Fusion and instrumentation at C1 3 via the high anterior cervical approach

Transcription

1 J Neurosurg (Spine 1) 92:24 29, 2000 Fusion and instrumentation at C1 3 via the high anterior cervical approach JOHN R. VENDER, M.D., STEVEN J. HARRISON, M.S., AND DENNIS E. MCDONNELL, M.D. Division of Neurosurgery, Medical College of Georgia, Augusta, Georgia Object. The high anterior cervical, retropharyngeal approach to the anterior foramen magnum and upper cervical spine is a favorable alternative to the transoral and posterolateral approaches, which both cause instability of the craniovertebral junction. Previously, such instability was corrected via an occipitocervical fusion during a separate surgical procedure. Methods. Seven patients requiring C-2 corpectomy (foramen magnum meningioma [two patients], critical stenosis secondary to rheumatoid arthritis [two patients], C-2 fracture [two patients], and stenosis secondary to Rickets [one patient]) are presented. All patients underwent C1 3 fusion followed by instrumentation with a Caspar plate. A solid fusion was achieved in six patients. One patient experienced erosion of the anterior arch of C-1 requiring posterior stabilization. Conclusions. Fusion and instrumentation at C1 3 can be performed safely and with minimal increase in surgical time. In selected patients, this may eliminate the need for an additional posterior procedure and maintain occipital C1 mobility. KEY WORDS anterior C1 3 arthrodesis craniovertebral junction Caspar plate foramen magnum transcervical approach N UMEROUS surgical approaches to the anterior foramen magnum and ventral surface of the upper cervical spinal cord have been described. 6,11,12 The high anterior cervical approach provides wide, bilateral exposure, avoids the potential contamination of the oral and pharyngeal cavities, and allows access to cervical spine segments below C-4. In the past, after decompressive surgery was performed, patients were maintained in traction and returned to the operating room for a second posterior occipitocervical fusion procedure. We present our experience with seven patients in whom C1 3 fusion was performed and instrumentation placed directly after the decompressive procedure was completed. The surgical approach allows for easy access to the anterior arch of C-1. Arthrodesis and placement of an anterior plate system in which bicortical screw purchase is used (Caspar plate) does not significantly increase operative time or perioperativerelated morbidity. The inclusion of arthrodesis and placement of instrumentation during the primary surgical procedure obviates the need for a separate procedure. In addition, because the anterior fusion does not include the occiput, occiput C1 mobility is preserved. Our experience to date suggests that, with careful patient selection and meticulous surgical technique, C1 3 fusion and placement of instrumentation via the high anterior cervical retropharyngeal approach can be accomplished safely and successfully. 24 Clinical Material and Methods Seven patients requiring a high anterior cervical retropharyngeal procedure underwent a C1 3 fusion procedure in which instrumentation was used. High Anterior Cervical Dissection The high anterior cervical retropharyngeal approach to the craniocervical junction has been described in detail Key technical points include wide, sharp dissection of each fascial plane, identification of landmarks that are easily visualized through the fascial planes, and countertraction in which a pickup forceps is used to help identify each plane. The patient is positioned with the head slightly extended and rotated 30 contralateral to the surgical approach. A horizontal incision is then created 2 cm inferior, and parallel to, the mandible. A subcutaneous flap, superficial to the platysma, is created on both sides of the incision to permit easier retraction. The platysma is incised vertically in the midline fascial raphe (linea alba) and transected horizontally in line with the original incision. The inferior edge of the submandibular gland is elevated, and the fascial capsule is opened and dissected in line with the skin incision. The facial artery and vein cross the field of dissection posterior and lateral to the gland, and they are dissected free. The facial vein is ligated and transected, and the facial artery is

