Pediatric pedicle screws: comparative effectiveness and safety: a systematic literature review from the Scoliosis Research Society and the Pediatric Orthopaedic Society of North America task force

Repeat Surgical Interventions Following "Definitive" Instrumentation and Fusion for Idiopathic Scoliosis: 25-Year Update

STUDY DESIGN

Single-institution, retrospective review of prospectively collected data on pediatric patients with adolescent idiopathic scoliosis (AIS) undergoing spinal fusion with a minimum two-year follow-up.

OBJECTIVE

To determine the rate of reoperation in AIS patients undergoing spine fusion from 2008 to 2012.

SUMMARY OF BACKGROUND DATA

Recent trends in the surgical treatment of AIS have included increased use of all-pedicle screw constructs, smaller implants, more posterior-only approaches, and improved correction techniques.

METHODS

A retrospective review of 467 patients undergoing spinal fusion from 2008 to 2012 was performed. Demographic, clinical, radiographic, and surgical data were collected prospectively on all patients for the index procedure and any reoperations. Data were compared to previously published cohorts of patients from the authors' institution who underwent spinal fusion for AIS between 1988 and 2007.

RESULTS

The rate of reoperation in this five-year cohort of patients was 9.9%. The most common indications for reoperation were infection (4.5%: 2.4% delayed infections and 2.1% acute infections), symptomatic implants (2.1%), and misplaced pedicle screws (1.7%). When compared to the 2003-2007 cohort, the rate of reoperation for acute infection and malpositioned pedicle screws increased significantly (p = .01 and p = .04), whereas the rate of reoperation for curve progression decreased (p = .01). Reoperations for acute infections and malpositioned pedicle screws also increased significantly (p = .047 and p = .042) compared with the 1988-2002 cohort, whereas the rate of reoperation for pseudarthrosis decreased (p = .002).

CONCLUSION

Reoperation rates for AIS have not improved with more sophisticated implants and techniques, predominantly because of increased acute infections and malpositioned pedicle screws despite decreasing pseudarthrosis rates and curve progression.

LEVEL OF EVIDENCE

Level II.

Quality, Safety, and Value in Pediatric Spine Surgery

The article addresses patient safety topics in spine surgery, including infection, length of stay, instrumentation strategies, pedicle screw malposition, radiation exposure, and neurologic events. Quality, safety, and value are concepts that are practical, easy to understand, and can be implemented on any scale and may be matched to individual practices. Further, with quality improvement, there is a culture shift to openly share information, protocols, and strategies so that more patients can rapidly benefit.

Posterior Spinal Fusion Extended to Stable Vertebra Provides Similar Outcome in Juvenile Idiopathic Scoliosis Patients Compared with Adolescents with Fusion to the Touched Vertebra

BACKGROUND AND AIMS:

To compare outcomes between posterior spinal fusion of juvenile idiopathic scoliosis and adolescent idiopathic scoliosis patients with a minimum of 2-year follow-up. The juvenile idiopathic scoliosis patients were fused to the stable vertebra and adolescent idiopathic scoliosis to the touched vertebra. We hypothesized that extending the spinal fusion to the stable vertebra in juvenile patients would provide similar outcomes compared with fusion to the touched vertebra in adolescents.

MATERIALS AND METHODS:

A prospective comparative study of 21 consecutive children with juvenile (Risser 0) and 84 adolescent (Risser ⩾2) idiopathic scoliosis (1:4 ratio) undergoing bilateral segmental pedicle screw instrumentation and direct vertebral derotation with a minimum of 2-year follow-up.

RESULTS:

Juvenile patients had a significantly larger main curve (58° vs 53°, p = 0.003), more fused levels (p = 0.012) and posterior column osteotomies (p = 0.014) than adolescent patients. Distal adding-on (>10°) was observed in one (4.7%) juvenile and three (3.6%) adolescent patients (p = 0.80), without the need for revisions. Scoliosis Research Society 24 total score averaged 101 in juvenile and 97 in adolescent group at 2-year follow-up (p = 0.047).

CONCLUSION:

Posterior spinal fusion with bilateral segmental pedicle screw instrumentation to the stable vertebra provides similar clinical and radiographic outcomes in juvenile patients as compared with adolescents with fusion to the touched vertebra in idiopathic scoliosis. Health-related quality of life as measured using the Scoliosis Research Society 24 questionnaire at the end of follow-up was better in the juvenile as compared with the adolescent group.

Postoperative urinary retention or difficulties to empty the bladder in young patients undergoing posterior spinal fusion for adolescent idiopathic scoliosis

BACKGROUND

Postoperative urinary retention has been reported to affect up to 27% of adults undergoing degenerative lumbar spine surgery and approximately one-third of children undergoing lower-extremity orthopedic surgery. No data exist on the incidence and risk factors of postoperative urinary tract retention/difficulties to empty the bladder in young patients undergoing instrumented posterior spinal fusion. We aimed to characterize incidence, risk factors and treatment of postoperative urinary retention (POUR) and difficulties to empty the bladder in young patients undergoing posterior spinal fusion (PSF) for idiopathic scoliosis.

METHODS

One hundred and eleven consecutive patients (mean age 16years [range, 11-21years], 81 females and 30 males) undergoing PSF for adolescent idiopathic scoliosis were screened after removal of urinary catheter postoperatively for inability to void and residual volume of urinary bladder. The latter was measured using ultrasound on two separate occasions. POUR and the need for intermittent catheterization were defined as an inability to void after catheter removal and documented full bladder with ultrasound (a residual of 300mL or more) or a significant residual volume after voiding (>2mL/kg or >100mL).

RESULTS

Fifty-one (46%) of the patients were either unable to void or had a clinically significant amount of residual volume after voiding. These fifty-one patients required intermittent catheterization for a mean of two days. Thirty patients (27%) had POUR, a residual volume of 300mL or more. Two (1.8%) patients experienced urinary tract infection postoperatively. Patients with urinary retention had a significantly higher mean intraoperative blood loss (mean 626mL vs. 464mL; p=0.020) and longer operation time (mean 3.3h vs. 2.8h; p=0.009) as compared with those not having urinary retention. In multivariate analyses the main risk factor for urinary retention was male gender (odds ratio 3.2 [95% confidence interval 1.1-9.2], p=0.028).

CONCLUSIONS

Postoperative voiding difficulties affect almost half of the patients with age under 21years undergoing PSF for idiopathic scoliosis. The main risk factors were increased intraoperative blood loss, longer length of surgery and male gender. POUR should be actively screened and treated in this patient population.

LEVEL OF EVIDENCE

Prospective Cohort Study II.

Implant density is not related to patient-reported outcome in the surgical treatment of patients with idiopathic scoliosis

Aims

There is little information about the optimum number of implants to be used in the surgical treatment of idiopathic scoliosis. Retrospective analysis of prospectively collected data from the Swedish spine register was undertaken to discover whether more implants per operated vertebra (implant density) leads to a better outcome in the treatment of idiopathic scoliosis. The hypothesis was that implant density is not associated with patient-reported outcomes, the correction of the curve or the rate of reoperation.

Patients and Methods

A total of 328 patients with idiopathic scoliosis, aged between ten and 20 years at the time of surgery, were identified in the Swedish spine register (Swespine) and had patient reported outcomes including the Scoliosis Research Society 22r instrument (SRS-22r) score, EuroQol 5 dimensions quality of life, 3 level (EQ-5D-3L) score and a Viual Analogue Score (VAS) for back pain, at a mean follow-up of 3.1 years and reoperation data at a mean follow-up of 5.5 years. Implant data and the correction of the curve were assessed from radiographs, preoperatively and a mean of 1.9 years postoperatively. The patients were divided into tertiles based on implant density. Data were analyzed with analysis of variance, logistic regression or log-rank test. Some analyses were adjusted for gender, age at the time of surgery, the flexibility of the major curve and follow-up.

Results

The mean number of implants per operated vertebra in the low, medium and high-density groups were 1.36 (1.00 to 1.54), 1.65 (1.55 to 1.75) and 1.91 (1.77 to 2.00), respectively. There were no statistically significant differences in the correction of the curve, the SRS-22r total score, EQ-5D-3L index or number of reoperations between the groups (all p > 0.34). In the SRS-22r domains, self-image was marginally higher in the medium implant density group (p = 0.029) and satisfaction marginally higher in the high implant density group (p = 0.034).

Conclusion

These findings suggest that there is no clear advantage in using a high number of implants per operated vertebra in the surgical treatment of patients with idiopathic scoliosis. Cite this article: Bone Joint J 2018;100-B:1080–6.

Improved restoration of thoracic kyphosis using a rod construct with differentiated rigidity in the surgical treatment of adolescent idiopathic scoliosis

OBJECTIVE The objective of this study was to compare postoperative sagittal alignment among 3 rod constructs with different rigidity profiles. METHODS This was a dual-center retrospective cohort study involving 2 consecutive cohorts in which patients were surgically treated for adolescent idiopathic scoliosis. Lenke Type 5 curves were excluded. Patients were operated on with all-pedicle screw instrumentation using 3 different rod constructs. The first group was operated on using a hybrid construct (HC) consisting of a normal circular rod on the convex side and a beam-like rod (BR) on the concave side. The second group was operated on with a standard construct (SC) using bilateral BRs in the full length of the fusion. The third group was operated on with a modified construct (MC). The modified rods have a beam-like shape in the caudal portion, but in the cranial 2 or 3 fusion levels the rod transitions to a circular shape with a smaller anteroposterior diameter. Radiographs were analyzed preoperatively and at the first postoperative follow-up (range 1-8 weeks). The primary outcome was pre- to postoperative change in thoracic kyphosis (TK), and the secondary outcome was the ability to achieve postoperative TK within the normal range. RESULTS The HC, SC, and MC groups included 23, 70, and 46 patients, respectively. The 3 groups did not differ significantly in preoperative demographic or radiographic parameters. The mean ± standard deviation of the preoperative main curve was 60.7° ± 12.6°, and the mean of curve correction was 62.9% ± 10.4% with no significant difference among groups (p ≥ 0.680). The groups did not differ significantly in coronal balance or proximal or thoracolumbar curve correction (p ≥ 0.189). Mean postoperative TK was 23.1° ± 6.3°, 19.6° ± 7.6°, and 23.4° ± 6.9° in the HC, SC and MC groups, respectively (p = 0.013), and the mean change in TK was -3.5° ± 11.3°, -7.1° ± 11.6°, and 0.1° ± 10.9°, respectively (p = 0.005). The MC group had significantly higher postoperative TK and less loss of TK compared with the SC group (p ≤ 0.018). Postoperative TK ≤ 10° was found in 12 patients (17%) in the SC group, 1 patient (5%) in the HC group, and 1 patient (2%) in the MC group (p = 0.021). There were no differences in proximal alignment, thoracolumbar alignment, or sagittal vertical axis (p ≥ 0.249). Lumbar lordosis was 58.9° ± 11.2° in the HC group versus 52.0° ± 1.3° and 55.0° ± 11.0° and the SC and MC groups, respectively (p = 0.040). CONCLUSIONS In the 3 rod constructs with different rigidity profiles, significantly better restoration of kyphosis was achieved with the use of bilateral modified rods compared with bilateral standard rods. In the MC and HC groups, the rate of severe postoperative hypokyphosis was significantly lower than in the SC group. This is the first study to describe the clinical use of a rod with a reduced proximal diameter and show marked radiographic improvement in sagittal alignment.

