Lumbar fusion remains the current standard of care for lumbar instability, but the rate of lumbar fusion is not proportional to the rate of clinical satisfaction, and there is a potential for lumbar fusion to lead to accelerated degeneration of adjacent segments. This suggests that the surgical approach of load elimination by segmental fusion alters the load transfer in the lumbar spine and introduces some new problems, and the design of a technique that helps to limit abnormal loads rather than simply eliminate them was the original intention of the nonfusion internal fixation technique. In recent years, a large number of basic and clinical studies on nonfusion fixation techniques have been conducted both at home and abroad. The relevant literature is reviewed as follows. 1.Basic research and design concept The normal disc nucleus pulposus is composed of collagen and proteoglycan, which can conduct the load from different postures or positions evenly. Degeneration of the disc changes its uniform chemical composition and its physical properties, which leads to inconsistent load transmission to the endplate, resulting in increased stress and stress concentration, resulting in degeneration and pain. Therefore, the development of pain is related to the form of load transmission rather than to the magnitude of the load.McNally and Adams [3] performed internal pressure measurements of degenerated discs and similarly came to the above conclusion. Non-fusion internal fixation, or kinetic internal fixation, first proposed by Mulholland [2] in the 1980s and also referred to as soft fixation or flexible fixation, is a form of fixation that alters the range of motion and load on the lumbar motion segment without fusion, producing localized anterior convexity by placing the posterior structure in tension, which shifts the load from the anterior column to the posterior column, limiting the motion of the motion segment to This shifts the load from the anterior column to the posterior column, limiting the motion of the motor segment to normal or near normal, avoiding abnormal loads and thus relieving pain. The non-fusion internal fixation system was given a dual vision: first, by restoring more of the biomechanical properties of the treated segment, it would not only relieve or prevent the symptoms of lower back pain associated with instability, but also change the rate of disc degeneration in that segment, even allowing repair of mildly degenerated discs; second, if the system preserved more of the motor function, the degenerative process in the adjacent segment will progress more slowly. 2.Types of non-fusion internal fixation technology and clinical application At present, non-fusion internal fixation technology includes four types: 1.interspinous bracing system, 2.power stabilization system via arch root fixation, 3.semi-solid system via arch root fixation, 4.artificial disc and artificial nucleus pulposus. The first three types are all posterior systems, which are minimally invasive procedures. 2.1. Interspinous distraction device. These systems are designed as a cushion between the spinous process and are fixed to the spinous process by means of an elastic band on the cushion. The system was initially called the “Mechanomechanical Normalization System” and was later identified as the “First Generation Wallis Implant” to distinguish it from the current updated version. The first generation Wallis implant was based on the concept of extra-articular manipulation, which allowed for a reversible surgical procedure with all anatomical structures except the interspinous ligament intact, making it possible to remove the implant and perform fusion in the event of persistent or recurrent lower back pain. Senegas et al. conducted a prospective, nonrandomized, controlled trial of two groups of 40 patients who had previously undergone L45 discectomy but had recurred and required a second discectomy; the improvement in leg pain was essentially the same in both groups, and the improvement in lower back pain was more pronounced in patients who received the interspinous implant, and more of them stopped taking pain medication. After careful analysis of the first-generation implant for certain areas of improvement, a second-generation implant was developed and named the “Wallis” system. The interspinous pad of the “Wallis” system is made of PEEK instead of the metal material of the past, and the shape has been changed somewhat. Due to the shape of the interspinous pad and the nature of the PEEK material itself, the new interspinous pad is more flexible and its use gives it sufficient mechanical advantage. When the spine is loaded, the interspinous pad shifts the mechanical restraint to the dorsal side of the spine, reducing the load acting on the discs and small joints. In addition, the entire implant system constitutes a “floating” device fixed to the spine, thus preventing