2 High anterior cervical fusion and instrumentation preserved and retracted superolaterally. The tendon of the digastric muscle runs parallel to the incision under the inferior edge of the submandibular gland. The fascial sling tethering this tendon to the hyoid bone is transected, the tendon and undersurfaces of the anterior and posterior muscle bellies are freed, and the digastric muscle is retracted rostrally. The hypoglossal nerve courses deep, slightly inferior, and parallel to the digastric tendon; it is dissected free and retracted superiorly, exposing the hypoglossal muscles (Fig. 1). The greater wing of the hyoid bone is now visible and palpable. The fascia overlying the hyoid bone is incised along its course laterally to the carotid sheath, and the carotid artery is retracted laterally to open the retropharyngeal space. Care must be taken not to injure the superior laryngeal nerve. This nerve courses deep to the internal carotid artery along the middle pharyngeal constrictor muscle, toward the superior wing of the hyoid bone and adjacent to the superior pharyngeal constrictor muscle. Although not exposed in this dissection, the nerve is vulnerable to stretch injury from retraction. Wide dissection of the fascial planes will help reduce the risk of causing this injury because less force is required for retraction. The pharyngeal muscles are retracted medially with a deep rightangled retractor. The retropharyngeal areolar tissue is then opened sharply. The anterior tubercle of C-1 and the anterior surfaces of C-2 and C-3 are easily palpated. The longus colli and longus capitis muscles are freed from the ventral vertebral artery surface. A laser can be used to facilitate this part of the dissection (Fig. 2). The odontoid process and C- 2 vertebral body are removed using a 5-mm cutting burr drill until only a shell of cortical bone remains. A diamond burr drill is used for the remainder of the dissection. Bone removal begins at the apex of the odontoid process and proceeds inferiorly, which allows for better control of the odontoid process during its removal. On occasion, it is necessary to remove a small portion of the dorsal aspect of the anterior arch of C-1 to aid in exposure. After the corpectomy has been completed, the laser is again helpful in resecting the transverse ligament. Decompression is performed laterally until the entire ventral epidural space is exposed and the dura is bulging and free of compression. If an intradural lesion is present, the dura can be incised and resected. After completion of the intradural portion of the surgery, the dura is repaired with either autograft or allograft fascia lata. Fibrin-thrombin glue can be used to reinforce the repair. Arthrodesis and Instrumentation The interval between the inferior aspect of the anterior arch of C-1 and the superior endplate of C-3 is measured with a caliper. A graft of tricorticate ilium is prepared by notching the superior end of the graft. Allograft or autograft can be used depending on individual patient requirements. In the last two cases in our series allograft humerus was used instead of ilium. Humerus appears preferable to ilium because of the presence of circumferential cortical bone, which strengthens the notched end of the graft. Some shaving of the outer diameter of the graft may be required so that the graft fits into the corpectomy defect. The cavity of the graft can be filled with autograft or allograft cancellous bone. The distance between the base of the notch and the inferior end of the graft is equal to the FIG. 1. Diagram depicting the superficial surgical anatomy of the high anterior cervical dissection. m = muscle. distance previously measured between C-1 and C-3. The notched end of the graft is wedged under the anterior arch of C-1. The inferior end is then seated onto the superior endplate of C-3. A narrow curved osteotome is used as a lever to aid in the positioning of the graft into the corpectomy defect (Fig. 3). Manual traction on the skull or mandible can be used as well. A plate is selected that spans the distance from the top of the graft (and underlying C-1 arch) to the body of C-3 caudally. The plate is fixed to C-1 and C-3 by using four bicorticate screws. We consider bicorticate purchase to be essential to the biomechanical stability of this construct. It is not essential that the posterior part of the allograft, which forms the back of the notch, be traversed by the screws. One or two additional, unicortical screws are then placed in the fusion mass. Pin and screw placement is guided radiographically (Fig. 4a and b). Postoperative Care Patients remain intubated 3 to 5 days postoperatively to allow edema in the pharynx and retropharyngeal space to resolve. Patients should be weaned from mechanical ventilatory support as soon as they can tolerate it to avoid deconditioning of the respiratory muscles and ventilator dependency. Patients may require enteral nutritional support for several weeks; a nasojejunal tube may suffice. However, many patients undergo operative enteric access after induction of anesthesia and prior to the start of the cervical operation. The patient is weaned from reliance on this tube as soon as acceptance of oral nutrition improves. The enteric tube can be removed easily when it is no longer required, usually within 2 weeks of surgery. A lumbar drain is placed preoperatively when intradural surgery is anticipated or postoperatively if the dura is opened. Lumbar drainage is continued for 5 days postsurgery. Patients remain in a halo 25

3 J. R. Vender, S. J. Harrison, and D. E. McDonnell FIG. 2. Diagram depicting the deep surgical anatomy of the high anterior cervical dissection. The underlying angles of the mandibles are marked with an X to maintain orientation of view. Inset shows the craniocervical orientation after correct positioning has been achieved. brace for 3 months and then undergo evaluation with flexion extension radiography. Results Six patients who underwent treatment were followed for a mean of 18 months after removal of their halo brace and one patient was followed for 2.5 months postsurgery (Table 1). Two patients underwent intradural resection of a meningioma located in the anterior foramen magnum (Fig. 5). In five patients extradural, decompressive procedures were required: one to treat a pathological fracture of C-2 caused by metastatic breast carcinoma; one for a subacute traumatic fracture of C-2 causing spinal cord compression; one for spinal stenosis secondary to rickets; and two for spinal stenosis caused by advanced rheumatoid arthritis with pannus formation. All patients initially experienced improvement in their presenting neurological symptoms. In five of six patients solid fusion was achieved. In the seventh patient stable alignment has been maintained, and this patient remains asymptomatic in a halo orthosis. No clinically detectable alterations of occipitocervical or cervical mobility were noted after removal of the halo orthosis. In all seven patients extubation was performed 3 to 5 days postoperatively without difficulty. Residual dysphagia was limited, FIG. 3. Lateral cervical spine schematic drawings demonstrating the placement of the notched, bicortical iliac crest allograft. Left: A curved osteotome can be used to assist in the insertion of the inferior end of the graft. Right: The anterior cervical plate and bicortical screw purchase is shown. The superior screws may include the ventral portion of the fusion mass as well as anterior arch of C-1. Two additional screws have also been placed into the fusion mass for greater stability. 26