Treatment strategies for early-onset scoliosis

Early-onset scoliosis (EOS) is defined as a spinal deformity occurring before the age of ten years.

Untreated EOS or early spinal fusion resulting in a short spine is associated with increased mortality and cardiopulmonary compromise.

EOS may progress rapidly, and therefore prompt clinical diagnosis and referral to a paediatric orthopaedic or spine unit is necessary.

Casting under general anaesthesia can be effective and may prevent or delay the need for surgery in curves of less than 60°.

‘Growing’ rods (traditional or magnetically-controlled) represent the standard surgical treatment in progressive curves of 45° or greater.

Children with congenital scoliosis associated with fused ribs benefit from surgery with a vertical titanium prosthetic rib.

Surgery with growth-friendly instrumentation is associated with a high risk of complications.

Cite this article: EFORT Open Rev 2018;3 DOI: 10.1302/2058-5241.3.170051

Which Malpositioned Pedicle Screws Should Be Revised?

BACKGROUND

Up to 10% of free-hand pedicle screws are malpositioned, and 1 in 300 patients may undergo return to surgery for revision of malpositioned screws. The indications for revision of asymptomatic malpositioned screws have not been carefully examined in the literature. We sought to evaluate the threshold among spinal deformity surgeons for revision of malpositioned screws.

METHODS

Twelve experienced spine surgeons reviewed x-ray and computed tomographic images of 32 malpositioned pedicle screws with variable degrees of anterior, medial, and lateral breeches. The surgeons were asked whether based on the image they would revise the screw: (1) intraoperatively before rod placement; (2) intraoperatively after rod placement; (3) in clinic with an asymptomatic patient. For each scenario, we assumed stable neuromonitoring and no neurological changes. Agreement and multirater κ was calculated.

RESULTS

There was good agreement as to which screws were malpositioned (80% agreement, κ=0.703). After the rod was placed or postoperatively (scenarios 2 and 3), surgeons less frequently recommended screw revision, and there was greater variability among the surgeons' recommendations. For return to surgery from clinic for asymptomatic screw revision, % agreement was only 65% (κ=0.477). The majority recommended revision surgery for screws which approached the dura (10/12) or the aorta (7/12 surgeons). Half of the surgeons recommended revision surgery for an asymptomatic screw if the entire screw diameter was in the canal. Revision surgery was not recommended for asymptomatic patients with screws partially violating the canal (<½ the screw diameter), malpositioned laterally in the rib head, or with small anterior cortical violations remote from a vascular structure.

CONCLUSIONS

There is significant variability of opinion among surgeons regarding which malpositioned screws can be safely observed in an asymptomatic patient. Given the frequency of malpositioned screws and morbidity of surgical return to surgery, more long-term data are needed to develop practice guidelines for determining which screws require revision surgery.

LEVEL OF EVIDENCE

Level III-retrospective comparative study.

Intraoperative 3D Computed Tomography: Spine Surgery

Spinal instrumentation often involves placing implants without direct visualization of their trajectory or proximity to adjacent neurovascular structures. Two-dimensional fluoroscopy is commonly used to navigate implant placement, but with the advent of computed tomography, followed by the invention of a mobile scanner with an open gantry, three-dimensional (3D) navigation is now widely used. This article critically appraises the available literature to assess the influence of 3D navigation on radiation exposure, accuracy of instrumentation, operative time, and patient outcomes. Also explored is the latest technological advance in 3D neuronavigation: the manufacturing of, via 3D printers, patient-specific templates that direct implant placement.

Comparison of low density and high density pedicle screw instrumentation in Lenke 1 adolescent idiopathic scoliosis

BACKGROUND

The correlation between implant density and deformity correction has not yet led to a precise conclusion in adolescent idiopathic scoliosis (AIS). The aim of this study was to evaluate the effects of low density (LD) and high density (HD) pedicle screw instrumentation in terms of the clinical, radiological and Scoliosis Research Society (SRS)-22 outcomes in Lenke 1 AIS.

METHODS

We retrospectively reviewed 62 consecutive Lenke 1 AIS patients who underwent posterior spinal arthrodesis using all-pedicle screw instrumentation with a minimum follow-up of 24 months. The implant density was defined as the number of screws per spinal level fused. Patients were then divided into two groups according to the average implant density for the entire study. The LD group (n = 28) had fewer than 1.61 screws per level, while the HD group (n = 34) had more than 1.61 screws per level. The radiographs were analysed preoperatively, postoperatively and at final follow-up. The perioperative and SRS-22 outcomes were also assessed. Independent sample t tests were used between the two groups.

RESULTS

Comparisons between the two groups showed no significant differences in the correction of the main thoracic curve and thoracic kyphosis, blood transfusion, hospital stay, and SRS-22 scores. Compared with the HD group, there was a decreased operating time (278.4 vs. 331.0 min, p = 0.004) and decreased blood loss (823.6 vs. 1010.9 ml, p = 0.048), pedicle screws needed (15.1 vs. 19.6, p < 0.001), and implant costs ($10,191.0 vs. $13,577.3, p = 0.003) in the LD group.

CONCLUSIONS

Both low density and high density pedicle screw instrumentation achieved satisfactory deformity correction in Lenke 1 AIS patients. However, the operating time and blood loss were reduced, and the implant costs were decreased with the use of low screw density constructs.

All-Pedicle Screw Fixation With 6-mm-Diameter Cobalt-Chromium Rods Provides Optimized Sagittal Correction of Adolescent Idiopathic Scoliosis

PURPOSE

Recently introduced cobalt-chromium (CoCr) rods that rely solely on pedicle screws produce very good results in correcting scoliotic curves. All-pedicle screws constructs are also suspected of decreasing thoracic kyphosis. The current study was designed to evaluate sagittal correction in adolescent idiopathic scoliosis patients, using 6-mm CoCr rods and all-screw constructs.

MATERIALS AND METHODS

A total of 61 patients treated by posterior spinal fusion and instrumentation, using all-pedicle screw constructs were included. The mean age at surgery was 15.4 years (range, 12-18 y). Forty-five patients (group A) were diagnosed with decreased thoracic kyphosis, and 16 patients (group B) had normal (35-50 degrees) thoracic kyphosis.

RESULTS

The preoperative main Cobb angle was 62.93±19.38 degrees in group A and 73.45±22.13 degrees in group B. In group A, the postoperative main Cobb angle was 23.33±12.71 degrees. In group B, the postoperative main Cobb angle was 27.20±10.04 degrees. The T4-T12 thoracic kyphosis improved postoperatively from 18.15±10.29 to 28.18±8.35 degrees in group A. In group B, the postoperative T4-T12 thoracic kyphosis was 40.34±3.13 degrees. Statistical analysis showed a significant improvement between preoperative and postoperative values of T4-T12 thoracic kyphosis in group A. In group B, the differences in T4-T12 thoracic kyphosis values were not statistically significant.

CONCLUSIONS

Our result demonstrates a significant improvement of T4-T12 thoracic kyphosis in the hypokyphotic group of patients and confirms that CoCr rods can produce sagittal corrections in hypokyphotic adolescent idiopathic scoliosis patients. Our results confirm the benefit of combining all-pedicle screw constructs with a posterolateral translational in situ bending procedure to correct hypokyphosis directly.

Surgical Treatment of Thoracolumbar Segmental Spinal Dysgenesis: Optimal Type of Fusion

OBJECTIVES

We sought to evaluate long-term results of surgical treatment of thoracolumbar segmental spinal dysgenesis (SSD).

METHODS

We analyzed 8 patients with thoracolumbar SSD treated in our institution. Each case was evaluated for specific clinical and radiologic criteria and types and outcomes of treatment.

RESULT

The average age of primary surgery was 3.4 years (median 3.4 years, range 1.7-7 years). The average correction of kyphosis was 49.3° (mean 45°, from 25°-75°) and scoliosis 10.6° (mean 10°, from 0°-25°). Average follow-up time was 3.2 years (mean 2.6 years, from 1.8-5.6 years). Neurologic improvement was also achieved in all patients. The Japanese Orthopaedic Association scale score (Benzel's modification) was increased by 2.5 points on average (mean 2.5 points, from 2-5 points). One patient had complications: pseudarthrosis and rod fracture followed by refusion.

CONCLUSIONS

Our treatment strategy provides favorable deformity correction and neurologic improvement. It is limited by immature vertebral structures in newborns and infants, who should be carefully monitored from birth with braces until they reach the age when a fixing tool can be used.

How Does Patient Radiation Exposure Compare With Low-dose O-arm Versus Fluoroscopy for Pedicle Screw Placement in Idiopathic Scoliosis?

BACKGROUND

Intraoperative C-arm fluoroscopy and low-dose O-arm are both reasonable means to assist in screw placement for idiopathic scoliosis surgery. Both using pediatric low-dose O-arm settings and minimizing the number of radiographs during C-arm fluoroscopy guidance decrease patient radiation exposure and its deleterious biological effect that may be associated with cancer risk. We hypothesized that the radiation dose for C-arm-guided fluoroscopy is no less than low-dose O-arm scanning for placement of pedicle screws.

METHODS

A multicenter matched-control cohort study of 28 patients in total was conducted. Fourteen patients who underwent O-arm-guided pedicle screw insertion for spinal fusion surgery in 1 institution were matched to another 14 patients who underwent C-arm fluoroscopy guidance in the other institution in terms of the age of surgery, body weight, and number of imaged spine levels. The total effective dose was compared. A low-dose pediatric protocol was used for all O-arm scans with an effective dose of 0.65 mSv per scan. The effective dose of C-arm fluoroscopy was determined using anthropomorphic phantoms that represented the thoracic and lumbar spine in anteroposterior and lateral views, respectively. The clinical outcome and complications of all patients were documented.

RESULTS

The mean total effective dose for the O-arm group was approximately 4 times higher than that of the C-arm group (P<0.0001). The effective dose for the C-arm patients had high variability based on fluoroscopy time and did not correlate with the number of imaged spine levels or body weight. The effective dose of 1 low-dose pediatric O-arm scan approximated 85 seconds of the C-arm fluoroscopy time. All patients had satisfactory clinical outcomes without major complications that required returning to the operating room.

