Proceedings - 19th International Conference - IEEE/EMBS Oct. 30 - Nov. 2, 1997 Chicago, IL. USA
`SPINAL IMPLANTS: PAST, PRESENT, AND FUTURE
`Hassan A. Serhan, Ph.D.
`Manager, Research and Testing,
`AcroMed Corporation
`3303 Carnegie Ave. Cleveland, Ohio 441 15
`
`I. Introduction:
`
`All the constituent elements of the normal human spine interact
`simultaneously to provide flexibility of motion, protection of the
`spinal cord, and structural support for the musculoskeletal tom.
`Spinal disc herniation, arthritis, and spinal stenosis as well as
`congenital, idiopathic, and neuromuscular deformities are some
`of the widespread spinal diseases. These spinal disorders are
`frequently associated with back pain.
`Injuries, muscle
`dysfunction, and surgical procedures may also disturb the normal
`interactions of the spinal elements, the end result being an
`alteration in the behavior of the spine which may lead to spinal
`instabilityandbackpain.
`
`Disease and fri”s of the spine present challenging clinical
`and biomechanical problems to spine surgeons. Spinal cord
`decompression often results in an extensive destabilization of the
`spine. Historically, the spine surgeon walked a h e line when
`performing back surgery. Adequate neural decompmsion and
`subsequent relief from pain had to be weighed against
`destabilization of the spine by extensive cord decompression.
`Spinal fusion has become a widely used technique to treat a
`variety of spinal instability syndromes including those due to
`trauma, tumor, infection, degeneration, and deformity. Spinal
`fusion is dways performed using bone grafl with or without
`stabilizing implants. The degree of the associated instability
`usually determines the necessity of implants.
`
`Instrumentation of the spine has undergone revolutionary
`changes over the past decade. It has evolved from the use of only
`wire, to wire holding rods, to rods with hooks, to universal
`system which include hooks, wires, pedlcle screws, and rods or
`plates. Rods and plates can be contowed to enable segmental
`maneuvering of the individual vertebrae.
`
`11. Historical Background:
`Most of the early research on spinal fusions was built on the
`search for a treatment for spinal cu” (scoliosis) due to polio
`and Potts’ disease (tuberculosis of the spine). This application
`was eventually expanded to include idiopathic scoliosis, kyphotic
`
`and lordotic deformities, as well as degenerative diseases and
`spinalfractures.
`
`In 1909, Lange reported his technique for spinal iixation using
`steel rods which were attached to the vertebrae posteriorly.
`Posterior surgery was the procedure of choice until the mid-
`1930’s. During this period, anterior surgery became available as
`an alternative to address Pott’s disease degenerative disorders and
`spondylolisthesis @urns,1933, Speed 1938). King, in 1944,
`achieved fixation via facet screws. In 1962, Hanington
`introduced his technique for s p i d fixation by using stainless
`steel rods and hooks. In the 1970’s Luque used sublaminar wires
`attached to rods to achieve segmental fixation.. Dwyer and Zielke
`both approached the spine anteriorly using screws inserted
`laterally into the vertebrae. Dwyer used a tension cable and Zielke
`used a threaded rod to achieve the scoliosis reduction
`In France, Roy-Camille used screws and plates posteriorly to
`immobilize and maintain lordosis in the lumbar spine. In 1983,
`Dr. Arthur StefEee further developed pedxle screw fixation in the
`USA with his Variable Screw Placement System (VSP). The
`slotted plates allowed for variable screw placement and did not
`rely on a fixed distance between adjacent pedlcles as did the Roy-
`Camille thereby, enabling the surgeon to fit the instrumentation
`to the patient and not visa versa. In 1985, Dr. Marc Asher and
`associates expanded upon the work of S M e , Luque, C~tre.1 and
`the rod based ISOLA posterior spinal
`Dubowset and int.rodud
`system. In the past seven years over 16 Merent rod system
`have been in-
`to the market.
`The choice of an implant is based on several factors including in
`vivo and in vitro studies. Experimental and clinical studies of
`spinal fixation devices usudly provide the surgeon with an
`anaIyus of the risks and beneiits associated with each implant.
