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Graham C. Calvert, Brandon D. Lawrence, Amir M. Abtahi, Kent N. Bachus and Darrel S. Brodke

OBJECT

Cortical trajectory screw constructs, developed as an alternative to pedicle screw fixation for the lumbar spine, have similar in vitro biomechanics. The possibility of one screw path having the ability to rescue the other in a revision scenario holds promise but has not been evaluated. The objective in this study was to investigate the biomechanical properties of traditional pedicle screws and cortical trajectory screws when each was used to rescue the other in the setting of revision.

METHODS

Ten fresh-frozen human lumbar spines were instrumented at L3–4, 5 with cortical trajectory screws and 5 with pedicle screws. Construct stiffness was recorded in flexion/extension, lateral bending, and axial rotation. The L-3 screw pullout strength was tested to failure for each specimen and salvaged with screws of the opposite trajectory. Mechanical stiffness was again recorded. The hybrid rescue trajectory screws at L-3 were then tested to failure.

RESULTS

Cortical screws, when used in a rescue construct, provided stiffness in flexion/extension and axial rotation similar to that provided by the initial pedicle screw construct prior to failure. The rescue pedicle screws provided stiffness similar to that provided by the primary cortical screw construct in flexion/extension, lateral bending, and axial rotation. In pullout testing, cortical rescue screws retained 60% of the original pedicle screw pullout strength, whereas pedicle rescue screws retained 65% of the original cortical screw pullout strength.

CONCLUSIONS

Cortical trajectory screws, previously studied as a primary mode of fixation, may also be used as a rescue option in the setting of a failed or compromised pedicle screw construct in the lumbar spine. Likewise, a standard pedicle screw construct may rescue a compromised cortical screw track. Cortical and pedicle screws each retain adequate construct stiffness and pullout strength when used for revision at the same level.

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Matthew L. Goodwin, William Ryan Spiker, Darrel S. Brodke and Brandon D. Lawrence

The aim of this study was to report on 2 patients in whom metal-on-metal (MOM) facet replacements failed, with subsequent positive findings on allergy testing. Motion-preserving devices have been used with limited success when instrumentation is indicated in the mobile spine. MOM-bearing surfaces in orthopedics were developed to increase implant longevity, yet have been associated with numerous adverse outcomes, including local tissue reactions, pseudotumors, metallosis, and the need for revision surgery. Five patients with spinal stenosis and low-grade spondylolisthesis were randomized to undergo facet replacement surgery with the ACADIA facet replacement system at the authors’ institution. Two patients experienced a return of neurological symptoms after a pain-free interval (< 2 years) with development of local tissue reaction and positive findings on allergy testing to cobalt, the metal in the MOM-bearing surface. Both patients underwent successful removal of the implant and revision to titanium posterior spinal fusion and interbody fusion without further complication.

Motion-preserving devices have been designed and trialed for specific indications in the mobile spine. Given the adverse results from MOM devices in hip arthroplasty and now the early reports with MOM facet replacements, caution is warranted when moving forward with any MOM joint–bearing surface. Both patients presented here had an unusual tissue reaction locally and subsequent positive allergy testing results to cobalt. These 2 patients appear to have developed a delayed hypersensitivity reaction to the metal, likely from fine debris at the MOM interface.

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Marcus D. Mazur, Vijay M. Ravindra, Meic H. Schmidt, Darrel S. Brodke, Brandon D. Lawrence, Jay Riva-Cambrin and Andrew T. Dailey

OBJECT

S-2 alar-iliac (S2AI) screws are an attractive alternative to conventional fixation with iliac bolts because they are lower profile, require less muscle dissection, and have greater pullout strength. Few studies, however, compare outcomes between these techniques.

METHODS

The authors conducted a retrospective cohort study of consecutive adult patients at a single institution from December 2009 to March 2012 who underwent lumbopelvic fixation using S2AI screws or iliac bolts. Medical records were reviewed for patients with clinical failure, defined as an unplanned reoperation because of instrumentation failure and/or wound-related complications. Univariate, multivariate, and survival analyses were used to compare patients who required reoperation with those who did not. Method of pelvic fixation was the main predictor variable of interest, and the authors adjusted for potential confounding risk factors.

