Surgical technique of lumbar artificial disc replacement with the CHARITE™ Artificial Disc

OPERATIVE TECHNIQUE: NEW DEVICE

SURGICAL TECHNIQUE OF LUMBAR ARTIFICIAL DISC

REPLACEMENT WITH THE CHARITÉ ARTIFICIAL DISC

Fred H. Geisler, M.D.,Ph.D.Illinois Neuro-Spine Center,Aurora, Illinois

Reprint requests:Fred H. Geisler, M.D., Ph.D.,Illinois Neuro-Spine Center,Suite 335, 2020 Ogden Avenue,Aurora, IL 60504.Email: [email protected]

Received, September 17, 2004.

Accepted, December 3, 2004.

LUMBAR ARTIFICIAL DISC technology has been commercially available outside theUnited States for nearly 2 decades. With the Food and Drug Administration approvalof the Charité Artificial Disc in October 2004, an entirely new spinal surgeon popu-lation will be able to offer this technology to their patients as a treatment option. Aswith other techniques in spinal surgery, indications for lumbar total disc replacementare paramount to the success of the procedure. The correct surgical technique is alsoimportant to a successful outcome. This article describes the technique for placementof the Charité Artificial Disc in indicated patients. The technique is similar to that of ananterior lumbar interbody fusion procedure, but many differences between the tech-niques make lumbar total disc replacement a unique procedure in the spinal surgeon’sarmamentarium. Although this article is thorough in its description of the surgicaltechnique for total disc replacement with the Charité Artificial Disc, it should not beused as a substitute for company-sponsored training.

KEY WORDS: Lumbar spine, Operative technique, Total disc replacement

Neurosurgery 56:ONS-46–ONS-57, 2005 DOI: 10.1227/01.NEU.0000153215.60994.D3

In the authors’ opinion, lumbar artificial disc replacementcan be one of the most gratifying procedures a spine sur-geon performs, provided that the patient is indicated for

the procedure. Restoration and maintenance of lumbar seg-mental motion as an alternative to fusion represents a para-digm shift in the treatment of lumbar degenerative disc dis-ease (DDD). Good long-term results have been described forthe same implant as used in the United States Food and DrugAdministration (FDA) investigational device exemption (IDE)trial, with 5 to 14 years of follow-up (5, 8, 9). Just as ourorthopedic surgeon colleagues made the transition from totaljoint fusion to total joint replacement, spine surgeons will bemaking the transition from fusion of a degenerative lumbarsegment to total disc replacement (TDR) in indicated patients.The surgical technique for TDR has many similarities to that ofanterior lumbar interbody fusion (ALIF) via the same retro-peritoneal or transperitoneal approach, with the same poten-tial for approach-related complications (3, 6, 11, 13).Approach-related complications would be handled in thesame manner as during an ALIF procedure. There are, how-ever, important differences in surgical technique between anALIF procedure and a TDR procedure, and that is the subjectof this surgical technique article.

One primary difference between TDR and ALIF is the pre-cision necessary during disc space preparation and for precisesizing, placement, and angulation of the prosthesis. Precise

placement of fusion cages or allograft spacers produces moreesthetic postoperative radiographics after an ALIF procedure.However, this precise placement is not necessary to achieve amature fusion with biomechanical stability and a good clinicaloutcome. What is important in a lumbar surgical arthrodesis isthe endplate preparation, bone graft quality and placement,adequate surface area, and joint mechanical stability to allowhealing of the bone graft site.

Each artificial disc design incorporates its own instrumen-tation, meaning that each technique for implantation is differ-ent and prosthesis-specific. Therefore, it is recommended thatsurgeons attend a training course provided by the individualdevice manufacturers before performing TDR procedureswith a specific prosthesis.

The Charité Artificial Disc (DePuy Spine, Raynham, MA) (Fig.1) is composed of two cobalt chromium alloy endplates and anultra-high-molecular-weight polyethylene (UHMWPE) slidingcore. Each of the endplates has six teeth for fixation to thevertebral endplates. The endplates are available in four footprintsizes and four angles (0, 5, 7.5, and 10 degrees) for restoration oflordosis from 0 to 20 degrees. The core is available in five differ-ent heights and mimics the translation of the normal lumbar discin full flexion and extension (4). The Charité Artificial Disc isintended to provide near-normal physiological motion to thefunctional spinal unit (4, 10). The Centreline TDR instruments areused to implant the Charité Artificial Disc.