CONCLUSIONS

Radiation exposure required for O-arm scans can be higher than that required for C-arm fluoroscopy, but it depends on fluoroscopy time. Inclusion of more medical centers and surgeons will better account for the variability of C-arm dose due to distinct patient characteristics, surgeon's preference, and individual institution's protocol.

LEVEL OF EVIDENCE

Level III-case-control study.

Proximal Junctional Kyphosis Following Posterior Hemivertebra Resection and Short Fusion in Children Younger Than 10 Years

STUDY DESIGN

A retrospective study.

OBJECTIVE

To investigate whether proximal junctional kyphosis (PJK) or obvious proximal junctional angle (PJA) changes in the sagittal plane develops following short fusion in children younger than 10 years of age with congenital scoliosis, and to investigate the possible risk factors.

SUMMARY OF BACKGROUND DATA

PJK following long spinal fusion in adolescents and adults is a serious postoperative complication. Although the same problem may occur in patients with early-onset scoliosis who have undergone spine fusion, few studies have been reported any relationship between PJK and spinal fusion in young children with congenital scoliosis.

MATERIALS AND METHODS

Thirty-seven children treated in a single institution between 1998 and 2010 were reviewed retrospectively. The inclusion criteria included (1) younger than 10 years of age at the time of operation; (2) simple congenital deformity; (3) hemivertebra treated by posterior hemivertebrectomy with short fusion at a maximum of 5 motion segments; and (4) minimum follow-up for 2 years. The PJA from the caudal endplate of the upper instrumented vertebra (UIV) to the cephalad endplate of the vertebra adjacent to the UIV, thoracic kyphosis (T5-T12), lumbar lordosis (T12-S1), global sagittal balance, and magnitude of scoliosis of the major curves and upper compensated curves were measured on lateral radiographs. PJK was defined by a PJA>10 degrees during the follow-up and at least 10 degrees greater than the preoperative or early postoperative measurement. Wilcoxon tests were performed for statistical analysis.

RESULTS

PJK occurred in 7 of 37 patients (18.9%), during an average of 4.5±3.2 years of follow-up (2-12 y). The UIV level of children with PJK was on T9 in 4 patients, and T11, T12, and L1 in 1. Screw malposition at UIV was confirmed by postoperative computed tomography images in 6 patients. Only 1 patient with a screw deviation did not develop PJK during the follow-up period. None of the patients with PJK was symptomatic, and no patients required revision surgery because of PJK. PJK occurred and progressed during the first 6 months after surgery followed by almost no progression or slight improvement in patients that could be followed up beyond 6 months postoperatively; in association with an increase of the lumbar lordosis.

CONCLUSIONS

PJK occurred in pediatric patients with simple congenital deformities following hemivertebrectomy and short fusion. PJK was more common in patients with (1) greater immediately postoperative segmental kyphosis and PJA; (2) screw malposition on the UIV; and (3) hemivertebra located on the lower thoracic or the thoracolumbar region.

Correction Capability in the 3 Anatomic Planes of Different Pedicle Screw Designs in Scoliosis Instrumentation

STUDY DESIGN

Computer simulations to compare the correction capabilities of different pedicle screws in adolescent idiopathic scoliosis (AIS) instrumentations.

OBJECTIVE

To compare the correction and resulting bone-screw forces associated with different pedicle screws in scoliosis instrumentations.

SUMMARY OF BACKGROUND DATA

Pedicle screw fixation is widely used in surgical instrumentation for spinal deformity treatment. Screw design, correction philosophies, and surgical techniques are constantly evolving to achieve better control of the vertebrae and correction of the spinal deformity. Yet, there remains a lack of biomechanical studies that quantify the effects and advantages of different screw designs in terms of correction kinematics.

METHODS

The correction capabilities of fixed-angle, multiaxial, uniaxial, and saddle axial screws were kinematically analyzed, simulated, and compared. These simulations were based on the screw patterns and correction techniques proposed by 2 experienced surgeons for 2 AIS cases. Additional instrumentations were assessed to compare the correction and resulting bone-screw forces associated with each type of screw.

RESULTS

The fixed-angle, uniaxial and saddle axial screws had similar kinematic behavior and performed better than multiaxial screws in the coronal and transverse planes (8% and 30% greater simulated corrections, respectively). Uniaxial and multiaxial screws were less effective than fixed-angle and saddle axial screws in transmitting compression/distraction to the anterior spine because of their sagittal plane mobility between the screw head and shank. Only the saddle axial screws allow vertebra angle in the sagittal plane to be independently adjusted.

CONCLUSIONS

Pedicle screws of different designs performed differently for deformity corrections or for compensating screw placement variations in different anatomic planes. For a given AIS case, screw types should be determined based on the particular instrumentation objectives, the deformity's stiffness and characteristics so as to make the best of the screw designs.

A New Navigational Tool for Pedicle Screw Placement in Patients With Severe Scoliosis: A Pilot Study to Prove Feasibility, Accuracy, and Identify Operative Challenges

STUDY DESIGN

Pilot study.

OBJECTIVE

To develop and validate the feasibility and accuracy of a newly designed navigational spinal instrument guiding tool for patient-matched thoracic and lumbar pedicle screw placement in patients with severe scoliosis, and to identify intraoperative challenges that may be relevant.

SUMMARY OF BACKGROUND DATA

Pedicle screw placement is challenging in severely rotated scoliotic spine with small diameters and asymmetrical shape of the pedicles and vertebrae. Patient-specific drill/positioning guides with preplanned trajectory have been developed as a promising solution in spinal surgery for precise screw insertion.

METHODS

In 4 patients with severe scoliosis, navigational templates and models of all vertebrae to be instrumented were manufactured using a computed tomography (CT)-based 3-dimensional model of the thoracic and lumbar spine. The guides were designed differently for thoracic and lumbar segments according to the individual anatomy to achieve an optimal coupling to the surface of the patient's spine, to maximize the stability of the device itself, and to increase user friendliness for the complete screw positioning process. Intraoperative challenges and opportunities for device and process improvements regarding the handling of the guides during the surgery were recorded. Postoperatively, the intrapedicular screw positions were evaluated versus the preoperative plan and evaluated for cortical violation based on CT scans.

RESULTS

A total of 76 pedicle screws were implanted (56 thoracic, 20 lumbar). Two screws (2.6%) were assessed to be misplaced intraoperatively and repositioned. Eighty-four percent of the pedicle screws were completely intrapedicular, 96.1% within <2 mm cortical breech. CT scans did not demonstrate medial pedicle violation, or misplaced screw contact to neurovascular structures. No screw-related clinical complaints were reported postoperatively.

CONCLUSIONS

The new custom-made positioning guide is a feasible navigational tool that permits a safe and accurate implantation of pedicle screws in patients with severe scoliosis.

Biomechanical effect of pedicle screw distribution in AIS instrumentation using a segmental translation technique: computer modeling and simulation

BACKGROUND

Efforts to select the appropriate number of implants in adolescent idiopathic scoliosis (AIS) instrumentation are hampered by a lack of biomechanical studies. The objective was to biomechanically evaluate screw density at different regions in the curve for AIS correction to test the hypothesis that alternative screw patterns do not compromise anticipated correction in AIS when using a segmental translation technique.

METHODS

Instrumentation simulations were computationally performed for 10 AIS cases. We simulated simultaneous concave and convex segmental translation for a reference screw pattern (bilateral polyaxial pedicle screws with dorsal height adjustability at every level fused) and four alternative patterns; screws were dropped respectively on convex or concave side at alternate levels or at the periapical levels (21 to 25% fewer screws). Predicted deformity correction and screw forces were compared.

RESULTS

Final simulated Cobb angle differences with the alternative screw patterns varied between 1° to 5° (39 simulations) and 8° (1 simulation) compared to the reference maximal density screw pattern. Thoracic kyphosis and apical vertebral rotation were within 2° of the reference screw pattern. Screw forces were 76 ± 43 N, 96 ± 58 N, 90 ± 54 N, 82 ± 33 N, and 79 ± 42 N, respectively, for the reference screw pattern and screw dropouts at convex alternate levels, concave alternate levels, convex periapical levels, and concave periapical levels. Bone-screw forces for the alternative patterns were higher than the reference pattern (p < 0.0003). There was no statistical bone-screw force difference between convex and concave alternate dropouts and between convex and concave periapical dropouts (p > 0.28). Alternate dropout screw forces were higher than periapical dropouts (p < 0.05).

CONCLUSIONS

Using a simultaneous segmental translation technique, deformity correction can be achieved with 23% fewer screws than maximal density screw pattern, but resulted in 25% higher bone-screw forces. Screw dropouts could be either on the convex side or on the concave side at alternate levels or at periapical levels. Periapical screw dropouts may more likely result in lower bone-screw force increase than alternate level screw dropouts.

Comparison of Effective Dose of Radiation During Pedicle Screw Placement Using Intraoperative Computed Tomography Navigation Versus Fluoroscopy in Children With Spinal Deformities

BACKGROUND

We compared the effective dose of radiation associated with pedicle screw placement in posterior spinal fusion in children using intraoperative computed tomography (CT) navigation versus intraoperative fluoroscopy (C-arm).

METHODS

In this review of posterior spinal fusion patients, height, weight, local density function, dose area product, body region, number of views, and part of the body were used to calculate the effective dose to the patient in millisieverts (mSv) in 37 children in whom pedicle screw placement was aided by intraoperative CT versus 44 children in whom pedicle screw placement was aided by C-arm. Both groups had posterior spinal fusions during the same time period by 3 surgeons between November 2012 and August 2013. Calculation of the radiation dose was made by the following method: for the C-arm, and the fluoroscopic/digital acquisitions part of the CT examinations, we estimated the effective dose using the program PCXMC 2.0. For the cross-sectional imaging part of the CT examinations, we used the dose-length product from the radiation dose reports of the CT unit and published dose-length product to effective dose conversion factors. The overall effective dose for the CT group was the total of the cross-sectional imaging dose and the fluoroscopic/digital acquisition imaging dose. An unpaired T test was used to determine significant difference between the C-arm and CT navigation groups.

RESULTS

The average effective dose was 1.48±1.66 mSv for the CT patients and 0.34±0.36 mSv for the C-arm patients. These values for the 2 groups are significantly different (P=0.0012). Obese children had very high mSv values in the CT group.

CONCLUSIONS

Intraoperative CT for navigational instrumentation placement associated with spinal fusion in children results in significantly more radiation to the child than C-arm. Families need to be counseled about radiation exposure associated with intraoperative CT, especially in obese children. Intraoperative CT use should be tailored to placing instrumentation where the benefit is the highest.

LEVEL OF EVIDENCE

Level II.

