Skeletal Radio1 (1990) 19:441445 Skeletal Radiology

Ultrasound in degenerative cystic meniscal disease of the knee L u e a D e Flavi is , M . D . 1, P ie tro S c a g l i o n e , M . D . 1, R e n a t o Ness i , M . D . 2, and Walter Albisett i , M . D . 3

1 Radiological Service, Istituti Clinici di Perfezionamento, C.T.O., Milan, Italy, 2 Institute of Radiology and 3 Institute of Orthopaedics, University of Milan, Italy

Abstract. Ultrasonography of the knee joint using small- parts probes was performed on 27 patients with clinical findings suggestive of meniscal cystic degeneration. Sur- gical or arthroscopic confirmation of sonographic find- ings was obtained in all cases. Sonography delineated the shape and structure of the meniscal profile and any degenerative changes. In the initial stage (6/27 patients, 22%), minor structural irregularities could be observed. Small, round, transonic cysts were found in 8 patients (30%); these lay mainly within the meniscus and were movable during stress flexion of the leg. In more ad- vanced cases (8/27, 30%), larger cysts sometimes pro- truded on the skin surface. In 3 patients (12%), the soft tissue swelling was associated with a normal sonographic aspect of the menisci, but sonography could demonstrate an effusion of extra-articular origin. Ultrasound is a sim- ple and effective method for the assessment of degenera- tive cysts of the menisci. It allows a reliable differential diagnosis between meniscal cysts and other causes of soft tissue swelling, and it is well suited for monitoring the course of the disease.

Key words" U l t r a s o u n d - K n e e - Menisc i - Meniscal cyst

Degenerative disease of the menisci is far less common than meniscal injury. It may therefore be responsible for long-lasting pain and for disabling functional limita- tions. The pathological basis of degenerative meniscal disease is related to regressive changes within the menis- cal structure, with the formation of intrameniscal cysts [8]. These fluid-filled cavities are probably a conse- quence of repeated microtraumas [4, 10, 12, 15]. This hypothesis is confirmed by the higher frequency of cysts in the lateral meniscus than in the medial one. The lateral

Address reprint requests to: Luca De Flaviis, M.D., v. le Tunisia 22, 1-20124 Milano, Italy

meniscus, in fact, is mainly submitted to static pressure forces, which may result in repeated microtraumas, while the medial meniscus is much more involved in rotation and flexion of the leg and is therefore mainly exposed to acute injuries [1, 3, 7]. In addition, the lateral men- iscus is more circular in shape, and it is more mobile than the medial one. All these points help to explain why cystic degeneration occurs more frequently in the lateral meniscus.

The clinical presentation of cystic meniscal change is usually characterized by pain, which is mainly present at evening or after joint overloading. On physical exami- nation, a localized swelling can sometimes be observed at the level of the joint space; this mass may change its shape and size with different degrees of flexion of the leg.

The radiographic diagnosis of meniscal degeneration is quite difficult, and it may be impossible in some pa- tients. Plain x-ray films of the knee are often completely negative, or they may disclose only signs of osteoarthro- sis. Arthrography may show an increase of meniscal width and a protrusion of the outer edge of the meniscus [14]; sometimes, an associated meniscal tear may reveal the cyst by contrast filling of its cavity. Such findings are, however, unpredictable, and they require an invasive and time-consuming procedure like arthrography. Mag- netic resonance imaging (MRI) is a very effective diag- nostic procedure in meniscal diseases [13], but the costs and complexity of this examination may limit its wide- spread application as a first step in patients presenting with swelling or pain of the knee joint.

For these reasons, it was considered worthwhile to assess the value of ultrasonography in the diagnosis of meniscal degenerative changes. The possibilities of so- nography for the study of trauma to the knee joint and ofcapsuloligamentous disorders have been reported else- where [5, 11, 14]. Sonography is becoming a useful diag- nostic aid in orthopedic and rheumatologic diagnosis [6, 9, 13, 14].

�9 1990 International Skeletal Society

442 L. De Flaviis et al. : US in degenerative cystic meniscal disease

Materials and methods

Sonographic examination of the knee was performed on 27 pa- tients, predominantly male (17/27, 63%), with clinical symptoms suggestive of meniscal cystic degeneration; in 2 (7%), symptoms had recurred after surgical treatment.