RESULTS

Of the 60 patients included, 23 received S2AI screws. Seventeen patients (28%) underwent an osteotomy. The mean follow-up was 22 months. A Kaplan-Meier survival model was used to evaluate the time to reoperation from the initial placement of lumbopelvic instrumentation. The failure-free rate was 96.6% at 6 months, 87.0% at 1 year, and 73.5% at 2 years. Reoperation was more common in patients with iliac bolts than in those with S2AI screws (13 vs 2; p = 0.031). Univariate analysis identified potential risk factors for unplanned reoperation, including use of iliac bolts (p = 0.031), absence of L5–S1 interbody graft (p = 0.048), previous lumbar fusion (p = 0.034), and pathology other than degenerative disease or scoliosis (p = 0.034). After adjusting for other risk factors, multivariate analysis revealed that the use of S2AI screws (OR 8.1 [1.5–73.5]; p = 0.030) was the only independent predictor for preventing unplanned reoperation.

CONCLUSIONS

Both S2AI screws and iliac bolts were effective at improving fusion rates at the lumbosacral junction. The use of S2AI screws, however, was independently associated with fewer unplanned reoperations for wound-related complications and instrumentation failures than the use of iliac bolts.

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Cecilia L. Dalle Ore, Robert C. Rennert, Alexander J. Schupper, Brandon C. Gabel, David Gonda, Bradley Peterson, Lawrence F. Marshall, Michael Levy and Hal S. Meltzer

OBJECTIVE

Pediatric traumatic subarachnoid hemorrhage (tSAH) often results in intensive care unit (ICU) admission, the performance of additional diagnostic studies, and ICU-level therapeutic interventions to identify and prevent episodes of neuroworsening.

METHODS

Data prospectively collected in an institutionally specific trauma registry between 2006 and 2015 were supplemented with a retrospective chart review of children admitted with isolated traumatic subarachnoid hemorrhage (tSAH) and an admission Glasgow Coma Scale (GCS) score of 13–15. Risk of blunt cerebrovascular injury (BCVI) was calculated using the BCVI clinical prediction score.

RESULTS

Three hundred seventeen of 10,395 pediatric trauma patients were admitted with tSAH. Of the 317 patients with tSAH, 51 children (16%, 23 female, 28 male) were identified with isolated tSAH without midline shift on neuroimaging and a GCS score of 13–15 at presentation. The median patient age was 4 years (range 18 days to 15 years). Seven had modified Fisher grade 3 tSAH; the remainder had grade 1 tSAH. Twenty-six patients (51%) had associated skull fractures; 4 involved the petrous temporal bone and 1 the carotid canal. Thirty-nine (76.5%) were admitted to the ICU and 12 (23.5%) to the surgical ward. Four had an elevated BCVI score. Eight underwent CT angiography; no vascular injuries were identified. Nine patients received an imaging-associated general anesthetic. Five received hypertonic saline in the ICU. Patients with a modified Fisher grade 1 tSAH had a significantly shorter ICU stay as compared to modified Fisher grade 3 tSAH (1.1 vs 2.5 days, p = 0.029). Neuroworsening was not observed in any child.

CONCLUSIONS

Children with isolated tSAH without midline shift and a GCS score of 13–15 at presentation appear to have minimal risk of neuroworsening despite the findings in some children of skull fractures, elevated modified Fisher grade, and elevated BCVI score. In this subgroup of children with tSAH, routine ICU-level care and additional diagnostic imaging may not be necessary for all patients. Children with modified Fisher grade 1 tSAH may be particularly unlikely to require ICU-level admission. Benefits to identifying a subgroup of children at low risk of neuroworsening include improvement in healthcare efficiency as well as decreased utilization of unnecessary and potentially morbid interventions, including exposure to ionizing radiation and general anesthesia.