Original Article
Age-related changes in axial and sagittal orientation of the facet joints: Comparison with changes in degenerative spondylolisthesis

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Abstract

Background

Despite facet joints being three-dimensional structures, previous computed tomography and magnetic resonance imaging studies have evaluated facet joint orientation in only the axial plane. Facet joint orientation in the sagittal plane has rarely been studied using these imaging techniques. The aim of this study was to elucidate facet joint orientation in both the axial and sagittal planes on computed tomography.

Methods

A total of 568 patients (343 men, 225 women) (excluding orthopedic outpatients) for whom abdominal and pelvic computed tomography scans were obtained at our hospital between September 2010 and October 2012 were included. Mean age was 63 (range 21–90) years. Patients were divided into a degenerative spondylolisthesis group (67 patients; 30 men, 37 women) and a control group (313 patients; 313 men, 188 women). Facet joint orientation was evaluated in the control group according to patient age (≤50, 51–60, 61–70, or ≥71 years). The findings in the control group were then compared with those in the degenerative spondylolisthesis group. The orientation of the lumbar facet joints at each level was measured in the axial and sagittal planes on computed tomography images.

Results

Facet joint angles decreased with age at L4/5 and L5/S1 in women in the axial plane and at L4/5 in men and L3/4 and L4/5 in women in the sagittal plane. The variation in facet joint angle was greatest at L4/5 in women. Patients with degenerative spondylolisthesis showed more sagittally and horizontally oriented facet joints in the axial and sagittal planes; facet tropism showed an association with degenerative spondylolisthesis in the axial plane.

Conclusions

The axial and sagittal orientation of facet joints in the lower lumbar vertebra, especially L4/5, was negatively correlated with age. This finding could help to explain why older people are more prone to degenerative spondylolisthesis.

Introduction

Degenerative spondylolisthesis is common in the elderly population and is one of the most common indications for spinal surgery in older adults [1], [2]. The facet joints provide posterior mechanical support that protects the motion segments from anterior shear forces and from excessive rotation and flexion [3], [4]. Some researchers have reported that one of the causes of degenerative spondylolisthesis is degeneration of the facet joints, in particular sagittalization of the facet joints in the axial plane [5], [6], [7], [8], [9], [10]. Furthermore, there are studies suggesting that the facet joints become more sagittal in the axial plane with advancing age [10], [11]. Although a number of studies have investigated the orientation of the facet joints in the axial plane using computed tomography (CT) or magnetic resonance imaging (MRI), there is still limited information available on the orientation of the facet joints in the sagittal plane using these modalities [8], [10]. We hypothesized that it would be important to evaluate the orientation of the facet joints not only in the axial plane but also in the sagittal plane, given that the facet joints are three-dimensional structures. To our knowledge, CT reconstruction studies of the correlation between orientation of the facet joints in the axial and sagittal planes and age have not been reported.

The primary aim of this study was to clarify the relationship between orientation of the facet joints and age in both the axial and sagittal planes using CT. A secondary aim was to improve our understanding of changes in facet joint morphology by comparing a group of control subjects (without degenerative spondylolisthesis, spondylolysis, or spondylolytic spondylolisthesis) and a group of patients with degenerative spondylolisthesis.

Section snippets

Materials and methods

This research has been approved by the IRB of the authors’ affiliated institutions. In order to evaluate the general public, we identified 628 patients (excluding orthopedic outpatients) who had undergone abdominal and pelvic CT scanning between September 2010 and January 2012 at our hospital. Patients with a history of spondylolysis, spondylolytic spondylolisthesis, previous back surgery, or metastasis to the lumbar vertebra were excluded, leaving data for 568 patients of mean age 63 (range

Interobserver and intraobserver agreement

The both interobserver and intraobserver agreements for the facet joint angle measurement were excellent (axial plane; κ = 0.93 and κ = 0.90, respectively: sagittal plane; κ = 0.90 and κ = 0.87, respectively).

Facet joint orientation in the axial plane

The facet joint angles in the axial plane did not change with age in men (Fig. 2). However, the angles decreased with age in the lower lumbar spine in women, especially at L4/5 and L5/S1; there were statistically significant differences at L4/5 between the group aged ≤50 years and the

Discussion

The main findings of this study were as follows: the facet joint angles decreased significantly with increasing age at L4/5 and L5/S1 in the axial plane and at L3/4 and L4/5 in the sagittal plane in women; the facet joint angles decreased significantly with age at L4/5 in the sagittal plane in men; the facet joint angle most affected by age in women was L4/5; the facet joint angle in patients with degenerative spondylolisthesis was decreased in both the axial and sagittal planes and facet joint

Conclusions

This study showed that facet joint angle decreases with increasing age at L4/5 and L5/S1 in the axial plane in women, at L4/5 in the sagittal plane in men, and at L3/4 and L4/5 in the sagittal plane in women. Sagittalization and horizontalization of the facet joints was found in patients with degenerative spondylolisthesis. Facet joint tropism was greater at L4/5 in the axial plane in patients with degenerative spondylolisthesis than in controls.

Conflicts of interest

None.

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