Avoiding early complications and reoperation during occipitocervical fusion in pediatric patients

Clinical article

Free access

Object

Surgical arthrodesis for pediatric occipitocervical (OC) instability has a high rate of success in a wide variety of challenging circumstances; however, identifying potential risk factors can help to target variables that should be the focus of improvement. The aim of this paper was to examine risk factors predictive of failure in a population of patients who underwent instrumented OC arthrodesis using a uniform surgical philosophy.

Methods

The authors conducted a retrospective cohort study of pediatric patients who underwent OC fusion from 2001 to 2013 at a single institution to determine risk factors for surgical failure, defined as reoperation for revision of the arthrodesis or instrumentation. The primary study outcome was either radiographic confirmation of successful OC fusion or surgical failure requiring revision of the arthrodesis or instrumentation. The secondary outcome was the underlying cause of failure (hardware failure, graft failure, or infection). Univariate analysis was performed to assess the association between outcome and patient demographics, cause of OC instability, type of OC instrumentation, bone graft material, biological adjuncts, and complications.

Results

Of the 127 procedures included, 20 (15.7%) involved some form of surgical failure and required revision surgery. Univariate analysis revealed that patients with deep wound infections requiring debridement were more likely to require surgical revision of the hardware or graft (p = 0.002). Subgroup analysis revealed that patients with skeletal dysplasia or congenital spinal anomalies were more likely to develop hardware failure than patients with other causes of OC instability (p = 0.020). Surgical failure was not associated with the method of C-2 fixation, type of rigid OC instrumentation, bone graft material, use of bone morphogenetic protein or biological adjuncts, cause of instability, sex, age, or having previous OC fusion operations.

Conclusions

Pediatric patients in the present cohort with postoperative wound infections requiring surgical debridement had higher surgical failure rates after OC fusion. Those with skeletal dysplasia and congenital spinal anomalies were more likely to require reoperation for hardware failure. Better understanding of the mode of surgical failure may enable surgeons to develop strategies to decrease the need for reoperation in pediatric patients with OC instability.

Abbreviations used in this paper:BMP = bone morphogenetic protein; DBM = demineralized bone matrix; OC = occipitocervical.

Abstract

Object

Surgical arthrodesis for pediatric occipitocervical (OC) instability has a high rate of success in a wide variety of challenging circumstances; however, identifying potential risk factors can help to target variables that should be the focus of improvement. The aim of this paper was to examine risk factors predictive of failure in a population of patients who underwent instrumented OC arthrodesis using a uniform surgical philosophy.

Methods

The authors conducted a retrospective cohort study of pediatric patients who underwent OC fusion from 2001 to 2013 at a single institution to determine risk factors for surgical failure, defined as reoperation for revision of the arthrodesis or instrumentation. The primary study outcome was either radiographic confirmation of successful OC fusion or surgical failure requiring revision of the arthrodesis or instrumentation. The secondary outcome was the underlying cause of failure (hardware failure, graft failure, or infection). Univariate analysis was performed to assess the association between outcome and patient demographics, cause of OC instability, type of OC instrumentation, bone graft material, biological adjuncts, and complications.

Results

Of the 127 procedures included, 20 (15.7%) involved some form of surgical failure and required revision surgery. Univariate analysis revealed that patients with deep wound infections requiring debridement were more likely to require surgical revision of the hardware or graft (p = 0.002). Subgroup analysis revealed that patients with skeletal dysplasia or congenital spinal anomalies were more likely to develop hardware failure than patients with other causes of OC instability (p = 0.020). Surgical failure was not associated with the method of C-2 fixation, type of rigid OC instrumentation, bone graft material, use of bone morphogenetic protein or biological adjuncts, cause of instability, sex, age, or having previous OC fusion operations.

Conclusions

Pediatric patients in the present cohort with postoperative wound infections requiring surgical debridement had higher surgical failure rates after OC fusion. Those with skeletal dysplasia and congenital spinal anomalies were more likely to require reoperation for hardware failure. Better understanding of the mode of surgical failure may enable surgeons to develop strategies to decrease the need for reoperation in pediatric patients with OC instability.

Surgical failure after pediatric occipitocervical (OC) arthrodesis is a significant event, in terms of both human and hospital costs. Failure may be caused by factors such as hardware malposition, loosening, or breakage; infection; or arthrodesis failure. Rehospitalization, reoperation, and repeat physician visits to address failures are only the first ripple of a wave that may affect many aspects of a patient's life, such as missed school, lost time at work for the patient's parents, and the uncertainty of whether success will be achieved with a revision. Therefore, every effort must be made to ensure that initial surgical procedures are successful in pediatric patients with OC disorders.

An excellent starting point is to identify potential risk factors for surgical failure in a large cohort of patients undergoing OC fusion. Previous studies have not directly addressed this issue. The work of several authors, including that of the senior author (D.L.B.), has focused mainly on overall surgical success rates without examining the specific underlying factors.2,6,10,13,18 Potential risk factors for failure may include the cause of the instability, patient age, the type of instrumentation used, the type of graft material used, and the use of biologics. The aim of this paper was to examine risk factors predictive of OC fusion failure in a population of patients who underwent instrumented OC arthrodesis using a uniform surgical philosophy.

Methods

Data Collection

Prior to data collection, the study was approved by the Institutional Review Boards at the University of Utah and Primary Children's Hospital. A search of the pediatric neurosurgical operative database at Primary Children's Hospital for the period from January 2001 to March 2013 identified all operations performed to manage OC instability. Data from procedures performed prior to 2001 were not included because of variations in surgical technique. Conservatively managed patients were also excluded. Additional cases were excluded for the following reasons: patients had undergone occipitocervicothoracic fusion operations, age older than 18 years, patients lost to follow-up, and patients had not undergone postoperative CT scanning to evaluate arthrodesis.

The medical records and radiographs of patients who underwent OC fusion were double-reviewed for data collection and accuracy. Clinical variables were recorded, including sex, cause of OC instability, age at surgery, operation performed, number of previous fusion operations, method of cervical fixation, OC rigid fixation device, bone graft material, use of bone morphogenetic protein (BMP) or other biological adjuncts, postoperative bracing, use of the O-arm surgical imaging system (Medtronic, Inc.), and surgical complications requiring reoperation.