ONS-46 | VOLUME 56 | OPERATIVE NEUROSURGERY 1 | JANUARY 2005 www.neurosurgery-online.com

The Charité Artificial Disc is the first and only TDR deviceapproved by the FDA. DePuy Spine was granted approval formarketing the Charité Artificial Disc in the United States onOctober 26, 2004, with the following FDA labeling: “TheCharité Artificial Disc is indicated for spinal arthroplasty inskeletally mature patients with DDD at one level from L4 toS1. DDD is defined as discogenic back pain with degenerationof the disc confirmed by patient history and radiographicstudies. These DDD patients should have no more than 3 mmof spondylolisthesis at the involved level. Patients receivingthe Charité Artificial Disc should have failed at least 6 monthsof conservative treatment before implantation of the CharitéArtificial Disc.” The only valid comparison, the only Class Imedical evidence, between any lumbar artificial disc replace-ment and lumbar arthrodesis that exists today is the IDE studyof the Charité Artificial Disc (1, 7, 10).

PATIENT SELECTION/PREOPERATIVE PLANNING

The specific FDA-approved indications for the Charité Ar-tificial Disc are listed above. In the IDE study, patients clini-cally had primarily low back pain, with some having referredupper leg pain without nerve compression. Patients with ra-dicular pain from nerve root compression were excluded fromthe IDE study. Charité Artificial Disc patients have either theL4–L5 or the L5–S1 disc abnormalities imaged with magneticresonance imaging demonstrating loss of height, loss of seg-mental lordosis, loss of water on T2 (dark disc), Modic end-plate change (2) in the vertebral bodies adjacent to the DDD,and normal or near-normal imaging at all the other lumbarlevels (Fig. 2). As with fusion procedures, patients shouldundergo a thorough review of clinical symptoms and radio-graphic testing. Provocative discography is recommended tolocalize pain generators. Diagnostic blocks may also be helpfulin localizing the pain generator. Exclusion criteria in the

FIGURE 1. Photograph of the Charité Artificial Disc. The disc is com-posed of two cobalt chromium alloy endplates and a UHMWPE slidingcore.

FIGURE 2. Radiographic presentation of four different patients entered into theUnited States FDA IDE study to illustrate several radiographic features of thesepatients. A, radiographic demonstration of a collapsed L5–S1 disc space. B, severeDDD at L5–S1 with secondary Modic endplate changes on a T2-weighted magneticresonance image and collapse of the disc space. Discogram (not shown) excludedL4–L5 as a concordant pain generator. C, severe changes at the L4–L5 disc space withadjacent Modic endplate changes and reduction of height of the disc space comparedwith the L3–L4 disc space. Discogram (not shown) excluded L5–S1 as a concordantpain generator. D, discogram demonstrating abnormality of the L5–S1 disc; thispatient had concordant pain with only the L5–S1 injection.

FIGURE 3. Diagram. The patient is placed in the supine position withthe break in the table directly below the affected disc. The upper limbs arepositioned so as not to interfere with intraoperative fluoroscopy.

LUMBAR DISC REPLACEMENT WITH CHARITÉ ARTIFICIAL DISC

NEUROSURGERY VOLUME 56 | OPERATIVE NEUROSURGERY 1 | JANUARY 2005 | ONS-47

TABLE 1. Additional instrumentation for complete discectomy phasea

Instrument name Model no. Manufacturerb

A Gyne punch biopsy forcep 91-463 Millennium

B SALS suction tip SN 51234 Thompson

C Collis 8-mm shaver 2028-808 DePuy Spine

D Collis 8-mm distractor 2028-908 DePuy Spine

E 1⁄4-inch custom chisel DS698325181 DePuy Spine

F 12-mm-long, 4.5-mm diameter self-tapping cervical Codman screws 46-4196 DePuy Spine

G Screwdriver for Slimlock ACF screw system 46-4141 DePuy Spine

H 11-mm by 0 degree Rake curette from AETI Set From AETI Set #6300-411 DePuy Spine

I Anterior spine elevator (customized-flattened) 771-1838-0 Life Instruments

J Thompson Quick Frame 90011C Thompson

K Radiolucent anterior lumbar kit 91035N Thompson

a Capital letters refer to instruments shown in Figure 6.b Millennium Surgical Corp., Haverford, PA; Thompson Surgical Instruments, Inc., Traverse City, MI; DePuy Spine, Raynham, MA; Life Instruments Corp., Braintree,MA.

