K EYSTONE GRAFT INSTRUMENTS S U R G I C A L T E C H N I Q U E I NTERBODY FUSION
C O NTENTS Surgical Technique Keystone Graft Instruments I NTRODUCTION The cervical Keystone Graft Instruments simplify the placement of structural interbody grafts in anterior cervical procedures. The long-term success of these procedures is often determined by the surgeon s ability to obtain adequate disc space distraction, allowing for placement of an appropriately sized graft and restoration of the patient s sagittal alignment. Many techniques are used to obtain distraction in anterior cervical procedures, including longitudinal distraction and Caspar-type pin distractors. As with any technique, there are risks and limitations that must be acknowledged and overcome. The use of longitudinal distraction can be inconvenient and imprecise. Caspar pins can loosen after repetitive use during discectomy, resulting in a decreased ability to distract for subsequent graft insertion. Poor bone quality resulting from osteoporosis and other patient risk factors can further complicate this issue. The Keystone instruments offer a systematic approach to graft insertion that can replace or complement other forms of distraction. In doing so, this technique allows precise distraction by using the structural characteristics of the graft to provide simultaneous disc space distraction and graft insertion. The instruments also offer a broad platform on which to distract, making them appropriate for use in patients with suboptimal bone quality. S U R G I C A L T E C H N I Q U E 1 Additionally, the Keystone instruments also include half-moon-shaped impactors that better distribute insertion loads on the graft and a comprehensive intraoperative templating system for accurate assessment of the intervertebral space. Authored by: Ronald Moskovich, M.D., F.R.C.S., Hospital for Joint Diseases, New York, NY. Anterior Cervical Discectomy and Arthrodesis.......................... 2-9 Cervical Corpectomy............................................ 10-13
Keystone Cervical Graft Instruments (876 B) Surgical Technique Anterior Cervical Discectomy and Arthrodesis STEP 1 Position the patient in neutral orientation (supine) with a support under the mid-cervical spine to maintain normal lordosis. The support, which may simply be a firm cotton/wool roll, is necessary to provide resistance when the graft is impacted later in the procedure. A transverse skin-crease incision usually provides adequate exposure and may be cosmetically superior to a longitudinal incision. Longitudinal traction is unnecessary with this technique (Figure 1). Figure 1 2 STEP 2 Expose the requisite vertebrae and discs via a routine anterior surgical approach (Cloward-Robinson). Incise the deep investing fascia along the medial border of the sternocleidomastoid. Develop a plane between the trachea and esophagus medially and the carotid sheath laterally. Displace the omohyoid upwards or downwards to expose the vertebral column (Figure 2). Figure 2 STEP 3 A thyroid vein may require ligation and division. Elevate the longus colli muscles to expose the lateral edges of the intervertebral disc (Figure 3). Figure 3
STEP 4 Excise the intervertebral disc and clear the endplates of cartilage. An interbody distracter placed laterally in the disc space may be used to facilitate this process (Figure 4). STEP 5 Resect the uncinate process, if necessary, to relieve foraminal compression. The relationship of the process to the vertebral artery is illustrated here. Additional mobilization of the longus colli muscle is necessary if this procedure is to be performed (Figure 5). Figure 4 S U R G I C A L T E C H N I Q U E 3 Figure 5 STEP 6 Under image magnification (an operative microscope is ideal here), resect the uncinate process with a diamond burr. Widen the foramen to completely decompress the nerve root (Figure 6). Figure 6
STEP 7 Continuing under image magnification, resect the posterior vertebral osteophytes to relieve spinal stenosis. Resect the posterior annular fibers completely, but the posterior longitudinal ligament may be left intact if it is not ossified (Figure 7). Figure 7 STEP 8 Prepare the endplates depending on the type of interbody graft to be used (i.e., Smith-Robinson or Simmons). The size of the graft will be determined by templating the interbody space using the Cervical Spanners (see steps 9 and 10) or the Graft Trials in combination with the Insertion Ramp (see steps 11-14). The Smith-Robinson iliac crest graft or cortical ring allograft are parallel-sided. The Simmons iliac crest graft or cortical ring allograft is 4 wedge-shaped, so the graft bed must be prepared to accept the graft by undercutting the endplates, leaving a posterior shell of bone to prevent retropulsion of the graft. The wider part of the graft is positioned more posteriorly (Figure 8). Smith-Robinson Simmons Figure 8 STEP 9 Use a spanner to trial the disc space by placing it between the vertebral bodies and rotating it into a position perpendicular to the endplates. Increase the size of the spanner until a firm fit is achieved (Figure 9). Figure 9
