Rigid endoscopes are used for applications with straight access paths. The diameter and length depend on the intended use of the endoscopes. For example, rigid endoscopes for laparoscopic applications can have a diameter of 5, 10 or 12 mm and a length between 300 and 500 mm. For neuro or nose applications, diameters are between 2 and 4 mm with a short length of 60&#;200 mm. Some variants of rigid endoscopes are shown in a. Common designs show the following components ( b): The main body is usually made out of massive stainless steel, the eyepiece made out of plastic, a stainless steel pipe as the shaft and housing for the optical path and a glass cover at the distal end. The optical path is built up as a stack of glass lenses with an additional separated light channel integrated into the outer stainless steel pipe and main body. A connector for a light cable, usually with a thread that&#;s shape is dependent on the manufacturer, is placed on the side of the main body of the endoscope. Rigid endoscopes come with a variety of angles of view. The most common variants are 0° straight view and 30°, 45°, 70°, 90° side view. Some rigid endoscopes can have steerable fields of view or integrated zooming options.
For imaging, the camera can be connected at the proximal end of the standardized eyepiece. This allows the use of separated cameras with higher image quality and a significant focus and zoom range. Another advantage of a separate camera is the avoidance of a hot and wet sterilization process that is crucial for the camera&#;s electronics. Some manufacturers have autoclavable camera heads in their portfolio others still use wipe disinfection and/or sterile covers. The rigid endoscopes themselves can be sterilized with a standard hot steam procedure in the autoclave and have a long lifetime. Only kinking or hard beats on the shaft can destroy the sensitive glass lenses, especially for small diameter scopes. Most manufacturers include flexible dampers that hold the lenses to reduce this risk. The imaging quality is highly dependent on the whole imaging chain, including optics, camera, video processor, monitor, light source and light cable or enhancement technologies.
Additionally, endoscopes are frequently used with other equipment like trocars, guides, sheets or holders. To visualize compatibility to the user, colored rings can be added to the endoscope and the additional equipment. A wide range of particular types of rigid endoscopes is available for various use cases. For example, there are endoscopes with a steerable field of view, realized by a rotatable prism inside the tip or a short flexible part ( a). Zooming and focusing options can be integrated, and even high magnification to observe the tiniest structures, e.g., in contact endoscopy. Work channels for instruments, flushing, or even a lens cleaning mechanism can be integrated for some applications. For robotic applications, the cameras can be integrated directly into the tip of the endoscope. This allows a side-by-side placement of two cameras to achieve stereo view and realize depth perception.
Flexible endoscopes are used to examine anatomies that are hardly or not reachable with rigid endoscopes. Mainly they are entered via the natural human orifices following the shape of the anatomy. There are two types of these endoscopes, fiber endoscopes and video endoscopes. In fiber endoscopes, the optical channel is created by a bundle of glass fibers combined with a lens on the tip, defining the focus point and the field of view. The ocular with a standardized eyepiece is mounted on the proximal end. A light source can be connected to a light post on the main body to illuminate the field of view. Some additional fibers transmit the light in the bundle to the tip of the endoscope. Depending on the diameter and construction, the number of fibers is limited. Since every fiber represents one pixel, the image&#;s resolution is limited to the number of imaging fibers. This reduces the image quality. The significant advantage of fiber endoscopes is their thickness and flexibility. Endoscopes with fibers come with a diameter of only 0.5 mm and can tolerate a bending radius of less than 7 mm. Endoscopes with 10,000 fibers and a diameter of 1 mm still reach a 10 mm bending radius [36]. Fiber endoscopes are mainly used to image very small anatomies, for example, in bronchoscopy or the upper urinary tract.
Video endoscopes have an integrated camera sensor on the tip. The image is transmitted via cables to the video processor of the imaging system. Diameters in everyday clinical use start from 2.9 mm for trans nasal applications up to 15 mm in Gastroenterology. The field of view illumination is usually realized by integrated light fibers connected to an external light source. The camera sensor provides at least HD image resolution and is combined with a lens stack for zoom and focus. Some video endoscopes can even realize magnifications up to 500 times with integrated optics.
