Arthroscopic Excision of Posterior Cruciate Ligament Cysts Using a Double Posteromedial Approach

Summary

We present a surgical approach to treat posterior cruciate ligament cysts by an arthroscopic double posteromedial approach.

Abstract

Cruciate ligament cysts of the knee are a rare condition. Posterior cruciate ligament cysts of the knee are less common than anterior cruciate ligament cysts. In patients with asymptomatic isolated cruciate ligament cysts of the knee, conservative treatment is recommended. Symptomatic cruciate ligament cysts of the knee are mostly manifested as knee hyperflexion pain, straightening pain, knee discomfort after standing for a long time or walking for a long time, etc., which seriously affects the quality of life, surgical treatment can be performed. The surgical treatments can be divided into ultrasound-guided cyst puncture and fluid extraction procedure and arthroscopic cystectomy. Cysts are mostly lobulated with a multi-layer cyst wall, cyst fluid extraction does not remove the cyst wall completely but simply extracts cyst fluid, leading to a high recurrence rate. Arthroscopic surgery can completely remove the cyst wall with little trauma, a low recurrence rate, and fast postoperative recovery, so arthroscopic resection is the most common and preferred method of treatment. Since posterior cruciate ligament cysts mostly occur posterior to the ligament, we remove the cyst wall by adding a double posteromedial approach to the knee joint, and the cyst wall is removed under direct vision, which is simple to operate, the cyst wall is completely cleared, the trauma is small, the postoperative recovery is fast, and there is no recurrence. Here, 8 posterior cruciate ligament cysts were removed with complete postoperative symptom relief, no surgical complications, and no recurrence at 1-year follow-up.

Introduction

Joint cysts are cystic lesions, and the cyst fluid is a transparent jelly-like fluid that can be found in the ligament, meniscus, synovial membrane, and other parts of the knee joint^1,2. High mechanical stress can easily lead to cyst formation, which is why cysts are most common in the knee joint^3,4, and Baker's cysts are the most common type of cysts⁵. Cruciate ligament cysts of the knee are rare, occurring incidentally in 0.2% to 1.3% of cases scanned using knee magnetic resonance imaging (MRI) and in 0.6% of patients tested using knee arthroscopy^6,7. Posterior cruciate ligament cysts are rarer, with Brown and Dandy reporting that after performing knee arthroscopy on 6,500 patients, they found only 35 ligament cysts and only 6 from the posterior cruciate ligament⁵. Knee ligament cysts can occur regardless of sex or age but are more common in men aged 20 years to 40 years^4,8.

The cause of cruciate ligament cysts is unknown. For the non-invasive diagnosis of knee ligament cysts, MRI can clearly show the relationship between the size and position of the cyst and is the most accurate diagnostic method^4,6,9,10. Arthroscopic removal of cysts is the most effective and recommended treatment method^4,6,9,10. Arthroscopy can see the cyst site directly and completely remove the cyst wall, the recurrence rate is extremely low, and the patient recovers quickly after surgery^7,9,10. Posterior cruciate ligament cysts are mostly lobulated or multiloculated, most of which are located mainly behind the posterior cruciate ligament, and in 12.5% of patients, the cyst is mainly located anterior to the posterior cruciate ligament¹¹ (Figure 1A,B).

Many treatments can be used to treat posterior cruciate ligament cysts, such as ultrasound and computed tomography-guided joint paracentesis. However, several studies have shown that there is a potentially higher risk of recurrence because of which these procedures do not remove the cyst walls¹². Arthroscopic removal of cysts is the gold standard for the treatment of posterior cruciate ligament cysts. Arthroscopic surgery can completely remove the cyst wall, but it's hard to remove dorsal cruciate ligament cysts by the anterior approach alone. Abreu et al.¹² introduced an approach to the arthroscopic excision of PCL cysts using a trans-septal portal, and it's safe and effective. Tsai et al.¹³ reported that the trans-septal approach to the resection of posterior cruciate ligament cysts was successful in 15 patients, and there was no recurrence. The trans-septal approach requires the addition of a posterolateral approach, so it increases the risk of damaging the common peroneal nerve and popliteal neurovascular bundle. To avoid these risks, we present a surgical approach to treat posterior cruciate ligament cysts by an arthroscopic double posteromedial approach. Our approach does not require an additional posterolateral approach; there is no risk of injuring the common peroneal nerve. We use the double posteromedial approach, which keeps the entire surgical process on the medial side of the posterior septal, thus reducing the possibility of damaging the popliteal neurovascular bundle. The technique produces the same results while being safer than the trans-septal approach. This surgical approach is particularly suitable for the removal of cysts located on the dorsal side of the posterior cruciate ligament. The surgical approach is more advantageous if the cyst is compartmentalized or close to the tibial end.

