Knee menisci are made up of thick, fibrous tissue that is of triangular shape when cut and is situated between the femur and the upper part of the shinbone. The upper and lower sides are free, the grafting is done at the basis of the triangle on the knee surface.
Meniscus surfaces enter, through pressure, into contact with their femur and tibia cartilaginous counterparts. The menisci possess a certain degree of mobility in flexing and extending, amplified by movements of tibia rotation with regards to the femur. While the menisci play the role of joints or holds, they contribute very moderately to knee stability.
A serious meniscus injury, constituting a mobile stick coming between the femur and tibia, may generate joint locking but also a certain degree of cartilage wear.
The knee joint includes two internal or medial, external or lateral menisci. The internal meniscus has a “C” shape, while the external meniscus is more closed and can sometimes have the shape of a real disk, in which case it is called discoidal meniscus.
The menisci contribute to the increase in congruence between the femoral and tibia joint surfaces, which means that they increase the contact area, so as to decrease mechanical constraints and deterioration risks. They can be considered “constraint lowering” structures, but, unfortunately, they are poor in vessels, which explains their low spontaneous wound-healing capacities when injured, even if the injury is only partial.
1 – Acute injuries.
The topography and natural mobility of the meniscus apparatus can explain the occurrence of acute injuries. After an excessive flexion movement (squatting), the internal meniscus' recoiling may lead to its being actually smashed during an extension movement between the femoral condyle and the corresponding tibial plateau. The tear might be partial or total, depending on the meniscus' axis, leading to the creation of a “loop” which may permanently intervene between the femur and the tibia. Such injury will provoke a painful and unavoidable lock.
A meniscus injury may also occur at the same time as a sprain mechanism leading to a ligament injury and hence to an important and unusual displacement of bone pieces with regards to each other's positions.
2 – Chronic injuries
They are the most common ones and are isolated or associated to an unknown ligament damage. There are indeed complex meniscus injuries but are surgically revealing (pile-up, partial cracking, injuries involving several meniscus segments, meniscus fragments released into the joint, ...).
See opposite, an endoscopic view of a meniscus injury
Two clinical pictures help orient the diagnosis in a definite way toward either an acute injury or a deterioration or chronicle injury.
1 – Acute meniscus injuries.
Meniscus lock. This form remains the least common but it indicates an injury due to meniscus tear. Because of painful discomfort, the patient is unable to completely stretch his knee after a bending period.
Flexing remains possible. However, the patient cannot have a straight knee, as would a person with a healthy joint. Any excessively flexing movement produces very sharp pain.
This lock can occur through an apparently harmless movement. The lock may trigger the illness or be already known to the patient. The patient can regain full movement either through a specific gesture combining a flexing and twisting of the joint, or spontaneously after a period of rest, such as a good night's sleep.
Locking occurs as a result of a fragment being stuck between a condyle and the tibial plateau.
Locking is very regularly accompanied or followed by an impression of joint swelling (hydarthrosis).
The lock's duration may be relatively short. Pain will then fade away and disappear almost completely in a few days, helped by an intake of analgesics and anti-inflammatories.
2 – Chronic meniscus injuries.
In the absence of obvious locking or a similar event communicated by the patient, the diagnosis of meniscus injury is more difficult. Sometimes, the diagnosis is misled for months or even years into detecting the sequels of a sprain or “tendinitis”, in which case the surgeon will more readily uncover rear deterioration injuries for the internal meniscus and frontal ones for the external meniscus.
Practising endurance sports will more readily lead to injuries of this kind. Be they acute or chronic injuries, the doctor has at his/her disposal specific clinical tests combining flexing and twisting leg movements so as to make the best possible diagnosis.
For doctors experienced in this pathology and in most cases, it is not necessary to seek arthrography (the injection of a radio-opaque product in the knee) or NMR to support the diagnosis.
However, such exams or others may be useful, when the diagnosis is unsure or another pathology is associated with the menisus damage (cartilaginous, ligamentary).
The weak natural capacities of the meniscus tissue to spontaneously heal means that injury, as soon as it occurs, will at best remain stable and at worst become more serious and spread. The spread of this injury will lead to joint attacks, i.e. painful episodes with locking or pseudo-locking, effusion, a feeling of insecurity. Such episodes are triggered by squatting movements, twisting or increasing physical or professional activities.
It must be noted that within the framework of meniscus conservation, injuries that may be sutured (those located at the edge of the meniscus, where vessels are less vulnerable) will only have a chance at healing if the treatment is made early.
With the spread of meniscus injuries, the locking risk through interposition between the femoral condyle and the tibial plateau will be more frequent, leading to a weakening of physical capacities and to abandoning athletic activities.
The potential for osteoarthritis increases in certain morphological types (bow-leggedness, knock-knees).
