Plica syndrome of the knee

INTRODUCTION — 

The diagnosis and treatment of plica syndrome of the knee are reviewed here. The causes and diagnostic approach to knee pain in young athletes and adults are discussed separately:

●Knee examination – (See "Physical examination of the knee".)

●Adult knee pain – (See "Approach to the adult with unspecified knee pain" and "Approach to the adult with knee pain likely of musculoskeletal origin".)

●Child knee pain – (See "Approach to acute knee pain and injury in children and skeletally immature adolescents" and "Approach to chronic knee pain or injury in children or skeletally immature adolescents".)

DEFINITION — 

Plica syndrome is a painful condition of the knee, often reported in runners and other athletes. The abnormal plica, an intraarticular band of thickened, fibrotic tissue, may cause pain and a popping sensation by rubbing across either the medial femoral condyle or undersurface of the patella.

ANATOMY AND CLASSIFICATION — 

Plicae are considered normal mesenchymal structures. They represent remnants of the septations created by the various cavitations that coalesce to form the knee joint in utero. These septations begin to involute about the 12^th week of fetal life, but they persist in up to 50 percent of individuals based upon autopsy findings [1,2].

The normal plica is seen arthroscopically to be a thin, vascular structure that is easily deformable with a probe, often appearing as a thin, narrow veil of tissue. An abnormal plica is thick, fibrotic, and relatively avascular, at least in its midportion, and is often taut and cord-like (picture 1).

There are four types of plica based on their origin and insertion (figure 1):

●Suprapatellar – The suprapatellar plica lies between the suprapatellar bursa and the knee joint [3]. The incidence of normal suprapatellar plica in knees undergoing arthroscopy approaches 87 to 91 percent.

●Medial – The medial plica arises from the medial wall of the knee joint, passes inferiorly and around the medial femoral epicondyle, and inserts into the synovium surrounding the infrapatellar fat pad (IFP) [2,3]. Normal medial plica appears in 55 to 92 percent of knees undergoing arthroscopy, depending on the definition applied [4].

Medial plicae are most commonly symptomatic. As an example, in a series of 400 knees explored arthroscopically for knee pain without other major cartilage, ligament, or bone derangement, 72 percent of patients had medial patellar plicae (MPP) [5]. Of these, 60 percent were type C (shelf) according to their classification.

In the medical literature, medial plicae are also referred to as medial shelf, plica synovialis mediopatellaris, plica alaris elongata, lion's bands, or Aoki edge.

●Infrapatellar – The infrapatellar plica (or ligamentum mucosum) arises from the intercondylar notch and inserts into the synovium surrounding the IFP [2,3]. A normal infrapatellar plica is commonly found at arthroscopy, with one series finding it in 86 percent of patients [5].

●Lateral – The lateral plica occurs rarely [2,3]. It was found in less than one percent of 400 patients undergoing arthroscopy in one series [5].

It is common for an individual to have more than one plica. There are no distinct combinations of multiple plica [5].

A classification system based upon morphology has been developed for each type of plica (ie, suprapatellar, medial patellar, infrapatellar, and lateral patellar). As an example, the following morphologic designations are used for MPP [5]:

●Type A – Absent

●Type B – Vestigial – A line of elevation 1 mm or less arises from the medial synovial shelf.

●Type C – Shelf-like – The medial synovium forms a complete fold with a sharp, free margin.

●Type D – Reduplicated – Two or more shelves run parallel along the medial wall of the knee.

●Type E – Fenestrated – The shelf has a central defect.

●Type F – High-riding – A shelf occurs anterior and medial to the medial facet where it cannot touch the femur.

Medial plicae are also described by the degree of contact with the medial femoral condyle, as follows:

●Not touching

●Contacting the condyle

●Widely covering the condyle

Classification systems for suprapatellar, infrapatellar, and lateral patellar plica are discussed separately [3,5].

