Extreme posterolateral lumbar disc herniation Extreme posterolateral (also known as the most posterolateral) lumbar disc herniation is a specific type of lumbar disc herniation in which a herniated disc compresses a nerve root emanating from the same intervertebral space level. It was first reported by Abdullah in 1974, and its incidence has been inconsistently reported, accounting for approximately 1% to 11.7% of all patients with lumbar disc herniation, with an average of about 10%. In the past, there was a lack of understanding of this particular condition, so clinical failure of lumbar spine surgery was often caused by underdiagnosis and misdiagnosis. With the continuous development of diagnostic imaging, especially CT technology, the clinical summary of extreme posterolateral lumbar disc herniation has increased year by year, but it is still necessary to write a detailed article to draw attention to it. Pathogenesis A series of clinical symptoms are caused by degenerative degeneration of the lumbar intervertebral disc and its protrusion on the extreme lateral side. Pathogenesis The lumbosacral nerve roots generally emanate from the cauda equina above the corresponding intervertebral foramen, travel for some distance in the spinal canal and then enter the nerve root canal, and then pass out from the corresponding intervertebral foramen. There is a gap on the lateral side of the intervertebral foramen, called the farlateral space, in front of which are the vertebral body and intervertebral disc, accounting for about 30% to 40% of the transverse diameter of the lumbar spine, with the posterior longitudinal ligament attached to the surface, the posterior yellow ligament, and the lateral intertransverse ligament. The nerve roots emanate from the intervertebral foramen and enter the extreme lateral space, crossing posterior to the intervertebral disc. In this space, epidural fat and veins are abundant, and the dorsal side of the nerve roots and posterior root ganglion is often covered by veins, and the root artery and root vein can be found further laterally near the intertransverse process ligament. Anatomical studies have shown that the lumbar peduncle emanates from the vertebral body from the lumbar 1 to the lumbar 5 with a gradual anterolateral bias, while the transverse process emanates from the peduncle with a gradual anterior bias. The width of the lumbar arch increases as the lumbar arch gradually thickens from top to bottom and slopes to the lateral side. According to previous literature, the nerve roots travel laterally through the intervertebral foramen posterior to the disc. However, according to Fournier et al. the nerve roots actually travel obliquely from superior to inferior within the nerve root canal, with the angle reaching almost vertical. In contrast, the course of the 1st to 3rd lumbar nerve within the nerve root canal is more vertical, and its course outside the intervertebral foramen is located posteriorly and externally to the intervertebral disc, whereas the course of the 5th lumbar nerve within the nerve root canal is oblique and longer, and its course outside the intervertebral foramen is located just lateral to the intervertebral disc of the lumbar 5th to sacral 1st. Thus, when the intervertebral discs of the upper lumbar vertebrae protrude outwardly into the intervertebral foramen, they are farther away from the nerve roots behind them and are less likely to cause compression; whereas in the nerve roots of the lower lumbar vertebrae, the chances of compression are obviously much greater. The presence of the sacral wing reduces the extreme lateral gap from lumbar 5 to sacral 1, which undoubtedly increases the chance of compression of the lumbar 5 nerve root. According to the location of the herniated nucleus pulposus, extreme lateral lumbar disc herniation can be further divided into two types, namely intraforaminal and extraforaminal herniation. As the nucleus pulposus protrudes from the annulus fibrosus, it presses outward and upward on the nerve roots that will emanate from the intervertebral foramina, and the nerve roots have little room for movement due to the restriction of the pedicle and/or foraminal ligaments, and are easily compressed and cause symptoms. The most common posterior lateral disc herniation differs from the posterior lateral disc herniation in that the site of compression is at or outside the intervertebral foramen where the nerve roots emerge from the previous intervertebral space, i.e., lumbar 3-4 disc herniation compresses the lumbar 3 nerve roots, and lumbar 4-5 and lumbar 5-sacral 1 disc herniation compresses the lumbar 4 and lumbar 5 nerve roots, respectively. In addition, the incidence varies among the intervertebral spaces, i.e., lumbar 4-5 herniation is the most common, followed by lumbar 3-4, lumbar 5-sacral 1, lumbar 2-3 and lumbar 1-2, with a relatively high proportion occurring in lumbar 3-4, whereas posterior lateral disc herniation occurs mostly in lumbar 4-5 and lumbar 5-sacral 1. Extremely lateral lumbar disc herniation usually does not involve the sacral nerve roots. Low back pain and radiating pain in the lower extremities are the most common clinical symptoms. Since the posterior