The general design of flexible video endoscopes shows tubular steel braided or coiled support structure that is compression resistant but flexible for bending. The frontal part is usually more flexible and can have an integrated steering mechanism usually realized by two or more steering wires. Cables, light transmission fibers, steering wires and for some applications working, flushing, air or suction channels run inside the support structure. A rubber-like outer tube seals the inner part from the environment. The endoscope is operated with a multifunctional handgrip with wheels and knobs for steering, zoom, focus, image acquisition and light control. If a working channel is integrated, the access is usually placed on the distal part of the handgrip. The connection plug can integrate channels for flushing, air and suction. Sterilization of flexible video endoscopes is challenging and includes precleaning, manual or automatic chemical cleaning, drying and leakage testing. The sensitive rubber coat can be damaged during use and underlies aging over time, limiting the lifetime of flexible video endoscopes. a shows different types of flexible endoscopes, and b shows a detailed view of a connection plug, handgrip and different types of distal tips of flexible endoscopes.
Particular types of endoscopes are small imaging capsules ( b down left). These systems look like a pill with a diameter of approximately 11 mm and a length between 25 and 35 mm. The capsule can be swallowed and follows the natural path through the intestinal tract acquiring images. The capsule contains one or two cameras and LED lights and is powered by a stack of batteries providing energy for 8&#;12 h. The images are transmitted wireless to an antenna and recording system outside the body placed in a belt. The stored image series with up to 50,000 single shots can be evaluated after the examination with the help of particular software.
This video illustrates a minimally invasive spine surgery technique for addressing L5&#;S1 listhesis with paracentral disc protrusion. This technique offers the advantage of unilateral biportal endoscopy while mitigating the need for a wet medium.1&#;3 Moreover, it does not necessitate additional instruments beyond those used in the standard microscopic minimally invasive transforaminal lumbar interbody fusion.
The 33-year-old lady presented with severe low backache with left L5 radiculopathy following a recent bike accident. Examination revealed weakness in the left extensor hallucis longus (EHL) and sensory loss along the left L5 dermatome.
Standing x-ray lateral view indicated grade 1 L5&#;S1 anterolisthesis with a pars interarticularis fracture. Based on spinopelvic parameters, the patient was classified as type 2 according to the modified Spine Deformity Study Group (mSDSG) classification.4 On MRI, there was a left L5&#;S1 paracentral disc with foraminal extension and a cranially migrated portion.
The patient was diagnosed with L5&#;S1 grade 1 listhesis with L5&#;S1 migrated paracentral disc with foraminal extension. She was planned for MIS-TLIF using a 4-mm rigid endoscope, followed by percutaneous pedicle screw fixation (PPSF).
The patient was positioned prone, under general anesthesia.
Skin markings were made under fluoroscopic guidance. The midline, a line along the lateral edge of the pedicles, and the upper endplates were marked. A 16-gauge needle was inserted as a guide for docking the Destandau&#;s system, pointing to the L5&#;S1 disc space on the contralateral side.
A 2-cm longitudinal incision was marked along the pedicle line, starting from the S1 pedicle and extending toward the L5 pedicle for Destandau&#;s system insertion.
Docking was done and the level was confirmed with C-arm. Initial docking is done at the spinolaminal junction.
Lateral exposure to the laminofacet junction is performed by removing the soft tissue and a small amount of muscle with monopolar and bipolar cautery.
The facet joint is thus exposed. It is called the "valley between two mountains" view, showing the L5 inferior facet, S1 superior facet, and the intervening joint space.
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The inferior edge of the L5 lamina is removed with No. 3 Kerrison punch.