the implant from loosening. [Biomechanical studies have shown that the “Wallis” system can limit intervertebral motion by 35% and increase the strength of the fixed segment by 1.5 times. “Yizhar Floman et al. treated 37 patients with disc herniation using the second-generation Wallis system, and the results of the one-year follow-up showed that the patients had significant relief of back and leg pain, but did not reduce the incidence of secondary surgery for disc herniation. In addition, Boeree 2005 reported follow-up results of “rehydration” of the disc nucleus pulposus in patients treated with the second generation “Wallis” system, which is not comparable to fusion techniques. Extension [when the lumbar spine is hyperextended, the compressive stresses in the posterior column are rationally distributed through the interspinous pads, relieving pressure on the posterior edge of the vertebral body and the small articular processes]. Flexion [In lumbar hyperflexion, the compressive stresses in the anterior column are reduced by the interspinous strapping action, relieving pressure on the anterior edge of the vertebral body and the tension on the supraspinous ligaments]. The Wallis system is indicated for disc herniation; degenerative disc disease in adjacent segments at the fusion site; and chronic lower back pain due to simple Modic I endplate degeneration. Lumbar disc removal with interspinous pad fixation preserves the spinous process and performs interspinous restrictive fixation based on traditional surgery. It removes the herniated nucleus pulposus, completely relieves the nerve compression, increases the stability of the fixed segment, and preserves the motor function of the fixed segment. The operation is easy and safe. The results of the clinical application of the Wallis system still need further follow-up. The X-STOP System, developed by Francis Medical Technologies, Inc. in 2001, is a dynamic stabilization device specifically designed for lumbar spinal stenosis due to the increased volume of the spinal canal by keeping the spine in flexion. The implant can be placed under local anesthesia using a minimally invasive technique and is suitable for elderly patients who cannot tolerate major surgery. lee et al. applied the X-STOP system to 10 elderly patients with lumbar spinal stenosis and followed them for at least 9 months, with satisfactory results in 7 of them. The indications for the clinical studies were all selected as the clinical manifestations of lumbar spinal stenosis were evident in extension and reduced in flexion. zucherman et al. treated 100 patients with lumbar spinal stenosis with the X-Stop implantation and another 9l patients were selected for conservative treatment and the efficacy of the two groups was compared. By 2-year follow-up, the patient satisfaction level was 73.1%, compared with 35.9% in the control group, demonstrating the good effect of the X-Stop system in the treatment of lumbar spinal stenosis. In addition to the advantages of increasing the stability of the fixed segment, preserving the motion function of the fixed segment, and avoiding the acceleration of the degeneration of the adjacent segment, it is more encouraging that the dynamic stabilization of the lumbar interspinous process can, to a certain extent, lead to the reversal of the intervertebral disc tissue, i.e., the rehydration of the nucleus pulposus, which is difficult to achieve with any other non-fusion and fusion techniques. This is difficult to achieve with any other non-fusion and fusion techniques. At the same time, the lumbar interspinous dynamic stabilization system is simple and safe to implant, with minimal tissue trauma, minimal bleeding, no risks associated with any surgical operation, and a correspondingly shorter postoperative recovery time for the patient. 2.2. Dynamic stabilization devices for transpedicular arch fixation: including Graf system, Dynesys system and Fass system. The Graf system was first proposed by Graf in 1992 and consists of an arch root nail and a polyester band attached to the end of the nail. The system uses the articular eminence as the fulcrum to stabilize the fixed segment in full posterior extension by tensioning the polyester band and eliminating abnormal movement of the lumbar spine. The system increases the load on these structures by using the articular eminence as the fulcrum and leads to lateral saphenous fossa stenosis and nerve root entrapment, and is recommended for young patients with adequate lumbar back muscle strength and mild degeneration of the lumbar minor joints.Grevitt et al. reviewed the follow-up of 50 patients with Graf ligament fixation and concluded that it could achieve similar results to fusion fixation in the short term. The Dynesys system, also known as the dynamic neutral fixation system, consists of an arch nail with a polyester band attached to the end of the nail and a hollow spacer