primary
hip flexors, the RF is also a knee extensor 2-5. Because of this
feature, its fusiform shape, its tendency to an eccentric contraction and its high percentage of type II rapid contraction
fibers, the RF is more frequently injured than the rest of the
quadriceps vastus muscles 6-9.
Patients with RF injury present with various symptoms; therefore, imaging methods play an essential role in determining
the type of tear, topography and severity. Ultrasound is a lowcost modality and permits examination of muscle fibers and
soft tissue, but magnetic resonance imaging (MRI) has higher
specificity for diagnosing the etiology, mainly in the subacute
and chronic stages of the injury, when soft tissue edema is
minor6,10,11.
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This article describes the anatomy and current concepts in
MRI of rectus femoris tear, from its proximal insertion site to
involvement of the quadriceps tendon.
Anatomic aspects
of the rectus femoris
The RF is the only one of the four portions of the quadriceps
that crosses two joints. While the VM, VL and VI extend from
the femur to the tibia and are essential for knee extension,
the RF extends from the hip bone to the tibia, and also acts
as flexor of the coxofemoral joint12, 13.
The RF is a bipennate muscle; i.e., it is composed of fascicles
that are arranged at an angle to the central tendon or oriented
with the longitudinal axis of the muscle, giving greater muscle
strength12. The anatomy of the RF is complex but easily differentiated on MR imaging (figs. 1 and 2). Its proximal site
of insertion is made up of two portions, a direct head (DH)
and an indirect or reflected head (IH): the former arises from
the anterior inferior iliac spine, while the latter arises from the
superior acetabular ridge and the lateral aspect of the hip joint
capsule1. The DH acts mainly in the beginning of hip flexion,
while the IH acts once the hip joint flexion has started2.
A few millimeters from their proximal insertion, both heads
form a conjoined tendon; however; they are then located at
C.A. Mariluis et al.
different sites in the thigh. The DH lies in the anterior and
slightly medial aspects; it has a short course with a proximal
myotendinous junction in the thigh and its tendinous fibers
course towards the anterior surface of the RC, blending with
the proximal fascia1,14,15. At this level, under normal conditions, it may be difficult to anatomically differentiate between
the anterior fascia and the myotendinous junction, as there is
a slight focal tendon thickening in continuity with the fascia
(fig. 1c). On the other hand, the IH has a horizontal ovoid
shape; it extends through the muscle belly, then it becomes
thinner, reaching the inferior third of the thigh with a lineal
shape with a sagittal major axis1,16-18.
The quadriceps tendon is a trilaminar structure formed by the
coalescence of four tendons. The RF (superficial plane) and
vastus intermedius (deep plane) insert on the superior border
of the patella, while the VM and VL insert on the medial and
lateral aspects, respectively, forming the patellar retinacula
(intermediate plane). Then as the patellar tendon they reach
the anterior tuberosity of the tibia19-21.
Magnetic Resonance Imaging
Because of the large size of the RF in the thigh, complete visualization of this muscle may be difficult on MRI. For this reason,
we suggest first obtaining coronal images with a wide field
of view (FOV 400/420 mm) including both thighs, from the
anterior-inferior iliac spine to both patellae in order to make
a comparative assessment of their volume and determine the
site to be studied. Then selective sequences may be obtained
with higher resolution, focused on the region of interest.
Our study protocol includes coronal and axial T2-weighted
fat-suppressed images (repetition time [TR]/echo time [TE]
2500/90 ms), axial double echo T2-weighted images (TR/TE1
a
b
c
d
Figure 1, Normal anatomy. Axial proton density (PD)-weighted images: (a) proximal insertion of the DH (black arrow) and (b) of
the IH (white arrow); (c) proximal myotendinous junction of the IH (white arrow) and of the DH (black arrow) in the proximal
third of the thigh; (d) myotendinous junction of the IH in the middle third of the thigh (white arrow).
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a bc
Figure 2. Normal anatomy. PD-weighted images in the oblique sagittal plane (a and b) and in the strict sagittal plane (c). (a) The
arrow points to the proximal insertion of the DH. (b) The solid arrow points to the insertion of the IH, while the dashed arrow
identifies the close contact of both tendon ends proximally. (c) Note the usual trilaminar appearance of the quadriceps tendon
with interdigitation of the fatty tissue (arrow).
2400 / 8 ms; TR/TE2 2400/ 110 ms) and coronal T1-weighted
images (TR/TE 500/ 18 ms).
