Minimally invasive surgery is one of the fastest growing areas of modern surgery, enabling small “bore” incisions combined with visualization techniques that allow for better visualization of the surgical area. The origin of the term “Minimallyinvasivesurgery” is somewhat controversial; Wickham coined the term in 1986, and in 1992, Cuschieri used the term “Minimallyaccesssurgery. Minimallyaccesssurgery”. In the last decade, minimally invasive spine surgery techniques have evolved rapidly. Minimally invasive spine surgery reduces postoperative pain and recovery time because it involves less stretching and stripping of soft tissues. With the development of microendoscopic techniques and the clinical application of special surgical instruments and equipment, surgeons can perform previous surgical operations through one or more tiny incisions. As with open surgery, minimally invasive spine surgery also enables minimally invasive nerve decompression, spinal stabilization and fusion, and correction of spinal deformities. I. Current status and outlook of minimally invasive spine technology 1. posterior posterolateral percutaneous discectomy Percutaneous discectomy for decompression of lumbar disc herniation has undergone a history of development for more than 20 years. On the basis of Craig’s lateral posterior percutaneous lumbar disc puncture biopsy route, Hijilkata and Onik et al. reported lateral posterior percutaneous lumbar discectomy manually and automatically, Kambin et al. reported endoscopically assisted lumbar discectomy and aspiration, followed by Forst and Schreiber et al. who reported lumbar discectomy and decompression under direct endoscopic view, respectively. With the continuous improvement and development of minimally invasive spinal endoscopes and surgical instruments, as well as the clinical application of advanced surgical equipment such as laser, radiofrequency, and navigation, percutaneous laminectomy techniques have been revolutionized. From the early blind postero-lateral percutaneous lumbar discotomy to today’s endoscopically assisted excision and aspiration, from the YESS technique of indirect disc decompression by simply entering the disc through the Kambin safety triangle to the TESSYS technique of direct nerve root release and decompression by entering the spinal canal directly through the intervertebral foramen, from the past when only simple inclusive lumbar disc herniation could be performed to the present day when all types of lumbar disc herniation can be completed. The procedure has become the most promising and minimally invasive endoscopic technique of the spine today. Efforts are being made to explore percutaneous lumbar fusion, nucleus pulposus replacement and stem cell transplantation. This procedure has become the most promising and minimally invasive endoscopic technique of the spine today. Percutaneous lumbar discectomy (PELD) is performed through a posterior-lateral approach to the intervertebral disc through the “safe triangle of work” of the foramen. This zone is located on the posterior aspect of the annulus fibrosus and allows safe passage of instruments without injury to the traveling nerve roots (Exitingnerveroot). Minimally invasive posterior posterolateral percutaneous discectomy can be performed under local anesthesia so that the surgeon can obtain direct feedback from the patient during placement of the working channel to avoid injury to the nerve roots. Despite the significant advantages of this procedure, such as minimal bleeding, minimal surgical trauma and scarring, there are still some drawbacks. If the patient’s iliac crest is high or the patient’s spinal space has collapsed, it can be difficult to find the precise point of access. It is also difficult to operate when the disc fragments are already free. The risk of nerve root injury is also higher in patients requiring general anesthesia or deep sedation. With the continuous improvement and development of minimally invasive spinal endoscopy and surgical instrumentation, as well as the clinical application of advanced surgical equipment such as laser, radiofrequency, and navigation, percutaneous laminectomy techniques have been revolutionized. From the early blind postero-lateral percutaneous lumbar disc dissection to today’s endoscopically assisted excision and suction, from the past, when indirect disc decompression was performed simply by entering the disc through the Kambin safety triangle, to today’s direct nerve root release and decompression by entering the spinal canal directly through the intervertebral foramen, from the past, when only simple inclusive lumbar disc herniation could be performed, to the present day, when all types of lumbar disc herniation and In addition to direct surgical removal of all types of herniated and prolapsed lumbar discs and percutaneous foraminal enlargement for foraminal stenosis, we are now exploring percutaneous lumbar fusion, nucleus pulposus replacement and stem cell transplantation. This procedure has become the most promising and minimally invasive spinal endoscopic technique today. Percutaneous foraminoscopic lumbar interbody fusion is an important future development direction. Currently, scholars are trying to fill the disc with a balloon with a gel or polymer expansion device through a special surgical tool, and the balloon can be expanded to the desired size. Another way is to use an expandable intervertebral fusion device that is implanted into the disc through the percutaneous intervertebral foramen “safety triangle” and then expanded to the appropriate size, thus achieving true minimally invasive percutaneous intervertebral implantation, intervertebral