Posterior cervical fusion in chidren

Allograft versus autograft for pediatric posterior cervical and occipito-cervical fusion: a systematic review of factors affecting fusion rates

OBJECT Fusion rates are high for children undergoing posterior cervical fusion (PCF) and occipito-cervical fusion (OCF). Autologous bone has been widely used as the graft material of choice, despite the risk of donor-site morbidity associated with harvesting the bone, possibly because very low fusion rates were reported with posterior allograft cervical fusions in children several decades ago. Higher overall fusion rates using allograft in adults, associated with improvements in internal fixation techniques and the availability of osteoinductive substances such as bone morphogenetic protein (BMP), have led to heightened enthusiasm for the use of bank bone during pediatric PCF. A systematic review was performed to study factors associated with successful bone fusion, including the type of bone graft used. METHODS The authors performed a comprehensive PubMed search of English-language articles pertaining to PCF and OCF in patients less than 18 years old. Of the 561 abstracts selected, 148 articles were reviewed, resulting in 60 articles that had sufficient detail to be included in the analysis. A meta-regression analysis was performed to determine if and how age, fusion technique, levels fused, fusion substrate, BMP use, postoperative bracing, and radiographic fusion criteria were related to the pooled prevalence estimates. A systematic review of the literature was performed according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) statement. RESULTS A total of 604 patients met the specific inclusion and exclusion criteria. The overall fusion rate was 93%, with a mean age of 9.3 years and mean follow-up of 38.7 months. A total of 539 patients had fusion with autograft (94% fusion rate) and 65 patients with allograft (80% fusion rate). Multivariate meta-regression analysis showed that higher fusion rates were associated with OCF compared with fusions that excluded the occiput (p < 0.001), with the use of autograft instead of allograft (p < 0.001), and with the use of CT to define fusion instead of plain radiography alone. The type of internal fixation, the use of BMP, patient age, and the duration of follow-up were not found to be associated with fusion rates in the multivariate analysis. CONCLUSIONS Fusion rates for PCF are high, with higher rates of fusion seen when autograft is used as the bone substrate and when the occiput is included in the fusion construct. Further study of the use of allograft as a viable alternative to autograft bone fusion is warranted because limited data are available regarding the use of allograft in combination with more rigid internal fixation techniques and osteoinductive substances, both of which may enhance fusion rates with allograft.

Severe spinal cord injury in craniocervical dislocation. Case-based update

BACKGROUND

Craniocervical distraction injuries, including atlanto-axial dislocation (AAD) and atlanto-ocipital dislocation (AOD), are often associated with severe spinal cord involvement with high morbidity and mortality rates. Many patients with these injuries die at the accident scene, but advances in emergency resuscitation and transport permit that many patients arrive alive to hospitals.

DISCUSSION

Children with craniocervical distraction injuries usually present with a severe cranioencephalic traumatism that is the most relevant lesion at admission. After resuscitation and hemodynamic stabilization, the spinal cord damage appears as the main lesion. Apnea and quadriparesis, or quadriplegia, are usually present at the onset. Early diagnosis and management perhaps decrease life-threatening manifestations of the spinal lesion. But even so, the primary spinal cord insult is often irreversible and precludes obtaining a satisfactory functional outcome.

PATIENTS AND METHODS

We report the findings of four children with craniocervical distraction injuries (AOD and AAD) who presented with severe spinal cord damage. All patients were admitted with respiratory distress or apnea together with significant brain injuries. The medical records pertaining to these patients are summarized in regard to clinical features, management, and outcome.

CONCLUSIONS

In spite of timely and aggressive management, craniocervical injuries with spinal cord involvement continue to have a dismal prognosis. Outcome is closely related to the severity of the initial brain and spinal cord damage and is nearly always fatal in cases of complete spinal cord transection. Priority should be given to life-threatening complications. Ethic issues on indications for surgery deserve a detailed discussion with the children's parents.

Outcomes of instrumented fusion in the pediatric cervical spine

Object

The most common cause of cervical spine arthrodesis in the pediatric population is instability related to congenital or traumatic pathology. Instrumenting the cervical spine can be challenging given smaller anatomical structures, less ossified bone, and future growth potential and development. Studies in adult patients have suggested that using screw constructs results in improved outcomes with lower rates of instrumentation failure. However, the pediatric literature is limited to small retrospective series. Based on a review of the literature and their own patient series, the authors report that instrumenting the pediatric cervical spine with screw constructs may be safer and more effective than using wiring techniques.

