J Neurosurg 76: 159-163, 1992
Anterior cervical vertebrectomy and interbody fusion Technical note DEEPAK
AWASTHI,
M.D.,
AND RAND
M.
VOORHIES,
M.D.
Department of Neurosurgery, Louisiana State University Medical Center and Ochsner Medical Institutions, New Orleans, Louisiana V' This report discusses the authors' technique in performing anterior cervical vertebrectomy and interbody fusion for multilevel cervical disease. The technique is performed with a high-speed drill and bone-bank fibular strut graft. After decompression of the cervical canal, ledges are made in the intact vertebral bodies to create a rectangular bed for safe seating of the bone graft. The bone-bank fibular strut graft is a feasible alternative to autograft. The simplified and safe nature of this procedure reduces postoperative morbidity as well as the length of hospital stay.
KEY WORDS
•
interbody fusion
bone graft allograft • cervical spond~losis • operative technique
A
cervical vertebrectomy with interbody fusion is one of the surgical procedures used for multilevel cervical disease, including cervical spondylosis and ossification of the posterior longitudinalligament (OPLL).6,7,9,16.17 This report discusses our technique in performing this procedure using a highspeed drill and bone-bank fibular strut graft. This technique seeks to combine the relative safety of the SmithRobinson operation with the improved exposure of the Cloward procedure. Its most frequent application is for multilevel cervical disease involving large posterior marginal osteophytes. Less common indications include OPLL and trauma. In addition, bone-bank allografts (used in our technique) represent a feasible alternative to autografts. NTERIOR
Operative Technique
Initial Dissection After endotracheal intubation and induction of general anesthesia, the patient is placed in the supine position. The neck is mildly hyperextended by placing a roll under the shoulder blades. A Gardner-Wells tong is used for subsequent intraoperative traction in order to have a wide operative field, We prefer to operate from the patient's left side. An oblique skin incision is made along the anteromedial border of the left sternocleidomastoid muscle. The platysma is incised and undermined to improve the exposure. The anterior border 1. Neurosurg. I Volume 76 / January, 1992
• vertebrectomy
•
of the sternocleidomastoid muscle is mobilized and the muscle retracted laterally. The dissection is continued medial to the carotid sheath. The omohyoid muscle crosses the operative field and is usually transected. The esophagus and trachea are retracted medially, and the carotid sheath is retracted laterally. The prevertebral fascia is then identified, cauterized, and incised to expose the anterior longitudinal ligament. The appropriate level is confirmed by an intraoperative lateral x-ray film of the cervical spine.
Discectomy After confirmation of the level by x-ray film, dissection continues with at least partial removal of the discs at the rostral and caudal limits of the involved area. It is important to start with the discs for two reasons. The first is to gain a three-dimensional appreciation for the location of the spinal cord; otherwise, it is difficult to center the decompression over the anterior spinal dura. The other reason is that it is possible in cases with distorted anatomy, such as tumor, to leave behind a disc that should be removed. This can occur when dissection is begun in the middle of the vertebral body without first finding the disc space. The hard cortical bone at the inner border of the endplate can be mistaken for the outside of the neighboring vertebral body's endplate. This error results in an unstable construct which will fail since one end of the graft rests on a nonviable remnant of the cortical endplate, on the other 159
D. Awasthi and R. M. Voorhies
A.
B.
c.
FIG. I. Schematic diagram of the lateral cervical spine.
A: Intact vertebral bodies, emphasizing the inferior ang~latlOn
of the disc spaces. B: The extent of the osteotomy In our technique. C: The relationship of the fibular strut graft and the bone removal. The graft is actually slightly longer than the receptor site. Placement is fac!litated. by in-line skeletal traction at the moment of graft ImpactIOn. Also note the removal of the upper end of the lower intact vertebral body; this is important in eliminating the inferior angulation of the disc space and creating a rectangular bed.
side of which is a soft disc. After disc removal, the selfretaining Cloward retractor is placed underneath the lip of the longus colli muscles bilaterally - a plane developed with bipolar cautery and a curved elevator.
Bone Dissection Bone removal is accomplished with a high-speed drill. * The shaft should be long enough to permit good visualization in the deepest part of the exposure, and the size of the bit appropriate to allow accurate sculpting of the bony central trench with its ma~gin~lled~es. The high speed of the drill promotes rapid dlssectlO.n, but working with such a powerful tool of course entails significant risk. One ever-prese~t danger is the ~ote~tial for the drill bit to "skip" or "Jump." To aVOid spmal injury, it is important always to keep the shaft ?f the drill perpendicular to the dural surface. Thus, If the drill "jumps," the movement will be from side to si~e and not from superficial to deep. Another potentIal danger is the tendency for the drill to wrap up loose objects in the wound. All cottonoid pledgets should therefore be removed, and soft tissue not covered by blades of the self-retaining retractor should be protected with malleable retractors. Drilling is continued to the posterior longitudinal ligament using loupe magnification a~d headl.ig~t ~llu mination. The posterior longitudinal hgament IS mClSed or drilled (if ossified) to expose the dura. There is no consensus regarding the handling of the posterior longitudinal ligament. Saunders,I6 for example, r~com mends completely excising the ligament to achIeve a good decompression, while others believe in preserving the ligament. 26 We do not believe that it is necessary to
* High-speed drill and Model AM-8 attachment, manufactured by Midas Rex, Fort Worth, Texas. 160
FIG. 2. Schematic diagram of the rectangular receptor site. A "decompression" (smaller) rectangle is made through th.e center of the vertebral bodies with a width (12 mm) approxImately equal to that obtained in a standard Smith-Robinso.n exposure. A second rectangular trench ("fusion" rectangle) IS fashioned slightly wider and longer but about 2 mm shallower than the first central trough, and is superimposed over the first one. In this way, the surgeon creates a marginal ledge upon which the bone graft can safely rest. Despit~ these ledges, it is possible to achieve a wide lateral decompressIOn, especially at the disc levels. Significant osteophtyes are usually at the disc level.
