So far, surgeons have not paid much attention to the mainly BP caused by LDH. On the one hand, according to our clinical findings, the incidence of LDH leading to BP as the main symptom is not high, and few surgeons associate BP with LDH. On the other hand, clinical misdiagnosis and mistreatment often occur. Under such conditions, the symptoms of patients often cannot be effectively resolved, affecting the quality of life of patients.
In addition to LDH, there are other factors that can cause BP, such as referred pain caused by facet joint or sacroiliac joint, proximal sciatica, deep gluteal syndrome (17–19), PS and peripheral nerve injury, among which PS is most easily confused with the cases described in this study. PS describes non-discogenic pain in the buttock caused by extrapelvic compression of the sciatic nerve (20). Factors leading to sciatic nerve compression include piriformis spasm (21, 22), anatomical changes of piriformis (23–25), piriformis hypertrophy (26) and buttock trauma (27). Walking/bending/lifting will aggravate the symptoms (28). Signs include piriformis tenderness, piriformis muscle stretch pain, positive signs of straight leg raising test, gluteal atrophy and weakness (29). Among the participants included in this study, several patients had been misdiagnosed as PS and were ineffective after treatment. Therefore, the accurate diagnosis of the disease before operation is very important. Surgeons should carefully review the MRI of patients, conduct a careful physical examination before surgery, and further rule out other diseases through selected nerve root blocks. During the operation, actively communicate with the patients and ask whether the pain has been alleviated. Long-term follow-up of patients after operation is also essential.
Studies have shown (30) that there is a significant correlation between nerve root symptoms caused by LDH and BP. But the specific mechanism is not clear. Based on previous studies (17), we have identified the following possible causes of BP, and further found that BP may be related to intervertebral discs. (1) Referred pain in buttock caused by sinus vertebral nerves (SVN): Li (31) has studied the SVN and found that 100% of the SVN can be seen in the intervertebral foramen. Most of the trunk of the SVN originated from the spinal ganglion of the posterior root of the spinal nerve (77, 58%). Nucleus pulposus itself is not an inert substance, but has biological activity, which can generate a series of inflammatory mediators (32), resulting in changes in vascular endothelial cells, which will increase vascular permeability, dilate blood vessels, and make immune cells adhere to this site. Lead to the transmission of inflammatory cytokines (33). Therefore, when the lumbar intervertebral disc is herniated, the nerve terminal receptors of SVN were in a highly sensitive state (34), which reduced the pain threshold. Because the SVN and the L5 nerve root are located in the same spinal cord. There may be referred pain in the buttock. (2) All the anterior branch of L5 nerve root forms the superior and inferior gluteal nerves: The sacral plexus is composed of the lumbosacral trunk from the lumbar plexus and the anterior branches of the sacral and coccygeal nerves. The lumbosacral trunk is synthesized below the lumbar plexus by some of the fibers of the anterior branch of the L4 and all the fibers of the L5. The sacral plexus emits many branches, including the superior gluteal nerve formed by the confluence of L4-S1, and the inferior gluteal nerve synthesized by L5-S2. They control the sensation and movement of gluteal muscles (35, 36). BP may occur when the protruding nucleus pulposus oppresses the anterior branch of the L5 nerve root. (3) Compression of the posterior branch of the spinal nerve: In anatomy, the anterior root is connected to the anterolateral sulcus of the spinal cord, which is composed of motor nerve filaments, and the posterior root is connected to the posterolateral sulcus of the spinal cord, which is composed of sensory nerve root filaments. From this, a mixed nerve root is formed in intervertebral foramen. Many studies have shown (37, 38) that the posterior branches of L4 and L5 spinal nerves are also involved in forming superior cluneal nerves. Through anatomical studies, Iwanaga et al (39) have confirmed that about 10% of the superior cluneal nerves come from the L5 nerve, which is a group of pure sensory nerve fibers that control the gluteal region (40, 41). Therefore, we speculate that when L4-5 disc is herniated, the nucleus pulposus oppresses the posterior branch of the L5 nerve root, resulting in BP.
At present, there is no research on the treatment of this kind of LDH. Therefore, we have drawn a plan for endoscopic treatment of gluteal pain, and proved that our treatment method has a certain clinical significance in operation. (1) Removal of herniated nucleus pulposus: relieving mechanical compression and inflammatory stimulation of nerve roots. (2) Denervation of annulus fibrosus by bipolar electrocoagulation: Li et al (31) have shown that the SVN originates from the posterolateral edge of the intervertebral disc to the spinal canal, and the accessory branches of the SVN enter directly into the posterolateral margin of the intervertebral disc. Among them, 55.8% of the main trunk of the SVN originates from the spinal ganglion of the posterior root of the spinal nerve. When disc herniation, the SVN is in a highly sensitive state (34), resulting in discogenic gluteal pain. The use of bipolar electrocoagulation to eliminate the SVN around the intervertebral disc to reduce nerve hypersensitivity. (3) Lateral recess formation: During the operation, we performed the method of “decompression around the lateral recess” to remove hyperplastic osteophytes from the posterior edge of the vertebral body. Besides, we also used high-speed grinding drill and endoscopic osteotome to remove the facet joints with hyperosteogenesis, and removed part of the ligamentum flavum near the lateral recess so as to achieve complete decompression. (4) Partial resection of PLL and fibrous annulus at the upper edge of the inferior vertebral body: LDH is one of the most common chronic degenerative diseases of the lumbar spine (1, 42). Patients may have a long history of disease, characterized by hypertrophy of annulus fibrosus and PLL. Through cadaver experimental study, Raoul et al. (43) found that some of the ascending branch of the SVN originates from the PLL, the ventral side of the dura mater and intervertebral disc, and the descending branch originates from the deep layer of the PLL and the intervertebral disc. Through microscopic observation of the sensory fibers of the PLL (44), it was found that it received a large number of traffic fibers from the SVN and formed a fiber network with the SVN from the opposite side. There are many branches of the SVN on the PLL and fibrous annulus in the posterolateral part of the superior edge of the inferior vertebral body. Therefore, in addition to the above treatment, resection of part of the PLL and fibrous annulus are helpful for the relief of BP. 12 patients with BP were treated by the method described in this study. All patients had L4/5 disc herniation with BP that lasted for at least 6 months. The BP of 11 patients was relieved after the PTED operation, and the pain was significantly relieved or even disappeared after 6 months of follow-up. One patient had recurrence of LDH at 1 month postoperative and the other two patients developed slightly residual BP after the operation. There were no adverse events such as nerve root injury, massive bleeding and cerebrospinal fluid leakage during the operation. and no postoperative infection, lower extremity thrombosis, pressure sores and other postoperative complications. We attribute all these good results to accurate preoperative diagnosis and the removal of the disc by PTED technique.
There are also some limitations: (1) A relatively small sample size may lead to differences in the results. (2) All the patients included in this study had L4/5 disc herniation, This study did not explore whether other disc herniation would cause BP.