DOI:10.2214/AJR.06.0509
AJR 2007; 188:W446-W450
© American Roentgen Ray Society
The Meniscal Roots: Gross Anatomic Correlation with 3-T MRI Findings
Jeffrey M. Brody1,
Michael J. Hulstyn2,
Braden C. Fleming3 and
Glenn A. Tung1
1 Department of Diagnostic Imaging, Brown Medical School, Rhode Island Hospital,
593 Eddy St., Providence, RI 02903.
2 Department of Orthopaedic Surgery, Brown Medical School, Rhode Island
Hospital, Providence, RI.
3 Bioengineering Laboratory, Brown Medical School, Providence, RI.
Received April 10, 2006;
accepted after revision August 18, 2006.
Address correspondence to J. M. Brody
(jbrody{at}lifespan.org).
WEB This is a Web exclusive article.
Abstract
OBJECTIVE. The purpose of this article is to highlight the normal
anatomic features of the meniscal roots on photographs of dissected cadaveric
knee specimens and 3-T MR images.
CONCLUSION. The meniscal roots, which are critical attachment sites
of the medial and lateral menisci to the central tibial plateau, are
well-visualized on intermediate-weighted, turbo spin-echo 3-T MRI and can be
identified in proximity to the tibial insertions of the anterior and posterior
cruciate ligaments.
Keywords: anatomy • knee • meniscus • MRI
Introduction
The meniscus of the knee has several important biomechanical
functions, the most important of which are load transmission and shock
absorption [1]. When a person
is upright, as much as 55% of the downward pressure exerted by the femoral
condyle on the articular surface of the tibial plateau is dissipated by
stretching of the circumferential collagen fiber bundles that make up the
central portion of the fibrocartilaginous menisci
[1,
2]. By converting the axial
load to a radially directed force or hoop stress, the meniscus reduces wear on
the hyaline articular cartilage
[2]. Among the first to observe
this critical function of the meniscus was Fairbank
[3], who described the
development of premature chondromalacia and osteoarthritis in patients who had
undergone meniscectomy. Researchers
[4] eventually found a positive
correlation between volume of meniscal tissue resected and subsequent severity
of osteoarthritis.
The meniscus is maintained in optimal position during knee motion by
various direct and indirect attachments to the tibia and femur. The peripheral
borders of the medial and lateral menisci, except at the popliteal tendon
hiatus, are attached to the fibrous joint capsule
[5,
6]. The medial meniscus has a
firm attachment to the deep medial collateral ligament. The lateral meniscus,
however, has no attachment to the lateral collateral ligament
[5]. Meniscofemoral ligaments
course superomedially from the posterior horn to attach the lateral meniscus
directly to the femur [5]. More
laterally, part of the popliteal tendon is attached to the lateral meniscus
[5]. The menisci are attached
to each other anteriorly by the transverse genual ligament
[5]. Direct fixation of the
menisci to the central tibial plateau by fibers originating from the anterior
and posterior horns, the meniscal roots, or entheses is also critical to
proper biomechanical function
[3]. The anterior and posterior
meniscal roots help to resist hoop stress and thereby prevent outward
displacement of the meniscus during axial loading
[3,
7]. These central meniscal
attachments have well-defined relations to each other and the cruciate
ligament insertions (Fig. 1A,
1B,
1C,
1D).
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Fig. 1A —Cadaver of 59-year-old man. Long black arrow indicates anterior root
of medial meniscus (MM); short black arrow, posterior root of medial meniscus;
long white arrow, anterior root of lateral meniscus (LM); short white arrow,
posterior root of lateral meniscus. Superior-view drawing shows relative
insertion site positions on right tibial articular surface.
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Fig. 1B —Cadaver of 59-year-old man. Long black arrow indicates anterior root
of medial meniscus (MM); short black arrow, posterior root of medial meniscus;
long white arrow, anterior root of lateral meniscus (LM); short white arrow,
posterior root of lateral meniscus. Superior-view drawing shows relations to
anterior cruciate ligament (asterisk), posterior cruciate ligament
(P), posterior meniscofemoral Wrisberg's ligament (black arrowhead),
and transverse genual ligament (white arrowhead).
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Fig. 1C —Cadaver of 59-year-old man. Long black arrow indicates anterior root
of medial meniscus (MM); short black arrow, posterior root of medial meniscus;
long white arrow, anterior root of lateral meniscus (LM); short white arrow,
posterior root of lateral meniscus. Superior-view drawing shows relative
locations of tibial insertion sites with soft-tissue structures removed.