The causes of OC instability were classified into the following groups: skeletal dysplasia, congenital spinal anomalies, Down syndrome, Chiari malformation, trauma, and os odontoideum. Each patient was assigned to one group based on their primary disorder, if known. Diagnoses were made based on clinical features and imaging characteristics on preoperative CT scans with consultation from a pediatric neuroradiologist. Skeletal dysplasia included disorders involving abnormal bone and/or cartilage formation, growth, and remodeling such as achondroplasia, spondyloepiphyseal dysplasia, osteogenesis imperfect, Jeune syndrome, Kniest syndrome, Larsen syndrome, Loeys-Dietz syndrome, and Morquio syndrome.20 Cases were classified into the congenital spinal anomalies group if no known primary disorder or syndrome could be identified. Congenital spinal anomalies included malformations arising from improper fusion of chondrification or ossification centers involving the craniocervical junction, such as Klippel-Feil syndrome, basilar invagination or impression, odontoid dysgenesis, basioccipital dysgenesis, and defects of the anterior or posterior arch of C-1.15 Cases were classified into the os odontoideum group if their abnormality was diagnosed incidentally and there was no history of acute trauma, a concurrent diagnosis of skeletal dysplasia, or other congenital spinal anomalies.

Outcomes

All postoperative radiographs and CT scans were reviewed by the senior author (D.L.B.) to determine the presence of arthrodesis, nonunion, and/or hardware-related complications. Successful fusion was defined by a solid bony bridge from the occiput to the posterior elements of C-2 on postoperative CT scan. The primary study outcome was either radiographic evidence of a successful fusion or a reoperation that required revision of the arthrodesis and/or instrumentation. Wound revisions or washouts that did not require manipulation of the graft or hardware were not included in the reoperation cohort as failures, nor were cases in which hardware was removed after successful fusion.

For each revision operation, the underlying cause of failure was retrospectively identified as a secondary outcome: immediate hardware failure, hardware failure before arthrodesis, graft failure, or infection. Immediate hardware failure was defined as cervical screw replacement because of misplacement or construct failure within 48 hours after the initial operation (Fig. 1). Hardware failure before arthrodesis included cases in which instrumentation loosening or breakage occurred after 48 hours but before radiographic evidence of fusion (Fig. 2). Graft failure was defined as the presence of nonunion in the setting of adequate positioning of the cervical screw(s) and occipital instrumentation (Fig. 3). Infection refers to the cases in which the hardware and/or graft was revised either during or after surgical debridement of a wound infection (Fig. 4). Only one cause was attributed to each revision operation.

Fig. 1.
Fig. 1.

Axial CT scan depicting early hardware failure due to a malpositionedtranslaminar C-2 screw.

Fig. 2.
Fig. 2.

Sagittal CT scans depicting cervical screw breakage (upper) and loosening (lower) in patients with late hardware failure.

Fig. 3.
Fig. 3.

Sagittal CT scans depicting graft failure.

Fig. 4.
Fig. 4.

Sagittal CT scans taken immediately after surgery (upper) and 4 months after debridement of a wound infection (lower) depicting resorption of the graft material (arrow).

Surgical Technique

All operations were performed by the senior author (D.L.B.). Details regarding the selection of rigid internal fixation construct and the surgical technique were described previously.2,4,9,10 In all patients preoperative finecut (1-mm) CT scans with 2D sagittal and coronal reconstructions were acquired to determine the anatomical suitability of screw placement, the course of the vertebral artery, and the presence of congenital vertebral anomalies that might require a nonstandard screw trajectory. Multiplanar reconstruction of the CT scanning in the trajectory along the entire length of the screw was performed to determine whether a C1–2 transarticular screw, C-2 pars screw, or C-2 translaminar screw could be placed safely as an anchor for the OC rod/loop construct. C1–2 transarticular screws were preferred prior to 2009, but we now place bilateral C-2 pars screws when anatomically feasible because they provide adequate biomechanical rigidity without the additional risk of vertebral artery injury.10,25 A secondary option is instrumentation into the C-2 lamina. If a congenital C2–3 fusion is present or fixation at C-2 cannot be achieved safely, screws may be placed in the C-3 pars or lamina. In patients who have complex craniocervical anatomy that precludes standard screw insertion, alternative methods of internal fixation are performed using a combination of screw configurations or, in a small but important number of cases, placement of a unilateral construct.2

For surgery, general anesthesia is induced, and the patient is secured in a Mayfield 3-point fixation head holder. Electrophysiological monitoring is only used in cases with preexisting myelopathy or if intraoperative bony reduction is planned. The patient is carefully placed in the prone position. Direct lateral fluoroscopic guidance is used during all cervical manipulations and for screw placement. The patient's neck is slightly distracted, flexed, and posteriorly translated into a mild military tuck position. A posterior OC incision is made in the midline, and the occiput and upper cervical region are exposed. Posterior cervical screw fixation is performed bilaterally using polyaxial screws inserted into C-2 or C-3. During OC fusion, the patient is realigned into a neutral position prior to rigid instrumentation placement. For those patients who require intraoperative odontoid reduction, the patient's head is slightly distracted and extended under direct fluoroscopic visualization to cause anterior C-2 translation. Next, a rigid OC fixation device consisting of a custom loop-shaped plate (Wasatch plate, Medtronic), a rod/plate system (Vertex, Medtronic, Inc.), or a U-loop (Ohio Medical Instruments Surgical Products) is cut to size, contoured to fit between the occiput and C-2 or C-3, superiorly secured to the occipital bone with 4.0-mm screws, and inferiorly anchored to the polyaxial cervical fixation screws. Iliac crest or rib autograft is the preferred substrate for bone graft. The graft material is held in place with a multistranded titanium cable (Atlas cable, Medtronic, Inc.) at the cervical end, and a small (1.5-mm) maxillofacial screw is placed through the graft into the suboccipital bone. Demineralized bone matrix (DBM; Medtronic or Grafton, Osteotech) is placed around the graft. The O-arm is used to verify screw positioning at the conclusion of the procedure, and the incision is closed in a multilayered fashion.

Postoperatively, all patients were prescribed either a fitted Miami-J or custom built cervical collar augmented with molded plastic occipital support. Patients who were considered to have a high risk of fusion failure were maintained in the cervical collar at all times until radiographic evidence of fusion. This decision was made on a case-by-case basis depending on the screw purchase, instrumentation security, and bone surface available for fusion. Otherwise, patients were instructed to wear the cervical collar for comfort only.

