Historical Review of Endoscopic Spinal Decompression

Trying to see inside a human body with an instrument was a theme that went in tandem with the development of lenses and image capturing. By looking back at the history, we can foresight the future of minimally invasive endoscopic techniques. History of endoscopy goes way back to 100AD, in which medical instruments that can examine inside the body were discovered in the ruins of Pompei [1,2]. The first time a tube was used to examine the inside of an organism was done in 1805 by Philipp Bozzini. He inserted a tube inside the body, and by using a candle as the light source, he became the first person to examine inside the body. He also tried to examine the inside of the ear, urethra, rectum, and a woman’s bladder by using a 13zoll (35cm) by 5.9 cm sized box-like device called a Lichtleiter (light guide) [3]. Antoine Jean Desormeaux was a French urologist who worked at the Necker Hospital, a hospital still presents in Paris and in 1853, he examined the urethra, bladder, and the rectum using an autoscope. He is the first person to create the phrase endoscope, a device to look inside the body. Known as the father of endoscopy, Desormeaux committed to popularize endoscopy. The light source was made by burning mixture of alcohol and turpentine and reflecting the light into a lens tube. Until the invention of incandescent light bulb by Edison, light source was made by using candles, gas, and turpentine. In 1879, with Edison inventing the incandescent light bulb, the development of endoscopy also found a new light. In 1970, George Smith (1930-) and Willard Boyle (1924-2011) invented the Charged Coupled Device (CCD), which converts light into electrical signals. With this device, images were converted into electrical signals, which then were displayed onto a monitor for everyone to see.

Rigid endoscope – semi-flexible endoscope period (1868-1957) (Table 1) 

Table1: Era of rigid endoscopes (1805 to 1957). 

The first person to look inside the stomach of a live person using anesophago-gastroscope was a German doctor by the name of Adorf Kussmaul (1822-1902) in 1868. Using a metal tube with a length of 47cm and a width of 13mm, the process was extremely painful for the patient. The tip was shaped into an oval, but as it was a rigid endoscope, it was not able to bend at all during examination [1]. In 1887, Nitze and an Austrian technician by the name of Josef Leiter developed an urethro-cystoscope that used a molten platinum glow wire as a light source [4,5] (Figure 1). 

In 1881, Josef Leiter collaborated with Mikulicz to develop the first widely-used rigid gastroscope [1,5,6]. Afterwards in 1911, Jacobaeus invented the laparo-thoracoscope, enabling the endoscope to reach most of the body’s tube-shaped organs and cavity [7]. 

Figure 1: Dr. Nitze and an Austrian engineer, Josef Leiter developed an urethro-cystoscope, J. Leiter received the first international patent for an endoscope. 

The new age of endoscopy arrived in 1932 when Rudolf Schindler invented a flexible gastroscope that had a flexible optic axis, with the help of an optical engineer by the name of Georg Wolf [8]. In 1959, after countless trials, Masaki Watanabe and Tsunekichi Fukuyo invented the the 21^st Watanabe Arthroscope, which enabled not only examinations but also surgery and filming inside the joint [9] (Figure 2).

 Figure 2: Dr. Masaki Watanabe and an engineer, TsunekichiFukuyo invented the the “21^st Watanabe Arthroscope”. 

Cold light source video endoscopy period (1952-now) (Table 2) 

Table 2: Era of cool-ray lamps and videoendoscopy (1957 to present). 

Fourestier developed the cold light fiberglass in 1952 [10]. The technical advancement of the endoscopy accelerated with the development of the quartz rod lens by Hopkins [11], a lens still used today. This incorporates a new theoretical concept of light transmission called the total internal reflection, and this made it possible for the light to be transmitted inside the endoscopy lens without lowering the luminosity. Hopkins’ “Rod Lens” and the flexible light fiber scope enabled the image to be brighter and clearer [12]. In 1970, by using CCD camera that converts light into electrical signals, operations were done by multiple surgeons using TV monitor displays, and the development of the CCD camera accelerated the development and the popularization of the endoscope. Even now, small-sized CCD camera and robots are continued to be in development to miniaturize video endoscopy with clearer resolution.

Each type of endoscopeis categorized depending on the thinness (Table 3) 

Table 3: Classification of endoscopes used in decompression techniques. 

PELD (Percutaneous Endoscopic Lumbar Discectomy) is an optical technique innovation expanded from the PN (Percutaneous Nucleotomy) method, and a rigid-type endoscopy called Full endoscopy is used for the spine. It is also used in uniportal bilateral decompression of the thoracic spine OYL resection, and biportal bilateral decompression is also in consideration. 

Although tubular surgery with assistant of endoscopy (an approach similar to when using the miscroscope) expanded into a technique suitable for the posterior region [24-26], as it is a natural cavity, a suction tube becomes necessary, and there is a limit to the size of the working channel. For the anterior region, both anterior lumbar discectomy and fusion during laparoscopy of aeroperitoneum and retroperitoneoscopy uses endoscope as a support for lateral approach. Also, this technique is used in VATS and applied during the decompression andcorrection of thoracic and thoracolumbar transitional vertebrae. 