`Experimental studies include mechanical testing and analysis of
`components, connections, and implant constructs to determine
`their biomechanical characteristics including, stability, fatigue
`life performance, pullout strength, StifFneSs, and yield and
`ultimate strength.
`Material biocomgatibility and imaging characteristics also play a
`major role in implant selection Acceptable and FDA recognized
`materials include cobalt, stainless steel, and titauium alloys,
`although several polymer based materials are being standardize&
`Clinical studies combine functional evaluation and biomechanical
`
`(0-7803-4262-3/97/$10.00 (C) 1997 IEEE)
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`WARSAW2054
`NuVasive, Inc. v. Warsaw Orthopedic, Inc.
`Case IPR2013-00206
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`Proceedings - 19th International Conference - IEEE/EMBS Oct. 30 - Nov. 2, 1997 Chicago, IL. USA
`
`Spinal Instrumentation: Past, Present And Future, H.A. Serhan, 1997
`
`instrumentation
`includes
`implant. This
`the
`behavior of
`performance in vivo and in vitro, method of application, quality
`of instrumentation, and the safety (FDA) approval. Obviously,
`surgical philosophy and the basic advantage and benefit of the
`device as well as implant approval and safety record may be the
`most important factors in selecting a given implant. Patient bone
`and compliance, exprience and knowledge of the various
`@ty
`spinal devices and pathology influence the surgeon.
`111. Spinal Fusion Devices:
`
`The use of internal fixation implants for spinal fusion has gained
`increasing acceptance over the last 10 years.
`Speclallzed
`implants have been developed for each region of the spine, often
`based on surgical philosophy and treatment methodology
`developed by surgeons. Typicauy there are several techniques
`Surgeon
`and products for the treatment of each pathology.
`preference is based on clinical performance, ease of use, training,
`and cost However, many procedures are still accomplished
`without spinal instrumentation, usually with bone graR
`Hospitalization time and the ability of the w e n t to return to
`work may also be influenced by the choice of surgical procedure.
`
`Fixation devices can be divided into four major groups based on
`the area or pathology being treated: 1) CeMcal, 2) Deformity, 3)
`Degenerative, and 4) TraWumor.
`
`1. centical:
`
`There are several commercially available systems and techniques
`available for the spine surgeon to treat ceMcal pathologies.
`Depending on the pathology, the technique can be relatively
`simple posterior wiring to more complicated total vertebral
`replacement. Anterior ceMcal plates can be divided into locking
`and non-locking systems. The non-locking systems such as
`AmMed‘s Amplate (Figure l), and Aesculap’s Caspar plate,
`have shown higher fusion rates in single level fusions and an
`equivalent rate for two levels. However, in multi-level fusions,
`locking systems such as the AmMed anterior cervical
`stabilization system, Synthes’s ceMcal plate and Danek’s Orion
`system have shown higher fusion rates.
`Several posterior lateral mass plate systems are also available in
`the market. These plates that are not yet approved by the FDA are
`being used “off-label” to stab*
`ceMcal motion segments and
`accomplish fusion. Surgeons in both Japan and Korea have
`treated ceMcal pathologies using ceMcal pedicle
`!iux&u&
`screws.
`Single strand wires and multiple strand wires (cables) have an
`extensive clinical history. Multi strand cables are flexiile t h e m
`reducing the chance of inadvertent penetration of soft tissues.
`Surgical cables such as Songer cable and wires have been used in
`
`263
`
`conjunction with bone graft for posterior stabilization of the
`ceMcal spine.
`
`Figure 1: The AmMed Amplate CeMcal System
`
`I
`External fixation with a halo can be used as a collservative non-
`surgical treatment method for spine stabilization. Halo’s achieve
`stabilization by rigidly fixing (securing) the head to the trunk
`with the tenet that the neck remains immobile.
