P. Van Dyck, MD
J. L. Gielen, MD, PhD, Associate Professor F. M. Vanhoenacker, MD, PhD
Department of Radiology, University Hospital Antwerp, Wilrijkstraat 10, 2650 Edegem, Belgium
Sports-related Meniscal Injury
16
Pieter Van Dyck, Jan L . Gielen, and Filip M. Vanhoenacker
Box 16.2. Ultrasound
● No signifi cant role for the detection of meniscal tears
Box 16.4. Standard MRI
● Non-invasive
● The dominant imaging technique for the assessment of meniscal lesions
Because both asymptomatic grade 3 and symptomatic grade 2 lesions exist, MRI fi nd- ings need to be correlated with clinical symp- toms in order to plan treatment optimally.
Box 16.3. MR Arthrography and CT Arthrography
● High accuracy for the evaluation of meniscal injury
● Invasive
● May be useful for the evaluation of the post- operative meniscus
C O N T E N T S
16.1 Introduction 265
16.2 Anatomy and Function 266 16.3 Imaging Modalities in Meniscal Injuries 268 16.3.1 Plain Radiography and
Conventional Arthrography 269 16.3.2 Magnetic Resonance Imaging 269 16.3.2.1 Technique 269
16.3.2.2 Normal MR Anatomy 270
16.3.2.3 Classifi cation of Meniscal Tears 270 16.3.2.4 MR Accuracy and Limitations 274 16.3.3 Computed Tomographic Arthrography 276 16.4 Postoperative Meniscus 276
16.5 Therapeutic Management in Athletes 278 16.6 Specifi c Sports and
Overuse Trauma of the Meniscus 279 16.6.1 Injury Mechanisms in Sports Injury 279 16.6.2 Symptomatic and Asymptomatic Meniscal Lesions in Athletes 280
16.6.3 Musculoskeletal Tumors Around the Knee in
Athletes 280
16.7 Conclusion 281
Things To Remember 281 References 281
Box 16.1. Plain Radiography and Conventional Arthography
● Have been replaced by other (cross-sectional) imaging techniques for the evaluation of meniscal injury
16.1
Introduction
Meniscal injuries are very common among profes- sional and amateur athletes and are a major cause of functional impairment of the knee. It is the most common indication for arthroscopic surgery of the knee. For athletes, unnecessary treatment or inter- vention may be as damaging to a competitive future as failure to diagnose a clinically signifi cant injury.
Therefore, rapid and accurate evaluation of possible injuries in this group is crucial (Ludman et al. 1999).
segments: anterior horn, body, and posterior horn.
Each meniscus measures approximately 5 mm in height along its periphery and tapers to a thin inner edge such that it demonstrates a triangular shape in cross section. The outer rims of the menisci are convex and attached to the fi brous joint capsule and through it to the edges of the articular surfaces of the tibia. The inner edges are concave, thin and free. Their superior surfaces are slightly concave for reception of the femoral condyles, whereas their inferior surfaces that rest on the tibial condyles are fl atter (Fig. 16.1).
The medial meniscus is C-shaped and occupies 50% of the articular contact area of the medial com- partment (Fig. 16.2). Its posterior horn is wider than the anterior horn. Although anatomic variations in meniscal morphology and attachments exist, the anterior horn of the medial meniscus has a fi rm bony attachment to the tibia anterior to the anterior cruci- ate ligament (ACL). The posterior horn is attached immediately in front of the attachment of the pos- terior cruciate ligament (PCL). The outer border of the medial meniscus is fi rmly attached to the knee joint capsule. The meniscotibial and meniscofemoral ligament attach the meniscus to the tibia and femur, respectively, and is referred to as the deep medial col- lateral ligament (Fig. 16.3).
The lateral meniscus is more uniform in width and semicircular, covering 70% of the lateral tibial pla- teau (Fig. 16.2). The anterior horns of the medial and lateral menisci are attached to each other through the transverse ligament. The posterior horn of the lateral Acquisition of a precise history of the injury
mechanism may be diffi cult, as is performance of an accurate physical examination in the setting of an acute injury (Karachalios et al. 2005).
Magnetic Resonance Imaging (MRI) is performed more commonly on the knee than on any other joint, and it is an excellent diagnostic tool that can aid in the evaluation of a host of sports-related injuries involving the ligaments, tendons, menisci, osseous structures, and articular surfaces. It has currently become the most widely used noninvasive imag- ing method for detecting meniscal injuries, with a reported diagnostic accuracy of as high as 98%, com- pared to arthroscopy, remaining the gold standard for confi rming the diagnosis of meniscal tear. MRI is a valuable, cost-effective tool for the preoperative evaluation of the menisci, and proved useful, on the basis of its high negative predictive value, to exclude patients from unnecessary arthroscopy, and, thus, avoiding unnecessary hospitalization, morbidity, and waste of limited fi nancial and manpower resources (Karachalios et al. 2005; Elvenes et al. 2000).
However, radiologists must be aware of numer- ous imaging pitfalls and artefacts simulating a tear and leading to an erroneous diagnosis. Moreover, it must be kept in mind that “silent” meniscal abnor- malities in athletes exist and knowledge of these MR appearances is important in order to avoid attribut- ing a greater signifi cance to these than is clinically justifi ed.
For many years, the meniscus was treated with dis- respect as an unnecessary appendage that could be sacrifi ced with the fi rst hint of malfunction. As long term results after major meniscectomy were disap- pointing, a conservative approach to the manage- ment of meniscal tears has developed over the past two decades, with emphasis on meniscal preservation (Rath and Richmond 2000).
16.2
Anatomy and Function
To evaluate and treat meniscal injuries adequately, understanding of meniscal anatomy and function is necessary. From a gross anatomic perspective, the menisci are C-shaped fi brocartilaginous structures, fi rmly attached to the anterior and posterior aspects of the tibial plateau by the so-called ‘root ligaments’.
