Elsevier

Clinics in Sports Medicine

Volume 16, Issue 1, 1 January 1997, Pages 87-122
Clinics in Sports Medicine

SYNOVIAL PLICAE OF THE KNEE: Controversies and Review

https://doi.org/10.1016/S0278-5919(05)70009-0Get rights and content

In the vast array of mechanical internal derangements of the knee, the meniscal and ligamentous pathologic conditions are by far the best known and understood by orthopedic surgeons. The link between the presence of synovial plicae or pleats of the synovial membrane of the knee and symptoms is a more troublesome and recent discovery. This relationship became evident with the onset of diagnostic and therapeutic arthroscopy, allowing an easy assessment and treatment of the condition. The subject is controversial, especially because the related abundant literature is often redundant, confusing, and unclear. The exact incidence of medial plica syndrome is a subject of debate, as well as are the criteria that allow recognition of a clinically significant plica.

The confusion surrounding synovial plicae stems from many sources and can cause future problems:

  • Failure to diagnose a symptomatic plica leads to delays in treating patients but also to wrong indications or unnecessary patellar surgery, among other errors.

  • Labeling of any synovial fold identified at arthroscopy as responsible for symptoms and resecting it abuses both the physician and the patient. It also demonstrates poor clinical judgment and is costly for third-party payers.

  • Searching rigidly for strict macroscopic criteria to conclude that a plica merits resection may lead to failure to recognize some of the symptomatic plicae, as they do not always fulfill these criteria.

  • Publication of more or less outdated theories, which were proposed when the knowledge on the subject was slim, in today's literature does not help to improve understanding of the problem.

This article, therefore, aims to reevaluate the subject, considering both an analysis of the literature and personal studies.

Section snippets

SYNOVIAL PLICAE IN THE LITERATURE

Historically, the first anatomic description of the synovial pleats of the knee goes as far back as 1555 (see ref. 26). Vesalius84 identified the inferior plica and named it the ligamentum mucosum. The complete superior plica and the medial plica were described by the great classical anatomists in the late nineteenth and early twentieth centuries in several countries (e.g., Fullerton, Holbaum, Heineke, Malgaigne, Poirier, Charpy, Testut, Rouviere, and Mayeda48a). These descriptions were purely

EMBRYOLOGY OF THE SYNOVIAL FOLDS OF THE KNEE

Untrue statements may be found in the literature, such as “[the medial plica], in early life, separates the medial and lateral compartments of the knee as well as the suprapatellar pouch.” Such a statement really leaves the reader puzzled.20

The theory most commonly found in the literature was developed after Pipkin68, 69 and accepted without much discussion by many authors.6, 38, 39a, 50, 54, 56, 62, 64, 71 This theory explains the presence of synovial folds within the knee joint cavity by the

ANATOMIC DESCRIPTION OF THE PLICAE

Hughston et al,40 in 1973, stated that the medial and the superior plica are one entity. This means that there would be only two plicae: the superomedial and the inferior. Some authors still use this classification, even in recent articles.2 Harty39 described the medial and the superior synovial plicae but classified the inferior plica as a “mucosal fold.” Most authors describe three plicae4, 11, 38, 46, 50, 53, 56, 62 and do not mention the lateral one. There are, however, four possible

THE FREQUENCY OF PLICAE IN ANATOMIC AND ARTHROSCOPIC STUDIES

To analyze these four different plicae, the author and colleagues43 dissected 200 cadaveric knees, without distinguishing age, sex, or race. Most were white. The type and frequency of the plicae and the symmetry and the associations between these plicae were considered. Only 10% of the knees had no plica of any kind. Eleven percent had the three main plicae simultaneously. Medial and inferior plicae were found predominantly in men. No differences were evident between men and women for the

RADIOLOGY

Nickerson55 and Pipkin69 were the first authors to demonstrate the visualization of synovial folds at arthrography, and others later followed suit.2, 13, 45 Several imaging techniques can be used to demonstrate plicae, but they all require a trained and motivated radiologist.15, 20, 66 Those with poor technique or untrained physicians may overlook the presence of synovial folds easily. Incidentally, Broukhim et al12 stated that arthrography is usually normal.

Exceptionally, an indirect sign of

The Superior Plica

The potential role of the superior plica in internal derangements of the knee is still a subject of debate. Pipkin68, 69 and Hughston et al40, 40a focused on the superior plica and published 49 cases. Because of poor definition of the pathologic conditions, however, they have included in their cases medial plicae as well (discussed in ref. 62). Pipkin68 accused the plica of creating synovial retention and favoring the creation of Baker's cyst, which seems unlikely.65 Moyen et al52 described a

THE MEDIAL PLICA SYNDROME

Considering that the medial plica is a normal element of the knee joint anatomy, it is questionable that it can produce symptoms. This phenomenon apparently was first raised by Iino (see ref. 42). The reality of this syndrome, nevertheless, is obvious for clinicians who are used to its diagnosis and treatment. Arthroscopy, once again, plays an important role. It assesses the plica precisely, therefore allowing the relationship between the plica and the patient's symptoms to be established,

HISTOLOGIC FINDINGS

Histologic study of a resected plica may result in interesting data. It often confirms a mechanical and chronic conflict with pathologic changes, such as deep fibrosis, abrasion of the superficial synovial layer or, conversely, hypertrophy of a synovitis, infiltration of inflammatory cells, or thickening of vessels walls (Fig. 10). These signs are inconstant, however. In 45 cases that underwent histologic examination of the plica, Richmond and McGinty71 found 19 with no such abnormalities and

Conservative Treatment

If a medial plica syndrome is diagnosed, conservative treatment is always preferable initially, as it is cost-effective compared with arthroscopic surgery. It combines rest and avoidance of overuse activities, including sports. Massage, ice, and physiotherapy can be combined with the use of a patellar brace and stretching exercises or quadriceps isometric exercises (although some of these treatments are questionable in situations of chronic mechanical conflict or an inflammatory lesion).

Pathomechanics of the Medial Plica Syndrome

The medial plica commonly is presented as a normal finding of the knee, as well as a lesion,64 an ailment,2 a pathologic condition,42 or a hypertrophy.71 Most authors describe the medial plica as either normal, or abnormal (i.e., pathologic—fibrotic, wide, tense, and impinging on the femoral condyle). A theory was developed to explain how a normal plica can become abnormal. A normal plica is considered to be a thin, soft, pliable, pink structure.2, 4, 38, 62, 75, 77 It supposedly becomes

CONCLUSIONS AND SUMMARY

Plicae are some of the normal synovial structures of the knee joint cavity. They are remnants of the mesenchymal tissue that occupies the space between the distal femoral and proximal tibial epiphyses in the 8-week-old embryo. The incomplete resorption leaves synovial pleats in most of the knees. The superior and the inferior plicae are the most common (50% to 65%) but have extremely little clinical relevance. Each may be of many various morphologic types. The lateral plica is rare (1% to 3%).

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