What is Discoid Meniscus?

The menisci are two moon-shaped structures in the knee that act like shock absorbers between the thigh bone (femur) and shin bone (tibia), softening the impact of stress and spreading out pressures. These structures are made up of a type of tissue, called fibrocartilage, predominantly composed of a protein called type I collagen. They distribute forces, improve the fitting of the joint, and help stabilize the knee. The inner meniscus usually has a C-shape and is closely attached to the surrounding tissue, while the outer meniscus is rounder and more flexible, as it’s less connected to the surrounding tissue.

A discoid meniscus is a variation of the normal moon-shaped meniscus. It is often thicker and shaped like a disc or saucer. These types of menisci are more prone to injuries compared to the normally shaped menisci. When a discoid meniscus is present and causes symptoms, it can often cause knee pain and a feeling of the knee ‘popping’, commonly called the “popping knee syndrome.” There are three types of discoid menisci, differentiated by the shape of the meniscus: complete, incomplete, and Wrisberg variant. In terms of treatment, doctors may simply monitor the condition or suggest keyhole surgery to reshape the discoid meniscal tissue. The choice of treatment depends on the shape and the patient’s symptoms.

What Causes Discoid Meniscus?

A discoid meniscus is thought to be something a person is born with. However, it’s a topic of debate whether it’s a natural variation in shape or a difference in structure. A discoid meniscus has various distinct features, such as instability around the edges.

Compared to a normal lateral (side) meniscus, the discoid lateral meniscus (DLM) has been shown to have more instability in the front and back parts, but not the middle, in patients who had surgery for a tear in the medial (inner) meniscus. This instability of the DLM could potentially lead to more tears in people with this particular variation.

Risk Factors and Frequency for Discoid Meniscus

A discoid meniscus is a condition that often goes unnoticed. It is most commonly found in the United States, where about 3% to 5% of the population have it. However, it’s much more common in some Asian countries, being found in up to 10.6% of people in Korea and 13% of people in Japan. A related condition, discoid medial meniscus, is quite rare, affecting only about 0.1% to 0.3% of the population.

  • Discoid meniscus often goes unnoticed.
  • In the U.S., about 3% to 5% of people have discoid meniscus.
  • In Korea and Japan, the condition is more common, affecting up to 10.6% and 13% of people respectively.
  • Discoid medial meniscus is a rarer condition, affecting only 0.1% to 0.3%.
  • About a quarter of people who have a discoid meniscus have it in both knees.
  • In Asia, it’s even more common to have discoid meniscus in both knees, with 79% to 97% of patients having both knees affected.
  • For patients who have the condition in one knee, it’s often recommended to check the other knee too.

Signs and Symptoms of Discoid Meniscus

A discoid lateral meniscus, or DLM, often does not show any signs or symptoms. However, if it tears or becomes unstable, some people might start to experience symptoms. These include pain in the front and side of the knee, and an accumulation of fluid in the knee, with or without the knee making mechanical sounds like clicks or locks, especially when the knee is straight. People may lose some flexibility, and the muscles in the upper leg (quadriceps) may shrink.

The discoid meniscus is sometimes referred to as “snapping knee syndrome” because it can cause a snapping sound when the knee is bent. This sound is usually linked to an unstable version of DLM that isn’t attached at the back. This snapping noise doesn’t happen all the time. Instead, it tends to occur more often during physical activity and may be accompanied by pain, limited movement, and fluid in the knee. Symptoms can start either after an injury or spontaneously. The mechanical sounds, like catching, locking, and clicking, are not necessarily signs of instability.

Factors such as the type of discoid meniscus, whether there is a tear or instability, and the patient’s age can influence symptom presentation. Most cases are seen in teenagers. Younger children may experience spontaneous snapping noises when the knee is fully bent, while older children typically show symptoms of a torn DLM.

During examination, the knee should be visually inspected, physically felt, and its movement assessed. Other facets include checking for any nerve or blood supply issues, confirming the stability of the ligament, and performing specific tests to check for meniscus issues. Some of these specific tests include pressing on the inside or outside of the joint (McMurray’s test, Apley’s compression test, Thessaly’s test) to check for pain. Because DLM often affects both knees, the other knee should also be checked. The overall sensitivity of these medical examinations in diagnosing DLM is about 88.9%.