Conventionally, they are described as having three
Fig. 16.1 Meniscal anatomy. Each meniscus is arbitrarily divided into anterior horn ( ), body and posterior horn ( ) segments. A cross-section to the body illustrates the superior (SUP) and inferior (INF) articular surfaces, and the more vascularized periphery of the meniscus (red zone), and the relatively avascular inner two thirds of the meniscus (white zone)
Body
**
SUP
INF
*
White
zone Red
➥ zone
meniscus is attached to the medial femoral condyle through the posterior meniscal-femoral (Wrisberg) and anterior meniscal-femoral (Humphrey) liga- ment. Therefore, during rotation, the motion of the lateral meniscus is coupled with that of the femoral condyle. The lateral meniscus has loose attachments to the joint capsule and is separated from it by the popliteus tendon posterolaterally where it courses through a meniscocapsular tunnel. In this region, the superior and inferior popliteal meniscal fascicles are seen, running from the peripheral margin of the meniscus, around the popliteus tendon, to the joint capsule (Fig. 16.4). The lateral meniscus is more mobile and is not anchored to the lateral collateral ligament. In fl exion and internal rotation, the popli- teal tendon retracts the posterior horn, thus reduc- ing entrapment of the lateral meniscus between the femur and the tibia. It is therefore less likely to be injured than the relatively immobile medial menis- cus (Rath and Richmond 2000).
The microanatomy of the menisci may explain injury patterns (Fig. 16.5). A network of type I col- lagen fi bers arranged in a circumferential direction
Fig. 16.2. Diagram of the menisci (seen from above). Note the transverse intermeniscal ligament anteriorly (small arrow), the meniscofemoral ligament attaching to the posterior horn of the lateral meniscus (large arrow), an oblique meniscome- niscal ligament (open arrow) and the popliteus tendon (curved arrow)
Fig. 16.3. The “deep medial collateral ligament”. Coronal fat suppressed PD-WI. The meniscofemoral (small arrow) and meniscotibial (coronary) ligament (large arrow) attach the meniscus to the femur and tibia, respectively, and is referred to as “the deep medial collateral ligament”
Fig. 16.4. Popliteal meniscal fascicles. Sagittal PD-WI. The superior (small arrow) and inferior (large arrow) popliteal meniscal fascicles are seen, running from the peripheral margin of the meniscus, around the popliteus tendon, to the joint capsule
➥
that meniscal tissue is approximately one half as stiff as articular cartilage. The shock absorption capacity of the normal knee is reduced by 20% after meniscec- tomy (Voloshin and Wosk 1983).
It is important to remember that the menisci are not stationary structures. With fl exion and extension of the knee, the medial meniscus translates about 2 to 5 mm on the tibia, and the lateral meniscus translates about 9 to 11 mm (Greis et al. 2002).
The menisci play a key role in enhancing joint stability, largely as secondary soft tissue restraints which prevent anterior tibial displacement (Rath and Richmond 2000). The body of the meniscus prevents the femur from gliding too far off the tibia.
Shoemaker and Markolf (1986) demonstrated that the posterior horn of the medial meniscus is the most important structure resisting an applied ante- rior tibial force in an ACL defi cient knee. Patients who tear the posterior meniscal horn may feel instability – even if their ACL is intact – because this stabilizing effect is lost.
Finally, the menisci contribute signifi cantly to joint lubrication, probably by fl uid exudation across their surfaces. Compression squeezes the liquid out into the joint space, to allow smoother gliding of the joint surfaces. This also helps to distribute synovial fl uid throughout the joint and aids the nutrition of the articular cartilage (Rath and Richmond 2000).
16.3
Imaging Modalities in Meniscal Injuries Although meniscal injuries are extremely common, the clinical history and mechanism of injury are usually non-specifi c, and must be regarded as of little value in determining the diagnosis. Mechanical symptoms of popping, catching, locking or buckling along with joint line pain are suggestive, but not con- clusive, of meniscal pathology, and other types of intra- and extra-articular pathology may confound the clinical picture.
Numerous specialized tests have been described that may aid in making the diagnosis of meniscal tear.
These include joint line palpation, McMurray test, the Apley grind test, and many others. Although confl ict- ing results regarding the diagnostic accuracy of the various meniscal tests have been reported, no spe- cifi c examination maneuver has impressive test per- formance characteristics, with the exception of the
Fig. 16.5. Micro-anatomy of the meniscus. Most collagen bun- dles course in a circumferential direction with fewer radially oriented fi bers, resisting longitudinal splitting
is the dominant morphological pattern, allowing dis- persion of compressive loads and the development of
“hoop stresses”. Radial oriented fi bers (“tie fi bers”) may function to restrain motion between circumfer- ential fi bers and resist longitudinal splitting. At the surface of the meniscus, fi ber orientation is more of a random confi guration (Greis et al. 2002).
The blood supply to the menisci originates from the lateral and medial superior and inferior genicu- lar arteries. These vessels reach the periphery of the meniscus through the synovial covering of the anterior and posterior horn attachments. Vessels are present throughout the substance of the fetal menisci.
Beginning at birth, there is a progressive decrease in vascularity proceeding from the inner to the outer regions of the meniscus. The adult meniscus is avas- cular in the inner two thirds (“white zone”) and ves- sels are most prominent in the peripheral one third of the menisci and in the adjacent coronary and cap- sular ligaments (“red zone”) (Fig. 16.1) (Rath and Richmond 2000).
The menisci are important in many aspects of knee function, with the main functions being tib- iofemoral load transmission and shock absorption (Greis et al. 2002). The menisci compensate for sig- nifi cant incongruity between the femoral and tibial articulating surfaces and increase tibiofemoral con- tact area, with subsequent reduction in joint contact stresses. The menisci transmit at least 50–70% of the load when the knee is in extension. This increases to 85–90% with 90q of knee fl exion. These loads are well distributed when the menisci are intact (Greis et al.
