Mismatch between rod bending and actual post-operative lordosis in lumbar arthrodesis with poly axial screws - 29/03/19

Doi : 10.1016/j.otsr.2019.03.003

Abdollah Yassine Moufid ^a,^⁎ , Thibault Cloche ^b, Soufiane Ghailane ^c, Amine Ounajim ^d, Tanguy Vendeuvre ^a, Olivier Gille ^c
^a Université de Poitiers, Poitiers university hospital, centre hospitalo-universitaire de Poitiers Unité rachis, 1, rue de la Milétrie, 86021 Poitiers, France
^b Polyclinique Bordeaux Nord Aquitaine, 15–35, rue Claude-Boucher, 33300 Bordeaux, France
^c Université de Bordeaux, Bordeaux university hospital, centre hospitalo-universitaire de Bordeaux, Spine Unit 1, place Amélie-Raba Léon, 33076 Bordeaux, France
^d Centre hospitalo-universitaire de Poitiers Prismatics, 1, rue de la Milétrie, 86021 Poitiers, France

^⁎Corresponding author at: Université de Poitiers, Poitiers University Hospital, orthopedic Department, CHU de Poitiers, 1, rue de la Milétrie, 86021 Poitiers, France.Université de Poitiers, Poitiers University Hospital, orthopedic Department, CHU de Poitiers1, rue de la MilétriePoitiers86021France

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Abstract

Background

The question of rod bending is essential during posterior lumbar fusion. The role of posterior instrumentation during spinal surgery remains to be defined. Despite an appropriate bending, a mismatch between rod lordosis and lumbar lordosis can occur. There is no study on the link between rod bending and lordosis. The purpose of this study was to evaluate parameters that explain the mismatch between lumbar lordosis and rod bending in lumbar surgery using polyaxial screws.

Hypothesis

Radiological parameters explain the mismatch between the rod and the lordosis.

Methods

This study was monocentric, retrospective, descriptive and analytic. All patients with posterior L3L5 fusion in an university-affiliated hospital in 2017 were included. Patients with past surgical history of anterior fusion on the levels L3L5, Coronal malalignment with a Cobb angle superior to 5°, the use of dynamic fixation systems were excluded. We measured on immediate post-operative standing profile x-ray: pelvic incidency, lumbar lordosis, lordosis of the instrumented segment, the distance between posterior wall and rod (EcarT) which reflect how homogeneously the screws are put in depth, the angle between screw and rod (thetaMA), the angle between screw and superior endplate (lambdaMA), the rod lordosis. Univariate and multivariate analysis were conducted to see if there was a link between all those parameters and the mismatch: vertebral lordosis-rod lordosis.

Results

A total of 74 patients were included, mean age was 67. Eighteen were 360° fusion and 56 were postero-lateral fusions. There was no statistical association between demographic data, pelvic parameters, use of interbody devices and the mismatch. There was a statistical association between thetaMA, lambdaMA, EcarT and the mismatch (P<0,0001). A multivariate linear regression model was developed to create a new index: Mismatch analysis index.

Conclusion

Our study is the first on the link between rod bending and lumbar lordosis. Three radiologic factors are involved in not obtaining the planned lordosis in short lumbar fusion with polyaxial screws. Two factors depend on the way the surgeon positions screw parallel to the superior vertebral endplate(lambdaMA), and with a homogeneous depth (EcarT). And the last factor: ThetaMA is depending on the surgical technique (compression on screws, osteotomies, monoaxial screws, use of interbody devices).