Analysis of injury and pain scores during fusion surgery for multisegmental lumbar spinal stenosis in elderly patients

Introduction

Lumbar spinal stenosis (LSS) refers to the narrowing of the anteroposterior and transverse diameters of the spinal canal, resulting in compression of the dural sac, spinal cord, or nerve roots, thus leading to a series of neurological disorders [6]. The disease is mostly caused by lumbar degenerative diseases, such as intervertebral disc degeneration, vertebral facet joint hyperplasia, hypertrophy and cohesion, ligamentum flavum hypertrophy and ossification, which can lead to different degrees of lumbar spinal stenosis. Lumbar spinal stenosis occurs in the elderly. Lumbar spinal stenosis is the leading cause of spinal disease requiring surgery in patients over 65 years of age [18]. Therefore, it is urgent to find an effective treatment for the elderly.
In recent years, the incidence rate of intervertebral canal stenosis has been increasing, which has a serious impact on the quality of life of the middle-aged and elderly [13]. When conservative treatment fails, patients are often referred for surgery. The common surgical treatment methods are traditional open laminectomy, lumbar fusion and interspinous device. In the above common clinical treatment methods, clinical evidence has shown that traditional open laminectomy has the disadvantages of large trauma, more intraoperative bleeding and postoperative paravertebral muscle weakness or atrophy [12]. As for the interspinous device, although there is evidence that patients may have clinical benefits [17], due to the insufficient sample size, large-scale trials are still needed to supplement the evidence.
The concept of interbody fusion was first proposed by Cloward [2], and then Lin improved it [14]. This treatment method has been increasingly popular in the clinic [26]. Lumbar interbody fusion (LIF) has excellent fatigue resistance and fusion rate [29], which is considered to be the first choice for the treatment of lumbar degenerative diseases to reconstruct lumbar stability. The posterior lumbar interbody fusion (PLIF) is a classic method, which is recognized as the gold standard for the treatment of LSS [4]. Posterolateral fusion (PLF) is also a common choice among various techniques that can be used to treat lumbar spondylolisthesis. The advantages of this method are that it is relatively simple and quick, does not require disc management, has less bleeding, and reduces the possibility of the spinal cord and nerve root injury. But its disadvantages are also obvious [10]: in the process of bone grafting, the treatment of the bone graft bed is relatively difficult. The area where the graft is performed is on the tension side of the spine rather than on the pressure side, which is likely to result in a fusion failure. Intervertebral fusion is another effective treatment of choice for symptomatic lumbar instabilities. The inter-vertebral fusion has the advantage of a high fusion rate and high safety, and there are also shortcomings, such as difficulty and high treatment costs [19].
The purpose of our study is to observe the excellent effect of fusion while reducing local trauma and postoperative pain response and to analyse and summarize the operation methods of bone graft fusion.

Material and methods

General information
Data were collected from 173 elderly patients with lumbar spinal stenosis admitted to our department from 2013 to 2019. The patients were divided into groups based on the type of fusion operation received: the posterolateral fusion group (group P) and the intervertebral fusion group (group I). Patients are further divided into groups according to the number of fusion segments: 2-segment group (P2 and I2 groups), 3-segment group (P3 and I3 groups), and 4-segment group (P4 and I4 groups). This research has been approved by the institutional review board (IRB) of the authors.

Inclusion and exclusion criteria
Surgical indications included: 1) patients diagnosed with multi-segment lumbar spinal stenosis and lumbar spine instability before surgery or segments that may be unstable after surgery, 2) difficulty walking and intermittent claudication, 3) recurrent low back pain impeding normal life, 4) the appearance of cauda equina neurosis symptoms, and 5) the failure of 3 months of conservative treatment. Exclusion criteria were: 1) cervical or thoracic spinal stenosis diagnoses, 2) obvious abnormal function of lower limb joints, 3) infection or tumour in the spinal canal, 4) associated varicose veins, vasculitis, etc., and 5) serious medical diseases not suitable for surgical operation.