root ganglion is often compressed together with the nerve roots, the radiating pain of the lower extremities can be quite severe. Involvement of nerve roots from lumbar 1 to lumbar 3 will cause pain in the hip, inguinal region and anterior thigh. Some patients may also present with atrophy of the quadriceps muscle. In some cases, the straight leg raise test may be positive. The rate of positive straight leg elevation test varies; Broom reported 13 cases, of which 10 were positive, Jackson and Glah reported 16 cases, of which 8 were positive, and Epstein counted 170 cases of extreme lateral lumbar disc herniation, of which 94% were positive. In a group of 138 cases treated by Abdullah et al, 65% of the patients had a negative straight leg elevation test, and if the remaining 35% of positive straight leg elevation tests were combined with intracanal disc herniation, severe spinal stenosis, and scarring from previous surgery, the negative rate was as high as 85% to 90%. Epstein et al. reported that most patients had low back pain and lower extremity radiating pain on standing and walking. 22 of the 26 patients examined by Kanogi and Hasue had pain on posterior extension of the lumbar spine, while Abdullah et al. found that pain was induced by flexion of the spine to the affected side and considered this sign to be reliable. When the superior lumbar nerve is compressed, the femoral nerve pull test is mostly positive, but it has been suggested that this sign is not specific. In addition, compression of the nerve root can produce corresponding motor and sensory deficits and diminished reflexes. Cases with congenital developmental lumbar spinal stenosis not only have an early onset, but also have significantly more severe symptoms. Based on the medical history and clinical symptoms and signs, when the diagnosis cannot be made clearly by ordinary X-ray and myelography. The clinical diagnosis is mainly based on CT, discography, MRI examination and laboratory tests to confirm the diagnosis. Skouen et al. performed biochemical measurements of serum and cerebrospinal fluid in 143 patients with lumbar disc herniation and found that the total protein, albumin, IgG content, cerebrospinal fluid to serum albumin ratio, and cerebrospinal fluid to serum albumin IgG ratio of cerebrospinal fluid gradually increased with the location of the herniated disc from the inside to the outside, and the correlation was statistically significant, and concluded that this phenomenon was caused by the leakage of plasma proteins from the nerve root The correlation was statistically significant. Since the clinical presentation of this disease is essentially the same as that of the postero-lateral disc herniation in the previous interval, the diagnosis is based primarily on imaging. The imaging examination also helps to exclude other disorders that can cause similar symptoms, such as lateral saphenous stenosis, retroperitoneal hematoma, retroperitoneal tumor, nerve root malformation or tumor, etc. 1.X-ray plain film: It is generally believed that X-ray plain film has no diagnostic value for extremely lateral disc herniation. Myelogram: Since the subarachnoid space terminates in the posterior root ganglion, myelogram is difficult to show the extreme lateral type disc herniation, and therefore myelogram, like X-ray plain film, is mainly used to exclude other lesions. Therefore, when a patient has symptoms of nerve root entrapment and the myelogram results are negative or not consistent with the clinical presentation, disc herniation within or outside the intervertebral foramen should be highly suspected. Nerve root imaging has also been advocated, but it is less commonly used clinically. 3, discography: there has been a lot of debate about the diagnostic value of discography. There was a group of 77 cases of discography, the correct diagnosis rate was 92.2%, but the operation is more complicated, so it is not commonly used. 4, CT examination: CT examination can show the location and degree of disc herniation more clearly, so with the widespread use of this imaging technology in clinical practice, the number of reports on extreme lateral disc herniation has increased significantly. The soft tissue density of the herniated disc nucleus pulposus has good contrast with the dural sac and epidural fat, but when the herniated disc is located inside or outside the intervertebral foramen, the adjacent nerve roots and/or posterior root ganglia have approximately the same density, which may make the diagnosis difficult or even misdiagnosed as a tumor. Furthermore, CT examinations that do not include the level below the pedicle may also lead to diagnostic omission. CT discography can further improve the diagnostic accuracy and can be used when appropriate, and Segnarbieux et al. suggested that CT discography should be performed when the diagnosis of extreme posterolateral disc herniation is suspected on CT and difficult to determine. A comparative study of various imaging methods showed that the correct diagnostic rate was only 12.5% for myelography, 37.5% for discography, 50% for both CT and CT myelography, and 93.8% for CT discography. However, Epstein et al. concluded that CT myelography was superior to CT alone. In addition, some scholars have reported that CT examination of herniated discs outside the intervertebral foramen shows a vacuum phenomenon, that is, the presence of air in the herniated nucleus pulposus. 