FIGURE 4. Diagram. The L4–L5 disc space is exposed by mobilizing thevena cava and left iliac vein as well as the aorta and left iliac artery. It isimperative to mobilize or ligate the iliolumbar vein (not shown), whichoften lies across the L4–L5 disc space.

FIGURE 5. Diagram. The L5–S1 disc space is exposed by blunt dissectionof the left and right iliac arteries and veins and retraction of these vesselsbilaterally. If necessary, the sacral veins are ligated.

GEISLER


Charité Artificial Disc IDE study include but are not limited tospondylolisthesis of more than 3 mm; scoliosis; symptomaticmultilevel DDD; facet joint arthrosis; pars fracture; and insta-bility caused by previous surgical procedures. If the patienthas previously had abdominal surgery, examination by theapproach surgeon for potential approach-related complica-tions and incision location is highly recommended. As withselection of lumbar fusion patients, surgical planning is themost important part of the entire Charité Artificial Disc pro-cedure. Excellent surgical technique and precise placement ofthe prosthesis will not overcome poor patient selection toproduce a good clinical outcome.

PATIENT POSITIONING

The patient is placed in the supine position on a foldingoperating table, with the break in the table directly below theaffected disc. An inflatable pillow may be used if a foldingtable is not available. By breaking the table or inflating/deflating the pillow, the lordosis of the segment can be in-creased or decreased accordingly. The ability to change thelordosis at the operative segment is often important duringdiscectomy and implantation of the prosthesis. Intraoperativefluoroscopy of both the anteroposterior plane (Fergusonview), parallel to the superior endplate of the inferior bodyadjacent to the level operated on, and the lateral plane isrequired for correct placement of the prosthesis. The patient’supper limbs are positioned so that they do not interfere withthe C-arm movement over and around the operative level (Fig.3). It is recommended that “practice” fluoroscopy images beperformed in both planes before the patient is draped. Theseimages not only serve to provide an operative baseline butalso will uncover problems that could occur in obtaining theimages during the procedure so that they may be fixed beforethe patient is draped. It is often useful to mark the position ofthe fluoroscope wheels on the floor during these “practice”images to aid in obtaining rapid and correct alignment forintraoperative images.

FIGURE 6. Photographs. A, Gyne punch biopsy forceps: removes thetenacious posterior lateral disc by punching it and then sucking it up. B,SALS suction tip: this sturdy suction can be used to wedge the disc spaceopen and simultaneously suck at the bottom of the disc space. C, Collis8-mm shaver: removes the bulk of the center of the disc without endplatedamage. D, Collis 8-mm distractor: used to angle open the disc space andcan be used to open the space between the metal endplates to remove thecore if repositioning of the implant is necessary. E, 0.25-inch custom chis-el: used to flatten the endplates and remove the posterior osteophytes. F,Self-tapping cervical Codman screw: historically used for marking the mid-line. G, screwdriver for Slim-Loc ACF screw system: historically used toinsert a midline marker screw. H, 11-mm by 0-degree rake curette: used toremove residual disc and cartilaginous endplate and for minor bony end-plate flattening; and I, anterior spine elevator (customized-flattened): toinitially separate the disc and cartilaginous endplate from the bonyendplate.

FIGURE 7. Preparation of the disc space. A, artist’s illustration of discremoval. B, video still image showing the removal of the disc. C, a chiselmay be used to flatten out the endplates as necessary.



SURGICAL APPROACH

It is strongly recommended that a spinal access surgeon(general surgeon, vascular surgeon, cardiovascular surgeon,thoracic surgeon, or urologist with specific training in spinalaccess surgery) perform the approach, particularly in patientswith potential retroperitoneal scarring because of previousabdominal surgery. In addition, the spinal access surgeon isessential to mitigating vascular complications. There are anumber of options with respect to approach and incisionlocation. The transperitoneal approach to L5–S1 may be used,but Sasso et al. (11) have reported a 10-fold increase in theincidence of retrograde ejaculation with a transperitoneal ap-proach. A standard left-sided retroperitoneal approach toL4–L5 or L5–S1 with a 4- to 6-cm flank incision is describedhere. Fluoroscopy should be used to identify the approachangle and the location of the disc space to be addressed withmarkings on the patient’s abdomen. It is imperative that theincision be placed for coplanar access to the disc space tobetter facilitate prosthesis insertion. Insertion instrumentationfor current artificial disc designs require that they be insertedin a precise midline trajectory, directly in the central axis of thedisc space. The anterior dissection needs to provide this tra-jectory with room for the instrumentation, from the disc spaceoutward all the way to the skin opening.