EPIDEMIOLOGY — 

Plica of the knee is described in children and adults, but the prevalence of symptomatic (presumably abnormal) plica is not known, primarily due to the absence of clear diagnostic criteria [2]. Many experts suggest that plica syndrome is an underdiagnosed cause of anterior knee pain in adolescents and young adults. Based upon small arthroscopic series of children, adolescents, and young adults with acute knee pain, estimates of the frequency of plica syndrome range from 8 to 45 percent [6-8]. An abnormal medial plica was found most often.

Plica syndrome is reported most often in runners, in whom repetitive motion combined with abnormal mechanics or biomechanical stress at the knee causes excessive contact between the medial plica and either the medial femoral condyle or medial patellar facet. Symptomatic plicae also occur in swimmers, rowers, cyclers, and basketball players [9]. A plica may become symptomatic in the absence of a history of trauma or intraarticular pathology, especially in patients with a knee valgus. (See 'Physical examination' below.)

PATHOPHYSIOLOGY — 

Pathologic plica may develop after direct trauma (eg, direct blow to the knee or twisting injury) or following repetitive knee movements that cause injury and inflammation of the plica with subsequent fibrosis [3,10]. Intraarticular abnormalities, such as loose foreign bodies, osteochondritis dissecans (OCD), or inflammatory arthritis, may also inflame a plica. The resulting thickening and loss of elasticity of the structure cause it to rub over the medial femoral condyle leading to synovitis, chondral damage, and pain.

CLINICAL MANIFESTATIONS

History — Plica of the knee most often affects adolescents and young adults. Individuals with symptomatic plica often complain of anterior and medial knee pain that develops over weeks to months and increases in severity over time [3,11]. Medial plicae are most commonly symptomatic.

Some patients report that pain began with a direct blow or twisting injury to the knee. They frequently describe the pain as worse with activity, such as running, squatting, going up or down stairs, or kneeling, and after prolonged sitting (theater sign). The pain may be accompanied by a popping sensation with knee flexion. Patients may also report clicking, catching, knee pseudo-locking (false locking), or giving way. In most patients, only one knee is involved.

Physical examination

General findings — Findings of plica syndrome are often nonspecific and may include the following in symptomatic patients:

●Palpable fibrotic fold or cord over the medial femoral condyle (medial plica) that is painful when the knee is either in full extension or is flexed [12]; this finding is not specific for medial plica syndrome [13,14]. The cord is most readily palpated with the knee in full extension.

●Vague tenderness over the medial femoral condyle or medial patellar facet (picture 2).

●Soft tissue swelling just medial to the patellar border.

●Because of pain during knee flexion, over time tightness can develop in the hamstring, quadriceps, and gastrocnemius muscles, with limited dorsiflexion of the foot [15].

●Quadriceps atrophy [3].

●Weakness of hip abduction, similar to patients with patellofemoral pain. (See 'Patellofemoral pain' below.)

●Effusion; joint swelling typically indicates the presence of chondral injury associated with a plica and is frequent in adults but uncommon in adolescents [16].

●Rarely, active or passive range-of-motion testing of the knee produces clicking or popping.

Abnormalities of lower extremity alignment that predispose to plica may be present upon inspection of the lower extremity:

●Genu valgus, or knock knees, (picture 3 and figure 2) tend to worsen the tension of the medial plica as it passes obliquely over the medial femoral condyle in the coronal plane and is a predisposing finding.

●Abnormalities at the ankle and hip that cause valgus angulation at the knee during activity (picture 3) may contribute to the pain and clicking. These include weakness of the hip abductors or tight hip adductors.

●Predisposing abnormalities of the foot include loss of longitudinal arch (figure 3) from posterior tibial dysfunction or spring ligament insufficiency leading to resting pronation at midfoot associated with calcaneal valgus at the rear foot (picture 4) or congenital changes such as pes planus (picture 5). (See "Midfoot pain in adults: Evaluation, diagnosis, and select management of common causes", section on 'Spring ligament (calcaneonavicular) rupture' and "Non-Achilles ankle tendinopathy", section on 'Medial ankle tendinopathy'.)