Does higher screw density improve radiographic and clinical outcomes in adolescent idiopathic scoliosis? A systematic review and pooled analysis

OBJECTIVE The radiographic and clinical outcomes of low-density (LD) versus high-density (HD) screw constructs in patients with adolescent idiopathic scoliosis (AIS) treated with all-pedicle screw constructs are still controversial. A systematic review and pooled analysis were performed to compare radiographic, perioperative, and quality-of-life (QOL) outcomes and complications in patients with moderate AIS treated with LD or HD screw constructs. METHODS The MEDLINE, Embase, and Web of Science databases were searched for English-language articles addressing LD versus HD screw constructs in AIS patients treated with all-pedicle screw constructs. The division of LD and HD groups was based on relative screw density and screw techniques. This systematic analysis strictly followed the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, and all articles included in the analysis met the criteria specified in the guidelines. Two reviewers independently assessed the quality of the studies using the Newcastle-Ottawa Scale. Date on radiographic, perioperative, and QOL outcomes and complications were extracted from the included studies. RESULTS Twelve studies, involving a total of 827 patients (480 treated with LD constructs, 347 with HD), were analyzed-1 randomized controlled trial, 1 quasi-randomized controlled trial, and 10 retrospective studies. The patients' age at surgery, preoperative Cobb angle of the major curve, amount of thoracic kyphosis, and major curve flexibility were reasonably distributed, and no statistically significant differences were found. Regarding the outcomes at most recent follow-up, there were no significant differences in the Cobb angle of the major curve (mean difference 0.96°, 95% CI -0.06° to 1.98°, p = 0.06, I² = 1%), major curve correction (mean difference -0.72%, 95% CI -2.96% to 1.52%, p = 0.53, I² = 0%), thoracic kyphosis (mean difference -1.67°, 95% CI -4.59° to 1.25°, p = 0.26, I² = 79%), complications (odds ratio [OR] 0.66, 95% CI 0.31-1.42, p = 0.29, I² = 0%), and QOL outcomes. Reduced operative time (mean difference -48.56 minutes, 95% CI -82.69 to -14.43 minutes, p = 0.005, I² = 87%), blood loss (mean difference -77.85 ml, 95% CI -153.10 to -2.60 ml, p = 0.04, I² = 0%), and hospital charges (mean difference -$5.92K, 95% CI -$6.59K to -$5.26K, p < 0.00001, I² = 0%) were found in the LD group, compared with the HD group. CONCLUSIONS LD and HD screw constructs are both associated with satisfactory radiographic and QOL outcomes with few complications. This study supports the use of LD screw constructs for the treatment of moderate AIS, because they resulted in reduced operative time, blood loss, and hospital charges while maintaining radiographic and QOL outcomes and complication rates similar to those achieved with HD screw constructs.

Reliability and Usefulness of Intraoperative 3-Dimensional Imaging by Mobile C-Arm With Flat-Panel Detector

STUDY DESIGN

Reliability and agreement study.

OBJECTIVE

To assess the reliability of intraoperative 3-dimensional imaging with a mobile C-arm (3D C-arm) equipped with a flat-panel detector.

SUMMARY OF BACKGROUND DATA

Pedicle screws are widely used in spinal surgery. Postoperative computed tomography (CT) is the most reliable method to detect screw misplacement. Recent advances in imaging devices have enabled surgeons to acquire 3D images of the spine during surgery. However, the reliability of these imaging devices is not known.

METHODS

A total of 203 screws were used in 22 consecutive patients who underwent surgery for scoliosis. Screw position was read twice with a 3D C-arm and twice with CT in a blinded manner by 2 independent observers. Screw positions were classified into 4 categories at every 2 mm and then into 2 simpler categories of acceptable or unacceptable. The degree of agreement with respect to screw positions between the double readings was evaluated by κ value. With unanimous agreement between 2 observers regarding postoperative CT readings considered the gold standard, the sensitivity of the 3D C-arm for determining screw misplacement was calculated.

RESULTS

A total 804 readings were performed. For the 4-category classification, the mean κ value for the 2 interobserver readings was 0.52 for the 3D C-arm and 0.46 for CT. For the 2-category classification, the mean κ value for the 2 interobserver readings was 0.80 for the 3D C-arm and 0.66 for CT. The sensitivity, specificity, positive predictive value, and negative predictive value of intraoperative imaging with the 3D C-arm were 70%, 95%, 44%, and 98%, respectively. With respect to screws with perforation ≥4 mm, the sensitivity was 83%. No revision surgery was performed.

CONCLUSIONS

Intraoperative imaging with a 3D C-arm was reliable for detecting screw misplacement and helpful in decreasing the rate of revision surgery for screw misplacement.

Delayed Dural Leak Following Posterior Spinal Fusion for Idiopathic Scoliosis Using All Posterior Pedicle Screw Technique

BACKGROUND

In pediatric patients, pedicle screws are malpositioned 5% to 15% of the time. Complications associated with malpositioned screws are infrequently reported in the literature. We present a series of adolescent idiopathic scoliosis (AIS) patients who presented in a delayed manner with positional headache and chronic dural leak adjacent to the pedicle screw tract.

METHODS

Scoliosis databases at 2 centers were reviewed, and cases of delayed positional headaches following posterior spinal fusion for AIS were identified. Demographic and clinical data were collected.

RESULTS

Of 322 patients, 4 patients presented with positional headaches at a mean of 12.8 weeks following posterior spinal fusion surgery for AIS, with an interval time to diagnosis of 5 months. Computed tomographic myelogram demonstrated severe pedicle screw malposition in 1 patient, and minimal malposition in 3 patients (<2 mm violation). The patients had delayed presentation with positional headaches secondary to dural leak. All patients successfully underwent revision surgery with repair of the dural leak. At the time of latest follow-up, all patients are asymptomatic.

CONCLUSIONS

Pedicle screw malposition can result in dural leaks. Patients may present in a delayed manner with positional headaches and an acquired Chiari malformation. Clinical suspicion should prompt imaging of the brain or cervical spine followed by computed tomographic myelogram to determine site of leak. This is a rare complication from pedicle screw malposition.

LEVELS OF EVIDENCE

Level IV-case series.

Complications following spine fusion for adolescent idiopathic scoliosis

Complications following spine fusion for adolescent idiopathic scoliosis can be characterized as either intra-operative or post-operative. The most serious and feared complication is neurologic injury, both in the intra- and post-operative period. Other intra-operative complications include dural tears and ophthalmologic or peripheral nerve deficits, which may be related to positioning. Among the most common post-operative complications are surgical site infection, venous thromboembolism, gastrointestinal complications, and implant-related complications. Significant blood loss requiring transfusion, traditionally considered a known sequelae of spine fusion, is now being recognized as a "complication" in large national databases. Pediatric spine surgeons who care for patients with AIS must be thoroughly familiar with all potential complications and their management.

Reliability of the Planned Pedicle Screw Trajectory versus the Actual Pedicle Screw Trajectory using Intra-operative 3D CT and Image Guidance

BACKGROUND

Technological advances, including navigation, have been made to improve safety and accuracy of pedicle screw fixation. We evaluated the accuracy of the virtual screw placement (Stealth projection) compared to actual screw placement (intra-operative O-Arm) and examined for differences based on the distance from the reference frame.

METHODS

A retrospective evaluation of prospectively collected data was conducted from January 2013 to September 2013. We evaluated thoracic and lumbosacral pedicle screws placed using intraoperative O-arm and Stealth navigation by obtaining virtual screw projections and intraoperative O-arm images after screw placement. The screw trajectory angle to the midsagittal line and superior endplate was compared in the axial and sagittal views, respectively. Percent error and paired t-test statistics were then performed.

RESULTS

Thirty-one patients with 240 pedicle screws were analyzed. The mean angular difference between the virtual and actual image in all screws was 2.17° ± 2.20° on axial images and 2.16° ± 2.24° on sagittal images. There was excellent agreement between actual and virtual pedicle screw trajectories in the axial and sagittal plane with ICC = 0.99 (95%CI: 0.992-0.995) (p<0.001) and ICC= 0.81 (95%CI: 0.759-0.855) (p<0.001) respectively. When comparing thoracic and lumbar screws, there was a significant difference in the sagittal angulation between the two distributions. No statistical differences were found distance from the reference frame.

CONCLUSION

The virtual projection view is clinically accurate compared to the actual placement on intra-operative CT in both the axial and sagittal views. There is slight imprecision (~2°) in the axial and sagittal planes and a minor difference in the sagittal thoracic and lumbar angulation, although these did not affect clinical outcomes. In general, we find that pedicle screw placement using intraoperative cone beam CT and navigation to be accurate and reliable, and as such have made it a routine part of our spine practice. This study was approved by the University of Minnesota IRB (#1303E30544).

Switching to a Pediatric Dose O-Arm Protocol in Spine Surgery Significantly Reduced Patient Radiation Exposure

BACKGROUND

Intraoperative computed tomography and image-guided navigation improve the accuracy of screw placement. Radiation exposure to the patient remains a primary drawback. The objective of the present study was to compare the total intraoperative radiation dose and assess the resultant image quality for O-arm-assisted pedicle screw insertion, among 3 protocols: default (manufacturer recommended), institutional (reduced dose utilized in our institution), and pediatric (new protocol with lowest dose).

METHODS

Thirty-seven consecutive patients under the age of 18 years underwent posterior instrumentation of the spine and underwent an intraoperative O-arm scan. Techniques (kV and mAs) for default and institutional dose settings were manually adjusted based on spinal level and body weight. Pediatric dose techniques were 80 kV/80 mAs with no adjustment for level or weight. The number of scans repeated because of inadequate imaging was assessed, and the mean estimated effective dose between the 3 protocols was compared.

RESULTS

Sixty-eight scans were performed in 37 consecutive patients with mean age of 14 years and mean weight of 55 kg. For reference, the effective radiation dose of a chest x-ray is approximately 0.10 mSv. Use of the default protocol resulted in higher mean effective dose per scan of 4.65 mSv, whereas institutional protocol resulted in 2.37 mSv. The pediatric protocol reduced the mean dose to 0.65 mSv. The total effective dose per surgery was: 1.17 mSv (pediatric), 3.83 mSv (institutional), and 12.79 mSv (default) (P<0.0001 each). All scans lead to satisfactory image quality except in 1 patient >100 kg with stainless steel implants. There were no neurological or other implant-related complications. The pediatric protocol resulted in satisfactory image quality with the lowest total radiation dose, only 1/10 of that of the default protocol.

CONCLUSIONS

We successfully switched to a pediatric low-dose O-arm protocol in clinical practice, reducing the dose to <1/4 of the mean annual natural background radiation. This may allow use of intraoperative computed tomography and navigation for pedicle screw placement without excessive radiation exposure to young patients.

LEVEL OF EVIDENCE

Level III-retrospective comparative study.

