LFC most commonly occurs at the L4-L5 level due to excessive loading of the facet joint involved with chronic higher mobility of the spinal segment, which is especially represented in degenerative spondylolisthesis [3–5]. Kusakage et al. [3] radiologically and histopathologically investigated 46 cases of LFC in which the communication channel between the cyst and facet joint was confirmed after evaluation by CT arthrography. They proposed the pathogenesis of LFC formation as degenerative arthritic changes and spinal instability that first causes ligament flavum degeneration, followed by fissures in the collagen capsular portion of the ligament flavum that develop into LFC, accompanied by joint fluid from the connecting facet joint and secretions from fibroblasts. In our study, 59.1% of LFC were found at the L4/5 level, and 49.5% had instability with spondylolisthesis, which is consistent with previous reports.
Previous studies also described the occurrence of LFC after posterior decompression surgery of the lumbar spine [16, 17], which was consistent with our results demonstrating 34 (36.6%) postoperative cases, 14 occurring after fenestration and 20 occurring after microendoscopic decompression.
Ikuta et al. [16] found that the prevalence of postoperative LFC after decompression surgery for lumbar spinal stenosis was 8.6%. They speculated that the cause of postoperative LFC development was weakening of the medial portion of the facet joint after ligament flavum removal; and mechanical stresses on the medial portion of the joint, such as postoperative segmental spinal instability. This instability was proposed to include a progression of spondylolisthesis and disc degeneration, and to cause the joint capsule on the treated side to easily protrude into the spinal canal.
Many surgical procedures for LFC were reported previously, such as cyst resection with or without spinal fixation [7–9]. Cyst resection with facetectomy and spinal fusion is the most reliable procedure for preventing cyst recurrence [7]; however, the highly invasive nature of the surgery and adjacent segmental disorders create postoperative challenges. Kusakabe et al. [8] performed en-bloc cyst resection through fenestration without fixation for 96 patients (mean postoperative follow-up: 2.5 years) and obtained satisfactory clinical results, with a JOA recovery rate of 86% and a recurrence rate of 2.1%. Some recent studies also suggest that microendoscopic resection is the most minimally invasive surgical procedure, with a small skin incision, limited tissue dissection, and improved visualization [9]. In contrast, surgeries for LFC require careful attention regardless of the surgical procedure due to adhesions between the cyst and dura that cause dural tears [8, 10, 18]. Takahashi et al. reviewed 1014 cases that underwent surgical procedures for degenerative spinal disease, including 22 LFC cases, and reported the total incident rate of durotomy was 4% (41 cases). In contrast, the 18% (4/22 cases) durotomy rate found among LFC cases was much higher than that found in cases with other degenerative disorders, such as disc herniation (2.0%), stenosis (1.8%), and degenerative spondylolisthesis (9%). Additionally, as demonstrated in our study, some LFC occurred after lumbar surgeries that involved more severe adhesions and were related to a higher risk of dural tear [18]. As a primary issue, surgical treatments cannot avoid the most serious disadvantages for patients, which are hospital stays and general anesthesia.
Aside from surgical treatments, percutaneous rupture of LFC was the only treatment able to directly reduce cysts without a hospital stay or general anesthesia. The systematic investigation by Martha et al. [12] included the largest sample size (101 cases) for this ambulatory treatment technique and demonstrated successful cyst rupture in 81% of cases, similar to our 84.3% (43/51 cases) successful rupture rate. However, 54% (55/101) of patients, including successful rupture cases, required subsequent surgery because of continued symptoms. In our study, no patients with successful cyst ruptures required subsequent surgeries, based on the confirmation of the cyst reduction by MRI and satisfactory pain relief. The overall rate of surgery prevention was higher in our study than in others previously published [11, 12, 19]. The most important procedural difference between ours and previous studies was that our procedure included an additional 8 mL fluid into the facet joint after confirmation of successful cyst rupture. Although the effectiveness of adding saline and mepivacaine after the rupture had not been previously demonstrated, the cyst might be decompressed immediately via enlargement of the rupture hole, which may help reduce the cyst and relieve the pain. Furthermore, our procedure may involve a healing process, as flushing pain-related substances out of the facet joint and from around the compressed nerve root allows their passage into the epidural space. This may enable phagocytes to gather in a similar mechanism to that of the percutaneous intradiscal high-pressure injection of saline into lumbar herniated discs proposed by Fukui et al. [20].
No serious LFC rupture complications had been reported previously. In our study, some patients complained of low back or leg pain during the procedure, especially when the cyst burst; however, the pain decreased after the treatment without a deterioration to lower-extremity paralysis, and all patients left the hospital after 2 hours of rest. By the time of the last follow-up, no serious complications were found in any case. Because percutaneous facet resolution itself may lead to complications, such as intravascular penetration, infection, hematoma, and vasovagal reactions [21, 22], careful attention is essential during the procedure and regular follow-up is necessary to monitor the condition.
Our study had several limitations, especially with respect to the follow-up period and sample size. The average follow-up period in our study was 26.0 months; therefore, the long-term effectiveness, including the recurrence risk, was not elucidated. Huna et al. [23] reported the long-term outcomes of 71 cases with an average follow-up of 44 months in which repeated cyst rupture was performed for 8 cases (12%). However, 6 of the 8 cases eventually required surgery for LFC resection, showing that the procedural effectiveness may decrease for recurrent cases. Although the reduction of the cyst was recognized on MRI after treatment in our study, the risk of LFC developing due to facet joint degeneration or spondylolisthesis remained. Continuous long-term observation is necessary post-treatment, even with pain relief and cyst reduction. Although the present study was the first in our country, except for case reports, to investigate the effectiveness of percutaneous cyst rupture, the sample size was still small. In our study, the cyst rupture failed in 8 cases, and the cause of failure was severe joint degeneration in 3 cases. For the other 5 cases, the cause was not determined; however, the communication between the joint and cyst might have been defective. By continuing this treatment for more cases, the limitations of this treatment, including identifying resistant cases that should receive surgery, may be clarified in the future.
In conclusion, our clinical results showed satisfactory effectiveness with the “percutaneous rupture for LFC” procedure, as the rate of surgery prevention after this treatment was 84.3% (43/51 cases).
Percutaneous rupture for LFC is not only safe and minimally invasive without any serious complications, need for hospitalization, or general anesthesia but also a very useful procedure that can prevent surgery for cases resistant to conservative treatments. Thus, percutaneous rupture for LFC should be the first-choice treatment for non-effective cases after conservative treatment instead of surgical treatments.