Although back pain has been around since the beginning of human history, most of our understanding of spinal problems developed only in the last 65 years, especially in the last three decades. Before the 1930's, there was a scarcity of literature regarding spinal disease. In 1934, Mixter and Barr first described herniation of the lumbar intervertebral disc and surgical treatment for this condition. In 1949, Verbiest published the first article on spinal stenosis. Disc disease and spinal stenosis came to be known as the two major causes of spinal disorders, yet spinal problems did not have the socioeconomic significance, as we see today, until the 1950s.

In the past three decades, great progress in the operative and nonoperative treatments of spinal disorders has been made. Today, every advance in the diagnostic capability or surgical technique opens up new possibilities for successful treatment. We now have improved spinal decompression and fusion techniques, as well as bone grafts and bone substitutes. There are great varieties of instrumentation, including segmental fixation devices, pedicle screw systems, fusion cages, as well as rods and plates. The new fixation systems allow more adequate decompression of entrapped neural tissues without jeopardizing spinal stability. As a result, we are now able to perform more aggressive surgical decompression, extensive bony removal, corpectomy, radical tumor resection and correction of severe spinal deformities. With the superior diagnostic studies available today, it is not necessary to "explore" the spine. In fact, there should be few surprises during surgery. Every spine surgeon should have the exact surgical technique planned in advance.

In spite of the tremendous strides made in science and technology, the diagnosis and treatment of spinal disorders are still challenging. At this time, it appears that spine care is more and more influenced by economic, political and sociological factors. For example, there are less resources and more constraints imposed by managed care organizations. For the next several years at least, surgical trends will favor doing less rather than more. There will be more emphasis on minimallyinvasive surgeries. The main intended objective will be to reduce cost from the standpoint of the business interest. Hopefully, these less invasive techniques will also reduce patient morbidity and mortality. In reality, many of the new surgical techniques have not been analyzed rigorously in terms of outcome. These have to pass the test of time.

In the year 2000 and beyond, there is no doubt technological progress will impact treatment of spinal disorders. Information or computer technology, as well as imaging and other diagnostic techniques, will have a significant influence. Advances in basic science will allow revolutionary application in diagnosis and treatment of spinal problems. Particular attention should be paid to molecular biology. New discoveries are being made of genes involving tumors, neurological, metabolic and degenerative spinal diseases. The new knowledge will increase our ability to treat these conditions. Currently, genetic engineering techniques are being used to produce substances which stimulate spinal fusions. Many bone growth factors have been identified. One group of these factors is the bone morphogenic proteins (BMPs), which are lowmolecular weight proteins, isolated from bone matrix, some of which are obtained through recombinant DNA synthesis. These BMPs presumably stimulate local progenitor cells in tissues to enhance bone collagen production. This initiates the bone formation necessary in spine fusions.

In the future, there will be greater understanding of neurological function. This will allow us to modify "pain experience" and provide relief through targeted therapies. This new knowledge can also be applied in more effective electrophysiological techniques to be used in diagnosis and at the time of spinal surgery.

There will be more advanced imaging technologies, which will increase the sensitivity and specificity of diagnosis. MRI, for example, will have better resolution and will be obtained in a shorter period of time, with more patient comfort. The MRI machine will be smaller, but will be more "open," thus causing less claustrophobia in patients during the examination. The studies may be obtained with the patient in a sitting, standing, prone or supine position, even when moving. There will be therapeutic MRI, which will allow surgery with real time visualization. These advance 1 imaging technologies will enhance minimally invasive spine surgical techniques.

The minimally invasive procedures will be more developed as diagnostic tools and therapeutic approaches. Percutaneous discectomy and fusion will be more effective. There will be more "userfriendly" endoscopic instruments for spine procedures.

Thoracoscopy, laparoscopy and retroperitoneoscopy will become less time consuming with improved optics, electronics and engineering. Many of the instruments will be computer aided, in fact, the computer and surgical technologies are converging, and are leading to more virtual reality surgeries. Totally different therapeutic approaches may emerge and become more accepted for certain spinal disorders. At this time, there is no satisfactory treatment for patients with multilevel painful degenerative spinal disease. The problem becomes more compounded when the patients are overweight and Reconditioned. The wide abdominal rectus plication surgery may be an answer for such patients. This is an actual back surgery without touching the back itself.

Severe spinal stenosis occurs in the elderly, many of whom also have other significant medical problems. For some of these patients, general anesthesia is a major risk. There will be minor surgical procedures which will provide relief with minimal risk. This type of "unconventional" or "indirect" surgical approach may become more popular in the future.

