CLDH, with a low incidence rate, is a relatively rare type of LDH. Although the pathogenesis is still uncertain, a study demonstrated that intervertebral disc calcification may be caused by some factors such as infection, trauma and blood supply disruption[11]. Intervertebral disc calcification is relatively rare in children, but more common in adults[12]. Some studies[13, 14] have shown that calcified disc herniation in children is usually treated conservatively, and calcified discs could even disappear spontaneously. However, the symptoms of adults are difficult to relieve or even worsen after conservative treatments such as non-steroidal anti-inflammatory drugs (NSAIDs), stay in bed, physiotherapy and epidural steroid injection[15, 16].
Some surgical techniques, with good clinical results, are applied to the treatment of CLDH[17–20]. Traditional open surgery, with complete removal of calcified disc, is the most commonly used surgical procedure. However, some complications of traditional open surgery, such as dural tear, cerebrospinal fluid leakage, incision infection, long-term chronic low back pain and spinal instability, still need to be widely concerned[5, 21, 22]. Some studies reported that percutaneous endoscopic transforaminal discectomy (PETD) was used to treat CLDH and achieved good clinical outcomes[23, 24]. Yu et al[25] reported that 25 CLDH patients were treated by PETD with ultrasonic osteotome. Unfortunately, they found that 7 patients had postoperative dysesthesia and 1 patient had recurrence of herniation. Shim et al[26] showed that PETD achievd a good clinical result in the treatment of CLDH. However, there were two serious complications of dural tear. The high incidence of complications seemed to be closely related to the variant anatomy of L5-S1, such as high iliac crest and intervertebral foramen stenosis. Moreover, PEID had a long and difficult learning curve, which limited the use of the procedure and increased the risk of surgical complications[27].
In this study, PEID combined with ultrasonic osteotome was performed to treat L5-S1 CLDH. The symptoms of all patients were relieved, and no serious complications occurred during the follow-up period. There is the natural advantage of a larger lamina space at L5-S1 level, but no the variant anatomy, such as high iliac crest or foraminal stenosis. Under endoscopic visualization, PEID can remove easily the calcified disc and release sufficiently the compressed nerve root with minimal damage to the nerve root and dural sac. The trephine may damage nerve root and dural sac when removing calcified disc[28]. Calcified intervertebral disc was safely and effectively removed with ultrasonic osteotome during operation in our study, which reduced the risk of nerve root injury and dural tear. Ultrasonic osteotome has some characteristics, such as tissue selectivity, anti-rolling, hemostasis and easy to handle[29–32]. According to our experience, the following points need to be emphasized. 1) The location and size of calcified intervertebral disc should be accurately evaluated by Preoperative X-ray, CT and MRI examinations. 2) A safe working area should first be created by removing epidural space fat and soft intervertebral disc. 3) A clear surgical view was ensured by timely and adequate hemostasis during operation. 4) violent separation, exposure and removal of the calcified disc could easily cause nerve root injury and dural tear because the calcified disc was hard and closely adhered to the nerve root and dural sac. Therefore, the calcified disc was carefully separated and exposed, and the nerve root and dural sac must be tracted gently during operation. 5) The purpose of procedure was to release the compressed nerve root and dural sac. However, the excessive pursuit of completed removal of calcified disc may increase the risk of complications such as nerve root injury and dural tear.
There were some previous studies on PEID in the treatment of CLDH[33, 34]. Dabo et al[28] reported that 30 patients with CLDH were treated by PEID. However, they concluded that the incidence of postoperative complications was significantly high due to the trephine. Chen et al[23] treated 13 cases with PEID. One case had a dural tear and cerebrospinal fluid leakage due to the adhesion. In our study, however, PEID combined with ultrasonic osteotome well solved the problems of trephine and adhesion, greatly reduced the risk of the procedure and significantly improved the clinical effects.
There were some limitations in this retrospective study. Firstly, this study had a small sample size and lack control group. Secondly, the short follow-up period did not evaluate the long-term efficacy. Prospective randomized controlled trials with large sample size, multicenter and long-term follow-up are still needed to better evaluate the clinical efficacy of this procedure in the future.