Medial plica irritation: diagnosis and treatment

Abstract
Medial plica irritation of the knee is a very common source of anterior knee pain. Patients can complain of pain over the anteromedial aspect of their knees and describe episodes of crepitation, catching, and pseudo-locking events with activities. Patients commonly have pain on physical examination upon rolling the plica fold of tissue over the anteromedial aspect of their knees and often have tight hamstrings. The majority of the patients will respond well to a non-operative treatment program consisting of quadriceps strengthening along with concurrent hamstring stretching. In cases which do not respond initially to an exercise program, an intraarticular steroid injection may be indicated. In those few patients who do not respond to a non-operative treatment program, an arthroscopic resection of their medial plica may be indicated, especially in those cases where a shelf-like plica has been found to be causing damage to the articular cartilage of the medial femoral condyle.

Keywords: Plica irritation
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Anatomy
The medial plica of the knee is a thin, well-vascularized intraarticular fold of the joint lining, or synovial tissue, over the medial aspect of the knee (Fig. 1). It is present in everyone, but is more prominent in some people. It has been noted to be present as a shelf of tissue over the medial aspect of the knee at the time of arthroscopic surgery in up to 95% of patients [6]. Proximally, it is attached to the genu articularis muscle, while distally it courses over the far medial aspect of the medial femoral condyle to attach to the distomedial aspect of the intraarticular synovial lining of the knee. At this location, it basically blends into the medial patellotibial ligament on the medial aspect of the retropatellar fat pad [9]. The medial plica is composed of relatively elastic tissues which asymptomatically conform to the changes in shape and lengths of the plica folds as the knee flexes and extends [7]. In some patients, particularly those who may have had injuries or multiple surgeries over the medial aspect of the knee, the medial synovial plica may become very thick and fibrotic and may catch over the medial aspect of the medial femoral condyle [7, 10].


Fig. 1
Intraoperative visualization of medial synovial plica
In all patients, the medial synovial plica will glide over the anteromedial aspect of the medial femoral condyle with flexion and extension of the knee. In most patients, this gliding motion of the plica will occur without any symptoms, because of the high viscosity of the native synovial fluid of the knee. However, in patients with effusions, which decreases the viscosity of their synovial fluid, patients may either have crepitation or a catching of their medial synovial plica with flexion and extension of the knee. This crepitation or catching can occur with patients while going up or down stairs, squatting and bending, and other types of activities.

Since the medial synovial plica does have an attachment to the genu articularis muscle, and also an indirect attachment to the quadriceps musculature due to its attachment to the joint lining, it is dynamically controlled by the quadriceps muscles [3]. Thus, medial plica irritation is more common in patients who have poor quadriceps tone or other problems with joint muscle balance around the knee.

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Diagnosis of medial plica pathology
One of the most important points in diagnosing medial synovial plica pathology is obtaining an appropriate history from the patient. Patients usually describe pain which is dull, achy, and increases with activity. When asked to point to the area of their pain, they will commonly point to the proximomedial aspect of the knee, proximal to the medial joint line. While some patients may note a history of trauma to this area of the knee, most patients do not have any specific history of trauma to their medial plica. Over half of patients have a history of participating in some type of strenuous activity which requires repetitive flexion and extension motion of the knee, which then irritates their patellofemoral joint.

