ESSAY - (lateral-) meniscus - posterior horn rupture

In sports and orthopedics, a tear of a meniscus is a rupture of one or more fibrocartilage strips in the knee called menisci.

Anatomy

There are two menisci in the knee. The menisci are C-shaped wedges of fibrocartilage located between the tibial plateau and femoral condyles. While the ends of the thigh bone and the shin bone have a thin covering of soft hyaline cartilage, the menisci are made of tough fibrocartilage and contain 70% type I collagen. They conform to the surfaces of the bones they rest on. One meniscus rests on the medial tibial plateau; this is the medial meniscus. The other meniscus rests on the lateral tibial plateau; this is the lateral meniscus.
The larger semilunar medial meniscus is attached more firmly than the loosely fixed, more circular lateral meniscus. The anterior and posterior horns of both menisci are secured to the tibial plateaus. Anteriorly, the transverse ligament connects the 2 menisci; posteriorly, the meniscofemoral ligament helps stabilize the posterior horn of the lateral meniscus to the femoral condyle. The coronary ligaments connect the peripheral meniscal rim loosely to the tibia. Although the lateral collateral ligament (LCL) passes in close proximity, the lateral meniscus has no attachment to this structure.[4]
The joint capsule attaches to the entire periphery of each meniscus but adheres more firmly to the medial meniscus. An interruption in the attachment of the joint capsule to the lateral meniscus, forming the popliteal hiatus, allows the popliteus tendon to pass through to its femoral attachment site. Contraction by the popliteus during knee flexion pulls the lateral meniscus posteriorly, avoiding entrapment within the joint space. The medial meniscus does not have a direct muscular connection. The medial meniscus may shift a few millimeters, while the less stable lateral meniscus may move at least 1 cm

These menisci act to distribute body weight across the knee joint. Without the menisci, the weight of the body would be unevenly applied to the bones in the legs - the femur and tibia. This uneven weight distribution would cause the development of abnormal excessive forces leading to early damage of the knee joint, so called shear forces. The menisci also contribute to the stability of the joint.

So, in summation the menisci of the knee have these several important roles: • shock absorption and distributing load throughout the joint • increasing stability • providing nutrition for articular cartilage • limiting extreme flexion and extension • controlling the movements of the knee joint.1,2

The menisci are nourished by small blood vessels but have a large area in the center with no direct blood supply (avascular), it is the superior and inferior branches of the medial and lateral geniculate arteries that supply the peripheral third of the menisci via the perimeniscal capillary plexus. This presents a problem when there is an injury to the meniscus, as the avascular areas tend not to heal. Without the essential nutrients supplied by blood vessels, healing cannot take place.
The two most common causes of a meniscal tear are traumatic injury (often seen in athletes) and degenerative processes, which are the most common tear seen in all ages of patients. Meniscal tears can occur in all age groups. Traumatic tears are most common in active people aged 10–45. Traumatic tears are usually radial or vertical in the meniscus and more likely to produce a moveable fragment that can catch in the knee and therefore require surgical treatment.

Pathophysiology, what is happening when the meniscus tears

Meniscal tears occur due to a shear force between the femur and tibia. In younger patients, this is typically a twisting force on a weightloaded flexed knee.The internally or externally rotated knee is then in a flexed position, with the foot being also in a flexed position. These are often 'bucket-handle tears', in which there is a vertical or oblique tear in the posterior horn running toward the anterior horn,5 forming a loose section which remains attached anteriorly and posteriorly. It is not uncommon for a meniscal tear to occur along with injuries to the anterior cruciate ligament ACL and the medial collateral ligament MCL — these three problems occurring together are known as the "unhappy triad," which is seen in sports such as football when the player is hit on the outside of the knee. Individuals who experience a meniscal tear usually experience pain and swelling as their primary symptoms. Another common complaint is joint locking, or the inability to completely straighten the joint. This is due to a piece of the torn cartilage preventing the normal functioning of the knee joint.
Degenerative tears are most common in people from age 40 upward but can be found at any age, especially with obesity. Degenerative meniscal tears are thought to occur as part of the aging process when the collagen fibers within the meniscus start to break down and give less support to the structure of the meniscus. Degenerative tears are usually horizontal, producing both an upper and a lower segment of the meniscus. These segments do not usually move out of place and are therefore less likely to produce mechanical symptoms of catching or locking.Meniscal tear incidence may be as high as six per 1000 population6 with a 2.5 to 4 times male predominance. Age of injury peaks at 20–29 years.7
Summary: The difference in tear type between these populations is explained by the three-dimensional fibrous structure of the meniscus: horizontal delamination occurs in degenerative injuries, while the fibrous structure is ruptured in a vertical fashion in younger patients.

