Sublaminar implants that encircle cortical bone are well-established adjuncts to pedicle screw-rod constructs in pediatric deformity surgery. Sublaminar bands (SLBs) in particular carry the advantage of relatively greater bone contact surface area as compared to wires and pullout loads that are independent of bone mineral density, in contrast to pedicle screws. Whereas the relevant technical considerations have been reported for pediatric deformity correction, an understanding of the relative procedural specifics of these techniques is missing for adult spinal deformity (ASD), despite several case series that have used distinct posterior tethering techniques for proximal junctional kyphosis prevention. In this paper, the authors summarize the relevant literature and describe a novel technique wherein bilateral tensioned SLBs are introduced at the nonfused proximal junctional level of long-segment ASD constructs.
Vibhu K. Viswanathan, Amy J. Minnema, Stephanus Viljoen and H. Francis Farhadi
Luke G. F. Smith, Nguyen Hoang, Ammar Shaikhouni and Stephanus Viljoen
Pedicle and lateral mass screws are the most common means of rigid fixation in posterior cervical spine fusions. Various other techniques such as translaminar screw placement, paravertebral foramen screw fixation, sublaminar and spinous process wiring, cement augmentation, and others have been developed for primary fixation or as salvage methods. Use of these techniques can be limited by a prior history of osteotomies, poor bone density, destruction of the bone-screw interface, and unfavorable vascular and osseous anatomy.
Here, the authors report on the novel application of cervical sublaminar polyester bands as an adjunct salvage method or additional fixation point used with traditional methods in the revision of prior constructs. While sublaminar polyester bands have been used for decades in pediatric scoliosis surgery in the thoracolumbar spine, they have yet to be utilized as a method of fixation in the cervical spine. In both cases described here, sublaminar banding proved crucial for fixation points where traditional fixation techniques would have been less than ideal. Further study is required to determine the full application of sublaminar polyester bands in the cervical spine as well as its outcomes.
Stephanus V. Viljoen, Nicole A. DeVries Watson, Nicole M. Grosland, James Torner, Brian Dalm and Patrick W. Hitchon
The objective of this study was to evaluate the biomechanical properties of lateral instrumentation compared with short- and long-segment pedicle screw constructs following an L-1 corpectomy and reconstruction with an expandable cage.
Eight human cadaveric T10–L4 spines underwent an L-1 corpectomy followed by placement of an expandable cage. The spines then underwent placement of lateral instrumentation consisting of 4 monoaxial screws and 2 rods with 2 cross-connectors, short-segment pedicle screw fixation involving 1 level above and below the corpectomy, and long-segment pedicle screw fixation (2 levels above and below). The order of instrumentation was randomized in the 8 specimens. Testing was conducted for each fixation technique. The spines were tested with a pure moment of 6 Nm in all 6 degrees of freedom (flexion, extension, right and left lateral bending, and right and left axial rotation).
In flexion, extension, and left/right lateral bending, posterior long-segment instrumentation had significantly less motion compared with the intact state. Additionally, posterior long-segment instrumentation was significantly more rigid than short-segment and lateral instrumentation in flexion, extension, and left/right lateral bending. In axial rotation, the posterior long-segment construct as well as lateral instrumentation were not significantly more rigid than the intact state. The posterior long-segment construct was the most rigid in all 6 degrees of freedom.
In the setting of highly unstable fractures requiring anterior reconstruction, and involving all 3 columns, long-segment posterior pedicle screw constructs are the most rigid.
Kelly B. Mahaney, Nohra Chalouhi, Stephanus Viljoen, Janel Smietana, David K. Kung, Pascal Jabbour, Ketan R. Bulsara, Matthew Howard and David M. Hasan
The use of an intracranial stent requires dual antiplatelet therapy to avoid in-stent thrombosis. In this study, the authors sought to investigate whether the use of dual antiplatelet therapy is a risk factor for hemorrhagic complications in patients undergoing permanent ventriculoperitoneal (VP) shunt for hydrocephalus following aneurysmal subarachnoid hemorrhage (aSAH).
Patients were given 325 mg acetylsalicylic acid and 600 mg clopidogrel during the coil/stent procedure, and they were maintained on dual antiplatelet therapy with acetylsalicylic acid 325 mg daily and clopidogrel 75 mg daily during hospitalization and for 6 weeks posttreatment. Patients underwent placement of VP shunt at a later time during initial hospitalization, usually between 7 and 21 days following aSAH. Postoperative CT scans obtained in each study patient were reviewed for hemorrhages related to placement of the VP shunt.
