Meniscal tear

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Meniscal tears arethe failure of the fibrocartilaginous menisci of the knee. There are several types and can occur in an acute or chronic setting. Meniscal tears are best evaluated with MRI.

Pathology

Acute meniscal tears occur after the rotatory trauma of the knee, whereas chronic degenerative meniscal tears often occur in the elderly after minimal rotatory trauma or stress on the knee.

In older adults, attritional changes in the meniscus lead to fragmentation of the meniscus and a variety of tears (there usually occur at the posterior horn of the medial meniscus) ⁸.

Types

There are different types of meniscal tears, describing the morphology of the injury. Identifying and accurately describing the type of meniscal tear can help the surgeon in patient education and planning of the surgical procedure. Meniscal tear types include ^1,5,6:

basic tears
- longitudinally oriented tears
  - horizontal tear (cleavage tear):
    - parallel to the tibial plateau involving one of the articular surfaces or free edge
    - divides the meniscus into superior and inferior parts
  - longitudinal tear (vertical tear):
    - perpendicular to the tibial plateau; and parallel to the long axis of the meniscus
    - divides the meniscus into medial and lateral parts
    - Wrisberg rip is a specific subtype
- radial tear: perpendicular to both the tibial plateau and the long axis of the meniscus
- root tear: ~~radial~~ typically radial-type tear located at the meniscal root

complex tear: a combination of all or some of horizontal, longitudinal and radial-type tears

displaced tear: tear involving a component that is displaced, either still attached to the parent meniscus or detached:

flap tear: displaced horizontal or longitudinal tears
bucket-handle tear: displaced longitudinal tear
parrot beak tear: displaced radial tear

Radiographic features

Plain radiograph

On plain radiographs, meniscal tears are not visible. In rare cases secondary signs can be seen, such as a soft tissue swelling next to the meniscus when a meniscal cyst is present ⁴. Only when associated with more complex injuries plain film may suggest a meniscal tear, e.g. arcuate sign, reverse Segond fracture, tibial plateau fracture.

MRI

With a sensitivity of ~95% and a specificity of 81% for medial meniscal tears and a sensitivity of ~85% and a specificity of 93% for lateral meniscal tears ^2,5, MRI is the modality of choice when a meniscal tear is suspected, with sagittal images being the most sensitive ⁵.

There are three basic MR characteristics/criteria of meniscal tears ⁵:

high intrameniscal signal extending to at least one ~~(if not both)~~ articular ~~surfaces~~surface
which should be seen in at least two slices-: two slice touch rule (do not have to be contiguous, e.g. sagittal and coronal slices)
distortion of the normal meniscal morphology if no prior surgery

Each type of meniscal tear has its own characteristics on MRI, but in most cases, the following can be seen ³:

T1: a hyperintense line in the meniscus can be seen, but it is difficult to differentiate between degeneration and meniscal tear on this sequence; in the case of a bucket-handle tear an empty groove can sometimes be seen
T2: a hyperintense line in the meniscus, which indicates synovial fluid in the meniscus
- the high T2 signal in mid-substance of the meniscus without extension to the surface is not necessary a tear and can be:
  - in an adult: secondary to degeneration
  - in children: high vascularity of meniscus

See MRI grading system for meniscal signal intensity.

Associated features that are suggestive of a meniscal tear include ⁵:

tibial subchondral bone oedema
parameniscal cyst
meniscal extrusion

Treatment and prognosis

Surgical arthroscopy is done in most of the cases. Meniscopexy or complete or partial meniscectomy can be performed, depending on the degree and type of meniscal tear.

Pitfalls

oblique ligament: with intercondylar bucket handle component
transverse ligament
femoromeniscal ligaments
meniscocapsular fibrofatty junction
previous surgery
fluid in normal central knee recesses
fluid in popliteal hiatus
ligamentum mucosum
chondrocalcinosis: can increase signal intensity on MRI

Differential diagnosis

The differential can be variable depending on the type of tear but in general, consider:

~~-<a href="/articles/horizontal-meniscal-tear">horizontal tear</a> (cleavage tear): parallel to the <a href="/articles/tibial-plateau">tibial plateau</a>~~
+<a href="/articles/horizontal-meniscal-tear">horizontal tear</a> (cleavage tear)<ul>
+<li>parallel to the <a href="/articles/tibial-plateau">tibial plateau</a> involving one of the articular surfaces or free edge</li>
+<li>divides the meniscus into superior and inferior parts</li>
+</ul>
-<a href="/articles/longitudinal-meniscal-tear">longitudinal tear</a> (vertical tear): perpendicular to the tibial plateau; parallel to the long axis of the meniscus<ul><li><a href="/articles/wrisberg-rip">Wrisberg rip</a></li></ul>
+<a href="/articles/longitudinal-meniscal-tear">longitudinal tear</a> (vertical tear)<ul>
+<li>perpendicular to the tibial plateau and parallel to the long axis of the meniscus</li>
+<li>divides the meniscus into medial and lateral parts</li>
+<li>
+<a href="/articles/wrisberg-rip">Wrisberg rip</a> is a specific subtype</li>
+</ul>
~~-<a href="/articles/radial-meniscal-tear">radial tear</a>: perpendicular to the tibial plateau and the long axis of the meniscus<ul><li>~~
~~-<a href="/articles/meniscal-root-tear">root tear</a>: radial-type tear located at the <a href="/articles/meniscal-root">meniscal root</a>~~
~~-</li></ul>~~
+<a href="/articles/radial-meniscal-tear">radial tear</a>: perpendicular to both the tibial plateau and the long axis of the meniscus</li>
+<li>
+<a href="/articles/meniscal-root-tear">root tear</a>: typically radial-type tear located at the <a href="/articles/meniscal-root">meniscal root</a>
~~-<a href="/articles/bucket-handle-tears">bucket-handle tear</a>: displaced longitudinal tear </li>~~
+<a title="Bucket-handle meniscal tear" href="/articles/bucket-handle-meniscal-tear">bucket-handle tear</a>: displaced longitudinal tear </li>
~~-<li>high intrameniscal signal extending to at least one (if not both) articular surfaces</li>~~
~~-<li>which should be seen in at least two slices- <a href="/articles/two-slice-touch-rule-knee-mri">two slice touch rule </a> (do not have to be contiguous, e.g. sagittal and coronal slices)</li>~~
+<li>high intrameniscal signal extending to at least one articular surface</li>
+<li>which should be seen in at least two slices: <a href="/articles/two-slice-touch-rule-knee-mri">two slice touch rule </a> (do not have to be contiguous, e.g. sagittal and coronal slices)</li>

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