2002). After meniscectomy, tibiofemoral contact area may decrease by 50–70%, leading to a proportional increase in contact and shear stresses across the joint.
These changes will lead eventually to joint degenera- tion. Furthermore, several studies have demonstrated
joint-line tenderness test, which showed an accept- able diagnostic accuracy (Karachalios 2005).
16.3.1
Plain Radiography and Conventional Arthrography
The imaging evaluation of the patient presenting with suspected meniscal pathology should always start with plain radiography. A standard series will include a 30q or 45q posteroanterior fl exion weight- bearing view of both knees, a true lateral radiograph, and a skyline view. The radiographs are inspected for associated skeletal injury or fracture, presence of loose bodies, or degenerative changes.
For decades, conventional fl uoroscopic arthrogra- phy (after sterile preparation and injection of intra- articular contrast medium), was the radiological tech- nique for investigating meniscal injury. Conventional arthrography has the merit of allowing dynamic examination of the knee with application of varus and valgus forces, helping to displace the apposed edges of a meniscal tear which may not otherwise be apparent.
This may be useful when evaluating the postopera- tive meniscus. Although it may be an alternative for patients with a cardiac pace-maker or claustropho- bic symptoms, this imaging modality has now been replaced by cross-sectional imaging techniques.
16.3.2
Magnetic Resonance Imaging
Because of its exquisite contrast resolution and abil- ity simultaneously to display the osseous and soft tissue structures of the knee in virtually any plane, MRI has currently become the most widely used non- invasive imaging method that can aid in the evalua- tion of the entire spectrum of internal derangements of the knee.
16.3.2.1 Technique
Equipment and techniques for MRI vary widely. A circumferential surface coil is mandatory to ensure uniform signal-to-noise across the entire image and provide better spatial resolution. Complete assess- ment of the knee requires that images be obtained in the sagittal, coronal and axial planes.
Sequences that use a short echo time (TE<20 ms), such as T1, proton density (PD) and gradient echo T2*-weighted images, are most sensitive for identi- fying meniscal tears (Fig. 16.6). Long echo-time (T2) sequences are less sensitive but more specifi c. Con- ventional spin-echo sequences are more sensitive to meniscal pathology than fast spin-echo sequences. If a fast spin-echo technique, which offers the advan- tage of faster data acquisition, is used, the echo train
Fig. 16.6a,b. Proton density vs T2-weighted imaging. Fifty-six-year-old male with knee pain at the medial joint line during running since several weeks. a Sagittal PD-WI shows equivocal grade 3 signal in the posterior horn of the medial meniscus. b These fi ndings are not well demonstrated on the sagittal T2-WI
a b
length (ETL) should be kept below four to fi ve and the interecho spacing minimized to reduce blurring effect inherent to this technique that can obscure a meniscal tear. Although useful for the evaluation of the morphology of the meniscus (in complex tears or postoperative partial meniscectomies), fast spin- echo sequences are not recommended for the pri- mary diagnosis of meniscal tears (Rubin et al. 1994).
T2-weighted images using either fast spin-echo techniques with spectral fat saturation (FS) or short inversion time inversion recovery (STIR) can be per- formed in conjunction to enhance the detection of bone marrow edema or contusion.
16.3.2.2
Normal MR Anatomy
The normal menisci demonstrate diffusely low signal intensity on all MRI pulse sequences because of their fi brocartilaginous structure. Menisci must be evalu- ated on both the sagittal and coronal images. Recently, Tarhan et al. (2004) have demonstrated the value of the axial imaging plane for the detection and charac- terization of meniscal tears in standard knee exami- nations, especially when disease existed in the periph- ery of the meniscus. Also, small radial tears of the free edge of the meniscus have been reported to be better visualized in the axial plane (Tarhan et al. 2004).
The most peripheral images of the sagittal plane demonstrate a “bow tie” appearance of the meniscus.
The normal meniscus should have 1.5 to 2 bow ties (5–13 mm) on 4–5 mm thick images. Broad and disk shaped menisci (>13 mm) with three to four or more bow ties are called “discoid” and are more prone to meniscal tears. The normal meniscus measures 3 to 5 mm in height. The medial meniscus varies in width from 6 mm at the anterior horn to 12 mm at the pos- terior horn. The lateral meniscus is approximately 10 mm in width throughout its length.
More centrally, the normal meniscus becomes tri- angular in appearance. The anterior and posterior horns of the lateral meniscus are nearly equal in size, whereas the posterior horn of the medial meniscus is nearly twice the size of the anterior horn.
16.3.2.3
Classifi cation of Meniscal Tears
To understand the signifi cance of increased signal intensity in meniscal abnormalities, an MR grad- ing system has been developed and correlated with a histopathologic model (Fig. 16.7) (Stoller et al.
1987): grade 1, intrasubstance globular-appearing signal not extending to the articular surface; grade 2, linear increased signal patterns not extending to the articular surface; grade 3, the abnormal signal extends to the articular surface. The clinical impor- tance of grade 2 signal abnormality in the meniscus, as seen on MRI and not visualized arthroscopically, is still not well understood. Grades 1 and 2 represent intrasubstance mucinous degeneration in an adult or prominent vascularity in a child and have no surgical signifi cance. Grade 3 is visible by arthroscopy and represents a meniscal tear.
In addition to observing increased signal intensity within tears, the morphology of the meniscus should be assessed when evaluating meniscal lesions.
The “direct” signs (De Smet et al. 2001) associated with meniscal tears on MRI (Fig. 16.8) include:
1. Unequivocal grade 3 signal
2. Abnormal meniscal morphology with displaced or missing meniscal tissue
x Absent bow tie sign (1 or fewer): either postsur- gical or displaced tear
x Double PCL sign: displaced bucket-handle tear of the medial meniscus
x Large anterior horn sign: displaced bucket- handle tear of the meniscus with fl ipped frag- ment
3. Meniscocapsular separation
Fig. 16.7. Grading of intrameniscal signal as seen on MRI.
