Twelve patients were investigated: eight women and four men; mean age 67 (range 52‒79) years; mean body height 176 (163‒184) cm; and mean body mass index 26 (22‒28) kg/m2. The patients were referred by General practitioners due to confirmed symptomatic DLSS on Magnetic Resonance Imaging (MRI).
Inclusion and exclusion criteria
Patients with symptom duration of neurogenic intermittent claudication (NIC) 6 month or more that was confirmed by MRI were included in this study. The exclusion criteria were spinal fractures, disc herniation causing sciatica, infection, previous lumbar spinal surgery and degenerative spondylolisthesis greater than grade 1 and cauda equine syndrome.
The present study was approved by the Regional Ethical Review Board.
All patients were operated with open laminectomy either with osteotomy or with resections of the spinal processes.
Each patient performed identical dynamic trunk flexion-extension movements (dynamic test) and isometric trunk extensions (Ito test) pre- and 3 months post-operatively. Both left and right sides of paraspinal muscle activity and intramuscular oxygenation were simultenously measured before, during and after both the dynamic test and the Ito tests using EMG and NIRS. See Figure 1 for a schematic flowchart of the test protocol.
Figure 1. A schematic flowchart of the test protocol.
Dynamic trunk flexion-extension test
All patients were instructed to sit in a semi sitting position with 70° of hip flexion. They were then asked to lift and lower a weight (7 kg) using a Lojer Pulley 14/20 traction device, from the floor to a specific height (Figure 2) individualized according to the patient’s spinal length in order to obtain a lumbar movement amplitude of 25° flexion to 5° extension (15). The test started with a trial for recognition, followed by 2 minutes rest for baseline data. The patients were instructed to keep their arms straight and keep a cyclic pace when performing the flexion-extension movement until fatigue or a maximum of 3 minutes (Figure 2).
Figure 2. Dynamic trunk flexion-extension test. A full stroke from 25° flexion to 5° extension was repeated for 3 minutes at a rate of one per 4 seconds.
Isometric trunk extension (Ito test)
The Ito test was performed according to Ito et al. (1996) with the patients in a prone starting position on an examination table (16). A 10 cm high pad was placed under the lower abdomen to decrease the lumbar lordosis. The arms were kept parallel to the body axis (Figure 3a). The patients were instructed to lift their upper body off the examination table to an individual adjusted endpoint. The cervical spine was held in a neutral position, looking down and both feet remained on the examination table throughout the entire test until voluntary fatigue or for a maximum of 1 minute (Figure 3b). The test started with a trial for recognition, followed by 2 minutes rest for baseline data and then three recorded trials with 2 minutes rest in between.
Figure 3a. Ito test starting position.
Figure 3b. Isometric trunk extension (Ito test), active position held for max 1 min.
Assessment of paraspinal muscle activity by EMG
Figure 4., NIRS sensors 1-2 and EMG sensors 1-2 positioned at L4 level. EMG sensors 3-4 positioned at L2.
Assessment of paraspinal muscle oxygenation by NIRS
Localized changes in the paraspinal muscle tissue oxygen saturation (MrSO2) were monitored continuously during the dynamic test and the Ito test using a NIRS device (INVOS® 5100C Oxymeter, Somanetics, Troy, Michigan, USA). Two self-adhesive disposable NIRS sensors (Adult SomaSensor® SAFB-SM, Somanetics, Troy, Michigan, USA) were positioned bilaterally over the paraspinal muscles 2 cm to the left and right of fourth lumbar vertebra (Figure 4). The INVOS uses two wavelengths between 730 and 810 nm and two detectors with a center separation from the light source of 30 and 40 mm, respectively. The penetration depth of the INVOS device is roughly 20-25 mm. For each patient, the MrSO2 values were determined every 5 seconds and collected.
The intensity of low back pain (LBP) and leg pain were evaluated with a 10 cm Visual Analogue Scale (VAS) ranging from 0 (no pain) to 10 (worst imaginable pain), before and after the dynamic test and the Ito test, respectively. The patients rated their perceived exertion with Borg RPE-scale (17), ranging from 6 (very light) to 20 (maximal exertion) after every test phase.
Subcutaneous tissue thickness measurements
The skin and subcutaneous thickness at the paraspinal muscles at L4-5 was identified and measured using ultrasound (L10-5, Acuson CV70, Siemens Medical Solutions Inc, USA). Blood pressure was measured in the beginning and at the end of the test protocol using a pressure manometer (NAIS, Matsushita, Electronic Works, Japan).
Data are presented as means and standard deviation (SD) unless otherwise indicated. A paired sample t -test was used to compare data between preoperative and postoperative for each time point measured.
For both EMG and NIRS measurements, recorded values at t=5s are used as a normalizing value and all values recorded at t=10, 20, 30, 40, 50 or 60s are expressed as a percentage of the value at t=5s. This procedure is used in the succeeding report of data evaluation unless noted. Statistical significance for all tests was accepted at the 5% level. The Wilcoxon signed rank test was used for comparison of pre- and post-operative VAS and Pearson’s Chi-Square test was used to compare pre- and post-operative RPE. Statistical analysis was conducted with IBM SPSS Statistics for Windows, Version 25.0. Armonk, NY: IBM Corp and Microsoft Excel (2016).