MENISCAL VARIATIONS AND TEARS
TYPES OF MENISCAL TEARS AND DISCOID MENISCUS VARIATIONS
The meniscus is normally a crescentic structure, although several forms of discoid lateral menisci have been described. These range from a complete disc to a very rare ring-shaped meniscus with abnormal thickness. The common explanation for these variant discoid forms assumes that the normal meniscus is formed from an original discoid shape and that the discoid lateral meniscus is a congenital variant in which the central portion does not degenerate with time. This theory would explain the variously shaped menisci found at surgery. However, no discoid menisci have been found in fetuses and a review of comparative anatomy shows no mammal with such a pattern of formation.
A second theory is a developmental one. Many discoid lateral menisci have
abnormal attachments to the tibia. When the attachment to the posterior tibial
plateau is deficient, there is a strong attachment to the medial femoral
condyle by the meniscofemoral ligament (Wrisberg’s ligament). This pattern of
attachment may allow abnormal movement of the lateral meniscus: the posterior
horn of the lateral meniscus moves into the center of the lateral compartment
during full extension of the knee. With time, scarring and fibrosis of the
lateral meniscus occur, with resultant thickening. These changes may account
for the popping on flexion and extension that is usually noticed during
childhood or early adolescence.
Treatment. Many discoid menisci are asymptomatic, and
the mere presence of one is not an indication for treatment. The popping itself
is not harmful unless it is accompanied by pain of swelling of the knee. Pain,
swelling, and a history of trauma are relative indications for arthroscopy.
Tears of the meniscus or degenerative changes on the
articular surfaces may necessitate resection. Arthroscopic techniques allow for
partial resection or saucerization of the discoid lateral meniscus, leaving a
peripheral rim that may function properly. Resection may be difficult because
of the increased thickness in such menisci. Prognosis for patients with discoid
menisci is good. Discoid menisci without degenerative changes have been found
in the joints of elderly persons. Therefore, every attempt should be made to
salvage function of the meniscus by avoiding complete excision simply to
eliminate the snapping, clicking sensation.
MENISCUS TEARS
Tears of the meniscus are common findings in a patient with an acutely
injured knee, especially in situations in which a traumatic twisting event has
occurred. Tears may occur in either meniscus or in both menisci at the same time. A
meniscus tear often becomes symptomatic if its torn portion is mobile and
slides into an abnormal position between the articular surfaces of the femur
and tibia. Patients with a displaced meniscus tear often report pain at the
joint line and blocked extension, flexion, or both. The affected knee
frequently gives way and exhibits recurrent effusions.
A bucket-handle tear is a longitudinal tear through the substance of the
meniscus. The torn portion remains attached to the anterior and posterior horns
of the meniscus. A small radial tear initially causes very few symptoms, but if
not treated it may progress to a deeper, more symptomatic parrot-beak tear. The
unstable flap of meniscus may cause mechanical signs in the injured knee such
as recurrent effusions, giving way, and a catching sensation. Horizontal tears
of the meniscus appear to be a delamination of the substance of the meniscus.
Neglected horizontal tears frequently result in an unstable flap of meniscal
tissue, which can also cause mechanical signs.
When an unstable portion of meniscus displaces into the intercondylar
notch and becomes incarcerated, it will cause the knee to lock. Manipulation of
the knee may be possible and often occurs with a loud, audible and palpable
“clunk.” This sound and the temporary resolution of symptoms indicate reduction
of the dis- placed portion into its normal anatomic position. A persistently
locked knee requires urgent intervention. If it is neglected, attempts at weight
bearing and knee movement cause severe, irreversible erosion of the articular
cartilage surfaces of the femur and tibia.
 |
| TEARS OF THE MENISCUS |
Physical Examination and Special Tests
·
Joint line tenderness: Tenderness
along the medial or lateral joint lines is among the most sensitive findings
for a meniscal tear.
· McMurray test: The patient is
supine and relaxed. The patient is asked to flex the knee maximally with
external tibial rotation (medial meniscus) or internal tibial rotation (lateral
meniscus). While maintaining rotation, the patient brings the knee into full
extension. A positive test is indicated by a painful pop occurring over the
medial joint line (medial meniscus) or lateral joint line (lateral meniscus).
· Apley compression test: The patient is
prone. The knee is flexed to 90 degrees with external tibial rotation (medial
meniscus) or internal tibial rotation (lateral meniscus). Axial compression is
applied to the tibia while the patient flexes and extends the knee. A positive
test is indicated by a painful pop over the medial joint line (medial meniscus)
or lateral joint line (lateral meniscus).
MEDIAL AND LATERAL MENISCUS
McMurray and Apley test results may vary considerably from one
examination session to the next owing to patient apprehension and chronicity of
injury. A joint effusion will often be present after an acute tear.
Chronically, atrophy of the quadriceps muscle may occur. With peripheral
meniscus detachment and positive anterior drawer test, a loud “clunk” may be
elicited as the meniscus displaces during anterior drawer testing. Imaging.
Plain films are usually normal, unless a meniscus tear has been present
for a significant time. After that time, they may show joint line spurring,
narrowing, or other arthritic changes. MRIs have now sup- planted arthrograms
for diagnosis of meniscal injury. MRI has a sensitivity as high as 95% for
demonstration of medial meniscus tears but has somewhat less sensitivity in
detection of lateral meniscus tears.
Treatment. In young, active persons, arthroscopic
repair of torn menisci should always be considered. In these younger patients
the loss of a large portion of a meniscus can be devastating because meniscal
deficiency can lead to earlier-onset arthritis and, potentially, total joint
arthroplasty.
At the time of the surgery, with the patient under anesthesia, a locked
knee may spontaneously unlock. The knee is then examined manually to determine
any ligament instability, and an arthroscopic examination is performed. To help
preserve the articular cartilage, the displaced part of the meniscus can be
removed during arthroscopy.
Repairs in the well-vascularized peripheral third (“red zone”) of the
medial and lateral menisci have been quite successful. With proper technique
and stabilization of the knee joint with ligament repair where necessary,
repair of the meniscus can be successful in 90% of cases. Multiple studies have
looked at establishing which tears outside the vascular peripheral third can be
repaired and whether there are biologic or pharmacologic means that may improve
the potential for healing. Although these tears have less chance of healing,
repair may well be indicated in younger patients. Approaches to repair include
all-inside, out-side-in, and inside-out
techniques, with most surgeons now preferring the all-inside approach when
possible.
Rehabilitation programs after arthroscopy and partial meniscectomy
generally include minimal immobilization of the knee, immediate weight bearing,
and early physical therapy. Therapy consists of gait training and active and
passive range-of-motion and quadriceps- strengthening exercises. Ice or heat
may be applied as needed. After repair of meniscus tears, vigorous
rehabilitation and range-of-motion exercises may be delayed a few weeks.
