DOI:10.2214/AJR.07.2947
AJR 2008; 190:W182-W186
© American Roentgen Ray Society
Normal Anatomy and Strains of the Deep Musculotendinous Junction of the Proximal Rectus Femoris: MRI Features
Soterios Gyftopoulos1,
Zehava Sadka Rosenberg2,
Mark E. Schweitzer2 and
Marcelo Bordalo-Rodrigues2
1 Department of Radiology, Beth Israel Medical Center, First Ave. at 16th St.,
New York, NY 10003.
2 Department of Radiology, NYU Hospital for Joint Diseases, New York, NY
10003.
Received July 26, 2007;
accepted after revision September 26, 2007.
Address correspondence to S. Gyftopoulos
(soterios20{at}gmail.com).
WEB
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Abstract
OBJECTIVE. The MRI features of the proximal rectus femoris
musculotendinous junction have scarcely been described in the literature. The
purpose of our study, based on a review of 50 asymptomatic and 20 symptomatic
MRI studies, was to define the normal MRI anatomy and MRI features of
intrasubstance injury of deep musculotendinous tears of the proximal rectus
femoris.
CONCLUSION. Axial and coronal MR images are optimal for visualizing
the direct and indirect heads, the conjoined tendon, and the deep
musculotendinous junction of the proximal rectus femoris. Tears of the deep
musculotendinous junction are longitudinal, involving a long segment of the
muscle. MRI features include a "bull's-eye" sign, longitudinal
scar, retraction, pseudocyst, and hematoma.
Keywords: hip • MRI • musculotendinous junction injuries • rectus femoris • sports medicine • trauma
Introduction
Injuries of the deep proximal musculotendinous unit of the rectus femoris
are infrequent and can be difficult to diagnose. The injuries, defined as
intrasubstance tendinous tears of the proximal rectus femoris, occur in young,
athletic individuals during activities such as sprinting and kicking
[1]. Predisposing factors
include muscle fatigue, insufficient warm-up exercises, overall poor muscle
conditioning, and a previous tear
[2].
The rectus femoris is a long, fusiform muscle forming the anterior
superficial portion of the quadriceps muscle group
[3]
(Fig. 1). Its main functions
include knee extension and hip flexion. The proximal rectus femoris has two
tendinous origins: the direct (straight) head, arising from the
anterior–inferior iliac spine, and the indirect (reflected) head,
arising slightly more inferiorly and posteriorly from the superior acetabular
ridge and hip joint capsule. The two heads form a conjoined tendon a few
centimeters below their origins. The direct head, making up most of the
superficial component of the conjoined tendon, blends more distally with the
anterior fascia of the rectus femoris. The indirect head, forming most of the
posterior component of the conjoined tendon, becomes intrasubstance and forms
a long, deep musculotendinous junction extending approximately two thirds of
the length of the muscle.
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Fig. 1 —Drawing of rectus femoris muscle. Direct head originates from
anterior–inferior iliac spine (gray arrow) and blends with
anterior fascia. Indirect head originates more posteriorly from acetabulum
(black arrow) and dives into rectus femoris muscle belly. Modified
with permission from [8].
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To the best of our knowledge, only a few reports in the literature focus on
the MRI features of the proximal rectus femoris muscle
[4–6].
The purpose of our study, based on a review of 50 asymptomatic and 20
symptomatic patients, was twofold: first, to define the normal MRI anatomy of
the proximal rectus femoris musculotendinous unit; and, second, to describe
the MRI features of proximal deep rectus femoris musculotendinous junction
tears.
Materials and Methods
MRI Technique
MR examinations of the hip were performed at 1.5 T (Magnetom, SP4000,
Siemens Medical Solutions) with a phased-array torso coil. The field of view
was 20–32 cm, and the matrix was 256 x 256. Axial T1-weighted
images (TR range/TE range, 500–650/12–14), coronal T1-weighted
images (500–650/12–14), coronal turbo spin-echo fat-suppressed
fluid-weighted images (5,000–6,000/45–65; echotrain length, 8),
and sagittal fluid-weighted images (5,000–6,500/50–65) were
obtained. The slice thickness was 4–5 mm with a 10% gap.
Institutional review board approval was obtained, and informed consent was
waived for this retrospective HIPAA-compliant study.