completely excise the ligament. We do, however, open the ligament in the midline to be certain that the dura is decompressed. The osteophytes are removed with a drill attachment, enabling osteophytes at the extremes of the exposure to be removed with a slight angulation of the drill. The remaining disc material is also removed using standard techniques. Figure I B shows the extent of the osteotomy in this procedure. We decompress the ventral cervical cord by drilling a rectangular central trough through the center of the vertebral bodies with a width (12 mm) approximately equal to that obtained in a standard Smith-Robinson exposure (Fig. 2). In addition, we fashion a second rectangular trench slightly wider and longer but about 2 mm shallower than the first central trough. The second trench is superimposed over the first one. In this way, the surgeon creates a marginal ledge or shelf upon which the bone graft can rest (Fig. 2). This allows countersinking of the fibular strut while preventing any injury to the spinal cord. The marginal ledges are constructed at the vertebral body level, and it is possible to go wide at the disc levels and excise osteophytes as far lateral as the uncinate processes. The width of the larger or outer rectangle is determined by the width of the partially squared-off fibular graft. In general, both the graft and the receptor site are fashioned as far as possible to be exactly matching rectangular shapes. The graft may, however, be slightly larger, and the receptor site may be slightly "undercut," J. Neurosurg. / Volume 76/ January, 1992
Cervical vertebrectomy and fusion ,FibUla Graft
I(;/f I
.L
I
.L
FIG. 3. Schematic drawing showing preparation of the bone-bank fibular strut graft. A: The graft is shaped with a high-speed drill. B: The bone graft is fashioned into an approximately rectangular contour to snugly fit the rectangular receptor site. C: The bone graft is beveled.
particularly at the lower end. These differences in shape are intended to discourage graft extrusion so it is important to keep them minimal. The best insurance against extrusion is an exact match in size and shape with the graft completely countersunk. The length of the outer "fusion" (larger) rectangle is greater than the inner "decompression" (smaller) rectangle, particularly at the lower end (Fig. 2). This is dictated by the inferior angulation of the disc spaces of about 20· (Fig. IA). After the lowest disc is removed, the superior vertebral end plate that is exposed presents a sloping surface, which could cause the graft to slide off and extrude. It is necessary to fashion a rectangular bed for the graft. Therefore, the drill is used to remove a portion of the upper end of the normal vertebral body (below the lowest removed disc) in the deep or posterior aspect of the fusion rectangle (Fig. 1C). This also creates more of a marginal ledge around the inferior part of the decompression rectangle (Fig. 2). This inferior shelf becomes useful when one impacts the graft. At the superior end of the fusion (larger) rectangle, the anterior lip of the inferior endplate of the next normal vertebral body (above the highest removed disc) is often too prominent. The temptation to preserve it is great, because it presents a surface that is naturally "undercut" due to the inferior angulation of the disc spaces. It is actuaIIy better to drill away some of this to make the fusion (larger) rectangle more of a rectangle and less of a parallelogram (Fig. 1B and C). Bone Graft Freeze-dried bone-bank fibular strut graftt is used for interbody fusion. The bone is recovered from a deceased donor under sterile procedures. The don OJ and the donated tissues are thoroughly tested and found negative for the major viral and bacterial antigens,
t Banked bone provided by Osteotech, Inc., Shrewsbury, New Jersey. J. Neurosurg. / Volume 76/ January, 1992
FIG. 4. Schematic illustration depicting the rectangular fibular strut graft countersunk in the rectangular receptor site. Note the marginal ledges preventing the graft from impinging upon the spinal cord.
antibodies, and species. No secondary sterilant such as ethylene oxide or irradiation is used. However, ethylene oxide-sterilized bone has been successfully used for interbody fusion (J Jackson, personal communication, 1991).14 The bone graft is preserved using lyophilization, which involves freezing the bone to -70·C and removing the water sublimation. 12 The bone is then sealed under vacuum in sterile glass containers using sterile stoppers and transported to the hospital. The bone graft is stored at room temperature and rehydrated prior to use. After reconstitution, the bone-bank fibular strut graft (4 cm for one-level vertebrectomy, 6 cm for two-level vertebrectomy) is fashioned with a driII attachment in a rectangular shape to sit snugly in the prepared site (Figs. 3 and 4). It is important to fashion the fibular strut graft with a high-speed driII as rongeurs tend to shatter the brittle bone-bank bone. Manual traction is applied by the anesthesiologist, and the bone graft is countersunk into position using an impactor and mallet (Figs. 4 and 5). The anesthesiologist then gently flexes the neck in order to observe the stability of the graft under direct vision, and bone dust, which had been collected during vertebral body resection, is placed over and around the bone graft. Closure The wound is irrigated with bacitracin solution. The platysma is closed with interrupted 3-0 Vicryl sutures, and the skin is closed with a running subcuticular 4-0 Dexon suture. The patient is placed in a hard cervical 161
D. Awasthi and R. M. Voorhies Single Level Fusion
B~ AP
and Robinson
Smith
B.
c.
