Occipitocervical Instrumentation Research Articles

Biomechanical Implications of Extending Occipitocervical Instrumentation to Include the Subaxial Spine

No clear biomechanical data exist regarding where to place the caudal end of a screw-rod occipitocervical instrumentation construct. This study examines whether range of motion (ROM) from the occiput to C2 is altered by subaxial extension of occipitocervical instrumentation constructs. Cadaver specimens underwent intact biomechanical testing followed by destabilization via an odontoid osteotomy. Subsequent biomechanical testing was performed of four occipitocervical constructs: occipital plate + C2 pars screws (construct 1), occipital plate + C2 pars screws + C4 lateral mass screws (construct 2), occipital plate + C1-C2 transarticular screws (construct 3), and occipital plate + C1-C2 transarticular screws + C4 lateral mass screws (construct 4). All constructs significantly reduced occiput-C2 ROM in all loading modes compared with the intact cervical spine, with one exception (construct 1, lateral bending). No significant ROM differences were noted when C4 lateral mass screws (construct 4) were added to construct 3. Addition of C4 lateral mass screws (construct 2) to construct 1 decreased the ROM in the flexion mode only. No significant ROM differences were seen between construct 2 and construct 3 in any loading mode. The addition of subaxial instrumentation to occipitocervical instrumentation constructs in this study decreased occiput-C2 ROM only when the construct was anchored by C2 pars screws and only in flexion. Screws that cross the C1 to C2 articulation provide stable fixation when combined with an occipital plate, and the addition of subaxial instrumentation to this construct for stabilizing the occipitocervical junction does not significantly decrease ROM.

Occipitocervical instrumentation in the pediatric population using a custom loop construct: initial results and long-term follow-up experience

Rigid occipitocervical instrumentation for craniovertebral instability is gaining widespread acceptance for use in pediatric patients; however, most of the instrumentation has been modified from adult-sized hardware. The Wasatch loop system (formerly the Avery-Brockmeyer-Thiokol loop system) is a rigid occipitocervical fixation device designed specifically for use in children. It affixes to the occiput and incorporates either C1-2 transarticular screws or C-2 pars screws. It is preformed and is available in a variety of sizes. The authors describe their clinical experience and long-term follow-up experience with the first 22 patients. An institutional review board-approved retrospective review of medical records and radiographs was performed for patients who underwent occipitocervical fusion with the Wasatch loop. The mean patient age was 4.9 years (1.2-13 years), and the overall mean follow-up was 4 years (1.5-6.5 years). Six patients had posttraumatic instability, and 16 patients had congenital instability. Twelve patients underwent placement of bilateral C1-2 transarticular screws, 6 patients had placement of a combination of C1-2 transarticular and C-2 pars screws, and 4 patients had placement of bilateral C-2 pars screws. One patient required a halo orthosis; the others were treated postoperatively with a hard cervical collar. All patients had radiographic evidence of solid occipitocervical arthrodesis on last follow-up examination. The Wasatch loop system is a novel internal fixation device for children who have posttraumatic or congenital occipitocervical instability. Successful arthrodesis was achieved in all patients with minimal use of halo orthoses.

Metastases to the Craniovertebral Junction

This study reviews the relevant literature regarding the management of craniovertebral junction (CVJ) metastases. These rare tumors present significant diagnostic and treatment challenges. A PubMed search of cervical spine, cervical spine metastasis, craniovertebral junction, atlantoaxial spine, and metastasis radiation was conducted to define the epidemiology, imaging, and treatment protocols in the management of metastatic CVJ tumors. CVJ tumors represent less than 1% of spinal metastases, and the literature is limited to small case series. CVJ tumors present with flexion, extension, and rotational pain, often associated with occipital neuralgia. Magnetic resonance imaging is the most sensitive imaging modality for the detection of spinal metastases, but plain x-rays, computed tomography, and [18F]2-fluoro-2-deoxy-D-glucose play a role in diagnosis and management. Conventional external beam radiation therapy or stereotactic radiosurgery effectively treat the majority of patients with normal spinal alignment or minimal fracture subluxations. Surgery should be considered in patients with fracture subluxations greater than 5 mm, or 3.5 mm subluxation with 11-degree angulation. The palliative goals for surgery favor posterior approaches only including laminectomy for decompression, without the need for anterior approaches with the associated morbidity. Occipitocervical instrumentation using screw-rod systems are effective for irreducible subluxations, but posterior strategies using C1-C2 or C1-C3 can be used for patients with reducible subluxations. Effective management of CVJ tumors using radiation and/or surgery results in significant pain and functional improvement in properly selected patients. Advanced surgical techniques and stereotactic radiation may improve outcomes with less morbidity.