The current protocol at our institution for radiographic evaluation of fusion includes plain radiographs obtained monthly for the first 2 months after surgery, followed by a noncontrast CT scan of the OC junction with thin-slice sagittal and coronal reconstructions obtained 4 months after surgery to determine arthrodesis. If arthrodesis has not developed at 4 months and no signs of a complication are present, the CT scan is repeated every 6 months or 1 year until successful fusion is radiographically confirmed. After successful fusion is documented, plain radiographs are obtained yearly until the patient is approximately 10 years of age. This protocol was developed based on our institutional experience and data from several studies that performed postoperative CT scanning at 3 or 4 months to determine successful fusion.2,3,6,9,10,12,24

If a patient develops hardware failure before arthrodesis occurs, it is our practice to revise the instrumentation with or without revising the graft material soon after failure is diagnosed, regardless of whether the patient develops new or worsening neurological symptoms. In some cases, the failure is diagnosed on imaging studies obtained after a patient experiences a “popping” sensation in the back of the neck, but often the diagnosis of hardware failure is made incidentally on routine postoperative CT in the setting of a stable neurological examination. It is our experience that intervening early on in cases of failed instrumentation will give patients the best chance of ultimately achieving a successful fusion.

Statistical Analysis

Patients were stratified according to the primary outcome of whether they had radiographic evidence of successful fusion or if they required reoperation for revision of the graft or instrumentation. Fisher exact tests and Student t-tests were used for univariate analyses on categorical and continuous variables, respectively, to identify potential predictors of fusion failure. We also performed a subanalysis on patients who experienced hardware failure to determine whether failure was more common in patients who had skeletal dysplasia or congenital spinal anomalies on preoperative imaging. This subanalysis was conducted because screw placement is often more technically challenging in patients with these anatomical disorders. A probability value < 0.05 was considered statistically significant. Statistical analysis was performed using the SAS software package (version 9.2; SAS Institute, Inc.).

Results

Patient Characteristics and Surgical Details

We identified 147 operations performed to manage OC instability. Of these, we excluded 14 cases that involved occipitocervicothoracic fusion, 5 in which patients were lost to follow-up, and 1 in which the patient was older than 18 years. Our study population included 127 OC fusion procedures in 107 patients. The mean age of the patients at surgery was 7.7 ± 4.7 years (range 1.2–17.9 years), and the mean follow-up period was 25 months (range 3–100 months). Sixty-nine patients (64%) had a follow-up longer than 1 year. Other baseline demographic data and surgical details of the 127 procedures are presented in Tables 1 and 2, respectively. The statistical analysis was performed by counting each procedure as a new event, so the values are out of 127. Male patients comprised 59.1% of the study group. The most common cause of OC instability was congenital spinal anomaly (29.1%) followed by Chiari malformation (19.7%), trauma (17.3%), Down syndrome (16.5%), skeletal dysplasia (14.2%), and os odontoideum (3.1%).

TABLE 1:

Patient characteristics of 127 OC fusion operations*

VariableNo. Procedures (%)
sex
 male75 (59.1)
 female52 (40.9)
cause of OC instability
 Chiari malformation25 (19.7)
 congenital spinal anomalies37 (29.1)
 skeletal dysplasia fixation18 (14.2)
 trauma22 (17.3)
 os odontoideum4 (3.1)
 Down syndrome21 (16.5)
outcome
 successful fusion107 (84.3)
 surgical failure20 (15.7)
primary reason for reoperation
 hardware failure12 (9.4)
 graft failure2 (1.6)
 infection5 (3.9)
 CSF leak1 (0.8)

Values are out of 127 procedures performed in 120 patients.

TABLE 2:

Details of 127 OC fusion operations*

VariableNo. Procedures (%)
previous OC fusion
 no100 (78.7)
 yes27 (21.3)
procedure
 occiput–C2 fusion120 (94.5)
 occiput–C3 fusion7 (5.5)
cervical fixation
 pars72 (56.7)
 translaminar6 (4.7)
 transarticular30 (23.6)
 pedicle2 (1.6)
 lat mass1 (0.8)
 combination of configurations16 (12.6)
occipital hardware
 Wasatch/ABT plate55 (43.3)
 Vertex rod/plate57 (44.9)
 OMI U-loop12 (9.4)
 other3 (2.4)
bilat fixation119 (93.7)
unilat fixation8 (6.3)
graft used
 autograft123 (96.9)
  iliac crest46 (36.2)
  rib76 (59.8)
  occiput1 (0.8)
 allograft1 (0.8)
 none3 (2.4)
biological adjuncts
 none26 (20.4)
 DBM101 (79.5)
 BMP7 (5.5)
brace
 no brace/comfort only54 (42.5)
 collar at all times71 (55.9)
 halo2 (1.6)
O-arm15 (11.8)

Values are out of 127 procedures performed in 120 patients. ABT = Avery-Brockmeyer-Thiokol; OMI = Ohio Medical Instruments.

Of the 127 fusion operations, 100 operations were performed as the initial fusion operation, 24 were performed as the first revision operation (4 of which had the initial fusion performed at an outside hospital), and 3 were performed as the second revision operation. Occiput–C2 fusion was performed in 120 cases (94.5%), and occiput–C3 fusion was performed in 7 (5.5%).

For cervical fixation, pars screws were most commonly used (56.7%), followed by transarticular screws (23.6%), translaminar screws (4.7%), pedicle screws (1.6%), and lateral mass screws (0.8%). In 12.6% of cases, the configuration consisted of various combinations of these screw fixation methods. Unilateral fixation constructs were used in 6.3% of cases. For the rigid OC device, a rod/plate system or custom loop-shaped plate was preferred and used in 44.9% and 43.3% of cases, respectively; the Ohio Medical Instruments U-Loop was used in 9.4% of cases; other OC plating systems were used in 3 patients (2.4%).

In the majority of cases (96.9%) we used autografts, harvested from the rib (59.8%) or iliac crest (36.2%), for bone graft material. One patient received an occipital bone graft to augment his fusion during a revision surgery for instrumentation failure. In another patient, an allograft was used to augment a partial fusion. Three patients underwent revision of instrumentation without augmentation of their fusion mass with additional bone graft. Biological adjuncts were used in 79.5% of cases. DBM was used frequently (78.7%). BMP was also used in 7 cases (5.5%), in 5 of which it was used for a revision operation.

The use of postoperative bracing varied widely. After 71 (55.9%) of the 127 procedures, the patients were instructed to wear a brace at all times for 4 weeks or longer; this recommendation was made by the senior author (D.L.B.) after reviewing their postoperative imaging. Two patients were placed in a halo postoperatively. The remaining patients were prescribed a brace to wear for comfort only.

Outcomes

Of the 127 OC fusion operations, 107 (84.3%) resulted in a successful fusion after the first procedure, and 20 (15.7%) were surgical failure requiring reoperation for revision of the arthrodesis or instrumentation. The details of the cases resulting in failure are presented in Table 3. All complications occurred within 1 year of the operation.