FIG. 5. Diagram showing countersinking of the fibular strut graft. A: Manual traction is applied by the anesthesiologist. B: The bone graft (slightly longer than the receptor site) is countersunk into position using an impactor and mallet. C: The graft countersunk in position.
(Philadelphia) collar and taken to the recovery room. As soon as recovery from the anesthesia is complete, the patient is allowed out of bed. Discussion
Background Anterior decompression and fusion operations have been performed since the 1950's, as described by Robinson and Smith,15,21 Southwick and Robinson,22 Bailey and Badgley, 1 Cloward,4 Dereymaeker and Muller,S Verbiest,23,24 and Simmons, et al. 20 ("keystone" technique). These represent single-level decompression and fusion techniques (Fig. 6). Anterior cervical vertebrectomy and corpectomy with interbody fusion is increasingly being performed to treat cervical spondylotic myelopathy.9,16,17 The decompression of the cervical canal in these procedures is more or less standard; however, there is some disagreement regarding the width of the decompression and the handling of the posterior longitudinal ligament. 16, 17 The greatest disagreement is in regard to the fusion techniques. One of the more popular techniques is notching the fibular strut graft, as described by Whitecloud and La Rocca25 (Fig. 6), Johnson and Southwick7 advocated carving keys on either end of the graft, which are fitted into "seating holes" or troughs drilled in the endplates of the upper and lower intact vertebral bodies (Fig. 6). This technique has also been described by other authors. 18,19 Other methods of grafting include recessing the graft behind the anterior cortical margin of the vertebra,I,7,24 multilevel "keystone" technique,16,17 and using plates to improve fixation,3
Advantages of the Present Technique Our anterior approach simplifies the vertebrectomy and interbody fusion while making it safer. Ledges are drilled to create a secure rectangular bed for the bone 162
Lateral
Multi-level Fusion Lateral
AP
~ ~ So~wick Robinson
:i~ ~~~
.~=~ ~ ~~= FIG. 6. Schematic diagram showing the various singlelevel (left) and multilevel (right) fusion techniques currently in use. Saunders' multilevel "keystone" graft16 is a modification of the single-level technique of Simmons, et aUo AP = anteroposterior view.
graft (Fig. 2). The ledges prevent the graft from injuring the ventral aspect of the spinal cord. The rectangular configuration of the graft and donor site with countersinking of the graft beneath the anterior surface of the spinal column prevents its extrusion, The present technique represents one possible method of making ledges; other modified methods can also be employed in making a similar construct (G Beach, personal communication, 1991). The present technique employs a fibular allograft instead of an iliac crest or a fibular autograft. Its shape is more easily fashioned into a rectangular graft, and donor site-related pain is eliminated. Nevertheless, the choice of bone-bank fibular strut for bone grafting is controversial. It is believed that bone grafts containing no cancellous bone fuse slowly.8,13 Many investigators also find that banked bone is inferior to fresh autogenous bone for incorporation into a solid fusion, 13 However, freeze-dried banked bone is readily available and is a feasible alternative to autogenous bone grafts. Freeze-dried allografts have been successfully used in clinical practice for many years,11,19 and the results obtained with freeze-dried banked bone have been comparable with those obtained from autografts. 2 ,10,14,19 Our technique also minimizes the postoperative morbidity and the length of the hospital stay, Postoperatively, the patients are placed in a hard cervical collar, obviating the need for a halo vest. Morbidity associated with harvesting the autograft is avoided by using banked bone. Most patients undergoing this procedure have a short hospital stay; most of our patients were discharged within 5 days postoperatively, Patients with longer hospital stays required postoperative rehabilitation because of severe preoperative myelopathy, J, Neurosurg. / Volume 76/ January, 1992
Cervical vertebrectomy and fusion
10, II, 12, 13, FIG. 7. Magnetic resonance (MR) images of the cervicothoracic spine, sagittal projection. Left: Preoperative T,weighted MR image showing a stable T -1 compression fracture with ventral compression of the cervical cord. Right: Postoperative spin-echo MR image showing the fibular strut graft (arrow) solidly in place between C-6 and T-2,
Between March, 1990, and September, 1990, seven patients have undergone anterior cervical vertebrectomy and interbody fusion using our technique. The results so far have been very good. There have been no postoperative neurological deficits or extrusions of the bone graft, and the mortality rate is 0%. In addition, postoperative diagnostic studies have revealed excellent positioning of the fibular strut grafts. Illustrative preand postoperative cervical magnetic resonance images are shown in Fig. 7. Clinical follow-up monitoring with objective assessment criteria is currently underway at our institution. In summary, the technique described offers the following advantages: 1) spinal cord protection; 2) no donor site morbidity; 3) no halo immobilization; and 4) a short hospital stay. References
14,
15, 16, 17,
18,
19, 20.
