Far lateral lumber disc herniation (FLLDH) is a condition in which the prolapsed disc tissue is located outside the intervertebral foramen and mechanically compresses or inflammably irritates the nerve roots of the same order, causing severe radiating pain in the lower extremities in the innervation area of the same order, combined with lumbosacral pain and varying degrees of impairment of skin sensory or motor function in the innervation area of the damaged nerve roots. The disease was first diagnosed in 1974 by a group of nerve roots. This disease was first reported by Abdullah et al. in 1974 and is a specific type of lumbar disc herniation, which is rare clinically. Its incidence has been inconsistently reported at home and abroad, accounting for 1% to 12% of all LDH, and about 30% of cases are misdiagnosed for the first time. The following is a review of the etiology, pathogenesis, clinical manifestations and typology of the disease, as well as the principles of treatment. I. Etiology and pathogenesis Extreme lateral lumbar disc herniation is common in elderly patients and may be related to the tilt of the small joints and the degree of degeneration of the diseased segment. In degenerated segments, FLLDH occurs in patients with greater small joint tilt, resulting in a biomechanical imbalance of the disc. Sun Fengxiang et al. suggested that rotational weight-bearing stress is a major factor in FLLDH, and suggested that its onset is related to long-term rotational load-based stress. The pain in extreme posterolateral lumbar disc herniation is more intense than in other disc herniation types, which may be related to FLLDH causing more inflammatory material to irritate the nerve roots. Recent national and international literature has shown that phospholipase A2, matrix metalloproteinases, and tumor necrosis factor, among others, can induce myelin damage and axonal degeneration can simultaneously cause nerve conduction dysfunction and be the initiating factor in the cytokine cascade response, and it has also been shown that studies have confirmed that endogenous tissue inhibitor of metalloproteinase (tissue inhibitor of FLLDH mostly ruptures the annulus fibrosus and the nucleus pulposus is free, which may release more inflammatory mediators and cause severe pain. Recently, it has been suggested that the dorsal root ganglion (DRG) has been implicated in causing low back pain, and Harrington et al. suggested that the greater the degree of pain caused by a herniated disc, the closer the disc is to the DRG. Based on animal studies, Ohtori et al. found that the dorsal portion of the lumbar disc in rats receives sensory innervation from the superior DRG via the sympathetic nerve trunk and from the inferior DRG via the sinus cavernosus. In FLLDH patients, the prolapsed nucleus pulposus is located outside the nerve root canal and intervertebral foramen, which is closer to the DRG, thus causing more intense pain. Clinical manifestations and typing Both extreme lateral type lumbar disc herniation and posterior lateral type herniation are different in clinical manifestations. The latter mostly manifests as the involvement of the next nerve root (e.g. posterior lateral herniation of L4-5 compressing the L5 nerve root), mostly presents sciatica, and the pain is mostly in the posterior lateral aspect of the lower limbs. FLLDH, on the other hand, presents clinically as femoral nerve or foraminal neuralgia because it occurs mostly in L4-5 and the interstitial space above it and presents with compression of the nerve root of this nerve (e.g., posterior lateral protrusion of L4-5 compressing the L5 nerve root). Therefore, anyone complaining of anterior thigh or anterior medial calf pain should be carefully examined for skin sensation, quadriceps strength, knee tendon reflexes, and femoral nerve pull test in this region.FLLDH tends to be more acute in onset and has a relatively short history compared to intradural lumbar disc herniation. In addition to the above reasons, patients with FLLDH have more severe back pain and lower extremity radiating pain than other disc herniations, and therefore patients with severe radicular symptoms and severe nerve damage encountered clinically, and whose symptoms do not match the imaging intradural manifestations, should be alerted to the possibility of this disease. Clinical case analysis also shows that the incidence of motor deficits in the innervated areas damaged by FL2LDH is significantly higher than that of sensory deficits, which has some reference value in differentiating it from intradural LDH signs. There are not many studies in the literature on the staging of this disease, but Jackson et al. classified lumbar disc herniation into four types: central, posterior posterolateral, foraminal, and extradural, the latter two being collectively referred to as the extreme posterolateral type of lumbar disc herniation. In addition, according to the regional positioning of lumbar disc herniation by Hu Yougu and others, zone 4 is the extreme lateral zone, i.e. the herniated material reaches beyond the lateral arch root. Nowadays, the more commonly used is the typing of Chen Zhongqiang et al. of the North Medical College, who divided FLLDH into: type Ia – herniated disc displaced cephalad to the inferior edge of the arch root; type Ib – type Ia combined with posterior lateral herniation; type IIa – very lateral type herniation with slight cephalad displacement of the herniated disc; type IIb – type IIa combined with posterior lateral herniation. This typing is important for the severity of clinical symptoms of FLLDH and guiding surgical treatment. According to Ding Yu et al, type I cases have severe lumbar and leg pain, especially the root damage of lower limbs, mostly manifested as femoral nerve damage; type II cases have relatively mild clinical symptoms, especially type IIa mostly without obvious lumbar and leg pain. III. Clinical diagnosis of FLLDH For the diagnosis of extreme lateral type lumbar disc herniation, we cannot rely on clinical symptoms alone. When the patient has heavy clinical radicular symptoms, the intradural lumbar disc herniation cannot be well explained, and the neurolocalization signs are complicated at the same time, the disease should be alerted to the possibility of this disease. When relying on clinical symptoms for diagnosis is difficult, imaging data is necessary. The diagnosis of extreme posterolateral lumbar disc herniation can be established if the clinical radicular symptoms are severe, there are no abnormalities in the spinal canal on CT scan (excluding high lumbar disc herniation), and the herniation is visible inside/outside the intervertebral foramen. Since extreme posterolateral lumbar disc herniation has a tendency to shift upward, CT scans that do not include the level below the pedicle may lead to a missed diagnosis, so patients with lumbar disc herniation should include the intervertebral foramen area on either CT or MRI to avoid missed or misdiagnosed cases, and thin-section CT may be more helpful. For those cases where diagnosis is difficult, discography + CT scan may be helpful. IV. Treatment of FLLDH For the treatment of extreme lateral disc herniation, there are many treatments, including conservative treatment and surgical treatment, and surgical treatment includes traditional open surgery and minimally invasive transforaminal discoscopic discectomy. The following is specific about the treatment of FLLDH. 