Morphometric measurement of the cervical spine for minimally invasive pedicle screw fixation using reverse engineering and three-dimensional reconstruction

BACKGROUND

Percutaneous cervical pedicle screw fixation has been proven to be an effective method of cervical screw instrumentation, which has the advantages of less invasiveness and low blood loss. Emerging evidence has indicated that the cervical spinous process plays an important role in percutaneous spine surgery. However, there is a limited amount of information on the fundamental research of pedicle and its associated imaging parameter measurement. The purpose of this study was to measure the anatomic data of the pedicle screw channel (PSC) using reverse engineering and three-dimensional reconstruction, and also to discuss the three-dimensional relationship between the cervical spinous process and the pedicle screw channel.

METHODS

Twenty adult subjects (10 males, 10 females, age range 19-46 years) were studied using the method of three-dimensional CT reconstruction and reverse engineering. The centrum was divided into 10 equal parts from front to back. The bisectors were defined as borderline depths of the centrum, from front to back, 100%, 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, 0% of borderline depths were presented. Then, a 3D coordinate system was constructed to measure all the data, including the radius of the inscribed circle, the length of the PSC, the insertion angle, the distances from entry point to cervical spinous process and skin depth. All the indexes were measured from 70% to 90% borderline depth.

RESULTS

The radius of the inscribed circles from C₃ to C₇ at 90% borderline depth were 2.94 ± 0.55 mm, 3.04 ± 0.40 mm, 3.15 ± 0.36 mm, 3.28 ± 0.47 mm, 3.89 ± 0.54 mm, respectively. The lengths of the PSC were between 25 and 32 mm. The insertion angles for 70% to 90% borderline depth were 28.33°, 34.28°, 37.92°, respectively. The relationship between the PSC and spinous process was measured as the distance from the entry point to the end of the spinous process, which were, respectively, 26.91 mm, 28.18 mm, 30.03 mm, 35.67 mm, 41.99 mm from C₃ to C₇ .The distance from the skin to the entry point of C_3-7 increased gradually.

CONCLUSIONS

The measurements of this study could provide detailed information for percutaneous cervical screw fixation. The data of the relationship between the cervical spinous process and the pedicle screw channel present valuable technical information for the design, optimization and clinical application of the aiming device for percutaneous cervical pedicle screw fixation. Copyright © 2016 John Wiley & Sons, Ltd.

Anterior versus posterior approach in Lenke 5C adolescent idiopathic scoliosis: a meta-analysis of fusion segments and radiological outcomes

Background

Radiological outcomes between anterior and posterior approach in Lenke 5C curves were still controversial. Meta-analysis on published articles to compare fusion segments and radiological outcomes between the two surgical approaches was performed.

Methods

Electronic database was conducted for searching studies concerning the anterior versus posterior approach in Lenke 5C curves. After quality assessment, data of means, standard deviations, and sample sizes were extracted. RevMan 5.3 was adopted for data analysis.

Results

Seven case-control studies involving 308 Lenke 5C AIS patients were identified in the meta-analysis. No significant differences were noted in correction rate of thoracolumbar/lumbar curve (95 % CI −6.02 to 4.32, P = 0.75) and incidence of proximal junctional kyphosis (95 % CI 0.12 to 7.19, P = 0.94) of final follow-up, in change values of thoracolumbar/lumbar curve (95 % CI −3.28 to 7.19, P = 0.46) and thoracic kyphosis (95 % CI −4.10 to 0.13, P = 0.07). The anterior approach represented a significant shorter fusion segments compared to posterior approach (95 % CI −1.72 to −0.71, P < 0.00001). The posterior approach obtained a larger increasing Cobb angle of lumbar lordosis than the anterior approach (95 % CI −6.06 to −0.61, P = 0.02).

Conclusions

The anterior and posterior approach can obtain comparable coronal correction, change values of thoracic kyphosis, and incidence of proximal junctional kyphosis. The anterior approach saves approximate one more fusion segment, and the posterior approach can obtain a larger increasing Cobb angle of lumbar lordosis, from preoperation to final follow-up.

Trial registration

The article type of this study is meta-analysis and prospective registration is not required.

Removal of Infected Posterior Spinal Implants: Be Prepared to Transfuse

STUDY DESIGN

Single-center retrospective review of spinal deformity patients undergoing removal of infected posterior spinal fusion implants over a 10-year period.

OBJECTIVE

To evaluate the intraoperative blood loss and perioperative complications of implant removal in posterior spinal fusions.

SUMMARY OF BACKGROUND DATA

To our knowledge, no studies examine blood loss or complications associated with removal of infected spinal implants in spinal deformity.

METHODS

A retrospective review of 28 consecutive cases of infected posterior spinal fusion implant removal from 2003 to 2012 was performed. Exclusion criteria were patients with ≤6 levels of instrumentation, a partial removal of implants or a bleeding disorder.

RESULTS

The average estimated blood loss was 465 mL (range 100-1,505 mL). Average estimated blood volume was 3,814 mL (range 1,840-9,264 mL). The average percentage of estimated blood loss was 14.2% (range 1.9%-43.5%). On postoperative labs obtained at the conclusion of the procedure, there was an average loss in hematocrit of 6.6 from preoperative values. Seventy-one percent of patients (20/28) received a blood transfusion; 39% (11/28) of these received a transfusion intraoperatively and 54% (15/28) received a transfusion postoperatively. Forty-six percent of patients (13/28) experienced an associated medical complication in the postoperative period. Among these 13, there were 16 total complications, with the most common being seizures (4/16), pneumonia (2/16), and sepsis (2/16). Average hospital stay was 14 days (range 4-52).

CONCLUSION

Seventy-one percent of patients undergoing removal of infected spinal implants received a blood transfusion. We recommend having blood products available when removing posterior spinal instrumentation >6 levels. Patients and families should be counseled on the high risk of complications and expected hospital stay in these cases.

LEVEL OF EVIDENCE

Level III.

Are We Underestimating the Significance of Pedicle Screw Misplacement?

STUDY DESIGN

A retrospective review of charts, x-rays (XRs) and computed tomography (CT) scans was performed.

OBJECTIVE

To evaluate the accuracy of pedicle screw placement using a novel classification system to determine potentially significant screw misplacement.

SUMMARY OF BACKGROUND DATA

The accuracy rate of pedicle screw (PS) placement varies from 85% to 95% in the literature. This demonstrates technical ability but does not represent the impact of screw misplacement on individual patients. This study quantifies the rate of screw misplacement on a per-patient basis to highlight its effect on potential morbidity.

METHODS

A retrospective review of charts, XRs and low-dose CT scans of 127 patients who underwent spinal fusion with pedicle screws for spinal deformity was performed. Screws were divided into four categories: screws at risk (SAR), indeterminate misplacements (IMP), benign misplacements (BMP), accurately placed (AP).

RESULTS

A total of 2724 screws were placed in 127 patients. A total of 2396 screws were placed accurately (87.96%). A total of 247 screws (9.07%) were BMP, 52 (1.91%) were IMP, and 29 (1.06%) were considered SAR. Per-patient analysis showed 23 (18.11%) of patients had all screws AP. Thirty-five (27.56%) had IMP and 18 (14.17%) had SAR. Risk factor analysis showed smaller Cobb angles increased likelihood of all screws being AP. Sub-analysis of adolescent idiopathic scoliotic patients showed no curve or patient characteristic that correlated with IMP or SAR. Over 40% of patients had screws with either some/major concern.

CONCLUSION

Overall reported screw misplacement is low, but it does not reflect the potential impact on patient morbidity. Per-patient analysis reveals more concerning numbers toward screw misplacement. With increasing pedicle screw usage, the number of patients with misplaced screws will likely increase proportionally. Better strategies need to be devised for evaluation of screw placement, including establishment of a national database of deformity surgery, use of intra-operative image guidance, and reevaluation of postoperative low-dose CT imaging.

LEVEL OF EVIDENCE

3.

What would be the annual cost savings if fewer screws were used in adolescent idiopathic scoliosis treatment in the US?

OBJECT

There is substantial heterogeneity in the number of screws used per level fused in adolescent idiopathic scoliosis (AIS) surgery. Assuming equivalent clinical outcomes, the potential cost savings of using fewer pedicle screws were estimated using a medical decision model with sensitivity analysis.

METHODS

Descriptive analyses explored the annual costs for 5710 AIS inpatient stays using discharge data from the 2009 Kids’ Inpatient Database (Healthcare Cost and Utilization Project, Agency for Healthcare Research and Quality), which is a national all-payer inpatient database. Patients between 10 and 17 years of age were identified using the ICD-9-CM code for idiopathic scoliosis (737.30). All inpatient stays were assumed to represent 10-level fusions with pedicle screws for AIS. High screw density was defined at 1.8 screws per level fused, and the standard screw density was defined as 1.48 screws per level fused. The surgical return for screw malposition was set at $23,762. A sensitivity analysis was performed by varying the cost per screw ($600–$1000) and the rate of surgical revisions for screw malposition (0.117%–0.483% of screws; 0.8%–4.3% of patients). The reported outcomes include estimated prevented malpositioned screws (set at 5.1%), averted revision surgeries, and annual cost savings in 2009 US dollars, assuming similar clinical outcomes (rates of complications, revision) using a standard- versus high-density pattern.

RESULTS

The total annual costs for 5710 AIS hospital stays was $278 million ($48,900 per patient). Substituting a high for a standard screw density yields 3.2 fewer screws implanted per patient, with 932 malpositioned screws prevented and 21 to 88 revision surgeries for implant malposition averted, and a potential annual cost savings of $11 million to $20 million (4%–7% reduction in the total cost of AIS hospitalizations).

CONCLUSIONS

Reducing the number of screws used in scoliosis surgery could potentially decrease national AIS hospitalization costs by up to 7%, which may improve the safety and efficiency of care. However, such a screw construct must first be proven safe and effective.

Feasibility of CT-based intraoperative 3D stereotactic image-guided navigation in the upper cervical spine of children 10 years of age or younger: initial experience

OBJECT Rigid screw fixation may be technically difficult in the upper cervical spine of young children. Intraoperative stereotactic navigation may potentially assist a surgeon in precise placement of screws in anatomically challenging locations. Navigation may also assist in defining abnormal anatomy. The object of this study was to evaluate the authors' initial experience with the feasibility and accuracy of this technique, both for resection and for screw placement in the upper cervical spine in younger children. METHODS Eight consecutive pediatric patients 10 years of age or younger underwent upper cervical spine surgery aided by image-guided navigation. The demographic, surgical, and clinical data were recorded. Screw position was evaluated with either an intraoperative or immediately postoperative CT scan. RESULTS One patient underwent navigation purely for guidance of bony resection. A total of 14 navigated screws were placed in the other 7 patients, including 5 C-2 pedicle screws. All 14 screws were properly positioned, defined as the screw completely contained within the cortical bone in the expected trajectory. There were no immediate complications associated with navigation. CONCLUSIONS Image-guided navigation is feasible within the pediatric cervical spine and may be a useful surgical tool for placing screws in a patient with small, often difficult bony anatomy. The authors describe their experience with their first 8 pediatric patients who underwent navigation in cervical spine surgery. The authors highlight differences in technique compared with similar navigation in adults.