Provocative tests — In addition to the above clinical findings, the following provocative tests are helpful in making a diagnosis of plica syndrome:

●Medial patellar plica (MPP) test – This test is performed as follows (figure 4) [17]:

•The patient lies supine with their knee in full extension.

•Next, the clinician applies pressure with their thumb over the inferior-medial aspect of the patellofemoral joint (figure 4). The purpose is to interpose the medial plica between the medial patellar facet and the medial condyle.

•While maintaining this pressure, the clinician uses their opposite hand to passively flex the knee from 0 to 90 degrees.

•Pain in extension that is relieved when the knee is placed in 90 degrees of flexion constitutes a positive test.

In a meta-analysis of seven studies (492 knees), the MPP test had a sensitivity and specificity for medial plica syndrome of 90 and 89 percent, respectively, when performed by an orthopedist [18].

●Knee extension test (Hughston test) – This test is performed as follows (figure 5) [19]:

•The patient lies supine with their knee in 90 degrees of flexion.

•With one hand, the clinician applies pressure to the lateral patella, moving it medially (figure 5).

•With the opposite hand, the clinician internally rotates the lower leg, and then slowly extends the knee.

•The test is considered positive if the typical popping sensation or pain is reproduced with the knee between 60 and 45 degrees of flexion.

This test was positive in all 136 patients with symptomatic plicae in one series [15]. However, in the author's experience, the knee extension test may be helpful but not always positive in patients with plica syndrome.

Imaging — Plica syndrome is a clinical and arthroscopic diagnosis. However, imaging is frequently required to exclude other causes of knee pain. The type of imaging performed is determined by the leading alternative diagnoses. (See 'Differential diagnosis' below.)

In the patient with plica syndrome without other intraarticular or joint pathology, such as synovitis, chondral injury, or loose foreign body, plain radiographs of the knee are normal.

Although arthrogram, flexed knee arthrogram, routine or dynamic ultrasound (US), and magnetic resonance imaging (MRI) can all demonstrate the presence of plicae, some studies have found them unreliable in predicting which plica are pathologic at surgery [13,20,21]. A systematic review of seven studies (492 knees) found the MPP test had the greatest diagnostic accuracy when compared with ultrasound or MRI, although the MPP test was similar to dynamic ultrasound in terms of sensitivity [18]. The sensitivity of MRI was 77 percent. However, none of the studies included in the review compared the accuracy of these tests when all are performed in the same patient.

In one series, dynamic ultrasonography with medial and lateral patella manipulation in 88 patients with clinical findings suggestive of medial plica syndrome had a sensitivity, specificity, and diagnostic accuracy of 90, 83, and 88 percent, respectively, when compared with arthroscopic diagnosis [22]. While there are no special maneuvers explicitly for examining the plica, performing the ultrasound examination while flexing and extending the knee (ie, dynamic ultrasound) may improve the visibility of the plica.

While not useful for identifying plicae, static knee ultrasound may identify other causes for anterior or medial knee pain that exclude the diagnosis of plica syndrome. (See "Musculoskeletal ultrasound of the knee".)

MRI is most useful when the clinician suspects intra-articular pathology causing pain that mimics plica syndrome. Plica may be visible on MRI if there is fluid in the joint (image 1). Increased thickness of the medial plica, as may be noted on ultrasound or MRI, is associated with plica syndrome [23].

DIAGNOSIS — 

The diagnosis of plica syndrome is based primarily upon clinical features and should only be made once other causes of knee pain have been excluded. It is suggested by a history of anterior and medial knee pain after direct trauma, twisting injury, or repetitive injury. The pain typically becomes worse with squatting, kneeling, going upstairs, or sitting for long periods of time (theater sign). Clicking upon knee flexion may also occur.