The typical meniscal pain profile comprises well localised joint-line pain with medial pain generally being indicative of a medial tear and vice-versa. Meniscal pain occurs during torsional, weight bearing knee movements (classically pivoting on the knee while walking) as a sharp stab lasting several seconds, often followed by a dull ache for several hours. Pain may wake the patient from sleep as the tender medial aspect of the knee strikes the other side as the patient rolls over in bed. There is no resting pain.
Locking presents in two ways. Most commonly it is impossible to fully extend the knee; more accurately described as stiffness also termed 'pseudo locking’ due either to a small effusion (requiring increased force to bend the tense joint capsule) or to pain inhibition as the femoral condyle compresses the torn meniscus. True locking is less common only in the so called „bucket-handle tear“, with the torn fragment preventing full extension. There is a history of sudden inability to fully extend the knee, with a rotational flexion/extension 'trick' required to regain full extension. Weakness, grinding, instability or giving way rarely result from meniscal pathology.

Symtpoms shortly summarized: pain swelling and stiffness whoch increases gradually from hours to days after injury locking of the joint
Instability with an accompanying inability to straighten the knee

Diagnosis and Discussion

On examination, there may be joint effusion, joint line tenderness, and the joint is held in a flexed position. in late presentations, there may be significant quadriceps wasting. McMurray (Figure 1) and Apley tests (Figure 2) are often positive, although these are specific but not sensitive – specificity being 57–98% and 80–99%, and sensitivity being 10–66% and 16–58% respectively. The most useful clinical test for meniscal injury is the Thessaly test, which is demonstrated in Figure 3. Although rarely taught and poorly utilised, recent validation demonstrated a sensitivity of 90%, and specificity of 98% in detecting meniscal injury.

McMurray test
The patient lies supine on the bed with the hip and knee both flexed. With the foot as close to the hip as possible, the clinician holds the knee joint (with fingers along the joint line) with one hand, and the other hand rotates the tibia internally and externally while extending and flexing the knee. If the test is positive (suggesting a meniscal tear), the patient will feel pain and the clinician will feel and/or hear meniscal movement when the meniscus is compressed between the tibia and femur.

Apley test
The patient lies prone, with their knee flexed to 90 degrees and their hip extended. The clinician applies axial pressure to the foot and rotates the tibia internally and externally. Pain and/or clicking on compression suggest a meniscal lesion.

Thessaly test
The clinician holds the patient's outstretched hands for support, while the patient stands flat-footed with their knee flexed to 20 degrees and rotates their body and knee three times, internally and externally. The test is positive if symptoms are reproduced on rotation.

Magnetic resonance imaging can confirm clinical concern for meniscal tear, review intra- and extra-articular anatomical structures and exclude alternative diagnoses. Sagittal peripheral meniscal images demonstrate the normal anatomical 'bow-tie configuration' (the central meniscal body with the anterior and posterior horns as well circumscribed triangles. On MRI, meniscal tears are evident as a linear signal intensity that extends through the meniscal substance to a free edge17 (Figure 4). Tears are typically vertical in young patients and horizontal in the elderly (Figure 5). Magnetic resonance imaging can also be effectively used to estimate the vascular zone classification of tears.18 This is useful for the orthopaedic surgeon to predict meniscal repairability, assisting informed discussion with patients and scheduling appropriate operating theatre time. It is essential to remember that just because a tear can be seen on MRI, this does not mandate surgery. It is rather like this: based of the findings, treatment can be considered in terms of four „R“s: Rest and Rehabilitate the patient with physiotherapy and if the patient is not improving on Review, Refer him/her to an orthopaedic surgeon. Research in new experimental surgical techniques is currently investigating the possibility of implantation of collagen, allogenic and xenogenic cells, embryonic and adult stem cells, or scaffolds derived from polymers, hydrogels, tissues and extracellular matrix,7 and action of biological stimuli (eg. growth factors) on meniscus tissue These are currently only being trialled in younger patients7 and the routine use of most of these technologies is some time away.

