Sublaminar banding as an adjunct to pedicle screw-rod constructs: a review and technical note on novel hybrid constructs in spinal deformity surgery

Proximal junctional kyphosis after adult spinal deformity operated patients with long fusion to the pelvis. Does the type of proximal anchor matter?

PURPOSE

To assess, in a large population of Adult Spinal Deformity (ASD) patients, the true interest of varying the upper anchors as a protective measure against Proximal Junctional Kyphosis (PJK), by analyzing and comparing 2 groups of patients defined according to their proximal construct. Another objective of the study is to look for any other factors, radiological or clinical, that would affect the occurrence of the proximal failure.

METHODS

Retrospective review of a prospective ASD database collected from 5 centers. Inclusion criteria were age of at least 18 years, presence of a spinal deformity with instrumentation from T12 or above to the pelvis, with minimum 2 years of follow-up. Demographic data, spinopelvic parameters, functional outcomes and complications were collected. Multiple logistic regression analysis was performed to identify the risk factors that would affect the occurrence of PJK.

RESULTS

254 patients were included. 166 in the group "screws proximally" (SP) and 88 in the group "hooks proximally" (HP). There was no difference between both groups for PJK (p = 0.967). The occurrence of PJK was rather associated with greater age and BMI, higher preoperative kyphosis, worst preoperative SRS22 and SF36 scores, greater postoperative Sagittal Vertical Axis (SVA), coronal malalignment and kyphosis.

CONCLUSION

The use of proximal hooks was not effective to prevent PJK after ASD surgery, when compared to proximal screws. Worse preoperative functional outcomes and worse postoperative sagittal and also coronal malalignment were the main drivers for the occurrence of PJK regardless the type of proximal implant.

Delayed stenosis associated with sublaminar band placement in the thoracic spine for proximal junctional kyphosis

Background

Proximal junctional thoracic kyphosis (PJK) is common following adult spinal deformity (ASD) surgery and may require revision operations. In this case series, we present delayed complications associated with the use of sublaminar banding (SLBs) for PJK prophylaxis.

Case Description

Three patients underwent long-segment thoracolumbar decompression and fusions for ASD. All had undergone SLB placement for PJK prophylaxis. All three subsequently developed neurologic complications secondary to cephalad spinal cord compression/stenosis requiring urgent revision surgery.

Conclusion

The placement of SLBs placed to prevent PJK may lead to sublaminar inflammation contributing to severe cephalad spinal canal stenosis and myelopathy following ASD surgery. Surgeons should be aware of this potential complication and may consider alternatives to SLB placement to avoid this complication.

Proximal junctional failure after surgical instrumentation in adult spinal deformity: biomechanical assessment of proximal instrumentation stiffness

STUDY DESIGN

Assessment of different proximal instrumentation stiffness features to minimize the mechanical proximal junctional failure-related risks through computer-based biomechanical models.

OBJECTIVE

To biomechanically assess variations of proximal instrumentation and loads acting on the spine and construct to minimize proximal junctional failure (PJF) risks. The use of less-stiff fixation such as hooks or tensioned bands, compared to pedicle screws, at the proximal instrumentation level are considered to allow for a gradual transition in stiffness with the adjacent levels, but the impact of such flexible fixation on the loads balance and complications such as PJF remain uncertain.

METHODS

Six patients with adult spine deformity who underwent posterior spinal instrumentation were used to numerically model and simulate the surgical steps, erected posture, and flexion functional loading in patient-specific multibody analyses. Three types of upper-level fixation (pedicle screws (PS), supralaminar hooks (SH), and sublaminar bands (SB) with tensions of 50, 250, and 350 N) and rod stiffness (CoCr/6 mm, CoCr/5.5 mm, Ti/5.5 mm) were simulated. The loads acting on the spine and implants of the 90 simulated configurations were analyzed using Kruskal-Wallis statistical tests.

RESULTS

Simulated high-tensioned bands decreased the sagittal moment at the adjacent level proximal to the instrumentation (1.3 Nm at 250 N; 2.5 Nm at 350 N) compared to screws alone (PS) (15.6 Nm). At one level above, the high-tensioned SB increased the sagittal moment (17.7 Nm-SB vs. 15.5 Nm-PS) and bending moment on the rods (5.4 Nm and 5.7 Nm vs. 0.6 Nm) (p < 0.05). SB with 50 N tension yielded smaller changes in load transition compared to higher tension, with moments of 8.1 Nm and 16.8 Nm one and two levels above the instrumentation. The sagittal moment at the upper implant-vertebra connection decreased with the rod stiffness (1.0 Nm for CoCr/6 mm vs. 0.7 Nm for Ti/5.5 mm; p < 0.05).

