Spinal Shortening Surgery for Lumbosacral Nerve Bowstring Disease: A Surgical Technique

Lumbosacral nerve bowstring disease (LNBD) is a syndrome comprising a series of neurological symptoms caused by high axial tension of the lumbosacral nerve due to congenital, iatrogenic, and other factors. Here, we introduce a surgical technique for the treatment of LNBD through spinal shortening surgery.

Lumbosacral nerve bowstring disease (LNBD) is a syndrome of neurological symptoms caused by differences in the development speed of lumbosacral bone tissue and nerve tissue, which result in a longitudinal stretch of the slow-growing nerve tissue. LNBD is usually caused by congenital factors and accompanied by other lumbosacral diseases, such as lumbar spinal stenosis, lumbar spondylolisthesis, and iatrogenic factors. The main symptoms of LNBD are lower extremity neurological symptoms and fecal dysfunction. The conservative treatment of LNBD includes rest, functional exercise, and drug therapy, but it usually fails to achieve satisfactory clinical results. Few studies have reported on the surgical treatment of LNBD. In this study, we used posterior lumbar interbody fusion (PLIF) to shorten the spine (0.6-0.8mm/segment). This reduced the axial tension of the lumbosacral nerves and relieved the patient's neurological symptoms. We report on the case of a 45 year old male patient whose main symptoms were left lower extremity pain, decreased muscle strength, and hypoesthesia. The above symptoms were significantly relieved 6 months after surgery.

Lumbosacral nerve bowstring disease (LNBD) comprises a series of symptoms associated with nerve damage. LNBD is caused by increased lumbosacral nerve tension due to congenital developmental factors, iatrogenic injury, and a variety of other reasons¹. LNBD can also be accompanied by other lumbosacral diseases, such as lumbar disc herniation, spinal stenosis, lumbar spondylolisthesis, and scoliosis². Previous studies have found that the lengthening of the nerve roots is accompanied by a decrease in their cross-sectional areas^3,4. Electrophysiological monitoring has shown that the nerve conduction velocity gradually decreases and is eventually completely blocked as tension on the nerve root increases⁵. The physiological curvature of the human lumbosacral region is like a bow. Due to the increase in axial tension, the patient's dural sac and nerve roots resemble a bowstring; therefore, LNBD is also called bowstring disease¹. The symptoms of lower back and leg pain worsen over time due to the increase in tension.

Physiological curvature of the spine caused by spinal surgery is also an important cause of LNBD^6,7. Due to the lack of typical clinical symptoms and imaging manifestations for LNBD, it is underdiagnosed. According to the pathogenesis, LNBD can be classified into developmental bowstring disease and degenerative bowstring disease¹. The disease usually has two peaks of incidence. The first peak is in adolescent children because patients at this age are in a stage of rapid growth and development, and the bone tissue of the spine grows faster than the nerve tissue, causing the nerve tissue to be stretched and the patient to become symptomatic. These patients usually present with varying degrees of lower back pain and lower extremity pain^8,9. The second peak is in the elderly, when LNBD is usually accompanied by other lumbosacral diseases. Lumbosacral diseases (such as scoliosis, lumbar spondylolisthesis, or lumbar disc herniation) lead to increased nerve root tension, which may also be the cause of LNBD in the elderly¹⁰. Often, LNBD is overlooked, and only the lumbosacral diseases are treated. The symptoms in these patients are usually more severe and manifest as intractable lower back pain, foot drop, and bowel dysfunction¹¹.

Conservative treatments for LNBD include drug therapy, bed rest, and physiotherapy ¹. However, none of these treatment methods can fundamentally solve the high-tension state of the stretched nerve and usually cannot achieve the expected therapeutic effect¹². Surgery is a promising and effective treatment for LNBD. Several osteotomies have been reported to shorten the spine in the treatment of LNBD, such as vertebrectomy and pedicle subtraction osteotomy (PSO)^13,14,15. Posterior lumbar interbody fusion (PLIF) is a commonly used surgical technique for spinal surgeons and can be applied to different spinal diseases¹⁶. Compared with other surgical techniques, this technique is relatively simple, and most spinal surgeons can master this technique skillfully. PLIF has higher security and reduces the risk of damaging other tissues¹⁷.

