Lateral meniscus

In the knee, the menisci form an interarticular fibrocartilage base for femural and tibial articulation. The menisci form a crescent shape in the knee. The lateral meniscus is located on the outer side of the knee, and the medial meniscus is located on the inside of the knee. If the knee bends and twists the menisci can overstretch and tear. Menisci tears occur frequentiy and the knee can sustain more than one tear at a time. If not treated appropriately, however, a menisci tear can roughen the cartilage and lead to arthritis. A meniscus tear acts like grit in the ball bearings of a machine. The longer the torn tissue remains affected, the more irritation it causes. 

Strength and modulus of the meniscus vary with different locations and with different orientations of the specimen due to structural and compositional changes (Table B2.4). For loading parallel to the fibers, it appears that the meniscus may be stronger in the anterior location, and that the lateral meniscus may be stronger than the medial meniscus. This may be explained in part by the fact that the fiber orientation is more random in the posterior part of the medial meniscus. 

Insertion sites on the tibial plateau. Distally, the ACL is attached to a fossa anterior and lateral to the anterior spine. It passes beneath the transverse meniscal ligament and it often blends with fibers from the anterior and posterior horns of the lateral meniscus. 

The tibial insertion of the ACL is demarcated anteriorly by the anterior ridge, posteriorly by the tibial spine, medially by the medial intercondylar ridge, and laterally by the anterior horn of the lateral meniscus (Figs. 2.1 and 2.4). The average tibial insertion area from the previous reports is 146 mm, which is slightly larger than that of the femoral insertiOTi (Table 2.1). In addition, the strict insertion area was scooped posteriorly by the nutrient artery of the ACL [7, 22]... 

The ACL conies into adjacency with the anterior horn of the lateral meniscus under gross observation, and parts of the ACL fiber are attached to the anterior horn with an anterior width ranging from 1/3-1/2 of its surface. Moreover, fat and scar tissues cover its border, and the border between the anterior horn of the lateral meniscus and ACL attachment cannot be grossly identified. When these surface layers of soft tissues are carefully detached, both structures are overlapped anteriorly and the lateral meniscus slips under the substratum of the ACL posteriorly (Fig. 4.3). The anterior horn of the lateral meniscus was attached on the base of the lateral groove and lateral aspect of the aforementioned bony protrusion, and the attachment was... 

Macroscopic observation of ACL tibial footprint, (a) ACL and lalraal meniscus arc overlapped anteriOTly, and the lateral meniscus slips under the substratum of the ACL posteriOTly. (b) After resection of ACL and lateral moiiscus attachmenL AH anterior hom of lateral mcmiscus, MM medial meniscus, UT lateral intercondylar tubercle, M7T medial intercondylar tubtucle, white dot area ACL tibial footprint, blue dot area attachment of anterior hom of lateral meniscus... 

Fig. 4.4 Coronal histological section of the lateral margin of ACL tibial footprint (original magnification x 1). The lateral meniscus attaches to the base of lateral groove and the lateral aspect of the protrusion with connective tissue. AC articular cartilage of lateral tibial plateau. White dot area connective tissue (CT) of anterior horn of lateral meniscus. Black dash line bony protrusion of ACL tibial footprint. Arrowhead base of lateral groove...

Anteromedial, L-shaped ridge lateral, anterior hom of lateral meniscus posterior, medial/lateral intercondylar tubercle... 

Fig. 4.6 Ideal tunnel position for (a) single-bundle reconstruction, (b) double-btmdle reconstruction from our results. White dot line, L-shaped ridge red line, attachment of anterior horn of lateral meniscus blue dot line, anterior margin of the medial and lateral intercondylar tubercle yellow circle, tibial tunnel for single-bundle ACL reconstruction red circle, tibial tunnel of anteromedial bundle for double-bundle ACL reconstruction blue circle, tibial tunnel of posterolateral bundle for double-bundle ACL reconstruction...

The second point is that the ACL attachment is extremely proximate to the anterior horn of the lateral meniscus attachment. Several articles reported the... 

