- Lateral meniscal tears are more common than medial tears.
- Isolated meniscal tears occur more commonly in younger pediatric patients, while older adolescents are more likely to sustain a tear in conjunction with a ligamentous injury.
- Meniscal tears in pediatric patients are often associated with other pathology such as ACL tears, tibial eminence fractures or the presence of a discoid meniscus.
- Meniscal tears in pediatric patients should be repaired if possible. The literature shows a high success rate for healing following repair.
Description:The meniscus is a C-shaped or semicircular fibrocartilaginous disc composed of collagen, proteoglycans, and glycoproteins (Greis, 2002). The main body (middle) has circumferential collagen bundles with radial fibers interspersed. The surface has a mesh network with random configurations of collagen bundles.
The blood supply to the menisci is from the perimeniscal capillary plexus. At birth, the entirety of meniscus is vascular. By 9 months of age, the inner third has become avascular. From age 10 years onward, only 10-30% of the outer rim is vascular. The location of tears is often referred to by the zones of vascularity:
- The peripheral 1/3 of the meniscus is the red-red zone
- The middle 1/3 of the meniscus is the red-white zone
- The inner 1/3 of the meniscus is the white-white zone
The menisci function in load transmission across the knee joint (Ahmed, 1983). The load varies by knee position. In extension, the menisci bear 50-70% of the load. The load born increases to 85% at 90 degrees of flexion. Removal of the medial meniscus results in a 50–70% loss of femoral contact and a 100% increase in contact stress (Radin, 1984). Removal of the lateral meniscus results in a 40% loss of femoral contact and a 200-300% increase in contact stress (Kettelkamp, 1972).
Epidemiology:Lateral meniscal tears are more common than medial meniscal tears. Adolescents are more likely to have associated ligamentous injuries. Children are more likely to have tears associated with discoid menisci. In addition, children with an isolated meniscal tear more commonly have a low BMI. A 2013 study found the distribution of meniscal tear type to be: complex (28%), vertical (16%), discoid (14%), bucket-handle (14%), radial (10%), horizontal (8%), oblique (5%), fray (3%), and root detachment (2%) (Shieh, 2013).
Clinical Findings:Patients with meniscal tears report pain and swelling at the time of injury. Mechanical symptoms such as catching, locking, or giving way may occur with a displaced meniscal tear. The medial and lateral joint line should be palpated to test for tenderness. Physical exam may demonstrate a loss of full extension, particularly with a bucket-handle tear that is flipped into the notch.
The McMurray Test is the standard diagnostic test for a meniscal injury. As this test may illicit pain, it is often difficult to perform in young children. The test is performed with the knee in flexion with the foot rotated toward the meniscus that is being tested (internal for medial, external for lateral). As the knee is extended, a force is applied opposite the meniscus being tested (valgus for medial, varus for lateral) while the foot is rotated away from the meniscus being tested (external for medial, internal for lateral). The test is positive when a “click” is felt indicating subluxation of the torn portion of the meniscus. The presence of pain on exam without the “click” does not indicate a positive test.
Imaging Studies:X-rays are usually normal in an isolated meniscus tear. Widening of the lateral joint space or squaring of the lateral femoral condyle may be seen with a discoid lateral meniscus. X-rays may show concurrent injuries such as a tibial eminence fracture or a Segond fracture (an avulsion of the anterolateral tibial plateau, often associated with an ACL tear).
MRI is the study of choice to image meniscus tears, but does not have perfect sensitivity[BK2] (Gans, 2015). Arthroscopy remains the gold standard for diagnosing meniscal tears.
Treatment:Non-operative treatment with bracing and physical therapy may be attempted in non-displaced, partial tears in the red-red zone. Conservative management is not warranted with tears in the red-white or white-white zones. Studies have shown that operative treatment of meniscus tears in pediatric patients typically produces good results (80-87%) (Shieh, 2016; Kraus, 2012).
There are numerous meniscal repair techniques available including:
- All-Inside Meniscal Repair is performed with a commercially available device consisting of sutures attached to implants which are placed on both sides of the tear. The suture is then cinched to reduce the tear. The repair survival rate is as high as 89.5% with the all-inside repair technique (Schmitt, 2016). Care should be taken in younger children because all-inside devices may deploy close to neurovascular structures.
- Inside-Out Meniscus Repair is performed with a cannula placed into the knee allowing a suture, double loaded with flexible needles, to be passed on either side of the tear and out through the capsule. The suture is then tied outside the capsule. An open approach for tying the knot is used to avoid entrapping neurovascular structures on the medial or lateral sides of the knee. This technique may be more appropriate for younger children where the neurovascular structures are in closer proximity to the knee joint capsule. The survival rate for inside-out meniscus repair is as high as 95.6% (Vanderhave, 2011).
- Outside-In Meniscus Repair is reserved for tears of the anterior meniscus.
- Meniscal Transplantation is considered for patients who have had a partial to total meniscectomy where there is concern for a poor long term outcome. An allograft meniscus can be transplanted into the meniscus deficient knee. Cartilage restoration or mechanical realignment procedures may be performed concomitantly. In adolescent patients, meniscal transplantation has shown an increase in functional outcomes, excellent meniscal allograft survival, and low reoperation rates (Riboh, 2016).
Complications:Re-tear after arthroscopic fixation has been reported more often for complex tears and bucket handle tears. The repair of simple tears has the highest success rate (Krych, 2008). Anatomic structures at risk include the saphenous nerve during medial meniscus repair and the personal nerve during repair of the lateral meniscus. Posterior repairs put the popliteal neurovascular structures at risk. Fortunately, arthrofibrosis is a rare complication following arthroscopic meniscus repairs.
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