Testing for Discoid Meniscus

If a person is experiencing pain in their knee or shows certain symptoms, they might have a condition called a discoid meniscus. This can also be discovered accidentally through an x-ray or an MRI scan after an injury.

Plain x-rays can be used in this scenario, but they might not always show clear signs of the condition. However, some people with a discoid meniscus might show certain features in their x-ray images. For example, the space in the affected joint can appear wider than usual (up to 11 mm), the end of the thigh bone (lateral femoral condyle) can appear squarish, a cupped shape can be seen in the top of the shin bone (lateral tibial plateau), and the lateral tibial spine (a part of the shin bone) can appear underdeveloped.

MRI scanning is really helpful in identifying a discoid meniscus in painful knees. MRI results can highlight key signs like the “bow-tie sign” – where continuous images show the meniscus tissue connecting, or a meniscus that appears unusually thick or flat. Images can also show the meniscus covering the entirety of the affected compartment. MRI scans have known measurements that are diagnostic of a discoid meniscus, such as a meniscus width greater than 15 mm from the edge to the free margin, and a ratio of the smallest meniscus width to the largest shin bone width exceeding 20%.

However, it can be a bit tricky to identify an incomplete discoid meniscus as it can look almost normal in the MRI. It may show a bright (hyperintense) signal between the meniscus and the knee joint capsule or the back of the outer meniscus moving forward.

An MRI can also help to spot any tearing or displacement in the meniscus, and it can be useful for planning any required surgery. However, its findings should always be considered along with the patient’s medical history and physical exam results, as an incomplete discoid meniscus can look normal on an MRI. Plus, some symptoms may be detected on an MRI that can’t be seen on an arthroscopy (a type of keyhole surgery used to look inside a joint).

Treatment Options for Discoid Meniscus

If a discoid meniscus (an abnormal disc-like shape of a usually crescent-shaped knee cartilage) is discovered but the patient is not experiencing any symptoms, surgery isn’t necessary. These patients can be monitored regularly without undergoing treatment. If symptoms appear, the first course of action is usually conservative management. However, if the symptoms persist for a long time before surgery is considered, this could increase the risk of developing severe arthritis in the knee.

Surgical treatment becomes a consideration when the discoid meniscus starts causing pain and/or physical knee problems, which are often due to a tear in the meniscus. For patients with occasional symptoms, treatment is based on managing these symptoms. But if there are persistent, severe symptoms, or the knee is locked, surgery is required. The main goals of surgical intervention are to restore the normal appearance and stability of the meniscus.

In the past, the go-to surgery for a symptomatic discoid meniscus was either a total or partial meniscectomy, which is the surgical removal of all or part of the meniscus. However, this approach has been linked to the development of arthritic changes in the long run. More recently, surgeons often prefer a procedure called arthroscopic saucerization, which is performed with a small camera inserted into the knee joint.

Arthroscopic saucerization is a type of partial meniscectomy. The purpose of this procedure is to reshape the discoid meniscus to look more like a normal meniscus, improving its function and ability to absorb shocks. While performing this procedure, it’s essential to preserve a stable rim around the meniscus to maintain its function and reduce the likelihood of a future tear. The challenge is striking a balance between leaving enough tissue to prevent future tears and not leaving too much, which may lead to arthritic changes.

Due to structural peculiarities, a discoid meniscus has a higher risk of tearing. Moreover, when certain types of discoid meniscus occur, the affected meniscus is hypermobile (moves more than usual), which may require additional surgical fixation.

After surgery, how much weight a patient can put on their leg is decided by the surgeon. Physical therapy is often prescribed to strengthen the muscles, increase the range of motion, decrease swelling, and improve balance and coordination.

If a discoid meniscus is damaged due to peripheral rim detachment or a tear within the meniscus, it presents additional complexities. Several surgical techniques, old and new, cater to different scenarios. For patients with unstable peripheral rim detachment (where the meniscus is not firmly attached), meniscal repair methods can be applied. A recent preservation technique called meniscopexy (which involves securing the meniscus to the tibia) can offer symptomatic relief. In some cases, the entire meniscus might be preserved without reshaping. Certain types of tears can be managed by reshaping the tear and applying appropriate repair techniques. However, some complex peripheral tears often result in removal of a significant part of the meniscus.