5.MRI examination: Multiplanar MRI technique is more ideal for the display of the intervertebral foramen structure, and the boundary between the herniated nucleus pulposus and the nerve root is clearer than that of CT examination, but the good display of the herniated nucleus pulposus on MRI images often depends on the selection of the examination orientation and plane. Three lesions were not shown in the sagittal plane, but were shown in both the transverse plane and the 15°-30° coronal plane, with the 15°-30° coronal plane images not only showing the disc herniation most clearly, but also accurately reflecting the nerve root compression. This scholar also found that the thicker nerve roots and dilated venous plexus are easily confused with the free nucleus pulposus in the intervertebral foramen. Theoretically, MRI should be more satisfactory in showing the site and extent of nerve root compression, but according to the literature, this technique is much less commonly used in the diagnosis of extreme lateral disc herniation than high-resolution CT scans. This may be due to the fact that MRI sagittal images often do not include the intervertebral foramen and have a higher layer thickness than CT scans. Non-surgical treatment If the patient has mild symptoms and no obvious neurological signs, non-surgical treatment can be used, including bed rest, braking, physical therapy and medication. Epstein suggests that about 10% of patients can be treated satisfactorily after 6 weeks of conservative treatment. Absolute bed rest and traction are still the easiest and most stable of the non-operative treatments. Surgical treatment The reports on the surgical treatment of extreme lateral lumbar disc herniation are inconsistent, and it is difficult to compare their efficacy with each other. However, it is generally believed that the safest and most effective surgical procedure should be selected according to the pathologic and anatomic characteristics of the specific case. 1, interlaminar window: The posterior median incision approach and the interlaminar window based on it are most commonly used in the surgical exposure of lumbar disc herniation, in which all of the corresponding vertebral plates and small joints should be fully exposed, and the medial edge of the small joints, especially the medial edge of the supra-articular eminence of the next vertebral body and the upper edge of the vertebral arch, should be removed along with the lower edge of the vertebral plates. The nerve roots travel obliquely in the nerve root canal from internal to external, so the prominent nucleus pulposus located above the nerve root canal can be revealed upward, while the prominent nucleus pulposus located below the nerve root canal or even outside the intervertebral foramen can be revealed outward. The nerve root canal at the level of lumbar 5 to sacral 1 is less likely to be narrowed, and the arch root spacing is wider, so this procedure can generally reveal the herniated nucleus pulposus better. However, because the protruding nucleus pulposus outside the intervertebral foramen is not well exposed, its removal under non-direct vision (especially when combined with nerve root canal stenosis) may easily cause nerve root injury. 2, trans-isthmic interlaminar opening: the upper edge of the vertebral plate and part of the arch isthmus are removed in the space above the space where interlaminar opening is usually performed, but the small joints are still preserved, i.e., the lumbar 4 nerve root compression is performed in the lumbar 3-4 space, and the lumbar 5 nerve root compression is performed in the lumbar 4-5 space. This procedure does not allow simultaneous exploration of the central spinal canal and the neurogenic canal, and is only suitable for simple extreme lateral herniations with very clear localization. 3.Intervertebral foraminotomy: When the site of nerve root compression is not clear, the intervertebral foramen can be incised in the direction of nerve root travel to better reveal the nerve root, and due to the large extent of subtotal resection, lumbar fusion is often performed at the same time. Therefore, this procedure is only suitable for cases with combined lumbar instability and the need for internal fixation through the interface of one small joint. 4.Total subtotal arthrotomy: When the patient is combined with severe nerve root canal stenosis, even the entire subtotal joint needs to be removed so that the entire nerve root and ganglion can be clearly exposed. However, this procedure can easily lead to lumbar instability after surgery, so some scholars believe that lumbar fusion should be performed simultaneously when combined with degenerative lumbar spondylolisthesis or after total subtotal arthroplasty. Even a mild degree of postoperative lumbar instability can adversely affect the efficacy of surgery, so when the small joint is completely removed, regardless of whether the patient is young or old, lumbar fusion should be performed, and the fusion method can be used in addition to the traditional posterior-lateral fusion, posterior interbody fusion and small joint fusion, etc. The single oblique interface internal fixator has been carried out and is quite popular. 