Image-Guided Placement of Occipitocervical Instrumentation Using a Reference Arc Attached to the Headholder

To develop a safe and accurate method of image-guided placement of instrumentation in the upper cervical spine and occiput in which the reference arc is fixed to the headholder. The authors describe a technique for placing screws at the occipital, C1, and C2 levels using 3-dimensional image guidance in which the reference arc is fixed to the headholder. Technical details are discussed as well as modifications to the technique to maximize navigation accuracy and decrease the need for re-registration. One of 2 paired systems, the BrainLAB Vector Vision system (BrainLAB Inc., Westchester, IL) used in conjunction with the Arcadis Orbic Isocentric C-arm (Siemens Medical Solutions, Erlangen, Germany) or the Stealth Treon system (Medtronic, Littleton, MA) paired with the O-arm (Medtronic), was used for image guidance in this study. A total of 18 patients had 82 screws placed at the occipital, C1, or C2 level using this technique. An independent radiologist interpreted postoperative computed tomographic scans of these patients and graded the screws for bony breach. No complications resulted from the use of image guidance or from the placement of instrumentation. Postoperative computed tomography revealed 1 screw with a minimal breach of the outer lamina of C2. Another screw was replaced intraoperatively secondary to a minimal bony breach. No other bony breach occurred. This technique allows safe and accurate placement of instrumentation in the posterior occipitocervical junction using 3-dimensional image guidance in which the reference arc is attached to the headholder.

Occipitocervical instrumentation in the pediatric population using a custom loop construct: initial results and long-term follow-up experience

Occipitocervical instrumentation in the pediatric population using a custom loop construct: initial results and long-term follow-up experience

Biomechanical Evaluation of Parasagittal Occipital Plating

Biomechanical evaluation of occipitocervical instrumentation techniques. Compare methods of occipital instrumentation by quantifying load sharing of occipital screws and measuring motion across instrumented occipitocervical spines. Newer occipitocervical plate/screw systems that attach to longitudinal rods have been developed to improve fixation. These devices place screws in the center of occipital bone or off-midline. Midline plates offer screw purchase in thicker bone. Off-midline systems may increase the effective moment arm for torsional and lateral bending control. Measurement of screw loads within occipital plates is useful for determining optimal plate configuration. Ten cadaveric specimens (occiput-C4) were tested in flexion/extension (FE), lateral bending (LAT), and axial rotation (ROT) over +/-3 Nm pure moment. After intact testing, 4 occipitocervical fixation constructs were tested using washer load cells to assess loading across screws used to fix the plates to the occiput. Parasagittal occipital plates were positioned either convex or concave side facing medially. Each plate was first fixed using 3 screws (rostral, middle, caudal), then with the caudal screw eliminated (simulated failure). Range of motion (ROM) and peak screw loads are reported. ROM decreased from intact to any of the 4 fusion plate configurations in FE, LAT, and ROT (P << 0.05), but not between plate configurations. Screw load significantly decreased from medially convex to medially concave configurations in LAT, but no significant changes were observed in FE or ROT. With caudal screws removed, middle screws peak loads significantly increased in FE and LAT (P < 0.05), but not ROT. Occipital screw placement off-midline improves screw loads under lateral bending forces on occipitocervical constructs, though loads for FE and ROT are unchanged. As screws pullout, the loads may be redistributed, resulting in increased screw pullout forces above. Despite the improvement in screw loads for laterally based plates during lateral bending, overall ROM across the occipitocervical junction is unchanged.