A discoid meniscus can cause quite a few troubling symptoms like knee pain, difficulty moving the knee, swelling in the knee, and a clicking or locking sensation in the joint. Any of these symptoms should be examined by a doctor, who will do a thorough physical examination of the painful knee, as well as the other knee for comparison. They will also do some imaging tests like x-rays or MRI’s.

There are several other health issues that can cause similar symptoms, so it’s important to rule these out to make sure the correct diagnosis is made. These can include:

  • Tears in different parts of the meniscus or knee ligaments
  • Injuries to the back part of the knee
  • Inflammation in the tendons around the kneecap or in the thigh muscle
  • Problems with the kneecap causing pain
  • Fractures or breaks in the bones around the knee

What to expect with Discoid Meniscus

The current medical literature reports that the surgical procedure known as partial meniscectomy, which may also involve meniscus repair, has given good to excellent results for patients with a symptomatic discoid meniscus condition. Studies conducted over 5 years show that about 85% of the patients have experienced beneficial outcomes from this surgery.

Partial meniscectomy has proven to be more favorable than total or subtotal meniscectomy. The reason for this is that after undergoing a total meniscectomy, the body is likely to experience increased contact pressures due to the absence of an adequate meniscus, which normally serves as a shock absorber. This situation might elevate the risk of developing degenerative joint disease.

Possible Complications When Diagnosed with Discoid Meniscus

Articular cartilage is a sort of cushion or shock absorber in your knee. When this gets injured, it can cause problems with the disc-like shock absorbers in your knee, known as the DLM. Certain things can increase your chance of having this type of injury. These include having symptoms for more than 6 months, being very active, and having an unevenly shaped DLM. Specifically, if you had a longer duration of symptoms and had difficulty in fully extending your knee before surgery, the chance of damaging your articular cartilage in cases of problematic DLM at the time of surgery is high.

Another thing that can happen after a specific type of knee surgery called saucerization, which is used to treat the DLM, is a unique complication. It is known as Osteochondritis Dissecans (OCD) and affects the outer part of your thigh bone. It is thought that repeated knee impact after partial meniscectomy, a surgical operation to remove part of the meniscus in your knee, might make a patient more susceptible to this problem. Therefore, doctors should be mindful of this possible outcome.

Potential Risk Factors for Articular Cartilage Injuries:

  • Having symptoms for more than 6 months
  • Being very active
  • Having an unevenly shaped DLM
  • Having difficulty fully extending your knee before surgery

Possible Complications after Saucerization Surgery:

  • Osteochondritis Dissecans (OCD) in the outer part of the thigh bone

Recovery from Discoid Meniscus

There’s isn’t one-size-fits-all recovery program after a surgical procedure for a discoid meniscus, a condition where the knee’s shock-absorbing cartilage is shaped abnormally.

After a procedure like saucerization or meniscectomy, which involve reshaping or removing the meniscus, patients can usually start moving around freely right away. The first steps towards recovery should focus on reducing swelling with ice and starting strengthening exercises for the thigh muscles around two weeks after surgery. By the eighth week, patients often regain a full range of motion and strength in their knees, gradually returning to sports and other recreational activities.

In contrast, patients having a combined saucerization with meniscal repair, where the meniscus is reshaped and also repaired, need to exercise more cautious during the initial recovery period, limiting weight-bearing and movements. They would then progressively increase weight-bearing and knee movements, aiming to fully bear their weight and achieve total knee mobility within six to eight weeks. When it comes to resuming sports, it’s handled on a case-by-case basis with no fixed timetable. Generally, full range of motion and strength is usually regained within three to four months.

Preventing Discoid Meniscus

If a doctor finds a discoid meniscus (a rare type of knee condition) by accident and there are no symptoms, treatment isn’t needed. However, if this condition is causing discomfort or issues with movement, a surgical operation might be necessary. The doctor should discuss the pros, cons, and potential risks of opting for or against surgery with patients—or if the patients are children, with their parents or guardians. This way, the patients and their families can make an informed choice. It’s also worth noting that surgical outcomes in young patients are generally positive.