Most patients will complain of an achy type pain over the medial aspect of their knee, which is aggravated by activity and can be particularly bothersome at night. Their complaints of night pain over this area of the knee are due to the effects of inflammation, which can be particularly bothersome with activities. Patients most commonly complain of pain with activities which stress their patellofemoral joints, such as ascending and descending stairs, squatting and bending, and arising from a chair after sitting for an extended period of time [11]. In addition, they may note difficulty with sitting still for long periods of time without having to move and stretch their knees. They also may complain of a catch over the anteromedial aspect of their knee upon arising from a chair following prolonged periods of sitting. In some patients, plica catching may present as a pseudo-locking event to their knee when they have been sitting down for an extended period of time and they first arise. Some patients may describe these pseudo-locking events as instability or catching of their patella. Clicking, giving way, and pseudo-locking have been reported in approximately 50% of all patients who present with medial plica irritation [8]. Patients who might have problems with activity-related effusions may also complain of pain over the anterior aspect of their knee. While these activity-related effusions may not be directly caused by medial plica pathology, and are more commonly due to underlying quadriceps mechanism weakness, meniscal tears, and/or osteoarthritis, but they can cause secondary medial plica irritation. In addition, patients who have had postoperative or post-injury weakness of their affected extremity may develop pain over the anteromedial aspect of their knee in the region of the medial synovial plica.

A definitive diagnosis of medial plica irritation is usually obtained by physical exam. A normal examination of the patellofemoral joint should always include an examination of the patient’s medial synovial plica fold to determine if they have any irritation of this structure.

In examining the medial synovial plica, it is important to make sure that the patient is relaxed, which is usually accomplished by having the patient lie supine on the examining table with both legs relaxed. The examiner then palpates for the medial synovial plica by rolling ones fingers over the plica fold which is located between the medial border of the patella and the adductor tubercle region of the medial femoral condyle (Fig. 2). The medial synovial plica will present as a ribbon-like fold of tissue under ones finger which can be rolled directly against the underlying medial femoral condyle [12]. While some patients may have a sensation of mild pain when palpating the medial synovial plica, it is important to ascertain while performing this test if this reproduces their symptoms. It is also very important to compare the sensation to the contralateral normal knee to see if there is a difference in the amount of pain produced. It has been well demonstrated that this portion of the medial joint line and synovium is well innervated and irritation of the medial plica can be quite painful in some patients [4].


Fig. 2
Medial synovial plica palpation (Plica snap test)
As with any other physical diagnosis, it is important to concurrently ascertain if there are other areas of pathology for structures that are located close to the medial synovial plica to confirm one’s diagnosis. In acute injuries, one should make sure that there is no injury to the meniscofemoral portion of the superficial medial collateral ligament. In this instance, one would apply a valgus stress to the knee and palpate at the joint line for both any potential joint line opening to application of the valgus stress and also to see if there is any well localized pain or edema in the region of the meniscofemoral portion of the superficial medial collateral ligament (Fig. 3). In addition, in acute injuries, one should make sure that there has not been a lateral patellar subluxation episode with injury to the medial patellofemoral ligament. The lateral patellar apprehension test, performed with the knee flexed to approximately 45° of knee flexion, can help to determine if there has been injury to the medial patellofemoral ligament by applying a lateral translation force to the patella when it is flexed to approximately 45° of knee flexion and assessing if this translation causes pain or an apprehensive feeling like the patella will dislocate (Fig. 4). This pain should be different from pain produced when the plica is rolled under ones fingers. Further, one should make sure that the pain over the medial aspect of the knee is not directly due to localized or diffuse areas of chondromalacia of the patellofemoral joint. In this instance, one would roll the superior and inferior poles of the patella both proximally and distally, as well as medially and laterally, in the trochlear groove, to determine if there is any true retropatellar crepitation with translation of the patella in the trochlear groove (Fig. 5a, b). This evaluation is different from assessing for crepitation of the patellofemoral joint with active flexion and extension of the knee (Fig. 6a, b) as many of these patients may have catching of their medial plica causing the crepitation with active flexion and extension of the knee rather than true patellofemoral chondromalacia causing this auditory occurrence. In addition, one should assess for hamstring tightness, which can cause stress to the anterior aspect of the knee, by assessing the hamstring-popliteal angle (Fig. 7) and by palpation of the main hamstring attachment sites of the knee (pes anserine bursa (Fig. 8), semimembranosus bursa (Fig. 9), and biceps bursa (Fig. 10)).