A posterior cruciate ligament (PCL) ganglion cyst, a benign fluid-filled sac that can develop in the knee joint which is seen in women in the third decade of life with a prevalence of < 0.3% [1,2]. The cyst may be associated with various knee injuries or conditions that put stress on the PCL. The exact aetiology of PCL cysts is not fully understood, but various suspected factors are PCL Injury, meniscal tears, osteoarthritis, rheumatoid arthritis, synovial disorders, repetitive stress, and congenital anomalies. The pathogenesis remains controversial with theories including mucoid degeneration, cyst formation from trauma or tissue irritation, hyaluronic acid release leading to cyst formation, synovial herniation, and congenital translocation of synovial cells [3]. A comprehensive evaluation of the patient's medical history, physical examination, and imaging studies, such as MRI or ultrasound, are typically performed, to diagnose a PCL cyst. These imaging modalities can help in visualizing the cyst, assessing its size, and identifying any underlying PCL injury [5].

A 42-year-old woman without any known comorbidities has been experiencing a sharp pain accompanied by a clicking sensation in her right knee during terminal flexion, for the past two years. The discomfort intensifies when kneeling, fully extending the knee, or engaging in strenuous activities, but she finds relief when resting. Notably, there is no history of any traumatic or twisting injuries to the leg. During the physical examination, there were no visible swellings noted, and on palpation, no supra-patellar effusion was detected. However, tenderness was observed in the popliteal fossa area. Interestingly, there was no tenderness along the joint line. The patient reported experiencing pain specifically during terminal flexion.

All tests conducted to assess the posterior cruciate ligament (PCL) were negative, including McMurray's test, Lachman's test, anterior drawer test, posterior drawer test, Clarke's test, patellar compression test, and patellar lateral apprehension sign. Additionally, there were no indications of any distal neurovascular deficits during the examination. The knee's plain film radiographs did not reveal any abnormal findings related to the bones. However, a 3 Tesla magnetic resonance imaging (MRI) of the right knee showed the following:

• A well-defined intra-articular encapsulated multilocular cyst measuring 1.5x1.8x2.3cm (anteroposterior, transverse, and craniocaudal dimensions) located in the posterior aspect of the knee, situated posterior to the posterior cruciate ligament (PCL). This cyst is seen to extend anteriorly, involving the distal posteromedial bundle fibres of the PCL and pushing them apart. It is limited posteriorly by an intact posterior joint capsule, indicating that it is likely a PCL ganglion cyst located within the joint space (Figure 1 and 2).
• Distal vertical limb of PCL postero-medial bundle shows linear ill-defined Proton density (PD) fat-saturation hyperintensity – suggestive of mucoid degeneration.
• Additionally, a small loculated cyst was identified between the anterior cruciate ligament (ACL) and the PCL in the intercondylar region. This cyst did not appear to have any obvious communication with the PCL cyst.
• The MRI also revealed a small area of partial thickness cartilage loss in the postero-central aspect of the patella, measuring 1.3x1.7mm.
• The menisci, other ligaments, cartilage, bones, muscles, and tendons in the knee joint exhibit normal morphology and signal on the MRI.

Figure 1: Lateral view of MRI of the right knee showing ganglion cyst in the PCL.

Figure 2: Axial view of MRI of right knee showing the PCL cyst.

In summary, the MRI findings indicate the presence of a well-defined PCL ganglion cyst within the knee joint, as well as a smaller cyst between the ACL and PCL. Moreover, there is a small area of cartilage loss on the patella. After explaining the pros and cons of the treatment, patient elected to undergo arthroscopic cyst excision.

The patient underwent arthroscopic PCL ganglion cyst decompression in the right knee, performed under combined spinal and epidural anaesthesia. The patient was positioned supine on a well-padded operating room table without the use of a leg holder. Preoperative prophylactic antibiotics (Inj Cefotaxime 1.5g IV ATD and Inj Vancomycin) were administered, and the right lower extremity was prepared and draped in a sterile manner.