Asymptomatic Population
A retrospective review of the normal MRI anatomy of the proximal rectus
femoris was performed in 50 MRI studies of 47 patients (23 men, 24 women; age
range, 30–71 years; mean age, 44 years). The studies were obtained from
a computer data search of MRI examinations of the hips and thighs performed at
our institution during a 2-year period. Review of the asymptomatic sides in 47
patients assessed for a variety of unilateral symptoms such as hip or groin
pain, avascular necrosis, trauma, tumor, or neurologic conditions was
performed. In three patients with sciatic neuropathy, both sides were
reviewed. The MR studies were reviewed by one musculoskeletal radiologist with
20 years' experience.
Symptomatic Population
MRI studies of the hip were obtained through a search of our institution's
computer data files. The search words included "rectus femoris
injury," "rectus femoris tear," and "rectus femoris
strain." Only cases with MRI evidence of deep muscu lotendinous junction
injury, defined as injuries of the intrasubstance tendon, were included in the
study. A total of 20 patients with deep muscu lotendinous junction injuries
were identified (16 males, four females; age range, 12–54 years; mean
age, 32 years).
Two musculoskeletal radiologists, one with 15 years and one with 20 years
of musculoskeletal radiology experience, in consensus, reviewed the studies.
The following parameters were recorded: grade of injury; presence of
"bull's-eye" sign, retraction, or hematoma; and age of injury.
Grading of the tears was based on accepted MRI characteristics of
musculotendinous strains [7]. A
grade I tear is defined as high signal intensity focally or diffusely at the
musculotendinous junction on fluid-sensitive images. A feathery appearance to
the muscle on all pulse sequences is compatible with interstitial hemorrhage
and edema. The musculotendinous junction is maintained. A grade II tear shows
partial disruption of the musculotendinous junction with interstitial feathery
high signal intensity or hematoma in the acute setting. Low signal
representing either fibrosis or hemosiderin can be seen in chronic or old
injuries. A grade III tear represents a complete musculotendinous disruption
with or without retraction. The bull's-eye sign was defined as bright signal
surrounding the low-signal deep tendon on axial T1 or fluid-sensitive
sequences (or both) and after administration of IV gadolinium.
The age of the injury was categorized as acute when interstitial edema,
fluid, and hemorrhage were present; old when there was fibrous encasement of
the tendon, muscle atrophy, and fatty replacement; or chronic when there were
MRI features of both acute and old injuries.
Results
Asymptomatic Population
The two tendinous origins of the rectus femoris muscle, the direct and
indirect heads, were optimally identified on axial images as linear low-signal
structures in all cases (Fig.
2A,
2B,
2C,
2D,
2E,
2F). The direct head originated
from the anterior–inferior iliac spine
(Fig. 2A), and the indirect
head originated slightly more distally and posteriorly from the acetabulum
(Fig. 2B). The two heads formed
a conjoined tendon approximately 1 cm below their origins. The tendon
transformed from a globular structure to a boomerang-like structure located
anterior and medial to the muscle fibers. The anterior component of the
conjoined tendon blended more distally with the anterior fascia of the rectus
femoris. The more posterior portion of the conjoined tendon gradually became
embedded within the muscle belly of the rectus femoris, forming a deep tendon
with a long, intrasubstance musculotendinous junction
(Fig. 2C).
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Fig. 2A —T1-weighted images show normal MRI anatomy of rectus femoris
in multiple patients. Axial image (TR/TE, 500/12) shows origin of direct head
(arrow) is off anterior–inferior iliac spine.
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Fig. 2B —T1-weighted images show normal MRI anatomy of rectus femoris
in multiple patients. Axial image (500/12) shows indirect head as it
originates, slightly more distally (white arrow), from superior
acetabulum and joins direct head to form conjoined tendon (black
arrow).
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Fig. 2C —T1-weighted images show normal MRI anatomy of rectus femoris
in multiple patients. Axial image (500/12) shows blending of direct head, more
distally, with anterior fascia of rectus femoris (black arrow). Note
that indirect head (white arrow) is now intrasubstance.
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Fig. 2D —T1-weighted images show normal MRI anatomy of rectus femoris
in multiple patients. Sagittal T1-weighted image (550/14) shows direct head
(black arrow), conjoined tendon (white arrow), and deep
tendon (arrowheads).