Here, we introduce a surgical technique for the treatment of LNBD by modified PLIF. We report on the case of 45 year old male patient whose main symptoms were left lower extremity pain, decreased muscle strength, and hypoesthesia.

The protocol was approved by the Ethics Committee of the Third Hospital of Hebei Medical University. Informed consent was obtained from the patient before inclusion in the study.

1. Inclusion and exclusion criteria

1. Select patients according to the following inclusion criteria and exclusion criteria.
   1. Inclusion criteria: 1) LNBD patients with severe neurological symptoms; 2) patients with complete clinical data, including basic data, treatment records, and imaging data.
   2. Exclusion criteria: 1) neurological symptoms due to a herniated lumbar disc; 2) more complicated surgical techniques due to fracture, degeneration, spondylolisthesis, infection, and other factors.
2. Ensure that the patients receive a complete physical examination and imaging examination before surgery, and confirm that the patients have no surgical contraindications. When everything is ready, arrange for the surgery for the patient.

2. Preoperative and surgical procedures

1. Before providing surgical anesthesia, reconfirm the patient information.
2. After general anesthesia with endotracheal intubation, place the patient in a prone position, and employ a frame to reduce the pressure in the patient's abdominal cavity. Use iodophor to sterilize the surgical area, and cover the patient with sterile sheets.
3. Use a routine posterior approach through a midline 15 cm incision at the operation site.
4. Use a scalpel to incise the skin and each layer of tissue in turn, and separate the tissues around the spinous processes, vertebral laminas, and articular processes.
5. Expose the L3, L4, and L5 spinous processes, lamina, and articular processes with the help of retractors. Pay attention to hemostasis during this process.
6. Take the apex of the triangular groove between the lateral edge of the vertebral lamina and the transverse process as the nail entry point.
7. According to the angle of the pedicle shown in the imaging data, place the pedicle screws into the pedicle and vertebral body under the guidance of the pedicle probe. Insert six pedicle screws into L3, L4, and L5.
8. Excise the spinous processes, lamina, and articular processes of the corresponding segments with bone knives and rongeurs. Carefully peel off other tissues in the spinal canal around the dural sac, such as ligaments and fat, to eliminate the factors oppressing the dural sac and nerve root.
   NOTE: Do not damage the nerve roots and dural sac during this process.
9. After exposing the L3/L4 and L4/L5 discs, use a scalpel and a rongeur to remove the surface fibrous ring, and use a curet to remove the nucleus pulposus and the fibrous ring in front of the intervertebral disc space. Finally, use a disc shaver of the appropriate size to smooth the irregular surface of the cartilage endplate.
10. Fill the autologous bone from the resected spinous processes, transverse processes, and vertebral laminas of the patient into cages of appropriate sizes, and place the cages in the middle of the intervertebral spaces. Place the remaining autologous bone around the cages. If the autologous bone is insufficient, take part of the patient's iliac bone.
11. Bend the rods to adapt to the inclination of the pedicle screws, place the rods in the groove of the pedicle screws on each side, and use the nuts to closely connect the rods and the pedicle screws. Confirm the correct position of rods and the pedicle screws by intraoperative X-ray examination.
12. Use compressors to reduce the distance between the screws and shorten the spine. Ensure that the shortened distance allows the cage to be firmly fixed in the intervertebral space. Lock all the nuts. Check the tension of the nerve roots in the intervertebral foramen to ensure that the nerve roots are not compressed.
13. Place a silicone drainage tube (F18) at the distal end of the incision site, and fix the drainage tube with a suture. Flush the surgical field with a large amount of saline. Fully stop the bleeding with bipolar electrocoagulation. Suture each layer of tissue and skin in turn. Finally, bandage the wound with sterile dressings.