10mm STEP 10 The tip of the spanner is 12mm in length and can be used to help determine the appropriate disc space depth. The height of the spanner will indicate the appropriate size piece of allograft or autograft to be used. When using a Smith-Robinson technique, the height of the spanner will equal the height of the graft since they are both parallel-sided. When using a Simmons technique, the height of the spanner will correlate to the anterior height of the graft. The posterior aspect of the graft should be approximately 2-3mm greater to ensure a secure fit (Figure 10). 12mm 10mm Smith-Robinson 10mm 12mm 12-13mm 10mm Simmons Figure 10 S U R G I C A L T E C H N I Q U E STEP 11 The ramp and trials* may also be used to trial the disc space. Place the ramp into the disc space perpendicular to the spine, ensuring that the outer flanges rest on the anterior vertebral surface (Figure 11). 5 Figure 11 STEP 12 Place the trial within the ramp and gently impact it into the intervertebral space. As the trial is impacted, the ends of the ramp will be forced open, thus distracting the disc space to accept the trial (Figure 12). *Trials constitute seperate and distinct Express Care sets, and must be ordered separately. Figure 12
STEP 13 The trial handle is marked with a series of lines (0, 5, 10, 20) so the depth of the trial can be monitored from outside the surgical site during insertion. As the trial is advanced into the disc space, the first mark will become aligned with the end of the ramp. At this point, the anterior-most portion of the trial will be aligned with the posterior edge of the flange on the ramp. If the flange is positioned appropriately against the anterior cortex of the vertebral body, this will indicate that the trial is now entirely within the disc space. Insert the trial further into the disc space until correct positioning is achieved. Increase the height of the trial until a firm fit is achieved (Figure 13). ------- ------------ Figure 13 STEP 14 Determine the height of the graft by adding 2mm to the height of the appropriate trial to account for the 6 thickness of the blades on the ramp. If the 8mm trial fits appropriately, a graft 10mm in height would be recommended. During subsequent placement of the graft, the ramp will briefly over-distract the interspace and allow the graft to slip in over the anterior vertebral cortex. 10mm 8mm When using a Smith-Robinson technique, the graft will Simmons Smith-Robinson Figure 14 be parallel-sided and will correspond to the combined height of the trial and the ramp. When using a Simmons technique, the combined height of the trial and ramp will correlate to the anterior height of the graft. The posterior aspect of the graft should be approximately 2-3mm greater to ensure a secure fit (Figure 14).
STEP 15 VertiGraft Spinal Spacers are available in sizes specifically designed for anterior cervical procedures. The circumferential cortical margin provides good structural support and, if desired, can be packed with morsalized autologous bone. Spinal spacers reduce the surgical time and patient morbidity associated with the harvesting and preparation of autograft (Figure 15). STEP 16 If a tricortical structural autograft is desired, first expose the anterior iliac crest and select an appropriate area approximately 4-5cm posterior to the anterior superior iliac spine. Select a part of the crest which is wide enough to fit the prepared disc space. Make the first cut across the crest using an oscillating saw (Figure 16). Figure 15 Figure 16 S U R G I C A L T E C H N I Q U E 7 STEP 17 Graft templates are available for both parallel-sided (Smith-Robinson) and tapered (Simmons) grafts. Apply the correct size cutting block and make the second cut. Graft removal can be accomplished using a pair of forceps or a graft removal instrument designed to cut across the base of the graft (Figure 17). Smith-Robinson Simmons Figure 17 STEP 18 The depth of the graft should be about 12mm, corresponding to the shoulder on the spanners. Other sizes may be used and should be measured with a depth gauge (Figure 18). 12mm Figure 18
STEP 19 Reinsert the ramp into the disc space perpendicular to the spine, ensuring that the outer flanges rest on the anterior vertebral surface. Maintain firm downward pressure on the ramp during subsequent graft insertion; otherwise, the device will tend to ride up out of the correct position as the graft is inserted (Figure 19). 8 STEP 20 Use the Bone Graft Holder to position the graft within the ramps. Align the graft in the desired orientation before placing it into the ramps since the grooves will not allow the graft to rotate during insertion. The bone graft holder with integral impaction platform is used initially, followed by the half-moon impactor to impact the graft into place. As the graft is impacted, the ends of the ramp will be forced open, thus distracting the disc space to accept the graft (Figure 20). Figure 19 STEP 21 The impactor is marked with a series of lines (0, 5, 10, 20) so that the depth of the graft can be monitored from outside the surgical site during insertion. As the graft is advanced into the disc space, the first mark (notch) will become aligned with the end of the ramp. At this point, the anterior-most portion of the graft will be aligned with the posterior edge of the flange on the ramp. If the flange is positioned appropriately against the anterior cortex of the vertebral body, this will indicate that the graft is now entirely within the disc space. Insert the graft further into the disc space until the desired position is achieved (Figure 21). Figure 20 Figure 21