Methods

The authors reviewed the existing pediatric cervical spine arthrodesis literature and contributed 31 of their own cases from September 1, 2007, to January 1, 2011. They reviewed 204 abstracts from January 1, 1966, to December 31, 2010, and 80 manuscripts with 883 total patients were included in the review. They recorded demographic, radiographic, and outcomes data—as well as surgical details—with a focus on fusion rates and complications.

Patients were then grouped into categories based upon the procedure performed: 1) patients who underwent fusions bridging the occipitocervical junction and 2) patients who underwent fusion of the cervical spine that did not include the occiput, thus including atlantoaxial and subaxial fusions. Patients were further subdivided according to the type of instrumentation used—some had posterior cervical fusion with wiring (with or without rod implantation); others had posterior cervical fusion with screws.

Results

The entire series comprised 914 patients with a mean age of 8.30 years. Congenital abnormalities were encountered most often (in 55% of cases), and patients had a mean follow-up of 32.5 months. From the entire cohort, 242 patients (26%) experienced postsurgical complications, and 50 patients (5%) had multiple complications. The overall fusion rate was 94.4%.

For occipitocervical fusions (N = 285), both screw and wiring groups had very high fusion rates (99% and 95%, respectively, p = 0.08). However, wiring was associated with a higher complication rate. From a sample of 252 patients, 14% of those treated with screw instrumentation had complications, compared with 50% of patients treated with wiring (p < 0.05).

In cervical fusions not involving the occipitocervical junction (N = 181), screw constructs had a 99% fusion rate, whereas wire instrumentation only had an 83% fusion rate (p < 0.05). Similarly, patients who underwent screw fixation had a lower complication profile (15%) when compared with those treated with wiring constructs (54%, p < 0.05).

Conclusions

The results of this study are limited by variations in construct design, use of orthoses, follow-up duration, and newer adjuvant products promoting fusions. However, a literature review and the authors' own series of pediatric cases suggest that instrumentation of the cervical spine in children may be safer and more efficacious using screw constructs rather than wiring techniques.

Cervical spine trauma in children: a review

Injuries of the cervical spine are relatively rare in children but are a distinct clinical entity compared with those found in adults. The unique biomechanics of the pediatric cervical spine lead to a different distribution of injuries and distinct radiographic features. Children younger than 9 years of age usually have upper cervical injuries, whereas older children, whose biomechanics more closely resemble those of adults, are prone to lower cervical injuries. Pediatric cervical injuries are more frequently ligamentous in nature, and children are also more prone to spinal cord injury without radiographic abnormality than adults are. Physical injuries are specific only to children. Radiographically benign findings, such as pseudosubluxation and synchondrosis, can be mistaken for traumatic injuries. External immobilization with a halo brace can be difficult and is associated with a high complication rate because of the thin calvaria in children. Surgical options have improved with the development of instrumentation specifically for children, but special considerations exist, such as the small size and growth potential of the pediatric spine.

Pediatric subaxial cervical spine injuries: origins, management, and outcome in 51 patients

OBJECT

In this study the authors evaluated the mechanisms and patterns of injury and the factors affecting management and outcome of pediatric subaxial cervical spine injuries (C3-7).

METHODS

Fifty-one pediatric patients (38 boys and 13 girls; mean age 12.4 years, range 10 months-16 years) with subaxial cervical spine injuries were reviewed retrospectively. Motor vehicle accidents (MVAs) were the most common cause of injury. Overall, 12% presented with a dislocation, 63% with a fracture, 19% with a fracture-dislocation, and 6% with a ligamentous injury. The most frequently injured level was C6-7 (33%); C3-4 (6%) was least frequently involved. Sixty-four percent of patients were neurologically intact, 16% had incomplete spinal cord injuries (SCIs), 14% had complete SCIs, and three patients (6%) died after admission and before assessment. Treatment was conservative in 64%: seven (13%) wore a halo vest and 26 (51%) wore a rigid cervical orthosis. Surgery was performed in the other 18 patients (36%), with the breakdown as follows: 15 (30%) underwent an anterior approach, two (4%) had posterior approaches, and one (2%) had a combined approach. Postoperatively, four patients (8% who had a neurological deficit improved. The overall mortality rate was 8%; all deaths were related to MVAs. There were no surgery-related deaths or complications.

CONCLUSIONS

Subaxial cervical spine injuries are common in children 9 to 16 years of age, and occur principally between C-5 and C-7. Multilevel injury is more common in children 8 years of age and older than in younger children and infants. Most patients with subaxial cervical spine injuries can be treated conservatively. Both anterior and posterior approaches are safe and effective.

