Discoid meniscus, also known as discoid cartilage, is an abnormal manifestation of knee joint meniscus, named after abnormal width and height increase of meniscus into a discoid shape. It includes meniscus shape and stability abnormalities that are easy to cause meniscus damage, which mostly occur on the outer side of the meniscus or occur on both sides. The contact area between discoid meniscus and femoral condyle is smaller than that of normal meniscus. When the knee joint rolls, slides and/or rotates, reverse movement, twisting or other non-physiological movements might occur to cause meniscus rupture and joint cartilage wear. These would cause a series of symptoms and signs, leading to premature degenerative changes in the joints.

Discogenic low back pain is an extremely common frequently-occurring disease in clinical practice. It is a chronic low back pain caused by intradiscal disorders (IDD) such as degeneration, annulus fibrosus and discitis, which stimulate pain receptors in the intervertebral disc. It does not have root symptoms, and there is no radiological evidence of nerve root compression or excessive displacement of vertebral segments. It can be described as chemical mediated discogenic pain.
For a long time, people have believed that lumbar disc herniation is the main cause of lower back pain. Recent studies have found that lower back pain mainly comes from the interior of the lumbar disc, while the appearance of the lumbar disc is normal, no lumbar disc herniation is identified, and the myelography and CT scanning results are normal. This low back pain caused by internal structure change of intervertebral disc, known as discogenic low backpain, is the most common chronic low back pain, accounting for approximately 40%.

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Etiology and Epidemiology

Epidemiology

• The incidence rate of discoid meniscus in China is higher than that abroad, reaching 3%~5%.

• The incidence of discoid meniscus on the outer side ranges from 1.2% to 16.6%, and that on the inner side ranges from 0.1% to 0.3%, 20% of which occurs bilaterally.

• The incidence rate of discoid meniscus with tears in China is higher than that in foreign countries, and may be up to 92.3%.

• Discoid meniscus is more common in young Asian people but has no seasonal specificity.

Disease type

Discoid meniscus may be divided into complete discoid meniscus, incomplete discoid meniscus and Wrisberg ligament-type according to the meniscus shape under arthroscopy, as follows:

Complete discoid meniscus

It refers to such a discoid meniscus that the anterior and posterior diameters of the meniscus are approximately consistent, the anterior and posterior angles are not clear, the tibial plateau is completely surrounded by meniscus tissues, while the meniscus accessories are normal.

Incomplete discoid meniscus

Mainly characterized by body enlargement, with clear anterior and posterior angles, with tibial plateau surrounded by meniscus tissues in the range of 80% to 100%, while the meniscus accessories are normal.

Wrisberg ligament-type

It means that the meniscus shape is normal, but the posterior angle is thickened, lacking attachment points to coronary ligament, meniscal ligament and rear meniscus. The sole rear attachment point is composed of the femoral plate ligament (Wrisberg) so that the external meniscus is unstable and prone to subluxation or other related clinical symptoms might occur.

Symptoms

Discoid meniscus generally has no clinical symptom in the early stage; after rupture or tearing occurs, meniscus pain might occur, the movement might be limited, and there may be clicking sound when the joint moves, and a child might often experience joint interlocking symptoms.

Typical Symptoms

Pain

Different patients might experience different degrees of knee joint pain after the meniscus rupture or tearing occurs. Most patients can still walk and continue to participate in activities that cause injury after a small meniscus tear occurs but the pain would worsen when performing twisting or rotating movements. Severe tear usually leads to more significant pain and early knee joint movement limitation, and the joint may quickly swell.

Clicking Sound

After the meniscus is injured, there may be a tearing sensation or clicking sound. After the acute phase, the joint clicking may be heard on the affected side during movement.