`
`2. Deformity:
`
`Scoliosis is a three dimensional deformity resulting in trunk
`imbalance, I.eduction of height and Cosmetic appearance. It may
`also result in pelvic imbalance, compmmise of pulmonary
`function and back pain External bracing was the treatment of
`choice before Paul Hanington introduced his hooks and rod
`system in the early 1960’s. The Hanington system became the
`gold standard for deformity and several other pathologies for
`several decades and is still wed, generally overseas. The
`longevity of this system is a testimony to its design
`The basis for several posterior instrumentation systems including
`the Harrington system for treatment of comnal plane deformities
`is to provide distractive forces on the concave side of the spine
`and compressive forces on the convex side. This type of deformity
`is often corrected wing posterior-lateral bony fusion and posterior
`instrumentation. Other existing systems rely on segmental
`treatment of the deformity together with the application of lateral
`and A-P forces and movement to achieve 3-D correction (e.g.
`ISOLA system, Figure 2).
`Kyphotic or other sagittal plane deformities are treated by
`applying distractive forces to resist the compnsive loads on the
`spine, and whenever possiile, segmental fixation to decrease
`sagittal bending moments, combined with intehody bony fusion.
`Some deformities can be W quicker, with reduced blood loss
`
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`Proceedings - 19th International Conference - IEEE/EMBS Oct. 30 - Nov. 2, 1997 Chicago, IL. USA
`
`Spinal Instrumentation: Past, Present And Future, H.A. Serhan, 1997
`
`and less muscle distraction using anterior systems. There are
`several FDA approved anterior deformity systems including:
`AmMed‘s single rod ISOLA system, Kostuik-Harrington
`system, Zeilke, m e r and others. Some of these systems can
`also be used for the treatment of trauma and tumors in the
`thoracic and thoracolumbar spine.
`
`Today, pecllcle fixation systems for the treatment of degenerative
`spine is considered to be a necessary tool to treat deformity and
`degenerative pathologies. h n t l y , there are several e c l e
`screw fixation devices with FDA clearance for specific
`applications while many others are being used “off label”. The
`Variable Screw Placement System (VSP) was introduced by Dr.
`Steffee in 1984 (Figure 3). The goal of this system was to
`segmentally treat the spine by using forces to realign and lix the
`spine in a low profile manner until fusion occu~s. As with most
`posterior systems, success is often achieved by using a Posterior
`Lumbar Interbody Fusion
`or Anterior Lumbar Interbody
`Fusion (ALF) graft to reduce loads through the instrumentation
`and transferring loads through the vertebral column. Rod based
`systems such as ISOLA, TSRH, Fixateur Intern, CD, etc. have
`been developed and will have specific nuances and techniques to
`help achieve fusion.
`
`Figure 2: ISOLA@ System
`
`3. Degeneraiive:
`
`Currently, the most common spinal surgery procedure is a
`disaxtomy, pedonned 300,000 - 400,000 times a year in the
`United States alone. The intexvertebral disc is vulnerable to
`herniation due to the high loads involved in bending and twisting
`motions. The spinal cord and the nexve system protected by the
`spine’s bony structure are sensitive to compression, causing
`sciatica that may result in severe pain syndmmes.
`With aging and continual loading of the spine, the fibrosis tissues
`in the intexvertebml disc are broken into short chains that retain
`less water and thus do not inflate the disc as much This
`segmental instability might cause spinal nexve compression and
`spinal instability, causing chronic pain.
`Facet degeneration could also increase spine stenosis and
`segmental instability. The lumbar spine is the most common site
`for degeneration. This is primanly due to the high loads in this
`region from the transfer of loads from the spine to the pelvis.
`treatment of facet joints andor disc degeneration
`Uni”ented
`or herniation include laminectomy and discectomy. Either
`treatment may cause further instability in the joint, possibly
`requiring further treatment or instrumented fusion.