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Fig. 2E —T1-weighted images show normal MRI anatomy of rectus femoris
in multiple patients. Coronal image (500/12) shows origin of direct head off
anterior–inferior iliac spine (black arrow), conjoined tendon
(white arrow), and deep tendon (arrowheads).
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Fig. 2F —T1-weighted images show normal MRI anatomy of rectus femoris
in multiple patients. Coronal image (500/12), more posterior than E,
depicts indirect head as it originates from acetabular ridge
(arrow).
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The two origins of the rectus femoris tendon and the deep musculotendinous
junction were also seen clearly on coronal images, but they were less
optimally visualized on sagittal images
(Fig. 2D). Anterior coronal
images depicted the direct head's origin from the anterior–inferior
iliac spine as a relatively thick, somewhat rectangular low-signal structure
(Fig. 2E). The indirect head
was visualized on consecutive, slightly more posterior coronal images, in very
close proximity to the joint capsule, as a linear, low-signal structure
highlighted by fat and thinner than the direct head
(Fig. 2F).
Symptomatic Population
Seventeen (85%) of the 20 symptomatic patients had grade II injuries; one
(5%), a grade I tear; and one (5%), a grade III tear. One of the patient's
tears could not be accurately graded due to inadequate imaging technique. The
injuries were categorized as old (n = 9, 45%) or acute (n =
9, 45%). In two patients (10%), it was difficult to distinguish between a
subacute and old injury.
In all of our patients, the injuries extended along a long portion of the
deep musculotendinous junction. The most common MRI tear pattern was a
bull's-eye appearance (n = 13, 65%): a halo of bright signal around
the deep tendon, noted on multiple consecutive axial T1 or fluid-sensitive
images (Fig. 3A,
3B). Tendon thickening
(n = 6, 30%) and partial muscle retraction (n = 6, 30%) were
also seen. Other findings included hematoma (n = 8, 40%); pseudocyst
(n = 4, 20%) (Fig.
4A,
4B); focal fatty muscle
replacement (n = 3, 15%); and longitudinal, low-signal scars
(n = 6, 30%) (Fig.
5). Scarring either encased the tendon or extended longitudinally
into the adjacent muscle.
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Fig. 3A —"Bull's-eye" sign after rectus femoris injury.
Bull's-eye sign after rectus femoris injury in 19-year-old man after tearing
sensation in thigh. Axial T2 fat-suppressed image (TR/TE, 5,050/50) depicts
halo of increased signal (white arrows) around deep tendon (black
arrow).
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Fig. 3B —"Bull's-eye" sign after rectus femoris injury.
Bull's-eye sign after rectus femoris injury in 35-year-old woman. Axial
T1-weighted image (600/13) shows halo of increased signal (arrow)
surrounding low-signal deep tendon, which is consistent with fatty atrophy due
to remote injury.
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Fig. 4A —Fibrous scarring after remote rectus femoris injury.
19-year-old man who presented with persistent thigh pain after remote rectus
femoris injury. Coronal T1-weighted image (TR/TE, 500/14) shows longitudinal
scar (arrow) adjacent to deep tendon and scarring and irregularity of
distal tendon (arrowhead).
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Fig. 4B —Fibrous scarring after remote rectus femoris injury.
21-year-old man with fibrous scarring from remote rectus femoris injury. Axial
T1-weighted image (500/14) shows low signal surrounding left deep tendon
(white arrow) representing fibrous encasement. Compare this finding
to normal-appearing right deep tendon (black arrow).
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Fig. 5 —Pseudocyst in 12-year-old boy with remote rectus femoris
injury. Axial fat-saturated T1-weighted image after IV gadolinium injection
(TR/TE, 600/14) reveals fluid collection with rim enhancement (white
arrow); these findings are consistent with pseudocyst adjacent to deep
tendon (black arrow).
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All of the grade I and II tears were treated conservatively, and the
patient with the grade III tear was lost to follow-up.
Discussion
The tendinous origins of the rectus femoris muscle have been well outlined,
but the proximal musculotendinous junction is incompletely defined in most
anatomy textbooks [3]. A
detailed description of the normal anatomy of the rectus femoris was provided
by Hasselman et al. in 1995
[8]. They reported that the
direct head arises from the anterior–inferior iliac spine, while the
more posterior and inferior indirect head originates from the superior
acetabular ridge and hip capsule. The two heads form a conjoined tendon. The
superficial conjoined tendon, made mostly of fibers of the direct head, then
blends with the anterior fascia of the muscle while the posterior conjoined
tendon, made mostly of fibers of the indirect head, becomes intrasubstance to
form a long, deep musculotendinous junction.
