Original Article
Anatomical analysis of the human ligamentum flavum in the thoracic spine: Clinical implications for posterior thoracic spinal surgery

https://doi.org/10.1016/j.jos.2018.08.023Get rights and content

Abstract

Background

Knowledge of the ligamentum flavum anatomy is important for posterior spinal surgery. However, only a few studies have evaluated the relationship between the thoracic ligamentum flavum and its surrounding structures. This study aimed to clarify the anatomy of the thoracic ligamentum flavum.

Methods

The entire spines from 20 human embalmed cadavers were harvested in an en bloc fashion. All pedicles were vertically cut using a thread bone saw, and the ligamentum flavum from T1-T2 to T12-L1 was painted using a contrast agent containing an iron powder. Computed tomography was performed, and the ligamentum flavum shape (width and height) and its relationship with the spinal bony structures (lamina and foramen height percentage covered by the ligamentum flavum) were analyzed using a three-dimensional analyzing software.

Results

The thoracic ligamentum flavum height and width gradually increased from T1-T2 to T12-L1. The caudal lamina height ventrally covered by the ligamentum flavum also increased gradually from the upper (T1-T2: 31.7%) to the lower levels (T12-L1: 41.7%); however, the cranial lamina height dorsally covered by the ligamentum flavum decreased from the upper (12.6%) to the lower levels (4.3%). The neural foramen was covered by the ligamentum flavum in all thoracic spines, except for T1-T2. Between T2-T3 and T12-L1, approximately 50% of the cranial part of the foramens was covered by the ligamentum flavum; however, the caudal part was not covered.

Conclusions

This study using contrasted ligamentum flavum and reconstructed CT provided information on the thoracic ligamentum flavum shape and its relationship with the bony structures. The ventral ligamentum flavum coverage of the cranial lamina increase from cranial to caudal, and the cranial half of the neural foramen is covered by the ligamentum flavum below T2-T3 but not in T1-T2. These findings would help spine surgeons to design and perform safe and adequate posterior thoracic spinal surgeries.

Introduction

The ligamentum flavum (LF) plays an important role in the control of intervertebral movements, provision of intrinsic stability to the spine in sitting and standing postures, and maintenance of a smooth surface on the posterior wall of the spinal canal and neural foramina [1], [2], [3]. Meanwhile, a degenerated and hypertrophied LF accompanied with bulging discs or osteophytes can cause spinal stenosis and neurological damages that sometimes require a spinal surgery.

As a result of many anatomical research studies regarding the lumbar LF [1], [2], [4], [5], [6], [7], [8] and cervical LF [9], [10], there is a clear visualization of the LF in these areas, including the borders, attachments, dimensions, and relationship of the LF with the surrounding structures ventrally and dorsally. The information reported in these studies is helpful in performing a safe and sufficient posterior cervical and lumbar decompression surgery.

Although thoracic LF hypertrophy is not as common as lumbar and cervical LF hypertrophies, ossification of the LF (OLF) is more common in the thoracic spine than in the cervical and lumbar spines. Posterior decompression is one of the surgical options for the management of LF hypertrophy and OLF; however, an inadequate removal of the LF can cause insufficient decompression or re-stenosis due to the ossification of the LF remnant. Knowing the border and attachment of the LF and the relationship with the surrounding structures is necessary for a safe and sufficient posterior decompression surgery. However, only a few studies have focused on the thoracic LF, and the anatomy of the LF and its relationship with the surrounding bony structures have not been well elucidated.

The aim of the present study was to investigate the LF from the dorsal and ventral aspects of the thoracic spine, describe the relationship between the LF borders and surrounding structures, and reveal the differences between the LF in the upper and lower thoracic spines.

Section snippets

Materials and methods

Ethical approval was obtained from the institutional review board before study commencement. We harvested the spinal columns from nine male and 11 female embalmed human cadavers donated for medical education and research. The mean age at the time of death was 84 years (range, 68–103 years). Cadavers that had spinal column tumors and/or undergone previous spinal surgeries were excluded from this study.

We harvested the entire spines in an en bloc fashion from the atlas to the coccygeal bone. All

Results

In each thoracic inter-laminar space, there are two LF, i.e., the right and the left LF, which join in the midline forming an acute angle with a ventral opening (Fig. 1). The LF covers the cranial laminae ventrally and the caudal laminae dorsally.

The LF height at midline gradually increased from cranial to caudal, and the mean height was 11.8 ± 1.6 mm at T1-T2 and 15.1 ± 0.1 mm at T12-L1 (Table 1).

The LF width also gradually increased from the cranial level to the caudal level; the mean width

Discussion

The LF includes 23 pairs from the second cervical to the first sacral vertebra stretching between two adjacent laminae. Several studies have focused on the cervical and lumbar LF; however, only a few studies have focused on the thoracic LF. Yoon et al. conducted an anatomical study of the cervical and high thoracic LF (C3-T6) [9]. They reported a lower incidence of an LF midline gap in the upper thoracic spine, but have not investigated the precise anatomy of the thoracic LF. The present

Conclusions

The new analytical method using contrasted LF and reconstructive CT enabled us to explain the relationship between the LF and posterior bony structures. The ventral LF coverage of the cranial lamina increases from cranial to caudal, and the cranial half of the neural foramen is covered by the LF below T2-T3 but not in T1-T2. These findings would help spinal surgeons design and perform safe and adequate posterior thoracic spinal surgeries.

Conflicts of interest and source of funding

No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.

Acknowledgments

We would like to thank the individuals who donated their bodies for medical research and also the Department of Anatomy at Osaka City University for their kind cooperation and support.

References (22)

  • M.M. Panjabi et al.

    Quantitative anatomy of cervical spine ligaments. Part II. Middle and lower cervical spine

    J Spinal Disord

    (1991 Sep)
  • View full text