TABLE 3:

Cases of surgical failure requiring revision of instrumentation or graft*

Case No.Age (yrs), SexReason for FusionPrior FusionProcedurePrimary Reason for Revision
16.0, MChiarinoOc–C2, bilat TA screwswound infection requiring washout; hardware loosening 4 mos later
23.4, Mskeletal dysplasia (SED)noOc–C2, bilat pedicle screwshardware failure; C-2 screws backed out 6 wks postop, revised & placed in halo vest for 4 mos
311.6, FDown syndromeyesOc–C2, rt TA screw, lt pars screwhardware failure; occipital & cervical screw loosening 4 mos postop; cervical collar non-compliance
416.9, FChiarinoOc–C2, bilat TA screwsgraft failure nonunion at 8 mos
51.5, Fcongenital skeletal anomalynoOc–C3, lt C-2 pars screw, rt C-3 pars screw, lt C-3 TL screwimmediate hardware failure; lt C-2 screw malpositioned
62.4, Fcongenital skeletal anomalynoOc–C2, bilat pars screwshardware failure; C-2 screws backed out at 1 mo
711.3, Mcongenital FG syndromenoOc–C3, bilat pars screwswound infection requiring washout & removal of hardware, hardware/graft revised after 6 wks of antibiotics
85.7, Fskeletal dysplasia (SED)noOc–C2, bilat pars screwsimmediate hardware failure; C-2 pars screw malpositioned
9a2.0, FtraumanoOc–C2, bilat pars screwsimmediate hardware failure; after 1st op, C-2 screw malpositioned & persistent C1–2 subluxation
9b2.2, FtraumanoOc–C2, bilat pars screwswound infection after 2nd op requiring washout; 4 mos later developed graft resorption requiring revision
103.8, FDown syndromenoOc–C2, unilat pars screwgraft failure; nonunion at 5 mos; unilat construct because C-2 pars screw broke out, abandoned
117.0, FChiarinoOc–C2, bilat pars screwsCSF leak from redo Chiari decompression, & OC fusion, required primary repair; found to have C-2 screw loosening, revised during same op
122.2, Mskeletal dysplasia (achondroplasia)noOc–C2, bilat pars screwslate hardware failure; occipital screw backed out at 2 mos
134.5, MChiariyesOc–C2, bilat pars screwswound infection requiring washout; found to have C-2 pars screw loosening, hardware revised during washout
149.9, MChiarinoOc–C2, rt TL screw, lt pars screwimmediate hardware failure; misplaced translaminar screw
1512.8, FChiarinoOc–C2, bilat pars screwsinfected pseudomeningocele 2 mos after redo Chiari decompression & OC fusion; graft removed, underwent treatment for 5 mos w/ antibiotics; VP shunt placed; graft revised
163.4, Mcongenital skeletal anomalynoOc–C2, unilat TL screwhardware failure; occipital & TL screw loosening 2 mos postop; unilat fixation, 1 TL screw placed due to anatomy
1713.4, Mcongenital skeletal anomalynoOc–C2, bilat pars screwshardware failure; nonunion, C-2 screw backed out at 4 mos
182.1, Fcongenital skeletal anomalynoOc–C2, bilat pars screwshardware failure; cervical hardware loosening, revised at 4 mos
1912.6, Mcongenital skeletal anomalynoOc–C2, bilat pars screwshardware failure; occipital & cervical screw pullout at 2 mos

Oc = occiput; SED = spondyloepiphyseal dysplasia; TA = transarticular; TL = translaminar; VP = ventriculoperitoneal.

Immediate hardware failure occurred in 4 cases and required reoperation for malpositioned cervical screws within the first 48 hours postoperatively. Hardware failure before arthrodesis occurred in 8 cases, including failure of the cervical screws in 4 cases, occipital screw backout in 1, and loosening of both the C-2 and occipital screws in 3.

Graft failure occurred in 2 patients in whom we observed widening of the space between the graft material and either the occiput or a cervical lamina on the postoperative CT scan. In both cases, graft failure occurred despite appropriate screw positioning.

In 5 cases, revision of the instrumentation or bone graft was performed during or after surgical debridement of an infection; these are described below.

One patient was found to have C-2 screw loosening during a revision operation for primary repair of a CSF leak.

In 15 cases, the O-arm was used at the end of the operation to verify screw positioning, and 14 cases resulted in successful fusion. One patient developed cervical and occipital instrumentation loosening 2 months after the initial operation. None of the cases in which the O-arm was used resulted in misplaced cervical screws.

Risk Factors for Surgical Failure

The results of the univariate analysis of risk factors associated with surgical failure after OC fusion are presented in Table 4. The following variables were not associated with surgical failure: age (p = 0.33), sex (p = 0.22), cause of OC instability (p = 0.69), having a previous OC fusion performed at our hospital or an outside hospital (p = 0.74), method of C-2 fixation (p = 0.36), type of rigid OC fixation device (p = 0.96), whether unilateral or bilateral fixation was performed (p = 0.61), use of BMP (p = 1.00) or biological adjuncts (p = 0.76), bone graft material (p = 0.12), or postoperative bracing (p = 1.00).

TABLE 4:

Univariate analysis of variables associated with failure after OC fixation*

VariableSurgical FailureSuccessful FusionUnivariate p Value
no. of cases20107
mean age (yrs ± SD)6.7 ± 4.87.9 ± 4.70.33
males9 (45.0)66 (61.7)0.22
cause of OC instability0.69
 Chiari malformation6 (30.0)19 (17.8)
 congenital spinal anomalies7 (35.0)30 (28.0)
 skeletal dysplasia3 (15.0)15 (14.0)
 trauma2 (10.0)20 (18.7)
 os odontoideum0 (0)4 (3.7)
 Down syndrome2 (10.0)19 (17.8)
previous fusion op3 (15.0)24 (22.4)0.74
procedure0.30
 Oc–C2 fusion18 (90.0)102 (95.3)
 Oc–C3 fusion2 (10.0)5 (4.7)
C-2 screw fixation0.36
 pars13 (65.0)59 (55.1)
 translaminar1 (5.0)5 (4.7)
 transarticular2 (10.0)28 (26.2)
 lat mass0 (0)1 (0.9)
 combination of configurations3 (15.0)13 (12.1)
 pedicle1 (5.0)1 (0.9)
rigid OC device0.96
 Wasatch/ABT plate8 (40.0)47 (43.9)
 vertex rod/plate10 (50.0)47 (43.9)
 OMI U-loop2 (10.0)10 (9.3)
 other0 (0)3 (2.8)
side of fixation0.61
 bilat18 (90.0)101 (94.4)
 unilat2 (10.0)6 (5.6)
BMP1 (4.8)6 (5.6)1.00
graft0.12
 autograft18 (90.0)105 (98.1)
 allograft1 (5.0)0 (0)
 none1 (5.0)2 (1.9)
autograft location0.10
 none2 (10.0)2 (1.9)
 rib14 (70.0)62 (57.9)
 iliac crest4 (20.0)42 (39.3)
 Oc0 (0)1 (0.9)
biological adjuncts
 none3 (15.0)23 (21.5)0.76
 DBM17 (85.0)84 (78.5)
brace1.00
 no brace/comfort only9 (45.0)45 (42.1)
 collar at all times11 (55.0)60 (56.1)
 halo0 (0)2 (1.9)
complication
 infection5 (25.0)3 (2.8)0.002
 CSF leak1 (5.0)0 (0)0.16
O-arm used1 (5.0)14 (13.1)0.46

