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.
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
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 of cysts around the knee joint include:
- 1. Resnick D, Kransdorf MJ. Bone and joint imaging. W B Saunders Co. (2005) ISBN:0721602703. Read it at Google Books - Find it at Amazon
- 2. Bergin D, Morrison WB, Carrino JA et-al. Anterior cruciate ligament ganglia and mucoid degeneration: coexistence and clinical correlation. AJR Am J Roentgenol. 2004;182 (5): 1283-7. AJR Am J Roentgenol (full text) - Pubmed citation
- 3. Roberts CC, Towers JD, Spangehl MJ et-al. Advanced MR imaging of the cruciate ligaments. Magn Reson Imaging Clin N Am. 2007;15 (1): 73-86. doi:10.1016/j.mric.2007.02.006 - Pubmed citation
- 4. Stoller D, Tirman P, Bredella M et-al. Diagnostic imaging. AMIRSYS. (2004) ISBN:0721629202. Read it at Google Books - Find it at Amazon
The knee is a complex synovial joint that can be affected by a range of pathologies:
- bone and cartilage
- distal femoral condyle fracture
- tibial plateau fracture (classification)
- patella fracture
avulsion fractures of the knee
- Segond fracture
- reverse Segond fracture
- anterior cruciate ligament avulsion fracture
- posterior cruciate ligament avulsion fracture
- arcuate complex avulsion fracture (arcuate sign)
- biceps femoris avulsion fracture
- iliotibial band avulsion fracture
- semimembranosus tendon avulsion fracture
- Stieda fracture (MCL avulsion fracture)
- patella fracture
- chronic avulsion injuries
- chondromalacia patellae
- osteoarthritis of the knee
- osteochondral defects
- osteochondritis dissecans of the knee
- pattern of bone contusion in knee injuries
- knee fractures
- meniscal lesions
- synovial lesions
- fat pad
- popliteal fossa