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.
ABBREVIATIONSASD = adult spinal deformity; BMD = bone mineral density; CT = computed tomography; INT = intact; LB = lateral bending; MT = Mersilene tape; PJ = proximal junctional; PJF = PJ failure; PJK = PJ kyphosis; PSF = pedicle screw fixation; SLB1 = sublaminar band at UIV+1; SLB2 = sublaminar band at UIV+1 and UIV+2; UIV = upper instrumented vertebra; ΔIDP = change in intradiscal pressure.
Correspondence H. Francis Farhadi: The Ohio State University Wexner Medical Center, Columbus, OH. email@example.com.
INCLUDE WHEN CITING Published online November 2, 2018; DOI: 10.3171/2018.7.SPINE18136.
Disclosures The authors report that research support was provided by Implanet America Inc. for the cadaver experiments performed at the University of Iowa and that Implanet had no role in data gathering, analysis, interpretation, or manuscript preparation. Dr. Grossbach reports a consultant relationshp with DePuy Synthes. Dr. Viljoen reports honorarium receipt from DePuy Synthes for speaking at spine deformity courses.
CahillPJWangWAsgharJBookerRBetzRRRamseyC: The use of a transition rod may prevent proximal junctional kyphosis in the thoracic spine after scoliosis surgery: a finite element analysis. Spine (Phila Pa 1976)37:E687–E6952012
CammarataMAubinCEWangXMac-ThiongJM: Biomechanical risk factors for proximal junctional kyphosis: a detailed numerical analysis of surgical instrumentation variables. Spine (Phila Pa 1976)39:E500–E5072014
GlattesRCBridwellKHLenkeLGKimYJRinellaAEdwardsCII: Proximal junctional kyphosis in adult spinal deformity following long instrumented posterior spinal fusion: incidence, outcomes, and risk factor analysis. Spine (Phila Pa 1976)30:1643–16492005
Gonzalez-BlohmSADoulgerisJJLeeWEIIISheaTMAghayevKVrionisFD: The current testing protocols for biomechanical evaluation of lumbar spinal implants in laboratory setting: a review of the literature. Biomed Res Int2015:5061812015
HartRMcCarthyIOʼBrienMBessSLineBAdjeiOB: Identification of decision criteria for revision surgery among patients with proximal junctional failure after surgical treatment of spinal deformity. Spine (Phila Pa 1976)38:E1223–E12272013
HassanzadehHGuptaSJainAEl DafrawyMHSkolaskyRLKebaishKM: Type of anchor at the proximal fusion level has a significant effect on the incidence of proximal junctional kyphosis and outcome in adults after long posterior spinal fusion. Spine Deform1:299–3052013
HostinRMcCarthyIOʼBrienMBessSLineBBoachie-AdjeiO: Incidence, mode, and location of acute proximal junctional failures after surgical treatment of adult spinal deformity. Spine (Phila Pa 1976)38:1008–10152013
KimHJLenkeLGShaffreyCIVan AlstyneEMSkellyAC: Proximal junctional kyphosis as a distinct form of adjacent segment pathology after spinal deformity surgery: a systematic review. Spine (Phila Pa 1976)37 (22 Suppl):S144–S1642012
Mac-ThiongJMLevasseurAParentSPetitY: The influence of proximal anchors on the risk of proximal junctional fracture in the osteoporotic spine: biomechanical comparison between pedicle screws and transverse process hooks. J Spinal Disord Tech27:E49–E542014
MetzgerMFRobinsonSTSvetMTLiuJCAcostaFL: Biomechanical analysis of the proximal adjacent segment after multilevel instrumentation of the thoracic spine: do hooks ease the transition?Global Spine J6:335–3432016
SmithJSLafageVShaffreyCISchwabFLafageRHostinR: Outcomes of operative and nonoperative treatment for adult spinal deformity: a prospective, multicenter, propensity-matched cohort assessment with minimum 2-year follow-up. Neurosurgery78:851–8612016
ThawraniDPGlosDLCoombsMTBylski-AustrowDISturmPF: Transverse process hooks at upper instrumented vertebra provide more gradual motion transition than pedicle screws. Spine (Phila Pa 1976)39:E826–E8322014
ViswanathanVKKukrejaSMinnemaAJFarhadiHF: Prospective assessment of the safety and early outcomes of sublaminar band placement for the prevention of proximal junctional kyphosis. J Neurosurg Spine28:520–5312018
WatanabeKLenkeLGBridwellKHKimYJKoesterLHensleyM: Proximal junctional vertebral fracture in adults after spinal deformity surgery using pedicle screw constructs: analysis of morphological features. Spine (Phila Pa 1976)35:138–1452010