Correct combination
Case 143
【Progress】She was given nonsteroidal anti-inflammatory drug. She underwent intraarticular hyaluronic acid injection and rehabilitation with supporter brace.
【Discussion】
Meniscus composes of anterior horn, body, posterior horn and root. Medial meniscus (MM) is larger in size than lateral meniscus (LM). The posterior horn of MM is larger than the anterior horn of MM, while the posterior horn of LM is the similar size as the anterior horn of LM. The attachment of MM is firmly fixed to medial collateral ligament, inducing less mobile and the attachment of LM is loosely fixed to lateral collateral ligament, inducing mobile. Both menisci have the anterior and posterior roots attached to the central tibial plateau that are shown on MRI coronal images of the knee joint. Discoid meniscus is seen in less than 5 % of knees and 10 – 20 times more common in LM than in MM (1-3). Discoid meniscus is diagnosed when the body measures 15 mm or more on a middle coronal image (1-3).
Meniscus tear is categorized into three forms: transverse tear, longitudinal tear and radial tear.
Transverse tear occurs in patients older than 40 years without trauma. The typical MRI imaging appearance is a horizontal line with high signal intensity that contacts the meniscus surface. Parameniscal cyst formation is associated with complete horizontal tear secondary to direct communication with joint fluid (4, 5).
Longitudinal tear occurs in young patients after significant trauma. The typical MRI imaging appearance is a vertical line with high signal intensity that contacts one or both articular surfaces. Longitudinal tears of MM and LM are associated with anterior crucial ligament tears with the incidence of 90% and 83%, respectively (6).
Comparing to transverse tear and longitudinal tear, radial tears weakens meniscal hoop strength, leading to a dramatic loss of function and possible meniscal extrusion. The radial tears are difficult to repair because they are located within the avascular zone (white zone) (1, 7). The cleft sign can occur with both longitudinal and radial tears. However, the typical MRI imaging shows truncated triangle sign or ghost meniscus sign either on sagittal or on coronal slices. Truncated triangle sign often indicates a partial thickness tear and ghost meniscus sign often indicate a full-thickness tear. Root tear is a radial tear and complete radial tears are associated with meniscal extrusion particularly when the tear occurs in the MM (1, 7).
A bucket-handle tear is a longitudinal tear with central migration of the inner teared fragment like a bucket handle configuration. This occurs seven time more in the MM. The typical MRI imaging appearance is : an absent bow tie, a fragment within the intercondylar notch and a double PCL (8, 9).
Meniscal extrusion is defined as meniscus deviation extends 3mm or more beyond the edge of tibial plateau. There is a close association between meniscal extrusion and root tears, large radial tears and complex tears, indicating they occur due to disruption of the collagen fibers in the meniscus, namely the loss of the meniscal hoop strength.
In our patient, her left knee joint MRI showed meniscus complicated tears, meniscus extrusion, loose body and anterior cruciate injury.
【Summary】
We present a sixty nine-year-old female suffering from her left knee joint. Coronal and sagittal MRI showed meniscus injury, meniscus extrusion, loose body and anterior cruciate injury. It is borne in mind that medial meniscus is larger, less mobile and more fixed to collateral ligament than lateral meniscus. Transverse tears occur in ages of 40 or older and forms a parameniscal cyst especially in case of complete tears. Longitudinal tears occur after significant trauma and associate with injury of anterior cruciate ligament with the incidence of 90%. Severe longitudinal tear causes a bucket-handle tear that means central migration of the inner teared fragment whose typical MRI appearances are an absent bow tie, a fragment within the intercondylar notch, and double posterior cruciate ligament sign. Radial tear disrupts more damages of collagen fibers within the meniscus inducing weakness of hoop strength and inducing the possibility of extrusion of meniscus, especially in case of root tear. Meniscus extrusion is caused by large radial tears, root tears and complicated tears. The MRI appearances of radial tears are truncated triangle sign and a ghost meniscus sign which indicate a partial thickness tear and a full-thickness tear.
【References】
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2.Renström P, et al. Anatomy and biomechanics of the menisci. Clin Sports Med 1990;9(3):523–538.
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8.Ververidis AN, et al. Meniscal bucket handle tears: a retrospective study of arthroscopy and the relation to MRI. Knee Surg Sports Traumatol Arthrosc 2006;14(4): 343–349.
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2019.5.8