Surgical methods
All surgeries were performed by the same group of senior doctors. In all groups, general intravenous combined anaesthesia was used for anaesthesia, the posterior midline approach was used in surgery, and pedicle screw internal fixation was performed. During the operation, all or part of the vertebral lamina and ligamentum flavum within the narrow range were resected. In general, the volume of the spinal canal at the narrow segment became smaller and local tension increased. It was necessary to pay attention to the protection of the dura sac while it was exposed. The nerve root was found and fully decompressed. The end of decompression was marked by the absence of mechanical compression on the nerve root and the ease with which it was moved.

Preparation of autogenous bone
The autogenous bone used for the graft was obtained from the spinous process or lamina excised during the operation. The soft tissue or cartilage on the surface of the bone was removed, and a piece approximately 0.1 cm3 in size was cut for use. Prolonged compression of skin and muscle tissue should be avoided as much as possible. Haemostasis should be thorough during the operation and bipolar coagulation should be used as long as possible.

Intervertebral fusion group (Group I)
The nerve root was gently led toward the inside and was properly protected. The inferior articular process of the upper vertebral body, or the superior articular process of the lower vertebral body, were removed according to the surgical requirements. The lateral recess was enlarged. The intervertebral disc and cartilage endplate were removed while the subchondral bone was protected from damage. The fusion cages used were made of hollow polyether ether ketone (PEEK) material. Sufficient amounts of autogenous bone graft were used to fill the anterior intervertebral space and the fusion cage. The PEEK fusion cage is a single piece and is generally placed diagonally forward on the side with severe symptoms or on the concave side with degenerative scoliosis.

Posterolateral fusion group (Group P)
The intervertebral joints were retained, and the lateral recesses were expanded stealthily in posterolateral fusion operations. The posterior side of the transverse processes was exposed and decorticated with a ball drill. The intervertebral facet articular cartilage was destroyed. Autogenous bone grafts were placed on the surfaces of the transverse processes and in the spaces of the intervertebral joints on both sides.

Postoperative management
The patients were treated with antibiotics for 3-5 days and 10 mg dexamethasone for 3 days.
The patients were treated with neuronutrition drugs, dehydrating agent and hormone according to the condition (hormone and dehydrating agent were routinely used, including dexamethasone sodium phosphate injection (10 mg, IVGTT, qd, 3d) and mannitol (125 ml, IVGTT, bid, 3d) or furosemide (40-60 mg, IVGTT, bid, 3d). In case of decreased spinal cord function, methylprednisolone (500-1000 mg, IVGTT) rapid impact can be considered. Neurotrophic drugs mainly include ganglioside, nerve growth factor, adenosine cobalamin, etc., mainly considering the economics of drugs and the acceptance ability of patients, not routine application). The patients were re-examined in the anteroposterior and lateral position of lumbar vertebra after operation, and then they were put on the brace to move down
the ground. They continued to wear the brace when they moved down the ground after discharge. During the period, they actively carried out the functional exercise of lumbar and dorsal muscles.

Efficacy evaluation indicators
The operative time, intraoperative blood loss, blood transfusion volume, and postoperative drainage volume were recorded. Postoperative wound healing and the numeric rating scale (NRS) for pain preoperatively, at 2 weeks, 3 months, and at the final follow-up after surgery were also recorded. The NRS was composed of 11 numbers (0 through 10), with 0 indicating no pain. The larger the number was, the stronger the pain, with 10 being the most severe. The Oswestry disability index (ODI) and the Japanese Orthopedic Association (JOA) scores were recorded before surgery and at the final postoperative follow-up [24].
Main outcome measures include operative time, intraoperative blood loss, blood transfusion, postoperative drainage, postoperative wound healing, and NRS score before surgery, 2 weeks, 3 months after surgery, and at the end of follow-up; secondary outcome measures include ODI score and JOA score before and at the end of follow-up.