A total of 206 patients were admitted to the University of Iowa Hospitals and Clinics with aSAH between July 2009 and October 2010. Thirty-seven of these patients were treated with a VP shunt for persistent hydrocephalus. Twelve patients (32%) had previously undergone stent-assisted coiling and were on dual antiplatelet therapy with acetylsalicylic acid and clopidogrel. The remaining 25 patients (68%) had undergone surgical clipping or aneurysm coiling and were not receiving antiplatelet therapy at the time of surgery.
Four cases (10.8%) of new intracranial hemorrhages associated with VP shunt placement were observed. All 4 hemorrhages (33%) occurred in patients on dual antiplatelet therapy for stent-assisted coiling. No new intracranial hemorrhages were observed in patients not receiving dual antiplatelet therapy. The difference in hemorrhagic complications between the 2 groups was statistically significant (4 [33%] of 12 vs 0 of 25, p = 0.0075]). All 4 hemorrhages occurred along the tract of the ventricular catheter. Only 1 hemorrhage (1 [8.3%] of 12) was clinically significant as it resulted in occlusion of the proximal shunt catheter and required revision of the VP shunt. The patient did not suffer any permanent morbidity related to the hemorrhage. The remaining 3 hemorrhages were not clinically significant.
This small clinical series suggests that placement of a VP shunt in patients on dual antiplatelet therapy may be associated with an increased, but low, rate of symptomatic intracranial hemorrhage. It appears that in patients who are poor candidates for open surgical clipping and have aneurysms amenable to stent-assisted coiling, the risk of symptomatic hemorrhage may be an acceptable trade-off for avoiding risks associated with discontinuation of antiplatelet therapy. The authors' results are preliminary, however, and require confirmation in larger studies.
Vibhu K. Viswanathan, Ranjit Ganguly, Amy J. Minnema, Nicole A. DeVries Watson, Nicole M. Grosland, Douglas C. Fredericks, Andrew J. Grossbach, Stephanus V. Viljoen and H. Francis Farhadi
Proximal junctional kyphosis (PJK) and failure (PJF) are potentially catastrophic complications that result from abrupt changes in stress across rigid instrumented and mobile non-fused segments of the spine (transition zone) after adult spinal deformity surgery. Recently, data have indicated that extension (widening) of the transitional zone via use of proximal junctional (PJ) semi-rigid fixation can mitigate this complication. To assess the biomechanical effectiveness of 3 semi-rigid fixation constructs (compared to pedicle screw fixation alone), the authors performed cadaveric studies that measured the extent of PJ motion and intradiscal pressure changes (ΔIDP).
To measure flexibility and ΔIDP at the PJ segments, moments in flexion, extension, lateral bending (LB), and torsion were conducted in 13 fresh-frozen human cadaveric specimens. Five testing cycles were conducted, including intact (INT), T10–L2 pedicle screw-rod fixation alone (PSF), supplemental hybrid T9 Mersilene tape insertion (MT), hybrid T9 sublaminar band insertion (SLB1), and hybrid T8/T9 sublaminar band insertion (SLB2).
Compared to PSF, SLB1 significantly reduced flexibility at the level rostral to the upper-instrumented vertebral level (UIV+1) under moments in 3 directions (flexion, LB, and torsion, p ≤ 0.01). SLB2 significantly reduced motion in all directions at UIV+1 (flexion, extension, LB, torsion, p < 0.05) and at UIV+2 (LB, torsion, p ≤ 0.03). MT only reduced flexibility in extension at UIV+1 (p = 0.02). All 3 constructs revealed significant reductions in ΔIDP at UIV+1 in flexion (MT, SLB1, SLB2, p ≤ 0.02) and torsion (MT, SLB1, SLB2, p ≤ 0.05), while SLB1 and SLB2 significantly reduced ΔIDP in extension (SLB1, SLB2, p ≤ 0.02) and SLB2 reduced ΔIDP in LB (p = 0.05). At UIV+2, SLB2 similarly significantly reduced ΔIDP in extension, LB, and torsion (p ≤ 0.05).
Compared to MT, the SLB1 and SLB2 constructs significantly reduced flexibility and ΔIDP in various directions through the application of robust anteroposterior force vectors at UIV+1 and UIV+2. These findings indicate that semi-rigid sublaminar banding can most effectively expand the transition zone and mitigate stresses at the PJ levels of long-segment thoracolumbar constructs.