Protocol

The protocol follows the guidelines of the Ethics Committee of the Third Hospital of Hebei Medical University. Informed consent was obtained from the patients for including them and the data generated as a part of this study. Patients enrolled in this study were between the ages of 18-60. A total of eight patients were included in the study, five females and three males.

1. Preoperative preparation

1. Use the following inclusion and exclusion criteria for enrolling patients in this study.
   1. Use these inclusion criteria: Patients with a clear diagnosis of posterior cruciate ligament cyst by MRI of the knee; patients with significant knee pain, hyperextension pain, and other symptoms that may be caused by posterior cruciate ligament cyst or patients with combined meniscal injuries that require arthroscopic treatment; patients who have an interest in surgery because of the impact on their quality of life.
   2. Use these exclusion criteria: Patients with other serious medical conditions who cannot tolerate surgery; patients who refuse surgical treatment; patients with posterior cruciate ligament cyst diagnosed by MRI but without symptoms; patients with combined anterior cruciate ligament rupture or posterior cruciate ligament rupture.
2. Use general anesthesia or neuraxial anesthesia for all patients. Place the patient in the supine position on the surgical bed. Apply a tourniquet to the affected limb in the middle and upper part of the thigh for no more than 1 h. Disinfect the affected limb 2x with iodophor and lay the surgical sheet.

2. Establishment of arthroscopic approaches

1. Use a blood-repellent belt to expel blood from the affected limb. Tighten the blood-repellent belt from the end of the limb to the proximal end. Make each lap overlap by 1/3. Do not insert soft tissue between each turn. Drain blood from the soft tissues of the operated limb. Inflate the tourniquet by applying 50 kPa pressure/force.
2. Establish an anterolateral approach, 1 cm above the lateral knee line and 1 cm lateral to the patellar tendon margin. Make an incision of about 0.5 cm in size from the skin to the joint cavity using an 11G sharp blade.
3. Establish an anteromedial approach, 1 cm above the medial knee articular line and 1 cm medial to the patellar tendon margin. Make an incision of about 0.5 cm in size from the skin to the joint cavity using an 11G sharp blade.
4. Insert the arthroscope parallel to the tibial platform towards the intercondylar fossa in medial and lateral approaches, respectively. Explore the suprapatellar capsule, patellofemoral joint, medial trochanteric clearance, lateral trochanteric sulcus, anterior cruciate ligament, posterior cruciate ligament, medial meniscus, and lateral meniscus.
5. Partially remove the injured meniscus or suture the injured meniscus. Remove the joint-free body. Treat all injuries within the joint.
6. Establish a normal posteromedial approach as described below.
   1. Flex the knee at 90°. Insert the arthroscopy in the anteromedial approach to monitor the intercondylar fossa and place the switching rod in the anterolateral approach.
   2. Insert the exchange rod between the posterior cruciate ligament (PCL) and the medial femoral condyle into the posteromedial joint capsule under arthroscopic surveillance. There is usually a distinct sensation of slipping in and out.
   3. Rotate the lens to the medial posterior joint capsule. See the triangular area formed by the reverse fold of the joint capsule, the medial femoral condyle, and the medial meniscus.
   4. Turn off the operating room lights. Observe the translucent area of the posterior medial skin surface of the knee (Figure 2).
   5. Use a lumbar needle to assist positioning (Figure 3). Eccentric puncture into the joint capsule in the translucent area (usually 0.5-1 cm behind the posterior femoral condyle and proximal to the articular line).
   6. Make a small incision of about 0.5 cm in the skin using an 11G sharp blade. Insert a straight clamp into the joint capsule under arthroscopic surveillance. Establish a normal posteromedial approach.
7. Establish a high posteromedial approach as described below.
   1. Insert the arthroscopy into the posteromedial approach. Insert the lumbar needle in the direction of the joint, 2-3 cm proximal to the posteromedial approach.
   2. Make the lumbar needle penetrate into the joint capsule in the triangular space of the medial posterior condyle, medial meniscus, and posterior joint capsule.
   3. Make a small incision in the skin. Insert a straight clamp into the joint capsule under arthroscopic surveillance. Establish a high posteromedial approach.

