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Biomechanics and Implant Materials: The Anterior Column
Summary of Key Points
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Interbody cages are commonly used to supplement fusion procedures and function to stabilize the anterior spine, increase the area for fusion, provide indirect decompression of nerve roots, and restore lumbar lordosis.
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Cages may be inserted via anterior, lateral, or posterior approaches.
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Cage designs incorporate features to provide immediate stability and resistance to migration, allow ingrowth of fusion, and localize the implant on radiographs.
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Supplemental fixation increases biomechanical stability of the cage construct.
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Subsidence is related to disc space preparation, cage material and implantation, host bone quality, and supplemental fixation.
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Common cage materials include polyetheretherketone, titanium, and cortical allograft, each of which have inherent strengths and weaknesses.
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Complications of cage usage can be minimized by understanding the local anatomy, employing a careful and durable insertion technique, and using intraoperative radiography and neuromonitoring.
Lumbar fusion procedures have become increasingly common in the treatment of degenerative, traumatic, neoplastic, and deforming conditions of the lumbar spine. As techniques have advanced over time to increase the success of these procedures, the adjunctive use of interbody cages to add structural stability and improve fusion rates has become more common. This chapter describes the types, biomechanical properties, and advantages and disadvantages of the various interbody fusion devices applicable to the anterior column.
Historical Perspective
The concept of interbody fusion was first introduced in the 1940s by Ralph Cloward, who pioneered the posterior lumbar interbody fusion technique. Toward the end of the 1970s, Dr. George Bagby introduced the stainless steel basket as an adjunct to spinal arthrodesis. He implanted a cervical interbody cage made of stainless steel in a racehorse with successful fusion. He called his technique distraction-compression stabilization. In the 1980s, Kuslich and others adapted Bagby’s basket for human use. Subsequently, threaded posterior lumbar interbody fusion (PLIF) cages were introduced. Threaded PLIF cages were thought to have biomechanical advantages over traditional posterolateral fusion, including the provision of anterior column support, placement closer to the vertebral center of rotation, and reduced bone graft requirement. The US Food and Drug Administration approved anterior lumbar interbody fusion cages in 1996. Until the end of the 1990s, most cages were made of titanium. It was not until the late 1990s that the first cages made of radiolucent polymer implants (e.g., polyetheretherketone [PEEK]) were introduced. Since the early 2000s, the field of interbody cage technology has vastly expanded, and a variety of implants have been introduced to the market.
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