Plica syndrome

Plica syndrome is a condition that causes pain in the middle knee area.¹ This is due to inflammation or irritation of the plica (a fold over the knee) from traumatic injury, over-, or repetitive use.¹ It can affect all ages of patients, but mostly those from 20-30 years old.²

Structure

The knee joint is between the tibia and femur (thigh) bone with surrounding soft tissue - ligaments and tendons. They are provided with necessary nutrients and kept properly lubricated by the synovial fluid. The synovial membrane secretes this synovial fluid. The plica is the inward fold of the synovial membrane, and it is present in most knee joints bilaterally. They are formed in the fetal stage of development and are remodelled, typically reducing in size, as the knee joint continues to develop. The size and elasticity of the plica will vary across persons.¹ 

The knee has four different types of plica:³

1. Suprapatellar plica: This is located in between the knee joint and suprapatellar bursa
2. Infrapatellar plica: It is found in the synovial tissue just below the area of the knee cap
3. Medial plica: This is found on the inside of the knee joint. They are the most common cause of plica syndrome
4. Lateral plica: This is located on the outside of the knee joint

Causes of plica syndrome

When a plica is irritated or inflamed, it can become tighter, thicker, and/or less elastic. This then causes pain and affects the normal movement of the knee.⁴

Plica syndrome could be idiopathic. Other causes include:

1. Knee injuries, either direct from a fall or indirect after twisting.
2. overuse or repetitive usage with activities like cycling or stair climbing.
3. Teenagers who are experiencing a growth spurt might also present with synovitis (inflammation of the synovial tissue), leading to plica syndrome.
4. The plica is indirectly inserted into the quadriceps, and plica syndrome can present in persons with weak quadriceps (thigh muscle) function or other imbalances at the knee.

Symptoms

1. Pain: This is the most common symptom, presenting with pain at the front and inside of the knee. One will report pain after activities like stair climbing, squatting, and prolonged sitting¹ 
2. Swelling: This accompanies the irritation and inflammation that is ongoing with the pain³
3. Clicking or snapping in the knee, especially when it is in flexion¹

Other symptoms include stiffness, locking, or a feeling of the knee giving way. These symptoms are also present in other knee-related conditions like osteoarthritis and meniscal injuries.¹ Therefore, it is important to ensure proper diagnosis.

History, diagnosis, and investigations

As noted above, it can be a challenge diagnosing plica syndrome due to the many other knee conditions that present similarly.⁵ One presenting with an anterior knee pain should visit a clinician, who can then carry out appropriate tests as required. The history of the pain provides a picture of a possible diagnosis. One might complain of pain with a job that requires repeated stair climbing and bending or with work that involves long hours of sitting.6 The pain is usually absent during the initial activity but worsens with increased irritation from prolonged activity.

During examination, the examining clinician will try to feel for the plica folds with your knee relaxed in extension. Patients with plica syndrome will present with pain on palpation of the folds. If it is a recent direct traumatic injury, an X-ray or MRI may be requested to investigate the other surrounding soft tissue and bony structures and rule them out as potential causes.

The use of an MRI is not encouraged for the diagnosis of plica syndrome. The plica can be visible if the affected knee is also swollen. But it's usually only suitable for complex conditions and for investigating other differentials.⁷ A knee arthroscopy is recommended as the gold standard to investigate plica syndrome.⁸

Management⁹

The goal of treatment is to reduce pain and improve strength in the knee. Treatment of plica syndrome is generally through conservative means such as physiotherapy, exercises, and activity modification. Whatever method is adopted for treatment will vary depending on the severity of symptoms. 

1. Activity modification: One will have to modify one's usual activities, especially those that have been identified as aggravating factors. In the acute stage of plica syndrome, a regimen of rest and ice packs may be enough to ease the pain
2. Medication: Paracetamol or the use of a topical or non-steroidal anti-inflammatory cream can also provide pain relief
3. Physiotherapy: After evaluation of your knee, an exercise program will be prescribed to increase the strength in your quadriceps and stretch the hamstrings. It is essential that you are educated on the importance of these exercises and that you follow the recommended routine for best outcomes
4. Intra-articular injection: A steroid injection can be introduced in the early stages of plica syndrome for considerable pain relief. It is not recommended as a sole treatment, and exercises are usually encouraged after the injection

Factors that influence conservative management¹

Several factors influence whether conservative management will be successful or not. They include:

1. Type of plica: The lateral and infrapatellar plicas will usually require surgery. The medial plica has been known to improve with exercises
2. Patient’s age: Patients who are younger and are treated at the acute onset of plica syndrome generally show improvements
3. Symptom duration: Patients with chronic knee pain might report poor results with conservative measures

Patients with chronic plica syndrome can present with chronic pain, stiffness, and arthritis.

Surgical intervention

Surgery is only considered if all conservative measures do not relieve pain. This is usually offered after a period of at least 3-6 months. The surgery involves the excision of the pathological plica during an arthroscopy if no other joint condition correlates to the pain.¹¹ A large number of persons who underwent surgery reported to be pain-free, while others will have chronic knee issues. These risks can be discussed with your surgeon.

Following surgery, post-surgical care and rehabilitation are vital for full recovery from symptoms. Physiotherapy is advised as early as possible and no later than 72 hours after surgery to prevent complications.⁶

The rehabilitation process will typically follow these patterns:

1. Mobilization: One is given a range of movement exercises and simple weight-bearing activities. This is to promote the healing process and prepare you for normal gait and full weight-bearing activities.

The physiotherapist will also be available to recommend personalized exercises to strengthen and improve the flexibility of your quadriceps, hamstrings, and other lower limb muscles. Outside the gym, a simple way to strengthen your knee is with the use of a resistance band or an ankle weight. The resistance provided by the band or weight as you bend and straighten your knee will improve the function of the quadriceps and hamstrings.

2. Return to Activity: Under the supervision of the physiotherapist, the patient will then start to include high-impact activities like running. For athletes, the physiotherapist will work with you to return to your level of sporting activity without any pain.

Professional advice on self-management and education on the condition are essential to understand mechanisms on avoiding any re-injuries or pain recurrence. Most patients will report no postoperative pain after two to four weeks. 

Surgical complications

Following surgery, postoperative complications are rare. However, if not properly managed, complications include the following:12

1. Recurring synovitis
2. Decreased range of knee movement
3. A reduction in the bulk of the muscles that attach to the knee 

Prognosis

Overall, plica syndrome is associated with a positive prognosis. Most patients will report an improvement in their symptoms and can resume their usual activities of daily living, work or sports after their rehabilitation.²

Summary

Plica syndrome is a condition that affects the anterior knee. It is caused by injury, overuse, and repetitive use leading to inflammation and irritation of the plica. The common symptoms are pain, swelling, and clicking. Plica syndrome can be difficult to diagnose, and other possible knee conditions are ruled out with an MRI. A diagnostic arthroscopy is the gold standard for plica syndrome. Conservative management with rest, activity modification, physical therapy, injections, and medication. Surgery is only considered if conservative management fails. There are rare complications with plica syndrome, and the prognosis is generally positive.