**4. Imaging**

The first imaging that detected medial meniscus root bony avulsion was in 1935 by plain radiograph [2]. We recommended to do plain radiograph in all patients suspected of medial meniscus root tear to evaluate degree of osteoarthritis change and axis deformity. The Kellgren and Lawrence (K-L) classification was a common and popular method to classify the severity of osteoarthritis change [30]. They classified 5 grades (**Figure 4**).

#### **Figure 4.**

*Kellgren and Lawrence (K-L) classification, Grade 0 (none): definite absence of x-ray changes of osteoarthritis***,** *Grade I (doubtful): doubtful joint space narrowing and possible osteophytes***,** *Grade II (minimal): definite osteophytes and possible joint space narrowing***,** *Grade III (moderate): moderate multiple osteophytes, definite narrowing of joint space and some sclerosis and possible deformity of bone ends***,** *Grade IV (severe): large osteophytes, marked narrowing of joint space, severe sclerosis and definite deformity of bone ends.*

#### **Figure 5.**

*MRI finding of meniscal root tear. A: Ghost sign (absent of posterior horn medial meniscus), B: Cleft sign (vertical linear defect on coronal images), C: Radial linear defect on axial image, D: Medial meniscus extrusion (*≥*3 mm), E: Bone contusion at the articular bearing area which is associated with medial meniscus root tear.*

However, with popularize of MRI, soft tissue that avulsed from the attachment of the meniscus to the tibia could be easier to detect. Hence, MRI is now the goal standard in detecting medial meniscus root tear because of high sensitivity

*Medial Meniscus Root Tear: Current Update Review DOI: http://dx.doi.org/10.5772/intechopen.98763*

(93.3%) and specificity (100%) [31]. Finding from MRI included absent of posterior horn meniscus called "ghost sign" on sagittal imaging adjacent to posterior cruciate ligament, vertical linear defect on coronal images called "cleft sign", radial linear defect on axial image, and medial meniscus extrusion (≥3 mm) on coronal image. Medial meniscus extrusion less than 3 mm could be found in general populations [32] (**Figure 5**). Medial meniscus that extruded usually larger and thicker than normal meniscus due to swelling and degeneration of meniscal tissue. The MRI study Okazaki showed that 3D MRI could estimate volume and thickness of extruded medial meniscus more precisely when compared to conventional 2D MRI [33].

Medial meniscus posterior root tear had an association with multiple findings including spontaneous osteonecrosis of the knee (SONK), subchondral insufficiency fracture, cartilage injury especially at the medial femoral condyle, and osteoarthritis change [34, 35].