Asterisk indicates anterior cruciate ligament. P = posterior cruciate
ligament.
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Fig. 1D —Cadaver of 59-year-old man. Long black arrow indicates anterior root
of medial meniscus (MM); short black arrow, posterior root of medial meniscus;
long white arrow, anterior root of lateral meniscus (LM); short white arrow,
posterior root of lateral meniscus. Photograph corresponds to C. MP =
medial tibial plateau, MT = medial tibial tubercle, LT = lateral tibial
tubercle, LP = lateral tibial plateau. P = Posterior cruciate ligament.
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Malposition of the meniscus is well visualized on MRI. MRI has been used to
detect meniscal extrusion, which is abnormal subluxation of the meniscus, and
to help identify its cause. Meniscal extrusion has been associated with a tear
that disrupts the meniscal ring, as in disruption of the posterior meniscal
root, deep radial tears, and complex meniscal tears
[2]. An important association
also has been reported between meniscal extrusion and increasing degrees of
intrasubstance meniscal degeneration in which loss of the integrity of
collagen in a degenerated but not torn meniscus allows hoop stress to displace
the meniscus [2].
A specific association between tears of the posterior lateral root and
anterior cruciate ligament (ACL) has been reported (Armfield DR et al.,
presented at the 2004 annual meeting of the Society of Skeletal Radiology
[SSR]). Defects of the articular cartilage of the posterior medial femoral
condyle have been linked to tears of the posterior medial meniscal root
(Pessis E et al., presented at the 2005 annual meeting of the Radiological
Society of North America). Despite the growing orthopedic and imaging
literature on tears of the meniscal root, little has been written correlating
the gross anatomic features of normal meniscal roots with their appearance on
MRI. To better understand the MRI appearance and highlight the normal anatomic
features of the meniscal roots, we dissected cadaveric knee specimens after
3-T MRI performed with an intermediate-weighted turbo spin-echo pulse
sequence.
Imaging Parameters
Imaging was performed with a 3-T MRI system (Trio 3-T, Siemens Medical
Solutions) with a 40-mT/m gradient. Coronal turbo spinecho images were
obtained with the following parameters: TR/TEeff, 3,700/29; field
of view, 140 cm; echo-train length, 7; slice thickness, 3 mm; gap, 0 mm;
matrix size, 307 x 384; bandwidth, 352 Hz/pixel; number of signals
averaged, 1. Sagittal turbo spin-echo images were obtained with the following
parameters: TR/TEeff, 3,700/29; field of view, 160 mm; echo-train
length, 5; slice thickness, 3 mm; gap, 0 mm; matrix size, 313 x 448;
bandwidth, 248 Hz/pixel; number of signals averaged, 1.
Anterior Roots of the Menisci
The anterior intercondylar portion of the tibia is divided into medial and
somewhat depressed lateral segments by a sagittal ridge of bone called the
anterior intercondylar crest
[6,
8] (Fig.
2A,
2B,
2C). The anterior root of the
medial meniscus has the largest footprint of the four meniscal roots and
inserts broadly on the anterior intercondylar crest
[7,
8]. On intermediate-weighted MR
images, the meniscal root appears as striated hypointense fibers compared with
the homogeneously hypointense signal intensity of the meniscal body and horns
(Fig. 3A,
3B,
3C,
3D). The anterior root of the
lateral meniscus inserts on a smaller area posterior in relation to or on a
portion of the anterior intercondylar crest in front of the lateral tibial
tubercle and lateral to the ACL, with which it partially blends
[7,
8] (Fig.
2A,
2B,
2C).
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Fig. 2A —Cadaver of 59-year-old man. Photographs show anatomic relations of
anterior meniscal roots, transverse genual ligament, and tibial insertion of
anterior cruciate ligament (ACL). Anterior view of knee with menisci and
ligaments removed shows outlined insertional footplate of anterior root of
medial meniscus (black arrow) on anterior intercondylar crest
(arrowheads), anterior root of lateral meniscus (white
arrow), and tibial insertion site of ACL (asterisk). LP =
lateral tibial plateau, LT = lateral tibial tubercle, MP = medial tibial
plateau, MT = medial tibial tubercle.
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Fig. 2B —Cadaver of 59-year-old man. Photographs show anatomic relations of
anterior meniscal roots, transverse genual ligament, and tibial insertion of
anterior cruciate ligament (ACL). Anterior view of knee with meniscus and
ligaments in place shows relations of anterior root of medial meniscus
(black arrow), anterior root of lateral meniscus (white
arrow), ACL (asterisk), and transverse genual ligament
(hook).
