Meniscal Lesions: Diagnosis and Treatment

Robert S. P. Fan, MD, Richard K. N. Ryu, MD

Disclosures
In This Article

Biomechanics and Function

The menisci provide several integral elements to knee function. These include load transmission, shock absorption, joint lubrication, and joint nutrition and stability.

The menisci act as a structural transition zone between the femoral condyles and tibial plateau. As such, they increase the congruence between the condyles and the plateau. The menisci appear to transmit approximately 50% of the compressive load through a range of motion of 0 to 90 degrees.[8,9] The contact area is increased, protecting articular cartilage from high concentrations of stress. The circumferential collagen fiber orientation within the meniscus is uniquely suited to this capacity. As load is applied, the menisci will tend to extrude from between the articular surfaces of the femur and tibia. In order to resist this tendency, circumferential tension is developed along the collagen fibers of the meniscus as hoop stresses. The circumferential continuity of the peripheral rim of the meniscus is integral to meniscal function. Partial meniscectomy, or bucket-handle tearing, will still preserve meniscal function so long as the peripheral rim is intact. Conversely, if a radial tear extends to the periphery and interrupts the continuity of the meniscus, the load-transmitting properties of the meniscus are lost.[9]

Fairbank[10] was the first to significantly appreciate the load-bearing function of the meniscus with his observations in the postmeniscectomy knee. He documented an increase in degenerative changes of the articular surface after total meniscectomy, which he attributed to loss of meniscal function. Consequently, he recognized the potential for long-term alterations in joint function and biomechanics following total meniscectomy. The tibial femoral contact area decreased by up to 75% in postmeniscectomy knees as demonstrated by Baratz and Mengator.[11] This decrease resulted in a 235% increase in contact stresses after total meniscectomy. Ahmed and Burke[12] found a 40% increase in contact stresses. Other reports have been quite variable, with estimates of the increase in contact stress ranging from 450% to 700%.[8] In contrast, partial meniscectomy results in only a 10% decrease in contact area and a 65% increase in contact stress.[11]

Joint stability is also affected by the menisci. The medial meniscus is recognized as a secondary stabilizer to anterior translation.[13] This becomes particularly important in the anterior cruciate ligament-deficient knee, in which an increase in anterior translation after total meniscectomy has been demonstrated.[13] Consequently, the medial meniscus is vulnerable to injury in the anterior cruciate ligament-deficient knee as it attempts to limit anterior translation. The menisci have also been demonstrated to contribute to varus/valgus stability, as well as to internal and external rotational stability.[14,15]

Meniscal motion has been studied with 3-dimensional MRI and cinematic MRI. Medial meniscal excursion was approximately 5.1 mm, and lateral meniscal excursion, 11.2 mm. The posterior horn excursion has been noted to be less than that of the anterior horn, both medially and laterally.[16] DePalma[17] has demonstrated that most lateral meniscal motion occurs after 5 to 10 degrees of flexion, whereas most medial meniscal displacement occurs after 17 to 20 degrees of flexion. The posterior oblique ligament is firmly attached to the posterior medial meniscus, thereby limiting its displacement and rotation. This likely accounts for the increased risk of injury to the medial meniscus. Conversely, the relatively increased mobility of the lateral meniscus is also responsible for the more frequent occurrence of injuries on the medial side.

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