Biomechanical assessment of proximal junctional semi-rigid fixation in long-segment thoracolumbar constructs

Abstract

<jats:sec><jats:title>OBJECTIVE</jats:title><jats:p>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).</jats:p></jats:sec><jats:sec><jats:title>METHODS</jats:title><jats:p>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).</jats:p></jats:sec><jats:sec><jats:title>RESULTS</jats:title><jats:p>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 &lt; 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).</jats:p></jats:sec><jats:sec><jats:title>CONCLUSIONS</jats:title><jats:p>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.</jats:p></jats:sec>

Biomechanical comparison of semirigid junctional fixation techniques to prevent proximal junctional failure after thoracolumbar adult spinal deformity correction

“…Previously, Viswanathan et al performed a biomechanical study in which one-and two-level clamped sublaminar tapes as semirigid junctional fixation was compared with segmental PSF in eight vertebrae spine segment [20]. The present study demonstrated similar results for the one-and two-level semirigid junctional fixation with clamped sublaminar tapes.…”

“…However, this was only demonstrated in porcine specimens, which hampers comparison to other techniques [21,22]. One-and two-level clamped sublaminar tape as a semirigid junctional fixation technique also demonstrated to reduce the ROM at the junctional zone in human cadaveric spine segments [20,23]. However, two-level junctional fixation with clamped sublaminar tapes did not result in a gradual ROM transition over both levels but primarily at the most proximal level.…”

Combination of sacral-alar-iliac screw and cortical bone trajectory screw techniques for lumbosacral fixation: technical note

“…The supplemental use of sublaminar taping was applied proximal to the upper instrumented vertebra to prevent screw pullout and mitigate adjacent-segment stress if necessary. 24 All patients received posterior lumbar interbody fusion for the L5-S1 segment. Lumbosacral bone fusion assessment was made using CT performed 1 year postoperatively with coronal and sagittal reconstruction according to an evaluation described by Ito et al 25…”

Letter to the Editor concerning "Strap stabilization for proximal junctional kyphosis prevention in instrumented posterior spinal fusion" by Rodriguez-Fontan F, et al. (Eur Spine J; [2020]: 1287–1296, https://doi.org/10.1007/s00586-020-06,291-0)

“…Although the same knot configuration was applied in their study, the subject that I wonder most is the tightness of the Mersilene tape knot. Viswanathan et al demonstrated that sublaminar bands at two levels allow the most gradual force distribution [2]. The clamps of sublaminar bands allow to control the tightness of the bands.…”