Search for: All records

Abstract PurposeTo assess the effect of various pelvic fixation techniques and number of rods on biomechanics of the proximal junction of long thoracolumbar posterior instrumented fusions. MethodsA validated spinopelvic finite-element (FE) model was instrumented with L5–S1 ALIF and one of the following 9 posterior instrumentation configurations: (A) one traditional iliac screw bilaterally (“2 Iliac/2 Rods”); (B) T10 to S1 (“Sacral Only”); (C) unilateral traditional iliac screw (“1 Iliac/2 Rods”); (D) one traditional iliac screw bilaterally with one midline accessory rod (“2 Iliac/3 rods”); (E) S2AI screws connected directly to the midline rods (“2 S2AI/2 Rods”); and two traditional iliac screws bilaterally with two lateral accessory rods connected to the main rods at varying locations (F1: T10–11, F2: T11–12, F3: T12–L1, F4: L1–2) (“4 Iliac/4 Rods”). Range of motions (ROM) at T10–S1 and T9–T10 were recorded and compared between models. The T9–T10 intradiscal pressures and stresses of the T9–10 disc’s annulus in addition to the von Mises stresses of the T9 and T10 vertebral bodies were recorded and compared. ResultsFor T10–S1 ROM, 4 iliac/4 rods had lowest ROM in flexion and extension, while 2 S2AI/2 rods showed lowest ROM in rotation. Constructs with 3 or 4 rods had lower stresses on the primary rods compared to 2-rod constructs. At the proximal adjacent disc (T9–10), 4 iliac/4 rods showed lowest ROM, lowest intradiscal pressures, and lowest annular stress in all directions (most pronounced in flexion–extension). Under flexion and extension, 4 iliac/4 rods also showed the lowest von Mises stresses on the T10 vertebral body but the highest stresses on the T9 vertebral body. ConclusionsDual iliac screws with 4 rods across the lumbosacral junction and extending to the thoracolumbar junction demonstrated the lowest T10–S1 ROM, the lowest adjacent segment disc (T9–T10) ROM, intradiscal pressures, and annular stresses, and the lowest UIV stresses, albeit with the highest UIV + 1 stresses. Additional studies are needed to confirm whether these biomechanical findings dictate clinical outcomes and effect rates of proximal junctional kyphosis and failure. 

Background: Slipped capital femoral epiphysis is a prevalent pediatric hip disorder. Recent studies suggest the spine’s sagittal profile may influence the proximal femoral growth plate’s slippage, an aspect not extensively explored. This study utilizes finite element analysis to investigate how various spinopelvic alignments affect shear stress and growth plate slip. Methods: A finite element model was developed from CT scans of a healthy adult male lumbar spine, pelvis, and femurs. The model was subjected to various sagittal alignments through reorientation. Simulations of two-leg stance, one-leg stance, walking heel strike, ascending stairs heel strike, and descending stairs heel strike were conducted. Parameters measured included hip joint contact area, stress, and maximum growth plate Tresca (shear) stress. Findings: Posterior pelvic tilt cases indicated larger shear stresses compared to the anterior pelvic tilt variants except in two leg stance. Two leg stance resulted in decreases in the posterior tilted pelvi variants hip contact and growth plate Tresca stress compared to anterior tilted pelvi, however a combination of posterior pelvic tilt and high pelvic incidence indicated larger shear stresses on the growth plate. One leg stance and heal strike resulted in higher shear stress on the growth plate in posterior pelvic tilt variants compared to anterior pelvic tilt, with a combination of posterior pelvic tilt and high pelvic incidence resulting in the largest shear. Interpretation: Our findings suggest that posterior pelvic tilt and high pelvic incidence may lead to increased shear stress at the growth plate. Activities performed in patients with these alignments may predispose to biomechanical loading that shears the growth plate, potentially leading to slip. 

Cervical laminoplasty is a useful for treatment for cervical myelopathy. However, this procedure has limitations for kyphotic cervical alignments. We used the finite element (FE) analysis and investigated the biomechanical changes in intact and laminoplasty models with lordosis, straight, and kyphosis cervical alignments. A three-dimensional FE model of the cervical spine (C2–C7) with ligaments was created from computer tomography. The model was modified with the following cobb angles (a) intact–lordotic model (intact–L; C2–C7 angle: −10°), (b) intact–straight model (intact–S; C2–C7 angle: 0°), and (c) intact–kyphotic model (intact–K; C2–C7 angle: 10°). The C3–C6 laminoplasty was conducted on the three intact models, represented by the laminoplasty–lordosis model (LM–L), laminoplasty–straight model (LM–S), and laminoplasty–kyphosis model (LM–K), respectively. Pure moment with compressive follower load of 100 N to represent the weight of the head/cranium and cervical muscle stabilization was applied to these models and the range of motion (ROM), annular stress, nucleus stress and facet forces were analyzed. ROM of intact–K and LM–K increased when compared to the other models. The LM–K had the highest mobility with 324% increase in ROM observed under extension, compared to LM–L. In addition, the annular stresses and nucleus stresses in intact–K and LM–K were higher compared to the other models. The maximum increase in annular stresses was about 309% in LM–K compared to the LM–L, observed at the C3–C4 segment. However, the facet contact forces were lower in the intact–K and LM–K, compared to the other models. Cases with cervical kyphosis alignment are at a disadvantage compared to cases with lordosis or straight alignment and should be treated with caution.