The procedure began with the application of a tourniquet. Evaluation under anaesthesia indicated no instability in the knee. Diagnostic arthroscopic examination was conducted using anterolateral (AL) and anteromedial (AM) portals in the right knee (Figure 3). Within the medial compartment, a flap tear was observed at the medial aspect of the medial femoral condyle, near the root of the intercondylar notch. Additionally, fibrillation was found in the patellofemoral joint. Both menisci were intact, and the anterior cruciate ligament (ACL) was also found to be intact. The cyst was identified anterior to the PCL, and the scope was passed between the ACL and PCL to visualize the posterior compartments (Figure 4).

Figure 3: Right knee, knee flexed. Medial knee with skin markings to establish dual posteromedial portals.

Two posteromedial portals were established to gain access to and remove the cyst. A large cystic mass was located behind the PCL, extending posteriorly and interiorly, covering the lower third of the PCL. A shaver and a rapid frequency wand (Arthrocare) were introduced through the posteromedial portals to excise the cyst. Care was taken to clear the cyst wall from the PCL fibers while preserving the shiny white fibers of the posterior horn of the medial meniscus.

A posterolateral portal was made under arthroscopic guidance. Through this portal, a shaver and radiofrequency wand were used to remove the remaining part of the cyst. An additional cyst was found anterior to the PCL and was also removed using the shaver and radiofrequency tools. Throughout the procedure, the shaver blade was positioned facing anteriorly without suction.

Figure 4: A well-defined intra-articular encapsulated multilocular cyst measuring 1.5x1.8x2.3cm (anteroposterior, transverse, and craniocaudal dimensions) located in the posterior aspect of the knee, situated posterior to the posterior cruciate ligament (PCL).

Following the cyst decompression, the posterior drawer test yielded negative results, indicating stability. Chondral lesions and fibrillation were stabilized as well. Distal pulse was felt, and the limb saturation was normal, indicating good blood flow. The patient tolerated the procedure well. Post-procedure, the patient was informed about the necessary precautions and the use of knee mobilizers, ice, elevation, and prescribed medications.

Ganglion cysts were documented from the dorsum of the wrist, but rare in knees, even rare to encounter PCL cysts. There is a lower incidence of cysts originating from the posterior cruciate ligament (PCL) than from the anterior cruciate ligament and not all PCL cysts are symptomatic; however, in a few cases, they may be clinically relevant, causing knee pain and limiting flexion [6]. Treatment options for PCL cysts depend on the size of the cyst, its location, and the presence of symptoms. In many cases, if the cyst is small and asymptomatic, conservative management may be recommended, including rest, activity modification, pain management, and physical therapy to strengthen the surrounding muscles.

In cases of symptomatic or larger cysts that do not respond to conservative treatment, aspiration (draining) of the cyst under ultrasound guidance may be attempted to relieve pressure and alleviate symptoms. However, it's important to note that cysts can recur after aspiration.

In cases where the PCL is significantly injured or torn and the cyst is causing persistent symptoms or complications, surgical intervention may be considered. The surgical procedure may involve arthroscopic techniques to address the PCL injury and remove or repair the cyst [7]. In comparison to Bertrand Sonnery-Cottet’s technique, we have developed a "two portal posteromedial technique," as described by Ahn J.H. and Ha, which aims to reduce the chances of injury to the cyst during the procedure [8,9].

The surgical approach begins with inserting the scope through the trans-notch, allowing visualization of the posterior compartment, including the adductor, gastrocnemius, and semi-membranous folds. To avoid potential injury, we carefully insert two 16G cannula needles, taking special care to protect the saphenous vein and sartorial branch of the saphenous nerve [9]. In this technique, we utilize the superior posteromedial port as a viewing port and the inferior posteromedial port as a working port. The shaver is inserted, and trans-septal tissue is carefully excised superior to the ganglionic mass, ensuring preservation of the supreme genicular artery. As the shaver is guided into the posterolateral compartment, we place the shaver tip against the deeper surface of the lateral skin, specifically anterior and superior to the short head of the biceps femoris, away from the common peroneal nerve, which is marked on the skin after preparation and drape to safeguard it.