The anterior rectus sheath is identified and opened longitu-dinally with a scalpel. The rectus abdominal muscle is mobi-lized to the midline by removing the inscriptions on the lateralrectus sheath and exposing the posterior rectus sheath, whichis intimately attached to the peritoneum. The posterior rectussheath is sharply incised in a careful manner to ensure thestructural integrity of the peritoneal membrane. The posteriorrectus sheath is bluntly dissected free of the peritoneum, fol-

lowed by blunt dissection of theperitoneal sac away from the ab-dominal wall. The dissection isperformed over the soleus majorand past the midline, exposingthe general femoral nerve andthe great vessels. An abdominalretraction system is placed ac-cording to surgeon preference.Further blunt dissection is per-formed to expose the affecteddisc space.

VASCULARRETRACTION

Each patient has a differentvascular anatomy across thelower levels of the lumbar spine(12, 14). The following are exam-ples with the most commonanatomy. The L4–L5 disc spaceis exposed by mobilizing the

vena cava and left iliac vein as well as the aorta and left iliacartery (Fig. 4). It is imperative to identify and mobilize or ligatethe iliolumbar vein, which lies on the left anterolateral aspectof the left iliac vein. This must be performed before widemobilization of the vena cava and left iliac vein. The vena cavaand left iliac vein are in intimate contact with the L4–L5 discspace. Careful blunt dissection is necessary to mobilize thevena cava and left iliac vein from left to right, exposing themidline of the L4–L5 disc space. The sympathetic chain atL4–L5 is identified on the anterior border of the psoas muscle.This is in intimate contact with the L4 and L5 vertebral bodiesand runs beneath the iliolumbar vein. It may be necessary tomobilize the sympathetic chain to provide adequate exposureat L4–L5. Great care should be taken during mobilization andretraction of the sympathetic chain, because injury to thissensitive neural structure may result in reflex sympatheticdystrophy. In addition, transection of the sympathetic chainwill result in symptoms of a sympathectomy.

The L5–S1 disc space generally lies below the bifurcation ofthe aorta into the left and right iliac arteries and the bifurca-tion of the vena cava into the left and right iliac veins. TheL5–S1 disc space is exposed by blunt dissection of the left andright iliac arteries and veins and retraction of these vesselsbilaterally (Fig. 5). The sacral veins should be managed withbipolar cautery, which minimizes the risks of retrograde ejac-ulation, impotency, and vaginal numbness. Monopolar cau-tery should have limited use in anterior lumbar surgery. Re-traction of the sympathetic chain is avoided unless necessaryfor complete disc space exposure and then should only beretracted gently, especially in males.

After exposure, dynamic hand-held retractors may be usedto retract the vessels, or if preferred, retractor pins may be

FIGURE 8. Diagrams. The Charité Artificial Disc should be placed in the exact center of the disc space in thecoronal plane and 2 mm dorsal to the midline of the disc space in the sagittal plane.

GEISLER


placed in the vertebral bodies cranial and caudal to the discspace. The author uses a table-mounted retraction system(Thompson Quick Frame retractor with radiolucent anteriorlumbar kit; Thompson Surgical Instruments, Traverse City,MI; see Table 1) to obtain retraction. Fluoroscopy is then usedto verify exposure of the correct disc space. Historically, dur-ing the time of the IDE study, at this point in the procedure,the author placed a 12-mm-long, 4.5-mm-diameter self-tapping cervical Codman screw in the midline of the superioror inferior body to serve as both a radiographic and visualmarker of the midline (Table 1 and Figs. 6 and 15). However,

with the development of the new Centreline TDR instrumen-tation, which contains a similar midline marking mechanism,this step has been removed from the technique.

COMPLETE DISCECTOMY/ENDPLATE PREPARATION

Unlike an ALIF procedure, performing a complete discec-tomy is critical to achieving successful prosthesis placement.The discectomy is performed with standard instruments suchas rongeurs, curettes, and disc elevators. In addition to thestandard instruments, the author uses the instruments shownin Table 1 and Fig. 6 during the complete discectomy phase ofthe procedure.

