Discoid meniscus is a congenital developmental pathology in which the external, less often internal cartilaginous lining in the knee joint is not a crescent–shaped structure, as usual, but a flat disk. The violation is associated with an increased tendency to injury. It can manifest itself by clicking during movements, pain, blockages, recurrent synovitis, swelling of the joint. The diagnosis is made on the basis of anamnesis and objective examination, the results of radiography, ultrasound, MRI and arthroscopy. In the absence of symptoms, treatment is not required. In case of injuries, the presence of clinical manifestations, partial, less often complete meniscectomy is performed.
M23.1 Discoid meniscus (congenital)
Discoid meniscus is a congenital anomaly that often proceeds asymptomatically, but is accompanied by an increased likelihood of injury. The altered external meniscus was first described in 1889, occurs in 1-5% of the population. Discoid internal meniscus, known since 1941, is found much less frequently – in 0.1-0.9% of the total number of cases of pathology. In about 20% of cases, the violation is bilateral in nature. Japanese suffer most often, Americans and residents of Scandinavian countries less often.
The causes of the formation of discoid menisci have not been definitively established. In the middle of the last century, the leading theory was that pathology appears because the meniscus “gets stuck” at the embryonic stage of development, without going through the resorption phase of the central parts. Subsequently, this concept was refuted, since it was not possible to identify the discoid stage of the formation of this anatomical structure in embryos.
Currently, most researchers adhere to the point of view that the discoid meniscus is a consequence of a violation of morphogenesis. The hypothesis regarding the possibility of pathology after birth due to certain features of the ligamentous apparatus is not accepted by most scientists, since it does not explain the presence of intermediate variants of the structure of the lateral and medial meniscus lesion. Some experts consider this condition to be an inherited variant of the norm.
The meniscus is a cartilaginous layer, which is located between the articular surfaces of the tibia and femur, plays the role of a shock absorber during movements. Normally it has the shape of a crescent (the central part is missing). If the meniscus looks like a disk (the central part is completely or partially filled), they talk about a discoid meniscus.
Such a meniscus differs from a normal one not only in shape, but also in structural features. Histological examination reveals a decrease in the number of collagen fibers and a violation of their location. Often there are signs of mucosal degeneration, an abnormally large number of vessels. These changes, combined with increased thickness, increase the tendency of the meniscus to rupture.
In modern traumatology and orthopedics , the following classification of discoid menisci is used:
- Full type. The cartilaginous pad completely covers the plateau of the tibia, its fixation is without deviations, there is no hypermobility.
- Incomplete type. The meniscus is thin, covers the tibial plateau by less than 80%.
- Hypermobile type. It is detected only from the outside. There is no fixation of the meniscus to the posterior surface of the plateau, the Wrisberg ligament is revealed.
There is a systematization taking into account the MRI signs of the presence or absence of meniscus displacement, which allows to determine the tactics of treatment. According to this classification, there are 4 variants: without displacement, with an offset to the center, anteriorly and to the center, posteriorly and towards the center. When determining the surgical intervention option, an arthroscopic classification can be applied at the site of the rupture: by the type of posterolateral angle, anterior or posterior horn.
With pathology of the complete and incomplete type, clinical manifestations are not detected in the first 5-14 years of life. Subsequently, clicks appear for no reason during movements. After injury, effusion, blockages, swelling, and atrophy of the thigh muscles may occur. Patients note stiffness, a feeling of instability and the presence of a foreign object in the joint. In the absence of treatment, the symptoms gradually worsen.
The hypermobile type is characterized by early development and progression of symptoms due to constant meniscus encroachments in the interstitial space. Patients complain of pain on the outer surface of the joint, which increases with overextension of the limb. Clicks, recurrent synovitis, repeated blockages, restriction of movements, atrophy of the femoral muscles, swelling of the knee joint are detected.
The main complication is damage to the meniscus – tears, tears and compression of the cartilaginous layer by articular surfaces. In the absence of therapeutic measures, a damaged discoid meniscus increases the likelihood of gonarthrosis due to the constant traumatization of the cartilage covering the articular ends of the bones.
The diagnosis of a discoid meniscus is established by an orthopedic surgeon taking into account anamnestic data, the results of external examination and objective studies. The examination program includes:
- Anamnesis collection. The survey confirms the appearance of a “clicking knee” in childhood or adolescence. The presence of traumatic knee injuries in the patient’s history is revealed, the dynamics of clinical manifestations is investigated.
- Physical examination. When palpating during movements, a clap or crunch can be detected. Sometimes the edge of the meniscus protrudes beyond the joint and is felt at the level of the articular gap. Possible soreness with passive extension of the joint (Baykov’s symptom) and pain with extension with a turn of the shin inside (McMurray’s symptom).
- Knee x-ray. Does not allow to assess the condition of cartilage tissue. It is prescribed to exclude other pathologies and identify concomitant changes in bone structures: expansion of the articular gap, flattening of the articular surfaces of the femur and tibia on the side of the lesion.
- Knee ultrasound. Due to the presence of anatomical structures that prevent the study of the structural features of the menisci, it does not always make it possible to confirm the diagnosis. Detects meniscal tears, effusion, signs of cystic degeneration.
- Knee MRI. It is the gold standard for this pathology. Confirms the increased thickness of the meniscus, the violation of the relationship between the maximum diameter and width of the horns, the change in the relationship between the width of the meniscus and the tibial plateau.
- Knee arthroscopy. It is prescribed for ambiguous MRI results or at the stage of preparation for surgery. Reveals an unusually large area of the meniscus, detects ruptures with traumatic injuries.
Differential diagnosis is carried out with injuries of unchanged menisci, congenital or post-traumatic instability of the articulation of the tibia and fibula. Sometimes differentiation with patellar instability is required.
With an asymptomatic course, therapeutic measures are not required. In the presence of clinical symptoms, surgical intervention is indicated. Operations are performed using arthroscopic equipment. Depending on the nature of the pathology , possible:
Resection of the meniscus. Removing excess tissue and giving the discoid meniscus a normal anatomical shape is the best option in the absence of gross lesions of the cartilaginous lining, since it allows you to preserve its cushioning function. With the hypermobile type, the posterior horn is additionally sutured to the articular capsule.
Total meniscectomy. Eliminates the risk of subsequent ruptures of the altered cartilage tissue, but entails loss of congruence of articular surfaces, constant overload of the joint. Complete excision provides the worst long-term results, therefore it is used mainly for severe ruptures.
In the early postoperative period, the use of an elastic bandage or wearing a knee pad is recommended. Support on the leg is allowed from the first day after the intervention, it is advisable to use a cane or crutches to unload the limb. Physical therapy classes begin from the first day.
First, exercises with isometric muscle tension, movements in the ankle joint and foot joints are performed. From the second day, painless passive movements are added, from the seventh – active movements in the knee joint area. The stitches are removed for 7-10 days. Massage and physiotherapy procedures are prescribed: laser therapy, magnetotherapy, ultrasound therapy. Electrical stimulation and lymphatic drainage are performed.
The prognosis is usually favorable. The presence of discoid cartilage pads of types 1 and 2 may not manifest itself in any way during life. Partial meniscectomy for injuries and discoid hypermobile meniscus provides a good long-term effect, allows you to fully restore the function of the joint. With the right choice of surgery tactics, the risk of developing arthrosis is insignificant.
Primary prevention is absent due to the innate nature and ambiguity of the causes of the formation of the discoid meniscus. People with this pathology need to pay increased attention to determining the mode of physical activity when doing sports, avoid overloading the joint, use orthopedic means to reduce the likelihood of injury.
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