Discoid meniscus
Encyclopedia
Discoid meniscus is a rare human anatomic variant that usually affects the lateral meniscus
of the knee
. Usually a person with this anomaly has no complaints, however, it may present as pain, swelling, or a snapping sound heard from the affected knee. Strong suggestive findings on magnetic resonance imaging
includes a thickened meniscal body seen on more than two contiguous slices.
is a thin crescent-shaped piece of cartilage
that lies between the weight bearing joint surfaces of the femur
and the tibia
. It is attached to the lining of the knee joint along its periphery and serves to absorb about a third of the impact load that the joint cartilage surface sees and also provides some degree of stabilization for the knee. There are two menisci in the knee joint, the outside one being the lateral meniscus the inner one the medial meniscus
. A discoid meniscus is a congenital anomaly of the knee found in 3% of the population. It typically affects the lateral meniscus and may be found bilaterally (20%). Instead of the narrow crescent shape, as seen in a normal meniscus above, a discoid meniscus is thickened, and has a fuller crescent shape. In addition, a discoid meniscus does not taper as much towards the center of the joint and is shaped like a disc. The thickness of the meniscus, its diminished vascular blood supply, and in some instances, weak capsular attachment, makes it more prone to tears compared to a normal meniscus. The anomaly in itself is asymptomatic, however, a tear of the meniscus can result in pain, swelling, and snapping of the affected knee. The orthopedic classification of discoid menisci includes: complete, incomplete or Wrisberg-ligament types as depicted here. Coverage of the lateral tibial plateau determines the designation of complete or incomplete. The Wrisberg-ligament type has an abnormal posterior attachment by attaching to part of the posterior cruciate ligament
.
may show lateral joint space widening, squaring of the lateral condyle, cupping of the lateral tibial plateau and hypoplasia
of the lateral tibial spine that suggest discoid meniscus.
study would be done to rule out any bony pathology
such as a fracture
. Since it is difficult to diagnose meniscal anomalies with X-ray
, an MRI would be necessary to visualize the discoid meniscus. If the patient is asymptomatic and does not complain of significant locking sensation in the knee or pain, treatment is conservative and consists of stretching and strengthening exercises for the quadriceps and hamstring muscles. “In cases where there is significant disability, surgical excision may be needed. When the discoid meniscus is severely damaged, total excision of the meniscus may be necessary. In most cases where the meniscus is still generally intact, a partial excision to preserve the cushioning function may be sufficient.”
Lateral meniscus
The lateral meniscus, also called the external semilunar fibrocartilage, is a fibrocartilaginous band that spans the lateral side of the interior of the knee joint. It is one of two menisci of the knee, the other being the medial meniscus. It is nearly circular and covers a larger portion of the...
of the knee
Knee
The knee joint joins the thigh with the leg and consists of two articulations: one between the fibula and tibia, and one between the femur and patella. It is the largest joint in the human body and is very complicated. The knee is a mobile trocho-ginglymus , which permits flexion and extension as...
. Usually a person with this anomaly has no complaints, however, it may present as pain, swelling, or a snapping sound heard from the affected knee. Strong suggestive findings on magnetic resonance imaging
Magnetic resonance imaging
Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...
includes a thickened meniscal body seen on more than two contiguous slices.
Description
The Watanabe classification of discoid lateral meniscus is: (A) Incomplete Tear, (B) Complete Tear, and C) Wrisberg-ligament variant Normally, the meniscusMeniscus (anatomy)
In anatomy, a meniscus is a crescent-shaped fibrocartilaginous structure that, in contrast to articular disks, only partly divides a joint cavity. In humans it is present in the knee, acromioclavicular, sternoclavicular, and temporomandibular joints; in other organisms they may be present in other...
is a thin crescent-shaped piece of cartilage
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
that lies between the weight bearing joint surfaces of the femur
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
and the tibia
Tibia
The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....
. It is attached to the lining of the knee joint along its periphery and serves to absorb about a third of the impact load that the joint cartilage surface sees and also provides some degree of stabilization for the knee. There are two menisci in the knee joint, the outside one being the lateral meniscus the inner one the medial meniscus
Medial meniscus
-External links: *...
. A discoid meniscus is a congenital anomaly of the knee found in 3% of the population. It typically affects the lateral meniscus and may be found bilaterally (20%). Instead of the narrow crescent shape, as seen in a normal meniscus above, a discoid meniscus is thickened, and has a fuller crescent shape. In addition, a discoid meniscus does not taper as much towards the center of the joint and is shaped like a disc. The thickness of the meniscus, its diminished vascular blood supply, and in some instances, weak capsular attachment, makes it more prone to tears compared to a normal meniscus. The anomaly in itself is asymptomatic, however, a tear of the meniscus can result in pain, swelling, and snapping of the affected knee. The orthopedic classification of discoid menisci includes: complete, incomplete or Wrisberg-ligament types as depicted here. Coverage of the lateral tibial plateau determines the designation of complete or incomplete. The Wrisberg-ligament type has an abnormal posterior attachment by attaching to part of the posterior cruciate ligament
Posterior cruciate ligament
The posterior cruciate ligament is one of the four major ligaments of the knee. It connects the posterior intercondylar area of the tibia to the medial condyle of the femur...
.
Diagnosis
The transverse diameter of a normal meniscus is approximately 10 to 11 mm; therefore a normal meniscus body will be visible on only 2 slices of a MR with 4-5-mm sagittal slices. A discoid meniscus should be considered if more than two contiguous body segments are present. However, this method may lead to a false negative when evaluating people with the Wrisberg variant of discoid meniscus since it maintains a narrow crescent shape. Coronal and radial images of the meniscus are useful to demonstrate the extension of the aberrant meniscus into the joint as seen here. On coronal images, it is diagnosed when the horizontal measurement between the free margin and the periphery of the body is more than 1.4 cm. Rarely, X-rayX-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
may show lateral joint space widening, squaring of the lateral condyle, cupping of the lateral tibial plateau and hypoplasia
Hypoplasia
Hypoplasia is underdevelopment or incomplete development of a tissue or organ. Although the term is not always used precisely, it properly refers to an inadequate or below-normal number of cells. Hypoplasia is similar to aplasia, but less severe. It is technically not the opposite of hyperplasia...
of the lateral tibial spine that suggest discoid meniscus.
Treatment/Management
In a patient complaining of acute onset knee pain, an X-rayX-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
study would be done to rule out any bony pathology
Pathology
Pathology is the precise study and diagnosis of disease. The word pathology is from Ancient Greek , pathos, "feeling, suffering"; and , -logia, "the study of". Pathologization, to pathologize, refers to the process of defining a condition or behavior as pathological, e.g. pathological gambling....
such as a fracture
Bone fracture
A bone fracture is a medical condition in which there is a break in the continuity of the bone...
. Since it is difficult to diagnose meniscal anomalies with X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
, an MRI would be necessary to visualize the discoid meniscus. If the patient is asymptomatic and does not complain of significant locking sensation in the knee or pain, treatment is conservative and consists of stretching and strengthening exercises for the quadriceps and hamstring muscles. “In cases where there is significant disability, surgical excision may be needed. When the discoid meniscus is severely damaged, total excision of the meniscus may be necessary. In most cases where the meniscus is still generally intact, a partial excision to preserve the cushioning function may be sufficient.”
External links
- Discoid Meniscus in eMedicineEMedicineeMedicine is an online clinical medical knowledge base that was founded in 1996 by Scott Plantz and Richard Lavely, two medical doctors. The website is searchable by keyword and consists of approximately 6,800 articles, each of which is associated with one of 62 clinical subspecialty textbooks...