Pedicle Screw Fixation Study in Immature Porcine Spines to Improve Pullout Resistance during Animal Testing

The porcine model is frequently used during development and validation of new spinal devices, because of its likeness to the human spine. These spinal devices are frequently composed of pedicle screws with a reputation for stable fixation but which can suffer pullouts during preclinical implantation on young animals, leading to high morbidity. With a view to identifying the best choices to optimize pedicle screw fixation in the porcine model, this study evaluates ex vivo the impact of weight (age) of the animal, the level of the vertebrae (lumbar or thoracic) and the type of screw anchorage (mono- or bi-cortical) on pedicle screw pullouts. Among the 80 pig vertebrae (90- and 140-day-old) tested in this study, the average screw pullout forces ranged between 419.9N and 1341.2N. In addition, statistical differences were found between test groups, pointing out the influence of the three parameters stated above. We found that the the more caudally the screws are positioned (lumbar level), the greater their pullout resistance is, moreover, screw stability increases with the age, and finally, the screws implanted with a mono-cortical anchorage sustained lower pullout forces than those implanted with a bi-cortical anchorage. We conclude that the best anchorage can be obtained with older animals, using a lumbar fixation and long screws traversing the vertebra and inducing bi-cortical anchorage. In very young animals, pedicle screw fixations need to be bi-cortical and more numerous to prevent pullout.

Comparison of Radiographic Postoperative Outcomes Between Males and Females With AIS

The primary aim was to compare postoperative radiographic outcomes between sexes among adolescent idiopathic scoliosis (AIS) patients. A total of 162 AIS patients (42 males and 120 females) undergoing pedicle screw instrumentation and posterior fusion were included. Coronal and sagittal curves and flexibilities were measured and calculated. The postoperative correction rate (CR), fulcrum bending correction index (FBCI), and Cincinnati correction index were evaluated to compare the surgical benefits between sexes.Males were older (16.79 vs 14.79 years, respectively; P < 0.01) and had stiffer curves than females (lateral bending flexibility percentage: 47.77 vs 52.57, respectively, P = 0.21; traction flexibility percentage: 35.48 vs 36.98, respectively, P = 0.98; fulcrum bending flexibility percentage: 56.13 vs 66.57, respectively, P < 0.05). Males and females exhibited similar Lenke classification schemes (P = 0.72), but had different Risser signs (P < 0.01). Although males had greater postoperative curves (20.81° vs 16.83°, respectively; P = 0.009), no obvious differences in the CRs were noted between males and females (FBCI: 145.20% vs 108.37%, respectively; P = 0.92). Smaller preoperative lumbar lordosis was noted in males than in females (40.05° vs 45.72°, respectively; P = 0.03), yet no statistically significant differences in the preoperative and postoperative sagittal curves were observed between the sexes. In conclusion, considering the preoperative flexibilities, the 2 sexes achieved comparable surgical benefits without sacrificing the sagittal balance.

Strategies to improve the credibility of meta-analyses in spine surgery: a systematic survey

BACKGROUND CONTEXT

Meta-analyses are powerful tools that can synthesize existing research, inform clinical practice, and support evidence-based care. These studies have become increasingly popular in the spine surgery literature, but the rigor with which they are being conducted has not yet been evaluated.

PURPOSE

Our primary objectives were to evaluate the methodological quality (credibility) of spine surgery meta-analyses and to propose strategies to improve future research. Our secondary objectives were to evaluate completeness of reporting and identify factors associated with higher credibility and completeness of reporting.

STUDY DESIGN

This study is based on a systematic survey of meta-analyses.

OUTCOME MEASURES

We evaluated credibility according to the Users' Guide to the Medical Literature and completeness of reporting according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses checklist.

METHODS

We systematically searched MEDLINE, EMBASE, and The Cochrane Library, and two reviewers independently assessed eligibility, credibility, and completeness of reporting. We used multivariable linear regression to evaluate potential associations. Interrater agreement was quantified using kappa and intraclass correlation (ICC) coefficients.

RESULTS

We identified 132 eligible meta-analyses of spine surgery interventions. The mean credibility score was 3 of 7 (standard deviation [SD], 1.4; ICC, 0.86), with agreement for each item ranging from 0.54 (moderate) to 0.83 (almost perfect). Clinical questions were judged as sensible in 125 (95%), searches were exhaustive in 102 (77%), and risk of bias assessments were undertaken in 91 (69%). Seven (5%) meta-analyses addressed possible explanations for heterogeneity using a priori subgroup hypotheses and 24 (18%) presented results that were immediately clinically applicable. Investigators undertook duplicate assessments of eligibility, risk of bias, and data extraction in 46 (35%) and rated overall confidence in the evidence in 24 (18%). Later publication year, increasing Journal Impact Factor, increasing number of databases, inclusion of Randomized Controlled Trials, and inclusion of non-English studies were significantly associated with higher credibility scores (p<.05). The mean score for reporting was 18 of 27 (SD, 4.4; ICC, 0.94).

CONCLUSIONS

The credibility of many current spine surgery meta-analyses is limited. Researchers can improve future meta-analyses by performing exhaustive literature searches, addressing possible explanations of heterogeneity, presenting results in a clinically useful manner, reproducibly selecting and assessing primary studies, addressing confidence in the pooled effect estimates, and adhering to guidelines for complete reporting.

At What Levels Are Freehand Pedicle Screws More Frequently Malpositioned in Children?

STUDY DESIGN

Retrospective case series.

BACKGROUND

Previous studies report that 5% to 17% of pedicle screws placed in children are malpositioned. Knowledge of the long-term effects of malpositioned screws is limited. We sought to further characterize risk factors for malpositioned pedicle screws in order to establish a more proactive role in limiting future complications.

OBJECTIVE

We undertook this study to answer the following: 1) Is the rate of freehand pedicle screw malpositioning higher in children with spinal deformity, particularly at the apical concavity? 2) At what vertebral levels do freehand pedicle screws have the highest rates of malpositioning? 3) In which direction (medial or lateral) do freehand pedicle wall violations occur most often?

METHODS

Incidental postoperative computed tomographic (CT) exams were retrospectively reviewed in 85 pediatric patients (605 screws) treated with posterior spinal fusion using freehand pedicle screw technique. Of the screws imaged, 355 were in patients without deformity and 250 in patients with deformity. Breaches were categorized as mild (<2 mm), moderate (2-4 mm), or severe (>4 mm).

RESULTS

Screws in pediatric deformity patients were more frequently malpositioned by 2 mm or more than were screws in patients without deformity (26% vs. 19%, p = .02). In patients with deformity, no higher rate of screw malposition was detected at the apical region. Overall, the highest rates of severe screw malposition were between T3 and T8. Pedicle breaches were more commonly in a medial direction compared with lateral (74% vs. 26%, p < .0001). However, severe breaches within the T3-T8 region were more often directed lateral than medial (92% vs. 8%, p ≤ .0001).

CONCLUSIONS

The clinical significance of asymptomatic pedicle screw breaches in children has not yet been determined. In this study, screws at the apical concavity were no more likely to be malpositioned than those at other sites. Efforts to reduce pedicle screw malposition would likely be most effective at the T3-T8 levels.

LEVEL OF EVIDENCE

Level IV, Therapeutic Study. See the Guidelines for Authors for a complete description of the levels of evidence.

Hybrid fixation with sublaminar polyester bands in the treatment of neuromuscular scoliosis: a comparative analysis

BACKGROUND

Segmental spinal instrumentation with Luque wire fixation has been the standard treatment of neuromuscular scoliosis for >30 years. More recently, pedicle screw constructs have become the most widely utilized method of posterior spinal fixation; however, they are associated with complications such as implant malposition. We report the use of polyester bands and clamps utilized with pedicle screws in a hybrid fixation construct in the treatment of neuromuscular scoliosis.

METHODS

A retrospective review was conducted of 115 pediatric spinal deformity cases between 2008 and 2010 at a single center performed by a single surgeon. Intraoperative and postoperative complications were recorded. Radiographs were reviewed preoperatively and at the latest follow-up. A systematic review of the literature was conducted. Data from case series reporting outcomes of sublaminar wires and all-pedicle screw constructs in the treatment of neuromuscular scoliosis were compared with outcomes of the present study.

RESULTS

Twenty-nine patients with neuromuscular scoliosis who underwent segmental spinal instrumentation with a hybrid construct including sublaminar bands and pedicle screws were included. There was an average follow-up of 29 months (range, 12 to 40 mo). The average postoperative correction of coronal balance was 69% (range, 24 to 71 degrees). Sagittal balance was corrected to within 2 cm of the C7 plumbline in 97% of patients. The loss of coronal and sagittal correction at latest follow-up was 0% and 2%, respectively. There were 2 intraoperative clamp failures of the 398 implants (0.5%). There were 2 major (6.9%) and 7 minor (24%) complications in 7 patients (24% overall). These results compared favorably to previous case series of sublaminar wire and all-pedicle screw fixation techniques.

CONCLUSIONS

The polyester band technique is an excellent adjunct in the correction of spinal deformity in patients with neuromuscular scoliosis. Sublaminar bands utilized in a hybrid construct appear to be safe, can achieve corrections equivalent to all-pedicle screw constructs, and may decrease the potential complications associated with every level transpedicular fixation in the patient with a highly dysmorphic and osteoporotic spine.

LEVEL OF EVIDENCE

Level IV: cohort study.

Instrumenting the small thoracic pedicle: the role of intraoperative computed tomography image-guided surgery

OBJECT

Traditionally, instrumentation of thoracic pedicles has been more difficult because of their relatively smaller size. Thoracic pedicles are at risk for violation during surgical instrumentation, as is commonly seen in patients with scoliosis and in women. The laterally based "in-out-in" approach, which technically results in a lateral breach, is sometimes used in small pedicles to decrease the comparative risk of a medial breach with neurological involvement. In this study the authors evaluated the role of CT image-guided surgery in navigating screws in small thoracic pedicles.

METHODS

Thoracic (T1-12) pedicle screw placements using the O-arm imaging system (Medtronic Inc.) were evaluated for accuracy with preoperative and postoperative CT. "Small" pedicles were defined as those ≤ 3 mm in the narrowest diameter orthogonal to the long axis of the pedicle on a trajectory entering the vertebral body on preinstrumentation CT. A subset of "very small" pedicles (≤ 2 mm in the narrowest diameter, 13 pedicles) was also analyzed. Screw accuracy was categorized as good (< 1 mm of pedicle breach in any direction or in-out-in screws), fair (1-3 mm of breach), or poor (> 3 mm of breach).

