MECHANISM OF MENISCI AND LIGAMENTS INJURY

ANDALIB.A.MDALZAHRA HOSPITAL

medial meniscus

The medial meniscus is a C-shaped structure larger in radius than the lateral meniscus, with the posterior horn being wider than the anterior. The anterior horn is attached firmly to the tibia anterior to the intercondylar eminence and to the anterior cruciate ligament

LATERAL MENISCUS The lateral meniscus is

smaller in diameter, thicker in periphery, wider in body, and more mobile than the medial meniscus. It is attached to both cruciate ligaments and posteriorly to the medial femoral condyle by either the ligament of Humphry or the ligament of Wrisberg, depending on which is present; it is also attached posteriorly to the popliteus muscle

The lateral meniscus is smaller and more mobile than the medial meniscus. The inner portion of the menisci are avascular. The outer portion has some blood supply, making healing of tears possible.

lateral medial

MENISCUS TEARING

The menisci follow the tibial condyles during flexion and extension, but during rotation, they follow the femur and move on the tibia.

the medial meniscus becomes distorted. Its anterior and posterior attachments follow the tibia, but its intervening part follows the femur; thus it is likely to be injured during rotation

LATERAL MENISCUS

because it is firmly attached to the popliteus muscle and to the ligament of Wrisberg or of Humphry, follows the lateral femoral condyle during rotation and therefore is less likely to be injured.

Meniscal Lesions

Most common MOI is rotary force with knee flexed or extended

Tears may be longitudinal, oblique, or transverse

Medial meniscus is more commonly injured due to ligamentous attachments and decreased mobility Also more prone to disruption through

torsional and valgus forces

Mechanisms of injury

An acute twisting injury from impact during a sport Usually the foot stays fixed on

the ground and the rest of body rotates

Getting up from a squatting or crouching position

Loading the knee from a fixed position

MENUSCAL TEARING

ARTHROSCOPIC VIEW

B, Horizontal tear of degenerative lateral meniscus.

C, Oblique tear of posterior horn of lateral meniscus.

D, Incomplete radial tear of lateral meniscus.

E, Degenerative tear of lateral meniscus.

F, Resection of tear of lateral meniscus. Remaining tissue shows fatty degeneration.

Four mechanisms have been described as capable of disrupting the ligamentous structures around the knee:

(1)abduction, flexion, and internal rotation of the femur on the tibia;

(2) adduction, flexion, and external rotation of the femur on the tibia;

(3) hyperextension;, and

(4) anteroposterior displacement

LIGAMENT INJURY

By far the most common mechanism is abduction, flexion, and internal rotation of the femur on the tibia when the weight bearing leg of an athlete is struck from the lateral aspect by an opponent.

the unhappy triad” of O'Donoghue

the medial collateral ligament and the medial capsular ligament—are the initial structures injured.

If the force is of sufficient magnitude, the anterior cruciate ligament also can be torn. The medial meniscus may be trapped between the condyles of the femur and the tibia, and it may be torn , thus producing “the unhappy triad” of O'Donoghue

the unhappy triad” of O'Donoghue

The mechanism of adduction, flexion, and external rotation of the femur on the tibia is much less common and produces the primary disruption laterally

The lateral collateral ligament usually is disrupted initially, and depending on the magnitude of the trauma and displacement, the capsular ligaments, the arcuate ligament complex, the popliteus, the iliotibial band, the biceps femoris, the common peroneal nerve, and one or both cruciate ligaments may be disrupted.

hyperextension mechanism

Force directed to the anterior aspect of the extended knee, a hyperextension mechanism, usually injures the anterior cruciate ligament, and if the force continues or is severe, stretching and disruption of the posterior capsule and posterior cruciate ligament may result.

hyperextension mechanism

Mechanisms reported as possibly able to disrupt the anterior cruciate ligament with minimal injury of other supporting structures are hyperextension, marked internal rotation of the tibia on the femur, and pure deceleration

all the supporting structures around the knee function in concert

no single ligament can be disrupted without some degree of injury being sustained to other supporting structures. Injury to the other structures may be minimal and thus may heal with conservative measures, leaving what is apparently an isolated injury to clinical examination.

Isolated posterior cruciate disruption can result from a direct blow to the front of the tibia with the knee flexed.

PCL Injuries

When the knee is forcefully twisted or hyperextended BUT other ligaments are usually injured or torn, before the posterior cruciate ligament (PCL) is torn

Most common mechanism for PCL alone to be injured is from a direct blow to the front of the knee while the knee is bent. 

Automobile accident1. Automobile strikes another and stops suddenly2. Front passenger or driver slides forward.  3. Bent knee hits the dashboard just below the knee

cap forcing tibia backwards on the femur tearing PCL.

The same force can occur during a fall on the bent knee, where the force of the fall on the tibia pushes it back against the femur and tears the posterior cruciate ligament (PCL).

When the tibia is displaced too much in the posterior direction the PCL may rupture.

Common mechanism ofPCL injury in football is being tackled while the knee is fully extended.

Gender issues related to ACL injuries

females more likely to sustain an ACL injury than males

soccer - 2.6Xbasketball - 5.75X

wider pelvisgreater flexibilityless-developed musculaturehypoplastic vastus medialis obliquusnarrow femoral notchgenu valgumexternal tibial torsion

Ligament Injuries

injuries to MCL more prevalent than LCL

MCL foot planted and force

applied to the lateral side of knee football

ML

A noncontact mechanism was reported in 71 (72%) knees and a contact injury in 28 (28%) knees. Most of the injuries were sustained at footstrike with the knee close to full extension. Noncontact mechanisms were classified as sudden deceleration prior to a change of direction or landing motion, while contact injuries occurred as a result of valgus collapse of the knee.

NON-CONTACT INJURY

The more common opposite non-contact injury occurs when the athlete plants the foot and rotates to the opposite side, such as illustrated by this badminton player.

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