Appearance of Knee joint Cartilage Lesions on MRI

The appearance of cartilage lesions on MRI depends on whether they are degenerative or posttraumatic in cause. Early degenerative cartilage lesions in patients with osteoarthritis appear as fibrillation, pitting, and fissuring of the articular surface. As the disease progresses, a focal partial-thickness cartilage defect with obtuse margins develops in the area of cartilage degeneration . In patients with advanced osteoarthritis, multiple partial-thickness and full-thickness cartilage defects, cartilage delamination, and diffuse cartilage thinning involving opposing articular surfaces of the knee joint are typically present .

Degenerative cartilage lesions can be associated with changes in the underlying subchondral bone marrow. The bone marrow edema pattern, which consists of ill-defined areas of high T2 signal, is the most common finding and can be seen adjacent to 5–54% of cartilage lesions depending on their size and depth . Although the high T2 signal within the subchondral bone marrow was originally thought to represent marrow edema, studies have shown that these areas of signal abnormality actually correspond to areas of marrow necrosis, fibrosis, and trabecular disorganization on histologic analysis . The bone marrow edema pattern may be a particularly important secondary finding in patients with degenerative cartilage lesions because its presence has been correlated with pain and disease progression in some research studies. In patients with advanced osteoarthritis, high T2-signal cysts or low T1- and T2-signal sclerosis can be seen within the subchondral bone marrow adjacent to deep partial-thickness and full-thickness cartilage defects.

Posttraumatic cartilage lesions within the knee joint are the result of shearing, tangential, or rotational forces on the articular surface, and their appearance on MRI depends on the mechanism of injury. Shearing forces secondary to injuries, such as transient patellar dislocation, typically result in deep partial-thickness or full-thickness cartilage defects with acutely angulated margins that may also involve the underlying subchondral bone. Linear cartilage flap tears and delamination injuries at the junction between the articular cartilage and subchondral bone also can occur . Cartilage shearing injuries are commonly unstable and result in partially or completely displaced cartilaginous or osteochondral fragments with associated intraarticular loose bodies .

Tangential and rotational forces on articular cartilage secondary to injuries, such as anterior cruciate ligament tear, typically result in osteochondral impaction injuries. These impaction injuries manifest as areas of high T2-signal subchondral bone marrow edema within the anterior lateral femoral condyle and posterior tibial plateau with occasional depression of the articular surface and trabecular fracture lines . The articular cartilage overlying areas of bone marrow edema usually appears normal on MRI and even at arthroscopy . However, evidence of acute cartilage injury is apparent on histologic analysis and when using physiologic cartilage imaging techniques, such as delayed gadolinium-enhanced imaging and T1 rho imaging

Source:http://www.ajronline.org/