Minimally invasive lumbar decompression and fusion surgery

1) Minimally invasive lumbar hemilaminectomy

One important principle of minimally invasive lumbar decompression is to preserve the tendinous insertion point of the multifidus muscle on the spinous process. In traditional total laminectomy, the spinous process is removed and the multifidus muscle is pulled to both sides. When closing the wound, the starting point of the multifidus muscle cannot be repaired to the spinous process. However, using semi laminectomy technique, complete spinal canal decompression can be performed on one side through the working channel. Tilting the work channel towards the back reveals the lower part of the spinous process and the contralateral vertebral plate. Gently press down on the dural sac to remove the ligamentum flavum and the contralateral superior articular process, thus completing the classic unilateral approach for bilateral decompression. The anatomical structure of the upper lumbar spine is different from that of the lower lumbar spine. At L3 and above levels, the vertebral plate between the spinous process and the articular process is very narrow. If a unilateral approach is used, in order to decompress the ipsilateral recess, more excision of the ipsilateral upper articular process is necessary. Another option is to use a bilateral approach technique, which involves decompression of the right lateral recess through left hemilaminectomy, and vice versa. A study used this bilateral approach technique to decompress 7 segments of 4 patients, with a total average surgical time of 32 minutes per segment, an average blood loss of 75ml, and an average postoperative hospital stay of 1.2 days. All patients with preoperative neurogenic claudication disappeared without any complications.

Multiple studies have evaluated the safety and effectiveness of minimally invasive posterior lumbar decompression. The learning curve of minimally invasive spinal surgery has received attention, and in the initial stages of some studies, its complication rate is relatively high. Ikuta reported their experience of using a unilateral approach for bilateral lumbar spinal decompression to treat lumbar spinal stenosis, with 38 out of 44 patients showing good short-term efficacy. The JOA scoring index improved by an average of 72%. The postoperative complications are lower, and compared with open surgery, the intraoperative blood loss is significantly reduced. The need for postoperative painkillers is significantly reduced, and the hospital stay is greatly shortened. There is a 25% complication rate, including 4 cases of dural tears, 3 cases of lower articular process fractures on the surgical approach side, 1 case of cauda equina syndrome requiring reoperation after surgery, and 1 case of epidural hematoma requiring reoperation.

In a prospective study by Yagi, 41 patients with lumbar spinal stenosis were randomly divided into two groups: one group (20 cases) underwent minimally invasive endoscopic decompression, and the other group (21 cases) underwent traditional laminectomy decompression, with an average follow-up of 18 months. Compared with the traditional laminectomy decompression surgery group, the minimally invasive surgery decompression group has a shorter average hospital stay, less blood loss, lower muscle isoenzyme levels of creatine kinase in the blood, lower VAS score for lower back pain one year after surgery, and faster recovery. 90% of patients in this group achieved satisfactory neurological decompression and symptom relief. No cases of postoperative spinal instability occurred. Castro used an 18mm working tube to perform endoscopic spinal canal decompression surgery on 55 patients with lumbar spinal stenosis. Through an average of 4 years of follow-up, 72% of patients achieved excellent or excellent results, and 68% of patients had subjective satisfaction as excellent. The ODI score decreased on average, and the VAS score index for leg pain decreased by 6.02 on average.

Asgarzadie and Khoo reported 48 cases of lumbar spinal stenosis treated with minimally invasive lumbar spinal decompression. Among them, 28 patients underwent single-segment decompression, while the other 20 underwent two-stage decompression. Compared with the control group, which underwent traditional open laminectomy, the minimally invasive group had lower average intraoperative bleeding (25 vs 193ml) and shorter hospital stay (36 vs 94 hours). 32 out of 48 patients were followed up for 4 years after surgery. Six months after surgery, the walking tolerance of all patients improved, and 80% of patients maintained it until an average of 38 months after surgery. During the follow-up period, the improvement in ODI score and SF-36 score was consistently maintained. In this group of cases, no complications of nerve damage occurred. For cases of degenerative lumbar spondylolisthesis, minimally invasive lumbar spinal decompression without fusion is also an effective method. Pao only performed minimally invasive lumbar spinal decompression on 13 cases of lumbar spinal stenosis combined with Ⅰ ° lumbar spondylolisthesis. All postoperative cases showed good clinical outcomes and no worsening of slippage. Sasai treated 23 cases of degenerative lumbar spondylolisthesis and 25 cases of degenerative lumbar spinal stenosis using unilateral and bilateral decompression techniques. After two years of follow-up, although the neurogenic intermittent claudication score and ODI score of the degenerative lumbar spondylolisthesis group were slightly worse, overall, the scores of the two groups were similar. Among the 23 cases of degenerative lumbar spondylolisthesis, 3 patients experienced an increase of ≥ 5% in postoperative slip. Kleeman applied decompression techniques that preserved the spinous process and interspinous ligament to treat 15 patients with lumbar spinal stenosis complicated with degenerative lumbar spondylolisthesis, with an average slip of 6.7mm. After an average of 4 years of follow-up, 2 patients experienced worsening of slip and symptoms, and 12 patients achieved good or excellent clinical outcomes.

