Outpatient minimally invasive spine surgery using endoscopy for the treatment of lumbar spinal stenosis among obese patients

Abstract

Introduction

The safety and effectiveness of outpatient endoscopic minimally invasive spinal surgery (MISS) for the treatment of lumbar spinal stenosis among obese patients is not well documented.

Methods

Pain, disability, and surgical variables were examined on 41 adult obese patients that underwent lumbar laminotomy and foraminotomy surgeries.

Results

A significant decrease in pain and disability scores between preoperative and postoperative were found (p-value's < 0.001).

Discussion

MISS using endoscopy can achieve sufficient decompression that results in a significant reduction in the level of pain and disability among obese patients with minimal blood loss and no complications.

The standardized method of determining obesity is by measuring an individuals' body mass index (BMI). BMI is an index relating weight to height and is calculated by taking a patient's weight (kg) by the square of the patients' height (m²).¹ Based on this computation, guidelines have been set for classifying individuals as underweight (BMI ≤ 18.49), normal weight (BMI 18.50 – 24.99), overweight (BMI 25.00 – 29.99), or obese (BMI ≥ 30.00).¹

The prevalence of obesity has been steadily increasing.² Between the early 1960's and 2002, mean BMI for men and women aged 20–74 increased from around 25 to 28.² More recently, national data reported from 2007 to 2008 indicated that 33.8% of the U.S. population over the age of 20 was defined as obese.³ During this same time period, if one were to take into account those that were overweight (34.2%), approximately 68% of the U.S. population over the age of 20 was defined as such.³

Some studies indicate that obesity is an independent risk factor in the development of low back pain and that being overweight increases the risk for disc degeneration.⁴ A commonly diagnosed degenerative condition that can cause severe chronic back pain among the adult population is lumbar spinal stenosis (LSS). In 1911, Baily and Casamajor⁵ first defined LSS as the narrowing of the spinal canal. The cause has been described as multi-factorial, but includes age-related degenerative processes such as enlargement of the facet joints, bony overgrowth, ligamentum flavum hypertrophy, or bulging and herniated discs.⁶ The narrowing of the spinal canal can cause the natural elements within the canal to become compressed. This can result in intense back pain, neurogenic claudication, and radicular symptoms.⁶

To treat LSS, conservative treatments such as medications, chiropractic care, and physical therapy can provide relief for some individuals. However for most people with symptomatic LSS, conservative treatments cannot provide an adequate amount of pain relief. For such individuals, surgical treatment may be needed.⁷ The conventional surgical treatment for LSS, open spine decompression, is considered to be invasive so less destructive surgical treatments are being sought.⁸ To fulfill this need, outpatient minimally invasive spine surgery (MISS) has advanced and gained popularity.⁸ Studies indicate that MISS is successful at providing satisfactory decompression for the treatment of LSS as open surgery without the larger incisions, or damage to the posterior ligamentum, muscles, and tissues.^8–10 This is significant because the extensive surgical dissection and muscle detachment can cause weakness and has led, at times, to paraspinal muscle denervation and atrophy; which is linked to an increased prevalence of “failed back surgery syndrome” and chronic pain.¹¹

Although any patient can experience a variety of complications from surgery, there is evidence that minimally invasive spinal procedures result in fewer complications that do not significantly vary between weight classes. For example, Park et al¹² examined the complication rate among overweight and obese patients that underwent MISS. Results indicate no significant relationship between BMI and number of complications. Thus, being overweight or obese did not increase the chance of experiencing perioperative complications with MISS.

The objective of this study is to examine surgical outcomes and self-reported pain and disability at preoperative and 12-months postoperative among obese patients who underwent an outpatient endoscopic MISS for the treatment of LSS.

1. Methods

1.1. Inclusion criteria

Analyses included patients who underwent lumbar laminotomy and foraminotomy surgery for the treatment of LSS during an 8-month period, who have not had previous lumbar surgery, did not have more than one moderate or severe level of LSS, over the age of 18, had complete preoperative and postoperative data, had a BMI ≥ 30.0, and were not classified as a worker's compensation case.

After implementing the inclusion criteria, 41 patients were eligible for participation in the study. The eligible sample consisted of adults between the ages of 20 and 72 years (M = 55.10, SD = 12.31). The sample was mostly male (68.3%) and Caucasian (92.7%). See Table 1 for demographic statistics.

Table 1.

Demographics.

Demographics	N = 41
Age in years (M (SD))	55.10 (12.31)
Diabetes (% Non-diabetic)	82.9%
Smoker (% Non-smoker)	85.4%
Gender (% males)	68.3%
Race (% white)	92.7%

1.2. Outcome measures

In past spine surgery studies, the Visual Analog Scale (VAS) and Oswestry Disability Index (ODI) have been frequently used.^9,10 In this study, the VAS was used to measure pain intensity. Patients were asked to rate their current level of pain ranging from 0 to 10 with 0 indicating no pain and 10 indicating the worst pain they can imagine. The ODI was used to measure patients' level of disability. For this measure, scores range from 0 to 100. Lower scores on the VAS and ODI indicate a lesser amount of pain and disability respectively.

1.3. Operative variables

Data pertaining to estimated blood loss (EBL), number of intraoperative and postoperative complications up to 30-days out (NOC), and length of surgery (LOS) were retrieved from patients' medical records.