21,
I. Bailey RW, Badgley CE: Stabilization of the cervical spine
2. 3. 4. 5.
6. 7. 8. 9.
by anterior fusion. J Bone Joint Surg (Am) 42:565-594, 1960 Brown MD, Malinin TI, Davis PB: A roentgenographic evaluation of frozen allografts versus autografts in anterior cervical spine fusions. Clin Orthop 119:231-236, 1976 Caspar W, Barbier DD, Klara PM: Anterior cervical fusion and Caspar plate stabilization for cervical trauma, Neurosurgery 25:491-502, 1989 Cloward RB: The anterior approach for removal of ruptured cervical disks. J Neurosurg 15:602-617, 1958 Dereymaeker A, Muller J: Nouvelle cure chirurgicale des discopathies cervicales. La menisectomie par voie ventrale, suivie d'arthrodese par greffe intercorporeale. Neurochirurgie 2:233-234, 1956 Harsh GR IV, Sypert GW, Weinstein PR, et al: Cervical spine stenosis secondary to ossification of the posterior longitudinal ligament. J Neurosurg 67:349-357, 1987 Johnson RM, Southwick WO: Surgical approaches to the spine, in Rothman RH, Simeone FA (eds): The Spine, ed 2. Philadelphia: WB Saunders, 1982, Vol I, pp 124-127 Kaufman HH, Jones E: The principles of bony spinal fusion. Neurosurgery 24:264-270, 1989 Kojima T, Waga S, Kubo Y, et al: Anterior cervical
J. Neurosurg. / Volume 76/ January, 1992
22, 23. 24, 25, 26.
vertebrectomy and interbody fusion for multi-level spondylosis and ossification of the posterior longitudinalligament. Neurosurgery 24:864-872, 1989 Malinin TJ, Brown MD: Bone allografts in spinal surgery. Clin Orthop 154:68-73, 1981 Pelker RR, Friedlaender GE: Biomechanical aspects of bone autografts and allografts. Orthop Clin North Am 18: 235-239, 1987 Pelker RR, Friedlaender GE, Markham TC: Biomechanical properties of bone allografts. Clin Orthop 174: 54-57, 1983 Prolo DJ: Osteosynthesis in lumbar interbody fusion, in Lin PM, Gill K (eds): Lumbar Interbody Fusion. Principles and Techniques in Spine Surgery. Rockville, Md: Aspen, 1989, pp 71-75 Prolo DJ, Oklund SA, Butcher M: Towards uniformity in evaluating results of lumbar spine operations: a paradigm applied to posterior lumbar interbody fusions. Spine 11:601-606, 1986 Robinson RA, Smith GW: Anterolateral cervical disc removal and interbody fusion for cervical disc syndrome. Bull Johns Hopkins Hosp 96:223-224, 1955 (Abstract) Saunders RL: Anterior reconstructive procedures in cervical spondylotic myelopathy. Clin Neurosurg 37: 682-721, 1989 Saunders RL, Bernini PM, Shirreffs TG Jr, et al: Central corpectomy for cervical spondylotic myelopathy: a consecutive series with long-term follow-up evaluation. J Neurosurg 74: 163-170, 1991 Schmidek RH, Smith DA: Anterior cervical disc excision in cervical spondylosis, in Schmidek HH, Sweet WH (eds): Operative Neurosurgical Techniques: Indications, Methods and Results, ed 2. Orlando: Grune & Stratton, 1988, Vol 2, pp 1327-1342 Schneider J, Bright RW: Anterior cervical fusion using preserved bone allografts. Transplant Proc 8 (Suppl 1): 73-76,1976 Simmons EH, Bhalla SK, Butt WP: Anterior cervical discectomy and fusion: a clinical and biomechanical study with eight-year follow-up. With a note on discography: technique and interpretation of results. J Bone Joint Surg (Br) 51:225-237, 1969 Smith GW, Robinson RA: Treatment of certain cervicalspine disorders by anterior removal of the intervertebral disc and interbody fusion. J Bone Joint Surg (Am) 40: 607-624, 1958 Southwick WO, Robinson RA: Surgical approaches to the vertebral bodies in the cervical lumbar regions. J Bone Joint Surg (Am)39:63 1-644, 1957 Verbiest H: A lateral approach to the cervical spine: technique and indications. J Neurosurg 28: 191-203, 1968 Verbiest H: Anterolateral operations for fractures and dislocations in the middle and lower parts of the cervical spine. J Bone Joint Surg (Am) 51:1489-1530,1969 Whitecloud TS III, La Rocca H: Fibular strut graft in reconstructive surgery of the cervical spine. Spine 1: 33-43, 1976 Zdeblick TA, Bohlman HH: Cervical kyphosis and myelopathy: treatment by anterior corpectomy and strutgrafting. J Bone Joint Surg (Am) 71: 170-182, 1989
Manuscript received February 21, 1991. Accepted in final form May 29,1991. Address reprint requests to: Rand M. Voorhies, M.D., Department of Neurosurgery, Ochsner Clinic, 1514 Jefferson Highway, New Orleans, Louisiana 70121.