2) Transforaminal lumbar interbody fusion surgery

Transforaminal lumbar interbody fusion (TLIF) was first proposed by Blume and Rojas, and promoted by Harms and Jeszensky. This technology evolved from Cloward's earliest proposal of posterior lumbar interbody fusion (PLIF). PLIF surgery requires extensive spinal decompression and bilateral nerve root traction to expose the lumbar intervertebral space, while TLIF surgery exposes the lumbar intervertebral space from one side through the intervertebral foramen. Therefore, compared with PLIF surgery that requires bilateral completion, TLIF surgery requires less traction on the neural structure. Another major advantage of TLIF surgery is that it allows for simultaneous posterior lumbar spinal decompression and anterior intervertebral fusion through a separate posterior incision.

Peng et al. compared the clinical and imaging results of minimally invasive TLIF surgery with traditional open TLIF surgery. The two-year follow-up results were similar, but the minimally invasive group initially had less postoperative pain, faster recovery, shorter hospital stay, and lower complications. Dhall et al. retrospectively compared 21 patients undergoing minimally invasive TLIF surgery and 21 patients undergoing traditional open TLIF surgery. After two years of follow-up, it was found that there was no difference in clinical outcomes between the two groups. However, the open group showed a significant increase in bleeding volume and prolonged hospital stay. Selznick et al. believe that minimally invasive TLIF surgery for revision cases is technically feasible and does not increase the reported increase in bleeding volume and neurological complications. However, the incidence of dural tears in revision cases is relatively high, so minimally invasive TLIF surgery for revision cases is challenging and should be performed by experienced minimally invasive surgeons.

A prospective study by Kasis et al. found that minimally invasive PLIF surgery with limited exposure can achieve better clinical outcomes and shorter hospital stay compared to traditional open surgery. He believes in the following 5 points: (1) preservation of the posterior structure of the spine; (2) Avoid peeling outward from the transverse process; (3) Complete resection of bilateral articular processes and joints; (4) Less complications of neurological damage; (5) Avoiding the use of autologous iliac bone grafting is closely related to the improvement of clinical outcomes.

Posterior endoscopic disc replacement surgery is expected to effectively replace partial fusion surgery in the near future. The currently available intervertebral disc replacement implants are designed for total replacement, but due to their large size, they cannot be inserted through posterior endoscopic surgery. Ray et al. developed a nucleus pulposus prosthesis that acts like a cushion to maintain intervertebral disc height. Currently, commercial nucleus pulposus implants are available. Raymedia et al. conducted a clinical study on nucleus pulposus implants in Germany in 1996, followed by another study in the United States in 1998. Raymedia et al. reported in 1999 that 101 patients underwent nucleus pulposus implantation. Although Raymedia et al. reported that 17 out of 101 patients experienced implant dislodgement or displacement, the vast majority of patients still achieved significant pain relief. To minimize the protrusion or displacement of nucleus pulposus implants and promote the development of minimally invasive intervertebral disc replacement technology, Advanced Biosurfaces (company) has developed a set of techniques that use polymers, transport balloons, balloon catheters, and polymer injection guns. This polymer is polyurethane, which can be polymerized in situ and has strong mechanical properties compared to industrial polymerized medical products. Balloon is composed of elastic material, which can expand significantly when polymer is injected into the filling, but the balloon is still very strong. Doctors can diffuse into the intervertebral space under controlled pressure. The company has conducted extensive in vivo and in vitro experiments to confirm the biocompatibility of the polymer in knee joint surgery. These studies suggest that there are very few leachable monomeric components. In a biomechanical study of a cadaveric intervertebral disc model, it was suggested that this substance can maintain the normal height and biomechanical properties of the intervertebral disc. At present, intervertebral disc nucleus pulposus implants can be inserted through a posterior open approach or a anterior laparoscopic approach. Ordway et al. also developed a disc replacement facility, called "hydrogel disc nucleus pulposus", which can be placed under endoscope. Recently, SaluMedica and others developed a kind of intervertebral disc prosthesis called Salubria, which is a strong and elastic hydrogel. According to current reports, it can reduce the herniation of intervertebral disc associated with nerve injury and low back pain. It is estimated that Salubria elastic disc replacement will be a major improvement in current fusion surgery, providing a prosthesis for the spine that better conforms to biomechanical characteristics and natural lumbar motion function.