Statistical analysis
Measurement data were presented as x ± SD. SPSS 19.0 was used for statistical analysis. A c2-test was used for general data (gender, age, and lesion segment) to determine whether there was comparability between the groups. An independent sample t-test was used for the mean comparison between the groups. The difference significance level was p < 0.05.

Results

Subject characteristics
There were 84 patients in group P (32 males and 52 females, with an age range of 60 to 83 years old and an average age of 67.63 ±5.86 years old) and 89 patients in group I (40 males and 49 females, with an age range of 60 to 84 years old and an average age of 67.05 ±5.47 years old). These two groups were subdivided into the 2-segment group (group P2 and group I2), the 3-segment group (group P3 and group I3), and the 4-segment group (group P4 and group I4) according to the number of segments fused in surgery. The number of cases in the P2, P3 and P4 groups were 25, 33 and 26, respectively. The number of cases in groups I2, I3 and I4 were 52, 29 and 8, respectively. There was no significant difference in the statistical analysis of general information, such as gender, age, and surgical segments of the patients, so it was comparable.

Comparison of related indexes in the perioperative period
As is demonstrated in Table I, the operative time of groups P2 and P3 was lower than in groups I2 and I3 (p < 0.05), and the difference between group P4 and group I4 was not statistically significant. Intraoperative blood loss in group P2 was less than in group I2 (p < 0.05), and there were no statistically significant differences between groups P3 and I3 or between groups P4 and I4. The blood transfusion volume of groups P2 and P3 was less than in groups I2 and I3, respectively (p < 0.05), and the difference between group P4 and group I4 was not statistically significant. The postoperative drainage volume of group I4 was less than in group P4 (p < 0.05), and the differences between groups I2 and P2 and groups I3 and P3 were not statistically significant.

Comparison of functional indicators and fusion before and after operation
There were no perioperative deaths. In the follow-up period of 13 to 38 months (an average of 15.8 months), there were 44/173 cases (25.4%) with incision and surrounding soft tissue complications, including 32/84 cases (37.9%) in group P and 12/89 cases (13.3%) in group I (Figs. 1, 2). There were significant differences between the two groups (p < 0.05). These complications mainly included superficial incision skin ulcers (8 cases), subcutaneous dropsy (11 cases), skin blackening and hardening (10 cases), and pain around the incision (15 cases). Debridement and dressing change should be given for treatment of these complications. No bacterial infection was found in the incision tissue or exudate cultures during hospitalization. Acute pain around the incision was treated with nerve blocks. As shown in Table II, postoperative NRS pain scores were significantly lower than those before surgery (p < 0.05). At 2 weeks and 3 months after surgery, the NRS scores of groups P2 and P3 were lower than those of groups I2 and I3 (p < 0.05), and those of group P4 were higher than those of group I4 (p < 0.05).
There were significant differences in ODI and JOA scores preoperatively and postoperatively (p < 0.05) but there were no statistically significant differences between group P and group I at the end of follow-up (Table III). This may indicate that the two fusion methods have no direct impact on the final surgical effect.

Discussion

In older populations, lumbar spinal stenosis can cause obvious symptoms. The general symptoms of lumbar spinal stenosis are complicated in nature and long in duration, while medically there are more affected segments, slower healing times, and limited surgical opportunities with these patients. Most patients require surgical intervention, especially when non-operative treatment has failed for 6 months or more, or if there is nerve damage progression or cauda equina syndrome. Operative treatment is superior to non-operative treatment in pain reduction and in improved lower limb functional recovery [8,16,21,28]. Decompression can effectively remove the degenerative bone or fibrous tissues that lead to spinal canal stenosis, which is key to the success of the operation.
Rigid internal fixation and correct selection of bone graft materials can improve the fusion rate
Internal fixation provides immediate stability of the spine. Fusion can maintain stability of the spine for a long time and may help prevent any recurrence of spinal stenosis [1]. On the premise of excluding osteoporosis, a longer bed rest time can subjectively ensure the effective braking of patients and create conditions for bony fusion. It should be noted that moderate movement of limbs should be closely combined with bed rest.
At present, the most common methods of posterior fusion include posterolateral fusion, PLIF, and TLIF [15,20]. It is generally believed that the fusion efficiency in the intervertebral method is higher than in the posterolateral method when the size and mass of the bone graft is suitable enough [25]. A major determinant of successful fusion is the bone graft [22]. The materials of bone fusion include autogenous bone [9], bone marrow extract, etc. Autologous bone has good tissue compatibility and can reduce the cost of patients [27]. For all patients, the autogenous bone taken during decompression was used for bone transplantation. The autogenous bone used for graft was obtained from the spinous process or vertebral lamina removed during the operation. This process not only avoided the complications of iliac bone extraction, but also improved the economic benefits [3].