4 High anterior cervical fusion and instrumentation FIG. 4. Intraoperative lateral radiographs. a: The retractor (r) placed above C-1 is seen. Bicortical screws have been placed into the body of C-3. Guidewires are seen in the superior graft and underlying arch of C-1. The working trajectory can be noted by the angle of the guidewire at C-1. The degree of exposure created by this approach allows for easy visualization and comfortable surgical access, even at the C-1 level. b: The final position of the fusion mass and cervical plate is shown. Bicortical screws are seen at C-1 and C-3. An additional screw has been placed into the body of the fusion mass for greater stability. and all patients were weaned without difficulty from their feeding tubes. The prolonged period of intubation and the need for enteral feeding did not contribute to any perceptible increase in morbidity. The increase in intubation and enteral feeding times associated with this approach is not necessarily inconsistent with that associated with other surgical approaches. In one patient (Case 5; Table 1), erosion of the anterior arch of C-1 and graft migration resulted in esophageal erosion and concomitant neurological deterioration so that her postoperative status was the same as it was preoperatively. This patient underwent reoperation anteriorly for removal of the construct and a posterior fusion. In another patient with rheumatoid arthritis who underwent arthrodesis and placement of instrumentation, stable alignment has been maintained near the end of her course of halo orthosis therapy. In this case, no bone was resected from the posterior portion of the arch of C-1. Discussion The high anterior cervical approach is designed to expose the basiocciput of the clivus, the anterior rim of the foramen magnum, and the rostral cervical spine to C-4. With minimal additional dissection, the entire cervical spine can be exposed. This procedure offers the same direct access to the rostral ventral cervical spine and foramen magnum as that provided via the transoral route; however, in the case of the former approach, entry into the bacteria-contaminated environment of the oral cavity and pharynx is not required. This provides a safer environment for placement of instrumentation and/or management of a cerebrospinal fluid fistula. This approach allows a greater degree of lateral exposure (to and beyond the C-1 and C-2 lateral masses) than the transoral approach. In addition, compared with the transoral route, this approach offers greater caudal access if needed. 1 3 The posterolateral approach can also be used to good advantage for lesions at the craniocervical junction. 4,5,7 This technique requires extensive dissection including partial removal of the occipital condyle, and it provides very limited access to the contralateral lateral epidural space. Resection of bilateral intradural lesions is also extremely difficult. In this approach the lower cranial nerves are encountered early in the exposure, and further surgical exposure and decompression is performed around these nerves. In the high anterior cervical approach, the exposure is broad and bilateral, and in the case of intradural lesions, the cranial nerves are encountered deep in the exposure after the offending lesion has been resected. This essentially eliminates the significant risk of perioperative complications and potential long-term morbidity attributable to surgery-related lower cranial nerve injuries. The high anterior cervical technique can be performed with standard instruments. The surgical principles of this approach are more familiar than other approaches to surgeons trained in anterior cervical surgery. Our experience suggests that C1 3 anterior arthrodesis can be accomplished via the high anterior cervical approach, and thus it avoids the need for a second occipitocervical procedure. No intra- or perioperative complications were attributable to the fusion or instrumentation phase of the procedure. In five of the patients solid fusion was eventually demonstrated and spinal alignment was maintained. In all patients normal head and neck posture were observed after removal of the external orthosis. Overall, the procedure was well tolerated. 27

