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Anterior Knee Pain

The pitfalls of plica and chondromalacia patellae

As the increasingly health-conscious population participates in more rigorous activities, both at much younger and much older ages, sports-related anterior knee pain also will be on the rise. The anterior aspect of the knee is a small area with many possible pathologies and common diagnostic pitfalls; detecting specific subtle indicators can avoid those pitfalls, especially the misapplication of chondromalacia patellae as a catchall diagnosis for anterior knee pain.

Chondromalacia properly refers to injury to any articular cartilage; nevertheless, healthcare providers and patients alike use the term to apply specifically to knee chondromalacia.1 The presence of anterior knee pain related to overuse of the undersurface of the patella, which is common in young adults, does not necessarily indicate the presence of chondromalacia patellae.

Patellar Function, Injuries

The knee comprises three articulating bones: the femur, the tibia and the sesamoid patella. Smooth articular hyaline cartilage on the surfaces of bones allows them to glide against each other; in the knee, patellar cartilage articulates with the trochlear surface of the femur. On average, the articular surface is about 3 mm thick; because it also is radiolucent, it gives the illusion of a space when visualized on radiographs.

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One of the patella's two main functions is to act as a bony shield of the distal femur. During traumatic anterior impact, this sesamoid bone fractures before injury can occur in the distal femur.

The other primary function of the patella is to serve as a lever to give the quadriceps a mechanical advantage during leg extension. In normal range of motion, compressed forces are distributed over the entire undersurface of the patella. When the knee is hyperextended, the patella is compressed into the proximal aspects of the trochlear groove, with the inferior and/or middle facets focally absorbing the entire weight. This localized increased compression also occurs when the knee is flexed beyond 90 degrees.

In the past, high school and college athletes would "run the stadium steps" as a means of conditioning. We now know that this form of repetitively flexing the knee beyond 90 degrees, followed by active leg extension with the athlete's entire weight, causes irreversible injuries to the hyaline cartilage of the femoral trochlear groove and the undersurface of the patella. Prolonged use of stair-stepper machines and mountain-climbing devices, especially on higher intensity or higher resistance settings, can yield similar injuries.2

A typical athlete may perform repetitive flexion and extension of the knee with and without resistance for months and sometimes years without symptoms. With no obvious trauma or specific traumatic event, anterior knee pain subtly creeps in, eventually compromising the ability to perform athletic activities.

When such a patient visits a primary care provider or orthopedist complaining of knee pain, routine radiographs of the knee show no alarming findings. Often, a diagnosis of chondromalacia patellae is offered; however, chondromalacia patellae applies only when actual degradation and disruption of the smooth articular undersurface have occurred - which is arthritis in its truest description. Arthritis of articular cartilage is classically described with the Outerbridge classification system (Table).3

Plica Bands

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Plicae (from the Latin for "folds") are remnants of embryonic structures that can be found across the joints of the body. These structures originate in the 6- to 9-week-old fetus. At that point in development, the embryonic synovial mesenchyme is solid - cavities do not develop until the ninth week in utero. In the ninth week, three primitive compartments are formed, lined by septa of embryonic synovium. By the 12th week, a single cavity finally is formed by way of absorption of the lining tissue through a process of involution. It is at this time when persistent synovial partitions emerge as the plicae.

As the baby or toddler increases joint range of motion, these remnant structures usually spontaneously rupture. If spontaneous rupture does not occur, the plicae mature and are nourished by the body over the years. At first, plicae can be thought of as thin rubber bands; if they do not rupture, over time they evolve into hearty, thick fibrotic bands.

About the knee are four common plicae: the superior (or suprapatellar) plica, the medial plica, the inferior (or infrapatellar) plica and, to a lesser degree, the lateral plica. Medial patellar plicae are the most frequently encountered culprit when a patient presents with vague anterior knee pain. Suprapatellar, infrapatellar and lateral plicae usually are asymptomatic.

In early literature from Japan and Canada, the presence of synovial plicae has been reported in 21% to 60% of the population.4,5 U.S. studies have reported a higher incidence. In a study of 200 cadavers, only 10% had no plicae.6 The inferior plica is common and is found in up to 65% of cadavers and in more than 85% of patients undergoing arthroscopy.6,7 Of cadavers with superior plicae, 63% had superior plicae that were bilateral and symmetric. Most plicae are small; more than 60% extend less than a third of the width of the suprapatellar pouch.7 Medial plicae have been reportedly found in 24% of cadavers, but medial plicae longer than 1 mm have been found in up to 70% of patients undergoing arthroscopy.6,7 Most medial plicae are less than 1 cm thick.6 Lateral plicae are rare, with an incidence of less than 1%.8

In our practice, however, as in other large-volume practices, we have found the plica prevalence to be much lower. Our surgical findings indicate that between 5% and 10% of patients have plicae at arthroscopy. This wide range of plica diagnosis may be examiner-dependent. Some authors measure plicae to as small as 1 mm in length whereas others consider a structure this small to be too insignificant to be labeled as a plica.4,5,8

As the knee flexes and extends against this static plica structure, it has a "windshield wiper" effect on the articular surface of the femoral condyle, where the thickness of articular cartilage is about 3 mm. When chronic friction sufficiently degrades the articular surface to reach subchondral bone, pain starts to mount. Often referred to as plica syndrome, this mechanism of injury may not produce symptoms until a person is in his or her 30s or 40s; the athlete is able to perform all activities without pain prior to the inflammatory insult.

