Elsevier

Spine Deformity

Volume 2, Issue 4, July 2014, Pages 291-300
Spine Deformity

Case Series
Effect of Lowest Instrumented Vertebra on Trunk Mobility in Patients With Adolescent Idiopathic Scoliosis Undergoing a Posterior Spinal Fusion

https://doi.org/10.1016/j.jspd.2014.04.006Get rights and content

Abstract

Study Design

Prospective.

Objectives

The goal of this study was to evaluate the effect of posterior spinal fusion surgery terminating at different lowest instrumented vertebrae (LIV) on trunk mobility in individuals with adolescent idiopathic scoliosis (AIS).

Summary of Background Data

Posterior spinal fusion with instrumentation is the standard surgical technique employed in AIS for correcting spine deformities with Cobb angles exceeding 50°. Surgical correction of curve deformity reduces trunk mobility and range of motion. However, conflicting findings from previous studies investigating the impact of different LIV levels on the reduction in trunk mobility after surgery have been reported.

Methods

The study was designed as a prospective study with 47 patients (7 males and 40 females) with AIS who underwent posterior spinal fusion. Patients were classified into 5 groups based on their surgical LIV level (ie, T12, L1, L2, L3, and L4). Trunk flexion-extension (sagittal plane), lateral bending (coronal plane), and axial rotation (transverse plane) kinematics were assessed during preoperative, 1 year postoperative, and 2 years postoperative evaluation visits.

Results

There were postoperative reductions of 41%, 51%, and 59% in trunk range of motion in the sagittal, coronal, and transverse planes, respectively (p < .0001). A trend toward greater postoperative reductions in peak forward flexion at more distal LIVs was observed (p = .04).

Conclusions

Fusion reduces trunk mobility in the sagittal, coronal, and transverse planes. More distal LIV fusions limit peak forward flexion to a greater extent which is considered clinically significant. After fusion, the reductions seen in axial rotation, lateral bending, and backward extension do not differ significantly at more distal LIVs.

Introduction

Posterior spinal fusion with instrumentation (PSFI) is the standard of care for correcting spine deformities in individuals with adolescent idiopathic scoliosis (AIS) and Cobb angles exceeding 50° [1], [2], [3]. Long-term results suggest that PSFI can effectively limit curve progression and ensure spine stability for individuals with AIS [4], [5], [6], [7].

Although PSFI effectively corrects spine deformity, postoperative limitations in intersegmental mobility among the fused vertebral levels ultimately result in reduction of overall trunk mobility (ie, forward flexion, backward extension, bilateral lateral bending, and bilateral axial rotation) [4], [5], [6], [7], [8], [9], [10]. Furthermore, some studies suggest that loss in trunk mobility may cause an increased compensatory mobility at unfused segments adjacent to the fusion, which may eventually lead to spinal degeneration of unfused segments and low back pain [4], [6], [8], [9], [10], [11], [12].

Currently, few studies have attempted to accurately measure reduction in trunk mobility after fusion. Recent studies have commonly employed either inclinometers or motion capture techniques to accurately quantify trunk mobility reduction after surgical fusion [8], [9], [10]. However, these studies are not without limitations, which range from being retrospective to using heterogeneous sampling of different fusion techniques (ie, anterior spinal fusion, posterior spinal fusion, or both), and to using unvalidated or nonstandardized models of kinematic computation for determining spine range of motion (ROM) [8], [9], [10], [13].

Despite the obvious reduction in trunk mobility after fusion, even fewer clinical studies conclusively address how surgical choice of the lowest instrumented vertebra (LIV) influences the amount of reduction. The direct impact of LIV level on postoperative trunk mobility in patients with AIS has not been conclusively demonstrated [8], [9], [10], [13], [14], [15], [16]. Today, many clinicians are still faced with difficult questions posed by families who inquire about changes to expect after fusion, particularly how reductions in trunk mobility vary with LIV over time. The purpose of this study was to quantitatively examine and compare trunk mobility in individuals with AIS undergoing posterior spinal fusion surgery at different LIVs preoperatively and at 1 and 2 years postoperatively. We hypothesized that PSFI terminating at a more distal LIV will result in greater reductions in sagittal, coronal, and transverse plane trunk kinematics during trunk bending tasks while standing. Specifically, we expected that fusion to the distal lumbar segments would result in greater reductions in kinematic peaks and overall trunk ROM than fusion terminating at proximal lumbar and thoracic segments.

Section snippets

Study design and participants

This was a prospective study performed on a sample of convenience between October 2007 and August 2012 at a single specialized pediatric orthopedic institution. A consecutive series of 120 patients had a posterior spinal fusion during that time, of which 47 patients (7 male and 40 female) agreed to participate in this institutional review board–approved study as the scoliosis group. Thirty-nine patients made the 1-year follow-up visit (mean, 1.15 years; range, 0.8–1.5 years) and 36 made the

Effect of surgery on trunk kinematics

There was a postoperative reduction in all trunk kinematic measures for trunk motion in all 3 planes (p < .0001). In the first postoperative evaluation visit, there was an average reduction of 16° (57%) in peak axial rotation to the left, 15° (61%) in average peak axial rotation to the right, and 31° (59%) in average axial rotation ROM. Postoperative mean reductions of 24° (56%), 17° (45%), and 41° (51%) were also observed in peak lateral bending to the left, to the right, and lateral bending

Discussion

The central finding of this study is that PSFI results in reduced trunk mobility in all motion planes (p < .0001). Distal LIV fusions limit postoperative peak forward flexion more than proximal fusions (p = .04) (Table 4). The limitation in peak forward flexion with distal LIV was considered clinically significant and trended toward statistical significance, although it did not achieve it at α = .01. Reductions in peak forward flexion after surgery were 28% at T12, 24% at L1, 36% at L2, 66% at

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    Author disclosures: UIU (grants from Helen Kay Charitable Trust, grants from Hainer Foundation, grants from DePuy Synthesis); JJK (grants from DePuy Synthesis, grants from Hainer Foundation, grants from the Helen Kay Charitable Trust); AG (grants from DePuy Synthesis, grants from Hainer Foundation, grants from the Helen Kay Charitable Trust); SH (grants from Helen Kay Charitable Trust, grants from Hainer Foundation, grants from DePuy Synthesis); ST (grants from Helen Kay Charitable Trust, grants from Hainer Foundation, grants from DePuy Synthesis); MR (grants from Helen Kay Charitable Trust, grants from Hainer Foundation, grants from DePuy Synthesis); PFS (consultant for DePuy Spine and Orthopediatrics; shareholder with Pioneer Surgical); KWH (grants from Helen Kay Charitable Trust, grants from Hainer Foundation, grants from DePuy Synthesis); PG (grants from Helen Kay Charitable Trust, grants from Hainer Foundation, grants from DePuy Synthesis); AKA (grants from Helen Kay Charitable Trust, grants from Hainer Foundation, grants from DePuy Synthesis); GFH (grants from Helen Kay Charitable Trust, grants from Hainer Foundation, grants from DePuy Synthesis).

    This study was supported by grants from DePuy Synthesis, the Hainer Foundation, and the Helen Kay Charitable Trust, US Department of Education NIDRR Grant H133P100008, and Grant UL1RR031973 from the Clinical and Translational Science Award (CTSA) program of the National Center for Research Resources (NCRR) and the National Center for Advancing Translational Sciences (NCATS).

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