Frequently asked questions

A discoid meniscus is a variation of the normal moon-shaped meniscus in the knee. It is often thicker and shaped like a disc or saucer. Discoid menisci are more prone to injuries compared to normally shaped menisci and can cause symptoms such as knee pain and a feeling of the knee 'popping'. Treatment options include monitoring the condition or keyhole surgery to reshape the discoid meniscal tissue, depending on the shape and symptoms of the patient.

In the U.S., about 3% to 5% of people have discoid meniscus.

Signs and symptoms of Discoid Meniscus include: - Pain in the front and side of the knee - Accumulation of fluid in the knee - Mechanical sounds like clicks or locks, especially when the knee is straight - Loss of flexibility - Shrinkage of the muscles in the upper leg (quadriceps) - Snapping sound when the knee is bent (referred to as "snapping knee syndrome") - Limited movement - Symptoms may start after an injury or spontaneously - Symptoms can vary depending on factors such as the type of discoid meniscus, presence of tear or instability, and the patient's age - Most commonly seen in teenagers - Younger children may experience spontaneous snapping noises when the knee is fully bent - Older children typically show symptoms of a torn discoid meniscus - The other knee should also be checked as DLM often affects both knees - Specific tests such as McMurray's test, Apley's compression test, and Thessaly's test can be performed to check for pain and diagnose DLM - The overall sensitivity of these medical examinations in diagnosing DLM is about 88.9%.

A discoid meniscus is thought to be something a person is born with.

The doctor needs to rule out the following conditions when diagnosing Discoid Meniscus: 1. Tears in different parts of the meniscus or knee ligaments. 2. Injuries to the back part of the knee. 3. Inflammation in the tendons around the kneecap or in the thigh muscle. 4. Problems with the kneecap causing pain. 5. Fractures or breaks in the bones around the knee.

The types of tests that are needed for diagnosing a discoid meniscus include: 1. X-rays: Plain x-rays can be used to detect certain features of a discoid meniscus, such as a wider joint space, squarish appearance of the thigh bone, cupped shape in the shin bone, and underdeveloped tibial spine. 2. MRI scan: MRI scanning is highly helpful in identifying a discoid meniscus in painful knees. It can show key signs like the "bow-tie sign," thick or flat appearance of the meniscus, and complete coverage of the affected compartment. MRI scans also help in spotting any tearing or displacement in the meniscus and can be useful for surgical planning. It is important to consider the patient's medical history and physical exam results along with the MRI findings, as an incomplete discoid meniscus can look normal on an MRI. 3. Arthroscopy: Arthroscopy is a type of keyhole surgery used to look inside a joint. It can help in visualizing the meniscus and detecting any tearing or displacement that may not be visible on an MRI. These tests, along with the patient's symptoms and physical examination, are essential for properly diagnosing a discoid meniscus and planning the appropriate treatment.

The treatment for a discoid meniscus depends on the presence of symptoms. If the patient is not experiencing any symptoms, surgery is not necessary, and regular monitoring is recommended. If symptoms appear, conservative management is usually the first course of action. However, if the symptoms persist for a long time, surgery may be required to prevent the development of severe arthritis in the knee. Surgical treatment options include arthroscopic saucerization, which reshapes the discoid meniscus to improve its function, and meniscal repair methods for unstable peripheral rim detachment or tears within the meniscus. The specific treatment approach will depend on the individual case and the severity of the symptoms.

When treating a discoid meniscus, there are potential side effects and complications that can occur. These include: - Development of severe arthritis in the knee if symptoms persist for a long time before surgery is considered. - Arthritic changes in the knee in the long run, especially after a total or partial meniscectomy. - Higher risk of tearing due to the structural peculiarities of a discoid meniscus. - Hypermobility of the affected meniscus, which may require additional surgical fixation. - Possible complications after saucerization surgery, such as osteochondritis dissecans (OCD) in the outer part of the thigh bone.

The prognosis for Discoid Meniscus is generally good. Studies have shown that about 85% of patients who undergo the surgical procedure known as partial meniscectomy experience beneficial outcomes. Partial meniscectomy is more favorable than total or subtotal meniscectomy because it helps maintain the shock-absorbing function of the meniscus and reduces the risk of developing degenerative joint disease.

Orthopedic surgeon

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