Synovial plica syndrome (SPS) is a condition that develops in the knee, when an otherwise painless and normal structure becomes a source of pain caused by overuse or excessive loading.
Patients typically go to general practitioners, physiotherapists, or surgeons with what can feel like anterior knee pain with or without pain when they move – the diagnosis can sometimes be difficult to make from a physical assessment.
Typically, more experienced consultants will be able to fully diagnose this issue using a combination of clinical assessment and imaging, but most likely, experience from having seen it before.
What is it and who gets it?
Synovial plica syndrome is an umbrella term which encompasses a collection of symptoms, usually affecting male and females and it is more common in people under 30, especially teenagers. .
Patients often mention the most common symptom of anterior knee pain combined with clicking, clunking, and a popping type sensation on loading activity such as squatting that works the patella femoral joint. Pain can be very intense on prolonged activity and sporting movements.
There are a few places in which the plica can get aggravated. According to their location, the synovial plicae are classified as suprapatellar, mediopatellar, infrapatellar, or lateral.
The medial plica is typically the most commonly painful part of the knee when people get diagnosed with synovial plica syndrome. This can be due to the knee being at it’s weakest on the medial aspect.
Teenagers involved in sporting activity have a higher risk of developing plica syndrome. Especially those who play multiple sports or are involved at performing at a high level. Medial plica syndrome within the football academy system due to their high level of performance and frequency of play.
Plicae are inward folds of the synovial joint capsule lining and are present in most knees. In their normal state, they are thin, flexible and appear almost see through.
The mediopatellar, which is considered the most involved / important, is attached to the articularis genus muscle, while it runs to the intra-articular synovial capsule lining and blends into the medial patella tibial ligament on the medial aspect of the retropatellar fat pad which provides cushioning for the kneecap.
Depending on how it is positioned, size, and elasticity in each individual, the plica may impinge (become trapped / pinched) between the quads tendon and femoral trochlea at 70 to 100 degrees of flexion – when the knee is bent, causing mechanical symptoms, meaning we get pain when we move it.
There are a number of reasons why plica syndrome develops – in some individuals, the elasticity and size of the synovial fold can be more developed compared to others – this can mean greater potential for the catching / pinching of the tissue.
Plicae become painful and a problem when its inherent qualities change due to an inflammatory process that changes the overall quality and pliability of the tissue.
The reason a plica becomes a problem and develops classification of being labelled plica syndrome is due to the changes that occur in the tissue. A synovial plica that has been through this inflammatory process can become symptomatic as it changes to being tight, thick and fibrous – this means less flexibility and less function, whilst also being painful.
When a synovial plica has been affected by the above changes it might bowstring across the femoral trochlea (the head of the thigh bone), causing impingement (catching) between the patella and femur when the knee bends.
Plica syndrome is not just a symptom of the plica and its location – pain can be referred to other parts of the knee and includes a variety of different symptoms.
Most cases of knee plica syndrome are spontaneous in nature, and symptoms have been known to occur in both limbs but not always at the same time.
There are many other causes and conditions that run alongside plica syndrome. Relationships have been identified associated with trauma, overuse, hematoma, diabetes, and inflammatory arthropathy. In teenage years – plica syndrome can develop when there is a growth spurt, and even more so when excessive exercise is performed during a growth spurt.
Any knee problem which is capable of producing temporary or long lasting synovitis which is inflammation of the joint and its surrounding tissues may therefore be a key reason in the development of synovial plica syndrome.
There is some research which also suggests that some people may genetically predisposition to developing plica syndrome. More research is currently needed on the topic and it is difficult to predict someone who will develop it currently.
Patients may report aggravation of symptoms with overuse, especially during running based sports or heavy activities involving flexion and extension of the knee like squatting.
The synovial plica is directly involved as part of the knee joint and is indirectly attached to the quadriceps muscle as the position of the plica is dynamically controlled during knee flexion and extension because of its attachment to the patellar fat pad.
Synovial plica irritation is more common in patients who have poor quadriceps strength and tone or any significant muscle imbalance at the knee. This is because excess pressure is placed upon the joint. Instead of muscles working the joint and offsetting the forces being placed upon it, the knee becomes overloaded and the joint absorbs more force than it should.