163
Anterior cervical vertebrectomy and interbody fusion Technical note DEEPAK
AWASTHI,
M.D.,
AND RAND
M.
VOORHIES,
M.D.
Department of Neurosurgery, Louisiana State University Medical Center and Ochsner Medical Institutions, New Orleans, Louisiana V' This report discusses the authors' technique in performing anterior cervical vertebrectomy and interbody fusion for multilevel cervical disease. The technique is performed with a high-speed drill and bone-bank fibular strut graft. After decompression of the cervical canal, ledges are made in the intact vertebral bodies to create a rectangular bed for safe seating of the bone graft. The bone-bank fibular strut graft is a feasible alternative to autograft. The simplified and safe nature of this procedure reduces postoperative morbidity as well as the length of hospital stay.
KEY WORDS
•
interbody fusion
bone graft allograft • cervical spond~losis • operative technique
A
cervical vertebrectomy with interbody fusion is one of the surgical procedures used for multilevel cervical disease, including cervical spondylosis and ossification of the posterior longitudinalligament (OPLL).6,7,9,16.17 This report discusses our technique in performing this procedure using a highspeed drill and bone-bank fibular strut graft. This technique seeks to combine the relative safety of the SmithRobinson operation with the improved exposure of the Cloward procedure. Its most frequent application is for multilevel cervical disease involving large posterior marginal osteophytes. Less common indications include OPLL and trauma. In addition, bone-bank allografts (used in our technique) represent a feasible alternative to autografts. NTERIOR
Operative Technique
Initial Dissection After endotracheal intubation and induction of general anesthesia, the patient is placed in the supine position. The neck is mildly hyperextended by placing a roll under the shoulder blades. A Gardner-Wells tong is used for subsequent intraoperative traction in order to have a wide operative field, We prefer to operate from the patient's left side. An oblique skin incision is made along the anteromedial border of the left sternocleidomastoid muscle. The platysma is incised and undermined to improve the exposure. The anterior border 1. Neurosurg. I Volume 76 / January, 1992
• vertebrectomy
•
of the sternocleidomastoid muscle is mobilized and the muscle retracted laterally. The dissection is continued medial to the carotid sheath. The omohyoid muscle crosses the operative field and is usually transected. The esophagus and trachea are retracted medially, and the carotid sheath is retracted laterally. The prevertebral fascia is then identified, cauterized, and incised to expose the anterior longitudinal ligament. The appropriate level is confirmed by an intraoperative lateral x-ray film of the cervical spine.
Discectomy After confirmation of the level by x-ray film, dissection continues with at least partial removal of the discs at the rostral and caudal limits of the involved area. It is important to start with the discs for two reasons. The first is to gain a three-dimensional appreciation for the location of the spinal cord; otherwise, it is difficult to center the decompression over the anterior spinal dura. The other reason is that it is possible in cases with distorted anatomy, such as tumor, to leave behind a disc that should be removed. This can occur when dissection is begun in the middle of the vertebral body without first finding the disc space. The hard cortical bone at the inner border of the endplate can be mistaken for the outside of the neighboring vertebral body's endplate. This error results in an unstable construct which will fail since one end of the graft rests on a nonviable remnant of the cortical endplate, on the other 159
D. Awasthi and R. M. Voorhies
A.
B.
c.
FIG. I. Schematic diagram of the lateral cervical spine.
A: Intact vertebral bodies, emphasizing the inferior ang~latlOn
of the disc spaces. B: The extent of the osteotomy In our technique. C: The relationship of the fibular strut graft and the bone removal. The graft is actually slightly longer than the receptor site. Placement is fac!litated. by in-line skeletal traction at the moment of graft ImpactIOn. Also note the removal of the upper end of the lower intact vertebral body; this is important in eliminating the inferior angulation of the disc space and creating a rectangular bed.
side of which is a soft disc. After disc removal, the selfretaining Cloward retractor is placed underneath the lip of the longus colli muscles bilaterally - a plane developed with bipolar cautery and a curved elevator.
Bone Dissection Bone removal is accomplished with a high-speed drill. * The shaft should be long enough to permit good visualization in the deepest part of the exposure, and the size of the bit appropriate to allow accurate sculpting of the bony central trench with its ma~gin~lled~es. The high speed of the drill promotes rapid dlssectlO.n, but working with such a powerful tool of course entails significant risk. One ever-prese~t danger is the ~ote~tial for the drill bit to "skip" or "Jump." To aVOid spmal injury, it is important always to keep the shaft ?f the drill perpendicular to the dural surface. Thus, If the drill "jumps," the movement will be from side to si~e and not from superficial to deep. Another potentIal danger is the tendency for the drill to wrap up loose objects in the wound. All cottonoid pledgets should therefore be removed, and soft tissue not covered by blades of the self-retaining retractor should be protected with malleable retractors. Drilling is continued to the posterior longitudinal ligament using loupe magnification a~d headl.ig~t ~llu mination. The posterior longitudinal hgament IS mClSed or drilled (if ossified) to expose the dura. There is no consensus regarding the handling of the posterior longitudinal ligament. Saunders,I6 for example, r~com mends completely excising the ligament to achIeve a good decompression, while others believe in preserving the ligament. 26 We do not believe that it is necessary to
* High-speed drill and Model AM-8 attachment, manufactured by Midas Rex, Fort Worth, Texas. 160
FIG. 2. Schematic diagram of the rectangular receptor site. A "decompression" (smaller) rectangle is made through th.e center of the vertebral bodies with a width (12 mm) approxImately equal to that obtained in a standard Smith-Robinso.n exposure. A second rectangular trench ("fusion" rectangle) IS fashioned slightly wider and longer but about 2 mm shallower than the first central trough, and is superimposed over the first one. In this way, the surgeon creates a marginal ledge upon which the bone graft can safely rest. Despit~ these ledges, it is possible to achieve a wide lateral decompressIOn, especially at the disc levels. Significant osteophtyes are usually at the disc level.
