The Meniscal Roots: Gross Anatomic Correlation with 3-T MRI Findings

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1 rody et al. Meniscal Root MRI Musculoskeletal Imaging Pictorial Essay Jeffrey M. rody 1 Michael J. Hulstyn 2 raden. Fleming 3 Glenn. Tung 1 rody JM, Hulstyn MJ, Fleming, Tung G Keywords: anatomy, knee, meniscus, MRI OI: /JR Received pril 10, 2006; accepted after revision ugust epartment of iagnostic Imaging, rown Medical School, Rhode Island Hospital, 593 Eddy St., Providence, RI ddress correspondence to J. M. rody (jbrody@lifespan.org). 2 epartment of Orthopaedic Surgery, rown Medical School, Rhode Island Hospital, Providence, RI. 3 ioengineering Laboratory, rown Medical School, Providence, RI. WE This is a Web exclusive article. JR 2007; 188:W446 W X/07/1885 W446 merican Roentgen Ray Society The Meniscal Roots: Gross natomic orrelation with 3-T MRI Findings OJETIVE. 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. ONLUSION. 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. he meniscus of the knee has several T 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]. y converting the axial load to a radially directed force or hoop stress, the meniscus reduces wear on the hyaline articular cartilage [2]. mong 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]. irect 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. 1). 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]. n 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]. specific association between tears of the posterior lateral root and anterior cruciate ligament (L) has been reported (rmfield R et al., presented at the 2004 annual meeting of the Society of Skeletal Radiology [SSR]). efects 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 merica). espite the growing orthopedic and imaging literature on tears of the meniscal root, W446 JR:188, May 2007

2 Meniscal Root MRI 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 intermediateweighted 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. oronal turbo spinecho images were obtained with the following parameters: TR/TE eff, 3,700/29; field of view, 140 cm; echo-train length, 7; slice thickness, 3 mm; gap, 0 mm; matrix size, ; bandwidth, 352 Hz/pixel; number of signals averaged, 1. Sagittal turbo spin-echo images were obtained with the following parameters: TR/TE eff, 3,700/29; field of view, 160 mm; echo-train length, 5; slice thickness, 3 mm; gap, 0 mm; matrix size, ; bandwidth, 248 Hz/pixel; number of signals averaged, 1. nterior 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. 2). 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. 3). 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 L, with which it partially blends [7, 8] (Fig. 2). Intermingling of fibers of the anterior root of the lateral meniscus with anterior and lateral fibers of the L is present in the cadaveric knee specimen (Fig. 2) and on the MR images (Fig. 3). 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. 3). Unlike tears of the posterior meniscal roots, tears of the anterior meniscal insertions have not been reported, to our knowledge. espite the shared tibial insertion site of both the L 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 L tears (rmfield R 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. 4). 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. 4). The posterior cruciate ligament (PL) inserts on a large portion of the posterior intercondylar area that slopes downward from and posterior in relation to both posterior meniscal roots (Fig. 4). oronal and sagittal MR images depict this anatomic configuration (Fig. 5). lthough the posterior root of the medial meniscus abuts the PL insertion site, neither posterior meniscal root shares its insertion site with the PL. onclusion 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 L and PL. References 1. Krause WR, Pope MH, Johnson RJ, Wilder G. Mechanical changes in the knee after meniscectomy. J one Joint Surg m 1976; 58: osta R, Morrison W, arrino J. Medial meniscus extrusion on knee MRI: is extent associated with severity of degeneration or type of tear? JR 2004; 183: Fairbank TJ. Knee joint changes after meniscectomy. J one Joint Surg r 1948; 30: Rath E, Richmond J. The menisci: basic science and advances in treatment. r J Sports Med 2000; 34: Soames RW. Skeletal system. In: Williams PL, ed. Gray s anatomy, 38th ed. New York, NY: hurchill Livingstone, 1995: Wilson S, Vigorita VJ, Scott WW. natomy. In: Scot WN, ed. The knee. St. Louis, MO: Mosby Year ook, 1994: Kohn. Moreno. Meniscus insertion anatomy as a basis for meniscus replacement: a morphological cadaveric study. rthroscopy 1995; 11: Jacobsen K. rea intercondylaris tibiae: osseous surface structure and its relation to soft tissue structures and applications to radiography. J nat 1974; 117: JR:188, May 2007 W447

3 rody et al. Fig. 1 adaver 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., 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)., Superior-view drawing shows relative locations of tibial insertion sites with soft-tissue structures removed. sterisk indicates anterior cruciate ligament. P = posterior cruciate ligament., Photograph corresponds to. MP = medial tibial plateau, MT = medial tibial tubercle, LT = lateral tibial tubercle, LP = lateral tibial plateau. P = Posterior cruciate ligament. Fig. 2 adaver of 59-year-old man. Photographs show anatomic relations of anterior meniscal roots, transverse genual ligament, and tibial insertion of anterior cruciate ligament (L)., nterior 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 L (asterisk). LP = lateral tibial plateau, LT = lateral tibial tubercle, MP = medial tibial plateau, MT = medial tibial tubercle., nterior 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), L (asterisk), and transverse genual ligament (hook)., nterior view of knee with L 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. W448 JR:188, May 2007

4 Meniscal Root MRI Fig. 3 adaver of 51-year-old woman. Intermediateweighted, 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 (L), and transverse genual ligament., oronal MR image through anterior tibial plateau shows separation of anterior root of medial meniscus (arrow) and transverse genual ligament (arrowhead). MM = medial meniscus., oronal MR image posterior in relation to 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 L (asterisk). P = posterior cruciate ligament, MM = medial meniscus., ontiguous 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 L (asterisk). lack arrowhead indicates Wrisberg s ligament. P = posterior cruciate ligament., Parasagittal MR image lateral to shows insertion of anterior root of lateral meniscus (arrow) intermingling with L (asterisk) posterior in relation to transverse genual ligament (white arrowhead). lack arrowhead indicates Wrisberg s ligament. Fig. 4 adaver 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., 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., Posterior view of knee with cruciate ligaments removed corresponds to. 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. JR:188, May 2007 W449

5 rody et al. E Fig. 5 adaver 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., oronal 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. and, oronal images sequentially more ventral to show insertions of posterior root of lateral meniscus (LM) (white arrow) and posterior root of medial meniscus (MM) (black arrow, ) covering more than one section thickness on posterior intercondylar area. MT = medial tibial tubercle., 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. rrowhead indicates anterior genual ligament. E, 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. ircle indicates shared insertion site of anterior cruciate ligament and anterior root of lateral meniscus. rrowhead indicates anterior genual ligament. P = posterior cruciate ligament. W450 JR:188, May 2007