Joint Interlocking

“Click” sounds may be heard suddenly during movement and the joint cannot be stretched. After forcibly stretching the calves a few times and hearing the “click” sound again, the joint can straighten again. This phenomenon is called “joint interlocking”. Interlocking does not mean that the knee joint is completely unable to move, but rather indicates that the knee joint cannot fully extend due to interference from the torn meniscus. The occurrence of interlocking is related to the meniscus injury severity and it generally would affect the daily life and exercise.

Accompanying Symptoms

An acute injury of discoid meniscus might be accompanied by the injury of corresponding ligaments of the knee joint, such as anterior (posterior) cruciate ligament, internal (external) collateral ligament, etc., while a chronic injury might be accompanied by rhombosis of quadriceps femoris muscle.

Treatment Options

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Etiology and Epidemiology

Discogenic low backpain is a disease frequently seen in the outpatient department, which greatly affect the quality of life and labor ability of patients. The lumbar intervertebral disc is composed of a cartilage plate, a fibrous ring, and a nucleus pulposus. Cartilage plate is composed of hyaline cartilage, which is a tissue without blood vessel and nerve. If it is injured, it would not produce pain and cannot repair itself. The fibrous ring is composed of fibrocartilage containing collagen fiber bundles, which is connected with the upper and lower cartilage plates and the front and rear longitudinal ligaments. The frontal portion and outer side are thicker and wider, and its rear portion is narrower and less-layered. The fibers in the innermost layer are fused with the intercellular matrix of the nucleus pulposus without obvious boundaries. The nucleus pulposus is an elastic gelatinous substance located in the middle of the fibrous ring, accounting for about 50-60% of the cross-sectional area of the intervertebral disc. Its ultrastructure is composed of collagen fiber network and contains semi-fluid gelatinous substances composed of polysaccharide protein complexes, chondroitin, keratin and hyaluronic acid, and a large amount of water, which enable it to function well. In the past, it was widely believed that intervertebral disc herniation was a prerequisite for lower back pain caused by intervertebral disc diseases. However, recent studies have shown that even without intervertebral disc herniation, lesions occurring inside the intervertebral disc can still cause lower back pain, which is related to the structural changes of the intervertebral disc itself. In addition that the injured intervertebral disc annulus directly stimulates the nerve endings to cause pain, chemical stimulation, intervertebral disc immune response, chemical mediator mediated inflammatory response and pain receptor sensitization are all involved in the mechanism of low back pain. This type of low back pain caused by intervertebral disc disease is called discogenic low backpain.

Symptom and Cause

1.According to recent overseas epidemiological studies, smoking, hypertension, and coronary heart disease are all risk factors to cause discogenic low back pain, and the pathogenesis is related to atherosclerosis or arterial embolism. The above risk factors to induce discogenic low back pain are accompanied by hypercholesterolemia. These findings support the hypothesis that atherosclerosis is a cause of discogenic low back pain and disc degeneration. The pathogenesis may be that the structural damage of the blood vessels around the intervertebral disc and small joints induces the discogenic low back pain.
2.Low back injuries, long-term excessive physical activity, repetitive injuries, poor lifestyle or work habits (such as long-term sitting or standing) and lumbar deformities all may lead to patient pain.

Common Diseases

Intervertebral disc degeneration, internal annulus disruption, discitis, etc.

High-risk Population

Teenagers, Elderly people

Symptoms

Clinical Characteristics

The main clinical feature is a decrease in sitting tolerance, and pain often intensifies during sitting. Patients usually can sit for about 20 minutes only and then must stand or walk to alleviate the pain. The reason is that the pressure inside the intervertebral disc is highest when the patient is sitting, especially when leaning forward.

Location of Pain

The pain location is mainly in the lower back, which sometimes may be spread to lower limbs, 65% accompanied by pain below the knee, maybe unilateral. The most common aggravating factor is fatigue.

Treatment Options

The low-temperature plasma nucleus pulposus ablation technique may be used to treat discogenic lower back pain, which has such advantages as small wound size, fewer complications, good therapeutic effect, safety, and reliability.