Plasmocitoma de base craneal con inestabilidad cráneo-cervical

Cranio-cervical instability is, in some cases, the main surgical concern in posterior skull base tumors. We report on a case in which a solitary plasmacytoma of the skull base presented with cranio-cervical instability. Vertebral artery was injured during surgery. The surgical anatomy is reviewed, with emphasis in vascular complications avoidance. A 66 year-old woman was diagnosed of a cranial base solitary plasmacytoma and treated with radio and chemotherapy with complete remission. After receiving that treatment, she presented with tetraparesis and a cranio-cervical instability was diagnosed. She was operated on, under cranial traction, of posterior occipito-cervical instrumentation with C1 to C2 transarticular Magerl screws. The right vertebral artery was injured during surgery without additional neurological deficit. Two years after the operation she remains independent for daily activities. Transarticular screws at the C1 to C2 level of the cervical spine may provide rigid fixation in posterior cranio-cervical instrumentation for osteolytic lesions, but there is a risk of injury to the vertebral artery, specially when some variations in the surgical anatomy exist.

SURGICAL TREATMENT OF OCCIPITOCERVICAL INSTABILITY

Instability of the occipitocervical junction can be a challenging surgical problem because of the unique anatomic and biomechanical characteristics of this region. We review the causes of instability and the development of surgical techniques to stabilize the occipitocervical junction. Occipitocervical instrumentation has advanced significantly, and modern modular screw-based constructs allow for rigid short-segment fixation of unstable elements while providing the stability needed to achieve successful fusion in nearly 100% of patients. This article reviews the preoperative planning, the variety of instrumentation and surgical strategies, as well as the postoperative care of these patients. Current constructs use occipital plates that are rigidly fixed to the thick midline keel of the occipital bone, polyaxial screws that can be placed in many different trajectories, and rods that are bent to approximate the acute occipitocervical angle. These modular constructs provide a variety of methods to achieve fixation in the atlantoaxial complex, including transarticular screws or C1 lateral mass screws in combination with C2 pars, C2 pedicle, or C2 translaminar trajectories. Surgical techniques for occipitocervical instrumentation and fusion are technically challenging and require meticulous preoperative planning and a thorough understanding of the regional anatomy, instrumentation, and constructs. Modern screw-based techniques for occipitocervical fusion have established clinical success and demonstrated biomechanical stability, with fusion rates approaching 100%.

Solitary fibrous tumor in the cervical spine with destructive vertebral involvement: a case report and review of the literature

Recently, solitary fibrous tumors occurring in spine-related lesions have been reported. However, the destruction of vertebral bodies by this type of tumor has not been reported. A 71-year-old female presented with pain from a mass on the right side of her neck. Plain radiographs of the cervical spine showed collapse of the C5 vertebral body and dislocation of the C4 vertebral body. The MRI image showed a large mass surrounding C4 and C5, which had low signal intensity in the T1W image and high signal intensity in the T2W image. At first, resection of the tumor and spinal fusion was performed by anterior approach. Histology revealed a solitary fibrous tumor with proliferating spindle cells. Immunohistochemistry showed positive stains for vimentin and CD34. One year postoperatively, a local recurrence manifested extensive destruction of the C4 and C5 vertebral bodies. Then, palliative surgery with posterior cervical instrumentation and radiation therapy were performed. Because the destruction proceeded and the rods were broken 2 years after, she underwent additional occipito-cervical instrumentation. This is the first report of a solitary fibrous tumor that involves the destruction of the spinal structure. An extensive destruction of the vertebral body by the solitary fibrous tumor needs to be aware in treating this tumor with spinal involvement.

