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Letters to the Editor |
zmir, Turkey
Dear Editor:
We read with great interest the article by Morgan-Jones et al. entitled "The Meniscal ‘Pseudocyst’-A Clinical Sign of a Torn Meniscus" (October 2001, pages 543 to 544). Our opinion, however, on the reported abnormality, that is, lateral joint line swelling, is somewhat different. We believe that we have enough experience to comment on the disorder and its findings on MRI. Magnetic resonance images demonstrate the abnormalities very nicely; in contrast to what they have been called in the literature, we believe these cysts-including the 30 cases in the current article-are not true (fluid-filled) cysts. We have done a study of mucoid (cystic) degeneration of the meniscus1; in brief, this malady is an excessive accumulation of mucopolysaccharides in the meniscal tissue. There are two forms of the degeneration, stromal and cystic parameniscal. The latter form is usually seen in the lateral meniscus due to loose capsular attachment, and appears as a swelling on the lateral joint line. This is the so-called lateral meniscal cyst. Meniscal mucoid degeneration is more frequently seen in the medial meniscus, but it is rarely seen as a medial joint line swelling, probably because of the medial collateral ligament; it appears as stromal degeneration.
The authors did not have any MRIs of their cases; if they have MRIs in the future, it is likely that they will notice a tumor-like protrusion of the affected meniscus peripherally. We think that their cases in both groups (30 cysts, 28 pseudocysts) may indeed be the same. The authors do not clearly describe the cyst that was found in 30 patients. Their decision as to whether there was or was not a cyst is not clearly stated. It is impossible to see a cyst arthroscopically; the surgeon can only see the mucoid degeneration with its typical yellowish discoloration at the beginning of the meniscal resection when using the mechanical hand instruments.
In the current article, the common abnormality in both cyst groups was a tear of the lateral meniscus. This is an important finding that supports our opinion. A torn meniscus is an expected finding in such cases because menisci affected by mucoid degeneration are easily torn; most of the time there is no history of trauma.
We would like to kindly warn the authors and the readers that important historical data are missing from the article. In their series, all the meniscal pseudocysts became most prominent at 45° of knee flexion. This sign was reported as the "disappearing sign" for lateral meniscal cysts by Antony J. Pisani2 in 1947. He stated that the swelling was most prominent in 25° to 30° of flexion and disappeared on acute flexion. We, as did Smillie,3 have also observed the sign in 45° of flexion. As Smillie reported, this sign either disappears or becomes much less prominent in full extension. As stated by Pisani, the sign is pathognomonic for lateral meniscal "cysts." Pisani’s sign was positive in all of the cases that we studied.1 The authors do not state if the sign was also positive for the 30 cases with "true" cysts.
We would like to share with readers our contribution to the verification of Pisani’s sign, which we hope will eventually be published.1 With the knee in 45° of flexion, the lateral swelling becomes even more prominent with external rotation of the leg and disappears with internal rotation. By using this external rotation maneuver, we have detected some cysts that were invisible, even in 45° of flexion in neutral rotation. Accordingly, this sign should be looked for whenever middle-third lateral joint line tenderness is elicited by palpation.
Thanks to the authors for giving us the opportunity to discuss lateral joint line swelling. It is our observation that their findings were not true cysts (filled with fluid); the term pseudocyst is also a misnomer. Surprisingly, little attention has been paid in the literature to meniscal mucoid degeneration. We hope our study will disclose at least some aspects of this particular "disease" of the meniscus.
REFERENCES
Cardiff, Wales
My coauthors and I thank Drs. Pinar and Boya for their letter and observations. We agree that the lateral joint line swellings described in our article were not true cysts filled with fluid. The pseudocystic swelling outlined in our article results from the hinged, infolded deformity of the torn meniscus. Our article was not the report of a histologic study and we therefore cannot comment on any meniscal mucoid degeneration that may have been present.
We believe the importance of our article was the advocation of a thorough clinical examination, which routinely includes inspection and palpation with side-to-side comparison of the medial and lateral joint lines for pseudocystic swellings, which may correlate with underlying meniscal tears requiring surgical intervention.
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