Case of the Week

By Dr Peter Counsel



A 68 year old male with knee pain.



1a and 1b Sagittal PD SPAIR and PD images.

1a Sagittal PD Spair





2a and 2b Coronal PD SPAIR and PD images.







3 Axial PD image




 Image Findings:

The anterior cruciate ligament is markedly expanded, with widening of the intercondylar notch appreciable on the coronal and axial images. There is ganglion formation within the adjacent bone. Although there is a mild diffuse hyperintensity, there is no evidence of fibre discontinuity to indicate a tear.



Mucoid degeneration of the anterior cruciate ligament.



Mucoid degeneration of the ACL involves interstitial glycosaminoglycan deposition among collagen bundles resulting in hypertrophy with knee pain and a restricted range of motion. It is believed to arise from a primary synovial lesion and is associated with arthritis or the sequelae of trauma. While reportedly rare, it is probably underappreciated and present on up to 5% of knee MRIs in one study of 1215 patients with a mean age of 44 years.

Clinical findings are most typically posterior pain exacerbated by flexion or climbing stairs, and sometimes painful limitation of extension. There is no evidence of ACL laxity, although there may be limited flexion to around 100 degrees. Grinding or catching symptoms may be present.

Imaging findings include fusiform expansion of the ACL with diffuse hyperintensity on T2 weighted imaging, but no evidence of fibre discontinuity that would indicate a tear. Both bundles should intact fibres from origin to insertion. The fibres are relatively poorly visualised on T1 and PD weighted imaging, but better appreciated on T2 weighted imaging. The appearance has been likened to a “celery stalk”. While differential diagnoses include an ACL tear or malignancy, in the majority of circumstances MRI findings are sufficiently diagnostic.

Management is initially conservative, but surgical options include partial or complete ACL resection, and notchplasty to counteract the impingement, with the decision for surgery balanced against the potential risk of instability.



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