Methods to sustain the cavity are categorized into full endoscopy (sustains by flowing saline into the cavity [27]). Laparoscopy (uses CO2 gas to sustain the cavity [28]), VATS: Video-Assisted Thoracic Surgery (uses a small natural cavity instead of saline to sustain the cavity [29,30]), tubular surgery (METRx tube [31,32]), and abdominal wall lifting [33]. 

Full Endoscopic Spine Surgery 

In 1975, Hijikata used a contrast needle to enlarge the surrounding cavity and set up a standard cannula (inner diameter 3.0m, outer diameter 3.5mm, 2.6mm) under fluoroscopic guidance [34,35]. This led to the devisal of PN method (Percutaneous Nucleotomy), a method to extract the nucleus pulposus of the intervertebral disc post-laterally. Kambin used a 4mm Craig cannula. In 1988, Pravis Kambin suggested that a triangular area surrounded by the exiting root, traversing nerve root, and the end plate of the lower vertebral body is safe for endoscopic spine surgery [36-38]. Currently, technique that fully utilizes this triangle by conducting until the pedicle is popularized (Figure 3) [27]. Onik resected the intervertebral disc using a mechanical suction tube in which the outer diameter was 2.5mm [39]. Foraminoscope (Field Lens of 6 degrees) designed by Hans-Jorg Leu was utilized for 21 years until 2012 [40]. YESS system created by Tony Yeung consists of a 2.5mm surgical instrument, washing channel, multi channel used for rod lens, and an egg-shaped endoscopy. In particular, the inside-out concept suggested by him was safe and easy to perform even for beginners, as decompression and extraction of the spinal cord herniation is done gradually by going into the avascular area of the intervertebral disc [41,42]. Contrary to this, the outside-in method proposed by Hoogland is complicated and needs much practice to control hemorrhage, as this method directly decompresses the intervertebral disc herniation by resecting parts of the pedicle and the zygapophysial joint transforaminal [43]. The strong endoscopic technique performed by Rutten et al. enabled decompression to be done even to the lateral canal and the hidden zone of MacNab [44-47]. Now, decompression techniques using endoscopy for wide areas of the spine, from the cervical to the lumbar area and from the anterior to the posterior area, is being popularized. Furthermore, it is started to be applied in decompression techniques of the anterior/posterior areas of the cervical spine and yellow ligament resection of the thoracic spine [48]. 

Figure 3: Illustration showing the boundaries of the Kambin triangular working zone: A: Exiting root, B: Dural sac C: Intervertebral disc, D: Traversing root.

Pravis Kambin suggested that a triangular area surrounded by the exiting root, traversing nerve root, and the end plate of the lower vertebral body is safe for endoscopic spine surgery. Currently, technique that fully utilizes this triangle by conducting until the pedicle is popularized. 

Tubular surgery with assistant of endoscopy 

In 1997, Forely and Smith performed a surgery where they extracted a herniation in the intervertebral disc by inserting an 18mm diameter microendoscopy (MED) [31,32]. Furthermore, vertebral arch resection was done by using a technique called the Destando syste [49] and Easy GO. 

Laparoscopic (retroperitoneoscopic) lumbar decompression surgery technique 

Decompression and fixation under pneumoperitoneum started in 1991 [28]. Furthermore, retroperitoneoscopy by lifting was performed. It became possible to decompress by dividing or moving the psoas major muscle anteriorly [33]. Also, at one point, operation performed anteriorly was done actively for thoracic spine herniation and degenerative diseases [29].

Future direction 

Until now, popularization and advancements of the endoscopic spinal surgery was affected by the ability of the operator to understand the anatomical structure and the relative positional relationship of each organs under endoscopy, and the ability to see the depth perception from a 2-dimentional video monitor. Also, acquiring hand-eye coordination under magnified images and organ sensation such as bone, ligament, and nerves, and leading technology such as the AI Navigation robotics will become the gold standard for endoscopic spinal decompression. In particular, decompression techniques such as the full endoscopic technique will likely be developed through meta-analyses and randomized clinical trials more in the future for lesions where the diameter is small and microscope cannot be used [50]. 

Improvements of the endoscopy in recent times are mesmerizing, decreasing the chance of approach-induced disabilities by making and sustaining a cavity using a dilator and using a high-resolution VTR image endoscope. Evolving from the traditional intervertebral disc resection surgery using a microscope, the current method can reach the lesion precisely by substantially thinning the working channel and still have a similar performance as the traditional method. 

The goal is utilizing the limited cavity as much as possible and obtain a clear visionary field to complete the surgery as fast and safe as possible. With the education system being standardized, minimally invasive techniques will provide a safe and nice treatment method for the people in the 21^st century.

The authors declare that they have no competing interests.

The authors declare that their article was not funded and financially supported by anybody or any corporation.