Lumbar spinal stenosis (LSS) is a progressive degenerative condition of the spinal canal that occurs due to the narrowing of the spinal canal in the lumbar region. This leads to compression of the neurovascular structures in this region. This is commonly found in the elderly population and is one of the important causes of lower back pain sometimes leading to functional disability [1].  The clinical symptoms of LSS include pain, numbness, and weakness in the lower extremities. These symptoms often get exacerbated by walking or standing and they are generally relieved by sitting or leaning forward [2]. As the age expectancy of the population is increasing, therefore, the prevalence of the older population and consequently prevalence of LSS is expected to increase which can be a significant health concern in the future.

The traditional management options for LSS include conservative management which incorporates physical therapy, medications, and epidural steroid injections. Surgical management includes treatments such as decompressive laminectomy [3]. In many cases, conservative management is effective however, some patients with severe progressive symptoms require surgical interventions to alleviate neural compression. Open surgical procedures are the traditional approach for treatment but are associated with significant risks which include prolonged recovery time, and postoperative complications. It may also lead to instability of the spinal column [4].  Recently minimally invasive surgical (MIS) techniques have been advocated as an alternative to traditional open surgery. This MIS approaches such as minimally invasive lumbar decompression (MILD) and endoscopic spinal surgery. These techniques aim to reduce tissue trauma and also preserve the stability of the spine [5]. These techniques depend on advanced imaging technologies and specialized instruments to access the spinal canal. The incisions in these techniques are smaller which results in faster recovery and shorter hospital stay time. They also reduce postoperative pain as compared to the conventional techniques [6].

The increased utilization of MIS techniques for LSS is supported by literature that demonstrates their safety and efficacy. Studies have shown that MIS decompression success rates are comparable to traditional open surgery with reduced complications and improved patient satisfaction [7]. Moreover, MIS techniques have proven to be advantageous to elderly patients with comorbidities where they are at risk of surgical-related complications [8]. Despite this evidence, there is a debate on the long-term outcomes of minimally invasive surgeries with respect to their durability and long-term functional outcomes. Based on these facts we in the current study tried to evaluate the efficacy and safety of minimally invasive surgical treatment for lumbar spinal stenosis with attention to the clinical and functional outcomes and complication rates in the cases presenting to our hospital.

This prospective study was done in the Department of Neurosurgery, Gandhi Medical College and Hospital, Secunderabad, Telangana. Institutional Ethical approval was obtained for the study after following the protocol for human research based on the Helsinki Declaration. Written consent was obtained from all the participants of the study after explaining the nature of the study in vernacular language.

This study included 24 consecutive patients who underwent bilateral MicroEndoscopic Tubular Retractor Decompression (METRx). A unilateral approach was used in these patients. A total of 36 levels were decompressed in these patients. These procedures were performed on an outpatient or inpatient basis based on the condition of the patients, under general anesthesia.  Preoperative VAS were recorded and kept as a baseline for comparison. Postoperatively the same VAS were recorded at 2, 6, 12, 26, and 52 weeks. The patient's satisfaction was recorded by using the PhDx Patient Satisfaction Questionnaire (Albuquerque, NM, USA). This includes questions on pain relief, functional improvement, and overall satisfaction with surgery.

Surgical procedure in brief

Patients were prepared and positioned for standard laminectomy. The procedure utilized in this study was a modification of microendoscopic discectomy (MED) described by Foley and Smith. The procedure begins with fluoroscopic localization of the target level. A paramedian incision of 20 mm was made followed by sequential muscle dilation and placement of the working channel (18mm) to a depth of 50 – 70 mm. Laminotomy was performed using an operative microscope it was extended cephalad to remove ligamentous compression and caudally to expose the pedicle. A partial medial facet resection was performed as needed for decompression of the lateral recess and foramina. The working channel was directed medially to expose and drill the spinous process. This allows the resection of residual lamina and ligamentum flavum on the contralateral side. This approach is similar to open laminectomy. This facilitated contralateral facet decompression under direct vision. A ball-tipped nerve hook confirmed the complete decompression. Local anesthetic bupivacaine with epinephrine was infiltrated before closure. The incision was closed in layers with Vicryl, Steristrips, and a bio-occlusive dressing. Postoperatively patients were advised to use ice and oral analgesics. Those patients with spondylolisthesis were placed in a chair-back brace for six weeks. Physiotherapy was started at six weeks with a gradual increase in activity progressively.

Statistical analysis

All the available data was refined, segregated, and uploaded to an MS Excel spreadsheet and analyzed by SPSS version 22 in Windows format. The continuous variables were represented as mean, standard deviation, and percentages, and the categorical variables were calculated by chi square test and the values of p less than 0.05 were considered as significant.