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Fig. 2C —Cadaver of 59-year-old man. Photographs show anatomic relations of
anterior meniscal roots, transverse genual ligament, and tibial insertion of
anterior cruciate ligament (ACL). Anterior view of knee with ACL removed
(asterisk) shows shared insertion of anterior root of lateral
meniscus (white arrow) and fibers of anterior root of medial meniscus
(black arrow) in foreground.
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Fig. 3A —Cadaver of 51-year-old woman. Intermediate-weighted, fat-saturated,
turbo spin-echo (TR/TEeff, 3,700/29) 3-T MR images of knee show
anatomic relations of anterior meniscal roots, anterior cruciate ligament
(ACL), and transverse genual ligament. Coronal MR image through anterior
tibial plateau shows separation of anterior root of medial meniscus
(arrow) and transverse genual ligament (arrowhead). MM =
medial meniscus.
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Fig. 3B —Cadaver of 51-year-old woman. Intermediate-weighted, fat-saturated,
turbo spin-echo (TR/TEeff, 3,700/29) 3-T MR images of knee show
anatomic relations of anterior meniscal roots, anterior cruciate ligament
(ACL), and transverse genual ligament. Coronal MR image posterior in relation
to A shows proximity of insertion (circle) of anterior root of
lateral meniscus (LM) on lateral slope of medial tibial tubercle (MT) to
tibial insertion site of ACL (asterisk). P = posterior cruciate
ligament, MM = medial meniscus.
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Fig. 3C —Cadaver of 51-year-old woman. Intermediate-weighted, fat-saturated,
turbo spin-echo (TR/TEeff, 3,700/29) 3-T MR images of knee show
anatomic relations of anterior meniscal roots, anterior cruciate ligament
(ACL), and transverse genual ligament. Contiguous midline MR image shows
insertion of anterior root of medial meniscus (arrow) on
intercondylar crest anterior in relation to transverse genual ligament
(white arrowhead) and ACL (asterisk). Black arrowhead
indicates Wrisberg's ligament. P = posterior cruciate ligament.
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Fig. 3D —Cadaver of 51-year-old woman. Intermediate-weighted, fat-saturated,
turbo spin-echo (TR/TEeff, 3,700/29) 3-T MR images of knee show
anatomic relations of anterior meniscal roots, anterior cruciate ligament
(ACL), and transverse genual ligament. Parasagittal MR image lateral to
B shows insertion of anterior root of lateral meniscus (arrow)
intermingling with ACL (asterisk) posterior in relation to transverse
genual ligament (white arrowhead). Black arrowhead indicates
Wrisberg's ligament.
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Intermingling of fibers of the anterior root of the lateral meniscus with
anterior and lateral fibers of the ACL is present in the cadaveric knee
specimen (Fig. 2A,
2B,
2C) and on the MR images (Fig.
3A,
3B,
3C,
3D). The transverse genual
ligament links the anterior horns of the medial and lateral menisci. On
sagittal MR images, the anterior root of the medial meniscus can be identified
just anterior in relation to the transverse genual ligament, and the anterior
root of the lateral meniscus is posterior to this ligament (Fig.
3A,
3B,
3C,
3D). Unlike tears of the
posterior meniscal roots, tears of the anterior meniscal insertions have not
been reported, to our knowledge. Despite the shared tibial insertion site of
both the ACL and anterior root of the lateral meniscus, tear of the posterior
root of the lateral meniscus has been reported in a small percentage of acute
ACL tears (Armfield DR et al., presented at the 2004 annual meeting of the
SSR).
Posterior Roots of the Menisci
Most of the posterior root of the lateral meniscus inserts on a horizontal
part of the posterior intercondylar area, but some fibers attach to the
posterior slope of the lateral tubercle and along the intertubercular bony
crest that connects the medial and lateral tibial tubercles (Fig.
4A,
4B,
4C). The small oval insertion
site of the posterior root of the medial meniscus is on the posterior slope of
the medial tibial tubercle, which is posterior in relation to the insertion
site of the posterior root of the lateral meniscus
[7,
8] (Fig.
4A,
4B,
4C). The posterior cruciate
ligament (PCL) inserts on a large portion of the posterior intercondylar area
that slopes downward from and posterior in relation to both posterior meniscal
roots (Fig. 4A,
4B,
4C). Coronal and sagittal MR
images depict this anatomic configuration (Fig.
5A,
5B,
5C,
5D,
5E). Although the posterior
root of the medial meniscus abuts the PCL insertion site, neither posterior
meniscal root shares its insertion site with the PCL.
