What Causes ACL Ganglions
ACL ganglion cysts are fluid-filled cystic formations with a myxoid matrix that arise from or adjacent to the anterior cruciate ligament, though their exact etiology remains unclear—they may develop spontaneously or following trauma, with some patients reporting a history of knee injury while others have no identifiable precipitating event. 1, 2, 3
Pathophysiology and Origin
The precise mechanism of ACL ganglion formation is not definitively established. The current understanding suggests:
Ganglion cysts are cystic swellings that typically arise close to tendons or joints, and when they occur intra-articularly in the knee, they most commonly originate from the ACL. 3
Some patients have a documented history of trauma preceding ganglion development, while others develop these lesions without any identifiable injury. 1, 2
The cysts contain fluid with a myxoid matrix and are characterized histologically as synovial cysts. 1, 2
Location and Anatomic Considerations
ACL ganglia can arise from various locations within or adjacent to the ligament:
Most commonly, these ganglia arise from the substance of the ACL itself (intrasubstance ganglia). 4, 5
While ACL is the most frequent site, ganglia can also originate from other cruciate ligament structures including the posterior cruciate ligament (PCL) or meniscus. 1, 3
The cysts typically extend in various directions—most commonly anteriorly toward the intercondylar notch, but can also extend posteriorly. 4
Clinical Presentation Patterns
The clinical manifestations vary widely:
Many ACL ganglia are asymptomatic and discovered incidentally during MRI or arthroscopy performed for other indications. 3, 5
Symptomatic cases present with non-specific findings including knee pain (especially after stressing activities), limited range of motion, clicks, locking, or restriction of knee extension. 3, 4, 5
Extension restriction is more common than flexion restriction—this occurs when the cyst extends anteriorly and impinges on the intercondylar notch roof during knee extension. 4
The relatively slow progression of symptoms often delays patients from seeking medical attention, which can complicate subsequent treatment. 5
Important Clinical Pitfall
ACL ganglia may mimic other intra-articular pathology, particularly ACL tears or meniscal tears, leading to diagnostic confusion. 1, 3 When evaluating chronic knee discomfort with non-specific clinical signs and no clear traumatic cause, consider intra-articular ganglion cyst as a potential diagnosis. 5
Diagnostic Approach
MRI is the investigation of choice for diagnosis, revealing typical signs of ganglion cysts within the substance of the ACL. 3, 5 The cysts appear as multi-lobed cystic structures adjacent to or within the ACL on MRI imaging. 2