- Patient enrollment
Four kyphoscoliosis patients diagnosed with lumbar spinal stenosis between March 2017 and January 2018 were enrolled in this study. (Fig. 1) Our inclusion criteria were as follows: lumbar central or lateral recess spinal stenosis with kyphoscoliosis, radicular leg pain or claudicationrefractory to conservative treatment for at least 6 months, absence of spinal instability confirmed by dynamic radiographs. Instability is considered as of sagittal angulation values >15°, values in millimeters of translation on the sagittal plane (or coronal plane) >4mm or shift >15% of the inferior vertebral endplate measure. We excluded patients with lumbar foraminal spinal stenosis, spondylolosthesis, compression or burst fracture, infection, tumor, previous lumbar surgery. The participants included four women with an average age of 80.25 years (range, 73-86 years). The average Body Mass Index (BMI) was 24.58 (range, 19.94-28.36). The affected levels ranged from L2-S1. The operation level was decided according to clinical presentation and MRI findings. As for the degree of spinal deformity, data were summarized in Table 1 According to Schwab Classification.[26]
- Outcome Evaluation
Radiology outcome measurement including serial radiographs (Fig. 1) and dural sac cross sectional area (DSCSA) on MRI were well documented. (Fig. 2) (Table 2) As for the clinical outcome evaluation, the Oswestry Disability index (%) (ODI), Visual analogue scale (VAS) were collected at the initial visit and at 1 month, 6 months and 12 months post-operatively. (Table 3)
- Statistical Analyses
Statistical Analyses were performed using SPSS for Windows, version 24 (SPSS Inc, Armonk, NY). The Friedman two-way analysis of variance (ANOVA) by ranks test was used as a non-parametric test. A p < 0.05 was considered statistically significant.
- Navigation system and Instruments
The O-arm/StealthStation system (Medtronic Inc., Minneapolis, MN, USA), a 3D real-time image-guided navigation system, is popular for its ability to provide automated registration with intraoperative, postpositioning computed tomography (CT). With SureTrak® II Universal Tracker (Medtronic Inc., Minneapolis, MN, USA) attached to the endoscope instrument, the depth and position of the endoscopic working channel could be observed in real-time fashion on the O-arm/StealthStation monitor.
The Vertebris® Spine Endoscope system (Richard and Wolf, Knittlingen, Germany) features high-resolution endoscope with a 6.9 x 5.6 mm diameter and a 4.1 mm intra-endoscopic working channel. The angle of vision is 25°. The working sleeve has an 8.0 mm outer diameter and a beveled opening, which enable visual and working fields creation in an area with a clear, anatomically preformed cavity.
Surgitron, a high-voltage bipolar probe (Ellman Innovations, New York, USA), is well-known for pinpoint coagulation in a wet field with simultaneously minimal burning or charring of soft tissue. The thermocoagulation device aims to maximized hemorrhage control and thus improves the visibility of the operative field.
- Surgical Technique
5.1 Patient Preparation
The surgery was conducted under general anesthesia. The patient was positioned prone on a well cushioned and supportive radiolucent table with the abdomen hanging free. Bilateral knees were flexed to over 90 degrees as possible for the opening of interlaminar space. Back skin was then well prepared and draped.
5.2 Reference Pin Insertion and Image Acquisition
First, we made a small incision over the iliac crest. We inserted the reference pin through the cannula, and used an impactor to nail the pin into the bone until the tap cap bottoms out on the cannula. Then we removed the tap cap and cannula from the pin, placed the spine reference on the pin and rotated the assembly to lock the frame in place.
The spinal segment of interest was scanned using the O-arm navigation and the images were automatically registered to the Stealth Station. All the navigational instruments were registered.
5.3 3D Real-Time Image-Navigated Percutaneous Endoscopic Decompression
Interlaminar approach was chosen. The skin incision was made under O-arm navigation, which was under the spinal laminal junction. A dilator, 8.0 mm in outer diameter, was bluntly inserted to the edge of the interlaminar window. Then, an operative sleeve with a beveled opening was directed towards the ligamentum flavum. After attaching the SureTrak® II Universal Tracker to the Vertebris® Spine Endoscope (Fig. 3), the endoscope was inserted into the working channel (Fig. 3).
After introduction of the endoscope, the bony boundaries of superior lamina, inferior lamina and facet joint were identified and the soft tissues were removed with bipolar probe, punch and forceps. To broaden the working space, a minimal bone resection was made from medial to lateral. 3-4mm of bone around superior and inferior lamina was removed with a diamond burr. Then, the approach proceeded to the superior ariticular process, creating space for lateral recess decompression. The depth and location of the bony landmark could be well visualized through the O-arm navigation system. (Fig. 4) The O-arm navigation system offered the real-time images as a warning sign before the facet joint was violated, which prevented the spinal column from instability. Not until the cranial, caudal, medial, and lateral bony boundaries of the operative field were well prepared should the ligamentum flavum being opened. A lateral window of approximately 4-6 mm was made on the ligamentum flavum. The neural structures and epidural fat tissues were exposed. The perineural membrane was dissected from the neural structure carefully under direct endoscopic visualization. The operating sleeve with beveled opening could be turned and used as a nerve hook. With the joystick technique, the hypertrophic ligamentum flavum could be removed by controlling endoscope in either direction. The contralateral lateral recess decompression was achieved through unilateral approach with bilateral decompression technique. Finally, epidural bleeding was checked and well-controlled by Surgitron bipolar probe. The whole procedure was done safely and effectively under precise O-arm navigation (Fig. 5).