To maintain a clear path, the tip of the shaver blade is then brought out through a portal wound in the lateral skin. A slotted cannula (half pipes) is rail-roded over the shaver blade, allowing the shaver blade to be withdrawn into the joint.

The result is the creation of two posteromedial and one posterolateral portal. By inserting the shaver through the posterolateral portal and using the high postero-medial portal for viewing, we further enhance visualization of the posterior compartment by inserting a Wissinger rod through the inferior postero-medial portal, retracting the posterior capsule posteriorly. During the procedure, a combination of a radiofrequency wand (Arthrocare) and the shaver is employed to remove the posterior cystic mass, ensuring the preservation of both the PCL and the shiny white fibers of the medial meniscus root.

In the subsequent anterior arthroscopy, we take care to apply a traction stitch on the cystic tissue anterior to the PCL, utilizing a knee scorpion (Arthrex) for traction. The cyst wall is gently peeled from the anterior aspect of the PCL using a Duckbell (Smith and Nephew) and shaver, with meticulous attention to preserving the PCL tissue.

Our "two portal posteromedial technique" differs significantly from the technique described by Sonnery-Cottet. Particularly, we emphasize the careful creation of the trans-septal portal with the aid of arthroscopic guidance, which has proven to be instrumental in providing excellent visualization of the entire posterior compartment, minimizing the risk of cyst injury during the procedure.

Advantages

• The trans-septal portal is carefully created under arthroscopic guidance, ensuring precision, and minimizing the risk of complications.
• The cyst is well visualized before the trans-septal portal is made, allowing for accurate planning and execution of the procedure.
• The shaver can be effectively utilized from both the posterolateral and posteromedial inferior ports, facilitating efficient cyst removal.

Disadvantages

• Possible risk of injury to the saphenous vein during the procedure.
• Potential for injury to the sartorial branch of the saphenous nerve, which requires careful attention to avoid.
• Risk of fluid extravasation into the calf, which needs to be managed to prevent complications.

Key Points

• Keeping the knee in a 90-degree flexion position aids in moving the popliteal neurovascular bundles posteriorly, improving the surgeon's view and maneuverability.
• Using a switching stick through the inferior posteromedial portal provides additional posterior capsule retraction, enhancing visualization and access during the procedure.
• Applying an elastic crape bandage approximately 10cm below the popliteal fossa can help prevent fluid extravasation into the calf, reducing the risk of complications.

In conclusion, this case report highlights the diagnosis and successful treatment of a symptomatic ganglion cyst of the posterior cruciate ligament (PCL) in a 42-year-old woman. The MRI findings revealed the presence of a well-defined PCL ganglion cyst within the knee joint, accompanied by a smaller cyst between the anterior cruciate ligament (ACL) and PCL, as well as a small area of cartilage loss on the patella.

To address the cyst, the patient underwent an arthroscopic PCL ganglion cyst decompression procedure using the "two portal posteromedial technique" as described by Ahn J.H. and Ha.

The surgery was successful, preserving both the PCL and the shiny white fibers of the medial meniscus root. The patient tolerated the procedure well, and post-operative outcomes indicated stability and relief from symptoms. While our technique presents certain advantages, such as precise visualization and efficient cyst removal, it is essential to be mindful of potential disadvantages, including the risk of injury to the saphenous vein and sartorial branch of the saphenous nerve, as well as the possibility of fluid extravasation into the calf.

The "two portal posteromedial technique" offers a valuable alternative for managing PCL ganglion cysts, providing valuable insights into optimal approaches for treating such rare knee lesions. As with any surgical procedure, careful consideration of patient-specific factors and potential risks is crucial to achieve favorable outcomes. Further research and studies are warranted to compare different techniques and refine surgical approaches for managing PCL ganglion cysts effectively.

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