Excerpt from Plica Syndrome

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Plica syndrome of the knee is a constellation of signs and symptoms that occur secondary to injury or overuse. An otherwise normal structure, a plica can be a significant source of anterior knee pain. Once an inflammatory process is established, the normal plical tissue may hypertrophy into a truly pathologic structure (see Image 1). This article provides an overview of pertinent anatomy as well as diagnosis and treatment of plica syndrome of the knee.

During embryonic development, the knee is divided initially by synovial membranes into 3 separate compartments. By the third or fourth month of fetal life, the membranes are resorbed, and the knee becomes a single chamber. If the membranes resorb incompletely, various degrees of septation may persist. These embryonic remnants are known as synovial plicae. Four types of synovial plicae of the knee have been described in the literature.¹

The suprapatellar plica, or plica synovialis suprapatellaris, divides the suprapatellar pouch from the remainder of the knee. Rarely, this plica may initiate a suprapatellar bursitis or perhaps chondromalacia, and symptoms secondary to these conditions may be present.² Anatomically, the suprapatellar plica can be complete or in the form of a porta, which only partially separates the compartments. It courses from the anterior femoral metaphysis or the posterior quadriceps tendon to the medial wall of the joint. The suprapatellar plica most commonly begins proximal to the superior pole of the patella but may begin anywhere.

The mediopatellar plica is the most frequently cited cause of plica syndrome. It lies on the medial wall of the joint, originating suprapatellar, and courses obliquely down to insert on the infrapatellar fat pad. This plica, sometimes known as a shelf, lies in the coronal plane.

The rare and poorly documented lateral synovial plica is a wider and thicker band than the medial plica. It is located along the lateral parapatellar synovium, inserting on the lateral patellar facet. The lateral plica has been argued to be derived from the parapatellar adipose synovial fringe rather than being a vestigial septum.

The plica found to be the least symptomatic of all, the infrapatellar plica or ligamentum mucosum, is, ironically, the most commonly encountered plica. Some authors even claim this plica is never responsible for plica syndrome. This bell-shaped remnant originates in the intercondylar notch, widens as it sweeps through the anterior joint space, and attaches to the infrapatellar fat pad. This plica's ability to obscure portal entry sites or interfere with visualization during arthroscopy is touted as its only significance.

For excellent patient education resources, visit eMedicine's Foot, Ankle, Knee, and Hip Center, Arthritis Center, and Bone Health Center. Also, see eMedicine's patient education article Knee Pain.

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Patient education resource Foot, Ankle, Knee, and Hip Center
Patient education resource Arthritis Center
Patient education resource Bone Health Center
Patient education article Knee Pain 

History of the Procedure

Both the normal and pathologic aspects of various synovial plicae readily became apparent to orthopedic surgeons with the advent of arthroscopy. Arthroscopy is a Japanese innovation that changed the face of orthopedics forever. Kenji Takagi (1888-1963) and Masaki Watanabe and others in Japan drove its early development, and early adopters in North America, such as Robert Jackson and Lanny Johnson, helped popularize this technology.^{3, 4}

The word plica comes from the Latin word meaning fold. This term is simply descriptive in nature, as there is no empirical evidence that true folding of the synovial lining ever occurs. The medial parapatellar plica has been referred to by some as the Aoki ledge or Iino band. The plica tends to course from the medial region of the parapatellar synovial cavity down to the infrapatellar fat pad region. These eponymic associations bear further testimony to the Japanese surgeons who were the early pioneers of arthroscopy.

Problem

Synovial plicae are normal structures found in many knees. Under normal circumstances, they are not associated with any painful conditions. However, with the right combination of events they can become quite problematic. These events almost certainly include a somewhat exuberant plical shelf at baseline combined with an inciting event (either discrete macrotrauma or repeated microtrauma). Once a painful and, at times, hypertrophic inflammatory cycle has been established, an athlete may be faced with finding a way to tolerate the knee pain or give up the particular inciting sporting activity.

Frequency

The precise incidence of plica syndrome is a source of ongoing controversy. The incidence of symptomatic or pathologic plica versus asymptomatic plica is even more debatable. Some authors contend that distribution is regional. Distribution differences based on race or ethnicity may exist.

The incidence of suprapatellar plica has been reported to be as low as 11%; however, one study reported a rate of 89% on autopsy.

