From April 2011 to September 2012, the Department of Spine and Orthopedics of our hospital has achieved good clinical results in 42 patients with degenerative lesions of the lumbar spine by using a minimally invasive system of expandable canal with multifracture muscle gap access for nerve root canal decompression, intervertebral implant fusion, and arch nail rod system fixation, which is reported below. 1. Data and methods 1.1 Clinical data There were 42 cases in this group, 24 males and 18 females, aged 46-70 years old, with an average of 62 years old. Among them, there were 8 cases of lumbar disc herniation, 20 cases of lumbar spinal stenosis, 12 cases of lumbar slippage (Ⅰ°4 cases, Ⅱ°8 cases), and 2 cases of revision surgery. All patients had symptoms of lumbar pain, radicular pain or numbness in the lower limbs. All patients routinely underwent preoperative lumbar front and side, hyperextension and hyperflexion radiographs, lumbar spine CT and MRI examinations. Preoperative C-arm X-ray machine was used for body surface positioning. 1.2 Surgical method After general anesthesia took effect, the patient was placed in prone position. A posterior median lumbar incision was made, and the skin and subcutaneous tissues were incised in turn. The lumbar dorsal fascia was separated bluntly on the surface of the lumbar dorsal fascia on both sides, 1.5-2.5 cm lateral to the spinous process, and the lumbar dorsal fascia was incised longitudinally, and the paravertebral muscles could be clearly exposed after incision. (The surgical incision can also be about 1.5 to 2.5 cm of skin incision next to the posterior median lumbar region, which allows direct access to the muscle space.) The position of the multifidus and longest muscles is determined, and a gentle blunt separation is made by hand between the natural division of the two muscles, from superficial to deep, to reach the articular surface of the vertebral body to be fixed. After the C-arm fluoroscopy is used for accurate positioning, the soft tissues of the upper and lower articular eminences, transverse processes, and lateral surface of the vertebral plate are peeled off by the electric knife, and a minimally invasive dilatation channel is installed to pull the multifidus and longest muscles apart to the left and right, clearly revealing the above bone structures. Firstly, the neural root canal on the healthy side was enlarged, and the transverse process was positioned for pedicle placement. The depth and direction of the positioning pin in the pedicle was determined under fluoroscopy, and the superior inferior vertebral body inferior articular eminence and the medial part of the inferior vertebral body superior articular eminence were excised with a sharp bone knife and lamellar forceps to enlarge the healthy neural root canal, and the excised bone was trimmed into granular bone for spare use. The appropriate pedicle screw is replaced, and the nail bar is installed, screwed into the nail cap, and left untightened for the time being. The nerve root canal on the affected side is then enlarged. After decompression of the nerve root canal by the same method of locating the pin, the ligamentum flavum is exposed and removed, and the canal without posterior bony structures between the upper and lower vertebral plates is entered, the dural sac and nerve roots are medially retracted, the intervertebral disc is removed, and the cartilage endplates are scraped. A portion of the spare granulated bone is compressed and implanted at the anterior edge of the vertebral space, and an intervertebral fusion device with granulated bone is implanted to a satisfactory position in the vertebral space. After the position of internal fixation was determined under C-arm X-ray machine, the incision was closed layer by layer and the drainage tube was left in place. 1.3 Postoperative treatment Routine application of antibiotics for 2-3 days, dehydrating agents and hormones for 3 days after surgery, drainage tubes were removed the next day, straight leg raising training and functional exercise of the lumbar back muscles were performed in bed, and the lumbar girth was worn on the floor for 3-5 days. Bed rest was the main focus in January, and no heavy physical labor and bending and heavy lifting in three months. 1.4 Postoperative observation indexes Observation of operation time, incision length and healing, operation bleeding, cerebrospinal fluid leakage, postoperative incision drainage, time to the ground, and low back pain (VAS score). 2. Results All patients completed the surgery successfully, operative time: single segment: 90-150 min, average 120 min; double segment: 180-270 min, average 210 min. incision length: single segment: median incision: 3.2-4.5 cm, bilateral incision: 2.8-3.5 cm; double segment: median incision: 5.6-6.4 cm, bilateral incision : 4.8～6.0cm. Incision healing: postoperative infection in one patient, incision and drainage, healing after 8 weeks, considering the following reasons: ① patient’s sensitive body, allergic to many antibiotics; ② postoperative patient informed that he had a history of tooth extraction surgery one week before. Intraoperative bleeding: single segment: 150-220 ml, mean 180 ml; double segment: 270-500 ml, mean 300 ml. Postoperative drainage: single segment: 20-70 ml, mean 40 ml; double segment: 40-100 ml, mean 65 ml. The drainage tube was removed the next day after surgery. 42 patients were not transfused, and there was no cerebrospinal fluid leak in 1 case. 42 patients were obtained follow-up for 6 to 12 months. The VAS scores for low back pain or lower limb pain at the preoperative, 1 week postoperative, and final postoperative follow-up were 7.2±1.8, 1.8±0.6, and 1.0±0.5, respectively, with significant differences (P<0.05) at 1 week postoperative and 6 to 12 months postoperative follow-up compared with preoperative. 