Physical findings are variable and nonspecific. In patients with a symptomatic medial plica, there may be subtle soft tissue swelling just medial to the patellar border. Careful palpation with the knee either in full extension or at 90 degrees of flexion may reveal a firm, tender cord of tissue running either perpendicular or obliquely to the medial border of the patella. Examination may also reveal tight quadriceps and hamstring muscles, weak hip abductors, and positive medial patellar plica (MPP) (figure 4), or knee extension (figure 5) tests.

While the MPP test has reasonable sensitivity and specificity, no single clinical test or maneuver is diagnostic of a pathologic plica. Dynamic ultrasound may help establish the diagnosis, but other imaging (eg, MRI) is performed primarily to exclude other knee pathology [18]. Relief of symptoms after injection of anesthetic (eg, lidocaine) into the plica may help to distinguish plica syndrome from other conditions. (See 'Clinical manifestations' above and 'Differential diagnosis' below.)

Arthroscopy provides a definitive diagnosis if a thickened, fibrotic plica is demonstrated (picture 1), but it is only performed when other diagnoses are considered or when conservative treatment fails. In patients with medial plica syndrome, intraoperative flexion of the knee causes the fibrotic plica to rub over the medial femoral condyle. (See 'Initial management' below.)

DIFFERENTIAL DIAGNOSIS — 

Plica syndrome is a diagnosis of exclusion after other injuries and conditions affecting the knee have been ruled out. The conditions most often mistaken for plica syndrome or that cause pain in the same locations are discussed below with a focus on features of the history, physical examination, and diagnostic imaging studies that allow clinicians to distinguish between them.

Diagnoses more common in young patients (adolescents) include the following:

Patellar subluxation — Patellar subluxation refers to excessive lateral motion such that the patella becomes completely or partially displaced from the trochlear groove. This may occur due to trauma or joint laxity. Patients experiencing subluxation often complain of knee pain and popping or clicking, and occasionally knee swelling, stiffness, or catching. Patellar subluxation differs on presentation from medial plica syndrome in several ways (see "Recognition and initial management of patellar dislocations", section on 'Patellar subluxation'):

●The history more often involves giving way followed by sharp pain that may be felt on both the medial and lateral patellar borders.

●Tenderness is more often present along the edge of the medial patella or adductor tubercle, rather than in the capsule as with medial plica syndrome.

●A positive apprehension sign is seen with lateral patellar displacement but absent in medial plica syndrome.

●An effusion is usually present with an acute patellar subluxation but absent in medial plica syndrome.

Patellofemoral pain — Patellofemoral pain (or runner's knee) describes anterior knee pain involving the patella and retinaculum that may arise from overuse, improper patella tracking during extension, or trauma. Several clinical features overlap with plica syndrome, including pain with increased activity, particularly going up and down stairs, during squatting, or after prolonged sitting. Patients with patellofemoral pain also often have tight hamstring, quadriceps, and calf muscles, evidence of excessive knee valgus with single-leg squat, and associated hip abductor weakness and hindfoot varus or mid-foot pronation. (See "Patellofemoral pain".)

Unlike plica syndrome, patellofemoral pain does not typically manifest with clicking or popping unless there is an associated chondromalacia or subluxation of the patella. Effusion or synovitis does not usually occur with patellofemoral pain, and pain is usually localized to the medial or lateral patellar facets by direct palpation in full extension. Weakness and possibly atrophy of the vastus medialis muscle is more common with patellofemoral pain.

Patellar tendinopathy — Patients with patellar tendinopathy usually report an insidious onset of anterior knee pain without an inciting event or associated swelling. Patients usually participate in running or jumping sports. When asked to indicate with one finger the location of the pain, the patient most often points directly to the patellar tendon. Physical examination findings consist of focal tenderness at the inferior pole of the patella or along the patellar tendon that is most readily appreciated with the knee in extension and the patella pushed distally so the tendon is relaxed. These examination findings allow the clinician to distinguish the condition from plica syndrome in most instances. (See "Patellar tendinopathy".)