CONCLUSION

Simulated sublaminar bands with lower tension produced smaller changes in the load transition across proximal junctional levels. Decreasing the rod stiffness further modified these changes, with a decrease in loads associated with bone failure, however, lower stiffness did increase the rod breakage risk.

LEVEL OF EVIDENCE

N/A.

Biomechanical assessment of the effect of sublaminar band tensioning on lumbar motion

OBJECTIVE

Adjacent-segment disease (ASD) proximal to lumbosacral fusion is assumed to result from increased stress and motion that extends above or below the fusion construct. Sublaminar bands (SBs) have been shown to potentially mitigate stresses in deformity constructs. A similar application of SBs in lumbar fusions is not well described yet may potentially mitigate against ASD.

METHODS

Eight fresh-frozen human cadaveric spine specimens were instrumented with transforaminal lumbar interbody fusion (TLIF) cages at L3-4 and L4-5, and pedicle screws from L3 to S1. Bilateral SBs were applied at L2 and tightened around the rods extending above the L3 pedicle screws. After being mounted on a testing frame, the spines were loaded at L1 to 6 Nm in all 3 planes, i.e., flexion/extension, right and left lateral bending, and right and left axial rotation. Motion and intradiscal pressures (IDPs) at L2-3 were measured for 5 conditions: intact, instrumentation (L3-S1), band tension (BT) 30%, BT 50%, and BT 100%.

RESULTS

There was significant increase in motion at L2-3 with L3-S1 instrumentation compared with the intact spine in flexion/extension (median 8.78°, range 4.07°-10.81°, vs median 7.27°, range 1.63°-9.66°; p = 0.016). When compared with instrumentation, BT 100% reduced motion at L2-3 in flexion/extension (median 8.78°, range 4.07°-10.81°, vs median 3.61°, range 1.11°-9.39°; p < 0.001) and lateral bending (median 6.58°, range 3.67°-8.59°, vs median 5.62°, range 3.28°-6.74°; p = 0.001). BT 50% reduced motion at L2-3 only in flexion/extension when compared with instrumentation (median 8.78°, range 4.07°-10.81°, vs median 5.91°, range 2.54°-10.59°; p = 0.027). There was no significant increase of motion at L1-2 with banding when compared with instrumentation, although an increase was seen from the intact spine with BT 100% in flexion/extension (median 5.14°, range 2.47°-9.73°, vs median 7.34°, range 4.22°-9.89°; p = 0.005). BT 100% significantly reduced IDP at L2-3 from 25.07 psi (range 2.41-48.08 psi) before tensioning to 19.46 psi (range -2.35 to 29.55 psi) after tensioning (p = 0.016).

CONCLUSIONS

In this model, the addition of L2 SBs reduced motion and IDP at L2-3 after the L3-S1 instrumentation. There was no significant increase in motion at L1-2 in response to band tensioning compared with instrumentation alone. The application of SBs may have a clinical application in reducing the incidence of ASD.

Ultra-high-molecular-weight polyethylene sublaminar tape as semirigid fixation or pedicle screw augmentation to prevent failure in long-segment spine surgery: an ex vivo biomechanical study

OBJECTIVE

Complications after adult spinal deformity surgery are common, with implant-related complications occurring in up to 27.8% of cases. Sublaminar wire fixation strength is less affected by decreasing trabecular bone density in comparison to pedicle screw (PS) fixation due to the predominant cortical bone composition of the lamina. Sublaminar fixation may thus aid in decreasing implant-related complications. The goal of this study was to compare fixation characteristics of titanium sublaminar cables (SCs), ultra-high-molecular-weight polyethylene (UHMWPE) tape, PSs, and PSs augmented with UHMWPE tape in an ex vivo flexion-bending setup.

METHODS

Thirty-six human cadaver vertebrae were stratified into 4 different fixation groups: UHMWPE sublaminar tape (ST), PS, metal SC, and PS augmented with ST (PS + ST). Individual vertebrae were embedded in resin, and a flexion-bending moment was applied that closely resembles the in vivo loading pattern at transitional levels of spinal instrumentation.

RESULTS

The failure strength of PS + ST (4522 ± 2314 N) was significantly higher compared to the SC (2931 ± 751 N) and PS (2678 ± 827 N) groups, which had p values of 0.028 and 0.015, respectively (all values expressed as the mean ± SD). Construct stiffness was significantly higher for the PS groups compared to the stand-alone sublaminar wiring groups (p = 0.020). In contrast to SC, ST did not show any case of cortical breach.

CONCLUSIONS

The higher failure strength of PS + ST compared to PS indicates that PS augmentation with ST may be an effective measure to reduce the incidence of screw pullout, even in osteoporotic vertebrae. Moreover, the lower stiffness of sublaminar fixation techniques and the absence of damage to the cortices in the ST group suggest that ST as a stand-alone fixation technique in adult spinal deformity surgery may also be clinically feasible and offer clinical benefits.