completely excise the ligament. We do, however, open the ligament in the midline to be certain that the dura is decompressed. The osteophytes are removed with a drill attachment, enabling osteophytes at the extremes of the exposure to be removed with a slight angulation of the drill. The remaining disc material is also removed using standard techniques. Figure I B shows the extent of the osteotomy in this procedure. We decompress the ventral cervical cord by drilling a rectangular central trough through the center of the vertebral bodies with a width (12 mm) approximately equal to that obtained in a standard Smith-Robinson exposure (Fig. 2). In addition, we fashion a second rectangular trench slightly wider and longer but about 2 mm shallower than the first central trough. The second trench is superimposed over the first one. In this way, the surgeon creates a marginal ledge or shelf upon which the bone graft can rest (Fig. 2). This allows countersinking of the fibular strut while preventing any injury to the spinal cord. The marginal ledges are constructed at the vertebral body level, and it is possible to go wide at the disc levels and excise osteophytes as far lateral as the uncinate processes. The width of the larger or outer rectangle is determined by the width of the partially squared-off fibular graft. In general, both the graft and the receptor site are fashioned as far as possible to be exactly matching rectangular shapes. The graft may, however, be slightly larger, and the receptor site may be slightly "undercut," J. Neurosurg. / Volume 76/ January, 1992
Cervical vertebrectomy and fusion ,FibUla Graft
I(;/f I
.L
I
.L
FIG. 3. Schematic drawing showing preparation of the bone-bank fibular strut graft. A: The graft is shaped with a high-speed drill. B: The bone graft is fashioned into an approximately rectangular contour to snugly fit the rectangular receptor site. C: The bone graft is beveled.
particularly at the lower end. These differences in shape are intended to discourage graft extrusion so it is important to keep them minimal. The best insurance against extrusion is an exact match in size and shape with the graft completely countersunk. The length of the outer "fusion" (larger) rectangle is greater than the inner "decompression" (smaller) rectangle, particularly at the lower end (Fig. 2). This is dictated by the inferior angulation of the disc spaces of about 20· (Fig. IA). After the lowest disc is removed, the superior vertebral end plate that is exposed presents a sloping surface, which could cause the graft to slide off and extrude. It is necessary to fashion a rectangular bed for the graft. Therefore, the drill is used to remove a portion of the upper end of the normal vertebral body (below the lowest removed disc) in the deep or posterior aspect of the fusion rectangle (Fig. 1C). This also creates more of a marginal ledge around the inferior part of the decompression rectangle (Fig. 2). This inferior shelf becomes useful when one impacts the graft. At the superior end of the fusion (larger) rectangle, the anterior lip of the inferior endplate of the next normal vertebral body (above the highest removed disc) is often too prominent. The temptation to preserve it is great, because it presents a surface that is naturally "undercut" due to the inferior angulation of the disc spaces. It is actuaIIy better to drill away some of this to make the fusion (larger) rectangle more of a rectangle and less of a parallelogram (Fig. 1B and C). Bone Graft Freeze-dried bone-bank fibular strut graftt is used for interbody fusion. The bone is recovered from a deceased donor under sterile procedures. The don OJ and the donated tissues are thoroughly tested and found negative for the major viral and bacterial antigens,
t Banked bone provided by Osteotech, Inc., Shrewsbury, New Jersey. J. Neurosurg. / Volume 76/ January, 1992
FIG. 4. Schematic illustration depicting the rectangular fibular strut graft countersunk in the rectangular receptor site. Note the marginal ledges preventing the graft from impinging upon the spinal cord.
antibodies, and species. No secondary sterilant such as ethylene oxide or irradiation is used. However, ethylene oxide-sterilized bone has been successfully used for interbody fusion (J Jackson, personal communication, 1991).14 The bone graft is preserved using lyophilization, which involves freezing the bone to -70·C and removing the water sublimation. 12 The bone is then sealed under vacuum in sterile glass containers using sterile stoppers and transported to the hospital. The bone graft is stored at room temperature and rehydrated prior to use. After reconstitution, the bone-bank fibular strut graft (4 cm for one-level vertebrectomy, 6 cm for two-level vertebrectomy) is fashioned with a driII attachment in a rectangular shape to sit snugly in the prepared site (Figs. 3 and 4). It is important to fashion the fibular strut graft with a high-speed driII as rongeurs tend to shatter the brittle bone-bank bone. Manual traction is applied by the anesthesiologist, and the bone graft is countersunk into position using an impactor and mallet (Figs. 4 and 5). The anesthesiologist then gently flexes the neck in order to observe the stability of the graft under direct vision, and bone dust, which had been collected during vertebral body resection, is placed over and around the bone graft. Closure The wound is irrigated with bacitracin solution. The platysma is closed with interrupted 3-0 Vicryl sutures, and the skin is closed with a running subcuticular 4-0 Dexon suture. The patient is placed in a hard cervical 161
D. Awasthi and R. M. Voorhies Single Level Fusion
B~ AP
and Robinson
Smith
B.
c.