Pes anserinus pain syndrome (formerly anserine bursitis) or tendonitis — The history of pes anserine bursitis differs sufficiently from medial plica syndrome such that the conditions are seldom mistaken for one another. Patients with pes anserinus pain syndrome or tendinopathy complain of medial knee pain and may report swelling. However, joint motion is unaffected and there is no clicking or popping, and no catching or pseudo-locking. Tenderness at the anatomical pes is below the location where patients experience pain from medial plica syndrome. Ultrasound can identify swelling in the pes bursa (image 2).

Osteochondritis dissecans — Osteochondritis dissecans (OCD) presents with insidious onset of knee pain and a history of repetitive activity, similar to some patients with plica syndrome. Patients with OCD may also report swelling. If the osteochondral lesion is stable, the patient rarely reports clicking or popping. However, the location of the pain may be similar to plica syndrome, as over 70 percent of lesions occur on the lateral aspect of the medial femoral condyle. In some patients with OCD, there is palpable tenderness near the medial edge of the intercondylar notch with the knee in partial flexion. However, a positive medial patellar plica (MPP) test is unlikely in patients with OCD. Examination or ultrasound commonly reveal a joint effusion in patients with OCD but not with plica syndrome. (See 'Provocative tests' above.)

Plain radiographs can be used to help distinguish medial plica syndrome from OCD, which is usually evident on plain films (image 3), although sometimes only with an anteroposterior (AP) tunnel (or intercondylar) view. Radiographs in patients with plica syndrome are usually normal. Should clinical uncertainty persist after examination and plain radiographs (eg, persistent symptoms but normal plain radiographs), MRI can establish a definitive diagnosis of OCD. (See "Osteochondritis dissecans (OCD): Clinical manifestations, evaluation, and diagnosis", section on 'Clinical presentation' and "Osteochondritis dissecans (OCD): Clinical manifestations, evaluation, and diagnosis", section on 'Magnetic resonance imaging'.)

Diagnoses more common in adults include the following:

Patellofemoral osteoarthritis — Individuals with osteoarthritis of the patellofemoral joint may also localize pain to the anterior-medial knee and complain of crepitus and clicking. However, with osteoarthritis tenderness is usually localized to the patellar facets and the patellar grind test is positive for crepitus. The grind test is performed with the examiner applying downward pressure on the patella with the knee extended, as the patella is gently moved medially and laterally. In addition, synovitis or an effusion may be present. (See "Clinical manifestations and diagnosis of osteoarthritis", section on 'Knee'.)

Clinical criteria for osteoarthritis of the knee include age >35 years, morning stiffness for less than 30 minutes, crepitus on active knee movement, and bony tenderness or enlargement. Reduced knee mobility is often present. In contrast, for patients with plica syndrome pain is most severe during dynamic knee flexion.

Patellofemoral osteoarthritis is usually diagnosed using clinical criteria and confirmed with standing knee radiographs, with special views obtained as needed. Plain radiographs may show a decrease in cartilage space with adjacent osteophytes and sclerosis (image 4). If necessary, questionable cases can be confirmed with MRI showing articular cartilage loss or by arthroscopy. (See "Clinical manifestations and diagnosis of osteoarthritis", section on 'Diagnosis'.)

Medial meniscus tear — Patients with a medial meniscus tear usually report an acute inciting event, often involving some twisting or rotational movement under stress without direct trauma. True locking and giving way more commonly occur with significant meniscal tears and are more pronounced than the catching or clicking felt by patients with medial plica syndrome. Patients with medial meniscus tears typically have tenderness along the posterior medial joint line and discomfort or a catching sensation on provocative tests, such as the Thessaly (movie 1), McMurray (picture 6), Apley compression, or bounce home tests (figure 6), as well as a knee effusion.

Degenerative tears of the medial meniscus typically develop in adults older than 40 and causes pain at the posterior medial joint line that is exacerbated by passive knee flexion. As with acute tears, degenerative tears are often associated with a joint effusion and provocative tests are positive.