RESULTS

Twenty-one consecutive patients (age range 32-71 years) had large (45 screws) and small (52 screws) thoracic pedicles. The median pedicle diameter was 2.5 mm (range 0.9-3 mm) for small and 3.9 mm (3.1-6.7 mm) for large pedicles. Computed tomography-guided surgical navigation led to accurate screw placement in both small (good 100%, fair 0%, poor 0%) and large (good 96.6%, fair 0%, poor 3.4%) pedicles. Good screw placement in very small or small pedicles occurred with an in-out-in trajectory more often than in large pedicles (large 6.8% vs small 36.5%, p < 0.0005; vs very small 69.2%, p < 0.0001). There were no medial breaches even though 75 of the 97 screws were placed in postmenopausal women, traditionally at higher risk for osteoporosis.

CONCLUSIONS

Computed tomography-guided surgical navigation allows for safe, effective, and accurate instrumentation of small (≤ 3 mm) to very small (≤ 2 mm) thoracic pedicles.

Adolescent idiopathic scoliosis correction achieved by posteromedial translation using polyester bands: A comparative study of subtransverse process versus sublaminar fixation

PURPOSE

Sublaminar polyester bands have been used in hybrid construct to achieve correction of adolescent idiopathic scoliosis since 2003. Despite the reported safety of the bands, some surgeons remain reluctant at the idea of approaching the canal because of the potential neurological complications reported with the Luque wiring. Sub transverse bands might be an alternative. The present study is the first to compare sublaminar polyester band fixation to fixation of polyester bands around the transverse processes in hybrid constructs used to treat AIS.

METHODS

Two cohorts of consecutive patients treated for thoracic AIS were retrospectively reviewed, with a minimum 2-year follow-up. Posteromedial translation was used for main curve correction in all cases. Sublaminar polyester bands were used in group 1 (20 patients). In group 2 (20 patients), the same implant was used, but the bands were passed around the transverse process instead of the lamina. Radiographic analysis included frontal Cobb angle measurements for each curve, thoracic kyphosis and rotation of the apical vertebra (RVA).

RESULTS

Mean operative time was similar in groups 1 and 2 (235±35 and 240±30minutes, respectively). Mean frontal correction achieved for the main curve was similar in both groups, 62.5±17.4% in group 1 and 54.1±19.4% in group 2. Sagittal correction was similar, with a final mean thoracic kyphosis of 30.9°±9.7° and 27.8°± 6.8° in group 1 and 2, respectively. Correction of RVA was similar in both groups postoperatively, 65.8% (±29.1) and 54.4% (±42.7) in group 1 and 2 respectively. No transverse process or lamina fracture was observed during insertion of the bands or curve correction in any of the groups.

CONCLUSION

This study confirms that anchorage of Universal clamps (UCs) around transverse processes is a safe and efficacious technique in both the frontal and sagittal planes, providing a useful alternative for the correction of moderate AIS. UCs attached to transverse processes can achieve correction of moderate AIS similar to that obtained with sublaminar UCs while further reducing risks of vertebral canal complications.

LEVEL OF EVIDENCE

Level IV.

Screw Versus Hybrid Constructs for Flexible Thoracic Curves in Adolescent Idiopathic Scoliosis: A Prospective, Randomized Study

STUDY DESIGN

Prospective, computer-randomized design.

OBJECTIVE

Compare screw and hybrid constructs in flexible, thoracic curves for adolescent idiopathic scoliosis (AIS) in a prospective randomized fashion.

SUMMARY OF BACKGROUND

The consensus in scientific literature is that all-screw constructs correct AIS better than hooks in the lumbar and in large, stiff thoracic curves. However, debate continues whether all-screw constructs outperform hybrid constructs in small, flexible thoracic AIS. To our knowledge, this is the first prospective, randomized scoliosis study that examines measures of correction and patient satisfaction with the Scoliosis Research Society-30 (SRS-30) questionnaire.

METHODS

A total of 45 enrolled AIS patients with flexible, thoracic curves were given an identification number with an associated computer-generated randomization to the hybrid (n = 22) or screw group (n = 23). The treating surgeon received the randomization 2-3 days before surgery. Data including major Cobb (MC), truncal rotation (TR), rib index (RI), secondary curve (SC), and SRS-30 questionnaire were collected preoperatively and postoperatively at 4 weeks and 3, 6, 12, and 24 months.

RESULTS

Thirty-seven patients in the hybrid (n = 18) and screw (n = 19) groups completed the study with a mean follow-up of 26 months (range, 24-49 months). Hybrid versus screw group means for preoperative, postoperative, and final follow-up were: MC 58° ± 8° versus 55° ± 6°, 18° ± 8° versus 15° ± 7°, and 23°± 8° versus 14° ± 6°; TR 14° ± 6° versus 16° ± 4°, 10° ± 5° versus 7° ± 3°, and 11° ± 5° versus 7° ± 4°; RI 3.0° ± 1.2° versus 3.4° ± 1.4°, 2.5° ± 0.7° versus 1.8° ± 0.6°, and 2.5° ± 0.8° versus 2.0° ± 0.5°; SC 35° ± 13° versus 31° ± 8°, 13° ± 11° versus 7° ± 9°, and 13° ± 12° versus 7° ± 7°; and SRS-30 3.9 ± 0.2 versus 3.9 ± 0.2, 4.1 ± 0.4 versus 4.0 ± 0.3, and 4.1 ± 0.3 versus 4.0 ± 0.2.

CONCLUSIONS

Intergroup preoperative and early postoperative values were comparable (p > .05). At final follow-up, owing to loss of correction in the hybrid group, differences in MC (9°; p = .000), RI (0.54; p = .016), and TR (4°; p = .039) correction were statistically significant as SC trended toward significance (6°; p = .052). All-screw constructs outperformed hybrid constructs, especially over time. No differences in SRS-30 scores occurred between groups.

Morbidity and radiographic outcomes of severe scoliosis of 90° or more: a comparison of hybrid with total pedicle screw instrumentation

OBJECTIVES

Untreated severe scoliosis is associated with increased mortality and remains a significant surgical challenge. Few studies have reported mortality after the surgical treatment of severe scoliosis beyond a 2-year follow-up. The objectives of this study were to evaluate mortality beyond standard 2-year follow-up and compare radiographic outcomes using hybrid or pedicle screw instrumentation for severe scoliosis.

METHODS

We evaluated 32 consecutive patients [11 males, mean age at surgery 15.3 (range 10.7-20.7) years] operated for a scoliosis of 90° or more using either hybrid (n = 15) or pedicle screw (n = 17) instrumentation. The follow-up time averaged 2.9 (2.0-6.6) years for radiographic and quality of life measurements and 5.5 years (2.0-9.0) years for mortality data. Of these patients, one had adolescent idiopathic scoliosis, three secondary scoliosis, and 28 neuromuscular scoliosis. Twelve patients in the hybrid and two patients in the pedicle screw groups underwent anteroposterior surgery (p < 0.001), and three patients in both groups had an apical vertebral column resection.

RESULTS

One (3.1 %) patient died during follow-up for severe pneumonia. Preoperatively, the mean magnitude of the major curve was 109° (90°-127°) in the hybrid and 100° (90°-116°) in the pedicle screw groups (p = 0.015), and was corrected to 45° (19°-69°) in the hybrid and 27° (18°-40°) in the pedicle screw groups at the 2-year follow-up (p < 0.001), with a mean correction of the major curve of 59 % (37-81 %) in the hybrid versus 73 % (60-81 %) in the pedicle screw groups, respectively (p = 0.0023). There were six postoperative complications, including one transient spinal cord deficit necessitating reoperation in the hybrid group as compared with five complications in the pedicle screw group (p = 0.53).

CONCLUSIONS

The mid-term mortality rate after the surgical treatment of severe scoliosis was low. Severe scoliosis can be treated safely with significantly better correction of the spinal deformity using pedicle screws than hybrid instrumentation.

Comparative radiation exposure using standard fluoroscopy versus cone-beam computed tomography for posterior instrumented fusion in adolescent idiopathic scoliosis

STUDY DESIGN

Retrospective cohort.

OBJECTIVE

The objective of this study was to define the intraoperative radiation exposure during freehand surgical technique with fluoroscopic assistance for placement and confirmation of posterior instrumentation in patients with adolescent idiopathic scoliosis and compare data with published values using intraoperative cone-beam computed tomography (CBCT) for similar cases.

SUMMARY OF BACKGROUND DATA

The treatment of idiopathic-like scoliosis used freehand placement of posterior instrumentation with fluoroscopic confirmation. Computer-assisted navigation systems coupled with intraoperative CBCT have been introduced to aid in accurate placement of instrumentation. Multiple studies report the improved accuracy of instrumentation using CBCT; however, there is a paucity of information regarding the radiation exposure when using CBCT in comparison with fluoroscopically assisted freehand technique.

METHODS

Forty-three idiopathic-like scoliosis operations performed by 4 spine surgeons at an academic institution were retrospectively reviewed. Radiation exposure was recorded intraoperatively for each case. Effective dose was determined using published effective dose to dose-length product conversion factors. Values were compared with previous studies reporting radiation exposure for similar cases using CBCT for intraoperative navigation and confirmation of instrumentation placement.

RESULTS

Calculated average effective dose using fluoroscopically assisted pedicle screw placement was 0.189 mSv (range, 0.00029-0.953 mSv; SD = 0.16711) per case. Average radiation exposure time was 26 seconds (SD = 18 s) per case, with an average of 11 vertebral levels fused. The literature reports effective dose for CBCT ranging from 7.29 to 9.72 mSv per case for intraoperative navigation and 14.58 to 19.44 mSv per case for both intraoperative navigation and confirmation of screw placement with CBCT.

CONCLUSION

We have demonstrated that the use of standard fluoroscopy results in markedly lower radiation exposure during a standard posterior instrumented fusion for idiopathic-like scoliosis than by the use of CBCT; this conclusion is limited by the retrospective nature of the study and lack of a control group.

LEVEL OF EVIDENCE

4.

Neuromonitoring with pulse-train stimulation for implantation of thoracic pedicle screws: a blinded and randomized clinical study. Part 2. The role of feedback

Object

The authors have reported in Part 1 of this study on a novel neuromonitoring test for the prevention of medial malpositioning of thoracic pedicle screws. In the present paper they examine the impact of providing the results of the test as intraoperative feedback to the surgical team.