Medial plica has an 18-60% reported incidence rate. The incidence of medial plica in anatomic studies is similar to that in arthroscopic studies. The most commonly cited incidence rate in the literature is approximately 20-25%.

Little literature exists on lateral plica. Most of this literature is Japanese, and few cases have been reported in English.⁵ Incidence of this kind of plica is less than 1%.

Dupont et al found some type of inferior plica in 65% of their 200 dissected cadaveric knees. They stated it was the most frequently found plica. In their review of the literature, infrapatellar plica was most common in some studies but not in others.¹

Etiology

The etiology of symptomatic plica is unclear. Potential causes of inflammation include repetitive stress, a single blunt trauma, loose bodies, osteochondritis dissecans, meniscal tears, or other aggravating knee pathology. The most common symptomatic plica is medial plica; occasionally, suprapatellar plica may also be symptomatic.^{6, 7, 8, 9}

A popular theory for the initiation of inflammation is that the plica is converted to a bowstring, which causes it to contact the medial femoral condyle. During flexion of the knee, the plica causes an abrasion to the condyle, resulting in symptoms. Others contend that a plica need not contact the femoral condyle to cause symptoms.

One study found the onset of symptoms was usually delayed until adolescence. Possible explanations include a decrease in tissue elasticity with age, and a biomechanical change resulting from a growth spurt.

Related eMedicine topic:
Osteochondritis Dissecans

Pathophysiology

Not all synovial plicae are symptomatic. For those that are, the etiology may not always be apparent. Inflammation leads to edema, thickening, and decreased elasticity of the plica. The plica may develop irregular edges and may snap over the femoral condyle, leading to a secondary synovitis and chondromalacia. Loose areolar fatty tissue appears to become gristlelike, and when plicae are soft, wavy, and vascular with synovial-covered edges, they are not pathologic. Numerous studies describe pathologic plicae as thick, fibrotic, white, and inelastic. Histologically, fibrosis, hyalinization, and calcification are present.

Clinical

The spectrum and diversity of symptoms can make this syndrome difficult to pinpoint. Often, symptoms resemble or overlap with those of other pathology.^{10, 11} Reported symptoms include anterior or anteromedial knee pain; intermittent or episodic pain; clicking; high-pitched snapping; occasional giving way; locking (really pseudolocking) and catching; and aggravation of symptoms by activity, by stair climbing, or by prolonged standing, squatting, or sitting. Meniscal tears, patellar tendinitis, Osgood-Schlatter disease, Sinding-Larsen-Johansson disease, and patellar instability are the most commonly found concomitant conditions.

On physical examination, the patient typically has tender points along the medial and inferior aspect of the patella (see Image 2); in some instances, a painful, hypertrophied membrane is palpable. The inferomedial quadrant (see Image 3) is the most consistently painful region. Occasionally, a medial apprehension test of the patella elicits a positive response, but careful evaluation reveals that it is due to direct tenderness to palpation in the region of the plica and is not true patellar instability.

Rovere et al state that a palpably tender plica in the absence of an intra-articular effusion conclusively establishes a diagnosis of plica syndrome, provided other causes of knee pain are ruled out.¹² A taut articular band that reproduces the patient's pain upon palpation of the medial peripatellar region is virtually pathognomonic for plica syndrome. This may be referred to as a positive TARP sign, in which TARP stands for the following:

• T - Taut
• A - Articular band
• R - Reproduces
• P - Pain

In addition to the history and physical examination, a radiograph is recommended to exclude other causes of knee pain. As stated previously, plica syndrome is difficult to differentiate from other pathology and remains a diagnosis of exclusion. Other adjunctive diagnostic studies include contrast pneumoarthrography and double-contrast arthrography, yet arthroscopy remains the standard for definitive diagnosis.¹³ Most plicae are found incidentally during knee arthroscopy.

Munzinger classified the mediopatellar plica into 4 types based on appearance, as follows¹⁴:

• A - Cordlike
• B - Shelflike, does not cover medial femoral condyle
• C - Does cover medial femoral condyle
• D - Double insertion

Other authors believe that to differentiate between symptomatic and asymptomatic plicae, the following criteria must be met upon arthroscopic examination: plica must appear, one must visualize impingement, and chondromalacia must be present in the areas of impingement.

Related eMedicine topic:
Osgood-Schlatter Disease
Knee, Meniscal Tears (MRI)

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