Patients with plica syndrome typically have pain along the medial capsule and above the joint line. While the McMurray and Thessaly tests rarely cause much pain in plica syndrome, they are often among the most painful in medial meniscus injury. Ultrasound or MRI can distinguish between a medial meniscus tear and medial plica syndrome if uncertainty remains after clinical evaluation. (See "Meniscus injury of the knee".)

Infrapatellar (hoffa) fat pad syndrome — The infrapatellar fat pad (IFP) is a highly innervated extra-articular structure located distal to the patella and directly beneath the patellar tendon (figure 1). IFP-related pain generally presents as anterior knee pain distal to the patella and may mimic that of patellar tendinopathy. Sprinting or squatting may exacerbate pain, but unlike plica syndrome focal tenderness is deep to the patellar tendon on either side but not at its insertion or more proximally. Such focal tenderness suggests inflammation and edema of the IFP. Ultrasound can confirm IFP edema and demonstrate the normal appearance of adjacent structures. (See "Approach to the adult with unspecified knee pain", section on 'Anterior knee pain'.)

INITIAL MANAGEMENT — 

The goals of treatment for plica syndrome are to reduce pain, treat inflammation, strengthen the knee extensor muscles (quadriceps) and hip abductors, mitigate mechanical factors that produce excessive knee valgus, and return the patient to as high a level of function as possible. Treatment during the first week focuses on pain control; the subsequent recovery phase focuses on modification of biomechanical deficits.

Acute phase (first week) — Treatment during the first week of care includes the following:

●Activity modification – Patients need to avoid activities that cause pain during rehabilitation. Most runners need to reduce running volumes and those with severe signs or symptoms (eg, limping) should curtail all running activities. Patients with less severe symptoms may modify their training by reducing the overall distance and avoiding running up hills or steps. Athletes can maintain aerobic fitness by using a stationary bicycle (recumbent or upright), an upper body cycle, or by swimming, water running, or other activities, provided they do not cause pain.

●Nonsteroidal antiinflammatory drugs (NSAIDs) – NSAIDs (eg, ibuprofen 10 mg/kg every six to eight hours, maximum dose 800 mg, or topical diclofenac gel) may be used for short-term pain relief during the first three days. No studies have specifically evaluated the benefit of NSAIDs for the treatment of plica syndrome.

●Ice application – Although formal studies are lacking, most experts consider applying ice to the medial knee important in the acute treatment of plica syndrome. The plica is a superficial structure, and ice can be applied effectively for 20 to 30 minutes duration three to four times per day.

●Glucocorticoid injection – Evidence is limited regarding outcomes for patients who receive glucocorticoid injection for plica syndrome. Glucocorticoid injection is not needed routinely. Sports medicine experts note anecdotally that injection into the thickened plica or intra-articular may reduce symptoms [2,24,25]. Benefit seems greatest in the early phase of the syndrome. Some expert clinicians prefer early injection while others would wait until failure of other conservative measures.

Our approach is to give a trial of conservative measures for six to eight weeks before performing an injection. We inject a combination of glucocorticoid and analgesic (eg, methylprednisolone and lidocaine) (table 1).

Theoretically, glucocorticoid injection directly into the plica has the potential to cause some atrophy of the thickened plical band [2,24,25]. In addition, improvement after injection into a plica may aid in diagnosis.

Recovery phase — Treatment beyond the first week of care consists of physical therapy to address tightness and weakness of specific muscle groups. Orthotics and additional interventions may be needed to correct heel valgus, longitudinal arch collapse, or dynamic foot pronation, if present.

Limited observational evidence from two small case series suggests that exercises to increase knee extensor strength and flexibility of the quadriceps, hip adductors (eg, adductor magnus), gastrocnemius, and hamstring muscles are successful in treating most patients with plica syndrome [1,15].