1, conservative treatment: conservative treatment includes pain relief, nerve nutrition and other drug therapy, as well as traction, physical therapy, etc. Conservative treatment can achieve pain relief, reduce neuroedema, relieve back pain, lower limb pain and other symptoms, through the system of conservative invalid cases can consider surgery. 2.Surgical treatment: For cases with heavy clinical symptoms, clear imaging diagnosis and no obvious effect by conservative treatment, surgical treatment should be performed as early as possible. In type I FLLDH, because the dislocated nucleus pulposus directly compresses the relatively fixed lumbar nerve in the intervertebral foramen and the area outside the foramen, it is difficult to relieve the continuous severe radicular pain, so conservative treatment is ineffective, and surgery is often the best choice. Surgical treatment includes traditional open surgery and minimally invasive transforaminal discoscopic removal of the herniated disc. There are more options for traditional open surgery, and the more commonly used ones are interlaminar openings, trans-isthmic openings, foraminotomy, total subtotal arthroplasty, vertebroplasty and anterior surgery. The interlaminar opening is the most classic approach, which can lead to severe postoperative back pain and requires interbody fusion in about 2-4% of cases. It has also been recently studied that only half of the lamina is removed and the medial 1/3 of the articular eminence on the affected side is knocked out by introducing a 3 mm kerf pin contralaterally, thus revealing the resected herniated very lateral disc. The lateral transmuscular approach (LTM) preserves the normal bony and soft tissue structures to the greatest extent possible, however, it is unable to manage cases with combined spinal stenosis or intradiscal herniation. The combined interlaminar and paraisthmic approach (CIP) has been proposed, but this procedure is highly traumatic, has many complications, and has a high incidence of postoperative back pain due to muscle atrophy, low back muscle dysfunction, and spinal instability, and the postoperative patient satisfaction rate is not high. Traditional open surgery also has disadvantages such as high trauma, bleeding, extensive muscle stripping, high chance of injury to the dorsal branch of the spinal nerve, and frequent postoperative muscle fiber scarring, muscle atrophy and low back muscle weakness syndrome [18]. Therefore, from the current point of view, the choice of surgical access for the treatment of FLLDH is patient-specific and requires adequate experience in surgical skills, as well as meticulous preoperative imaging to adequately show the site of lumbar disc herniation. Most of the research in recent years has focused on minimally invasive treatment of FLLDH as opposed to traditional open surgery. The MED system was first successfully applied to patients with lumbar disc herniation by Foley and Smith in 1997. The surgical approach for the microendoscopically assisted treatment of extreme posterolateral lumbar disc herniation is basically the same as that of traditional open surgery, with translaminar, transarticular posterolateral and transverse intertransverse approaches. The latter two approaches are less traumatic, do not enter the spinal canal, do not affect the microenvironment in the spinal canal, and are conducive to the patient’s recovery. bradley K et al. showed that the average satisfaction rate of FLLDH treated with discoscopy outside the spinal canal reached 85% at 5 years after surgery, and 60% of patients’ symptoms disappeared. This surgical approach is particularly suitable for patients with extreme posterolateral type disc herniation at L5-S1. According to Kadir Kotil et al, the use of this surgical approach in the treatment of L5-S1 extreme posterolateral disc herniation resulted in a satisfaction rate of 92.9% and no cases of lumbar instability, but permanent paralysis occurred in one patient. Complications such as dural tears and incomplete surgical resection for secondary surgery have also been reported in the literature [33]. This is due to the fact that discoscopic surgery is performed endoscopically with limited field of view and operating space and is prone to complications such as dural tears, nerve root injury and increased bleeding. Therefore, the use of discoscopy for FLLDH requires good surgical skills, very careful operation, great familiarity with the surrounding tissue anatomy, and some experience in open surgery. Other minimally invasive surgical treatments include percutaneous resection for FLLDH and total unilateral small synovectomy for FLLDH, which are less reported in the literature. Other treatments: Similar to other treatments for disc herniation, the treatment of FLLDH also includes percutaneous laser disc vaporization and decompression combined with ozone nucleus pulposus ablation, percutaneous puncture discotomy and collagenase lysis, collagenase treatment for FLLDH, and pressure sacral nerve block with 3D orthopedic therapy, etc. The efficacy of the above treatments needs to be confirmed by further studies. In conclusion, extreme posterolateral lumbar disc herniation is characterized by low incidence, difficulty in clinical diagnosis, high rate of misdiagnosis and omission, serious symptoms, difficulty in treatment, and many choices of surgical approaches and surgical methods. This requires us to pay full attention to extreme posterolateral lumbar disc herniation in clinical work, make specific analysis of specific patients, make correct diagnosis and choose appropriate treatment, and not to treat extreme posterolateral lumbar disc herniation as general disc herniation. In the future, it is necessary to further study the pathogenesis of extreme posterolateral lumbar disc herniation, develop a more reasonable typology, formulate different treatments for different types, and propose a more appropriate surgical plan to achieve less injury and less damage to the stability of the spine, as well as complete removal of the herniation and improvement of symptoms.