that wraps around the polyester band to maintain or restore normal or near-normal motion of the lumbar segments. Compared to the Graf system, the Dynesys system adds a stiffer tubular cuff between the connecting straps. In flexion with the polyester straps tightened, the Dynesys system eliminates abnormal lumbar spine motion and converts the compressive force of the posterior polyester straps into an anterior separator force, thereby reducing disc loading. In posterior extension the spacer resists the compressive forces.Although the Dynesys system reduces the synovial loads, it results in the loss of lumbar anterior convexity due to the bracing effect of the spacer.Schmoelz et al. used the intradiscal pressure (IDP) to measure the force during lumbar segmental motion.Experiments showed that the Dynesys system implantation significantly reduced the IDP during lumbar posterior extension and lateral bending,in The decrease in IDP in neutral position and axial rotation was not significant, and the decrease in IDP in flexion was smaller than the normal reference, and the effect on the IDP of adjacent discs was slight. Because the Dynesys system reduces both anterior flexion and posterior extension, it also allows limited motion and reduces the load on the intervertebral discs and synapses, so it can achieve the therapeutic purpose.Stoll [6] et al. reported that the Dynesys system was used to treat lumbar spinal stenosis, degenerative disc disease, disc herniation, and degenerative slippage, and at 38.1 months of follow-up, the low back pain score improved from 7.4 points before surgery to 3.1 before surgery, leg pain improved from 6.9 to 2.4 before surgery, and Oswestry score improved from 55.4 to 22.9 before surgery. The results suggest that the Dynesys system has comparable efficacy to conventional fusion surgery, but the Dynesys system is less invasive, has a shorter operative time, and does not increase adjacent stage degeneration.Bordes-Monmeneu [7] et al. reported similar results to those reported by Stoll et al. in 94 cases of lumbar spine disease. The Graf system increases the load on the articular processes and leads to lateral saphenous fossa stenosis and nerve root entrapment. the Dynesys system leads to loss of anterior lumbar convexity. To overcome these disadvantages, Sengupta et al. designed the FASS system, a lever-assisted soft fixation system in which a high-density polyethylene elastic support rod is placed between the pedicle nail and the polyester belt. When the polyester belt is tightened, the support rod converts the posterior compressive force into an anterior tensile stress, which increases the anterior intervertebral space, reduces disc pressure, maintains lumbar lordosis, and limits abnormal motion. In the FASS system, the improvement in disc loading is dependent on the tension and pressure generated by the brace and ligaments, but there is a possibility of loosening because the system assumes a greater tensile stress. 2.3. Semi-solid devices with transforaminal fixation: Spine surgeons still use fusion techniques mainly because of the unique configuration of the numerous intervertebral joints of the spine that form a “kinetic chain”, a multi-joint system that provides good compensation for a damaged segment accordingly. However, the high incidence of postoperative adjacent segment degeneration (ASD) has led to the emergence of a hybrid technique of dynamic stabilization accompanied by fusion – the semi-solid device. The DSS system (dynamic stabilization system) is its representative and was designed by Spinal Concepts, Inc. The DSS-1 system consists of an arch nail with a 3 mm “C” shaped elastic titanium rod posteriorly, and the DSS-2 system consists of an arch nail with a 4 mm elastic titanium coil posteriorly. The DSS-Ⅰ system appropriately distributes the disc load and limits spinal motion in lumbar flexion; in lumbar extension the disc load is reduced, and in full extension the spinal motion is almost completely limited and the disc load is minimized. Recent studies have shown that the optimal instantaneous axis of rotation (IAR) of the DSS-II system can be close to the normal motion segment, thus reducing disc loading more uniformly during flexion and extension of the lumbar spine. However, there are few reports on the clinical application of the DSS system. 