●Stretching – Once the initial pain has subsided, we suggest that patients with plica syndrome perform daily or twice daily therapeutic stretching exercises for tight muscles, including the quadriceps (movie 2 and movie 3), hip adductors (eg, adductor magnus), gastrocnemius (picture 7), and hamstring (picture 8) muscles. Ideally, patients should begin rehabilitation under the guidance of a physical therapist, athletic trainer, or comparable specialist.

Observational studies suggest that 40 to 78 percent of patients with a clinical diagnosis of plica syndrome regain their previous level of function without pain within three to six months of initiating stretching [1,15]. In one study, the patients with the greatest gains in flexibility had better outcomes [15].

●Quadriceps strengthening – Once the initial pain has subsided, we suggest that patients with plica syndrome perform quadriceps-strengthening exercises under the guidance of a physical therapist. Squats (picture 9 and picture 10 and picture 11) are one example of a useful exercise.

In one series of 63 patients with a clinical diagnosis of plica syndrome, knee extension exercises (picture 12) in addition to stretching of the quadriceps, hip adductors (eg, adductor magnus), gastrocnemius, and hamstring muscles resulted in a return to normal function in 86 percent of patients within three months [1].

●Treatment of dynamic knee valgus – Patients with mechanical factors producing excessive knee valgus (picture 3) as determined by a single leg squat (picture 13) or Trendelenburg sign (figure 7) should perform exercises to correct contributing biomechanical problems. These may include weak hip abductors and tight hip adductors or iliotibial band. Weak torso stabilizers (ie, "core" muscles) may contribute, and exercises to address such weakness (eg, planks (picture 14)) should be included as needed.

●Knee sleeves and braces – Compression knee sleeves or braces can be offered; however, in the author's experience, they may not help due to increased pressure on the anterior-medial knee, which can potentially worsen pain, especially in patients with medial plica syndrome. If a sleeve or brace provides relief, continued use is reasonable.

FOLLOW-UP CARE — 

We generally have the patient return for follow-up care at approximately six weeks during the recovery phase, or possibly earlier if symptoms persist despite appropriate physical therapy. If the patient reports recurrence or persistence of knee pain, we repeat the physical examination and review their compliance with the prescribed treatment plan. If the patient appears to be compliant with both therapy and activity modification, additional imaging may be needed to evaluate for other diagnoses that commonly cause anteromedial knee pain. (See 'Differential diagnosis' above.)

If the diagnosis is confirmed, we reinforce the importance of following the treatment plan and performing the exercises regularly. We may perform a glucocorticoid injection for added pain relief. We see the patient back in another four to six weeks.

For patients with recurrent or persistent pain, we ask them to explain in detail the exercises they have been doing. Useful questions may include:

●How long have you been seeing the physical therapist?

●How many times a week do you go to physical therapy?

●How often do you do your home exercise program? (Have the patient demonstrate some of the exercises.) How well are you tolerating the exercises?

●What sort of cardiovascular workouts are you able to do? (eg, "I can ride the stationary bike for 10 minutes until my knee hurts" versus "I'm still running 25 miles per week")

●Do activities that aggravated your symptoms still do so?

If there is improvement, the patient continues with physical therapy until they can perform all exercises without pain, and then we reintroduce activities that previously caused pain (eg, running). The intensity and demands of activities should be increased in a gradual, stepwise manner until the patient achieves the desired level of performance.

If the compliant patient has not improved after four to six months of physical therapy and local glucocorticoid injection, orthopedic consultation is reasonable to assess for another cause of pain and, if plica syndrome is confirmed, to consider arthroscopic debridement.

INDICATIONS FOR ORTHOPEDIC REFERRAL — 

Surgical intervention, consisting of complete arthroscopic excision of the fibrotic plica, may be indicated when symptoms have failed to improve with four to six months of appropriate conservative treatment. Arthroscopy should also be considered in cases of persistent knee effusion. In a systematic review of 12 studies (1 randomized trial) involving 643 knees, arthroscopic incision was associated with good or excellent results overall in 84.2 percent of cases (95% CI 72.8-91.4) [26]. (See 'Initial management' above.)