According to the previous reports on the functional anatomy of the ACL, however, it could be divided into three bundles the anteromedial (AM), the intermediate (IM), and the posterolateral (PL) [6, 7]. Additionally, it is well-known that the natural ACL forms a crescent-shaped footprint on the femur and a triangular one on the tibia. Furthermore, a recent macroscopic study by Siebold et al. showed that the C -shaped tibial insertion runs from along the medial tibial spine to the anterior aspect of the lateral meniscus [8]. 

Medially, some reports showed that the ACL was confluent with the apex of the medial intercondylar ridge (MIR) of the tibia [20-22]. Laterally, the fibers of the ACL blend with those of the anterior attachment of the lateral meniscus, and it has been thought to be the landmark for the ACL footprint. Furthermore, recent report by Siebold et al. revealed that the fiber of the attachment of the lateral meniscus was distinguishable from the ACL tibial attachment and it can be thought to be the lateral border [8]. 

Fig. 26.4 (a) Tibial attachment of the three ACL bundles. Dotted line MIR, Arrowheads the anterior horn of the lateral meniscus. (Redrawn from Ref. [10]) (b) Parallel pin guide (Smith Nephew E0014050-7). (c, d) Three tibial tunnels. Two tunnels for the AM and PL are created Just lateral to the apex of the MIR (Redrawn from Ref. [18])... 

We generally use a three-portal technique using the anterolateral portal, central anteromedial portal (CAM), and the far anteromedial portal (FAM) [20]. The anterolateral portal is positioned above the lateral meniscus, adjacent to the lateral border of the patellar tendon, and serves as a viewing portal for the tibial insertion. 

Fig. 30.5 ACL tibial attachment area of the right knee, (a) Arthroscopic view via the anteromedial portal with a 45 "arthroscope (b) 3D CT view. There are three landmarks to identify the attachment area medial intercondylar ridge (MIR), anterior intercondylar ridge (AIR), and anterior horn of the lateral meniscus (AHLM). MM medial meniscus...

Fig. 31.1 Tunnel position on the femur, (a) The shaded area represents the original ACL attachment area on the femur. The red area indicates the 5 x 10 mm rectangular aperture. The blue circle indicates the point at which a 10-mm diameter round tunnel is drilled, (b) The shaded area represents the area where the original ACL is attached to the tibia. Because of its proximity to the insertion of the lateral meniscus, the attachment area is narrow. The red area represents the 5 X 10 mm rectangular aperture. The blue circle indicates the point at which a 10-mm diameter round tunnel is drilled...

When the anterior tibial spine fragment displaces, it can lie on top of the anterior horn of the medial (and occasionally lateral) meniscus. This can prevent its reduction and must be looked for at the time of surgical reduction and fixation. 

Approximately 1.5%-3 % of the population have a discoid lateral meniscus. These congenital variants are prone to tears. Discoid meniscus is diagnosed if there is continuity of the anterior and posterior horns of the meniscus on three or more consecutive sagittal images (4-mm slices), there is loss of the normal semilunar morphology and greater than 50% coverage of the lateral tibial plateau by the meniscus. 

The femorotibial joint is one of the few articulations with menisci. The medial meniscus is semicircular. Its anterior end is attached to the anterior intercondylar area in front of the anterior cruciate ligament. The lateral meniscus is almost a complete ring. Its anterior end is attached in front of the intercondylar eminence of the tibia, blending partially with the anterior cruciate ligament. 

FIG. 98-5 Location of the tender points around the knee. PAT, patellar LM, lateral meniscus LH, lateral hamstring MM, medial meniscus MH, medial hamstring EX, gastrocnemius AC, anterior cruciate PC, posterior cruciate. 

FIG. 98-11 Counterstrain treatment for the lateral meniscus tender point. 

Tears of the medial or lateral meniscus are the most common cause of internal derangement found in the knee joint. Most lesions involve the medial meniscus because of the nature of its attachment about its periphery, which makes it less mobile than the lateral meniscus and more subject to injuries. A "bucket handle" lesion is usually found in young people, whereas a horizontal, posterior lesion is more apt to be found in the middle aged and the elderly patient. There usually is a history of acute trauma, which resulted in swelling, pain, and disability of the knee. 

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