Values are out of 127 procedures performed in 120 patients. PCMC = Primary Children's Medical Center.

Having a deep wound infection that required surgical debridement was associated with surgical failure requiring reoperation of the instrumentation or graft (p = 0.002). In 2 cases, the graft and hardware required revision several months after the wound debridement was performed, and the infections were treated with long-term antibiotics. One patient had graft resorption and the other had cervical screw backout 4 months after debridement. The hardware was found to be loose during the wound washout procedure in 1 patient. Two patients required removal of the graft material in addition to long-term intravenous antibiotics to treat the infection. In both of these patients, revision of the arthrodesis was performed several weeks after the infection was eradicated. Three of the cases in the fusion cohort underwent surgical debridement for wound infections but did not require manipulation of the graft material or instrumentation, and all 3 developed successful arthrodeses.

A subanalysis of the failure cohort revealed a significant association between hardware failure and patients with OC instability due to skeletal dysplasia or congenital spinal anomalies (p = 0.020; Table 5). Fifty-five OC fusion operations were performed in patients with skeletal dysplasia or congenital spinal anomalies, 10 of which resulted in initial failure. Of these 10 cases, immediate hardware failure occurred in 2, hardware failure before arthrodesis occurred in 7, and failure occurred in 1 patient, with a congenital spinal anomaly, after a wound infection.

TABLE 5:

Contingency table showing relationship between OC instability etiology and hardware failure*

VariableSkeletal Dysplasia or Congenital Spinal AnomalyOther Etiology of OC Instability
hardware failure93
other reason for reop17

There was a significant (p = 0.020) association between hardware failure and patients with OC instability due to skeletal dysplasia or congenital spinal anomalies.

Discussion

Previous work has shown that there is generally a high rate of surgical success in pediatric OC arthrodesis.6,10,13,18 Our study of a large cohort of pediatric patients undergoing OC fusion demonstrates that fusion success can be achieved across various etiologies of OC instability and using a variety of screw fixation techniques. Among the several potential risk factors that we evaluated, infection was the only independent predictor of surgical failure. Subgroup analysis revealed that patients with congenital vertebral anomalies and skeletal dysplasia are at higher risk for hardware-related complications resulting in surgical failure.

In light of previous research, our study sought to investigate several factors that might affect surgical decision making and techniques. Even though we found that most of these factors were not independent predictors of failure, we believe they are worthy of discussion and will address them below.

Infection

Deep wound infection after instrumented fusion has frequently been identified as a risk factor for nonunion.23 The most critical period for fusion is in the first 1–2 weeks when inflammation and revascularization occur, enabling the graft material to incorporate with the native bone.14 Microbes alter the bone regeneration process by impairing vascularization of the bone graft material, and cytokines from leukocytes alter osteoblast and osteoprogenitor cell biology. Preventing wound infections during the early postoperative period would increase the likelihood of a successful fusion and decrease the rate of revision surgery. The current initiative to standardize surgical site infection protocols is a step toward reducing postoperative infections.22 As variability in clinical practice decreases, research efforts may identify specific infection-preventing interventions that could be implemented in patients undergoing OC fusion.

CSF Leak

CSF leak is uncommon after OC fusion but, in some cases, such as revision surgery in Chiari malformation, the dura must be opened and a dural patch graft placed afterward. It is imperative that the duraplasty be closed in a watertight fashion because a CSF leak puts the patient at risk for meningitis and surgical failure. Despite our best efforts, CSF leaks and/or pseudomeningocele formation occurred in 3 cases, all of which required reoperation for dural repair. These cases were not considered failures in this study because the primary indication for reoperation was not failure of the instrumentation or graft material; however, because CSF leak is a risk factor for a deep wound infection, it merits mention.

Patient Age and Cause of Instability

Pediatric patients with normal C-2 anatomy and good occipital bone thickness are extremely likely to have successful OC arthrodesis, even at very young ages. Normal anatomy and good bone thickness are usually found in patients with atlantooccipital dislocation, Down syndrome, and Chiari malformations, which partly explains their very high rates of surgical success. In fact, successful fusion in these patient groups has been consistently achieved in patients as young as 16 months of age, with excellent long-term outcomes. We hypothesize that this success is due to active bone modeling in young patients that occurs within and around the fusion mass and implanted hardware. As these patients age, this bone modeling can manifest as vertical growth of the spine within the fused segment.1

Patients with congenital vertebral anomalies and skeletal dysplasia are a different story. Diminutive or abnormal C-2 anatomy, thin occipital bone, and small size-for-age patients may make instrumentation fixation technically difficult and may produce supraphysiological stress on the biomechanical integrity of the fixation. These situations may call for creative solutions, including a combination of C-2 fixation methods or even unilateral constructs. These techniques were used in several patients in the series to achieve, whenever possible, the twin goals of avoiding an external halo orthosis and avoiding extending the fusion level below C-2 (or C-3 if there is a congenital C2–3 fusion) so that motion segments can be preserved. Unfortunately, as the data in our series show, patients with congenital vertebral anomalies and skeletal dysplasia are at higher risk of hardware failure than patients with other etiologies. We do not believe that this is because of poor bone quality available for fusion. Rather, it is due to the inability of some hardware constructs to withstand the biomechanical stress imposed upon the craniocervical area during the fusion process. Despite these risks, it is our experience that patients with congenital vertebral anomalies and skeletal dysplasia ultimately have a high likelihood of successful fusion, even very young patients (< 2 years of age) in whom there is less bony surface area available for fusion and in whom screw fixation is technically challenging. For patients with congenital vertebral anomalies and skeletal dysplasia, this success may be partly attributable to stricter activity restrictions and more regimented postoperative cervical bracing instructions until arthrodesis is achieved. However, our study was not powered to evaluate this hypothesis.