spreading, and fusion. Although it is difficult to insert into the disc, it is possible to design a smaller size deformed intervertebral fusion device that can be inserted into the disc and then regain its shape to achieve minimally invasive intervertebral fusion. Currently, the development of a PEEK expandable intervertebral fusion device has been achieved and has been used clinically. MED minimally invasive lumbar disc removal is a new minimally invasive spine surgery technique first developed by Foley and Smith in 1997. The MED minimally invasive lumbar disc removal technique draws on the advantages of both the traditional posterior laminectomy technique and the minimally invasive endoscopic technique to create a series of dilated channels to complete the surgical approach and to complete the 1.6-1.8 cm diameter working channel for laminectomy, subtotal joint resection, nerve root canal decompression and disc removal that could only be accomplished through open surgery in the past. Compared to conventional lumbar disc removal, this technique creates surgical access through a series of dilating catheters, eliminates the need for stripping and distraction of the paravertebral muscles, and performs all surgical operations within a 1.6-1.8 cm diameter working channel. As a result, it has the advantages of a small surgical incision, minimal paravertebral muscle damage, minimal bleeding and rapid postoperative recovery. The advanced camera and video system magnifies the surgical field of view by 64 times, so that the dural sac, nerve roots and intravertebral vascular plexus in the surgical area can be more accurately identified and protected during surgery; at the same time, the clear surgical field ensures more precise completion of various surgical operations, effectively avoiding the shortcomings of deep field of view and large damage to the posterior bony joint structures of the spine in traditional surgery, and maximally preserving the integrity of the posterior ligamentous complex of the spine. The integrity of the posterior ligamentous complex of the spine is preserved to the maximum extent, thus effectively reducing the occurrence of postoperative scar adhesions and lumbar instability. The location of the working channel is determined by the pathological changes in the specific area. Minimally invasive lumbar decompression allows for adequate decompression of the central spinal canal, lateral saphenous fossa, and intervertebral foramen regions. In addition, the disc tissue outside the foramen can be removed. The surgical approach needs to be planned prior to decompression of the different areas. For extraforaminal nerve decompression, the working channel can be placed on the intertransverse intervertebral membrane between the transverse processes by first identifying the intertransverse intervertebral membrane and dissecting the intertransverse ligament to reveal the deeper exiting nerveroot, which can be located deep within the nerve root. Recent studies comparing minimally invasive disc nucleus pulposus removal with traditional open surgery have shown that minimally invasive surgery involves less tissue damage, less nerve interference, less blood loss, less postoperative pain, shorter hospital stay, and faster recovery and return to work. A randomized controlled study of traditional open microdiscectomy and microdiscectomy with minimally invasive access showed that the procedure was safer and more effective with minimally invasive access. The new discoscopic (MED) technique developed by Foley and Smith is a perfect combination of minimally invasive microsurgical techniques and endoscopic techniques.MED surgery is similar to open microscopic discectomy and can be used for laminectomy decompression and foraminotomy as well as herniated disc surgery.The ease of operation, broad indications and versatility of MED make it easier for surgeons to switch from traditional surgery to endoscopic surgery. Although endoscopic visualization not only provides a clear and magnified view of the surgical field, but also facilitates efficient surgical procedures, it provides only 2-dimensional images and is often hampered by bleeding and poor display, which is not as good as microscopic discectomy. Advances in endoscopic imaging and endoscopic image fusion techniques can help improve this problem. Bleeding control is particularly important for any visualization technique, and heavy bleeding increases the risk of dural sac tears and nerve root injury. Endius has developed a miniature bipolar electrocoagulation (MDS) device with a double sheath that can be applied to perform blunt dissection, aspiration and electrocoagulation to stop bleeding. A dual light source endoscopic system (infrared/visible) is also used, which incorporates an infrared channel in the current laparoscopic system. This system is able to find small arterial bleeds in a bleeding environment, identify the exact location of the bleed, and help the operator to rapidly cauterize the bleed and reduce repeated hemostatic operations when the bleeding point is unclear. Advances in computer technology and endoscopic techniques have enabled 3D reconstructed virtual images to be synthesized from preoperative images combined with intraoperative scans and then appended to intraoperative endoscopic images, and similar techniques have been used in cranial surgery to combine preoperative image reconstruction with intraoperative surgical microscopy images, which can assist the surgeon in identifying tumor boundaries and better removing tumors. Recently, (Mississauga, Canada) a neuroendoscopic trocar was developed that allows the endoscopic position to be seen based on MRI and CT data. Special software provides live endoscopic images as well as three-dimensional positioning of the instruments. Another development is the helmet display ophthalmoscope, which is attached to the operating microscope so that the operator can observe the transmitted display signal and the surgical field of view, which could also be used in the near future for spine surgery endoscopy to compensate for the lack of a two-dimensional spine endoscope. Future improvements in imaging technology will also include better optical image resolution, better focus similar to that of a surgical microscope, better flexibility and maneuverability, greater working channel role, and continued improvements in three-dimensional images. These improvements can advance spinal endoscopic surgery to a whole new level. 