COMPARISON OF CONTEMPORARY OCCIPITOCERVICAL INSTRUMENTATION TECHNIQUES WITH AND WITHOUT C1 LATERAL MASS SCREWS

This study was designed to test the kinematic properties of three occiput-C2 instrumentation constructs with and without supplemental rigid C1 fixation. The results are compared with intact specimens and with constructs incorporating contemporary cabling techniques. Five unembalmed human cadaver specimens underwent range of motion (ROM) testing in the intact condition, followed by destabilization with odontoid osteotomy. Destabilized specimens then underwent ROM testing with each of seven occipitocervical instrumentation constructs, all incorporating occipital screws: C1 and C2 sublaminar cables with cable connectors, C2 pars screws +/- C1 lateral mass screws, C2 lamina screws +/- C1 lateral mass screws, and C1-C2 transarticular screws +/- C1 lateral mass screws. All seven constructs demonstrated significantly lower ROM in all loading modes than intact specimens (P < 0.05). With a single exception, the addition of C1 lateral mass screws to the screw-based constructs produced no significant change in ROM in any of the loading modes. Compared with intact specimens, constructs anchored by C1-C2 transarticular screws demonstrated the greatest decrease in ROM, and those anchored by sublaminar cables demonstrated the least decrease in ROM. Any of the tested screw-based constructs are likely to provide adequate support for the patient with an unstable craniocervical junction. Therefore, the choice of construct should be based on anatomic considerations. The routine incorporation of C1 lateral mass screws into occipitocervical instrumentation constructs does not seem necessary.

Anatomical, biomechanical, and practical considerations in posterior occipitocervical instrumentation

Patients with cervical myelopathy secondary to craniocervical instability commonly present with spinal cord compression secondary to a combination of static forces and gross instability. Craniocervical arthrodesis is therefore indicated in the treatment of the majority of these conditions. In order to facilitate arthrodesis, techniques for occipitocervical instrumentation have been developed. To systematically review the anatomy, biomechanics, and practical considerations involved in posterior occipitocervical instrumentation. Retrospective literature review. Not applicable. Not applicable. Retrospective literature review. The anatomic elements of the craniocervical junction include the occipital bone, occipital condyles, atlas (C1), and axis (C2). The occiput-C1 and C1-C2 motion segments possess unique mechanical properties. Occipitocervical instrumentation constructs are comprised of points of fixation and longitudinal elements, each with characteristic strengths and weaknesses. Analysis of the anatomy, available points of fixation, and the movements to be controlled leads to the choice of a longitudinal element which can control movement by incorporating the strongest points of fixation. By going through this process for each patient, an informed decision may be made regarding the optimal occipitocervical instrumentation construct.

Indications for surgery and stabilization techniques of the occipito-cervical junction

Occipito-cervical (OC) instrumentation and fusion is indicated in traumatic atlanto-occipital dissociation and type III Anderson-Montesano occipital condyle fractures. The goals of surgery are to stabilize the mechanically compromised OC junction, correct deformity or displacement, and decompress compromised neural structures. The goals of instrumentation are to provide immediate stability, improve fusion rate, diminish the need for postoperative external immobilization, and decrease rehabilitation time. To successfully instrument the occipito-cervical spine, a working knowledge of the anatomy of the occipital-cervical junction is imperative. A wide variety of stabilization techniques and instrumentation systems are currently available, each with its own advantages and disadvantages. With familiarity of the constraints and benefits of the available instrumentation systems, the individual fixation needs of a clinical situation can be fulfilled and successful patient outcomes can be achieved.

Occipitocervical Fixation: Long-Term Results

The study is a retrospective review of 58 patients who underwent occipitocervical fusion between 1997 and 2001. Our objective is to study the clinical results after occipitocervical fixation with long-term follow-up and assess factors contributing to clinical success. Data from patient charts, operative notes, physician office notes, and imaging studies were incorporated in the study. Myelopathy was assessed using a Nurick scale for preoperative and postoperative evaluation. Fusion was assessed using cervical plane films with flexion and extension views. Mean follow-up was 36 months, with all patients having a greater than 1-year follow-up. The most common pathology was congenital cranial settling (41%) followed by trauma (22%) and rheumatoid arthritis (17%). Myelopathy was the most common presentation (62%) followed by pain (28%). A successful fusion occurred in 48 out of 51 patients (94%). Symptoms improved in 86% of patients, whereas 35% improved 1 Nurick grade. Complications occurred in 30% of patients. The cervical wound infection rate was 5%. The rate of adjacent level degeneration was 7%. The mortality rate was 1.7%. Occipitocervical instrumentation allows for very high fusion rates without the need for halo vest immobilization. All patients with successful fixation have pain resolution. Myelopathy improves in most patients, whereas one-third of patients demonstrate dramatic improvement.