Preliminary x-ray films were taken in all the patients; xerora- diography of the soft tissues was performed in 24/27 patients (89%). In the majority (22/27, 81%), the ultrasound scans were taken of the lateral compartment of the knee, in accordance with the clinical presentation and symptoms. Cystic degenerative disease is prevalent at the level of the lateral meniscus [2, 3].

Real-time ultrasound scans were obtained (Philips, Ansaldo- EsaOte Biomedica) with 5- and 6-MHz linear transducers used jointly with a transonic stand-off path (Proxon). In selected cases, the scans were taken with a small-parts 10-MHz sector probe (Phi- lips). This allowed us to perform the most accurate, detailed stu- dies. The scans were obtained mainly in the coronal plane, with the leg in extension or in mild flexion (30~ The examination was completed with multiple oblique and transverse views, to provide essential information about the articular space and the periarticular bursae. In the presence of small cysts (< 5 mm diameter), sonogra- phy was carried out during stress movements of the leg, with forced varus or valgus flexion, in order to distinguish between meniscal cysts and other fluid collections.

All the patients examined in this study were submitted to surgi- cal or arthroscopic control eventually. The records were retrospec- tively evaluated, and correlation between the sonographic picture and the pathological findings was established.

Results

The sonographic appearance o f normal menisci is quite typical [13, 14]. The meniscal f ibrocarti lage appears as a homogeneous structure, modera te ly echogenic, trian- gular in shape, with a clear-cut external border. The meniscal wall can be easily distinguished f rom the over- lying soft tissue planes, in part icular fascial and capsular structures (Fig. 1).

Sonography allowed us to appreciate the structural changes o f the menisci and to distinguish between differ- ent degrees o f degenerat ion that we classified into 3 stages according to the sonographic pattern.

In 6/27 patients (22%), only minor irregularities o f the meniscal border could be observed (stage I), with a ~prevalent hypoechoic structure and thickening o f the meniscal wall (Fig. 2). In all these patients, clinical symp- toms were present, but there was no palpable swelling on the knee surface; the rad iograph was always normal .

In 8/27 patients (30%), the structural irregularities o f the menisci were associated with the presence o f one or more t ransonic cavities, due to the fo rmat ion of men- iscal microcysts (stage 2), ranging f rom 1 to 4 m m in diameter (Figs. 3, 4).

In more advanced cases (8/27, 30%), the necrotic histolysis within the menisci causes the fo rmat ion o f large cysts (stage 3), which can be recognized in the ex- ternal por t ion o f the meniscus and o f the meniscal wall (Figs. 5, 6). In some cases, degenerative changes were related also to the presence o f meniscal calcifications (Fig. 7), which, however, were easily demons t ra ted in all cases by x-ray films or xeroradiography.

It is interesting to observe that in the remaining 3 pa- tients (12%) the presence o f typical symptoms and o f

soft tissue swelling was associated with a normal sono- graphic aspect o f the menisci. In each o f these patients sonography demons t ra ted the extra-art icular origin o f the swelling, which was due to synovial effusions at the level o f the pes anserinus (Fig. 8), o f peroneat muscles (Fig. 9) or o f Hoffa ' s adipose tissue (Fig. 10).

The displacement o f the lesion in the deeper por t ion o f the art icular space during stress movements o f the knee joint is a characterist ic sonographic sign o f a menis- cal cyst (Fig. 4). This happens dur ing varus flexion for the cysts o f the lateral meniscus and during valgus flex- ion for the cysts o f the medial one. This maneuver ma y be ineffective when the cysts are very large, or when p ro t rud ing cavities extend to the periart icular structures outside the joint space (Fig. 6).

Discussion

Our results conf i rm the value o f u l t rasound in the diag- nosis o f degenerative cystic lesions o f the menisci. It seems possible, on the basis o f the present evidence, to correlate the sonographic picture with the degree o f the cystic change and with the stage o f the disease, while x-ray diagnosis o f meniscal degenerat ion is very unpre- dictable and m a y be frankly impossible.