5, vertebroplasty: that is, through the arch of the vertebral isthmus to perform one or both sides of the whole plate removal, intracanal decompression and intervertebral disc removal and then implant the plate back to the original position to rebuild the stability of the lumbar spine. Although this procedure has many advantages, it is crucial to pay attention to the fixation of the implanted vertebral plate to prevent accidents. 6, lateral window surgery: in cases where the herniated nucleus pulposus is located on the lateral side of the intervertebral foramen and/or outside the intervertebral foramen, lateral window surgery is feasible, i.e., the lateral edge of the arch isthmus and the upper lateral edge of the small joint are removed. The advantage of this procedure is that the integrity of the lesser joint is preserved to the greatest extent possible, and the medial portion of the intertransverse ligament and the ligamentum flavum located at the external opening of the intervertebral foramen should be removed during decompression. The lateral opening can also be combined with an interlaminar opening to remove the medial malleolus or a trans-isthmic interlaminar opening to provide adequate exposure of the nerve roots while maximizing the preservation of stable lumbar structures. Theoretically, this procedure has many advantages, but in practice, it is more difficult to reveal lesions outside the intervertebral foramen through the posterior median incision, and the visual field is poor, which undoubtedly increases the risk of nerve root injury, so it should not be used clinically, except when the anatomical segment is combined with tumors and deformities. 7, paramedian incision approach: applicable to simple extreme lateral disc herniation. The operation is performed through a paramedian incision between the multifidus and longest muscles to reach the extreme lateral space between the small joint and the deep surface of the intertransverse process ligament, and the nucleus pulposus protruding outside the intervertebral foramen can be found after careful retraction of the nerve roots. The key to the success of this procedure is familiarity with the local anatomy: the posterior root ganglion is usually located in the intervertebral foramen, and at its distal end, the anterior and posterior roots merge to form the posterior and anterior branches of the lumbar nerve immediately afterwards. The anterior branch travels obliquely ventral-caudal immediately caudal to the arch and passes through the surface of the intervertebral space, while the posterior branch travels posteriorly and dorsally, dividing into a medial branch, a lateral branch, and a muscular branch that penetrates the very lateral space. There are also segmental vessels running lateral to the nerve root exiting the intervertebral foramen, of which the terminal branch of the segmental artery running with the lateral branch of the posterior branch of the lumbar nerve is the most important, and the accompanying veins are quite variable and often form a venous plexus around the nerve root. Injury to these structures should be avoided during surgery. When the herniated nucleus pulposus is located at the level of lumbar 5 to sacral 1, resection of the superior border of the iliac pterygoid will help to reveal it. However, some scholars have reported that in obese patients, it is more difficult to reveal. 8, microsurgery and percutaneous discectomy: Darden et al. resected the herniated nucleus pulposus under the microscope through a paramedian incision, and believed that the advantages of this method were a clear view and a small risk of nerve root injury. However, in recent years, it has been found that this technique is no longer used because of its high accidental injury rate and poor efficacy. Percutaneous discectomy is less commonly used in clinical practice because of its narrow scope of indications. 9, anterior discectomy: some scholars use transabdominal extraperitoneal discectomy, but it is not widely used because the nerve roots cannot be treated under direct vision and lumbar fusion needs to be performed at the same time. 10, posterior enlargement decompression and nucleus pulposus resection with preservation of small joints: the authors found that the majority of cases were combined with developmental lumbar spinal stenosis and constituted the main anatomical factor for its early onset and susceptibility to morbidity, so they advocated that the spinal canal should be enlarged while removing the nucleus pulposus, and the operation should not exceed the small joints, and only the medial part of the articular eminence can be removed for those with small joint deformity and root canal stenosis, and at this time, for the protruding nucleus pulposus. The herniated nucleus pulposus, whether lateral or extreme lateral, can be easily removed. The nucleus pulposus with dural adhesions or even in the dural sac can be removed under direct vision by incising the dural sac.