Development of New Technologies in Spine Surgery

History of Innovation in Spinal Surgery

Although early descriptions of spinal surgery date back to ancient Egypt and Greece, it was not until the early 19th century that consistent reports on spinal surgery began to appear. During this era, which preceded the development of aseptic principles and general anesthesia, the rare attempts at spinal surgery were consistently associated with a very high rate of morbidity and mortality. In 1827, Tyrell reported a 100% mortality rate on a small series of patients treated surgically for spinal dislocation and neurological injury. Other reports of spinal surgery had similar discouraging results, with such description such as “bloody and dangerous,” “appalling,” “formidable,” “unjustifiable,” and “well-nigh impossible” applied to the procedures.

The development of general anesthesia, aseptic principles, surgical analgesia, and instrument sterilization in the mid-19th century were innovative milestones that greatly contributed to advancing the field of surgery by reducing the morbidity and mortality of procedures. These advancements also were applied to spinal surgery, as evidenced by an increasing number of published reports of surgical procedures applied to the management of spinal trauma and tumors. Sir Victor Hoarsely described a thoracic laminectomy for removal of an extramedullary spinal tumor in 1887. Wilkins in 1888 and Hadra in 1891 described individual case reports in which wire was used to stabilize fractures of the spine.

In addition to the development of general anesthesia and aseptic techniques, the early advancement of spinal surgery was greatly aided by the development of imaging technology, beginning with the introduction of diagnostic x-rays by Wilhelm Roentgen in 1895. This was followed by the discovery of air myelography by Dandy in 1919 and contrast myelography by Sicard and Forestier in 1921. Each of these developments facilitated an improved understanding of spinal disorders and helped guide the development of surgical management options. However, it was the pivotal technological innovations of both computed tomography and magnetic resonance imaging ^, in the 1970s that were instrumental in the significant expansion of spinal surgery that followed over the next 4 decades.

Development of Surgical Techniques

The earlier advancements and innovations in spinal surgery were focused primarily on surgical technique. Many of these technique innovations were stimulated by unsolved problems and repetitive failure or suboptimal results. They may have occurred spontaneously or through thoughtful trial and error, but each innovation was driven by a continued desire to improve the care of the surgical patient.

A factor that is relatively unique to the field of spinal surgery is the contribution of innovation and development from two separate surgical disciplines: neurosurgery and orthopedic surgery. Each field, with its own experience in managing nonspine disorders, provided the opportunity to address spinal disorders through two different perspectives. This hybrid approach to innovation and problem-solving greatly benefited the early advancements in spinal surgery and continues to benefit the field today. Elsberg, a neurosurgeon, first described surgery to remove an intramedullary spinal cord neoplasm in 1911. Also in 1911, orthopedic surgeons Albee and Hibbs published their individual experience with posterior spinal fusions for the management of scoliosis and progressive deformities because of Pott disease. ^, In 1931, Elsberg described the removal of a cervical disc herniation through a posterior approach. This was followed in 1934 by Mixter and Barr’s report on the surgical management of lumbar disc herniations.

One of the more successful early innovators in spinal surgery was Ralph Cloward. In 1938 he started his neurosurgical practice in the Hawaiian territories where he was, for many years, the only neurosurgeon in the region. This professional isolation most likely contributed to his surgical creativity and resourcefulness. Early in his career he noted limitations in lumbar discectomy surgery when treating a relatively large population of heavy laborers. His suboptimal clinical outcomes in this patient population led to his development of the posterior lumbar interbody fusion (PLIF) technique, as well as the surgical instruments needed to perform the surgery.

In 1946, Cloward first presented his series of 100 PLIF procedures at the Harvey Cushing Society meeting. His report of the technique and its 94% successful outcome rate was met with skepticism and doubt. James Watt, a neurosurgeon in Virginia, commented that “we are neurosurgeons, and as such we should restrict our activities to the trephine and the rongeur, and leave the hammer and the chisel to the orthopedic surgeons.” Despite this early professional rejection, Cloward’s persistence and continued innovation and refinement of the technique and its related surgical instruments eventually led to an acceptance of lumbar interbody fusion as a standard of care for the management of degenerative disc disease and spinal instability.

The success he achieved with the PLIF technique led Cloward to apply the same principles to cervical disc pathology. Until then, cervical surgery was limited to a posterior approach. Through cadaver dissections he refined the anterior surgical approach to the cervical spine. He subsequently described anterior cervical discectomy and interbody fusion (ACDF) in 1958 and also developed numerous surgical instruments for the procedure. His report was soon followed by Smith and Robinson’s description of their version of ACDF.