Optionally, T2-weighted fat-suppressed images may also be
obtained in a strict sagittal plane parallel to the thigh axis (patients with myofascial junction injury or myotendinous injury
of the DH) and in the sagittal oblique plane paralleling the
anterior-inferior iliac spine (when proximal tendinous injuries
are suspected). The evaluation may be supplemented with
T1-weighted fat-suppressed images to assess blood collections with greater imaging contrast, as they appear spontaneously hyperintense at the acute stage; gradient echo (GRE)
sequences are helpful to identify sequellar lesions with hemosiderin deposits (blooming effect) appearing as markedly hypointense focal areas. Intravenous paramagnetic contrast administration is not usually necessary, although enhancement
may be occasionally observed predominantly in the periphery
of acute tears, associated with regionally hypervascularity.
sipation of forces during muscle contraction. Injuries may be
caused by a direct mechanism (contusion, laceration) or by an
indirect mechanism (stretching of fibers beyond their elastic
Tear of the rectus femoris
and MRI findings
Certain drugs (steroids, fluoroquinolone, among others) as
well as a history of diabetes, gout, systemic lupus erythematosus, rheumatoid arthritis, kidney failure and obesity may all be
predisposing factors for muscle tears. In addition, some cases
of bilateral RF tear have been reported in these patients22-25.
Muscle injuries most commonly occur in middle-aged male
patients due to indirect muscle overload, as a result of dis-
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Figure 3 Patient with a history of direct trauma in the anterior
region of the thigh. Axial T2-weighted fat-suppressed image
shows hyperintensity of posterolateral fibrillar signal of the
RF, demonstrating contusional edema (arrow).
C.A. Mariluis et al.
Figure 4 Coronal T2-weighted fat-suppressed images showing partial tear of the IH (arrow) and slight edema of the
proximal myotendinous junction suggestive of grade 1 tear.
Figure 5 Coronal T2-weighted fat-suppressed image shows
a peritendinous interstitial edema producing a “feathery”
appearance surrounding the IH (arrow), a finding consistent
with grade I tear of the myotendinous junction.
limit by a sudden and forceful contraction). As regards topography, these injuries are typically located in the tendon
portion, myotendinous junction (most common site of tear)
and/or myofascial junction7, 26.
Generally, in acute injuries highly marked symptoms often
occur immediately after the injury, but in acute injuries of
the myotendinous and myofascial junction of the IH of the
RF, symptoms may have an insidious onset1, 2. Furthermore, a
tear may remain asymptomatic because of recruitment of all
other quadriceps muscles, although in this case the patient
will not have the same muscle strength he/she had before
his/her injury27,28. For this reason, MRI plays an essential role
for determining the location, extent and severity of the RF injury and, consequently, for establishing a proper therapeutic
management. A fibrillar involvement larger than 15% of the
muscle area with a length greater than 13 cm and a location
central to the muscle belly, has a poor prognosis and longer
rehabilitation.
An early diagnosis is essential to prevent muscle retraction
and formation of scarring29, 30.
increased muscle volume compared with the contralateral
side31 (fig. 3).
In cases of RF injury from contusion, or in severe tears, hematomas are observed, which appear spontaneously hyperintense or hypointense on T1-weighted images, depending on
the composition and the time of evolution.
Hematoma results from intramuscular vein injury and it may
be either intramuscular or intermuscular. The former is limited by the intact muscle fascia, which increases intramuscular pressure and consequently compresses bleeding vessels,
limiting bleeding and size of hematoma. Instead, the intermuscular hematoma spreads into the interstitial and interfascial spaces due to rupture of the muscle fascia, without
an increase in the pressure within the region; therefore the
hematoma becomes larger in size31, 32.
Chronic hematomas should be differentiated from tumor
masses, as both have a heterogeneous appearance. The former may have mural nodules due to neovascularization with
a fibrous capsule that appears hypointense in all sequences.
Occasionally, the only way to differentiate them is by followup, observing a decrease in the size of hematomas2,33,34. For
this reason, radiologists should perform an accurate measurement of their size and determine the mass effect on adjacent
structures, as well as their relationship with the sartorious
muscle. If this muscle is compressed, recovery and drainage
of metabolites in the area may be impaired1.
Muscle contusion
Contusion is common on the surface of the RF in the thigh. It
is characterized by the presence of diffuse myofibrillar edema
with no defined tear, with or without associated bruises and
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Muscle injuries of the rectus femoris muscle. MR update
Proximal tendon injury
This injury is classified as partial or total (fig. 4). As mentioned
above, axial images and sagittal oblique images paralleling
the anterior-inferior iliac spine are very useful for determining
which tendon is affected (DH and/or IH of the RF), and in the
case of complete tears, these images are helpful for an accurate measurement of the gap of the tear.