Grade 0, normal; grade 1, intrasubstance globular-appearing signal not extending to the articular surface; grade 2, linear increased signal patterns not extending to the articular sur- face; grade 3, the abnormal signal extends to the articular sur- face. Only grade 3 signal represents meniscal tear
0
1
2
3
The “indirect” signs (Costa et al. 2004) associated with meniscal tears on MRI include:
1. Abnormal superior popliteomeniscal fascicle and posterior pericapsular edema: lateral meniscal tear, most commonly posterior horn.
2. Posterior bone bruise of the medial tibial plateau:
peripheral tears of the posterior horn of the medial meniscus or tears of the posterior root ligament of the medial meniscus. Tears of this ligament can be associated with ganglioncysts at the posterior aspect of the tibia as well.
3. Extrusion (>3 mm) of the medial meniscus: degen- eration, complex or large radial tear, tear involving the meniscal root.
Meniscal tears can be classifi ed into two primary tear planes: vertical and horizontal (Fig. 16.9). Verti-
cal tears are often of a traumatic origin and occur in younger individuals, whereas horizontal tears are usually secondary to meniscal (mucoid) degenera- tion and occur at later age.
Vertical tears are further subdivided into radial (perpendicular to the surface of the meniscus) and longitudinal (parallel to the long axis of the menis- cus) varieties. An oblique vertical (“fl ap”) tear is the most common meniscal tear type and demon- strates both radial and longitudinal components, as it courses obliquely across the meniscus, resulting in a fl ap of unstable meniscus. They most commonly affect the posterior horn and are seen as predomi- nantly horizontal on sagittal MR images originating along the inferior surface at the free edge.
Radial tears are relatively uncommon meniscal tears and most commonly occur at the junction of
Fig. 16.8a–d. Direct signs of meniscal tear. a Thirty-three-year-old marathon runner with pain at the medial knee joint. Sagittal PD-WI demonstrates equivocal grade 3 signal intersecting the inferior articular surface of the meniscus, representing oblique meniscal tear. b Twenty-two-year-old gym- nast after acute knee dislocation. Coronal fat suppressed PD-WI displays abnormal morphology of the medial meniscus with inferomedial displace- ment of meniscal fragment deep in relation to medial collateral ligament and adjacent to tibial plateau. c,d Fifteen-year-old male with sudden extension defi cit of his right knee while playing football. Coronal fat suppressed PD-WI (c) displays medially displaced lateral meniscal fragment (arrow). On sagittal PD-WI (d), the posterior horn of the lateral meniscus is missing ( ), and seen just behind the slightly anteriorly displaced anterior horn of the meniscus (arrow) (‘fl ipped meniscus’). Arthroscopically, lateral meniscal tear with sub- sequent anterior luxation of the posterior horn was seen
a b c
d
the anterior horn and body of the lateral meniscus and at the meniscotibial attachment of the posterior horn of the medial meniscus. They are often seen as blunting of the free edge on coronal (MR) images. On sagittal images, the only evidence of a radial tear may be increased signal intensity on one or two periph- eral sections (Figs. 16.10 and 16.11).
A bucket-handle tear is an important and not infrequent type of meniscal injury, occurring in about 10% of meniscal tears in most series. It typi- cally consists of a vertical or oblique tear in the pos-
terior horn that extends longitudinally through the body segment and anterior horn, usually occurring acutely with a sudden impact splitting the menis- cus longitudinally. Coronal and sagittal MR images demonstrate blunting of the meniscus donor with the remaining meniscus being smaller than normal.
The inner meniscal fragment is often displaced in the intercondylar notch, creating a “handle”. Reported MRI signs for bucket-handle tears include absent bow tie sign, the double PCL sign, the dispropor- tional posterior horn sign, the anterior fl ipped frag- ment sign and double anterior horn sign (Aydingôz et al. 2003) (Fig. 16.12).
Horizontal tears extend through the meniscus along a plane parallel to the tibial plateau, dividing the meniscus in inferior and superior segments. A horizontal cleavage tear is the most common type of tear to be associated with a meniscal cyst (Fig. 16.13).
These cysts occur as a result of fl uid extruding through the tear by a ball valve effect, and collecting either in the meniscus (intrameniscal cyst) or at the meniscocapsular junction (parameniscal cyst). These cysts tend to recur after resection if the underlying meniscal cyst is not repaired. With a horizontal tear, a portion of the meniscus may fl ip into the adjacent synovial gutter along the margin of the joint. These fragments may be missed easily at arthroscopy, when they are not identifi ed on MRI.
Complex meniscal tears display combinations of vertical and horizontal tear patterns.
Fig. 16.9. Classifi cation of meniscal tears (left to right): periph- eral, longitudinal tear; large and small radial tear; oblique parrot-beak tear; bucket-handle tear; vertical tear; horizontal tear
Fig. 16.10a,b. Radial tear. Thirty-fi ve-year-old female jogger with pain at the medial joint line for some weeks. a Sagittal PD-WI demonstrates vertical oriented grade 3 signal in the posterior horn of the medial meniscus. b Axial fat suppressed PD-WI shows radially oriented tear (arrow) at the junction of the body and posterior horn of the medial meniscus
a b
Fig. 16.12a,b. Bucket-handle tear of the medial meniscus. Twenty-eight-year-old male track athlete felt sudden knee pain after twisting injury. a Coronal fat suppressed PD-WI displays abnormal morphology and grade 3 signal in the medial meniscus with internally displaced meniscal fragment (arrow). b Sagittal fat suppressed PD-WI demonstrates the meniscal fragment (arrow) in front of the PCL (‘double PCL sign’)
a b
Fig. 16.11a–c. Radial tear. Twenty-nine-year-old man after clipping injury while playing football.