Occipitocervical stabilization for myelopathy in patients with rheumatoid arthritis. Implications of not bone-grafting.

Approximately 0.9 percent of the white adult population of the United States and 1.1 percent of the adult population in Europe are affected by seropositive rheumatoid arthritis. As many as 10 percent of those patients may need an operation for atlantoaxial subluxation. Severe instability, especially when associated with vertical subluxation of the odontoid process, can result in progressive cervical myelopathy. Typically, occipitocervical fixation has been performed for these patients with use of autograft bone to achieve long-term stability through a solid fusion. Harvesting the bone graft increases the operative risk to the patient and may result in increased morbidity. In our experience, patients who have had no clear radiographic evidence of fusion following use of occipitocervical instrumentation seemed to have done as well as those who have had obvious fusion. One assumption is that the clinical improvement might be attributable simply to stabilization of the joint rather than to osseous fusion. A longitudinal study was performed on patients with rheumatoid arthritis who required an operation because of craniocervical or upper cervical instability. The results of clinical, radiographic, functional, and self-evaluations were studied to determine the efficacy of treatment and to compare the outcomes of bone-grafting with those of procedures done without bone-grafting in a group of 150 patients who underwent posterior occipitocervical stabilization with use of a contoured metal implant (a Ransford loop) that was affixed by sublaminar wires. Internal fixation was performed in 120 patients without bone-grafting and in thirty patients with use of autogenous bone-grafting. Preoperatively, 23 percent (thirty-five) of the 150 patients had mild neurological involvement (class II, according to the system of Ranawat et al.), 45 percent (sixty-eight) had objective findings of weakness and long-tract signs but were able to walk (class III-A), and 29 percent (forty-three) were quadriparetic and unable to walk (class III-B). The age of the patients at the time of the operation ranged from twelve to eighty-three years (mean, sixty-two years). There were significant improvements in postoperative Ranawat classes at all time-periods (range, p < 0.00005 to p = 0.0066) and in patient ratings of neck pain (range, p < 0.00005 to p = 0.0044) compared with preoperative scores. With the numbers available, there were no significant differences between the patients managed with a graft and those managed without grafting with respect to survival after the operation, Ranawat class, head or neck-pain rating, presence of subaxial abnormalities, radiographic craniovertebral motion, or vertical subluxation. Overall mortality at one month was 10 percent (fifteen of 150), although this value varied directly with the degree of preoperative disability. A second cervical spine operation was required in 11 percent (sixteen) of the 150 patients. While patients who have rheumatoid disease with anterior atlantoaxial subluxation should be treated with posterior atlantoaxial arthrodesis with use of bone-grafting and internal fixation, we believe that those who present with vertical instability and multi-level involvement can be treated with posterior occipitocervical stabilization with use of a contoured occipitocervical loop and sublaminar wire fixation without bone-grafting. Furthermore, we believe that the use of preoperative traction, bone cement, or a postoperative halo vest is unnecessary. Avoiding the harvesting of autogenous bone for grafting reduced the morbidity of this operation without compromising the outcome in these already sick patients.