Postoperative Orthosis

Rather than placing patients in external halo orthoses, we generally apply a hard cervical collar postoperatively. A large percentage of patients in this series were placed in a custom hard cervical collar to be worn continuously for at least 1 month after surgery. At that point, a plain radiograph is taken to determine hardware integrity. The decision of whether to persist in continuous collar use until the arthrodesis has matured (usually 3–4 months) is based on the quality of the initial hardware fixation. For example, if a patient's instrumentation is secure as determined at the time of surgery and the likelihood of hardware failure is small, the restriction may be lifted after 1 month. If the instrumentation is not thought to be entirely secure, then collar use is continued for 4 months or until successful fusion is documented on a CT scan. However, this process is influenced by the patient's collar compliance and activity level. While most patients and families are compliant, some begin to lift the restriction on their own, thus endangering the construct. Of course, the surgeon has no control over this process outside of routine office visits. More than one pediatric patient has returned with a hardware failure that probably resulted from excessive activity, either in or out of the collar. These comments are not meant to blame patients or families but to point out that some factors that may determine surgical success remain out of the surgeon's control.

Method of C-2 Fixation

Early in this series, the senior author (D.L.B.) preferred to use C1–2 transarticular screws for C-2 fixation. Over time, we discovered that C-2 pars fixation achieved the same level of surgical success with significantly reduced risk of injury to the vertebral artery.10 Thus, we began to use pars screws or translaminar screws almost exclusively as our preferred method of C-2 fixation. Of the 2 methods, we prefer pars screws for 2 reasons: 1) they allow a larger amount of C-2 lamina to fuse and 2) they provide excellent mechanical advantage when craniocervical reduction is necessary as part of the procedure. As mentioned previously, we have used a mixture of C-2 fixation techniques in certain patients, with the instrumentation decisions driven entirely by individual anatomy.

Type of OC Instrumentation

A mixture of OC fixation devices was used in this series, with U-loops (Wasatch plate, Medtronic) and rod/ plate (Vertex Max, Medtronic) as the predominant constructs. The idea behind using a closed U-loop against the occiput is to fixate the midline occipital keel, which is often the only portion of the occiput bone able to provide adequate screw purchase, as well as to provide a biomechanically sound construct. In patients with adequate lateral occipital bone thickness, the suboccipital area may be used to fixate the plate portion of a rod/plate construct. In a Chiari malformation patient after suboccipital decompression, a lateral rod/plate construct is one of the few methods that can provide adequate occipital fixation.

The OC instrumentation devices used in this series (both the U-loop and rod/plate constructs) are prebent to a neutral alignment so that when the device is placed it allows for a natural position of the OC junction postoperatively. This is a great advantage when an intraoperative craniocervical reduction is part of the procedure, as may happen in patients with complex Chiari malformation or those with severe congenital craniocervical dislocations. Using the mechanical advantage of these devices, we have been able to achieve success in many challenging procedures.

Unilateral Versus Bilateral Constructs

Seemingly defying traditional biomechanical principles, 6 patients had successful OC arthrodesis following use of unilateral OC instrumentation. Four of these patients had a unilateral construct placed as a second procedure after a bilateral construct failed after the first procedure. Without resorting to a bone/wire/halo solution, we were successful in each of these cases by converting the instrumentation to unilateral plate/rod constructs. These patients had severe congenital vertebral anomalies or skeletal dysplasia. In each of these procedures, once unilateral C-2 fixation is achieved, a single rod/plate is bent so that it is oriented toward the midline occipital keel, where it is secured to the occiput with at least 2 occipital screws. Once a rib graft is added, this mode of instrumentation is surprisingly secure. In each case, the patient was kept in a hard collar until fusion occurred.

Type of Graft Used

Iliac crest or rib autograft was used in nearly all patients. After several patients with allograft were referred to our institution following OC fusion failure, we decided to avoid using allograft in our patients. We believe that allograft is not a good fusion substrate when placed in an on-lay position unless biologics are routinely used as a fusion adjunct. Thus, we cannot comment on the efficacy of allograft in our study. Little, if any, donor-site morbidity has been reported from using autograft, and the long-term results and cosmetic appearance of autograft incision sites have been favorable. We use an iliac crest autograft when the distance between the occiput and C-2 is short, as with patients with atlantooccipital dislocation or Down syndrome. In patients with long occiput–C2 distances to span (observed after Chiari decompression), or in patients with very small iliac crests, either 1 or 2 rib autografts are used. Full-thickness bone grafts are used in all cases, with the contact surfaces decorticated prior to their implantation. The grafts are held in place securely with multistranded titanium cable (Atlas cable, Medtronic) looped around the hardware and tightened to at least 30 foot-pounds.

Using this technique, we had a very low incidence of graft failure, which was seen in only 2 of the 127 procedures. While the concept of stable pseudarthrosis or fibrous union is discussed in the literature,5,7,11,13,17,21 this was not observed in any of our patients. Both instances of graft failure were notable for increased widening between the autograft material and native bone on postoperative CT.

Use of BMP

We do not routinely use BMP during our OC fusions. We believe the documented risks outweigh the benefits because its efficacy has not been clearly established in the literature despite initial documentation of its success.8,16,19 We only use BMP during salvage procedures for failed fusions or more extensive procedures, such as OC-thoracic fusions, in which severe instability is present. Thus, an insufficient number of patients in this series received BMP as part of their fusion to draw conclusions on its efficacy.

Hardware Failure and Use of the Intraoperative O-Arm

We defined immediate hardware failure to include either screw malpositioning or overt construct failure in the first 48 hours after surgery. This is in contrast with instrumentation failure that occurred after the immediate postoperative period but before arthrodesis. Both types of failure occurred in this series; however, we did not have any instances of immediate hardware failure once we began routinely using the intraoperative O-arm in 2012. Our protocol is to perform a nonsterile intraoperative spin to check the instrumentation after the wound is closed to confirm C-2 screw placement and OC reduction status (if any). If screw misplacement occurs, the incision can be reopened and the screw repositioned before the patient leaves the operating room. This could prevent costly and unnecessary reoperation for screw malpositioning should the instrumentation failure be diagnosed on a standard postoperative CT scan obtained 1 or 2 days later. After confirmation of satisfactory instrumentation based on intraoperative images, we do not perform further routine imaging until the 1-month postoperative clinic visit.