It is imperative to remove the posterior lateral recesses ofthe disc and release the posterior annulus. This thoroughrelease facilitates parallel distraction, allowing for restora-tion of disc space height and opening of the neuroforamenwith the Charité Artificial Disc. In addition, this providesparallel alignment of the inner surfaces of the vertebralendplates, which provides maximum range of motion anduniform loading of the UHMWPE sliding core. Using thespreading and insertion forceps, distraction is applied tothe disc space to visualize and remove any remaining disctissue. Distraction should be performed slowly to avoidoverdistraction and potential neurogenic injury. Removal ofthe cartilaginous vertebral endplate is performed with cu-rettes using a side-to-side motion. Great care should betaken not to damage the bony vertebral endplates. When

FIGURE 9. Diagrams. The trial is loaded into the trial inserter and usedwith anteroposterior and lateral fluoroscopy to assess correct sizing, place-ment, and lordotic angle.

FIGURE 10. Diagram. For a collapsed disc space, the loaded trial inserteris placed into the insertion guide, which distracts the disc space for inser-tion of the trial.

FIGURE 11. Diagram. With the trial inserter and trial still in place, themarker inserter is used to place the midline marker in the vertebral bodycranial to the disc space.



necessary, curved vertebral surfaces should be shaped andany osteophytes present should be removed to make thevertebral endplates as parallel as possible (Fig. 7).

Blood accumulating in the disc space can come from aretroperitoneal vessel, bone bleeding, or epidural bleeding. Inthe author’s experience, it is helpful with bleeding to use threestrips of collagen hemostat felt of approximately 0.25 � 2inches, floated on the top of the bleeding and then pushed intothe disc space against the posterior longitudinal ligament withan open 4 � 4-inch surgical sponge. Reliable hemostasis isobtained after approximately 3 minutes of mild pressure ap-plied to epidural and bone bleeding. Residual bleeding is thenregarded as vascular, with appropriate action taken. The thin-layer collagen hemostat felt pressed against the posterior lon-gitudinal ligament is not disturbed during the rest of theprocedure. A second application of the collagen hemostat isperformed just after insertion of the metal endplates before theinsertion of the UHMWPE sliding core. This reliably results ina dry surgical field before the initiation of wound closure.Bleeding in the posterior disc space from an epidural or bonysource after insertion of the UHMWPE sliding core is difficultto manage.

PROSTHESIS IMPLANTATION

Correct sizing, placement, and lordotic angle are crucial tothe proper functioning and optimal performance of an artifi-cial disc prosthesis. Placement of the Charité Artificial Discshould be in the exact center of the disc space in the coronalplane and 2 mm dorsal to the midline in the sagittal plane toalign the prosthesis with the floating center of rotation of anormal lumbar disc (4) (Fig. 8). The Centreline TDR instru-ments are used for implanting the Charité Artificial Disc.

Sizing and Trialing

Sizing gauges are used to assess the correct footprint size withlateral fluoroscopy. When selecting the footprint size, completecontainment of the fixation teeth should take precedence overlateral disc space coverage. At L5–S1, the L5 vertebral endplate issmaller than the S1 endplate. Selection of the footprint sizeshould be based on the L5 vertebral endplate. There is often athick anterior longitudinal ligament at the diseased disc spacethat can be greater than 1 cm in thickness. It is useful to performa wider ligament resection anteriorly, with a clear visual identi-fication of the anterior bony margin. This visualization of theanterior bony margin along with lateral intraoperative fluoros-copy images ensures correct placement of the anterior teeth of theCharité Artificial Disc posterior to the anterior bony margin.

The radiolucent trials mimic the footprint and angulationof the prosthesis endplates. The trial insertion instrument isloaded with a radiolucent trial (prosthesis) and placed inthe disc space (Fig. 9). Lateral and anteroposterior fluoros-copy are used to assess proper placement and lordoticangle. The lordotic angle is chosen to restore the desiredsegmental lordosis. On lateral fluoroscopy, there should begood bony apposition along both the superior and inferior

FIGURE 12. Diagrams. Under live lateral fluoroscopy, the pilot drivercorresponding to the chosen footprint size is aligned with the midlinemarker and carefully impacted into the disc space.

