At present, the most widely used approaches for endoscopic treatment of calcified lumbar disc herniation are the transforaminal approach and the translaminar approach. One of the most important aspects of the operation is the establishment of the working channel, which allows the calcification to be fully exposed under the microscope. Ruetten et al. [12,13] reported the surgical method of the translaminar approach, which was generally in the prone position, and the intraoperative anatomy was similar to that of traditional open surgery, which was in line with the operating habits of most operators and had a better effect on axillary and central lumbar disc herniation. However, patients with calcified lumbar intervertebral disc herniation often have a longer course of disease, severe vertebral degeneration, and narrow lamina space. To successfully place the pipeline, part of the upper and lower lamina, part of the medial part of the superior articular process and even the medial part of the pedicle should be removed . This degree of osteotomy may cause injury not only to the exit root but also to the walking root. The medial superior articular process and medial pedicle crypt are thick and hard, and it is difficult to establish the channel through osteotomy. In addition, pulling on the nerve root to expose calcification on the ventral side of the nerve root can easily cause nerve injury. Therefore, we performed a transforaminal approach to remove the bone at the ventral base of the superior articular process with a canard-bill cannula and a microscopic osteotomy with continuous visibility. This approach mainly has the following advantages:1. Facet joints were not damaged during the process, and the postoperative effect on vertebral stability was small. The approach from the physiological and anatomical space does not affect the structure behind the spine, does not damage the ligamentum flavum, and reduces postoperative scar adhesion in the spinal canal . Even if the operation fails, it is relatively easy to turn to open surgery. The base of the superior articular process is far from the exit nerve root, so the probability of nerve injury by osteotomy here is relatively low, and the operation time is shortened . The duck-bill cannula approximately envelops the superior articular process and acts as a barrier between the superior articular process and the nerve root during osteotomy to reduce nerve disturbance. The use of the microscopic power system and the side laser system may lead to transient deterioration of neurological function, and the cost is high [6,17]. However, under the microscope, osteotomy saves time and causes less disturbance to nerve roots. Visualize the whole operation to improve the safety factor of the operation. In the process of treatment, we also encountered some problems. As the intervertebral foramina of the lower lumbar spine were gradually reduced, the blocking effect of the superior articular process became increasingly serious. Especially in the L5-S1 segment, due to the obstruction of the iliac ridge and the large transverse process of L5, it becomes more difficult to establish the channel . Most physicians used the interlaminar approach to solve this problem [19,20]. We adopted a lateral decubitus position and raised the patient's lumbar pad so that the intervertebral space could be fully opened to minimize the impact of the position on the operation. The lateral opening was reduced to avoid obstruction of the iliac ridge to the cannula as much as possible, but it was still difficult to address the relatively extensive calcification. Therefore, on the basis of not destroying the articular surface as much as possible, we moderately expanded the resection range of the ventral articular process on the upper S1. Studies have shown that resection of the antermedial 1/3 of the superior articular process, the anterior part of the lower facet joint, and the part between them can increase the foraminal area by 45% without affecting the stability of the spine [15,21]. We controlled the range of facet excision within 1/3 in most patients, and during the postoperative follow-up, there was no obvious vertebral instability in the patients. However, it is interesting that we excised more than 1/3 of the upper articular process of S1 for some patients and excised part of the joint capsule, but no obvious vertebral instability occurred in the process of postoperative follow-up, which we believe may be due to the low activity of the L5-S1 segment, as well as the postoperative rehabilitation exercise guidance for each patient.
According to reports by Dabo et al., when central or paracentral calcified lumbar disc herniation is treated with an interlaminar approach, early postoperative paraesthesia is more likely to occur than conventional soft lumbar disc herniation, and the postoperative drug utilization rate is higher . Chen et al.  found in their study that postoperative lower limb sensory dysfunction mainly occurred in the translaminar approach. When the nerve root is pulled across the midline, the risk of nerve root injury is greatly increased [23,24]. We think this may be related to calcification type lumbar disc, oppression dural sac, highlight the material hard and dural sac to produce a kind of "half package", when revealed calcification for larger degree of nerve root and dural sac pull, when calcifications is located in the central, in order to expose calcifications, will increase the degree of the pull. Therefore, it is very important to obtain the right angle and sufficient operating space before removing calcifications. Chen et al.  reported that the peak method can reduce the traction of nerve roots and reduce postoperative neurological deterioration and other complications in calcification removal. However, intraoperatively, we found that the base of calcification was generally located at the posterior edge of the vertebral body, and some calcifications could even span the entire vertebral space. To expose the peak of calcification at this time, not only is the amount of osteotomy required during foraminal secondary forming increased, but the pulling of nerve roots is also inevitable. Therefore, after the formation of the secondary intervertebral foramen, the base of the calcified foci was exposed, and the calcified foci were excised by means of cannula rotation combined with a microscopic bone knife. The part of the base of the calcified foci that was connected with the vertebral body was excised to make the calcified foci free, and the calcified foci were removed by partitioning under the microscope(fig.4 and fig.5). For large calcification foci that are difficult to segment, the cannula can be removed with nucleus pulposus forceps, and the channel can be placed again after removal. This approach reduces the risk of more osteotomies affecting the stability of the vertebral body and has relatively little impact on nerve roots. Fibroannular damage may be associated with an increased risk of reherniation and may accelerate disc degeneration . Removal of the area where the calcified focus connects to the posterior edge of the vertebral body may damage the normal annulus, so careful annulus plasty is required to avoid postoperative re-protrusion due to annulus damage.