M R I o f the knee allows a clear and complete evalua- t ion o f the meniscal disorder; the procedure is, however, costly and t ime-consuming. For these reasons, we think that M R I canno t at present be accepted as the pr imary diagnostic tool in patients with knee pain and suspected meniscal cysts. Ul t rasound , on the contrary , provides a simple and effective first approach to evaluate the state

Fig. 1. Ultrasound longitudinal scan of the lateral aspect of a nor- mal knee. The articular space can be clearly seen between the femur (F) and the tibia (7). The meniscal wall is sharply outlined, and it possesses a homogeneous echoic pattern (arrow)

Fig. 2. In stage 1 meniscal degeneration the meniscal wall becomes hypoechoic and shows a heterogeneous structure; its border pro- trudes beyond the articular space (arrows). F, femur; T, tibia

Fig. 3A, B. In stage 2 degenerative disease the colliquative process may lead to meniscal cyst formation. In this patient, the meniscal wall is weakly echogenic (A) and a clear swelling of the periarticular soft tissues is seen (arrows). A small transonic cyst can be clearly seen within the meniscal profile. Note that the xeroradiographic picture is almost normal at this stage (B). F, femur; T, tibia

Fig, 4. This small meniscal cyst (left) tends to move into the articu- lar space when the knee joint is submitted to stress flexion (right)

Fig. 5A-C. In a more advanced case (stage 3) the meniscal cysts can be found grouped in clusters, which may determine a localized thickening of the periarticular soft tissues (hi). This may be well appreciated also with xeroradiography (B). See the operative find- ings for comparison (C), F, femur; T, tibia

Fig. 6A-C. Huge meniscal cyst that appears as a large hypoechoic cavity at sonography (A) and can be appreciated as a periarticular soft tissue swelling at xeroradiography (B). The surgical findings confirm the sonographic picture (C). F, femur; T, tibia

444 L. De Flaviis et al. : US in degenerative cystic meniscal disease

Fig. 7A, B. Chondrocalcinotic degenerative changes are easily dem- onstrated by x-ray films and xeroradiography (A). In the ultra- sound image (B) they correspond to hyperechoic plaques (arrows). In these cases, however, sonography may be less effective than x-ray studies owing to the deep location of the calcific deposits within the articular space. F, femur; T, tibia

Fig. 8A, B. Synovial cyst at the level of the pes anserinus. This fluid-filled cavity is well demonstrated by xeroradiography (A). The ultrasound picture shows the transonic pattern of the lesion and allows appreciation of its extra-articular location, distinguish- ing it from a meniscal cyst

Fig. 9. A peroneal cyst appears as a transonic cavity within the superficial soft tissue planes of the knee, well separated from the articular space. F, femur; T, tibia

Fig. IOA, B. Cysts arising from Hoffa's body are located in the anterior aspect of the knee. In this case, sonography (A) demon- strates the presence of a hypoechoic fluid collection (arrows) on the front of the articular space. The superficial position of the cyst is confirmed by this oblique view xeroradiograph (B)

o f the meniscal border and to detect the presence o f cystic cavities. Fur ther when these lesions are not yet evident, sonography m ay disclose an irregular structure o f the cartilage and o f the meniscal wall, which is the expression o f intercellular edema and vascular prolifera- tion. W h e n degenerative histolysis occurs, the presence o f intrameniscal fluid collections is easily detected by ul t rasound. Meniscal cysts are typically movable during

stress flexion o f the knee. This finding, together with their characteristic locat ion within the meniscal wall, is a diagnostic l andmark for distinguishing meniscal cysts f rom other para-ar t icular fluid collections.

Meniscal sonography is quick to perform, and it does no t cause any d iscomfor t to the patient. However , it requires a dedicated soft tissue probe. A 10-MHz trans- ducer is by far the best solution.

L. De Flaviis et al. : US in degenerative cystic meniscal disease 445

S o n o g r a p h y can c o m p l e m e n t cl inical e x a m i n a t i o n in all cases o f suspec ted menisca l cyst ic degene ra t i on or o f pa in in the knee j o i n t o f unexp la ined origin. The u l t ra - sonic p ic ture a lways a l lows a d i s t inc t ion be tween menis- cal cysts a n d pe r i - a r t i cu l a r synovia l effus ions o f the me- dia l a n d la te ra l aspects o f the knee. In es tab l i shed cases, u l t r a son ic m o n i t o r i n g is an effective w a y to assess p ro - gress a n d the effect iveness o f the the rapy .

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