Along with ganglion cysts arising from the alar folds that cover the infrapatellar fat pad, ACL ganglion cysts (also commonly referred to simply as ACL cysts) 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. Knee pain, benign the most common presenting complaint, is usually attribuatable 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
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.
References
- Resnick and Kransdorf “Bone and Joint Imaging” 3rd Edition, Elsevier
- D Bergin et al “Anterior Cruciate Ligament Ganglia and Mucoid Degeneration: Coexistence and Clinical Correlation” AJR 2004; 182:1283-1287
- CC Roberts et al “Advanced MR Imaging of the Cruciate Ligaments” Magn Reson Imaging Clin N Am 15 (2007) 73–86
- Credit: Dr Frank Gaillard
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