Synovial Plica Syndrome
Synovial Plica Syndrome
What is synovial plica syndrome?
  • Synovial plica syndrome arises when the otherwise normal asymptomatic plica becomes painful and can inhibit knee function
  • To better understand this, below are explanations of key anatomy features about the knee

What is the synovium?
  • Synovium is a specialised connective tissue membrane that lines the inside of the capsule that surrounds all synovial joints

What is a synovial joint?
  • A synovial joint is the most common type of joint in the human body
  • There are 206 bones and around 300 joints in the human body
  • All synovial joints have three common features:
    • Articular cartilage which covers the bony surfaces allowing for smooth free movement without damaging the underlying bone
    • Joint capsule which is lined internally by synovial membrane (synovium)
    • Synovial fluid which is the natural lubricant within the synovial cavity

What is a synovial plica?
  • A plica is a fold of synovium within the joint cavity and it projects out of the cavity like a thin shelf

How are plicas formed?
  • Plicas in the knee are formed during the first few weeks of development and disintegrate when the foetus is around 3 months old
  • Knee movement of the foetus within the uterus helps with the resorption of the plicas

Which joints are affected by plicae?
  • A plica can occur at any synovial joint but the most common joint affected is the knee

How many plicas exist within the knee?
  • There are 4 plicas within the knee during development:
    • Suprapatellar plica:
      • The suprapatellar plica is located above the patella 
    • Medial patellar plica:
      • The medial patellar plica is located on the medial (inner) side of the knee joint connecting it to the fat pad below the patella
      • Medial patellar plica is the most common plica and the one most commonly irritated
    • Infrapatellar plica:
      • The infrapatellar plica is also called ligamentum mucosum and connects the fat pad below the patella to the anterior cruciate ligament and the intercondylar notch (central part of the femur between the two femoral condyles)
    • Lateral plica:
      • The lateral plica connects the lateral (outer) part of the knee joint to the fat pad below the patella
      • This is the rarest type of plica

How frequent are plicae?
  • Knee plicae are thought to occur in 50-80% of adults
  • However not all are symptomatic

How frequent is medial plica syndrome?
  • Around 10% of people experience medial plica syndrome at some point in their life
Who is at risk?
  • It occurs in both sexes
  • Usually occurs in first through third decade of life
Aetiology
  • Synovial plicae are mostly asymptomatic and clinically of little consequence
  • However, if they are injured or irritated they can become inflamed and symptomatic:
    • The inflammation causes the plica to thicken and become fibrotic and stiff
    • This means that during knee motion the stiffer and thicker plica is tented over the femur during knee motion causing pain
  • Triggers that can cause a painful plica are:
    • Direct trauma to plica
    • Twisting injuries
    • Repetitive flexion/extension of the knee
    • Weakness of vastus medialis muscle (this makes up the lower inner part of the quadriceps muscle)
    • Significant muscle imbalance around the knee
    • Increased physical activity
    • Haematoma
Symptoms
  • Plicae become symptomatic when due to an inflammatory process they become tight, thickened, fibrotic and inelastic
  • Location of the pain is typically anteriorly or anteromedially but is non-specific and can be confused with other pathologies often leading to failure to successfully diagnose and treat
  • The medial plica:
    • is the most common symptomatic plica
    • can impinge on medial femoral condyle at 70-100 degrees of knee flexion
    • Impingement over time can cause abrasion and wear of the articular cartilage on the medial femoral condyle
  • Around 10% of the population are affected 
  • Can be bilateral (affect both knee) in 60% of cases but may not occur simultaneously
  • Patients can report:
    • Clicking
    • Clunking
    • Popping sensation when squatting
Which investigations help in the diagnosis of synovial plica syndrome?
  • X-rays:
    • X-rays of the knee are good baseline study but will not reveal a plica
  • MRI scan: 
    • MRI scan can show a synovial plica and its location
    • However they are not always easy to see nor evaluate confidently if they are symptomatic
    • MRI is very useful to exclude other pathologies as sources of pain 
  • Clinical examination by an experienced specialist knee surgeon has been shown to be more accurate, sensitive and specific at detecting a symptomatic plica than an MRI scan
  • Knee arthroscopy:
    • Knee arthroscopy is the gold standard for definitive diagnosis as well as management of the synovial plica

What are the treatment options for synovial plica syndrome?
  • A trial of conservative measures can be tried:
    • Avoiding exacerbating factors 
    • Activity modification:
      • In particular avoid high impact activities such as jumping, squatting and lunging
    • Analgesia:
      • Paracetamol
      • Nonsteroidal anti-inflammatories in form of topical creams or oral tablets
    • Once symptoms improve, focus on physiotherapy exercises:
      • Particularly to strengthen vastus medialis and core strength
      • Stretching of the hamstrings
  • Ultrasound guided steroid injection:
    • This can help improve symptoms
    • Will also help confirm the diagnosis 
  • Operative treatment:
    • Can be considered after a trial of conservative treatment
    • Arthroscopic plica debridement:
      • This is the definitive treatment
      • This involves key hole surgery to the knee 
      • Plica can be easily identified
      • The severity of impingement, abrasion to articular surface and knee position causing symptoms can all be assessed
      • Unfortunately, plicas are commonly debrided (erroneously) when no other source of pain can be identified 
      • These patients tend not to do well as the source of pain has not been identified and synovial tissue is sensitive and can cause scarring leading to more pain
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