Methods

This is the second part of a 2-part report of a prospective, blinded and randomized neuromonitoring study designed to lower the incidence of medially malpositioned thoracic pedicle screws. Details of the neuromonitoring technique and data supporting the alarm criteria used are contained in the companion article (Part 1). For the majority of pedicle screw placements, intraoperative test results were withheld from the study team (that is, the team members were blinded to the test results). However, for a limited number of pedicle sites the authors provided one of 2 forms of testing feedback to the surgical team: 1) “break the blind” feedback, if testing suggested that screw placement would result in direct contact between screw and the dura mater; and 2) “planned” feedback, beginning during the later stages of the study and provided for 50% of pedicle sites. Feedback gave the surgeon the opportunity to adjust the trajectory that the screw would ultimately take within the pedicle. The final screw position relative to the pedicle's medial wall for all sites in which feedback was withheld from the surgical team was compared with the screw position for those sites in which either form of feedback (“break the blind” or “planned”) was provided to and acted upon by the surgical team.

Results

Of the 820 pedicle tracks tested among the 71 surgical cases included in this study, a total of 684 were operated upon without any form of feedback. Planned feedback was provided for an additional 107 pedicle tracks, of which 15 triggered an intraoperative alarm (evoked electromyogram response in leg muscles to stimulus intensity ≤ 10 mA) leading to a warning to the surgical team of a medially biased pedicle track. Finally, the blind was broken 29 times, in each case when testing revealed a particularly low threshold (≤ 4 mA) for evoked responses in leg muscles when stimulating along the pedicle track with the ball-tipped probe. As detailed in the companion paper to this one, there were 32 screws with threads lying at least 2 mm medial to the pedicle wall. In all 32 instances (100%), either these screws were in the “no feedback” category (n = 29) or they were in a feedback category but the surgeon elected to not revise the pedicle-track trajectory. Two patients returned to the operating room for revision of screw placements because the screws were encroaching upon the central canal; the pedicle tracks for these screws had been in the “no feedback” category.

Conclusions

This is the first blinded and randomized study to prove that implementing a novel neuromonitoring strategy during placement of thoracic pedicle screws can significantly reduce the incidence of clinically relevant thoracic pedicle screw medial malpositioning.

Does higher anchor density result in increased curve correction and improved clinical outcomes in adolescent idiopathic scoliosis?

STUDY DESIGN

Retrospective review of prospectively collected data.

OBJECTIVE

To determine whether anchor density is associated with curve correction and patient-reported outcomes.

SUMMARY OF BACKGROUND DATA

There is limited information as to whether anchor density affects the results of adolescent idiopathic scoliosis surgery.

METHODS

A total of 952 patients with adolescent idiopathic scoliosis met inclusion criteria (Lenke 1, 2, and 5 curves) with predominantly screw constructs (no. of screws/no. of total anchors >75%). Anchor density was defined as the number of screws, hooks, and wires per level fused, with less than 1.54 considered low density. Analysis of covariance was undertaken to determine association of anchor density with percent curve correction, Scoliosis Research Society (SRS), and Spinal Appearance Questionnaire (SAQ) scores, controlling for flexibility, fusion length, demographics, and surgeon.

RESULTS

High- compared with low-anchor density was associated with increased percent curve correction in Lenke 1 curves at 1 year (69% vs. 66% correction, P = 0.0022), controlling for percent preoperative curve flexibility, length of fusion, and sex (model, P < 0.0001). Similar associations held at 2-year follow-up and for Lenke 2 curves. Decreased thoracic kyphosis was found with increased anchor density for Lenke 1 and 2 curve patterns. There were no associations found between anchor density and Lenke 5 curves. For Lenke 1 curve patterns at 2 years postoperatively, in the high- versus low-anchor density cohorts, there were statistically higher SRS Activity (4.3 vs. 4.2, P = 0.019), Appearance (4.3 vs. 4.1, P = 0.0005), Satisfaction (4.5 vs. 4.3, P = 0.028), and Total scores (4.3 vs. 4.2; P = 0.024). Similarly, the SAQ Appearance score at 1 year similarly was improved in the high-anchor density group (high: 14.1 vs. low: 15.0, P = 0.03) for Lenke 1 curve patterns only.

CONCLUSION

For Lenke 1 and 2 curve patterns, improved percent correction of major coronal curve was noted in the high-screw density cohort. Although statistical significance was reached, it is unclear whether screw density resulted in clinically significant differences in patient-reported outcomes.

Loss of correction in spinal cord injury-related scoliosis after pedicle screw fixation

PURPOSE

Spinal cord injury (SCI) in the pediatric population is an infrequent but clinically important disease to scoliosis surgeons. Spinal deformity after SCI is extremely common and almost uniformly develops in patients being injured before the growth spurt. Most treatment paradigms extrapolate management from both the adult literature as well as adolescent idiopathic scoliosis data. Since these patient populations are different in many respects, we sought out to investigate the rates of loss of correction over time as well as the factors associated with loss of correction in pediatric patients undergoing pedicle screw fixation for treatment of SCI-related scoliosis.

METHODS

All consecutive pediatric patients with spinal cord injury and paralytic scoliosis managed with pedicle screw constructs were identified at a single institution. Clinical and radiographic parameters were reviewed and analyzed with specific focus on parameters associated with loss of correction at an average follow-up of 2 years.

RESULTS

Approximately 15 % of patients had a loss of correction of greater than 10° of Cobb angle. Postoperative sagittal imbalance was found to be significantly greater in patients who lost greater than 10° of correction compared to patients who did not lose correction (53.6 ± 39.9 vs 4.3 ± 41.3 mm, p = 0.02).

CONCLUSIONS

Correction of patients with paralytic associated scoliosis should aim for a neutral sagittal balance in order to prevent postoperative loss of correction. Further study is needed on this subgroup of patients with scoliosis given the differences in strategies needed to correct and maintain their deformity correction.

Safety of pedicle screws and spinal instrumentation for pediatric patients: comparative analysis between 0- and 5-year-old, 5- and 10-year-old, and 10- and 15-year-old patients

STUDY DESIGN

Retrospective study.

OBJECTIVE

To investigate the safety of pedicle screws and constructs for infantile and juvenile patients with spinal deformity.

SUMMARY OF BACKGROUND DATA

Few studies have examined the safety and complication rates associated with the usage of pedicle screw for children younger than 10 years.

METHODS

Radiographical and clinical data were collected of patients treated with pedicle screws at a single institution. Patients were divided into 2 groups based on age (0-5 yr old, 5-10 yr) and compared with an older cohort of 10- to 15-year-old patients. Patient demographics, screw adjustment, and complication data were collected for each group. Outcomes were analyzed using analysis of variance (P < 0.05).

RESULTS

In total, 5054 pedicle screws were analyzed: 176 in the 0- to 5-year-old group (31 patients), 659 in the 5- to 10-year-old group (68 patients), and 4219 in the 10- to 15-year-old group (234 patients). Mean follow-up was 3.1 ± 1.8 years (range, 3 mo-9 yr). There were 7 pedicle screw-associated complications (3 required revision surgery). Overall pedicle screw-associated complication rates were 2.1% per patient and 0.1% per screw. There were no neurological complications associated with misplacement of a pedicle screw. The pedicle screw-associated complication rates per patient and per screw were 3.2% and 0.6% in the 0- to 5-year-old group, 2.9% and 0.3% in the 5- to 10-year-old group, and 1.7% and 0.1% in the 10- to 15-year-old group (P > 0.05). The 5- to 10-year-old group had a significantly higher overall surgically related complication rate (34%) than the 0- to 5-year-old group (7%) and the 10- to 15-year-old group (6%) (P = 0.005), primarily due to the "growth friendly" constructs common in this age group.

CONCLUSION

Pedicle screws can be used for infantile or juvenile patients, although complication rates associated with pedicle screws tended to be slightly higher in the younger groups.

Neurological risks in scheduled spinal surgery

Spinal surgery is a high-risk specialty with an ever-increasing patient volume. Results are very largely favorable, but neurologic damage, the most severe complication, may leave major sequelae, some of which can be life-threatening. Neurologic complications may be classified according to onset (per- vs. postoperative) and surgical site (cervical vs. thoracolumbar). The present paper provides quantitative data for the risks involved. Knowledge of these complications and their risk of onset is the best means of guiding prevention strategies. The spine surgeon is part of a multidisciplinary team, with the radiologist and electrophysiologist, which is able to identify risk factors preoperatively and diagnose neurologic complications per- or postoperatively.

CoCr rods provide better frontal correction of adolescent idiopathic scoliosis treated by all-pedicle screw fixation

PURPOSE

Pedicle screw fixation is considered biomechanically advantageous in adolescent idiopathic scoliosis (AIS) correction, because it uses as an anchor the pedicle, which is the hardest part of the vertebral body. The ability of the rod to correct and hold the correction is a key factor in the selection of rod material. The goal of this study was to compare the results obtained by stainless steel (SS) and cobalt-chromium (CoCr) rods materials for the treatment of AIS curves.

METHODS

Ninety patients were retrospectively included. Sixty-four patients (group 1) were operated on using CoCr rods. Twenty-six patients (group 2) were operated on using SS rods. All the patients were treated by the same surgeon using all-pedicle screw constructs.

RESULTS

In group 1, the correction was respectively 41.03° and 35.78° for main and secondary curves. In group 2, the correction was respectively 30.98° and 24.42° for main and secondary curves. Statistical analysis showed improved correction rates in patients operated with CoCr rods for main (P < 0.0001) and secondary (P = 0.0003) curves with a lower loss of correction at final follow-up. Regarding the sagittal profile, postoperative T4T12 thoracic kyphosis was 28.04° in CoCr group compared to 22.79° in SS group (P = 0. 0.0038).

DISCUSSION

The present study confirms the ability of the all-pedicle screw construct to reach the maximum coronal plane correction and prevent deformity progression while maintaining balance. CoCr rods have the ability to exert higher corrective forces on the spine with relatively small amounts of rod deformation. Our findings confirm that CoCr rods have the ability to produce higher correction rates in frontal plane compared to SS rods of the same diameter.

Updates on surgical treatments for pediatric scoliosis

Scoliosis in children poses serious problems including respiratory problems, trunk imbalance, and depression, as well as detracting from the child's appearance. Scoliosis can also contribute to back pain later in life. Advanced surgical techniques allow for good correction and maintenance of progressive curves, and growth-sparing treatments are now available for patients with early-onset scoliosis (EOS). Posterior corrective surgeries using pedicle screw (PS) constructs, which allow curves to be corrected in three dimensions, has become the most popular surgical treatment for scoliosis. Several navigation systems and probes have been developed to aid in accurate PS placement. For thoracolumbar and lumbar curves, anterior surgery remains the method of choice. Growth-sparing techniques for treating EOS include growing rods, the Shilla method, anterior stapling, and vertical expandable prosthetic titanium rib, which was originally designed to treat thoracic insufficiency syndrome. However, these advanced surgical techniques do not always offer a perfect solution for pediatric scoliosis, and they are associated with complications such as infections and problems with instrumentation. Surgeons have developed several techniques in efforts to address these complications. We here review historic and recent advances in the surgical treatment of scoliosis in children, the problems associated with various techniques, and the challenges that remain to be overcome.