Conclusions

Surgical arthrodesis for pediatric OC instability has a high rate of success in a wide variety of challenging circumstances; however, there are still several ways it can be improved. Our findings suggest that reducing surgical site infections and increasing understanding of the underlying biomechanical factors that contribute to hardware failure would improve the outcomes in this patient population.

Acknowledgment

We thank Kristin Kraus, M.Sc., for her help in the preparation of this paper.

Disclosure

The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

Author contributions to the study and manuscript preparation include the following. Conception and design: Brockmeyer, Mazur, Sivakumar, Riva-Cambrin. Acquisition of data: Brockmeyer, Mazur, Sivakumar, Jones. Analysis and interpretation of data: Brockmeyer, Mazur, Sivakumar, Riva-Cambrin. Drafting the article: Brockmeyer, Mazur. Critically revising the article: all authors. Reviewed submitted version of manuscript: Sivakumar, Riva-Cambrin, Jones. Approved the final version of the manuscript on behalf of all authors: Brockmeyer. Study supervision: Brockmeyer.

The research was presented at the 42nd Annual AANS/CNS Section on Pediatric Neurological Surgery, Toronto, Ontario, Canada, December 4, 2013.

References

  • 1

    Anderson RCEKan PGluf WMBrockmeyer DL: Long-term maintenance of cervical alignment after occipitocervical and atlantoaxial screw fixation in young children. J Neurosurg 105:1 Suppl55612006

  • 2

    Anderson RCERagel BTMocco JBohman LEBrockmeyer DL: Selection of a rigid internal fixation construct for stabilization at the craniovertebral junction in pediatric patients. J Neurosurg 107:1 Suppl36422007

  • 3

    Bollo RJRiva-Cambrin JBrockmeyer MMBrockmeyer DL: Complex Chiari malformations in children: an analysis of preoperative risk factors for occipitocervical fusion. Clinical article. J Neurosurg Pediatr 10:1341412012

  • 4

    Brockmeyer DLApfelbaum RI: A new occipitocervical fusion construct in pediatric patients with occipitocervical instability. Technical note. J Neurosurg 90:2 Suppl2712751999

  • 5

    Chang KCSamartzis DFuego SMDhatt SSWong YWCheung WY: The effect of excision of the posterior arch of C1 on C1/C2 fusion using transarticular screws. Bone Joint J 95-B:9729762013

  • 6

    Couture DAvery NBrockmeyer DL: Occipitocervical instrumentation in the pediatric population using a custom loop construct: initial results and long-term follow-up experience. Clinical article. J Neurosurg Pediatr 5:2852912010

  • 7

    Dailey ATHart DFinn MASchmidt MHApfelbaum RI: Anterior fixation of odontoid fractures in an elderly population. Clinical article. J Neurosurg Spine 12:182010

  • 8

    Fahim DKWhitehead WECurry DJDauser RCLuerssen TGJea A: Routine use of recombinant human bone morphogenetic protein-2 in posterior fusions of the pediatric spine: safety profile and efficacy in the early postoperative period. Neurosurgery 67:119512042010

  • 9

    Gluf WMBrockmeyer DL: Atlantoaxial transarticular screw fixation: a review of surgical indications, fusion rate, complications, and lessons learned in 67 pediatric patients. J Neurosurg Spine 2:1641692005

  • 10

    Hankinson TCAvellino AMHarter DJea ALew SPincus D: Equivalence of fusion rates after rigid internal fixation of the occiput to C-2 with or without C-1 instrumentation. Clinical article. J Neurosurg Pediatr 5:3803842010

  • 11

    Hart RSaterbak ARapp TClark C: Nonoperative management of dens fracture nonunion in elderly patients without myelopathy. Spine (Phila Pa 1976) 25:133913432000

  • 12

    Hwang SWGressot LVChern JJRelyea KJea A: Complications of occipital screw placement for occipitocervical fusion in children. Clinical article. J Neurosurg Pediatr 9:5865932012

  • 13

    Hwang SWGressot LVRangel-Castilla LWhitehead WECurry DJBollo RJ: Outcomes of instrumented fusion in the pediatric cervical spine. Clinical article. J Neurosurg Spine 17:3974092012

  • 14

    Kalfas IH: Principles of bone healing. Neurosurg Focus 10:4E12001

  • 15

    Klimo P JrRao GBrockmeyer D: Congenital anomalies of the cervical spine. Neurosurg Clin N Am 18:4634782007

  • 16

    Lindley TEDahdaleh NSMenezes AHAbode-Iyamah KO: Complications associated with recombinant human bone morphogenetic protein use in pediatric craniocervical arthrodesis. Clinical article. J Neurosurg Pediatr 7:4684742011

  • 17

    Mazur MDMumert MLBisson EFSchmidt MH: Avoiding pitfalls in anterior screw fixation for type II odontoid fractures. Neurosurg Focus 31:4E72011

  • 18

    Menezes AH: Craniocervical fusions in children. A review. J Neurosurg Pediatr 9:5735852012

  • 19

    Simmonds MCBrown JVHeirs MKHiggins JPMannion RJRodgers MA: Safety and effectiveness of recombinant human bone morphogenetic protein-2 for spinal fusion: a meta-analysis of individual-participant data. Ann Intern Med 158:8778892013

  • 20

    Song DMaher CO: Spinal disorders associated with skeletal dysplasias and syndromes. Neurosurg Clin N Am 18:4995142007

  • 21

    Vaccaro ARKepler CKKopjar BChapman JShaffrey CArnold P: Functional and quality-of-life outcomes in geriatric patients with type-II dens fracture. J Bone Joint Surg Am 95:7297352013

  • 22

    Vitale MGRiedel MDGlotzbecker MPMatsumoto HRoye DPAkbarnia BA: Building consensus: development of a Best Practice Guideline (BPG) for surgical site infection (SSI) prevention in high-risk pediatric spine surgery. J Pediatr Orthop 33:4714782013

  • 23

    Weiss LEVaccaro ARScuderi GMcGuire MGarfin SR: Pseudarthrosis after postoperative wound infection in the lumbar spine. J Spinal Disord 10:4824871997

  • 24

    Winegar CDLawrence JPFriel BCFernandez CHong JMaltenfort M: A systematic review of occipital cervical fusion: techniques and outcomes. A review. J Neurosurg Spine 13:5162010

  • 25

    Wolfla CESalerno SAYoganandan NPintar FA: Comparison of contemporary occipitocervical instrumentation techniques with and without C1 lateral mass screws. Neurosurgery 61:3 Suppl87932007

If the inline PDF is not rendering correctly, you can download the PDF file here.