The rest of the lower lamina is drilled at three strategic points using a 3-mm diamond burr. Firstly at the lower margin. Secondly at the junction of the pars interarticularis and the inferior facet by working laterally from the first point. This would help resection of the L5 inferior facet. And lastly at the root of the spinous process to allow over-the-top decompression of the spinal canal and the contralateral nerve root. The remaining bone is removed with a Kerrison punch.
As the pars interarticularis and the inferior facet junction was removed with the Kerrison&#;s punch, the whole of the inferior facet could be disconnected. The disconnection of the L5 inferior facet entails a careful separation from its ligamentous attachment. Utilizing biopsy forceps, it was divided into two halves so as to deliver it through the outer sheath. These bone pieces can be used to pack the polyetheretherketone (PEEK) cage to improve fusion rates.
Now the facetal surface of the S1 facet is seen. This facet is removed using No. 3 Kerrison punch, working medial to lateral until we reach the S1 pedicle. The surface is smoothened using a burr while avoiding any injury to the pedicle.
The ligamentum flavum is then removed in piecemeal. It will expose the underlying epidural fat. It should be retained till all the bony work is completed to avoid a dural tear.
Removal of the epidural fat exposes the thecal sac.
Working laterally to the thecal sac in a craniocaudal direction, the fat and soft tissue are dissected to expose the traversing nerve root.
The traversing nerve root is gently retracted medially at its shoulder to expose the disc space. The Destandau&#;s retractor is used to keep the nerve root retracted. The engorged epidural veins are coagulated and cut.
Using a marking needle, the disc level is confirmed under the C-arm.
The lower part of the Kambin&#;s triangle was thus exposed. Using a 15 No. blade, the annulus is cut. The nucleus pulposus and part of the annulus fibrosus are removed using biopsy forceps. Care is taken to remove all the herniated disc, including the migrated portion.
A 1.5-cm horizontal incision was made at the marked level for inserting the L5 percutaneous pedicle screw (PPS). This incision is deepened till the fascia. The first of the dilators for PPS is inserted, and sounding is done with the Destandau&#;s outer sheath to confirm alignment. The dilator is further navigated into the disc space under endoscopic vision. Triangulation of the instruments is thus achieved.
Successively, the second dilator is then inserted, followed by the third dilator sheath, which is used for screw insertion. It is inserted until its lower margin is just visible by the endoscope and left in situ to act as a new port. The endoscope is then inserted in this new port. The inner sheath of the Destandau&#;s system is removed, allowing the outer sheath to serve as an access port for the larger instruments to be introduced into the disc space.
Larger shavers can now be inserted through the Destandau&#;s outer sheath to prepare the disc space like in tubular discectomy. The endoscope can be freely advanced into the disc space to inspect the status of the endplate preparation.
The sizer for the cage was inserted under endoscopic vision, thus preventing nerve injury. Due to the transforaminal corridor, only a slight retraction of the traversing nerve root is required when using a large cage.
A 14 × 28&#;mm PEEK cage was inserted and its position was confirmed on the C-arm. For adequate visualization of the nerve root on the medial aspect of the cage, a 30° endoscope is required at times. The dislodged bone chips from the cage and remaining disc fragments were removed. At the end of the procedure, the L5&#;S1 left lateral recess and foramina were completely free.
The spinal canal and the contralateral nerve root were decompressed by the over-the-top technique. The thecal sac and the traversing nerve root (S1) can be seen to be well pulsatile and supple, confirming no compression. Afterward, L5&#;S1 PPSF was done.
The patient was ambulated 12 hours after the surgery. She was now able to walk without pain. There was a complete improvement in the left EHL power by the 3rd week of follow-up. Postoperative CT affirmed correction of the listhesis with optimal implant position. The total operative time was 4.5 hours, with an estimated blood loss of 300 ml. The patient was discharged in 5 days with significant improvement in the VAS scores.
The technique has its own benefits, nuances, and limitations. It expands the spectrum of Destandau&#;s system and is a bridge to unilateral biportal endoscopy, thus increasing the role of endoscopy in minimally invasive spine surgeries.
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