We were able to confirm the anatomy described by Hasselman et al.
[8] using MRI studies in an
asymptomatic patient population. Our findings confirm the MRI anatomic
descriptions in two previous reports
[5,
6]. The direct and indirect
origins of the proximal rectus femoris were best visualized on axial and
coronal MR images of the hip. Each head's destination, the anterior fascia for
the direct head and the intramuscular substance for the indirect head, was
also clearly depicted on sequential axial images. The lengthy, deep
musculotendinous junction was well depicted on axial, coronal, and sagittal
images.
Deep musculotendinous junction injuries of the proximal rectus femoris are
difficult to clinically diagnose partly because of the deep location of the
injury and partly because of the relatively nonspecific associated physical
findings. Typically, patients with acute deep musculotendinous junction
injuries present with a sudden onset of thigh pain and a tearing sensation.
Persistent pain, tenderness, and rectus femoris asymmetry may be present. A
discrete anterior thigh mass related to muscle retraction can be mistaken for
a soft-tissue neoplasm [4,
5,
8,
9].
Unlike typical strains that are depicted on MRI as focal, increased signal
at the musculotendinous junction
[7], strains of the deep
musculotendinous junction of the rectus femoris, in our study, showed a
longitudinal distribution of increased signal along the involved tendon,
optimally seen on sequential axial images. This type of appearance has also
been described in hamstring injuries
[10].
The most common type of injury noted in our study was a grade II strain
(85%). The relatively mild symptoms of a grade I strain, which rarely require
MRI examination, may explain its scarcity in our study. We speculate that the
length of the deep musculotendinous junction, approximately two thirds of the
muscle belly, may protect it from complete tearing and, thus, may explain the
rarity of grade III strains in our study. It is important to note that the
current grading system of strains was developed for injuries of focal
musculotendinous junctions. This grading system may be less applicable for
longitudinally oriented musculotendinous injuries such as those involving the
rectus femoris. A future prospective study of deep rectus femoris tendon
injuries with a larger patient population may be useful to further assess and
possibly to modify the present grading system.
The bull's-eye sign was seen in 65% of our patients. This sign, coined by
Hughes et al. [4] as increased
signal around the rectus femoris intrasubstance tendon, was seen in our study
in both acute and old injuries and before and after gadolinium injection. We
believe this sign represents evolving stages of injury and healing around the
deep tendon. Initially, the increased signal on fluid-sensitive images likely
represents edema and hemorrhage. Subsequently and after IV gadolinium
injection, the increased signal may reflect increased vascularity and
scarring. A bull's-eye sign with secondary atrophy and fatty infiltration of
the muscle around the tendon reflects remote injury.
The treatment for patients with rectus femoris strains depends on the
degree of injury and athletic involvement of the individual. In
nonprofessional athletes, conservative management aimed at symptom relief is
applied to grade I and II strains. Professional athletes require further
intensive physical therapy to avoid reinjury
[1,
11]. Surgical intervention is
reserved for grade III strains, especially in young, athletic individuals but
may also be necessary for evacuation of a symptomatic pseudocyst or hematoma.
Scar tissue resection has also been recommended to relieve pain and improve
elasticity of the rectus femoris muscle
[4,
12].
There are a few limitations to our study. The retrospective nature of the
study hindered our ability to get a complete clinical history and pertinent
follow-up and may have introduced a sample bias. The small sample pool of
patients and the lack of surgical correlation were other limitations. One
needs to keep in mind, however, that only a small percentage of rectus femoris
deep musculotendinous junction injuries require surgery.
In conclusion, we have outlined the normal MRI anatomy of the proximal
rectus femoris musculotendinous unit and the characteristic MRI features of
deep musculotendinous junction injuries. Greater familiarity with these
longitudinally oriented MRI findings will expedite accurate diagnosis and
appropriate treatment of proximal rectus femoris musculotendinous junction
tears.
Acknowledgments
We thank Leon Rybak for providing us with two cases for this study.
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Abstract
Introduction