During arthroscopy, the entire joint must be evaluated for other fibrotic plica, chondral injury to the undersurface of the patella and the medial femoral condylar articular surface, as well as other possible derangements (eg, arthrosis, loose bodies, or osteochondritis dissecans [OCD]) that may have led to the development of a pathologic plica. Although plica may grow back after excision, they are usually no longer symptomatic.

SOCIETY GUIDELINE LINKS — 

Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Knee pain".)

SUMMARY AND RECOMMENDATIONS

●Anatomy – A plica is an embryonic remnant commonly present in the population. Normally it consists of a thin, vascular, pliable band of tissue that originates from the synovial wall and crosses the synovial joint. It may be located in the suprapatellar, medial, infrapatellar, or lateral compartments of the knee joint (figure 1). (See 'Epidemiology' above and 'Anatomy and classification' above.)

●Pathophysiology – Direct blunt trauma to the knee, repetitive injury, or irritation from some other intraarticular abnormality can cause a plica to become thickened, fibrotic, avascular, and painful. Symptoms occur as the nonpliable band either rubs over the medial femoral condyle or is entrapped between the patella and femoral condyle. (See 'Definition' above and 'Pathophysiology' above.)

●Clinical diagnosis – Diagnosis is suggested by a history of anteromedial knee pain after direct trauma, twisting injury, or repetitive injury associated with pain that becomes worse with squatting, kneeling, walking upstairs, or sitting for long periods (theater sign). Patients may report clicking or catching during knee flexion.

Physical findings are variable. With medial plica, there may be subtle soft tissue swelling just medial to the patellar border. Careful palpation may reveal a firm, tender ridge of tissue running either parallel or slightly obliquely to the medial border of the patella. Other suggestive findings include tight quadriceps and hamstring muscles and positive medial patellar plica (MPP) (figure 4) and knee extension (figure 5) tests. (See 'Diagnosis' above and 'Provocative tests' above.)

●Diagnostic imaging – Imaging does not usually establish the diagnosis and is performed primarily to exclude other knee pathology. (See 'Clinical manifestations' above and 'Differential diagnosis' above.)

●Initial treatment – The acute phase of treatment focuses on reduction of pain through activity modification, application of ice, and short-term administration of nonsteroidal antiinflammatory drugs (eg, ibuprofen). (See 'Acute phase (first week)' above.)

●Glucocorticoid injection – Glucocorticoid injections are not routinely needed. However, injection directly into the painful plica when it is readily palpable may be helpful when conservative measures have not provided relief in six to eight weeks. (See 'Acute phase (first week)' above.)

●Physical therapy – Once initial pain has subsided, we suggest that patients with plica syndrome perform physical therapy to address contributing muscle tightness and weakness (Grade 2C). Ideally, exercises should be performed initially under the guidance of a physical therapist. Exercises typically include the following:

•Daily or twice daily stretching exercises for tight quadriceps, hip adductor (eg, adductor magnus), gastrocnemius, and hamstring muscles. (See 'Recovery phase' above.)

•Strengthening exercises for the quadriceps and hip abductors. (See 'Recovery phase' above.)

Mechanical factors contributing to excessive knee valgus, which may be identified with a single-leg squat maneuver, should be addressed with physical therapy.

●Indications for referral – If a patient who is compliant with activity restrictions and physical therapy exercises has not improved within four to six months, orthopedic or sports medicine consultation is indicated to assess for an alternative cause of pain or, if plica syndrome is confirmed, to reassess the physical therapy regimen. Surgical intervention may be reasonable in this setting. Surgical treatment consists of arthroscopic excision of the fibrotic plica. (See 'Indications for orthopedic referral' above.)

ACKNOWLEDGMENT — 

The UpToDate editorial staff acknowledges Jorge E Gomez, MD, who contributed to earlier versions of this topic review.