2.4 Artificial disc and artificial nucleus pulposus Because the design of the disc or nucleus pulposus prosthesis follows the biomechanical principle of dynamic fixation to equalize load transfer and protect the normal motion of the motion segment, it is also classified as a non-fusion fixation. The main advantage of ADR is that it restores the kinematic capacity and load characteristics of the spinal kinematic units, achieving load sharing, segmental stability and segmental motion. The purpose of ADR is to restore load sharing, segmental stability and segmental motion. It also removes the painful source of discogenic low back pain. There are two main types of artificial disc prostheses in clinical use: the German Link SB Charité and the American Prodisc disc prosthesis. The Prodisc disc prosthesis has a polyethylene nucleus that is fixed to the lower cover and is movable from above, while the Link SB Charité prosthesis is double-acting, allowing a certain range of rotation and translation. Currently it is mainly indicated for cases with degenerative single or multi-segmental lumbar spine lesions that have failed to respond to systematic conservative treatment, and without local infection, slippage, significant synovial arthropathy or spinal stenosis. zigler et al. showed no significant difference in patient satisfaction with symptom relief at 6 months postoperatively by comparing lumbar fusion with ADR, while lumbar mobility was significantly improved in the ADR group. However, artificial lumbar disc replacement still has the disadvantages of requiring surgery from the anterior lumbar spine, which is highly invasive; clinical outcomes are still controversial; and expensive. The purpose of artificial nucleus pulposus replacement is to restore uniform transmission of stress by the nucleus pulposus and thus relieve pain. The widely used artificial nucleus pulposus, known by the trade name PDN-SOLO, is composed of a hydrogel core and a polyethylene sleeve designed to function as a “cushion” for a healthy disc, restoring and maintaining disc height and allowing for a normal range of motion. The indications for nucleus pulposus replacement are mainly for chronic discogenic low back pain arising from degenerative single segment disc disease, with a gap height greater than 5 mm and no Schmorl nodes or fractures in the vertebral endplate, at the age of 18 years or older [11], who reported clinical results in 46 cases with a follow-up of more than 6 months, where the ODI score decreased from a mean of 58.9% preoperatively to 18.0% postoperatively, with a clinical success rate of 78.3%, with complications including: four cases of prosthesis displacement requiring revision and one case of infection. As for the clinical consideration of artificial disc or artificial nucleus pulposus replacement, there are two main considerations: first, artificial nucleus pulposus replacement can be performed only if the cartilage endplate is intact, while artificial disc replacement does not require consideration of the cartilage endplate; second, artificial nucleus pulposus replacement can be considered for milder lumbar disc degeneration, while artificial disc replacement can be considered for more severe cases. Of course, there must be some overlapping cases between the two. Theoretically, the obvious osteoarthritis of the small joints is a contraindication to disc prosthesis replacement. 3, non-fusion internal fixation surgery indications and contraindications to surgery non-fusion fixation main indications have been described in the previous article. Contraindications include: 1 lumbar spondylolisthesis of degree II or above; 2 lumbar dynamic instability; 3 severe DDD; 4 arch root diameter is too small for nail placement; 5 vertebral fracture, dislocation, tumor or infection; 6 patients with psychological disorders. 4. Advantages of non-fusion internal fixation and current problems Non-fusion internal fixation is an effective method for treating degenerative lumbar disc disease. This technique changes the weight-bearing pattern of the motion segment while stabilizing the lumbar spine, preserving the motion function of the operated segment, and relieving the degeneration of the adjacent segment. Several issues still need to be addressed with posterior nonfusion fixation: (1) the magnitude of stabilization of the motion segment, (2) how much abnormal loading needs to be shared, and (3) how to prevent implant failure. Anterior ADR and PDN offer greater feasibility for clinical application because they can maximize the restoration of spinal anatomy and biomechanical properties after disc or nucleus pulposus removal. However, whether ADR and PDN prostheses will sink, wear, or displace, thus requiring revision surgery; and what their long-term outcomes are compared to traditional fusion surgery. Further observation and research are needed. 5, non-fusion internal fixation technology prospect Non-fusion fixation technology is undoubtedly a proven method for the treatment of lumbar degenerative disc disease, and this method will play a very important role in the new staged surgical strategy, thus avoiding the final fusion of degenerative intervertebral segments. Its clinical application and basic research deserve attention and continuous improvement. The indications for surgery, surgical technique, revision after failure and long-term results remain to be studied and explored in depth, and we should be cautious in accepting this new technique.