Point of View: An Anatomic Study of the Thickness of the Occipital Bone: Implications for Occipitocervical Instrumentation

Point of View: An Anatomic Study of the Thickness of the Occipital Bone: Implications for Occipitocervical Instrumentation

Surgical management of atlantoaxial nonunions

Sixteen patients referred for atlantoaxial fixation failures were treated surgically with revision procedures during the past decade. Of these 16 patients, atlantoaxial instability occurred because of rheumatoid arthritis in five, as odontoideum in seven, transverse ligament disruption in two, and odontoid fracture nonunion in two. The 16 individuals (10 men, six women; mean age 43.7 years; age range 20-77 years) had undergone a total of 20 C1-2 internal fixation procedures that failed. Surgical strategies for definitive revision of the nonunions in these 16 subjects included 10 rigid internal fixations with transarticular screws, three revised C1-2 fixations with autogenous bone struts and wire or cables, and three extended fixations with occipitocervical instrumentation. Autogenous grafts were used in all revisions. A postoperative halo brace was used in five individuals with osteoporotic bone; all patients wore a restrictive postoperative cervical orthosis. Postoperatively, 15 patients (94%) had a stable construct (mean follow up 35 months; range 12-79 months), which included 13 osseous unions and two stable fibrous unions. One patient had nonunion; he fractured his anterior C1-2 transarticular screws 2 years postoperatively. He had occipital radicular pain without myelopathy but refused further surgery. Atlantoaxial pseudarthroses were effectively treated by addressing the pathological, biomechanical, and technical reasons for failed fusion. Successful fusion after reoperation was improved by using autologous bone grafts, adequately controlling atlantoaxial motion (with rigid transarticular screws internally or externally with a halo vest), compressing the bone grafts between the arches of C-1 and C-2 with wire cables, meticulously preparing the fusion bed, and by optimizing the pharmacological and clinical parameters to promote bone healing.

Occipitocervical fusion with posterior plate and screw instrumentation. A long-term follow-up study.

Thirty-two patients at one institution underwent occipitocervical fusions with posterior plate and screw instrumentation. The average follow-up was greater than 4 years (50 months). AO plates and screws were used and in more than 50% of the cases, the Magerl transarticular C1-C2 screw technique enhanced the occipitocervical instrumentation. In nine patients, cement was used and thus are excluded in evaluation of fusion results. All 23 patients attained solid fusions. No pseudarthrosis occurred. The average time to fusion was 13 weeks. Halos or traction immobilization was not used postoperatively. The average time of the simple orthosis wear was 11 weeks. Patients were out of bed on an average of the second postoperative day with a range of 1-4 days postoperatively. Reduction of the atlantoaxial joint was required in 10 of the 23 patients. At follow-up, nine remain reduced. In one patient, the atlantodens interval approximated the preoperative distance and radiographs demonstrated one transarticular C1-C2 screw was not placed satisfactorily. The average operative time was 172 minutes, and the average blood loss was 956 cc. The neurologic status of the patients improved or remained the same. No patient deteriorated neurologically. A total of 78 occipital screws were placed. No complications resulted from any of these screws. One intraoperative complication occurred secondary to massive bleeding after a transarticular screw hole was drilled. Bone wax was placed over the drill hole and the bleeding ceased. No postoperative problems occurred in this patient. Most specifically, no central nervous system sequela was evident. The conclusions from this study are that posterior occipitocervical fusion can be performed very safely with plate and screw instrumentation. An extremely high fusion rate can be expected with minimal complications and minimal postoperative immobilization. This technique, however, is technically demanding.

環軸椎転位例に対するＯｃｃｉｐｉｔｏ‐Ｃｅｒｖｉｃａｌ Ｉｎｓｔｒｕｍｅｎｔａｔｉｏｎの経験

We studied six cases of atlanto-axial dislocation treated by occipito cervical instrumentation. The diagnosis was RA in two cases and malignant tumors in four cases. The alignment of the upper cervical spine was severely destroyed in all cases. In the cases of RA, the clinical results and mechanical fixation of the instruments were good, but vertical redislocation between the atlanto-axial joint occurred on rentogenographic examination. Though all cases of malignant tumors died within four months after the operation, the symptomatic evaluation, including relief of pain, was excellent. In conclusion, occipito-cervical fusion with a modified U rod seemed to be the most useful instrumentation in selected cases.