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Fig. 4A —Cadaver of 59-year-old man. Photographs show anatomic relations of
posterior meniscal roots and tibial insertion of anterior and posterior
cruciate ligaments. Posterior view of tibial plateau with menisci and
ligaments removed shows outlined insertion sites of posterior root of lateral
meniscus (white arrow), posterior root of medial meniscus (black
arrow), and posterior cruciate ligament (P). MP = medial tibial plateau,
MT = medial tibial tubercle, LT = lateral tibial tubercle, LP = lateral tibial
plateau.
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Fig. 4B —Cadaver of 59-year-old man. Photographs show anatomic relations of
posterior meniscal roots and tibial insertion of anterior and posterior
cruciate ligaments. Posterior view of knee shows insertion of posterior root
of lateral meniscus (LM) (white arrow) is farther anterior than those
of posterior root of medial meniscus (MM) (black arrow) and posterior
cruciate ligament (P). Insertion of anterior cruciate ligament
(asterisk) is anterior to intertubercular ridge but appears closer to
posterior root of lateral meniscus owing to photographic distortion.
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Fig. 4C —Cadaver of 59-year-old man. Photographs show anatomic relations of
posterior meniscal roots and tibial insertion of anterior and posterior
cruciate ligaments. Posterior view of knee with cruciate ligaments removed
corresponds to B. Long white arrow indicates anterior root of lateral
meniscus (LM). Short white arrow = posterior root of lateral meniscus, black
arrow = posterior root of medial meniscus (MM), MT = medial tibial tubercle,
LT = lateral tibial tubercle, P = posterior cruciate ligament.
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Fig. 5A —Cadaver of 59-year-old man. Intermediate-weighted, fat-saturated,
turbo spin-echo (TR/TEeff, 3,700/29) 3-T MR images show anatomic
relations of posterior meniscal roots and cruciate ligaments. Coronal MR image
shows posterior root of medial meniscus (MM) (arrow) covering more
than one section thickness on posterior intercondylar area. LM = lateral
meniscus. LT = lateral tibial tubercle.
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Fig. 5B —Cadaver of 59-year-old man. Intermediate-weighted, fat-saturated,
turbo spin-echo (TR/TEeff, 3,700/29) 3-T MR images show anatomic
relations of posterior meniscal roots and cruciate ligaments. Coronal images
sequentially more ventral to A show insertions of posterior root of
lateral meniscus (LM) (white arrow) and posterior root of medial
meniscus (MM) (black arrow, B) covering more than one section
thickness on posterior intercondylar area. MT = medial tibial tubercle.
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Fig. 5C —Cadaver of 59-year-old man. Intermediate-weighted, fat-saturated,
turbo spin-echo (TR/TEeff, 3,700/29) 3-T MR images show anatomic
relations of posterior meniscal roots and cruciate ligaments. Coronal images
sequentially more ventral to A show insertions of posterior root of
lateral meniscus (LM) (white arrow) and posterior root of medial
meniscus (MM) (black arrow, B) covering more than one section
thickness on posterior intercondylar area. MT = medial tibial tubercle.
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Fig. 5D —Cadaver of 59-year-old man. Intermediate-weighted, fat-saturated,
turbo spin-echo (TR/TEeff, 3,700/29) 3-T MR images show anatomic
relations of posterior meniscal roots and cruciate ligaments. Sagittal image
through posterior cruciate ligament (P) shows insertion site of posterior root
of medial meniscus (arrow) just anterior in relation to insertion
site of ligament. MT = medial tibial tubercle. Arrowhead indicates anterior
genual ligament.
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Fig. 5E —Cadaver of 59-year-old man. Intermediate-weighted, fat-saturated,
turbo spin-echo (TR/TEeff, 3,700/29) 3-T MR images show anatomic
relations of posterior meniscal roots and cruciate ligaments. Sagittal MR
image through anterior cruciate ligament (asterisk) shows insertion
site of posterior root of lateral meniscus (arrow) slightly anterior
in relation to insertion site of medial meniscus. Circle indicates shared
insertion site of anterior cruciate ligament and anterior root of lateral
meniscus. Arrowhead indicates anterior genual ligament. P = posterior cruciate
ligament.
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Conclusion
The meniscal roots, which are critical attachment sites of the medial and
lateral menisci to the central tibial plateau, are well visualized on
intermediate-weighted turbo spin-echo 3-T MRI and can be identified in
proximity to the tibial insertions of the ACL and PCL.
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Abstract
Introduction