3)  Minimally invasive anterior sacral approach axial intervertebral fusion surgery

From a biomechanical perspective, it is feasible to place fusion instruments near the spinal flexion axis while performing longitudinal compression of the vertebral body. However, its development is limited due to the lack of available instruments and grafts. Recently, according to a series of cadaveric and clinical studies, percutaneous access from the anterior sacral space to the lumbosacral region has been achieved to avoid exposing the anterior, posterior, and lateral structures of the spine, without damaging the posterior muscles, ligaments, and posterior vertebral components, nor requiring entry into the abdominal cavity or traction of blood vessels and internal organs. The application of biplane X-ray fluoroscopy technology provides a reliable guarantee for reducing intraoperative complications.

Cragg et al. first reported percutaneous anterior sacral approach (AxiaLIF) for L5/S1 intervertebral fusion: ① Make a small incision of about 4mm next to the coccyx incision, insert a guide needle under X-ray fluoroscopy navigation, and ascend along the anterior surface of the sacrum to reach the sacral 1 vertebral body, establishing a working channel; ② Remove L5/S1 intervertebral disc and scrape off the cartilage endplate, and graft bone into the intervertebral space; ③ Using a specially designed 3D titanium alloy device to implant and restore intervertebral disc height, achieving automatic decompression of the nerve root foramen; ④ Percutaneous fixation from the rear: Provides immediate 360 ° fixation for L5-S1. Clinical follow-up found that patients with L5 slippage and L5/S1 discogenic lower back pain treated with AxiaLIF showed significant improvement in VAS and ODI scores compared to preoperative treatment. They were discharged within 24 hours and returned to work within 15 days. There was no dislocation, loosening, or sacral deformity after transplantation, and the 12 month fusion rate was 88%. Marotta et al. conducted further clinical studies, and the results are encouraging. AxiaLIF is a safe and effective method. AxiaLIF requires specialized technology and anatomical knowledge of unconventional approaches, and doctors cannot reach the spinal canal or perform discectomy directly under direct vision, which is a challenge for surgeons.

4) Lateral lumbar interbody fusion surgery

Lumbar interbody fusion is a very common technique that has three advantages: (1) removing intervertebral disc tissue as a source of pain; (2) Extremely high fusion rate; (3) Restore the height of the lumbar intervertebral space and lumbar lordosis. Lumbar interbody fusion includes anterior interbody fusion, posterior interbody fusion, intervertebral foramen fusion or endoscopic lateral interbody fusion via extraperitoneal approach. There have been literature reports on minimally invasive retroperitoneal lateral interbody fusion through the lumbar muscle pathway. This technique is performed through the lumbar major muscle retroperitoneum under neurophysiological monitoring and fluoroscopy guidance, known as DLIF or XLIF minimally invasive lumbar fusion surgery.、

Due to the fact that the lumbar plexus is located in the posterior half of the psoas major muscle, limited dissection of the anterior 1/3 to anterior 1/2 area of the psoas major muscle can reduce the risk of nerve damage. In addition, intraoperative use of electromyography monitoring can also reduce the risk of nerve damage. When dealing with lumbar intervertebral spaces and implanting intervertebral fusion devices, it is important to avoid damaging the bone endplate and determine the direction of the fusion device through anteroposterior and lateral fluoroscopy. Intervertebral fusion can achieve indirect decompression of the intervertebral foramen by restoring the height of the neural foramen and the alignment of the spinal dislocation. Determine whether posterior fusion and decompression are still necessary based on each individual's condition. Knight et al. reported early complications in 43 female patients and 15 male patients who underwent minimally invasive lateral lumbar interbody fusion surgery: 6 cases experienced sensory anterior thigh pain after surgery, and 2 cases experienced lumbar L4 nerve root injury.、

