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Meniscal Injury

Lateral meniscus is smaller in diameter, thicker around its periphery, wider in body, and more mobile; posteriorly, it is attached to medial femoral condyle by either anterior or posterior meniscofemoral ligament, depending on which is present, and to popliteus muscle
  1. Physiological locking occurs in last 30 degree of extension, when femur rotates medially (internally) over stabilized tibia. This very stable position is caused by quadriceps femoris muscle.
  2. Unlocking needed to initiate flexion is carried out by popliteus muscle, which moves femur laterally on stabilized tibia.
  3. The twisting force (rotation) in a weight bearing flexed knee is the commonest mode of meniscal (semilunar cartilage) injury.
  4. Medial meniscus is more frequently torn than the lateral because the medial meniscus is securely attached around the entire periphery of the joint capsule, which makes it less mobile.
  5. Where as the lateral meniscus is more mobile and has no weak point between a movable and relatively fixed point. Popliteus muscle sends few fibers into the posterior margin of lateral meniscus. Thus muscle contraction withdraws & protects the lateral meniscus by drawing it posterolaterally during flexion of the knee and medial rotation of the tibia.
    The commonest type of medial meniscal injury in a young adult is the bucket handle tear. This is vertical longitudinal tear that is complete.
  6. Smillie Classification is for Meniscus Injury
    Locking of knee joint (i.e. joint held in flexion) is seen in meniscus tear, loose body (osteochondral fracture) and fractures of tibial spine.
  1. Mechanism of Locking
    1. Normally the medial meniscus or at least its anterior movable portion glides slightly backwards towards the interior of joint as the knee is flexed.
    2. If the tibia is at the same time abducted (valgus) and the medial compartment of the knee thus opened up, the mobility of the meniscus is still further increased.
    3. Sudden medial rotation of femur on the fixed tibia forces the medial meniscus towards back of joint and causes medial ligament to become taut and it may undergo variety of transverse or oblique tear.
    4. The inner fragment slips into the interior of the joint and when, extension is attempted and the knee begins to screw home’ the fragment is nipped between the condyles and the joint is ‘locked’ i.e. held in flexion.
  2. Meniscal Injury
    1. Meniscus or semilunar cartilage are relatively avascular structure with poor healing potential.
    2. In adults, only 10- 25% of lateral meniscus and 10- 30% of medial meniscus is vascular. Because of the avascular nature of inner two thirds of the meniscus; cell nutrition is believed to occur mainly through diffusion or mechanical pumping. So inner avascular meniscus once torn does not heal.
    3. The meniscus may become completely displaced and locked between the femur and tibia, preventing full extension of the knee. More frequently the torn meniscus will cause pain, intermittent catching and occasionly locking as it flips into and out of the region of contact between the femur & the tibia.
    4. It is important to note that swelling occuring immediately after injury, is hemarthrosis; which may be caused by an injury to cruciate or collateral ligaments or by an osteochondral fracture.
    5. The swelling occuring next day to injury is due to effusion due to meniscal injury.
    6. Symptoms include- joint line pain, catching, popping and locking. Deep squatting and duck walking are usually painful.
    7. Attempts are made to remove only the torn portion of meniscus (if tear is in avascular portion), or repair the meniscus (in vascular peripheral portions if possible).
    8. Art hroscopy is the gold standard for making diagnosis and arthroscopic repair or removal is the treatment of choice.
  3. Mc Murray’s Test
    1. There is pain and occasional clicking along the joint line with forced flexion and rotation of the knee. It is positive in meniscal (medial & lateral) injury.
    2. A fully flexed knee is gradually extended while perforinig medial & lateral rotation applying valgus & varus stress click is heard in meniscal injury.

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