ACL mucoid degeneration

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

The appearance can mimic that of 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 ligament injuries. 

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

The pathogenesis remains controversial.  Possible aetiologies 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 to the formation of ACL ganglion cysts.

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

On arthroscopic examination the ligament is mechanically intact, but mucoid material can be expressed by probing. MRI is better at detecting mucoid degeneration than arthroscopy as the surface of the ligmanet is often intact. In fact the ligament may appear entirely normal especially using the standard anterior portal approach. A posterior approach will allow the arthrosopist to detect changes by probing the ligament. This is also true of ACL ganglion cysts.