Although we will continue to see newer techniques of spinal instrumentation and fusion, there will be a general trend away from spinal fusions.

Today, spinal arthrodesis provides satisfactory relief for many patients; however, there are major problems for at least 30% of the patients over time. Some of the problems include donor site pain, nonunion and failure of the metal fixation. Degeneration of adjacent motion segments is a long term sequelae. Surgical complications, early and longterm problems tend to increase with longer fusions. In general, patients who undergo spinal fusions for multilevel degenerative disc disease tend to do poorly. Even after solid fusion, pain relief is less than expected or it does not last as long. Instability and additional degeneration is accelerated at the adjacent levels, if there are already some degenerative changes at the nonfused level. In view of these problems associated with spinal fusions, it is therefore logical to develop a physiological disc replacement to preserve normal motion, disc height and stability.

A normal, natural intervertebral disc has a deceptively simple appearance with an outer annulus fibrosus and an inner nucleus pulposus; however, it is extremely difficult to design an effective artificial disc replacement. The basic requirements of a disc prosthesis include biocompatibility of the material, normal disc geometry, kinematics, dynamics, motion constraints, endurance and good fixation to bone. In addition, it must be failsafe. Let us consider only one of the basic requirements, endurance. Today, a typical spinal fusion is performed on patients between the ages of 35 and 50; therefore, the life span of a disc replacement should be at least 40 years. An average person experiences two million strides or one million gait cycles in one year and 125,000 spinal flexion and extension movements per year. These add up to at least 85 million spinal loading cycles in 40 years. Kostuik believes that the device and material should be tested to a least 100 million cycles. This number is a factor of 6.5 more than the longest wear and fatigue tests of any other orthopedic implant.

There have been numerous attempts to develop an ideal disc replacement. One of the earliest attempts was the ballbearing implant, which was used in a large number of patients. The disc space was often hypermobile, and the patient developed more pain. After several months or years, many of the ball bearings eroded into the vertebral bodies or displaced into the spinal canal and even into the abdominal cavity. There were many other failed prosthesis, such as the nested boxform device, with springs inside which became ineffective after scar tissue invasion. A number of "sandwich" implants were also designed with metal plates and silicone or elastomeric cushions; however, major problems developed, and they had to be discontinued.

At this time, the Kostuik device, with hinged metal components containing springs, is being studied. In this prosthesis, fibrous tissue may grow into the springs and hinges, causing it to be less effective. One concern with this type of articulating implant is the wear product. The body reacts to the volume of the wear particles, as well as to the biological incompatibilities. The SB Charite disc and endoprosthesis probably has the largest tract record. It was initially developed in East Germany and has been used in several hundred patients so far. It has two metal end plates and a highdensity polyethylene center; however, the motion is in the middle of the disc space, which is actually too anterior. The true physiological center of rotation is in the posterior aspect of the disc space. Ray is using Hydrogel placed in a pair of doublewoven jackets to replace the nucleus only. This device swells and locks in position after it is inserted after discectomy through an endoscopic approach or by open surgery.

A healthy, natural disc functions far superiorly to any manmade replacement available today. It is reasonable to transplant a normal disc from a different level of the same patient or from another individual or even a different species. Luk and Associates have performed disc autografting in monkeys. Others have published experiments in dogs, using allografts for disc replacement. An intact disc with its adjacent endplates or parts of the vertebral bodies is being transplanted as a unit. In dogs, the normal disc mechanical properties were preserved for as long as 1.5 years, but all dog allografts eventually developed loss of disc height and degenerative changes. The lack of diffusion of nutrition to the allografts may be the problem. In monkey autografts, there was minimal evidence of gross degeneration for up to one year. Although gradual loss of water content was noted, the nucleus pulposus reaccumulated proteoglycans after an initial drop in the first four months. There was significant increase in the hydroxyproline content in the annulus fibrosus and the nucleus pulposus. The study with monkey autografting showed that the transplanted disc could survive a period of ischemia.

Other researchers are planning the use of xenografts in disc transplantation. Instead of the entire disc and endplate unit, only parts of the disc may be transplanted. There are still major hurdles to overcome, including the lack of diffusion of nutrition, biocompatibility in allografts and xenografts and other problems inherent in transplant surgery.

It is probably too early to predict the future of disc transplantation. Yet, we can look back to only 50 years ago when no one predicted the possibility of heart and kidney transplantation.

In the next millennium, I believe that there will be developments in spine surgery which are unimaginable today. We may learn to cure most spinal diseases and repair or replace parts of the spinal cord or even the brain itself.

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