In this study, we found that MR imagines are valuable for the detection of these uncommon cysts, and arthroscopic management is effective. Thirty one cysts were found by MR examinations, giving an incidence of 0.36%. The incidence of patients undergoing surgical intervention for management of this condition was 0.88% with arthroscopic resection of the cysts being performed in 11 patients of 1253 cases that were screened and formed the part of this study. In a similar large series on ganglion cysts reported so far, Sarimo et al. found nine of 2400 knees demonstrated a cyst associated with a cruciate ligament upon arthroscopic examinations [5]. Fifteen cases of ganglion cysts (1.10% of all 1364 arthroscopies) relating to the ACL were reported by Parish in another study [6].
The youngest patient in the medical literature was a child of two years old [7]. Jawish et al., in another study, also reported a case of a seven year old boy [8]. The cause of cruciate ganglion cysts remains unclear and the literature presents diverging views as to its origin and inception. In this study, no antecedent knee trauma was found in any of the 31 patients. However, tissues of synovial membrane, collagen, and fascia were discovered by histological examination. Therefore, it could be hypothesized that some repeated minor knee trauma contributed to the development of the cyst. The fact that the cysts occurred predominantly in males (male : female ratio, 21:10) also supports this conclusion as females are traditionally considered to be less likely to suffer trauma and sporting injuries, a fact also supported by meta-analyses on the subject [9]. The position of cysts mainly behind the ACL suggested the possible cause could be a result of mechanical force and microtrauma associated with repetitive knee motion.
In this study, the clinical manifestations of ganglion cysts of the cruciate ligaments are varied and often non-specific. Literature review indicated that intra-articular ganglions of the knee could be both symptomatic and asymptomatic [1, 4–6, 10–13]. Most patients in the study presented with pain and described it mainly around joint line, accompanied with some restriction in flexion or extension because of the worsening pain. The incidence, severity, and duration of pain seem to vary depending on size and location of the cyst. Cysts located mainly anterior to cruciate ligaments tended to limit extension of the knee, whereas those located predominately posterior to the cruciate ligaments tended to limit flexion. It could be speculated that the changes in the length and torsion of the cruciate ligaments, due to knee motion, might result in traction or compression on the cysts that may stimulate the nerve endings on adjacent synovium and result in pain and abnormal sensation.
Differential diagnosis of cruciate ganglion cysts can be excluded safely by relying on the typical MR findings seen in this condition. Before the advent of MRI, these anterior cruciate ligament ganglia were identified only at open surgery or arthroscopy. MR imaging is a valuable tool in diagnosing cysts, especially when the patient presents without any specific history of trauma. In MR images, ganglion cysts demonstrate fluid characteristics with low signal intensity on T1-weighted images and increased signal on T2-weighted images. They are well-delineated structures, appearing as lobulated or multilobulated structures, and are easily distinguishable from Baker cysts or menisci cysts on the T2-weighted images. Usually located within or surrounding the cruciate ligament, these structures do not extend to the medial and lateral head of the gastrocnemius or are connected with meniscus. For the purpose of this study a relatively low tesla machine of 0.2 T, along with a section thickness of 4.5 mm was used. This might have theoretically decreased the sensitivity of detection of some small lesions for which high filed intensity MR scans may be more sensitive.
With the advent of arthroscopy, the treatment of cruciate ligament cysts becomes simple with a successful outcome. In our patients, no recurrence was found. A review of the literature indicated that arthroscopy with cyst removal or aspirate is recommended and always results in complete resolution without injury to adjacent structures [1, 4–6, 10–13]. A combined arthroscopic and open approach is considered appropriate when cysts are associated with other intra-articular lesions [14]. In our study, the 11 patients who received arthroscopic operation all had cysts that were clearly observed by a routine anteromedial or anterolateral approach. At arthroscopy, the cysts mainly presented as round- or ellipse-shaped, were associated with cruciate ligaments, and had a clear boundary from adjacent structures.
In our practice, preoperative MRI in diagnosis of ligament cyst aids the surgeon in planning ahead with respect for need for special instruments which in this case was a wide or larger angled arthroscope. In order to protect the cyst wall from damage and prevent exudation of the content from the cyst, a blunt dissection should be carried out using an arthroscopic probe. If the cyst is excessively large, fluid can be aspirated before attempting removal with a shaver. Blood vessels in synovium at the surface of ligament should be preserved and, if necessary, ablated with Radiofrequency ablator in order to avoid hemorrhage. One patient in our study had an acute hematoma in the knee joint that was treated with arthrotomy and subsequent drainage. All 11 patients in our study were symptom-free after complete excision of cyst wall by arthroscopy.
