Oral Posters: Thoraco-lumbar Degenerative

Presented by: J. Zavatsky - View Audio/Video Presentation (Members Only)

Author(s):

D. Briski(1), J. Zavatsky(2), R. McGuire(3)

(1) Ochsner Medical Center, New Orleans, LA, United States
(2) Spine and Scoliosis Specialists, Tampa, FL, United States
(3) University of Mississippi Medical Center, Jackson, MS, United States

Abstract

Background Context: PJK is not uncommon and can result in significant complication after spinal deformity surgery. Prophylactic vertebroplasty has been shown to reduce the rate of PJK, but optimal cement dosage and configuration has yet to be analyzed. Using a finite element (FE) model we analyzed various dosages and configurations of vertebral cement to see how it influences junctional endplate stress.

Purpose: To use finite element analysis (FEA) to evaluate the optimum dosage and configuration of prophylactic vertebral cement to maximize the reduction of junctional endplate stresses in long instrumented adult spinal deformity (ASD) constructs.

Study Design/Setting: Finite Element Analysis (FEA)

Patient Sample: Using finite element analysis (FEA) a validated T6-pelvis osteoporotic spinal model was modified with screws/rods from T10-S1 and various dosages and configurations of vertebral cement was used in T10 (UIV), T9 (UIV+1), and T8 (UIV+2).

Outcome Measures: T7, T8, and T9 endplate stresses.

Methods: A validated FE T6-pelvis osteoporotic spinal model was modified with screws/rods from T10-S1 and various dosages (0 - 5ccs) and configurations (anterior, anterior/central, and central placement) of vertebral cement was simulated in T10 (UIV), T9 (UIV+1), and T8 (UIV+2). With the pelvis fixed, load was applied 10mm anterior to the center of T6 to simulate a flexion moment. Endplate stresses were recorded from T7 to T9.

Results: FEA identified the optimal cement dosage of 2.5cc in T10, 2cc in T9, and 1cc in T8 resulted in the smallest change in stress observed at the inferior endplate of the unadulterated T7 vertebra, relative to the superior endplate of cemented T8 at -7.6%. Larger volumes of cement (5cc) resulted in larger changes in endplate stresses, including maximum changes of 37.3% and 61.1% with centrally and anteriorly placed cement, respectively. Using this dosage (2.5cc, 2cc, 1cc), optimal cement configuration included anteriorly placed cement in the UIV (T10), anterior/central placement in the UIV+1 (T9), and centrally placed cement in the UIV+2 (T8). This resulted in the lowest endplate stresses in the both cemented (T10, T9, and T8) and more importantly in the unadulterated non-cemented (T7) vertebra (Figure 1.).

Conclusions: Prophylactic vertebroplasty has been advocated to reduce the rates of PJK and revision surgery, but the number of levels, cement dosage, and configuration has not been evaluated. In this osteoporotic T10-S1 instrumented spine FE model, placing 2.5cc anteriorly in the UIV (T10), 2cc anterior/central in the UIV+1 (T9), and 1cc centrally in the UIV+2 (T8), reduced the endplate stresses in both the cemented (T10, T9, and T8) and more importantly in the supra-adjacent non-cemented T7 vertebra. Decreased endplate stresses may translate to vertebral bodies that are less prone to fracture and PJK.

Figure 1