CT arthrography with axial (a), coronal (b) and sagittal (c) reformatted images. Axial image dis- plays radially oriented tear at the junction of the body and anterior horn of the lateral meniscus.
Both coronal and sagittal images demonstrate blunting of the free inner edge of the meniscus, typically seen in radial meniscal tear
a
b c
Meniscocapsular separation is a subtype of menis- cal tear, occurring most commonly along the medial meniscus, but the lateral meniscus may be affected also. Typically, the posterior meniscal horn is sepa- rated from the capsule with displacement of the posterior meniscal margin from the posterior tibial border by more than 8–10 mm.
16.3.2.4
MR Accuracy and Limitations
With improved technology, the accuracy of MRI for detecting meniscal injury ranges is now considered to be approximately 95% or better, and it has been shown that the level of experience of the image reader is the most important factor in obtaining the highest level of accuracy (De Smet et al. 1994).
However, MR fi ndings do not always agree with surgical fi ndings. In a study by De Smet et al. (1994), the various causes of incorrect MR diagnoses were analyzed. Of the 83 original diagnostic errors made in the MR evaluation of 800 menisci (accuracy 90%), 33 (40%) were unavoidable errors, 32 (39%) were due to equivocal MR fi ndings and 18 (21%) were inter- pretation errors.
Unavoidable false positive results may be obtained when dealing with a healing or healed meniscal tear. A healing tear (e.g., after meniscal repair) may be seen as hyperintense signal intensity in menis-
cal substance owing to the presence of granulation tissue (Farley et al. 1991). Also, they may be related to incomplete arthroscopic evaluation of the menis- cus. Blind spots for the arthroscopist include the anterior horn of each meniscus, the extreme inner portion of the posterior horn of the medial meniscus, and the undersurface of both menisci. Therefore, it is important to describe any tear in these areas clearly, because they may be easily missed during arthros- copy. Confusion between what represents fraying and what represents a tear may be another source of erro- neous MR diagnosis.
Unavoidable false negative errors are due to limi- tations of the MR sequences and imaging planes and do not represent observer errors. Small meniscal tears may not be discernible with current MR imaging techniques because the edges of small tears may be very closely apposed. Radial tears have been reported to be very diffi cult to visualize on MR images, and these tears account for a large percentage (up to 11%
in the lateral meniscus) of meniscal tears missed by MRI (Justice and Quinn 1995; De Smet et al. 1994).
Furthermore, if a tear of the ACL is present, menis- cal tears are more likely to be missed on MR images.
Presumably, the biomechanical forces that result in an ACL tear cause meniscal tears that are diffi cult to diagnose on MRI, namely in the posterior and peripheral part of the lateral meniscus (De Smet and Graf 1994).
Fig. 16.13a,b. Meniscal cyst. Coronal fat suppressed PD-WI (a) and sagittal PD-WI (b) display large horizontal tear in the lateral meniscus with parameniscal cyst, extending laterally and posteriorly
a b
It is not always possible to neatly categorize menis- cal signal and determine if it is confi ned to the sub- stance of the meniscus or extends through the sur- face (Kelly et al. 1991). MR imaging fi ndings may be equivocal for a tear, leading to both false positive and false negative results. De Smet et al. (1993) found that menisci with signal possibly contacting the sur- face had the same frequency of tears as menisci with- out signal contacting the surface. Furthermore, only 55% of medial and 30% of lateral menisci with signal contacting the surface on only one image were torn.
Thus, when linear signal closely approximates, but
does not convincingly violate an articular surface, it is best to be descriptive rather than overcall a ques- tionable fi nding. If surface contact is seen on only one image, the diagnosis should be qualifi ed as a possible tear. Menisci with internal signal that only possibly contacts the surface should be considered intact.
Interpretation errors may occur due to normal variants (Fig. 16.14). Radiologists must be aware of numerous pitfalls simulating a meniscal tear, includ- ing normal anatomical structures in close proximity to the meniscus (anterior transverse ligament, oblique meniscomeniscal ligament, meniscofemoral liga-
Fig. 16.14a–e. Normal variants simulating a meniscal tear. a Sagittal PD-WI demonstrates the anterior transverse meniscal ligament (small arrow), mimicking a grade 3 signal as it attaches to the anterior horn of the lateral meniscus. Posteriorly, the normal appearance of the meniscofemoral ligament is shown (large arrow), as it arises from the posterior horn of the lateral meniscus, also mimicking a grade 3 signal. b Sagittal PD-WI demonstrates the normal appearance of the popliteus tendon (arrow) as it traverses posteriorly to the lateral meniscus, mimicking a grade 3 signal. c Wrisberg’s variant of discoid lateral meniscus. Sagittal PD-WI shows posterior horn of the lat- eral meniscus unattached to capsule, simulating a vertical meniscal tear. According to Watanabe’s classifi cation system (Watanabe and Takeda 1974) for the discoid lateral meniscus, this is referred to as a type 3 discoid meniscus (Wrisberg’s variant). This variant may have a normal appearance but there is defi ciency of attachment of the posterior-horn meniscotibial ligaments, resulting in instability of the posterior horn. d,e Axial fat suppressed PD-WI (d) shows oblique meniscomeniscal ligament (arrow). On coronal fat suppressed PD-WI (e), a displaced meniscal fragment is simulated (arrow)
a c
e b
d
ment, popliteal tendon, Wrisberg’s variant of discoid lateral meniscus), MR artefacts (volume averaging of adjacent bright structures e.g., fat or fl uid, trunca- tion and motion-blurring artefacts, magic angle phe- nomenon) and pathologic conditions (gas within the joint-vacuum phenomenon or iatrogenic, chondro- calcinosis, cartilage defects, meniscal ossicle).