1.4. Procedure

Patients who underwent a single-level laminotomy and foraminotomy for the treatment of LSS completed a VAS and ODI both preoperatively and 12-months postoperatively. Informed consent was obtained from all patients included in this study.

1.5. Surgical procedure

In brief, a scalpel was used to make a stab wound through which a guide-wire was inserted down to the facet region of the vertebral body. Over this guide-wire, the tissues were dilated with the use of a series of increasing diameter dilating tubes to approximately 18 mm. A drill bit was used to create a window into the lamina. This was confirmed through the use of fluoroscopy to determine the depth of penetration of the drill unit. Electrocautery and holmium lasers were used for hemocoagulation and soft tissue removal. Once this was accomplished, a standard mechanical burr system was utilized to grind away the lamina of the vertebral body and widen the opening that was created with the bit. Kerrison and pituitaries rongeurs were utilized during the entire process to assist in bone removal and for general debulking of soft tissues and loose bone fragments. Once the region of the lamina and foraminal canal was properly opened and decompressed, the tube was removed and the procedure was completed. All surgeries were performed in an outpatient setting.

2. Results

2.1. Missing data

Patients with missing data on the outcome measures were excluded from analyses. There was one missing data point for the EBL and NOC variables. There were no missing data points for the VAS, ODI, or LOS.

2.2. Outcome measures

An alpha level of 0.05 or below was considered statistically significant for all analyses. A significant decrease in VAS (p-value < 0.001) and ODI scores (p-value < 0.001) between preoperative and postoperative was observed. Descriptive statistics for the outcome measures are reported in Table 2. The average EBL was 59.00 mL and the LOS averaged at 78.46 min. There were no reported intraoperative or postoperative complications. See Table 3 for descriptive statistics and Figs. 1 and 2 for the frequency distribution of the surgical variables.

Table 2.

Mean and standard deviations for outcome measures.

Variable	M (SD)
VASa,b
Preoperative	6.70 (2.41)
Postoperative	2.54 (2.62)
ODIa,b
Preoperative	45.51 (11.17)
Postoperative	20.54 (17.75)

^aSignificantly lower scores between Preoperative and Postoperative; p-value < 0.001.

^bLower scores reflect better performance.

Table 3.

Estimated blood loss and length of surgery descriptives.

Variable	N	Minimum	Maximum	Mean	Standard deviation
EBL (mL)	40	10.00	300.00	59.00	57.68
LOS (minutes)	41	22	167	78.46	36.61

Fig. 1.

Estimated blood loss.

Fig. 2.

Length of surgery.

3. Discussion

This study demonstrates that MISS using endoscopy can achieve sufficient decompression that results in a significant reduction in level of pain and disability among obese patients with minimal blood loss and no complications.

The findings reported in this study are comparable with other studies that examine weight and lumbar MISS. For example, a study by Rosen and colleagues¹³ found that among obese patients that underwent a minimally invasive lumbar fusion, body habitus (as measured by BMI) did not have a significant relationship with outcomes measures that included the VAS, ODI, and number of complications. Thus, our results support previous studies indicating that obesity is not a contraindication to MISS.

Although our study examined outcomes one year postoperative, our findings are consistent with another study that examined outcomes four years postoperative. Using the sample from the Spine Patient Outcome Research Trial (SPORT), Rihn and colleagues¹⁴ found that at four years postoperative, obesity did not affect the primary outcomes which included the bodily pain and physical function domains of the 36-Item Short Form Health Survey (SF-36) and the American Academy of Orthopaedic Surgeons MODEMS (Musculoskeletal Outcomes Data Evaluation and Management System) version of the ODI of those treated operatively for LSS.

Other MISS studies produced similar results to ours.^12,15 For example, Senker and colleagues¹⁵ examined patients who underwent a lumbar MISS fusion or laminotomy. Results found no difference in the complication rate, blood loss, drainage, or length of hospital stay between the normal weight (BMI < 25), overweight (BMI > 25 and < 30), and obese (BMI > 30) patients. Our study supports the notion that the minimally invasive approach helps to minimize the number of complications among obese patients.

As with any study, this one is not without limitations. First, although the BMI calculation measure is well correlated with the degree of adiposity and simple to measure, BMI does not measure total body fat percentage because it cannot distinguish between fat-free mass (bones and muscles) and fat mass. Studies suggest that body habitus plays a role in complications and that BMI does not necessarily correlate with the depth of subcutaneous tissue. Thus, the measurement of weight is an all-inclusive measure rather than just a measure of fat. Second, although the surgeons can visually confirm decompression during surgery, this study does not include radiographic results for confirmation. Thus, conclusions can only be drawn from data pertaining to the self-reported outcomes. Third, our findings are limited due to the lack of a control group. This prevents an adequate comparison between obese patients that undergo an endoscopic MISS procedure versus an open fusion. Even without this direct comparison, the results of this study provide support for the safety of endoscopic MISS procedures.

This study demonstrates that the minimally invasive procedure performed in this study provides sufficient decompression that reduces levels of pain and disability among obese patients with no complications and minimal blood loss. Obese patients should consider minimally invasive endoscopic procedures for the treatment of LSS to achieve adequate decompression resulting in significant improvements in pain and disability with a low rate of complications.

Conflicts of interest

All authors have none to declare.