FIG. 5. Diagram showing countersinking of the fibular strut graft. A: Manual traction is applied by the anesthesiologist. B: The bone graft (slightly longer than the receptor site) is countersunk into position using an impactor and mallet. C: The graft countersunk in position.
(Philadelphia) collar and taken to the recovery room. As soon as recovery from the anesthesia is complete, the patient is allowed out of bed. Discussion
Background Anterior decompression and fusion operations have been performed since the 1950's, as described by Robinson and Smith,15,21 Southwick and Robinson,22 Bailey and Badgley, 1 Cloward,4 Dereymaeker and Muller,S Verbiest,23,24 and Simmons, et al. 20 ("keystone" technique). These represent single-level decompression and fusion techniques (Fig. 6). Anterior cervical vertebrectomy and corpectomy with interbody fusion is increasingly being performed to treat cervical spondylotic myelopathy.9,16,17 The decompression of the cervical canal in these procedures is more or less standard; however, there is some disagreement regarding the width of the decompression and the handling of the posterior longitudinal ligament. 16, 17 The greatest disagreement is in regard to the fusion techniques. One of the more popular techniques is notching the fibular strut graft, as described by Whitecloud and La Rocca25 (Fig. 6), Johnson and Southwick7 advocated carving keys on either end of the graft, which are fitted into "seating holes" or troughs drilled in the endplates of the upper and lower intact vertebral bodies (Fig. 6). This technique has also been described by other authors. 18,19 Other methods of grafting include recessing the graft behind the anterior cortical margin of the vertebra,I,7,24 multilevel "keystone" technique,16,17 and using plates to improve fixation,3
Advantages of the Present Technique Our anterior approach simplifies the vertebrectomy and interbody fusion while making it safer. Ledges are drilled to create a secure rectangular bed for the bone 162
Lateral
Multi-level Fusion Lateral
AP
~ ~ So~wick Robinson
:i~ ~~~
.~=~ ~ ~~= FIG. 6. Schematic diagram showing the various singlelevel (left) and multilevel (right) fusion techniques currently in use. Saunders' multilevel "keystone" graft16 is a modification of the single-level technique of Simmons, et aUo AP = anteroposterior view.
graft (Fig. 2). The ledges prevent the graft from injuring the ventral aspect of the spinal cord. The rectangular configuration of the graft and donor site with countersinking of the graft beneath the anterior surface of the spinal column prevents its extrusion, The present technique represents one possible method of making ledges; other modified methods can also be employed in making a similar construct (G Beach, personal communication, 1991). The present technique employs a fibular allograft instead of an iliac crest or a fibular autograft. Its shape is more easily fashioned into a rectangular graft, and donor site-related pain is eliminated. Nevertheless, the choice of bone-bank fibular strut for bone grafting is controversial. It is believed that bone grafts containing no cancellous bone fuse slowly.8,13 Many investigators also find that banked bone is inferior to fresh autogenous bone for incorporation into a solid fusion, 13 However, freeze-dried banked bone is readily available and is a feasible alternative to autogenous bone grafts. Freeze-dried allografts have been successfully used in clinical practice for many years,11,19 and the results obtained with freeze-dried banked bone have been comparable with those obtained from autografts. 2 ,10,14,19 Our technique also minimizes the postoperative morbidity and the length of the hospital stay, Postoperatively, the patients are placed in a hard cervical collar, obviating the need for a halo vest. Morbidity associated with harvesting the autograft is avoided by using banked bone. Most patients undergoing this procedure have a short hospital stay; most of our patients were discharged within 5 days postoperatively, Patients with longer hospital stays required postoperative rehabilitation because of severe preoperative myelopathy, J, Neurosurg. / Volume 76/ January, 1992
Cervical vertebrectomy and fusion
10, II, 12, 13, FIG. 7. Magnetic resonance (MR) images of the cervicothoracic spine, sagittal projection. Left: Preoperative T,weighted MR image showing a stable T -1 compression fracture with ventral compression of the cervical cord. Right: Postoperative spin-echo MR image showing the fibular strut graft (arrow) solidly in place between C-6 and T-2,
Between March, 1990, and September, 1990, seven patients have undergone anterior cervical vertebrectomy and interbody fusion using our technique. The results so far have been very good. There have been no postoperative neurological deficits or extrusions of the bone graft, and the mortality rate is 0%. In addition, postoperative diagnostic studies have revealed excellent positioning of the fibular strut grafts. Illustrative preand postoperative cervical magnetic resonance images are shown in Fig. 7. Clinical follow-up monitoring with objective assessment criteria is currently underway at our institution. In summary, the technique described offers the following advantages: 1) spinal cord protection; 2) no donor site morbidity; 3) no halo immobilization; and 4) a short hospital stay. References
14,
15, 16, 17,
18,
19, 20.