16.3.3
Computed Tomographic Arthrography
Although MRI is the preferred imaging modality for evaluating internal derangement of the knee, computed tomography (CT) has become a powerful imaging tool because of the development of the spiral acquisition mode and the availability of multidetec- tor row technology that enable submillimeter spatial resolution and multiplanar capacity. Multidetector CT arthrography (CTA) of the knee is an accurate and reproducible method for detecting meniscal abnor- malities (Vande Berg et al. 2000). Vande Berg et al.
found a sensitivity and specifi city for the detection of meniscal abnormalities of 98 and 94%, respectively.
These values are equivalent to those in most studies with MR imaging (Rubin et al. 1994). Furthermore, CTA proved to be an accurate technique for detection of unstable meniscal tears with a sensitivity and spec- ifi city of 97 and 90%, respectively. Poor performance of MR imaging in the recognition of displaced menis- cal fragments smaller than one-third of the meniscus has been reported (Wright et al. 1995).
Other potential advantages of CTA are the short examination time as well as the low sensitivity and limited degree of imaging artefacts related to the presence of microscopic metallic debris which may hinder MR imaging studies. Furthermore, CTA of the knee may be useful for evaluation of the postopera- tive meniscus.
Limitations inherent to the performance of this technique include invasiveness, possible allergic reaction, the use of ionizing radiation and limited value for detection of associated ligamentous and/or soft tissue disorders.
16.4
Postoperative Meniscus
Because meniscal surgery is so common in the young, athletic population, many patients who have under- gone meniscal surgery present with recurrent knee injury or pain. For the radiologist, imaging the post- operative meniscus remains a challenge. As in pre- operative patients, MR imaging is the most valuable imaging method for postoperative evaluation of the knee (McCauley 2005).
Standard MR imaging protocols are less reliable in imaging postoperative knees than in unoperated knees, especially for the diagnosis of meniscal tears, with accuracies ranging from less than 50% to 80%.
Contour abnormalities and diffuse signal changes may be present in both normal postoperative menisci and in recurrent meniscal tears. The basic criteria for identifying a meniscal tear – increased intrameniscal signal on a T1-weighted or proton density-weighted image extending to the meniscal surface – becomes an unreliable predictor in the postoperative knee.
A high signal line that reaches the articular surface (grade 3) may represent an area of meniscal healing and may be misinterpreted as a new tear. Further- more, a partial resection could convert a grade 2 intrameniscal signal into a grade 3 signal, extending to the new surface of the partly resected meniscus (Fig. 16.15). Fluid-intensity signal on a T2-weighted image extending into the meniscus is a stricter cri- terion for recurrent or residual tear, providing high specifi city (92%) but low sensitivity (60%) (Farley et al. 1991).
Fig. 16.15. Normal postoperative meniscus simulating a menis- cal tear. When a partial meniscectomy is performed (dotted lines), hyperintense intrasubstance (grade 1 or 2) signal inten- sity can be converted into grade 3 signal intensity, thus simu- lating a meniscal tear
In an attempt to increase the diagnostic accuracy, MR arthrography (MRA) (with direct injection of the joint with a dilute solution containing gadolinium) has been applied to the postoperative meniscus. The criterion for diagnosing a recurrent or residual tear of the meniscus using MRA is seeing extension of
the gadolinium into the meniscal fragment or into the site of a meniscal repair. Applegate et al. (1993) reported that in the patients in whom a great amount of the meniscus was removed (more than 25%), MR arthrography was signifi cantly more accurate com- pared to conventional MRI (87% vs 65%), whereas in patients with minimal meniscal resection (less than 25%), the two techniques performed equally well (89% accuracy).
However, a recent study comparing conventional MR imaging with MRA found that the increased accuracy of MRA for detection of retorn menisci was not statistically signifi cant (White et al. 2000).
Also, in a study by Sciulli et al. (1999), conventional arthrography, conventional MR, MRA with iodinated contrast material and MRA with gadolinium were compared for the detection of recurrent or residual tear in the postoperative meniscus. The only statisti- cally signifi cant difference was found between con- ventional arthrography and MRA using gadolinium, with accuracies of 58 and 92%, respectively.
Indirect MRA involves an intravenous injection of a gadolinium solution (0.1 mmol/kg) prior to the MRI. Synovial excretion of contrast medium occurs in the minutes after injection to shorten the relax- ation time of the synovial fl uid. This technique has the advantage of not requiring direct access to the joint but lacks the perceived advantages of joint dis- tension, which accompany an intra-articular injec-
tion. Recently, indirect MRA has been proposed for assessment of the natural healing process after meniscal repair (Hantes et al. 2004).
In conclusion, the design of an imaging strategy for investigating patients with recurrent or residual symptoms following meniscal surgery, depends on several factors, including local radiological expertise, hardware resources, multidisciplinary team activity and clinical case mix. Of utmost importance in the evaluation of the postoperative meniscus, is the avail- ability of the preoperative images if possible and the operative report with details of the extent of resec- tion.
In general, most patients do not need to undergo MR arthrography and conventional MRI should be considered as the fi rst line investigation (Magee et al. 2003) (Fig. 16.16). We look for unequivocal sites of fl uid-intensity signal within the meniscal remnant, displaced fragments or tears in a new location, as the only reliable criteria for a recurrent or residual tear.