The study included 24 patients (15 females, 9 males) with a mean age of 66.5 years (range 45–81). Twenty-seven had degenerative spondylolisthesis (Grade 1 = 12, Grade 2 = 1). All underwent preoperative MRI and lumbar X-rays. Additional radiological tests were performed as needed. Four patients required discectomies, and three had synovial cysts. A total of 36 levels were decompressed in 24 patients. Out of which 15 had single-level procedures, 7 had two-level procedures, 1 had three-level procedures and 1 had four-level procedures. The level of decompression was L4/5 in 19, L3/4 in 11, L5/S1 in 4, and L2/3 in 2 patients. Four patients had concomitant discectomies at index level and one patient had a discectomy at a nonstenotic level. Three had an associated synovial cyst.  The mean Body Mass Index (BMI) is 26.38 with a standard deviation of 0.94. This indicates that the patients, on average, are in the overweight category (25-29.9 kg/m²). The mean duration of symptoms was 38.55 months with a standard deviation of 12.8 months. This indicates that the patients had been experiencing symptoms for a considerable period (over 3 years) before undergoing surgery details depicted in Table 1.

 Table 1: showing the demographic profile of the cases included in the study

Table 2 shows the mean Visual Analog Scale (VAS) scores at different intervals. It is a 10-cm horizontal line, where 0 represents "no pain" and 10 represents "the worst pain imaginable.  At two weeks postoperatively, the mean VAS score decreased to 6.12 (SD = 0.95), though the reduction was not statistically significant (p = 0.229 compared to baseline). By six weeks, the mean VAS score further declined to 5.33 (SD = 0.67) but remained statistically insignificant (p = 0.067). At twelve weeks, a significant reduction was observed, with the mean VAS score decreasing to 4.19 (SD = 0.59, p = 0.012). By twenty-six weeks, the mean score declined further to 3.21 (SD = 0.27), demonstrating a highly significant reduction (p = 0.003). At fifty-two weeks, the VAS score reached its lowest level at 2.83 (SD = 0.26), indicating a highly statistically significant and sustained improvement in pain (p = 0.001). This table demonstrates a clear trend of decreasing pain scores following minimally invasive surgery for lumbar spinal stenosis. The pain reduction becomes statistically significant starting at 12 weeks postoperatively and remains highly significant at 26 and 52 weeks. The results suggest that the minimally invasive surgical treatment was effective in providing significant and sustained pain relief for patients with lumbar spinal stenosis.

  Table 2: Visual Analog Scale (VAS) Scores

Table 3 shows the PhDx Patient Satisfaction Questionnaire results. The most significant observation is the clear trend of increasing mean PhDx scores over time. This indicates a general improvement in patient satisfaction as patients recover from the minimally invasive surgical treatment of lumbar spinal stenosis. The largest increase in mean score occurs between 2 weeks (2.97) and 26 weeks (3.99). This suggests that the most substantial improvements in patient satisfaction happen within the first 6 months post-surgery. The increase from 26 weeks to 52 weeks is more modest, indicating that satisfaction levels tend to stabilize in the later stages of recovery.

Table 3. PhDx Patient Satisfaction Questionnaire

Table 4, shows the analgesic use in the cases of the study. This table provides information about the management of pain in a subset of the study population who reported back pain or leg pain. Opioids were the most frequently used analgesic type for back pain in this group (7 patients, 29.2%), followed by NSAIDs (5 patients, 20.8%). A small number used muscle relaxants or gabapentinoids. Notably, none of the patients with back pain in this specific group reported no analgesic use. For leg pain, NSAIDs and Opioids were used by the same number of patients (3 each, 12.5%). Gabapentinoids were used by a smaller number (2 patients, 8.3%), and no one with leg pain used muscle relaxants. A significant proportion of patients with leg pain (4 patients, 16.7%) reported no analgesic use. Opioids appear to be more commonly used for back pain compared to leg pain in this specific sample. A higher percentage of patients with leg pain reported no analgesic use compared to those with back pain (where none reported no use).

 Table 4: showing the Analgesic use in the cases of the study

Table 5 shows the complication rates in the cases of the study. The most frequent complication reported was infection (2 cases, 8.3%). Dural tears and hematoma each occurred in 1 case (4.2%). Nerve root injury and reoperation were not reported in any of the cases (0.0%). No other complications were specified. The total complication rate was 4 cases, representing 16.7% of the study population.