These injuries may be associated with avulsion of the anterior-inferior iliac spine at the DH, as this tendon acts primarily
in early hip flexion, which makes it more vulnerable. Avulsions typically occur in skeletally immature patients (avulsion
of the apophysis of the anterior inferior iliac spine) 2,35,36.
Repetitive microtrauma may result in chronic avulsion which
must be differentiated from tumors because they present excess bone growth2, 37,38.
Myotendinous junction injury
Myotendinous junction injury is the most common type of
tear of the RF (especially for the IH), as this is a point of biomechanical weakness of the muscle. As regards the severity
of myotendinous junction injuries, there are three categories2:
• Grade I: microscopic injury with no functional loss. The MRI
shows edema and peritendinous interstitial hemorrhage
with no focal area of tear. Edema extends into adjacent
muscle fibers producing a “feathery” appearance (fig. 5).
Less than 5% of myofibrils are affected1,6.
Figure 6 Grade II tear of the myotendinous junction of the IH.
Axial (a) and coronal (b) T2-weighted fat-suppressed images
show peritendinous edema (solid arrow) and focal discontinuity of muscle fibers with fluid content (dashed arrow). Note
the bull’s eye sign in the axial plane with central IH.
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• Grade II: partial tear with partial loss of muscle strength and
range of motion. The MRI shows partial tear of the myotendinous junction; the appearance of the tear will depend
on the extent and age of the injury. In acute injuries, there
is a fluid-filled partial defect and hemorrhage surrounding
the myotendinous junction. In axial T2-weighted sequences
the bull’s eye sign has been seen, characterized by a hypointense central tendon surrounded by an area of hyperintensity (hemorrhage and peritendinous fluid)2,38 (fig. 6).
•Grade III: complete tear with or without retraction with
complete functional impairment2 (fig. 7).
The location of the myotendinous junction injury of the DH
is anterior and proximal to the thigh. On MRI, this injury typically presents as edema and fluid between the proximal and
anterior third of the RF and the muscle fascia. Because of
its proximity to the anterior fascia, it may be difficult to distinguish a myotendinous junction injury from a tear of the
myofascial junction. Some authors suggest that myotendinous junction injuries of the DH may be associated with some
myofascial component1.
Anatomically, the myotendinous junction of the IH has a
greater cephalocaudal extension than the DH and it is located
at the center of the fibers of the RF muscle belly. Therefore,
it is far easier to visualize an injury at this level on MRI. Such
injuries are usually located between the proximal and middle
thirds of the thigh; fluid and edema are irregularly seen, depending on the severity of the injury1,2.
Figure 7 Axial T2-weighted fat-suppressed image showing
the absence of the IH with complete discontinuity of the
myotendinous junction and a heterogeneous area with intramuscular hematoma (arrow).
C.A. Mariluis et al.
Myofascial junction injury
Myofascial junction injury is less common than the above reported injuries, and it usually leads to false negative results in
ultrasound scans. Even if this injury may be located at any site
of the muscle belly with or without facial disruption, it is usually located between the proximal and middle thirds of the
thigh. On MRI, this injury presents as muscle fibers that lose
their typical morphology and present signs of edema with
partial involvement or complete tear of the adjacent fascia.
Fluid collections dissect the plane between the fascia and the
muscle belly (intact fascia) (fig. 8) and they may also spread
into the intermuscular plane (fascial tear)1 (fig. 9).
As noted earlier, it may be difficult to distinguish a myotendinous junction tear of the DH from a myofascial tear of proximal and anterior fibers, because of their proximity. On the
contrary, a posterolateral myofascial tear can be easily distinguished from a myotendinous tear of the IH, as the former
presents as edema and/or fluid collections distributed eccentrically to the muscle belly, while the latter is located around
the IH at the center of the RF muscle.1,2
Distal tendon injury
As reported earlier, the quadriceps tendon typically has a
trilaminar appearance (56% of cases), formed by the confluence of all four tendons in three layers (superficial layer:
RF; intermediate layer: VM and VL, and deep layer: VI) For
this reason, visualization of interdigitating fat among these
tendons is normal6. Injury at this level may be partial or total, and affect one or several tendons (fig. 10). This lesion is
frequently located in the superficial layer, i.e., in the portion
formed by the RF (fig. 11). Complete tears will require surgical therapy and findings will include retraction of the torn
ends of the tendon, waviness of the patellar tendon and a
decrease in patellar height10, 20, 21.