GEISLER


edges of the radiolucent trial. If gaps exist, a larger lordoticangle is recommended. The prosthesis endplate with thegreatest amount of lordosis should be placed inferiorly tominimize shear forces on the prosthesis core. It should benoted that the radiolucent trials do not assist in determiningindividual prosthesis endplate lordotic angles. If the discspace is collapsed, the trial insertion instrument can be usedto distract the disc space while placing the trial (Fig. 10).

Midline Identification/Confirm Positioning

Identification of the mid-line is critical to the successof TDR placement. Placingthe C-arm at the correct po-sition and angle in the an-teroposterior (Ferguson)view can be difficult. Onfluoroscopy, the pediclesshould be of equal size andmagnification and equidis-tant from the spinous pro-cess. The centering of thespinous processes betweenthe pedicles can be achievedby rotation of the fluoro-

scope arm or the operating table. This maneuver shouldeliminate parallax error from the position of the posteriorspinous process and the anterior surface of the vertebralbody. The complete discectomy also allows identification ofthe midline by careful examination of the circumferentialbony and ligamentous architecture. Any difference betweenthe anterior midline determined between the visual andfluoroscopy assessments requires resolution. In addition tolining up the markers in the midline marker with the fluo-roscopy by itself, the axis of the handle of the trial inserteris lined up with the spinous process of the rostral andcaudal lumbar levels to fully define the exact midline tra-jectory of the lumbar disc space. With the trial inserter andtrial still in place, the midline marker inserter is placed intothe grooves of the trial inserter. In addition, the contactpoint of the trial inserter handle to the skin is marked anda line drawn on the coversheet of the orthogonal projectionof the trajectory of the handle. Under live fluoroscopy, themidline marker is placed and verified in the vertebral bodycranial to the disc space (Fig. 11). Placement of the midlinemarker is facilitated by markings on the radiolucent trialsthat are visible on fluoroscopy. After this, the marker in-serter and loaded trial inserter are removed. The mark onthe sheets along with the midline marker screw are used todetermine the exact midline starting point and trajectoryused in the next steps of pilot driver insertion and metalendplate insertion. Impaction trajectory for both of thesesteps starts with the instrument centered at the midlinemarker screw and the handle lined up with the markedposition on the skin. As the instrument is impacted into thedisc space, the handle is centered on the mark on thecoversheet.

The pilot drivers match the footprint geometry andclosely approximate the height of the two prosthesis end-plates during implantation. If the pilot driver can be im-pacted to the desired location for the prosthesis, successfulimplantation of the endplates to that same location can beachieved. If this is not possible, additional discectomy or

FIGURE 13. Diagrams. The endplates are shown here loaded into the spreading and insertion forceps, lined up tothe midline marker. Under live fluoroscopy, the endplates are inserted into the disc space until proper placement isverified.

FIGURE 14. Diagram. The core is loaded into the core insertion instru-ment. After this, the core is placed between the prosthesis endplates.



endplate preparation will be required. Under live lateralfluoroscopy, the pilot driver corresponding to the chosenfootprint size is aligned with the midline marker and care-fully impacted into the disc space to the desired depth forthe final implant position (Fig. 12) Final position of the pilotdriver corresponding to the desired final location of theprosthesis is confirmed by lateral fluoroscopy.

Prosthesis Endplate Insertion

The prosthesis endplates are loaded into the tips of thespreading and insertion forceps. If one endplate has agreater lordotic angle than the other, the endplate with thegreater angle is loaded inferiorly. With the loaded end-plates, the spreading and insertion forceps are lined up withthe midline marker. Under live fluoroscopy, the endplatesare inserted into the disc space in a trajectory parallel to thebony endplates as determined from the lateral view (Fig.13). It may be necessary to increase segmental lordosis bybreaking the table and bringing it to a neutral supine posi-tion. In the treatment of collapsed disc spaces, the implant

is “walked” down the disc space by alternately moving thespreading and insertion forceps in a rostral and caudalangulation while hammering the guided impactor (notshown). This maneuver will release the posterior teeth fromthe bony endplate and allow posterior movement. The finalposition of the center of the endplates should be 2 mmdorsal to the lateral midline of the vertebral bodies andcentered in the anteroposterior view.