Standard criteria can be used to interpret areas of the menisci known to be separated from the site of prior surgery. Investigation with MRA (or CTA) could then be considered if conventional MRI is normal (no severe degenerative arthrosis, avascular necrosis, chondral injuries, native joint fl uid extending into a meniscus, or a tear in a new area), if the clinical suspi- cion of recurrent tear is high, or if conventional MRI is inconclusive. In particular, MRA may be useful
Fig. 16.16a–c. Postoperative meniscus-standard MRI. Forty-four-year-old woman received partial medial meniscectomy for bucket-handle meniscal tear after ski trauma 6 months ago. Actually, she presents with knee pain after twisting injury and standard MRI is performed. a,b Sagittal PD-WI (a) and coronal fat suppressed PD-WI (b) show abnormal morphology and increased signal intensity of the medial meniscus due to prior partial meniscectomy. There is no direct sign of recurrent nor residual meniscal tear. However, extensive bone bruise (arrow) in the medial femoral condyle is depicted on the coronal fat suppressed PD-WI. c Sagittal PD-WI shows rupture of the ACL. No further examinations are necessary
a b c
when there is prior knowledge of signifi cant meniscal resection (more than 25%) or meniscal repair with new symptoms in the same area as the initial symp- toms. Furthermore, MR arthrography is of additional value in assessing the articular cartilage, deteriorat- ing more rapidly after meniscectomy.
16.5
Therapeutic Management in Athletes
When faced with a meniscal tear, the orthopaedic surgeon has three options: (1) leave the tear alone, (2) attempt a primary meniscal repair, or (3) per- form a partial or complete meniscectomy. For opti- mal treatment planning, the overall clinical situation must be evaluated.
In older or less-active patients with minor symp- toms, a more conservative approach is often employed.
The mere presence of a meniscal tear in the degen- erative knee is not an indication for arthroscopy. One recent study demonstrated that meniscal tears were a very common magnetic resonance imaging fi nding in asymptomatic patients and that there was no dif- ference in pain or function between osteo-arthritic patients with or without meniscal tears (Miller 2004). However, in athletes, non-operative treatment is usually inadequate for a patient with high physical demands associated with sport, as the reduction in
activity necessitated by the symptoms is not accept- able (Ludman et al. 1999).
Meniscal tear location, extent and stability are essential criteria for deciding whether to resect, repair, or leave alone a meniscal lesion (Weis et al.
1989).
Although MRI provides valuable information by displaying the location and extent of the tear, it is often impossible to determine with certainty whether or not a tear is stable using MRI (unless a displaced fragment is present). Meniscal tear stability is best determined with direct depiction and palpation at arthroscopy (Dandy 1990). Following arthroscopic probing, only those parts that are found to be unstable (displacement of any portion of the meniscus more than 3 mm during probing) will be resected. How- ever, on MRI, tears that are considered stable include (1) a partial-thickness tear (less than half the height of the meniscus), (2) a full-thickness oblique or verti- cal tear measuring less than 7 to 10 mm in length, and (3) a radial tear measuring less than 5 mm (Matava et al. 1999).
Based on MR images, it is important to classify the location of the tear relative to the blood supply of the meniscus. This allows repair potential of the lesion to be predicted. A red-red tear is located at the meniscal periphery within the vascularised zone or represents capsular detachment. It has the best prognosis for healing, as the blood supply persists in this region (Fig. 16.17). The red-white tear has no blood supply from the inner surface of the lesion.
Fig. 16.17a,b. Meniscocapsular injury. Thirteen-year-old female patient sustained acute knee injury while playing tennis. a,b Sagittal PD-WI (a) and coro- nal fat suppressed PD-WI (b) display hyperintense grade 3 signal at the meniscocapsular junction of the posterior horn of the medial meniscus, con- sistent with vertical meniscal tear. As the blood supply per- sists in this region, it has the best prognosis for healing, and therefore, therapeutic manage-
ment will be conservative a b
The remaining vascularity is usually suffi cient for the healing process. A white-white tear is located in the avascular zone and therefore has no potential to heal. A red-red and red-white tear may sponta- neously heal or may be repaired. White-white tears need to be resected.
The treatment goal is to preserve as much func- tional meniscal tissue as possible to lessen the prob- ability of developing osteoarthritis, while addressing the clinical symptoms caused by meniscal tears. The stabilizing effect and vascularization of the periph- eral third of the meniscus is the basis for attempts to preserve this tissue in partial meniscectomies.
Meniscal allograft transplantation is a relatively new concept but the indications are not well defi ned yet. The role of MRI in patients who have undergone meniscal transplantation still requires clarifi cation.
16.6
Specifi c Sports and
Overuse Trauma of the Meniscus
16.6.1
Injury Mechanisms in Sports Injury
Sports-related meniscal tears may result from exces- sive application of force to a normal meniscus (in the young athlete) or normal forces acting on a degen- erative meniscus (in older patients). Meniscal injury, particularly sports-related injuries, usually involve damage due to twisting motions, which are common in sports, with a varus or valgus force directed to a fl exed knee. Contact with another player typically does not occur, nor does lunging or landing awk- wardly. A single “wrong” step is suffi cient.
The most common traumatic mechanism, accounting for nearly half of all injuries, combines valgus force directed to a fl exed knee with the tibia in exorotation (Hayes et al. 2000). Therefore, com- pression with impaction injury usually occurs in the lateral compartment, whereas tension with distrac- tion injury occurs in the medial compartment. Thus, the medial meniscus is at risk for peripheral avul- sion injury at the capsular attachment site resulting in peripheral meniscal tear (and/or meniscocapsular injury) whereas the lateral meniscus gets entrapped by compressive force, splays and splits (because of its more circular shape and decreased radius of curva- ture ) the free margin resulting in a radial tear.
In contact sports, tackles are often directed towards the lateral side of the knee, resulting in the same injury mechanism and type of (meniscal) lesions.
Injury to the medial meniscus is about fi ve times more common than injury to the lateral menis- cus. Compared to the lateral meniscus, the medial meniscus is relatively immobile because of its fi rm attachment to the medial capsule along its peripheral border. The lateral meniscus, loosely applied to the joint capsule, moves freely with the condyle and usu- ally can escape entrapment (Muller 1983).
The trauma-related medial meniscal tear typically demonstrates a vertical orientation extending across the full-thickness of the meniscus. It may redirect itself obliquely towards the free margin of the menis- cus, creating a fl ap confi guration.