21,
I. Bailey RW, Badgley CE: Stabilization of the cervical spine
2. 3. 4. 5.
6. 7. 8. 9.
by anterior fusion. J Bone Joint Surg (Am) 42:565-594, 1960 Brown MD, Malinin TI, Davis PB: A roentgenographic evaluation of frozen allografts versus autografts in anterior cervical spine fusions. Clin Orthop 119:231-236, 1976 Caspar W, Barbier DD, Klara PM: Anterior cervical fusion and Caspar plate stabilization for cervical trauma, Neurosurgery 25:491-502, 1989 Cloward RB: The anterior approach for removal of ruptured cervical disks. J Neurosurg 15:602-617, 1958 Dereymaeker A, Muller J: Nouvelle cure chirurgicale des discopathies cervicales. La menisectomie par voie ventrale, suivie d'arthrodese par greffe intercorporeale. Neurochirurgie 2:233-234, 1956 Harsh GR IV, Sypert GW, Weinstein PR, et al: Cervical spine stenosis secondary to ossification of the posterior longitudinal ligament. J Neurosurg 67:349-357, 1987 Johnson RM, Southwick WO: Surgical approaches to the spine, in Rothman RH, Simeone FA (eds): The Spine, ed 2. Philadelphia: WB Saunders, 1982, Vol I, pp 124-127 Kaufman HH, Jones E: The principles of bony spinal fusion. Neurosurgery 24:264-270, 1989 Kojima T, Waga S, Kubo Y, et al: Anterior cervical
J. Neurosurg. / Volume 76/ January, 1992
22, 23. 24, 25, 26.
vertebrectomy and interbody fusion for multi-level spondylosis and ossification of the posterior longitudinalligament. Neurosurgery 24:864-872, 1989 Malinin TJ, Brown MD: Bone allografts in spinal surgery. Clin Orthop 154:68-73, 1981 Pelker RR, Friedlaender GE: Biomechanical aspects of bone autografts and allografts. Orthop Clin North Am 18: 235-239, 1987 Pelker RR, Friedlaender GE, Markham TC: Biomechanical properties of bone allografts. Clin Orthop 174: 54-57, 1983 Prolo DJ: Osteosynthesis in lumbar interbody fusion, in Lin PM, Gill K (eds): Lumbar Interbody Fusion. Principles and Techniques in Spine Surgery. Rockville, Md: Aspen, 1989, pp 71-75 Prolo DJ, Oklund SA, Butcher M: Towards uniformity in evaluating results of lumbar spine operations: a paradigm applied to posterior lumbar interbody fusions. Spine 11:601-606, 1986 Robinson RA, Smith GW: Anterolateral cervical disc removal and interbody fusion for cervical disc syndrome. Bull Johns Hopkins Hosp 96:223-224, 1955 (Abstract) Saunders RL: Anterior reconstructive procedures in cervical spondylotic myelopathy. Clin Neurosurg 37: 682-721, 1989 Saunders RL, Bernini PM, Shirreffs TG Jr, et al: Central corpectomy for cervical spondylotic myelopathy: a consecutive series with long-term follow-up evaluation. J Neurosurg 74: 163-170, 1991 Schmidek RH, Smith DA: Anterior cervical disc excision in cervical spondylosis, in Schmidek HH, Sweet WH (eds): Operative Neurosurgical Techniques: Indications, Methods and Results, ed 2. Orlando: Grune & Stratton, 1988, Vol 2, pp 1327-1342 Schneider J, Bright RW: Anterior cervical fusion using preserved bone allografts. Transplant Proc 8 (Suppl 1): 73-76,1976 Simmons EH, Bhalla SK, Butt WP: Anterior cervical discectomy and fusion: a clinical and biomechanical study with eight-year follow-up. With a note on discography: technique and interpretation of results. J Bone Joint Surg (Br) 51:225-237, 1969 Smith GW, Robinson RA: Treatment of certain cervicalspine disorders by anterior removal of the intervertebral disc and interbody fusion. J Bone Joint Surg (Am) 40: 607-624, 1958 Southwick WO, Robinson RA: Surgical approaches to the vertebral bodies in the cervical lumbar regions. J Bone Joint Surg (Am)39:63 1-644, 1957 Verbiest H: A lateral approach to the cervical spine: technique and indications. J Neurosurg 28: 191-203, 1968 Verbiest H: Anterolateral operations for fractures and dislocations in the middle and lower parts of the cervical spine. J Bone Joint Surg (Am) 51:1489-1530,1969 Whitecloud TS III, La Rocca H: Fibular strut graft in reconstructive surgery of the cervical spine. Spine 1: 33-43, 1976 Zdeblick TA, Bohlman HH: Cervical kyphosis and myelopathy: treatment by anterior corpectomy and strutgrafting. J Bone Joint Surg (Am) 71: 170-182, 1989
Manuscript received February 21, 1991. Accepted in final form May 29,1991. Address reprint requests to: Rand M. Voorhies, M.D., Department of Neurosurgery, Ochsner Clinic, 1514 Jefferson Highway, New Orleans, Louisiana 70121.
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