In general, patients with a history of past injury of the quadriceps or hamstrings have an increased risk for reinjury of the
RF1, 20. For this reason, a single scan may show injuries at acute
or chronic stages, and/or as exacerbation of an old injury10, 21.
Chronic tears often manifest as fatty replacement and myofibrillar atrophy, associated with hypointense linear tracts on
T1- and T2-weighted images evidencing fibrosis and scar tissue around or adjacent to the tendon. Additionally, a blooming effect can be seen on GRE sequences, with a markedly
hypointense signal from hemosiderin deposition2 (fig. 12).
For educational purposes, two tables are included as a summary: table 1 describes anatomic aspects of the RF that are
relevant for MRI and table 2 summarizes the issues that
should be addressed in the radiologist’s report and which are
relevant for the orthopedic therapy approach.
In conclusion, MR imaging of the RF muscle provides accurate
data on the severity and extent of the injury, and it is also
helpful to determine whether this injury is a de novo tear
or an exacerbation of a chronic tear. A general assessment
of the thigh (ideally an initial MRI comparing both thighs)
followed by a few selective sequences with a higher resolution in the region of interest can provide accurate information about the location of the injury. Furthermore, MRI scans
play an essential role for differential diagnosis in patients with
uncertain symptoms, frequently associated with grade I myotendinous junction injury or myofascial junction tear that are
difficult to visualize on ultrasound.
Figure 8. Axial T2-weighted fat-suppressed image showing myofascial tear with
diffuse fibrillar edema at the center of the RF (solid arrow) associated with hematoma located between the muscle belly and the intact fascia (dashed arrow).
Figure 9 Myofascial tear with fascial discontinuity. Axial PD-weighted image
showing hematoma (solid arrow) with discontinuity of the muscle fascia in the posterolateral site and waviness of the torn
end of the fascia (dashed arrow).
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Muscle injuries of the rectus femoris muscle. MR update
Figure 10 Complete tear of the distal tendon of the RF. Coronal T1-weighted image showing retraction of the torn end of
the distal tendon (solid arrow) associated with waviness of
the muscle belly (dashed arrow).
Figure 11 Sagittal T2-weighted fat-suppressed image in a patient with complete tear of the distal tendon of the RF (solid
arrow) and intrasubstance injury of the torn end of the tendon.
The dashed arrow shows the standard insertion of tendons of
the VM and VL (intermediate plane) and VI (deep plane). The
scan also shows suprapatellar fat pad edema (asterisk).
Figure 12. Patient with exacerbated chronic tear of the proximal myotendinous junction of the IH (short arrows) and of
the posteroalteral myofascial junction of the RF (long arrows).
(a) Axial T-weighted fat-suppressed image showing edema
from tears in the acute stage. (b) Axial GRE sequence showing a hypointense signal from hemosiderin deposit, associated with a past history of sequellar tear.
Table 1: Anatomical and Imaging keys of the rectus femoris.
• The DH contributes to the most medial and anterior aspect of the muscle belly of the rectus femoris and the IH contributes to the posterolateral portion of the RF
• Under normal conditions, the DH can be visualized on MRI at the level of the hip; instead, if there is edema or fluid, it
can be visualized in its full length to the proximal third of the thigh.
• Sagittal oblique images paralleling the anterior-inferior iliac spine are helpful for visualization of proximal tendons (DH
and IH) and of the gap of the tear.
• Gradient echo (GRE) sequences are helpful to detect hemosiderin deposits in scar injuries. In addition, T1-weighted sequences identify the presence of fatty replacement in these injuries.
DH: direct head; IH: indirect or reflected head.
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C.A. Mariluis et al.
Table 2: Magnetic Resonance Imaging report: what does the orthopedist expect?
• Determining the topography of the tear: tendinous (DH and/or IH), myotendinous and/or myofascial junction.
• Extent of the tear (approximate percent of fibers affected in a section area).
• In cases of complete tear, report measurement of the size of the gap and status of the torn ends of tendons,
• Description of the topography and measurement of fluid collections or hematomas (impact on the sartorious muscle?).
• Intact or affected muscle fascia.
DH: direct head; IH: indirect or reflected head.
Ethical responsibilities
Protection of human subjects and animals. The authors declare that no experiments were performed on humans or animals for this investigation.
Confidentiality of data. The authors declare that this article
does not contain patient data.
Right to privacy and informed consent. The authors declare
that this article does not contain patient data.
Conflicts of interest
The authors declare no conflicts of interest, except for Dr. Mariluis, who declares a possible conflict of interest as member
of the Writing Committee of Revista Argentina de Radiología.
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