Primary Care Pitfalls

Here's a typical scenario: A 27-year-old man is seen in primary care with complaints of anterior knee pain for the past 8 months. He runs stadium stairs daily for exercise. He denies trauma and has no past medical history of any collagen vascular disorders. No obvious fractures are seen on radiographs. On physical examination, he has mild crepitus, full range of motion, a positive patella compression test (in which the patella is compressed into the femoral trochlear groove while the patient flexes and extends the knee and which correlates anterior knee pain with articular degeneration), and vague anterior knee tenderness.

This is where the pitfall of misdiagnosis can occur, since the symptoms of chondromalacia patellae are similar to those of plica syndrome - pain with flexion and extension, difficulty with stairs, crepitus, progressively worsening pain and no particular injury mechanism. In such cases, a primary care provider may very likely diagnose chondromalacia patellae and prescribe physical therapy. After 2 to 3 weeks of strengthening with physical therapy, the patient's condition continues to deteriorate until simple ambulation becomes difficult.

At this point, other pathologies must be investigated, and magnetic resonance imaging now is in order. Typically in this scenario, MRI images demonstrate a plica band that is thickened medially, and the primary care provider's prescription of aggressive strengthening and range-of-motion exercises in physical therapy have worsened the condition.

Not all cases of plica syndrome are cases of chondromalacia patellae. Put another way, plicae may contribute to chondromalacia patellae, but chondromalacia does not contribute to plicae. More common causes of chondromalacia patellae are subluxation or dislocation of the kneecap and repetitive overuse. Multiple occurrences of subluxation in the past history most likely lead to patellar articular surface injury later in life.9

Treatment Options

Treatment of a confirmed case of chondromalacia patellae should be approached in a stepwise escalating fashion. A conservative therapeutic regimen is instituted initially, with aggressive strengthening of the quadriceps. The goal of quadriceps strengthening is to allow it to apply a more centralized pull to the patella; in keeping the patella centralized, the compressive forces then will be distributed evenly over the facets of the patellar articular surface.

In uncomplicated chondromalacia patellae, physical therapy coupled with a regimen of nonsteroidal anti-inflammatory drugs usually can remedy symptoms. When conservative measures are not effective, invasive regimens of injections are recommended.

Injection of viscosupplementation (Synvisc, Euflexxa, Orthovisc, Hyalgan, Supartz, etc.) in the knee increases viscosity, allowing the articular surfaces to be better lubricated, and increases the quantity of joint fluid, allowing for better hydraulic protection.

If the pain persists after injections, minimally invasive surgical arthroscopy is the definitive treatment of choice. A slim camera lens is inserted through one of two small portals, and instruments, possibly including scissors, biters, punches, a thermal ablation probe and a synovial resector or shaver, are inserted through the other to correct an offending plica, if necessary. â– 

Amanda Chevestick is a research assistant at the Hackensack University Medical Center (HUMC) orthopedics and sports medicine department in Hackensack, N.J., and is a student at the Pace University-Lenox Hill Hospital PA program in New York. Gordon Huie is a senior PA in the HUMC orthopedics and sports medicine department. Yair D. Kissin is a senior associate in the HUMC orthopedics and sports medicine department and an assistant professor at the Insall Scott Kelly Institute for Orthopaedics & Sports Medicine in New York. Michael A. Kelly is chairman of the HUMC orthopedics and sports medicine department and codirector of the Insall Scott Kelly Institute. They have completed disclosure statements and report no relationships related to this article.


1. Moore KL. The lower limb. In: Clinically Oriented Anatomy. 3rd ed. Baltimore, MD: Williams & Wilkins; 1992:388-393.

2. Huie G, et al. High-tech exercise and anterior knee pain. Physician Assist. 1997;21(3):101-125.

3. Outerbridge RE. The etiology of chondromalacia patellae. J Bone Joint Surg Br. 1961;43-B(4):752-757.

4. Aoki T, et al. A case of internal derangement of the knee due to the so-called shelf. J Jap Orthop Assoc. 1965;39:933.

5. Jackson RW, et al. The pathologic medial shelf. Orthop Clin North Am. 1982;13(2):307-312.

6. Dupont JY. Synovial plicae of the knee: controversies and review. Clin Sports Med. 1997;16(1):87-122.

7. Dandy DJ. Anatomy of the medial suprapatellar plica and medial synovial shelf. Arthroscopy. 1990;6(2):79-85.

8. Boles CA, Martin DF. Synovial plicae in the knee. AJR Am J Roentgenol. 2001;177(1):221-227.

9. Insall J, et al. Chondromalacia patellae: a prospective study. J Bone Joint Surg Am. 1976;58-A(1):1-8.


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