Biomechanical comparison of inside-outside screws, cables, and regular screws, using a sawbone model

Our aim was to conduct a biomechanical comparison of the pull-out strengths of inside-outside (I/O) screws, cables, and bone screws to determine whether I/O screws provide greater pull-out resistance than cables or bone screws, and their effectiveness with the screw diameter. There is no remarkable biomechanical experimental study comparing the I/O technique with conventional spinal techniques. The diameter of the screw heads were also biomechanically tested to determine the optimal size that can be used. In this study, 45 blocks of 50x50x5 mm of "sawbone" (synthetic bone, model 1137, Pacific Research Laboratories, Vashon, WA, USA) were used as bone substitutes. Fifteen sets of 14-mm inside-outside Dynalok screws and nuts, 15 wire cables, and 15 bone screws were inserted into a separate sawbone block. An MTS Bionx materials testing machine was used to measure the load to failure of each implant. The mean values and standard deviations of each group were calculated and Student's t-test was used for comparison. The load to failure of the inside-outside screws was significantly greater than that of the cables (p<0.0000004) and the regular bone screws (p<0.000002). The results also revealed that increasing the diameter of the head of the screw also increases the resistance against the pull-out strengths. Thus, using a larger screw in occipitocervical stabilization provides safe and stable fixation of the occipital bone to the cervical spine. This study also proved that sawbone is a useful and reliable alternative to allogenic fresh cadaveric bone grafts or animal bones for certain biomechanical testing.

Delayed intracranial migration of cervical sublaminar and interspinous wires and subsequent cerebellar abscess. Case report

Delayed complications associated with sublaminar and interspinous wiring in the pediatric cervical spine are rare. The authors present a case of delayed complication in which a cervical fusion wire migrated into the cerebellum, causing subsequent cerebellar abscess 2 years after posterior cervical arthrodesis. A craniotomy was required to remove the wire and drain the abscess. Despite their history of safety and successful fusion, procedures involving sublaminar and interspinous wiring carry a risk of neurological injury secondary to wire migration. A thorough neuroimaging evaluation is required in patients who have undergone fusion and who have neurological complaints to detect late instrumentation-related sequelae.

Inside-outside technique for posterior occipitocervical spine instrumentation and stabilization: preliminary results

OBJECT

The authors present a series of 16 patients who underwent inside-outside occipital and posterior cervical spine stabilization.

METHODS

In this technique, the screw was placed from the inside of the occiput to the outside. An articular (lateral) mass plate was contoured to the shape of the occipital bone and the cervical spine and affixed to the occiput with a flat-headed screw or stud placed through a burr hole in the calvaria with the flat head of the screw in the epidural space and the threads facing outward. The bone plate was then secured with a nut to the occipital screw and the cervical plate was attached to the spine with a bone screw that coursed through the plate and into the articular pillar. Our series included six children and 10 adults. In five patients, previous fusion had failed; in two patients spinal instability was secondary to Down's syndrome; two patients' instability was related to developmental anomalies; and in five patients spinal instability was due to the presence of tumor. One patient with rheumatoid arthritis had undergone a transoral procedure. Two patients had suffered traumatic fracture. Three patients died of causes unrelated to the procedure, one patient died of metastatic cancer, and one patient died in a long term care facility of cardiopulmonary complications. One patient with renal failure suffered a hemorrhage from an arteriovenous fistula after being treated with dialysis. In one child, a nut backed off after 3 months. The nut was reseated, and a maturing arthrodesis was present.

CONCLUSIONS

The authors conclude that the inside-outside occipitocervical fixation is an effective technique for stabilizing the cervical spine.

A comparative analysis of fusion rates and donor-site morbidity for autogeneic rib and iliac crest bone grafts in posterior cervical fusions

OBJECT

Autogeneic bone graft is often incorporated into posterior cervical stabilization constructs as a fusion substrate. Iliac crest is used frequently, although donor-site morbidity can be substantial. Rib is used rarely, despite its accessibility, expandability, unique curvature, and high bone morphogenetic protein content. The authors present a comparative analysis of autogeneic rib and iliac crest bone grafts, with emphasis on fusion rate and donor-site morbidity.