3. Postoperative treatment

1. Give the patient the first-generation cephalosporin treatment according to the guidelines within 24 h after surgery.
2. Two to three days after the surgery, when the drainage volume is less than 50 mL, remove the drainage tube.
3. If the patient has no contraindications, use low-molecular-weight heparin (4,250 IU, subcutaneous injection every day) to prevent deep vein thrombosis until discharge.
4. If venous thromboembolism is not detected by postoperative deep vein ultrasound scanning, allow the patient to walk with the assistance of a thoracolumbosacral orthosis 3 days after the surgery. Use the orthosis for at least 3 months.

4. Follow-up of patients

1. Instruct all patients to have outpatient follow-ups 1-2 months and 6 months after the surgery, and ensure that they receive a physical examination (mainly sensory and muscle strength) and radiological examination (X-ray, CT, and MRI).

A 45 year old male patient complaining of pain and numbness in the left lower extremity for half a year was referred to the Spine Surgery Department of the Third Hospital of Hebei Medical University. Informed consent was obtained from the patient before using related information. This patient's main symptoms worsened with activity and decreased with rest. The patient received medication for 5 months without significant relief of the symptoms.

This patient underwent detailed physical and radiological examinations before surgery. The surgeons found that the patient had slightly limited mobility of the lumbar spine, decreased muscle strength of the left extensor hallucis longus (grade 3), and decreased sensation in the skin of the left calf and foot. The patient's visual analogue scale (VAS)¹⁸ score was 5 and Japanese Orthopaedic Association Score (JOA)¹⁹ was 19. The neurophysiological examination revealed extensive neurogenic lesions in this patient's lower extremities, with incomplete damage to the L4-S1 innervation area, which was more severe on the left side. The imaging examinations are shown in Figure 1.

This patient underwent modified PLIF surgery (L3/4 and L4/5) to shorten the spine. The patient received postoperative X-rays to determine the position of the internal fixation, as shown in Figure 2.

The patient was re-examined at the outpatient clinic more than 2 months after the surgery and underwent an X-ray examination. The patient's pain was significantly relieved compared with before surgery, and the VAS score was 3. The muscle strength of the left extensor hallucis longus was grade 4 and improved compared to the preoperative examination, as did the skin sensation. The JOA score was 23. The X-ray results are displayed in Figure 3.

The patient underwent an outpatient follow-up examination 6 months after the surgery and underwent an X-ray and MRI examination. The patient's VAS score was 2, and the JOA score was 24. The imaging results are shown in Figure 4.

By 6 months after the surgery, the patient's function had recovered to a nearly normal level. The functional improvement of this patient during the follow-up period can be seen in Table 1. The patient's surgery was successful. The patient's muscle strength increased from grade 3 to grade 4, the JOA score improved, and their pain was relieved. There was no problem with internal fixation during the follow-up.

Table 1: The improvement in the patient's function.

Figure 1: Results of the preoperative imaging examination. (A,B) The patient's preoperative lumbar spine X-ray showed no obvious fracture or dislocation. The physiological curvature of the lumbar spine was relatively straight. (C,D) The patient's preoperative lumbar spine CT showed that the L5/S1 had intervertebral disc herniation to the right and posterior and the dural sac was compressed. The remaining segments showed no obvious intervertebral disc herniation. (E,F) The patient's preoperative MRI showed that the signal of the patient's intervertebral disc changed significantly, suggesting the existence of intervertebral disc degeneration. The nerves in the spinal canal were close to the posterior wall of the spinal canal, suggesting that the nerves had high tension. Please click here to view a larger version of this figure.

Figure 2: Results of the postoperative X-ray. The patient's postoperative lumbar spine X-ray showed the cages and pedicle screw placement. The physiological curvature of the lumbar spine was improved compared with that before surgery. Please click here to view a larger version of this figure.

Figure 3: X-ray results 2 months after the surgery. The patient underwent a lumbar X-ray examination 2 months after surgery. No changes in the positions of the cages and pedicle screws were found. Please click here to view a larger version of this figure.