Development of Surgical Technologies

Although the innovation and development of surgical techniques greatly contributed to the early growth of spinal surgery, it was the gradual introduction of new technologies, primarily spinal fixation devices, that created a more rapid expansion of the field. For many decades, wire fixation was the sole implant technology available for managing spinal deformities and instability. Wires were passed through or around spinous processes to reduce segmental motion and could also be used to secure bone graft to the lamina. The clinical results with wiring techniques were limited and inconsistent.

In 1955, Paul Harrington, an orthopedic surgeon with an interest in adolescent scoliosis, developed a rod-based fixation device that was secured to the spinal column with a laminar hook on each end of the rod. This development can arguably be considered the initial step in the modern era of spinal technology innovation and development. Harrington rods, made from stainless steel, were used to reduce coronal curvatures and provide additional stability to spinal fusions. Harrington constructed the rods the night before surgery and made changes in his system based on their performance in his previous patients.

As the clinical experience with Harrington rods evolved, it became apparent that two points of fixation on either end of each rod limited the effectiveness of the system. This limitation led to the next significant technological advancement in spinal surgery. In 1973, Eduardo Luque, an orthopedic surgeon in Mexico with a large indigent patient population, developed a spinal instrumentation system that used sublaminar wiring to create multiple points of fixation for a pair of contoured rods. This segmental fixation design provided a greater degree of stabilization and allowed for a more efficient application of corrective forces. It also minimized the need for corrective bracing postoperatively in a patient population that did not provide Luque with a consistent opportunity for postoperative follow-up.

The clinical success of segmental fixation, as well as the concerns for neural injury with sublaminar wire passage, eventually led to the development of a multihook-based segmental fixation system by Yves Cotrel and Jean Dubousset in 1984. The use of hooks for fixation of rods to the spine was considered safer than the use of sublaminar wires. The ability to use multiple hooks to provide multiple points of fixation was also a significant advancement over Harrington’s hook-rod instrumentation. Although the system was relatively complex and difficult to master, it greatly advanced the options for spinal deformity correction and stabilization.

Development of Pedicle Fixation

Concurrent with the development of wire- and hook-based rod fixation systems was the development of the pedicle screw. In 1944, King first described a vertebral screw that was inserted across the facet joints. The screws were 0.75 inches long for women and 1 inch long for men. He noted a 10% pseudoarthrosis rate.

In 1959 Boucher described the use of longer (1–1.5-inches) stainless steel screws placed through the facet joint into the pedicle and the lower portion of the vertebral body. This technique was the first to use the pedicle as a point of fixation. He treated 49 patients with spondylolisthesis and noted a pseudoarthrosis rate of 8.2%.

In 1970, Roy-Camille described the use of posterior plates with spaced holes secured to the spine with 4.5-mm screws placed into the pedicles. Slots in the plate also allowed for two screws to be placed through one elongated plate hole into a single pedicle for improved bone purchase. His system was capable of partially reducing high-grade spondylolisthesis and was associated with a nearly 100% success rate in lumbosacral fusions. This system, although lacking widespread acceptance and commercialization, helped form the foundation for the current pedicle fixation technology.

Over the course of the next decade, several spinal surgeons were pivotal in further developing and refining pedicle screw fixation. Different variations of pedicle screw fixation were designed and developed by Harrington, Magerl, Dick, Louis, Olerud, and others, with varying degrees of clinical outcome and acceptance. However, it was not until the development of a pedicle screw system by Steffee in 1982 that a more widespread adoption of the technology began to occur. Steffee’s system employed a slotted plate with recessed “nests” in the slots, permitting easier multilevel insertion and positioning of pedicle screws. Following insertion of the screws, the plate was placed over stems extending from the screws and secured with locking nuts. The plate could be contoured to fit the sagittal alignment of the instrumented spine.

Compared with other systems, Steffee’s variable screw placement (VSP) system was more technically versatile, relatively easy to use, and clinically effective. Each of these factors contributed to a gradual adoption of the system by other spine surgeons and to the recognition of the expanding role of pedicle fixation technology in spinal surgery. The adoption of pedicle fixation gave more surgeons additional options to manage a greater number of patients with a wider array of disorders. Further refinement of the VSP system, the development of other pedicle screw systems, and the refinement of related technologies (i.e., rods, polyaxial screw heads) further added to the expansion and acceptance of pedicle screw fixation technology.