`
`2638
`
`I
`
`Fimue 3: VSP@ Svstem
`
`I
`
`In the last five years, metallic and c o w t e spinal interbody
`fusion devices have been used in ALE and PLIF operations to
`reduce the mohidity of the bone graft donor site or reduce the
`chance of disease transfer from allograft The carbon fiber
`composite Brantigan ALIF and PLIF cages have been used in
`Europe and the Pacific Rim for the past six years and have shown
`a high rate of fusion. Unlike the BAK, Ray and Stryker Titanium
`cages, the Brantigan cages are made &m radiolucent cubon
`fiber/polymer composite material. This material facilitates the
`assessment of bony h i o n and prevents stress shielding because
`its modulus of elasticity is similar to that of c o r t i ~ c e l l o u s
`bone (Figure 4).
`
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`Proceedings - 19th International Conference - IEEE/EMBS Oct. 30 - Nov. 2, 1997 Chicago, IL. USA
`
`Spinal Instrumentation: Past, Present And Future, H.A. Serhan, 1997
`
`accommodate spinal laads. Most systems are designed for mid
`thoracic to upper lumbar and few exist which can be suCCeSSfUUy
`used to the sacrum.
`
`VI. Future of Spinal Instrumentation:
`
`Eliminating pain or deformity of the spine and maintaining
`flexibility of motion will be the ultimate goal in any future spinal
`treatment. Paul IEaningtOn’s goal in his fmt attempts was to
`correct spinal deformities without fusion. With this goal in
`mind, non-fusion treatments of the spine such as mcial disc
`replacements, genetic engineering, artificial ligaments, and
`hydrogel merit have gained more attention in the past five
`years and will continue to be of great interest to spine surgeons.
`
`In the interest of eliminating donor site morbidity and
`accelerating the fusion process, bone morphogenic protein
`(BMP), bioactive ceramics, and biodegradable or bionsorbable
`materials are also being investigated for spinal application.
`
`In general the future goals of spinal instrumentation will be to
`treat and maore the functionality of diseased spine.
`
`V. References:
`
`1. Hitchon PW, Traynelis VC, RengachaIy s, Techniques in
`Spinal Fusion and Stabilization, Thieme Publisher, Inc. 1995.
`2. Fessler RG, Haid RW, Current Techniques in Spinal
`Stabilkation, MCGrawHill, 1996.
`3. White AA, Panjabi MM, Clinical Biomechanics of the Spine,
`2& Edition J.B. Lippincott Co., 1990.
`4. Lin PM, Gill K, Lumbar Interbody Fusion, An Aspin
`Publication, 1989.
`5. Orthopedics Today, The Wry of FDA Regulation of Spinal
`Fixation Devices, 1994.
`6. ‘“le Classic’’ Wiring of the Vertebrae as a Means of
`Immobilization in F~actwe and Potts’ Disease, Hadra BE,
`Clinical Orthopaedics and Related Research Journal, pp. 4-8,
`No. 112, Oct. 1975.
`7. “The Classic” Support of the Spondylitic Spine by Means of
`Buried Steel Bars, Attached to the Vertebrae, Lange F,
`Clinical Orthopaedics and Related Research Journal, pp. 3 4 ,
`No. 203, Feb. 1986.
`8. “The Classic” Transplantation of the Tibia Into the Spine of
`POUS’ Disease.A Prdihmy Report, Albee FH, Clinical
`Orthopaedm and Related Research Journal, pp. 5-8, No. 87,
`Sept. 1972.
`9. “Spinal Surgeq Update, Guest Speake?‘ colter JM, Surgical
`Rounds for Orthopaedm, pp. 10-11,1989.
`
`Figure 4: Brantigan’s PLIF and ALIF IE Cages@
`
`4. TraumalTumor:
`Fractures of vertebral bodies and posterior elements can lead to
`damage or compression of the spinal cord, and it may cause
` is present
`spinal instability, especially when ligamentous i n .
`Treatment of traumatic injury of the spine varies h m external
`fixation such as bracing to surgical intervention using anterior or
`posterior fixation devices. The choice of implant is based on the
`type of injury and the surgeon’s choice of implant.
`
`Figure 5: Kaneda SR anterior spinal system
`
`Anterior trauma and tumor systems are either rod or plate based
`(with the exception of cable based Dwyer system). As with
`posterior systems, the profile of the system must be low enough to
`reduce tissue or vessel impiigement yet strong enough to
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