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 an ACL injury are usually absent. Secondary signs include bone bruising, meniscal tears, anterior subluxation of the tibia and other ligamentous injuries.
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Epidemiology
ACL mucoid degeneration is present on ~10% (range 9-12%) of 3 T MRI examinations and 2% of 1.5 T MRI examinations 6.
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 fibers are best seen on T2WI.
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.
It has recently been postulated that mucoid degeneration of the ACL is related to the medial knee compartment joint space loss in patients with osteoarthritis or in the OA risk group 6.
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