3. Exposing and removing posterior cruciate ligament cysts

1. Insert the arthroscopy in the high posteromedial approach. Insert the shaver in the normal posteromedial approach (Figure 4).
2. Remove synovial tissue between the posterior cruciate ligament and the joint capsule using a shaver.
3. Find the cyst, which is a translucent, raised synovial membrane around the posterior cruciate ligament (Figure 1C). Remove the cyst wall and see yellow and translucent fluid flowing out of the cyst wall, visualize compartment-like tissue in the cyst.
4. Remove the posterior cyst wall completely. Avoid injury to the posterior cruciate ligament and posterior blood vessels and nerves and explore the posterior cruciate ligament without injury.
5. Insert the arthroscopy in the anterolateral approach. See a portion of the cyst at the femoral terminus of the posterior cruciate ligament.
6. Remove the anterior cyst wall and see yellow and translucent fluid flowing out of the cyst wall. Remove the cyst wall completely.
7. Remove the synovial tissue in the V-shaped space between the anterior cruciate ligament and the posterior cruciate ligament. Probe the posterior cruciate ligament and check for damage to the posterior cruciate ligament.
8. Insert the arthroscopy in the medial patellar approach. Check the V-shaped space between the anterior cruciate ligament and the posterior cruciate ligament for residual cysts.
9. Insert the arthroscopy in the posteromedial approach. Check for residual cysts.

4. Closure of the incision

1. Insert the arthroscopic sheath in the anterolateral approach. Squeeze the suprapatellar capsule and completely drain the intra-articular fluid. Check knee extension and flexion activities from 0° to 120°.
2. Suture the incision with silk thread No. 4.

5. Postoperative rehabilitation

1. Quadriceps exercise: Ask the patient to perform this exercise in the supine position. Straighten the affected limb, hook up the toes, slowly lift the leg upward to a height of about 15 cm on the heel, stay for 3 seconds, and then slowly lower it down.
2. Joint release training: Ask the patients to perform this as they sit at the bedside and extend and flex the knee joint by themselves.
3. Ask the patient to get out of bed on the second day after surgery and move appropriately, and gradually return to normal activities.
4. Change the dressing every 3 days after surgery and remove the stitches 14 days after surgery.
5. Ask the patient to perform non-confrontational activities such as jogging in the first month after surgery and resume normal activities in the third month after surgery.

6. Postoperative care and follow-up

1. Ask the patient to lie flat without the pillow for 6 hours after surgery. The patient was hospitalized for approximately 3 days.
2. At 3 months after surgery, check whether the patient's range of motion returns to normal and 12 months after surgery, perform an MRI examination of the affected knee combined with arthroscopy to check whether there is discomfort in the affected knee and whether the cyst has recurred.

Results

All eight patients were successfully operated on without any complications. Seven of the 8 patients had isolated posterior cruciate ligament cysts, and 1 patient had medial meniscal injury. The main symptoms of all patients before surgery are knee hyperflexion pain, inability to squat freely, pain, and discomfort in the back of the knee after standing for a long time or walking for a long time. After surgery, all symptoms were relieved and disappeared (Table 1).

Of the 7 patie...

Discussion

Posterior cruciate ligament cyst is a rare disease. Knee ligament cysts are usually discovered during MRI or knee arthroscopy exams. The causes of knee ligament cyst formation are varied, including post-traumatic formation, synovial tissue hernia formation during embryogenesis, and mesenchymal stem cell proliferation and formation. Recently, trauma and tissue stimulation have been recognized by most experts^2,7,14.

Materials

Name	Company	Catalog Number	Comments
Arthroscopic sheath	smith&nephew	72200829	6mm
Arthroscopy	smith&nephew	72202087	30 mm x 4 mm
Beam guide	smith&nephew	72204925	5 mm x 3.6 m
Beam guide-arthroscopy end connector	smith&nephew	2143
Beam guide-panel connector	smith&nephew	2147
Blood-repellent belt	selani	tpe15100	15 cm x 1 m
Blunt puncture cone	smith&nephew	4356	4 mm
Camera	smith&nephew	72200561	NTSC/PAL
Coupler	smith&nephew	72200315
DYONICS POWER II	smith&nephew	72200873	100-24VAC, 50/60Hz
DYONICS POWERMAX ELITE	smith&nephew	72200616
Endoscopic camera system	smith&nephew	72201919	560P NTSC/PAL
HD monitor	smith&nephew	LB500031	27 inch
Hook probe	smith&nephew	3312
Incisor plus platinum shaver	smith&nephew	72202531	4.5 mm
Lumbar needle  AN-E/S	tuoren	AN-E/S	1.6 mm x 80 mm
Micropunch,teardrop,left	smith&nephew	7207602
Micropunch,teardrop,right	smith&nephew	7207601
Micropunch,teardrop,straight	smith&nephew	7207600
Pitbull Jr. Grasper	smith&nephew	14845