Figure 4: Results of the imaging examination 6 months after the surgery. The patient received a lumbar X-ray and MRI examination 6 months after surgery. (A,B) No changes in the positions of the cages and pedicle screws were found. (C,D) Nerve tension was reduced compared to preoperatively. Please click here to view a larger version of this figure.

LNBD comprises a series of neurological symptoms caused by congenital or iatrogenic factors that lead to the traction of the lumbosacral nerve and excessive axial tension¹. The clinical symptoms of LNBD are lower extremity neurological symptoms, which mainly manifest as pain, numbness, and weakness of the lower extremities. Severe patients may have perineal numbness and fecal dysfunction. The imaging of LNBD generally shows no extraneural tissue localization or compression. Nerve root sedimentation signs (grey dots inside the white circle represent floating cauda equina, which constitute a positive nerve root sedimentation sign) can be seen on MRI in some patients. Increased nerve root tension can also be found during surgery²⁰.

The typical surgical treatment for LNBD involves shortening the length of the spine to a certain extent by removing part of the spinal structure, including the intervertebral disc, which is part of the vertebral body and posterior ligament and bone tissue. The aim of this treatment is to decrease the axial tension of the nerve and restore the natural state of the nerve roots²¹. The surgical technique reported in this study achieves the purpose of shortening the spine by the discectomy of the L3/4 and L4/5 segments and removing part of the posterior spinal tissue. Discectomy at each level can shorten the spine by 0.6-0.8 mm.

The critical step in the surgical technique is the necessary resection of the articular process at the corresponding level to ensure adequate compression of the intervertebral space. Another important step is that after compressing the intervertebral space, the surgeon must examine the intervertebral foramen to make sure that the nerve roots in the intervertebral foramen are not compressed by the intervertebral space.

Vertebrectomy is also a commonly used spinal osteotomy technique that can shorten the spine^22,23. Miyakoshi et al. reported another spinal shortening surgery¹³; specifically, they achieved the effect of shortening the spine by the vertebrectomy of L1 and part of the tissue behind T12-L2 and fixing by pedicle screws. The advantage of this surgical technique is that T12-L2 is more superficial, making it easier for the surgeon to expose the surgical site. At the same time, the internal fixation of this part has little effect on the normal physiological curvature of the spine, because the curvature of this segment itself is small. However, since this technique involves performing a larger osteotomy, it may cause more blood loss compared to the surgical technique we report here.

PSO is also a commonly used spinal orthopedic surgical technique. Compared with vertebrectomy, PSO has fewer osteotomies and less blood loss, a shorter operative time, and fewer surgeon requirements²⁴. Aldave et al. reported a spinal shortening surgical technique. They performed a PSO centered around L1 with fusion¹⁵. Huang et al. also reported a spinal shortening surgery around T6 for patients with congenital scoliosis²⁵. These two surgical techniques have different osteotomy positions, but both can achieve the effect of shortening the spine and alleviating the symptoms of nerve injury. Although PSO reduces the number of osteotomies, it leads to local iatrogenic protrusion²⁶.

Compared with the above surgical techniques, the surgical techniques reported in this study have the following potential advantages. By shortening the spine through interbody fusion, this technique avoids excessive osteotomy and reduces the risk of osteotomy complications (such as iatrogenic spinal protrusion, nerve injury, etc.). Additionally, this technique causes less bleeding and shortens the operation time. Herniated intervertebral discs can be treated simultaneously by discectomy^27,28,29. Since this surgical technique has not been applied to the treatment of LNBD before, we still need to further explore the advantages, safety, and disadvantages of this technique in clinical situations. We also need to further conduct a large sample size cohort study to compare this technology with other surgical techniques and continuously improve this technology.

This study shows a safe and simple surgical technique to achieve spinal shortening by discectomy and interbody fusion. This technique can effectively relieve neurological symptoms and improve the quality of life of patients with LNBD.

The authors have nothing to disclose.

No funding was used in this study.