 Table 5: Complication Rates in the cases of the study

The primary aim of surgical management of spinal stenosis is to decrease pain and improve the quality of living. Limiting the extent of surgical invasiveness is desired to decrease surgical-related morbidities. Preserving the extent of preexisting spinal elements will result in optimum clinical benefits for the patients following surgeries [9-12]. Precise surgical management will also reduce the risk of iatrogenic spondylolisthesis, postoperative pain, and disability and also reduce the overall treatment costs. This current study was done to evaluate the outcome of MIS) treatment for lumbar spinal stenosis (LSS) in 24 patients. The overall results of the study found satisfactory improvements in pain relief, functional outcomes and patients' satisfaction and acceptable safety. These findings show that the MIS approach for LSS may be done in selected patients with better outcomes. The results of this study showed that there is a progressive improvement in VAS pain scores from the mean of 7.9 to 2.83 at 52 weeks postoperatively (p=0.001) Table 2. Our results are in concordance with the findings of Phan et al. (2017), who demonstrated a similar reduction in VAS scores in their meta-analysis of MIS open versus decompression. Our study also shows that the pain relief improvements appeared at 12 weeks with continued improvement in the first postoperative year.  Ahn et al. [6] reported significant VAS reductions at 6 weeks postoperatively. One of the reasons could be due to the longer duration of symptoms (mean 38.55 months) compared to other studies suggesting a chronic neural compression requiring a longer duration of recovery. The progressive nature of improvement shows the importance of management of patients' expectations during the recovery period. In this study, we estimated patient satisfaction by PhDx questionnaire. We found an improvement from a 2.97 score at 2 weeks to a 4.10 score at 52 weeks. These findings are similar to the

findings of Parker et al. [5], who also reported that patient satisfaction continues to improve beyond 6 months postoperatively. Our observation of improved satisfaction which occurred in the first 6 months (2.97 to 3.99) shows the importance of a critical rehabilitation period during which physical therapy could yield maximum benefits.

The analgesic use pattern in this cohort showed that Opioids were more frequently used for back pain (29.2%) than leg pain (12.5%), while 16.7% of patients with leg pain required no analgesics postoperatively. The difference in response could be because of the biomechanical rationale for decompressive surgery since direct relief of neural compression improves radicular symptoms more reliably as compared to back pain [2].  Our findings support the clinical observation that patients with predominant leg pain may represent better surgical candidates, as suggested by Weinstein et al. [3] in the SPORT trial. The higher use of opioids for back pain was also reported by Overdevest et al. [4], who reported 38% opioid use in the postoperative period following decompression surgery. The overall complication rate in this study was 16.7% which is comparable to other similar studies on MIS and open procedures. The common complication in this study was infection (8.3%), followed by dural tear (4.2%) and hematoma (4.2%). These rates are consistent with the findings of a systemic review by Phan et al. [7] where they found the rate of complications ranges from 4-15%. However, Ahn et al. [6] have shown the typical rate of complication following MIS was 1 -3%. This could be because of the difference in inclusion criteria of patients. In this study, we had a mean BMI of 26.38 and the existence of comorbidities (58.3% with diabetes/hypertension), which are known risk factors for postoperative infection.

In this study we did not have any complication of nerve root injuries and reoperations, whereas, study by Rihn et al. [8]. Had reoperation rates of 5 – 10%. This shows that there could be an advantage of MIS technique in preserving the critical anatomical structures. The single case of dural tear was considerably less as compared to the open procedures where this complication occurs at the rate of 5 – 10%. This study strengthens the evidence for MIS decompression as an effective treatment for LSS in selected cases. The magnitude of VAS improvement (5.07-point reduction at 52 weeks) was much better as reported by Katz et al. [1], where the difference in pre and post-treatment VAS was 2.0 points. Our patient satisfaction shows the values of (mean 4.10/5 at 52 weeks) were comparable to that reported by Weinstein et al. [3] who have reported satisfaction rates of 70 – 80% with open surgery. The important consideration of our study was the operation of multi-level procedures (up to 4 levels) and the inclusion of patients with synovial cysts (12.5%) and concomitant discectomies (16.7%). The successful outcomes in these cases suggest MIS techniques can be safely performed beyond simple one-level decompression however; larger studies are needed for confirmation of these findings.

Limitations of the current study was the modest sample size (n=24) limits statistical power for subgroup analyses. The single-arm design precludes direct comparison with open techniques or conservative management. Longer follow-up beyond one year would help assess durability of results.

Within the limitations of the current study, we found that the MIS technique for LSS provides significant pain relief and acceptable patient satisfaction and has a good safety profile. The gradual improvement in the symptoms suggests that patients need to be counseled that maximum benefits could take 3 – 6 months. The complication rates of MIS were better then what is reported with open techniques. There is a slightly higher rate of infection could be important in cases of pre-existing comorbidities. These findings support MIS decompression as an effective treatment option for appropriately selected LSS patients.

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