5 J. R. Vender, S. J. Harrison, and D. E. McDonnell TABLE 1 Characteristics in seven patients in whom the high anterior cervical approach was used to perform C1 3 fusion and placement of instrumentation* Age (yrs), Case No. Sex Initial Exam Diagnosis Outcome Follow Up (mos) 1 71, F hemiparesis pathological fracture solid fusion 20; died 2 48, M tetraparesis rickets solid fusion , M tetraparesis FM meningioma solid fusion , F Brown Séquard FM meningioma solid fusion , F tetraparesis, severe rheumatoid arthritis graft migration 11; died of respiratory depression respiratory failure 6 88, M spasms, spinal cord Type II odontoid solid fusion 3 compression fracture (subacute) 7 85, F severe neck pain rheumatoid arthritis stable position in halo 2 * FM = foramen magnum. This patient died of systemic complications related to widely metastatic breast carcinoma. This patient initially improved but subsequently deteriorated to her preoperative baseline status. Workup revealed graft migration. Although she underwent a successful fusion posteriorly, she could not be weaned from the ventilator and died of medical complications 4 months after her second operation. Failure of the construct occurred in one patient with a small axial skeleton and moderate osteoporosis attributable both to postmenopausal bone demineralization as well as to chronic steroid use as part of her treatment for rheumatoid arthritis. As reviewed in the Arthrodesis and Instrumentation section, it is sometimes necessary to resect a portion of the dorsal surface of the anterior arch of C-1. This bone removal is performed to improve soft-tissue resection. The combination of a small, demineralized anterior arch of C-1 and partial surgical resection of its dorsal surface rendered this bone inadequate to accept the applied forces of the construct, even with the stabilizing effect of the halo orthosis. This reinforces the need to limit or avoid resection of any part of the anterior arch of C-1 if it is to be used to support an anterior arthrodesis. Moderate osteoporosis or chronic rheumatoid arthritis should be considered as relative exclusion factors for anterior instrumentation and fusion. Patients with extensive bone demineralization or those in whom technical considerations require removal of a substantial portion of the posterior part of the anterior arch of C-1 should undergo a conventional posterior fusion. FIG. 5. Contrast-enhanced T 1 -weighted MR images. Sagittal (a) and axial (b) images demonstrating the large, midline meningioma of the foramen magnum observed in the patient in Case 3. The wide bilateral exposure provided by this approach allowed easy and complete removal of the tumor. 28

6 High anterior cervical fusion and instrumentation Conclusions The high anterior cervical approach is an effective alternative to transoral and posterolateral approaches in selected patients for the treatment of ventrally located intra- and extradural compressive lesions of the foramen magnum and the upper cervical spine. Arthrodesis followed by placement of instrumentation can be safely and successfully accomplished via this approach, which preserves occipitocervical mobility and avoids the need for a second posterior surgical procedure. Patient selection is critical, however. Severely osteoporotic patients may not be candidates for fusion and placement of instrumentation via this approach. References 1. Al-Mefty O, Borba LA, Aoki N, et al: The transcondylar approach to extradural nonneoplastic lesions of the craniovertebral junction. J Neurosurg 84:1 6, Crockard HA, Sen CN: The transoral approach for the management of intradural lesions at the craniovertebral junction: review of 7 cases. Neurosurgery 28:88 98, Dickman CA, Locantro J, Fessler RG: The influence of transoral odontoid resection on stability of the craniovertebral junction. J Neurosurg 77: , George B, Dematons C, Cophignon J: Lateral approach to the anterior portion of the foramen magnum. Application to surgical removal of 14 benign tumors: technical note. Surg Neurol 29: , George B, Lot G, Boissonet H: Meningiomas of the foramen magnum: a series of 40 cases. Surg Neurol 47: , Kratimenos GP, Crockard HA: The far lateral approach for ventrally placed foramen magnum and upper cervical spine tumours. Br J Neurosurg 7: , Lang DA, Neil-Dwyer G, Ianotti F: The suboccipital transcondylar approach to the clivus and cranio-cervical junction for ventrally placed pathology at and above the foramen magnum. Acta Neurochir 125: , McDonnell DE: Anterolateral cervical approach to the craniovertebral junction. Neurosurg Op Atlas 3: , McDonnell DE, Harrison SJ: Anterolateral cervical approach to the craniovertebral junction, in Wilkins RH, Rengachary SS (eds): Neurosurgery, ed 2. New York: McGraw-Hill, 1996, Vol 2, pp McDonnell DE, Harrison SJ: High cervical retropharyngeal approach to the craniovertebral junction. Perspect Neurol Surg 7: , Sekhar LN, Wright DC, Richardson R, et al: Petroclival and foramen magnum meningiomas: surgical approaches and pitfalls. J Neurooncol 29: , Sen CN, Sekhar LN: Surgical management of anteriorly placed lesions at the craniocervical junction an alternative approach. Acta Neurochir 108:70 77, 1991 Manuscript received June 4, Accepted in final form September 21, Address reprint requests to: John R. Vender, M.D., Section of Neurosurgery, BIW 348, Medical College of Georgia, th Street, Augusta, Georgia jvender@mail.mcg.edu. 29