METHODS

A review was conducted of records and radiographs from 600 patients who underwent cervical spinal fusion procedures in which autogeneic bone grafts were used. Three hundred patients underwent rib harvest and posterior cervical fusion. The remaining 300 patients underwent iliac crest harvest (248 for an anterior cervical fusion and 52 for posterior fusion). The analysis of fusion focused on the latter subgroup; donor-site morbidity was determined by evaluating the entire group. Fusion criteria included bony trabeculae traversing the donor-recipient interface and long-term stability on flexion-extension radiographs. Graft morbidity was defined as any untoward event attributable to the graft harvest. Statistical comparisons were facilitated by using Fisher's exact test.

CONCLUSIONS

Demographic data obtained in both groups were comparable. Rib constructs were placed in the following regions: occipitocervical (196 patients), atlantoaxial (35 patients), and subaxial cervical spine (69 patients). Iliac crest grafts were placed in the occipitocervical (28 patients), atlantoaxial (10 patients), and subaxial cervical (14 patients) regions. Fusion occurred in 296 (98.8%) of 300 rib graft and 49 (94.2%) of 52 iliac crest graft constructs (p = 0.056). Graft morbidity was greater with iliac crest than with rib (p < 0.00001). Donor-site morbidity for the rib graft was 3.7% and included pneumonia (eight patients), persistent atelectasis (two patients), and superficial wound dehiscence (one patient). Pneumothorax, intercostal neuralgia, and chronic chest wall pain were not encountered. Iliac crest morbidity occurred in 25.3% of the patients and consisted of chronic donor-site pain (52 patients), wound dehiscence (eight patients), pneumonia (seven patients), meralgia paresthetica (four patients), hematoma requiring evacuation (three patients), and iliac spine fracture (two patients). Even when chronic pain was not considered, morbidity encountered in obtaining iliac crest still exceeded that encountered with rib harvest (p = 0.035). The fusion rate and donor-site morbidity for rib autograft compare favorably with those for iliac crest when used in posterior cervical constructs. To the authors' knowledge, this represents the largest series to date in which the safety and efficacy of using autogeneic bone graft materials in spinal surgery are critically analyzed.

Occipital calvarial bone graft in posterior occipitocervical fusion

STUDY DESIGN

Dorsal occipitocervical fusion is associated with a high rate of fusion failure and requires an additional surgical site for donor bone graft harvesting. In this series, an autologous occipital calvarial bone graft obtained from the same occipitocervical incision with contoured metal loops was used in 25 adults to achieve craniovertebral stabilization and fusion.

OBJECTIVES

To study the use of autologous occipital calvarial bone grafts in occipitocervical fusion.

SUMMARY OF BACKGROUND DATA

Cranial bone grafts have been used successfully in craniofacial reconstruction with good long-term results. In the plastic surgery literature, there are claims that membranous bone grafts are superior to endochondral bone grafts in fusions because of decreased resorption. In recent studies, results have shown successful use of calvarial bone in fusing the upper cervical spine in children. The use of autologous occipital bone in posterior occipitocervical fusions avoids many of the problems associated with traditional donor sites and provides a sufficient quantity of good quality bone for the fusion. This is especially true in the fragile rheumatoid arthritis patient with cranial cervical instability.

METHOD

Split-thickness, autologous calvarial bone grafts with contoured loop and cable instrumentation were used for posterior occipitocervical stabilization and fusion in 25 patients, most of whom had rheumatoid arthritis. The calvarial bone graft was harvested from the occipital skull, using a microair impactor, and was secured next to the loop construct. After surgery, all patients were immobilized with external orthoses.

RESULTS

None of the patients had hardware failure or complications from the occipital graft procurement. In 22 patients, good alignment, stability, and bony fusion were shown on radiographs.

CONCLUSIONS

Occipital calvarial bone graft appears to work as well as other autologous corticocancellous bone grafts routinely used in posterior occipitocervical fusions.

Occipitocervical fusion with C1 laminectomy in children

STUDY DESIGN

Eight children in whom atlantoaxial dislocation had developed underwent occipitocervical fusion using a rectangular rod. The postoperative results are presented, and the postoperative growth and deformation of the cervical spine were determined radiographically.

OBJECTIVES

To investigate in a relatively long-term follow-up study whether occipitocervical fusion affects the growth of the cervical spine and induces spinal deformation.

SUMMARY OF BACKGROUND DATA

It has been reported that children who have undergone C1-C2 posterior fusion are likely to develop abnormal curvature or deformation of the cervical spine as a result of a disturbance of growth of the fused vertebrae. There have been no studies, however, to confirm that these changes occur after occipitocervical fusion in children.

METHODS

The subjects were one boy and seven girls who had undergone occipitocervical posterior fusion during childhood. The average age at the time of surgery was 8.3 years, and the average follow-up period was 5.9 years. The following were assessed radiographically: redislocation of the atlas, bone union, changes in the curvature of the cervical spine, the height and width of the vertebral bodies, and the anteroposterior diameter of the spinal canal.