Radial tears are rare in the medial meniscus and appear to follow more severe forms of athletic trauma (Kidron and Thein 2002). Kidron and Thein described the presence of a small radial root tear in the posterior horn of the medial meniscus in 11 of the 1270 operated knees (0.86%). Each of these 11 patients, all active in demanding sports, including handball, judo and gymnastics, had a history of acute fl exion injury and medial joint line pain. Arthroscopic trimming of the edges of the tear revealed a develop- ing cleavage plane tear extending to the body of the meniscus, resulting in partial meniscectomy.
Moreover, according to a study by Magee et al.
(2004), the prevalence of meniscal radial tears may be increased in the postoperative knee due to the altered hoop mechanism of the meniscus and decreased ability to transmit loads. These authors found a prev- alence of meniscal radial tears of 32% in the postop- erative knee as opposed to a reported prevalence of 14% in the non-operated knee.
There are signifi cant regional differences in sports-related meniscal injuries depending upon the popularity of specifi c sports. In a study by Baker et al. (1985), meniscectomies performed in Syracuse, New York from 1973 to 1982 were reviewed. Medial vs lateral meniscus injury was 81 vs 19%. Football had a 75% predominance of medial meniscectomy; basket- ball, 75%; wrestling, 55%; skiing, 78%; and baseball, 90%. These data indicate that there are differences in the ratio of medial vs lateral meniscal disrup- tion associated with specifi c sports activities. Medial meniscal injuries were consistently more common in all sports categories, except wrestling, where the fre- quency of lateral meniscal tear is nearly equal to that of a medial meniscal tear.
16.6.2
Symptomatic and Asymptomatic Meniscal Lesions in Athletes
Asymptomatic or “silent” grade 3 intrameniscal signal abnormalities have been described in both athletes and less active patients (Ludman et al.
1999). The incidence of asymptomatic meniscal tears increases with age, with 5.6 to 13% of those less than 45 years old and 36% of those more than 45 years old (Greis et al. 2002). Some studies have suggested that athletic groups, including American football players and marathon runners, show an increased incidence of meniscal abnormalities (Shellock et al. 1991). In a study by Ludman et al. (1999), the overall incidence of grade 3 changes (13%) in gymnasts was not signifi cantly different from the incidence in the controls. However, when compared with the control group, the group of gymnasts had a signifi cantly different distribution of grade 3 intra- meniscal changes, preferentially involving the lat- eral meniscus (evenly divided between the anterior and posterior horn), whereas in the control group, grade 3 changes were mostly found in the medial meniscus (only posterior horn). The reason why the lateral meniscus of gymnasts is preferentially affected is unclear. Nevertheless, knowledge of these MR appearances is important when evaluating the lateral menisci within this group of athletes to pre- vent unnecessary treatment or intervention. This is particularly important when the imaging fi ndings do not closely correlate with the site of symptoms.
On the other hand, symptomatic grade 2 intra- meniscal signal has been described in athletes ( Biedert 1993). In 35 of 43 patients (77.7%) with clinical features of a possible meniscus lesion, a pure intrasubstance tear with linear grade 2 signal was identifi ed on MRI. This type of lesion in the posterior horn represents a frequent cause of false negative result on arthroscopy. All patients were free of symptoms after conservative treatment or par- tial meniscectomy. In this study, the highest rates of intrasubstance tears were found in soccer, running and ice hockey.
Although not specifi cally described in any sports branch, a potential source for false positive interpre- tation for meniscal tear in the MR evaluation of the posttraumatic knee, is the so-called “meniscal contu- sion”. Cothran et al. (2001) described focal signal abnormalities in the knees of six patients who had a history of acute knee trauma, associated with tears of the ACL and bone contusions. This signal reached
the articular surface of the meniscus, but did not meet criteria for a meniscal tear or degeneration. The meniscus gets trapped between, the femur and tibia during a traumatic event. The adjacent bone contu- sion should alert one to the possible presence of a contusion rather than a meniscal tear.
Meniscocapsular tears are a well known entity but may be more diffi cult to diagnose on MR images than meniscal tear. They are most commonly seen along the medial meniscus, which is more tightly adher- ent to the joint capsule. Small avulsed corners of the medial meniscus may be diffi cult to identify unless a directed search is made for them.
Recently, George et al. (2000) have found that anterolateral meniscocapsular separations of the lateral aspect of the knee were frequently missed on MRI reporting in a group of athletes presenting with lateral joint line pain suggestive of meniscal injury.
During arthroscopy, in all patients meniscocapsular separation was confi rmed and no meniscal tears were found. Meniscocapsular tears can also occur along the posterolateral corner of the joint, with disruption of the meniscopopliteal fascicles.
Another entity, recently described in severe acute (sports) injury of the knee by Bikkina et al. (2005), is the so-called “fl oating meniscus”, corresponding to a meniscal avulsion or detachment from the tibial pla- teau with an associated disruption of the meniscotib- ial coronary ligaments, which attach the meniscus to the tibia, allowing fl uid to encompass the meniscus.
It is usually seen as a sequela of high-impact (sports) injury or trauma. The presence of a “fl oating menis- cus” on MRI is often associated with signifi cant liga- mentous injury without evidence of a tear within the substance of the meniscus. Alerting the surgeon to the presence of a meniscal avulsion facilitates appro- priate surgical planning with meniscal reattachment to the tibial plateau.
16.6.3
Musculoskeletal Tumors Around the Knee in Athletes
Musculoskeletal tumors, both benign and malig- nant, are much less common in young athletes than sports-related lesions. However, they frequently occur in the same age group and have a predi- lection for the same joint. In addition, the clini- cal presentation of a musculoskeletal tumor may mimic that of a sports-related injury. At oncologic musculoskeletal centers, it is not uncommon to see
