The modern operating microscope with the optical beam splitter
5.2.2 The Retractor-Integrated Endoscope
Minimally invasive surgical methods are becoming increasingly popular. Post-traumatic nerve lesions are frequently, if not always, associated with severe scarring; it is advisable to widely expose such scarred post-traumatic nerve lesions. However, compression neuropathies and other pathological changes not accompanied by scarring may and can be explored through minimal skin incisions using the endoscope [9, 12, 13]. Formerly endoscopic surgery was limited to predefined body spaces such as paranasal sinuses, thoracic cavity, abdominal cavity, joint spaces, etc. The one exception of the use of endoscopy in nerve surgery was the carpal tunnel syndrome, where the tight canal was blindly dilated using blunt bougies in order to introduce the endoscope. This method is available both as monoportal and as biportal techniques, however limited to the decompression of the carpal tunnel . Beginning of this century, we designed the retractor-integrated endoscope named after the author, in cooperation with the Karl Storz Company of Tuttlingen, Germany (Fig. 5.2), which is a universal tool for use on any nerve on the body [12, 13].
The retractor-integrated Krishnan endoscope in two variations. The narrow one is used for releasing the median nerve at the carpal tunnel and the tibial nerve at the tarsal tunnel. For all other purposes, the broader blade is used
The principle is to create a space along the topographical course of the nerve [or any other structure of surgical interest] by means of soft-tissue retraction and manipulate the nerve [or the structure of interest]. This technique has found a wide range of indications and routine application in simple decompression and transposition of peripheral nerves irrespective of their anatomical location, extensive exploration of nerves for occult pathology, simple nerve suturing, and even harvesting nerves for grafting. The one main disadvantage of the retractor-integrated endoscope is its limitation for use only in non-scarred regions. Furthermore, the use of the retractor endoscope for the exploration of nerves in patients with a rich layer of subcutaneous adipose tissue requires extraordinary skills. Clinical trials have shown the feasibility of application of the retractor endoscope for the exploration of almost any nerve of the extremities [9, 12]. Figure 5.3 exemplarily depicts the decompression of the median nerve in carpal tunnel syndrome using the retractor endoscope. Trials comparing the open nerve release with the endoscopic release have shown that the long-term results of both methods are just the same; however, the short-term results of the retractor endoscopic nerve decompression are superior to the open technique .
The retractor endoscopic decompression of the carpal tunnel. (a–d) The steps of the surgery until the transverse carpal ligament (tcl) is transected, and the median nerve (m) is deroofed along its course within the carpal tunnel, atm accessory thenar muscle
One issue of endoscopic exploration of peripheral nerves worthy of mention here is the use of tourniquets on extremities. Application of exsanguinating or non-exsanguinating tourniquets at the proximal part of the extremity highly facilitates recognition and visualization of anatomical structures. However, improper application of very high pressures for prolonged periods might result in secondary iatrogenic compression neuropathies and might prove counterproductive. It is to be borne in mind that there is no single empirical pressure level for upper and lower extremities. My preferred method is to add 80–110 mm Hg to the present systolic pressure and pump up the tourniquet to that value. For example, I will apply 180 mm Hg tourniquet pressure (in a person with a thin arm) when the present systolic pressure is 100 mm Hg. In a person with abundant subcutaneous fat tissue with a systolic pressure of 100 mm Hg, I will recommend a tourniquet pressure of no more than 220 mm Hg. Blindly pumping up to 300 mm Hg for arms and 400 mm Hg for legs should be strongly discouraged. Tourniquets nullify the possibility of any and all electrophysiological measurements. Thus tourniquets should not be used, when one contemplates intraoperative monitoring or diagnostics.
5.2.3 The Video Telescope Operating Microscopy (ViTOM) or the Exoscope
The ViTOM telescope is an exoscope that was designed as an additional observation tool complementing the microscope in open surgical procedures [17, 20]. Being a derivative of the endoscope, the exoscope optic is held in place at a distance of 25–75 cm from the object of interest using a simple mechanical holding arm, the endoscope camera and the light cable are connected to the exoscope at the provided slots, and the high-definition image is projected to an external monitor (Fig. 5.4). The camera offers an optical magnification of 1–2×. The effective magnification achieved with the exoscope depends on the working distance and the size and resolution of the monitor used. For example, with a minimal working distance of 25 cm, the object field of approximately 3.5 cm is achieved with a 2× zoom of the camera; a 26″ monitor will offer a maximal effective magnification of 16×, whereas a 52″ monitor is capable of offering a 34× magnification. Encouraged by the sleekness of the system, several groups, including ours, studied the application of the exoscope, where usually one would use an operating microscope. In this feasibility study, we successfully performed lumbar spinal discectomies, anterior cervical discectomies and fusion, evacuation of intracerebral hematomas, removal of schwannomas from peripheral nerves, and even microvascular anastomoses and microneural sutures . A possible surgical setup for exoscopic surgery is shown in Fig. 5.5.
The setting of the exoscope. The mechanical arm is shown to hold the 90° exoscope, whereas the 0° exoscope is shown as an inset
A surgical procedure performed under HD-exoscopic illumination and magnification
The major disadvantage of the exoscope is its mechanical holding arm and the cumbersome refocusing and variation of magnification. This disadvantage has more to do with the holding system, rather than the optics and illumination offered by the exoscope. Various alternative holding arm systems are available, Endocrane, UniArm, Point Setter, and Versacrane, to name a few. Important features that are yet to be integrated with the exoscope are fluorescence microscopy and navigation match, whereas endoscopes already offer these prospects. In the recent years, augmented reality and image superimposition technology have shown rapid evolution and are put to use in the automobile industry. The magnifying high-definition exoscope, especially when integrated with such powerful tools, is capable of evolving into yet another advanced gadget for performing surgical operations.
Irrespective of the technology used for achieving illumination, magnification, and exposure, these appliances should be seen as tools in the armamentarium of the contemporary surgeon. Routine use of such technology will make the surgeon aptly recognize the indications for their application whenever and wherever found appropriate.
5.3 Techniques in Nerve Coaptation
Allegedly, the first reported nerve coaptation was performed by the celebrated Persian physician Avicenna. Before his times peripheral nerves belonged to the category of “noli me tangere” or “touch me not,” due to a false conception that touching severed nerves produced epileptic seizures. Avicenna himself advocated not touching the nerve, rather bring its severed ends together by adapting the surrounding connective tissue . The results of axonal growth depend directly on the amount of foreign [suture] material implanted to perform the nerve coaptation. Consequently, meticulous microsurgical techniques were employed, and neurorrhaphies came to be performed using microminiature suture material (Fig. 5.6). In order to achieve precision in coaptation of the individual proximal fascicles to their distal counterparts, the interfascicular nerve suturing technique became popular. However, this was quickly discarded, owing to the amount of tissue scarring the interfascicular suture technique had caused within the repaired nerve. The contemporary nerve repair technique involves the epineural adaptation of the nerve as a whole using a few microsutures, having provided the correct orientation of the proximal and distal stumps, and buttressing the suture with the application of fibrin glue [which is absorbed quickly and replaced by a fine film of autologous fibrous sheath] (also see Chap. 4). Some experimental works have tested suture-free methods such as laser welding of nerve ends, which have somehow failed to enter the main stream of clinical practice [2, 18]. A detailed description of microsurgical techniques and placement of microminiature suture of nerves are out of the scope of this chapter, and the reader is referred to Krishnan .