RESULTS

Solid bone union was achieved in all patients with maintenance of the reduced position at the time of surgery. None of the patients exhibited abnormal curvature of the cervical spine. The rate of increase in height of the C2 vertebral body was significantly less than that of vertebral bodies below C3. The rate of increase in width of the vertebral body and the anteroposterior diameter of the spinal canal of the C2 vertebral body and vertebral bodies below C3 did not differ significantly.

CONCLUSIONS

Occipitocervical fusion with a rectangular rod is useful for treating atlantoaxial dislocation in children and yields excellent results because of the firm internal fixation it achieves. This surgery induced no apparent postoperative spinal deformations.

Posterior cervical spine fusion with tension-band wiring

In this study the authors detail their experience with posterior tension-band wiring for stabilization of the subaxial cervical spine. Fifty-five patients underwent fusion for trauma (41 patients), degenerative disease (13 patients), and tumor (one patient). The fusion rate was 96% (50 of 52 patients) and postoperative immobilization was accomplished by means of a Philadelphia collar in the majority of cases. Tension-band wiring provides a stable construct that is simple to perform, requires fusion of a minium number of motion segments, and allows early mobilization with only a hard collar needed for support. The details of the technique, which has been modified from preliminary descriptions, are discussed.

Comparative experimental biomechanical study of different types of stabilization methods of the lower cervical spine

In a comparative experimental biodynamic study using thirty-two human cervical spines of cadavers the primary stabilization effect of different types of spondylodesis was examined. Whereas in flexion stress all methods showed a sufficient stability, the rotation tests proved, that in case of a dorsal instability of the lower cervical spine, posterior interlaminar wiring or anterior plate stabilization showed no reliable stabilization effect. However, the compression clamps by ROOSEN and TRAUSCHEL as well as the hook-plates by MAGERL are suitable dorsal stabilization methods with excellent rotation stability. In case of dorsal instability of the lower cervical spine a posterior spondylodesis is necessary and sufficient.

Complications of sublaminar wiring

Complications of sublaminar wiring are reported, including four cases that involved the cervical spine and one case that included the thoracolumbar spine. The complication rate at our institution involving the cervical spine was about 7% and less than 1% for the thoracic spine. A direct correlation exists between the degree of anterior bowing, number of consecutive laminae the wire passes beneath, and the complication rate. The clinical presentations, radiologic findings, and indications for surgical removal of the wires are discussed. To our knowledge, nothing has been reported in the literature regarding the complications caused by sublaminar wiring of consecutive vertebrae.

Pediatric neck injuries. A clinical study

This review of pediatric neck injuries includes patients admitted to Children's Hospital of Columbus, Ohio, during the period 1969 to 1979. The 122 patients with neck injuries constituted 1.4% of the total neurosurgical admissions during this time. Forty-eight patients had cervical strains; 74 had involvement of the spinal column; and 27 had neurological deficits. The injuries reached their peak incidence during the summer months, with motor-vehicle accidents accounting for 31%, diving injuries and falls from a height 20% each, football injuries 8%, other sports 11%, and miscellaneous 10%. There is a clear division of patients into a group aged 8 years or less with exclusively upper cervical injuries, and an older group with pancervical injuries. In the younger children, the injuries involved soft tissue (subluxation was seen more frequently than fracture), and tended to occur through subchondral growth plates, with a more reliable union than similar bone injuries. In the older children, the pattern and etiology of injury are the same as in adults. The entire cervical axis is at risk, and there is a tendency to fracture bone rather than cartilaginous structures.

Modern treatment of the symptomatic os odontoideum

A new surgical procedure for treatment of congenital, symptomatic atlanto-axial instability (os odontoideum ) is described. Two metallic clamps, with an integrated inner spring for maintaining continuous pressure on a cortico-cancellous bone-graft implanted into the interlaminar space, are fixed posteriorly on the vertebral arches C1/2 next to the graft. Because of the initial solid segment-stability external fixation is unnecessary. Posterior interlaminar osteosynthesis prevents late neurological complications caused by a mobile os odontoideum .

Special problems and indications of the palliative osteosynthesis of the cervical vertebra

The palliative internal fixation of the cervical spine becomes more and more important. Independent of the patients age, the procedure is indicated by neurologic complications, very severe pain, in patients of generally good condition. The tumorous lesion of the spine should be a local restricted one.