Core Trialing and Core Insertion

Once the endplates are inserted, the disc space is dis-tracted to the desired disc space height with the spreadingand insertion forceps. Distraction spacers are used in com-bination with the module T-handle to assess the correct coresize. Care should be taken not to scratch the polished innersurfaces of the prosthesis endplates with the distractionspacers. Once the correct height is achieved, the core trialsare introduced under visual or fluoroscopic verification asconfirmation of the correct core height. Distraction of theprosthesis endplates needs to be sufficient so that the cen-

FIGURE 15. Fluoroscopy. Charité Artificial Disc insertion at L5–S1 usingCentreline TDR instrumentation with a posterior osteophyte removal. A, ini-tial lateral fluoroscopy of the L5–S1 degenerative level. Note the large poste-rior osteophyte on the inferior L5 body projecting into the disc space. Thescrew in the inferior L5 body is a cervical 3.5-mm self-tapping screw insertedas a visual and radiographic marker of the midline. B, after initial discectomywithout bony resection, a size 3 trial spacer is placed into the disc space. Notethat because of the L5 posterior osteophyte, this is the largest size possible thatwill fit within the L5–S1 disc space with the anterior teeth of the Charité Arti-

ficial Disc posterior to the anterior cortical margin of L5 and S1. C, L5–S1 discspace is distracted after the posterior osteophyte, and the remaining disc isremoved with 0.25-inch chisel, Kerrison punch, and curettes. D, size 4 trialspacer can now easily fit into the disc space after resection of the posteriorosteophyte. E, 5-degree endplate trials with partially distracted disc space to aidin selecting the Charité endplate angles. F, Charité endplates (5 degrees rostraland caudal) in final position and distracted, ready for core insertion. G and H,final Charité Artificial Disc construct as visualized in lateral fluoroscopy andphotographic views, respectively.

GEISLER


ter of the core can pass the outermost part of the articulat-ing cups without contact. Once the core trial is in place, itmoves freely within the articulating surfaces of theendplates.

FIGURE 16. Diagrams. Final positioning of the Charité Artificial Disc.

FIGURE 17. Diagram. Once the final position has been confirmed, thesingle endplate impactor may be used to manually engage the ventral fixa-tion teeth of the endplates into the vertebral body.

FIGURE 18. Flexion/extension lateral x-rays of a Charité Artificial Disc at L4–L5.Note that the motion of the artificial disc exhibits both rotation and translation.



The core trial is removed, and a core of the same height isloaded into the core insertion instrument. This core is placedbetween the prosthesis endplates (Fig. 14) and delivered fromthe insertion instrument after distraction of the prosthesisendplates. After core placement, distraction is released on thespreading and insertion forceps, allowing the prosthesis end-plates to close around the core. At this point, the core positionis visually verified to be in the cups of the prosthesis endplatesand is demonstrated to rotate freely with forceps by gentlyapplying a tangential force on the radiographic marker wireon the outside of the core. The core insertion instrument andthe spreading and insertion forceps are removed with a slaphammer attached to its end.

Final Positioning

Final positioning is verified with anteroposterior andlateral fluoroscopy (Fig. 15). If necessary, the position of theprosthesis can be altered slightly using the appropriatelysized grooved driver. In the event of a gross malposition,the Charité Artificial Disc may be repositioned intraopera-tively. The entire prosthesis can be removed by distractingthe disc space open with a lever on the lateral portion of theprosthesis endplates and removing the core with a Kocherclamp. The author uses an 8-mm Collis spreader (Table 1).Once the core is removed, the metal endplates are easilydetached from the vertebral endplates with a Cobb elevatorand then removed with a Kocher clamp. Although the coreis usually damaged by this maneuver and needs to bereplaced, the prosthesis endplates are typically not dam-aged and are reused. The prosthesis endplates should becarefully inspected under magnification to verify the ab-sence of surface scratches on the inside of the cups. Ifsurface scratches are present, the prosthesis endplates mustbe replaced as well. Scratches on the implant wings willhave no effect on the performance of the implant. Once thefinal position has been confirmed (Fig. 16), the single end-plate impactor may be used to manually engage the ventralfixation teeth of the prosthesis endplates into the vertebralbody (Fig. 17).

CLOSURE ANDPOSTOPERATIVE MANAGEMENT

The Midline Marker is removed after final positioning andbefore closure. If retractor pins were used, they are removed,

and the wound is closed inlayers in the standard man-ner. Patients are releasedfrom the hospital in 2 to 3days and are advanced withactivities as tolerated (Figs. 18and 19). A postoperativebrace is not necessary.

KEY POINTS

1. Patient selection is the most important part of the entireTDR procedure. Excellent surgical technique and preciseplacement of the prosthesis will not overcome poor pa-tient selection to produce a good clinical outcome.