STEP 22 Remove the ramp by gently rocking and pulling, being careful not to dislodge the graft. Use the impactor to maintain pressure on the graft during removal of the ramp (Figure 22). STEP 23 Perform final adjustment and seating of the graft using the impactor (Figure 23). Figure 22 S U R G I C A L T E C H N I Q U E 9 Figure 23 STEP 24 Apply additional fixation at the surgeon s discretion (Figure 24). Figure 24
Cervical Corpectomy STEP 1 Carry out exposure and excise the intervertebral discs and uncovertebral osteophytes as previously described. Resect the intervening vertebral body. The amount of body removed should be adequate to decompress the spinal canal if necessary and to accommodate the width of the autograft or allograft strut to be used for reconstruction (Figure 1). Figure 1 10 STEP 2 Prepare the endplates depending on the type of graft technique to be used (i.e., Smith-Robinson, Simmons). A lip or shelf of posterior cortical bone should remain to prevent retropulsion of the strut (Figure 2). Smith-Robinson Simmons Figure 2 STEP 3 Use a Graft Trial to assess the endplate coverage of various-sized grafts and ensure the corpectomy is wide enough for graft placement (Figure 3). Figure 3
STEP 4 Once the appropriate graft segment has been selected and trimmed to size, use the Modular Insertion Ramp to facilitate insertion of the graft. The ramp consists of two grooved ramps and an adjustable handle. Insert the ramps into the intervertebral space. The handle can then be opened up to 50mm to allow passage of the graft between the ramps. Note: The opening mechanism on the ramp is not intended to be used for distraction of the disc space and should be opened just enough to allow passage of the graft. Distraction of the intervertebral space is achieved by the graft s advancement through the ramps (Figure 4). STEP 5 Place the graft into the ramps in the desired orientation since the grooves will not allow the graft to rotate during insertion. Ensure that the outer flanges of the ramp rest on the vertebrae before advancing the graft. Impact the graft gently into place using the half-moon impactor (Figure 5). Figure 4 S U R G I C A L T E C H N I Q U E 11 Figure 5 STEP 6 Remove the ramp by gently rocking and pulling, being careful not to dislodge the graft. Use the half-moon impactor to maintain pressure on the graft during removal of the ramps. Gently tapping on the impactor while pulling up on the ramps may help with their removal (Figure 6). Figure 6
STEP 7 Disconnect the modular handle of the ramp to allow easier removal of the individual ramps. Remove the individual ramps by gently rocking or pulling, being careful not to dislodge the graft. Placing a rod through the holes in the ramps may further assist with their removal (Figure 7). Figure 7 12 STEP 8 An alternative method for graft insertion uses a single modular insertion ramp as a skid on which to slide the graft into position. Wedge the bottom of the graft into a secure position on the exposed endplate of the caudal vertebral body and use a half-moon impactor to tap the graft into position by sliding it down the ramp (Figure 8). Figure 8
STEP 9 Once the ramp has been removed, perform final adjustment and seating of the graft using the impactor (Figure 9). Figure 9 S U R G I C A L T E C H N I Q U E STEP 10 Apply additional fixation at the surgeon s discretion (Figure 10). 13 Figure 10
Limited Warranty and Disclaimer: DePuy AcroMed products are sold with a limited warranty to the original purchaser against defects in workmanship and materials. Any other express or implied warranties, including warranties of merchantability or fitness, are hereby disclaimed. Keystone is covered by U.S. Patent 5,431,658. Additional U.S. Patents are pending and foreign patents are issued and pending. WARNING: In the USA, this product has labeling limitations. See package insert for complete information. CAUTION: USA Law restricts these devices to sale by or on the order of a physician. DEPUY ACROMED IS A JOINT VENTURE WITH BIEDERMANN MOTECH GMBH. DePuy AcroMed, the DePuy AcroMed logo, Keystone and the Interbody Fusion icon are trademarks of DePuy AcroMed, Inc. All products are not currently available in all markets. VertiGraft is a trademark of LifeNet. 2000 DePuy AcroMed, Inc. All rights reserved. TO ORDER, CALL DEPUY ACROMED CUSTOMER SERVICE (1-800-ACROMED). DePuy AcroMed, Inc. 325 Paramount Drive Raynham, MA 02767 IF06-20-000 5/00