In all cases, surgical treatment of a meniscus injury may be administered without opening the joint (arthrotomy) through the arthroscopy technique. This method, carried out by making two or three very small incisions, has the advantage of offering a global and complete exploration of the joint, thus specifically allowing control of the menisci (bilateral damage occurs in 10 to 20 % of cases). The intervention is carried out under general or local-regional anaesthetic, most often with a pneumatic tourniquet at mid-thigh, so at to avoid the flow of blood toward the joint.
The surgeon will take advantage of the analgesia to make a careful clinical inspection of the knee, particularly the ligaments. The operation always includes time for exploring. All compartments are successively checked. The injured meniscus or menisci are either sutured or have their devitalised and physiologically non-functioning part pulled out of the joint. This meniscus ablation may be made either completely, through fragmentation, or by using a mechanical device linked to an aspirator (Shaever).
In all cases, the surgeon will do his best to conserve as much of the healthy meniscus tissue as possible, as well as cut the meniscus in such a way as to give the new meniscus structure a shape as close as possible to the physiological one. Indeed, any irregular cut may become the locus of a new injury on the unremoved meniscus residue. It should mentioned that the conserved part is always the one situated in the thickest meniscus area, and that it is important to conserve it as much as possible.
Arthroscopic work always ends with a through washing of the joint. The use of short passages at first, added to post-operation washing of the joint, helps explain the rarity of infectious complications, related to this method, during the operation.
The public success of arthroscopic surgery is probably linked to its aesthetic advantage (short incisions), to the absence of overnight stay, to the moderate character of post-operation pain, and to a quick functional recovery. As far as doctors are concerned, they especially appreciate this method in the mid and long term. This technique has the advantage of allowing for a global exploration and of not ignoring, during the treatment of meniscus damage, the other meniscus or a related injury. Moreover, this operation seeks to preserve the meniscus, which goes along with the prevention of osteoarthritic injuries.
Endoscopic view: before treatment
Endoscopic view: after treatment
Arthroscopic treatment of meniscus injuries is done without overnight stay. The patient is admitted in the morning into the ambulatory surgery service. He/she may go back home, if no incidents occur, which is true in most cases, on the very evening of the day he/she is admitted.
The patient is allowed to drive a car 24 hours after the operation.
Considering the minimally invasive character of the method, time off school and off sedentary jobs, may be limited to 2 to 3 days.
In cases of intense jobs necessitating, for instance, long squatting, the expected average time off work is of 3 weeks.
Swimming and cycling are authorised starting on the 8th day after the operation.
Complete flexing may be recovered in three weeks' time. Athletes may start training again in the third week and competing after four or five weeks. These theoretical time periods are valid strictly for the treatment involving isolated meniscus injuries (with no associated cartilaginous or ligament damage).
Complications related to this method are rare. They must be distinguished from the natural development of a knee containing associated ligament or post-osteoarthritis injuries, which may, unfortunately, develop independently.
We will mention, in increasing order of gravity, the temporary clinical symptoms that may be treated or are slight. As for acute arthritis, it remains rare.
Hydarthrosis: Post-operation joint effusion ends most often totally in ten days. Sometimes, strong effusion, inducing pain and limiting bending movements, may take several months to disappear. Its development is often unpredictable, increasing and decreasing in volume depending on physical activity. It is no use trying to drain. If the effusion persists, it may be a syndrome of algodystrophy.
Sensitive arthroscopy orifices: It is usual to experience a certain sensitivity accompanied by a certain thickening and a small swelling of the arthroscopy orifices. Massages and continued flexing will eventually put an end to this problem, which may last two to three months.
Knee stiffening: It is rare when the knee is not the locus of associated injuries, and it may call for prescribing some re-education sessions, so that the patient may recover complete flexing.
Venous complication: The fact that post-operation pressure is not eliminated and the patient does not stay in bed for a certain period at the clinic make this complication the consequence of a predisposed condition with risk factors which the surgeon must take into account by prescribing a longer and more efficient anticoagulant treatment.
Algodystrophy: A trivial complication in any joint surgery. It happens very rarely. Its treatment is not specific.
Unfortunately, it may mar the results of an operation that is otherwise known for the simplicity of its ensuing condition, by generating stiffness and residual pain.
Acute arthritis: This is the most difficult complication as far as functional prognosis is concerned. It remains rather rare because of the quantity of liquid used for cleaning the joint and the reliability of the surgical material available (disposable material). The frequency of this acute complication is increased through certain factors (arteritis, diabetes, chronic tobacco addiction...).
Endoscopic treatment of meniscus injuries constitutes a major advance in the treatment of knee surgery.
This method is comfortable for the patient (no in-stay, micro-incisions, reduced post-operation pain, short work leave period). This method is compatible with total exploration of the joint. It also helps preserve the healthy part of the meniscus tissue and allows for a meniscus cut that respects the physiology of this fibrous cartilage.
Apart from rare complications, insufficient arthroscopy results are essentially due to associated injuries, in particular catilaginous and ligamentary ones.