The absolute indication for a specialist referral is the locked knee – loss of joint function necessitates surgical intervention always!! Referral is also indicated if the diagnosis is uncertain for review and to access MRI. In older patients, referral is appropriate if conservative management fails to improve symptoms. As the risk of osteoarthritis is increased if meniscal structures are not optimally functional,7 it may also be appropriate to refer all young patients for opinion if symptoms do not rapidly improve.

Proton weighted sagittal image demonstrates an example of a posterior horn medial meniscal horizontal tear (white arrow). The anterior horn of the medial meniscus demonstrates half of the normal anatomic 'bow-tie configuration'. Note: the cartilage deficit more anteriorly on the medial femoral condyle and altered subchondral cortical bone interface

Coronal proton weighted MRI of horizontal tear of lateral meniscus (white arrow) with complicating ganglion (black arrow) at the lateral margin of the meniscus
Bucket-handle tear of the lateral meniscus (red). Medial meniscus intact (green). MRI, coronal T2 *-weighted GRE sequence

Treatment

Nonoperative treatments are an important part of the management of all patients, regardless of whether surgery is being considered. Immediate conservative measures include the RICE regimen: Rest (with weight bearing as tolerated or with crutches), Ice, Compression bandaging and elevation of the affected limb to minimise acute swelling and inflammation.

Longer term measures include activity modification, nonsteroidal antiinflammatory drugs (NSAIDs) and physiotherapy.4,19–21 Nonsteroidal anti-inflammatory drugs are often recommended for 8–12 weeks,20 although paracetamol can be considered if NSAIDs are contraindicated or poorly tolerated.22 Where available, intensive physiotherapy is very useful and should include range of motion, proprioceptive work and muscle strengthening exercises. Physiotherapy at two visits per week for at least 8 weeks is recommended.20 There is little evidence for strapping of meniscal injuries and this is not currently recommended. Nonoperative treatments are often successful in patients with certain types of tear – patients who have no loss of joint function, suffer minimal pain or swelling and are willing to reduce their activities – temporarily or in the long term.

Since the lateral meniscus is an essential shock absorber on the outside aspect of the knee joint. and it absorbs about 70% of the shock of the lateral compartment, it’s best to avoid these kind of movements/ sports until or during a proper treatment took and takes place. Lateral meniscal tears are not as common as medial meniscus tears. This is partly because of this different shape, but also due to the fact that the lateral meniscus is more mobile and not secured as much to the lateral tibial plateau as the medial meniscus is to the medial tibial plateau (attachment to the medial collateral ligament).
Thus, when there is a lateral knee injury such as a lateral meniscus tear, it is very important to try to repair the tear, because if not repaired and is trimmed out there will be an increase to the load on the lateral compartment, which ultimately leads to osteoarthritis.
Partial meniscectomy (removal of the torn section) is one of the most commonly performed orthopaedic surgical procedures, but even that may lead to osteoarthritis. However, Surgical treatment is usually reserved for younger patients with a vertical longitudinal tear within the vascularised outer third of the meniscus. This is termed the 'red-red zone' (denoting area of vascularity).2,4 repair of the 'red-white zone' (watershed area between vascular and avascular meniscus) is controversial25 with many different surgical techniques.26 tears in the 'white-white zone' (avascular zone) are rarely repaired – rather the damaged segment is resected (meniscectomy). Damaged avascular meniscus must be removed.27 However, meniscectomy can cause long term osteoarthritis,28 so it should only be performed when the patient suffers joint locking or mensical pain that is refractory to conservative management. For patients requiring meniscectomy, meniscal autograft has been utilised with good outcomes, but is only performed in specialist centres.

Revision of all mentioned key points

• Meniscal injury is common with the medial meniscus being more frequently injured • Younger and elderly patients are prone to different types of tears • Optimal diagnosis and management is essential to prevent long term damage/pain • The Thessaly test is the most sensitive and specific clinical test to diagnose meniscal injury • Magnetic resonance imaging is first option for investigating potential meniscal lesions, but should not replace thorough clinical history and examination • Conservative management is important in all patients. Including acute rest, intensive rehabilitation with physiotherapy and modification of activity. Referral to an orthopaedic surgeon is important if the diagnosis is uncertain or there is minimal improvement at clinical review