3. Minimally invasive lumbar decompression and fusion 1) Minimally invasive lumbar hemilaminectomy An important principle of minimally invasive lumbar decompression is the preservation of the tendon stop of the multifidus on the spinous process. In a conventional total laminectomy, the spinous process is removed and the multifidus muscle is drawn to the sides. It is not possible to repair the start of the multifidus muscle on the spinous process when closing the wound. However, with the hemi-laminectomy technique, a complete decompression of the spinal canal can be performed unilaterally through the working channel. Tilting the working channel dorsally allows visualization of the spinous process inferiorly and the contralateral lamina, and gentle downward pressure is applied to the dural sac to remove the ligamentum flavum and the contralateral superior articular eminence, thus completing the classic bilateral decompression via a unilateral approach. The anatomy of the superior lumbar spine differs from that of the inferior lumbar spine in that the plate between the spinous process and the articular process is very narrow at the level of L3 and above, and if a unilateral approach is used, the superior articular process on the same side must be removed more in order to decompress the ipsilateral lateral fossa. Another option is to use a bilateral approach technique, in which decompression of the right lateral saphenous fossa is accomplished by hemilaminectomy on the left side, and vice versa. In one study, this bilateral approach technique was used to decompress 7 segments in 4 patients, with an overall mean operative time of 32 minutes per segment, a mean blood loss of 75 ml, and a mean postoperative hospital stay of 1.2 days. Preoperative neurogenic claudication disappeared in all patients and no complications occurred. 2) Transforaminal lumbar interbody fusion Transforaminal lumbar interbody fusion (TLIF) was first proposed by Blume and Rojas and popularized by Harms and Jeszensky. This technique evolved from the posterior lumbar interbody fusion (PLIF) first proposed by Cloward, which required extensive spinal canal decompression and bilateral nerve root retraction to expose the lumbar spine space, whereas the TLIF procedure exposes the lumbar spine space unilaterally through the intervertebral foramen, resulting in less strain on the neural structures than the PLIF procedure, which requires bilateral completion. Another major advantage of TLIF surgery is that posterior lumbar spinal canal decompression and anterior interbody fusion can be accomplished simultaneously through a single posterior incision. 3) Lateral lumbar interbody fusion Lumbar interbody fusion is a very common technique that offers three advantages: (1) removal of disc tissue as a source of pain; (2) very high fusion rates; and (3) restoration of lumbar spine gap height and lumbar anterior convexity. Lumbar interbody fusion includes trans-anterior interbody fusion, trans-posterior interbody fusion, trans-interbody fusion, or endoscopic lateral interbody fusion via an extraperitoneal approach. Minimally invasive retroperitoneal lateral interbody fusion via the lumbaris major route has been reported in the literature. This technique is performed retroperitoneally via the psoas major muscle under neurophysiological monitoring and fluoroscopic guidance and is referred to as DLIF or XLIF minimally invasive lumbar fusion. Because the lumbar plexus is located within the posterior half of the psoas major muscle, limited dissection of the anterior 1/3 to anterior 1/2 of the psoas major muscle reduces the risk of nerve damage. In addition, intraoperative use of electromyographic monitoring may also reduce the risk of nerve damage. Disruption of the bone endplate should be avoided when dealing with the lumbar spinal space and implanting an interbody fusion, and the orientation of the interbody fusion should be determined by positive and lateral fluoroscopy. Interbody fusion can achieve indirect decompression of the foramina by restoring neural foraminal height and spinal dislocation alignment. The decision to also perform a posterior fusion and decompression is made on a body-by-body basis.Knight et al. reported early complications in 43 female and 15 male patients who underwent minimally invasive lateral lumbar interbody fusion: six had postoperative abnormal sensory anterior thigh pain and two had lumbar L4 nerve root injury. Anterior fusion with an intervertebral fusion alone increases the incidence of pseudoarthrosis due to insufficient stability of the initially fused segment. In recent years, posterior adjunctive fixation has been used to improve the intervertebral fusion rate. Posterior percutaneous pedicle screw fixation (Sextant) is an effective method, which has the advantages of avoiding muscle destruction by posterior surgery, low intraoperative blood loss, rapid postoperative recovery, and can improve the fusion rate, but the operation is complicated. Kandziora et al. compared the biomechanical properties of PFSF, transforaminal pedicle screw and pedicle screw fixation in vitro and found that the initial biomechanical stability of lumbar pedicle screw fixation was similar to that of transforaminal pedicle screw fixation, but slightly less than that of pedicle screw fixation. Kang et al. reported that percutaneous transforaminal pedicle screw (TFS) fixation was performed under CT navigation and all screws were accurately implanted without complications. Percutaneous PFSF can be an effective complement to posterior pedicle screw fixation. 