3. Typical case Male patient, 55 years old, with low back pain with numbness and pain in the right lower limb for six months, aggravated for 10 days. Diagnosis: lumbar intervertebral disc herniation. Surgical procedure: posterior median incision with multi-cleft muscle gap access for nerve root canal decompression, intervertebral implant fusion, and internal fixation with arch nail rod system. The operative time was 100 min, intraoperative bleeding was 150 ml, total postoperative drainage was 50 ml, drainage tube was removed from the floor at 1 d, and stitches were removed at 14 d. Preoperative CT Preoperative MRI Postoperative lateral radiograph Postoperative orthopantomogram 4. The paravertebral muscles are widely stripped and strongly stretched for a long time, resulting in edema and necrosis of the paravertebral muscles, weakening of the lumbar back muscles, and intractable low back pain; surgical trauma, bleeding, and serious destruction of the posterior stability structure; surgical incision is not easy to heal, and the incidence of cerebrospinal fluid leakage is high, and the incision does not heal or has a high infection rate. In 1968, Wiltse et al. proposed an approach via the multifidus and longest muscle gaps, but at that time, it was not emphasized and widely used in surgery for degenerative lumbar spine lesions because of its inadequate exposure of the spinous process and the vertebral plate, which could only reveal the articular and transverse processes and could not do extensive decompression of the spinal canal. The main reason for this is the misunderstanding of the traditional concept of spinal stenosis, in which the stenotic canal is mainly understood and located in the "central spinal canal", resulting in the term "spinal stenosis" being widely used both as a diagnostic term and as a conceptual term for pathological anatomy. The term "stenosis" is widely used both as a diagnostic term and as a conceptual term for pathological anatomy. Based on this understanding, laminectomy and enlargement of the spinal canal is naturally the most effective decompression procedure. However, from a pathologic-anatomical point of view, most lumbar spinal stenosis is stage-specific and the entire lumbar spinal canal is rarely stenosed. The junction between the two adjacent vertebral segments, i.e., the superior and inferior vertebral segments, including the articular eminence, intervertebral disc, ligamentum flavum, and the upper and lower lamina junction, has motor and stabilizing functions and is the most prone to degeneration. The true level of spinal stenosis is concentrated slightly above the articular eminence, disc and plate junction. The most obvious pathological changes in degenerative lesions of the lumbar spine are the coalescence of the articular eminence, hypertrophy of the ligamentum flavum, protrusion of the intervertebral disc, and hyperplasia of the vertebral endplates, leading to abnormalities in the volume of the lumbar spinal canal, nerve root canal, lateral saphenous fossa, or intervertebral foramen, and secondary narrowing of the neural canal, resulting in nerve compression, which causes the corresponding symptoms and signs. Therefore, extensive laminectomy and synovectomy are not really meaningful in surgery for lumbar degenerative lesions, and the most effective decompression method is to remove the medial edge or all of the hyperplastic synovium, the hypertrophic ligamentum flavum, the herniated disc and the hyperplastic lamina, and Wiltse's interosseous approach to reveal the scope of decompression is sufficient! In our clinical work, we have learned that the advantages of minimally invasive surgery for lumbar degenerative lesions with a multifracture muscle gap approach are: (1) the muscle gap approach has less blood supply distribution, no cutting or stripping of muscles, and less intraoperative bleeding; (2) easy exposure, simple anatomy, direct access to the surgical site, and direct exposure of the nerve root canal for decompression; (3) direct access to the small joints and transverse processes, which facilitates determination of the pedicle nail entry point and abduction (3) Direct access to the small joints and transverse processes, easy to determine the pinning point and abduction angle of the arch nail, no need to pull the paravertebral muscles, avoiding muscle injury and edema, no decrease in the strength of the lumbar muscles after surgery, which is conducive to early postoperative activities; (4) Close attachment of the muscles after suturing the lumbar dorsal fascia, the muscle gap can be completely closed, leaving no dead space, less blood leakage from the incision and less drainage after surgery, reducing the infection rate. (5) The integrity of the anatomical structure of the spine is maximally preserved, ensuring the stability of the posterior column of the spine and effectively avoiding medically induced lumbar instability and intractable low back pain; (6) The approach is particularly suitable for revision surgery of the spine. Its shortcomings are: (1) it is not suitable for three and more stages of stenosis, and the operation time is too long; (2) it is not suitable for patients with particularly bony spinal stenosis, and such patients need extensive laminar decompression; (3) it is suitable for Ⅰ and Ⅱ degrees of lumbar spondylolisthesis, but not for Ⅲ and more degrees of spondylolisthesis, and it is difficult to reset in such patients.