Anterior cruciate ligament mucoid degeneration

Anterior cruciate ligament (ACL) mucoid degeneration, along with tears and anterior cruciate ligament ganglion cysts, is a relatively common cause of increased signal within the anterior cruciate ligament (ACL).

The appearance can mimic acute or chronic interstitial partial tears of the ACL. However, in the case of mucoid degeneration secondary signs of ACL injury are usually absent. Secondary signs include bone bruising, meniscal tears, anterior subluxation of the tibia and other ligamentous injuries. 

Clinical presentation

Typically patients present with knee pain or restricted movement, although often other potential causes for the patient's symptoms are found.

Pathology

The pathogenesis remains controversial. Possible etiologies include:

• age related (senescent) degeneration
• congenital or acquired synovial tissue entrapment between ACL fibers

It is postulated that mucoid degeneration may be a predisposing factor in the formation of ACL ganglion cysts.

Radiographic features

MRI

On MRI, the ligament is thickened and ill-defined with a "celery stalk" appearance. Its signal is increased on all sequences. Intact fibres are best seen on T2-weighted sequences.

MRI is better at detecting mucoid degeneration than arthroscopy as the surface of the ligament is often intact.

Treatment and prognosis

No treatment is usually required. If arthroscopy is performed the ligament may appear entirely normal, especially using the standard anterior portal approach. A posterior approach will allow for the detection of changes by probing the ligament and mucoid material can be expressed.