The necessity of postoperative analgesia guidance
The operative difficulties of the posterolateral method are relatively lower than in the intervertebral method. The posterolateral method is also a common option for elderly patients who are less active and show an increased trend toward spontaneous spinal fusion [15].
Currently, there is little literature about operative injuries and their effect on postoperative pain recovery with different fusion segments and methods. The results discussed in this article show that the degree of damage from posterolateral fusion is less than from intervertebral fusion when two or three segments are operated on. In a four-segment operation, the intraoperative blood loss and blood transfusion volume of the two fusion methods are similar, but the postoperative drainage volume from the posterolateral fusion is higher than that of that of the intervertebral fusion. This suggests that the degree of tissue damage from posterolateral fusion may be more severe in a four-segment operation. The process of operation may be responsible for these findings. In the intervertebral fusion procedure, more time is spent on the removal of articular processes, on the preparation of intervertebral spaces, and on haemostasis of the venous plexus.
In the posterolateral fusion, articular processes must be retained as much as possible, so more time is spent on nerve root decompression and exposure of more surface area of the transverse processes for bone grafting. In the posterolateral fusion procedure, there can be more damage to the paravertebral muscles, and increased blood loss when dealing with articular processes or transverse processes, which increases as the number of segments increases [7]. Posterolateral fusion procedures are more likely to cause obvious paraspinal muscle injuries, leading to increased muscle atrophy or necrosis, as well as intractable postoperative lower back pain [23]. These findings are reflected in our analysis. It is necessary to explain these issues to patients and instruct them on proper postoperative analgesic treatment.
At 2 weeks and 3 months postoperatively, pain improvement was greater in patients who underwent two- or three-segment posterolateral fusion. At these same time frames, pain improvement was greater in patients who received 4-segment intervertebral fusion. This may be due to the degree of local tissue damage sustained during the operation. Although the fusion method does not determine the final operative effect [30], we can reduce the degree of tissue damage and control postoperative pain through choosing different fusion methods according to the required number of fusion segments. There is no doubt that effective pain control will increase the safety of surgery for elderly patients. The demand for pain control is often required more than functional improvement in elderly patients because their activity is generally reduced [11]. The less damage that occurs during the operation means less pain and greater satisfaction postoperatively [5]. There are many methods to control intraoperative damage, including minimizing the scope of surgery, using bilateral simultaneous dissection and fixation, using an osteotome or ultrasonic knife to remove the lamina or articular process, and using an intravenous drip of tranexamic acid. These methods can shorten the operation time and reduce the amount of blood loss, ultimately reducing the degree of damage.

Conclusions

In conclusion, both intervertebral fusion and posterolateral fusion have good therapeutic effects, and different fusion methods can be selected based on the number of fusion segments. Posterolateral fusion should be used when 3 or less levels of surgery are required. When four-level surgery is required, interbody fusion should be used.

Ethics approval and consent to participate

This study was conducted in accordance with the Declaration of Helsinki and approved by the ethics committee of the 3rd medical centre of Chinese PLA General Hospital. All patients signed informed consent.

Availability of data and materials

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Disclosure

The authors report no conflict of interest.

References