In the treatment of degenerative lumbar spine diseases such as lumbar spinal stenosis and lumbar disc herniation, fixation and fusion along with decompression are required to maintain the stability of the operated segment and sustain long-term surgical outcomes. However, as research has progressed, it has been discovered that many patients have back pain related to body posture and that weight bearing can trigger and exacerbate pain. Although modern fixation techniques continue to improve, increasing the fusion rate of the spine to approximately 98%, there are still many patients who do not achieve a corresponding clinical improvement. It is evident that braking is not a major factor in the relief of low back pain. Establishing a normal pattern of lumbar spine load transfer is more important to achieve satisfactory clinical outcomes. Some scholars have begun to think about exploring new ways to “stabilize” the spine, i.e., stabilize but not fuse. A new concept of “dynamic stabilization” was proposed. The author used the dynamic neutralization system (Dynesys) to treat 42 patients with degenerative lumbar spine disease, which is retrospectively analyzed as follows. Data and methods I. General data From February 2010 to June 2012, 42 patients with degenerative lumbar spine diseases were treated with Dynesys in our department, including 24 males and 18 females; their ages ranged from 38 to 74 years old, with an average of 54.6 years old. All cases had degenerative lumbar spinal stenosis, combined or uncomplicated disc herniation. There were 32 single-segment cases and 10 double-segment cases. All patients in this group had obvious symptoms of lumbar pain and/or leg pain, and conservative treatment was ineffective. Preoperative radiographs and MRI of the lumbar spine were routinely performed in frontal and lateral and hyperextension and hyperflexion positions. The inclusion criteria were: low back pain and intermittent claudication due to lumbar spinal stenosis; low back pain due to single- or double-segment disc herniation; low back pain due to degenerative lumbar spondylolisthesis; and medically induced instability due to decompression operations. The preoperative VAS score for low back pain was 6.0±1.8, the preoperative VAS score for leg pain was 7.2±1.9, and the preoperative ODI index was ( 60.4±21.5 ) %. After the Dynesys screws were inserted according to the standard procedure, the diseased segment was decompressed by interlaminar opening and the disc was removed (or preserved). The thickened ligamentum flavum was removed, the medial portion of the superior articular eminence was excised, and the lateral saphenous fossa was opened. The PCU canal is measured, intercepted, and a PET cord is threaded between the PCU canal and the upper and lower pedicle nails, and the cord is tightened and locked to the pedicle nail connection [3]. Drainage tubes were placed bilaterally and the incision was closed. The lumbar collar was worn on the floor for 5 days after surgery and for 3 weeks. Evaluation of efficacy At the time of follow-up, frontal and lateral radiographs of the lumbar spine and lateral radiographs of anterior flexion and posterior extension were performed to measure the mobility of the implanted segment, the disc height (average of anterior and posterior margin heights), and the mobility of the adjacent segment on the cephalad side after surgery. The VAS scores of patients with low back pain and leg pain were measured, and the ODI index at the last follow-up was measured, all compared with that before surgery. Statistical methods The data were expressed by x±s, and SPSS11.0 statistical software was used for statistical analysis. Paired t-test was used to compare the data before and after treatment, and the test level α = 0.05, and P < 0.05 was considered statistically significant. Results Forty-two cases were followed up for 10 to 36 months after surgery, with a mean of 24.7 months. There was no death or neurological deterioration during the perioperative period, and the ODI index was 60.4±21.5% preoperatively and 23.9±13.5% postoperatively (P<0.05). The VAS leg pain score was 7.2±1.9 preoperatively and 1.9±1.1 postoperatively, ( P<0.05 ), with satisfactory clinical outcomes. The intervertebral mobility of the non-fused fixed segment was significantly reduced (3.2±2.1 °) compared with that of the preoperative segment (9.9±2.2 °) (P<0.05), and the range of motion was 2°-5°, with a mean of 3.7° (Figure 1). There was a decrease in the height of the intervertebral space and an increase in the mobility of the adjacent segment on the cephalad side (10.1±2.3 °) after surgery, but the difference was not statistically significant (P>0.05) compared with the preoperative (8.9±3.7 °). Discussion I. Biomechanical characteristics of the Dynesys dynamic stabilization system The Dynesys system was first used in clinical practice by Dubois in 1994. It consists of a titanium nail, a polyethylene terephthalate (PET) cord core, and a polyurethane trocar (PCU tube), which is attached to the nail by a fixed core that passes through the trocar. As envisioned by Dubois, the core has a certain tension, the trocar resists compression, and the dynamic push-pull relationship created by the pedicle nail connection provides stability to the fixed segment. The inherent stability of the entire device resists bending and shearing forces and controls abnormal motion in all planes while retaining a degree of mobility. After laminectomy, spinal stability is reduced and the balance point position shifts forward. After Dynesys fixation, the amplitude of flexion, extension and horizontal rotational motion is significantly reduced and the balance point position returns to normal. Biomechanical studies have shown that after removal of the bilateral synovial joint and supraspinous interspinous ligament, the mobility of the fixed segment and adjacent segments was near normal in the Dynesys fixation group, whereas both proximal and distal mobility increased in the conventional nail bar fixation group. The mild posterior column spreading of the Dynesys helps to improve lumbar spinal stenosis, with an 11% increase in spinal canal volume and a 19% increase in intervertebral foraminal volume with anterior lumbar flexion. These biomechanical features make the Dynesys system potentially useful for the treatment of degenerative lumbar spine diseases. Each new technology has its own scope of application, and the first thing that needs to be clarified in order to achieve good clinical results is the choice of surgical indications. A major challenge for the Dynesys system is whether it can relieve the pain of patients with low back pain. Many patients with low back pain due to lumbar instability require firm local stabilization to relieve pain, and some even require a so-called 360° fusion. A multicenter prospective clinical study showed that this system provided a safe and effective option for the clinical management of lumbar instability with a postoperative ODI index ranging from 55.4% to 22.9%. Kim et al. concluded that Dynesys reduced symptoms of low back pain while avoiding associated tissue destruction and was better than conventional fusion in the surgical management of degenerative spondylolisthesis and spinal stenosis. However, there is debate as to whether Dynesys fixation is superior to spinal fusion. In a follow-up study of at least 6 years, the long-term outcome of decompression combined with Dynesys fixation for lumbar stenosis and degenerative lumbar spondylolisthesis was good, and imaging assessment was good enough to maintain stability to stop the progression of lumbar spondylolisthesis, but there was no improvement in the progression of degeneration in the adjacent segments. Dynesys fixation did not improve the degeneration of adjacent segments. Indications for Dynesys surgery include: 1) patients with lumbar spinal stenosis or degenerative lumbar spondylolisthesis resulting in neurogenic pain or lower back pain with relatively normal intervertebral space height; 2) single- or multi-segment disc degeneration resulting in lower back pain; and 3) decompression surgery resulting in medically induced lumbar instability. III. Problems in the clinical application of Dynesys Complications of the Dynesys system include screw loosening, device displacement, component wear and fracture, and loss of lumbar anterior lordosis. Some investigators have analyzed Dynesys systems recovered from revision surgery and observed deformation, wear, and biodegradation of components. A review by Anand et al. suggests that the Dynesys system can neutralize harmful violent factors and preserve some mobility of the lumbar segment with no reported serious related complications, but its safety, efficacy, and applicability remain to be confirmed by long-term follow-up and prospective randomized studies. However, its safety, efficacy and applicability remain to be confirmed by long-term follow-up and prospective randomized studies.