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Anterior cruciate ligament ganglion cyst

Dr Henry Knipe and Dr Frank Gaillard et al.

Anterior cruciate ligament (ACL) ganglion cysts, commonly referred to simply as ACL cysts, along with ganglion cysts arising from the alar folds that cover the infrapatellar fat pad, make up the vast majority of intra-articular ganglion cysts of the knee.


These are uncommon findings, with the prevalence of ACL ganglion cysts has been reported to be between 0.3-1.3% of knee MRIs, and are usually incidental findings.

Clinical presentation

Knee pain, being the most common presenting complaint, is usually attributable to other pathology.


ACL ganglion cysts are histologically identical to the ganglion cysts seen elsewhere, most commonly around the wrist. The pathogenesis remains controversial with two theories being favoured:

  • sequelae of ACL mucoid degeneration
  • herniation of synovial tissue through a defect in the joint capsule or tendon sheath

Radiographic features


MRI is better at detecting these lesions than standard anterior portal approach arthroscopy as the surface of the ligament is often intact. In fact the ligament may appear entirely normal. A posterior approach will allow the arthroscopist to detect changes by probing the ligament, and will allow potential aspiration of the cysts. 

Typically the cysts appear as regions of high T2 signal, often multiloculated, centred on the distal ACL. Often there is some irregularity to the bone subjacent to the tibial attachment.

Differential diagnosis

Differential diagnosis of cysts around the knee joint include:

Related articles

Knee pathology

The knee is a complex synovial joint that can be affected by a range of pathologies:

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