Article Information

Drs. Mazur and Sivakumar contributed equally to this work.

Address correspondence to: Douglas L. Brockmeyer, M.D., Division of Pediatric Neurosurgery, Primary Children's Hospital, University of Utah, 100 N. Mario Capecchi Dr., Ste. 1475, Salt Lake City, UT 84113. email: neuropub@hsc.utah.edu.

Please include this information when citing this paper: published online August 29, 2014; DOI: 10.3171/2014.7.PEDS1432.

© AANS, except where prohibited by US copyright law.

Headings

Figures

  • View in gallery

    Axial CT scan depicting early hardware failure due to a malpositionedtranslaminar C-2 screw.

  • View in gallery

    Sagittal CT scans depicting cervical screw breakage (upper) and loosening (lower) in patients with late hardware failure.

  • View in gallery

    Sagittal CT scans depicting graft failure.

  • View in gallery

    Sagittal CT scans taken immediately after surgery (upper) and 4 months after debridement of a wound infection (lower) depicting resorption of the graft material (arrow).

References

1

Anderson RCEKan PGluf WMBrockmeyer DL: Long-term maintenance of cervical alignment after occipitocervical and atlantoaxial screw fixation in young children. J Neurosurg 105:1 Suppl55612006

2

Anderson RCERagel BTMocco JBohman LEBrockmeyer DL: Selection of a rigid internal fixation construct for stabilization at the craniovertebral junction in pediatric patients. J Neurosurg 107:1 Suppl36422007

3

Bollo RJRiva-Cambrin JBrockmeyer MMBrockmeyer DL: Complex Chiari malformations in children: an analysis of preoperative risk factors for occipitocervical fusion. Clinical article. J Neurosurg Pediatr 10:1341412012

4

Brockmeyer DLApfelbaum RI: A new occipitocervical fusion construct in pediatric patients with occipitocervical instability. Technical note. J Neurosurg 90:2 Suppl2712751999

5

Chang KCSamartzis DFuego SMDhatt SSWong YWCheung WY: The effect of excision of the posterior arch of C1 on C1/C2 fusion using transarticular screws. Bone Joint J 95-B:9729762013

6

Couture DAvery NBrockmeyer DL: Occipitocervical instrumentation in the pediatric population using a custom loop construct: initial results and long-term follow-up experience. Clinical article. J Neurosurg Pediatr 5:2852912010

7

Dailey ATHart DFinn MASchmidt MHApfelbaum RI: Anterior fixation of odontoid fractures in an elderly population. Clinical article. J Neurosurg Spine 12:182010

8

Fahim DKWhitehead WECurry DJDauser RCLuerssen TGJea A: Routine use of recombinant human bone morphogenetic protein-2 in posterior fusions of the pediatric spine: safety profile and efficacy in the early postoperative period. Neurosurgery 67:119512042010

9

Gluf WMBrockmeyer DL: Atlantoaxial transarticular screw fixation: a review of surgical indications, fusion rate, complications, and lessons learned in 67 pediatric patients. J Neurosurg Spine 2:1641692005

10

Hankinson TCAvellino AMHarter DJea ALew SPincus D: Equivalence of fusion rates after rigid internal fixation of the occiput to C-2 with or without C-1 instrumentation. Clinical article. J Neurosurg Pediatr 5:3803842010

11

Hart RSaterbak ARapp TClark C: Nonoperative management of dens fracture nonunion in elderly patients without myelopathy. Spine (Phila Pa 1976) 25:133913432000

12

Hwang SWGressot LVChern JJRelyea KJea A: Complications of occipital screw placement for occipitocervical fusion in children. Clinical article. J Neurosurg Pediatr 9:5865932012

13

Hwang SWGressot LVRangel-Castilla LWhitehead WECurry DJBollo RJ: Outcomes of instrumented fusion in the pediatric cervical spine. Clinical article. J Neurosurg Spine 17:3974092012

14

Kalfas IH: Principles of bone healing. Neurosurg Focus 10:4E12001

15

Klimo P JrRao GBrockmeyer D: Congenital anomalies of the cervical spine. Neurosurg Clin N Am 18:4634782007

16

Lindley TEDahdaleh NSMenezes AHAbode-Iyamah KO: Complications associated with recombinant human bone morphogenetic protein use in pediatric craniocervical arthrodesis. Clinical article. J Neurosurg Pediatr 7:4684742011

17

Mazur MDMumert MLBisson EFSchmidt MH: Avoiding pitfalls in anterior screw fixation for type II odontoid fractures. Neurosurg Focus 31:4E72011

18

Menezes AH: Craniocervical fusions in children. A review. J Neurosurg Pediatr 9:5735852012

19

Simmonds MCBrown JVHeirs MKHiggins JPMannion RJRodgers MA: Safety and effectiveness of recombinant human bone morphogenetic protein-2 for spinal fusion: a meta-analysis of individual-participant data. Ann Intern Med 158:8778892013

20

Song DMaher CO: Spinal disorders associated with skeletal dysplasias and syndromes. Neurosurg Clin N Am 18:4995142007

21

Vaccaro ARKepler CKKopjar BChapman JShaffrey CArnold P: Functional and quality-of-life outcomes in geriatric patients with type-II dens fracture. J Bone Joint Surg Am 95:7297352013

22

Vitale MGRiedel MDGlotzbecker MPMatsumoto HRoye DPAkbarnia BA: Building consensus: development of a Best Practice Guideline (BPG) for surgical site infection (SSI) prevention in high-risk pediatric spine surgery. J Pediatr Orthop 33:4714782013

23

Weiss LEVaccaro ARScuderi GMcGuire MGarfin SR: Pseudarthrosis after postoperative wound infection in the lumbar spine. J Spinal Disord 10:4824871997

24

Winegar CDLawrence JPFriel BCFernandez CHong JMaltenfort M: A systematic review of occipital cervical fusion: techniques and outcomes. A review. J Neurosurg Spine 13:5162010

25

Wolfla CESalerno SAYoganandan NPintar FA: Comparison of contemporary occipitocervical instrumentation techniques with and without C1 lateral mass screws. Neurosurgery 61:3 Suppl87932007

TrendMD

Metrics

Metrics

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 176 176 35
PDF Downloads 177 177 28
EPUB Downloads 0 0 0

PubMed

Google Scholar