Laminoplasty on Kyphotic Cervical Alignments Suggests Poor Surgical Outcomes: A Comparative Finite Element Analysis of Laminoplasty on Different Alignments

Abstract

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.