A common problem for people with plica syndrome is that having the knee bent for long periods of time causes their pain. One example of this can be when sleeping at night, this obviously prevents recovery and repair which in turn can lead to increased injury risk.
Management of synovial plica symptoms is currently not clear – symptoms can get progressively worse and there isn’t a set structure for management of this problem. Further research is required in the area.
How is plica syndrome diagnosed?
One of the most important points in diagnosing knee plica syndrome is getting a thorough and detailed history from the patient. Only then is it a clinical diagnosis that may be supported by specific tests and imaging.
Diagnosis of plica syndrome can be in someone of any age although it is less common among young children below 10 years old. Teenagers and people below the age of 30 are also common candidates for a plica syndrome diagnosis.
Diagnosis of plica syndrome can be couple with blunt trauma or a twist then swelling developing – once this has settled, pain can be reported at the medial plica where fibrosis of the tissue may have occurred.
Patients may give a history of anterior knee pain following exercise or work, which requires repetitive flexion and extension movements of the patellofemoral joint.
These aggravating activities may include ascending and descending stairs, squatting, bending and getting out of a chair after being seated for an extended period of time. This can also make sitting down and driving for long periods difficult, if they are unable to move their knee.
Anterior knee pain is a diagnosis in its own right but it can be the main symptom of pain that people experience.
The knee may be tender to touch, swollen, and stiff – symptoms are often difficult to separate from other joint conditions such as meniscal tears, articular cartilage injuries, or osteochondritic lesions – this is why it is such a problem to diagnose.
Patients may also complain of symptoms including pseudo locking of the knee – which is where the knee becomes difficult to move due to pain. This may present as local pain in the front of the knee or shin region.
As a safety note – where symptoms are isolated to locking and sharp pain within the joint, meniscal pathology should first be ruled out.
Conservative treatment can be managed in physiotherapy and referral made for orthopaedic opinion, if needed.
Physiotherapy is a great way to manage synovial plica syndrome, it responds well to general conservative management techniques such as activity modification, exercise therapy, and treatment.
There is another school of thought from the other side of the coin that orthopaedic management is more suited to plica syndrome. Each person will have a unique experience with plica and their chosen way to manage symptoms.
Clinically, the best way to manage plica syndrome is to aim for conservative management and improvement before anything too invasive. Adjusting exercise amounts and loads then looking at what therapies can be introduced to help with reduction of pain and improvement of function. Following improvement with this management, rehab should be a key focus of building the full lower limb.
Exercises for the knee are important but establishing if there are any imbalances within the hamstrings and glutes are key to improving symptoms.
People who do not experience a significant improvement in their synovial plica syndrome despite compliance with conservative management over a period of time of 3 to 6 months, should be offered further investigation and management via orthopaedics.
MRI scan is a one way of investigating the knee, but accuracy of MRI scan to diagnose plica syndrome is not great. An experienced orthopaedic surgeon will typically opt for an exploratory arthroscopy to have a more detailed look at the knee.
It used to be common practice to excise any plica during investigative arthroscopy, even if the tissue was not representative of the pain being reported by the patient, or other pathologies were found.
However, this isn’t always the best option, as plica tissue is highly sensitive and this can cause a reaction for it to become fibrotic. This is the reason that only tissue which matches the history and presentation of pain should be targeted for removal.
At the investigative arthroscopy, the plica should have a fibrotic appearance or seen to be impinging when the knee is moved and no other clear diagnosis, only then should the plica be re-sectioned.
Synovial plica syndrome of the knee is common and it is seen in both community and hospital settings, more typically within the younger generations who are active and experiencing growth spurts.
A clear diagnosis of plica syndrome should be suspected in patients with symptoms of intermittent pain, swelling, and snapping sensation affecting the knees, which is associated with repetitive activity that involves increased loading through the patellofemoral joint.
Non operative strategies are usually successful if the problem is caught and diagnosed early or if the symptoms are very mild in nature. For best results conservative management requires good compliance from the patient for a sustained period of time, but is often sufficient in reducing symptoms – plica syndrome tends not to typically occur. Surgery should only be considered at this stage when good conservative management fails.
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