Ozgur et al. reported 13 cases of single or multi segment lateral lumbar interbody fusion surgery. All patients experienced significant relief in postoperative pain, improved functional scores, and no occurrence of complications. Anand et al. reported 12 cases of simultaneous lateral and L5/S1 sacral interbody fusion. On average, 3.6 segments were fused, and the Cobb angle was corrected from preoperative 18.9 ° to postoperative 6.2 °. Pimenta et al. treated 39 patients with lateral fusion technology, with an average fusion stage of 2. The lateral curvature angle improved from an average of 18 ° before surgery to an average of 8 ° after surgery, and the lumbar lordosis angle increased from an average of 34 ° before surgery to an average of 41 ° after surgery. All cases can walk on the ground and have a regular diet on the day of surgery. The average blood loss is less than 100ml, the average surgical time is 200 minutes, and the average hospital stay is 2.2 days. The pain score and functional score both improved after surgery. Wright et al. reported 145 patients from multiple research institutions who underwent lateral lumbar interbody fusion surgery for lumbar degenerative disease. The fused segments range from 1 to 4 (72% being single segments, 22% being two segments, 5% being three segments, and 1% being four segments). Intervertebral support (86% PEEK material, 8% allograft, and 6% intervertebral fusion cage) was used in combination with bone morphogenetic protein (52%), demineralized bone matrix (39%), and autologous bone (9%), respectively. 20% of surgeries use intervertebral fusion alone, 23% use lateral screw rod system for assisted fixation, and 58% use posterior percutaneous pedicle screw system for assisted fixation. The average surgical time is 74 minutes and the average blood loss is 88ml. Two cases experienced transient damage to the reproductive femoral nerve, and five cases experienced temporary reduction in hip flexion strength. Most patients walk on the ground on the day after surgery and are discharged on the first day after surgery.

In terms of minimally invasive correction techniques for elderly lumbar degenerative scoliosis, Akbarnia et al. reported 13 patients who underwent multi segment lateral fusion treatment for lumbar scoliosis greater than 30 °. Three segments were fused on average, and all cases underwent posterior fusion and fixation simultaneously. After an average follow-up of 9 months, both lumbar scoliosis and lordosis showed substantial improvement. One case required revision surgery due to displacement of the intervertebral implant, while another case experienced incisional hernia at the site of the lateral fusion incision. Within 6 months after surgery, all cases experienced complete disappearance of weakness in the lumbar muscles or numbness in the thighs. Compared with before surgery, the short-term postoperative VAS score, SRS-22 score, and ODI score all improved. Anand et al. obtained similar results in their study of 12 patients, with fusion segments ranging from 2 to 8 (an average of 3.64) and an average bleeding volume of 163.89ml during anterior approach and 93.33ml during posterior percutaneous pedicle screw fixation. The average surgical time for anterior surgery is 4.01 hours, and the average time for posterior surgery is 3.99 hours. The Cobb angle improved from an average preoperative angle of 18.93 ° to an average postoperative angle of 6.19 °.

The simple use of intervertebral fusion cages for anterior fusion increases the incidence of false joint formation due to insufficient stability of the initial fusion segment. In recent years, posterior approach assisted fixation has been used to improve the rate of intervertebral fusion. Posterior percutaneous pedicle screw fixation (Sextant) is an effective method, which has the advantages of avoiding muscle damage during posterior surgery, reducing intraoperative blood loss, fast postoperative recovery, and improving fusion rate. However, the operation is complex. Percutaneous facet screw fixation (PFSF) is an effective method to assist ALIF, with low technical requirements and low cost, and quickly gained popularity. Kandziora et al. compared the biomechanical characteristics of PFSF, translaminar facet screw fixation, and pedicle screw fixation in vitro, and found that the biomechanical stability of lumbar facet screw fixation in the initial stage was similar to that of translaminar screw fixation, but slightly worse than that of pedicle screw fixation. Kang et al. reported that percutaneous translaminar articular process screw (TFS) fixation was performed under CT navigation, and all screws were accurately implanted without any complications. The follow-up results of a retrospective study by Jang et al. on PFSF+ALIF and TFS+ALIF showed no statistically significant difference in ODI and Macnab scores, surgical outcomes, and fusion rates. However, the former had higher surgical risks and safety. Percutaneous PFSF can be an effective supplement to posterior pedicle screw fixation surgery.