4. Minimally invasive posterior internal fixation technique The pedicle screw technique has been widely used in clinical practice for its safety and effectiveness since it was applied to the treatment of thoracic and lumbar fractures of the spine. However, traditional open surgery requires extensive tissue incision and prolonged intraoperative traction of surrounding tissues, which is traumatic and obviously affects the patient’s postoperative recovery. Therefore, the use of minimally invasive techniques for internal fixation of thoracolumbar pedicle screws has gradually developed. The first description of percutaneous lumbar external fixation was by Magerl, which was then mainly used for temporary external fixation of the lumbar spine, and in 2001 Foley et al. first reported the percutaneous pedicle screw internal fixation technique with the Sextant system. This percutaneous Sextant pedicle screw internal fixation system is based on the geometric trajectory principle, and the unique rod loading system makes percutaneous rod loading easier and more accurate, and is the first to place the rod deep in the muscle, achieving true percutaneous pedicle screw fixation. Minimally invasive pedicle screw placement can be achieved by either a percutaneous or a small paramedian incision, both of which are designed to preserve the function of the multifidus muscle as much as possible. The percutaneous pedicle screw placement technique is used under fluoroscopic guidance. A Jamshidi trocar is first used to perform a pedicle puncture. The trocar is placed into the pedicle, the needle is withdrawn, and a guide wire is inserted along the trocar. A serial expansion catheter is placed along the guidewire to expand the soft tissue, and then tapping and hollow pedicle screw placement is performed under the guidance of the guidewire. The connecting rod is placed in a percutaneous fashion to minimize soft tissue damage. The minimally invasive small incision pedicle screw placement technique involves a longitudinal incision slightly outside the lateral edge of the pedicle, followed by separation between the multifidus and longest muscles. After grade-by-grade expansion of the soft tissue, a working channel is placed to expose the isthmus and the cephalad and caudal papillae, and a high-speed grinding drill is used to open the opening, which is then tapered into the pedicle with an arch probe. Hollow or non-hollow pedicle screws can be used. The isthmus, synovial joint, and transverse process can be decorticated for implant fusion under working access. The minimally invasive small incision technique has several advantages over percutaneous pedicle screw placement: first, the anatomy can be identified under direct vision, using either hollow or non-hollow pedicle screws. Second, the technique reveals a larger area for posterior implant fusion. However, there is a high risk of injury to the medial branch of the posterior spinal nerve, which travels down to the transverse process of the caudal segment and branches posteriorly to innervate the multifidus, intertransverse process and intertransverse process ligaments, as well as the articular process of the cephalic segment, using a minimally invasive small incision technique. Regev et al. conducted a cadaveric comparison of two minimally invasive pedicle screw insertion techniques and found that minimally invasive small incision insertion techniques were more likely to cause injury to the medial branch of the posterior spinal nerve. He suggested that if one wants to reduce the loss of innervation of the multifidus muscle in the adjacent cephalad segment, a percutaneous implantation technique is preferable in the adjacent cephalad segment. Outlook In the last decade, research and clinical application of minimally invasive techniques have made great progress, and the clinical follow-up results are encouraging, but there are many issues that need improvement: how to further reduce complications, whether intervertebral fusion devices more suitable for minimally invasive implantation can be developed, and how to reduce the learning curve of minimally invasive techniques to facilitate the popularity of minimally invasive surgery. The long-term clinical results of minimally invasive surgery are rarely reported, and further follow-up is needed. Although minimally invasive surgery is less invasive, it does not mean that it is less risky. On the contrary, surgeons assume greater surgical difficulty and risk, requiring minimally invasive spine surgeons to be familiar with the three-dimensional anatomy around the spine, to strictly master the indications for minimally invasive surgery, and to continuously summarize their experience in clinical practice, along with the continuous development of new instruments, new biological agents, advanced imaging equipment, and highly sophisticated robotic systems, which are expected to promote a new revolution in minimally invasive spinal surgery.