2. The use of an approach surgeon to perform the approachand to be available to assist with vascular complicationsis strongly recommended.

3. Performing a complete discectomy and endplate flatteningis critical to achieving successful prosthesis placement.

4. Correct sizing, placement, and lordotic angle are crucialto the proper functioning and optimal performance of theCharité Artificial Disc.

5. Care should be taken not to scratch the polished innersurfaces of the prosthesis endplates.

REFERENCES

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FIGURE 19. X-rays. The Charité artificial disc is implanted at L5–S1. The x-rays demonstrate motion of the device in lateralbending, with both angulation and translation of the core. Lateral view of the same patient is shown on the right.

GEISLER


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COMMENTS

Artificial disc placement in the cervical and lumbar spineshould be considered as part of the treatment of disco-

genic disease. As repeatedly emphasized by the author, pa-tient selection is the most important part of total disc replace-ment procedures. Obviously, excellent surgical technique andprecise placement of the prosthesis must follow. Nevertheless,if the surgical technique is performed appropriately but usedon an inappropriate patient, results will be unsatisfactory. Theauthor nicely details the technique for placing the Charité disc.Long-term outcomes of lumbar and cervical artificial discs areyet to be determined. The author has provided a nice descrip-tion of this particular technique.

Volker K.H. SonntagPhoenix, Arizona

In this report, the author has provided us with a close ex-amination of the technique for lumbar disc arthroplasty

using the Charité Artificial Disc. This device, approved by theFood and Drug Administration in October of 2004, is the onlydisc replacement device currently available for general use inthe United States market. It is anticipated that the Charité discwill replace a large portion of the lumbar fusion market, andfor this reason, widespread education on the nuances of thesurgical technique that are presented here will be critical toensure the safe and effective treatment of candidate patients.

The implantation of all current varieties of lumbar artificialdiscs requires an anterior approach similar to anterior lumbarinterbody fusion. However, the devices are much bulkier, andimplantation of the appropriate-sized device in the properposition is critical to ensure its mechanical function. For thesereasons, the surgical procedure is more technically challeng-

ing than anterior lumbar interbody fusion. In addition, be-cause these devices are intended to retain near-physiologicalmotion, mechanical wear, device migration, and implant fail-ure can all occur. Revision strategies must thus be developed,and there is no doubt that a niche market will arise for cor-rective surgery. Although some will argue that lumbar discarthroplasty is simply another Pandora’s box for the spinesurgeon, the desire to improve upon the outcomes derivedfrom spinal fusion will prove to be an unrelenting force thatwill drive this technology in the United States market.

Michael Y. WangLos Angeles, California

Geisler has provided a clear and concise description of thesurgical technique for insertion of the Charité Artificial

Disc. This technique will be used increasingly in this country.It behooves us to read and learn from those with the greatestexperience. The author has made an important contribution.

Edward C. BenzelCleveland, Ohio

Dr. Geisler describes the surgical technique of lumbar ar-tificial disc replacement with the Charité Artificial Disc in

this excellent communication. I cannot agree more with thekey points as summarized at the end of the text. Similar tolumbar fusion for degenerative disc disease, patient selectionis critical to achieving good outcomes, and most likely, artifi-cial disc replacement will require more intense preoperativescreening. Arthrodesis also treats facet degeneration, but thatwill not necessarily be the case with arthroplasty, so particularattention will have to be directed to the posterior joints of theaffected motion segment. Adequate exposure of the anteriorlumbar spine can be challenging and is associated with risksnot generally experienced by neurosurgeons or orthopedicsurgeons, and Dr. Geisler’s suggestion to use an approachsurgeon should be taken seriously. Finally, all total disc re-placements require a level of surgical precision not necessaryfor an arthrodesis. The surgeon should be thoroughly familiarwith the nuances of the implant and invest the time necessaryto be certain that the joint is inserted in an exact manner.

These are exciting times, because total disc arthroplastyoffers a novel means of treating degenerative disc disease, butwe should act responsibly as we enter this new era. Thosesurgeons beginning to embrace this technology should do socautiously, selecting only the most suitable patients, and oneshould be ready and willing to convert the procedure to afusion if the device cannot be properly and safely inserted.

Vincent C. TraynelisIowa City, Iowa


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Surgical technique of lumbar artificial disc replacement with the CHARITE™ Artificial Disc