척추 후관절의 생체역학 - 2011년 최신 논문(수련의 몫)

[문형철]

허리디스크, 목디스크를 잘 치료하고, 척추움직임을 제대로 회복하기 위해서 잘 알아야 하는 것!

척추관절의 마지막 통증(중심화 이후의 통증)을 해결하기 위해 반드시 알아야 하는 것!

추나 테크닉, 관절가동 테크닉의 마지막! 

그것은 바로 spinal facet joint다. 

후관절의 생체역학.pdf

꼭 읽어야겠는데, 시간이 없구나!!

panic bird...

서론

The facet joint is a crucial anatomic region of the spine owing to its biomechanics role  in facilitating articulation of the vertebrae of the spinal column. It is a diarthrodial joint with opposing articular cartilage surfaces that provide a low friction environment and a ligamentous capsule that encloses the joint space. Together with the disc, the bilateral facet joints transfer loads and guide and constrain motions in the spine due to their geometry and mechanical function. 

- 후관절은 척주의 척추관절에서 생체역학적 역할때문에 해부학적으로 중요한 관절

- 마주하는 관절연골면을 가지고 있는 diarthrodial 관절이기 때문에 low friction 환경이고, 관절공간을 둘러싼 인대성 낭임. 

- 추간판과 함께 양측 후관절은 체중부하를 전달하고 기하학과 기계적 기능을 가진 척추에서 움직임을 안내하고, 조절하는 역할

Although a great deal of research has focused on defining the biomechanics of the spine and the form and function of the disc, the facet joint has only recently become the focus of experimental, computational and clinical studies.

- 많은 연구가 추간판의 기능, 형태, 척추의 생체역학에 초점이 맞추어져 있는데, 최근 연구에서 후관절은 많은 임상적연구, 실험적 연구가 진행되고 있음.

This mechanical behavior ensures the normal health and function of the spine during physiologic loading but can also lead to its dysfunction when the tissues of the facet joint are altered either by injury, degeneration or as a result of surgical  modification of the spine. 

- 생체역학적 행위는 생리적 부하가 척추에 주어지는 동안 정상 건강과 기능을 확실하게 함. 하지만 후관절 조직이 손상, 퇴행성변화 또는 수술적 변형에 의해서 변화하면 척추의 기능부전이 야기될 수 있음. 

The anatomical, biomechanical and physiological characteristics of the facet joints in the cervical and lumbar spines have become the focus of increased attention recently with the advent of surgical procedures of the spine, such as disc repair and replacement, which may impact facet responses. 

- 경추, 요추에서 후관절의 해부학적, 생체역학적 생리학적 특성이 최근에 많이 연구되고 있는데, 그 이유는 척추수술 동안 추간판 회복과 replacement가 후관절반응에 영향을 주기 때문임. 

Accordingly, this review summarizes the relevant anatomy and biomechanics of the facet joint and the individual tissues that comprise it. 

- 그래서 이 리뷰논문은 후관절의 해부학과 생체역학, 연관조직을 정리함. 

In order to better understand the physiological implications of tissue loading in all conditions, a review of mechanotransduction pathways in the cartilage, ligament and bone is also presented ranging from the tissue-level scale to cellular modifications. With this context, experimental studies are summarized as they relate to the most common modifications that alter the biomechanics and health of the spine—injury and degeneration.

- 모든 상황에서 조직에 가해지는 부하의 생리학적 의미를 잘 이해하기 위해서 연골, 인대, 뼈에서 mechanotransduction pathway의 연구는 세포 변화에서부터 조직단위까지 진행함. 

- 이러한 맥락과 함께 후관절의 손상과 퇴행화를 포함한 척추의 건강과 생체역학이 변화하는 가장 흔한 변화와 연관성을 탐구한 실험적 연구를 정리함. 

 In addition, many computational and finite element models have been developed that enable more-detailed and specific investigations of the facet joint and its tissues than are provided by experimental approaches and also that expand their utility for the field of biomechanics.

These are also reviewed to provide a more complete summary of the current knowledge of facet joint mechanics. Overall, the goal of this review is to present a comprehensive review of the breadth and depth of knowledge regarding the mechanical and adaptive responses of the facet joint and its tissues across a variety of relevant size scales. 

 1 Introduction

The zygapophyseal, or facet, joints are complicated biomechanics structures in the spine, with complex anatomy, mechanical performance and effects on overall spine behavior and health. At each spinal level, there is a pair of facet joints located on the postero-lateral aspects of each motion segment, spanning from the cervical to the lumbar spine (Fig. 1). 

These facet joints are typical diarthrodial joints with cartilage surfaces that provide a low-friction interface to facilitate motion during normal conditions in a healthy spine. 

- 후관절은 전형적으로 diathrodial 관절로 연골면이 저마찰면을 제공하여 정상적인 건강한 상황에서 움직임을 촉진하는 역할을 수행

Owing to the anatomy of the spine, the mechanical behavior of the facet joint is both dependent on the responses dictated

by the overall spine’s response and also can directly affect the spine’s response, via its relationship to the intervertebral disc, its anatomic orientation, and its own mechanical behavior. The kinematics and mechanical properties of the facet joint and its tissue components have been studied extensively for a variety of different loading conditions [1–11]. 

- 후관절의 기계적 행위, 척추의 구조때문에 ....

Recently, there is growing interest in the facet joint—its biomechanics and physiology—with the advent of disc arthroplasty and there has been increased attention to the relationship between spinal degeneration and its effects on

the mechanical environment of the different tissues in the facet joint [12–16]. 

Therefore, it is the primary goal of this review to present an updated perspective of the anatomy and global mechanics of the spinal facet joint and its individual tissue components in conjunction with their loading during physiologic and

nonphysiologic motion. In addition, this review will summarize the mechanotransduction processes by which  mechanical loading to the specific tissues of the joint translate into signals that drive physiologic responses in health, injury and trauma, and spinal degeneration. 

Computational models of the facet joint are also reviewed since there has been quite a bit of work in this area to

complement and expand findings from biomechanics experiments and to provide insight about facet joint mechanics otherwise not measureable in typical cadaveric studies. Overall, this review focuses on synthesizing this anatomical, biomechanics and physiological information to give an overview of the facet joint’s response to mechanical loading from the macroscopic to the cellular scale, with implications and perspective for future studies of this spinal joint. 

 2 Anatomy and Tissue Mechanics

The facet joints, together with the intervertebral discs and spinal ligaments, connect the adjacent vertebrae of the spine at all regions and provide support for the transfer and constraint of loads applied to the spinal column. These articulations insure the mechanical stability and also overall mobility of the spine, while protecting the spinal cord running through it. 

At each spinal level, the bilateral facet joints are positioned symmetrically relative to the mid-sagittal plane in the postero-lateral regions of the spine (Fig. 1(a)). Because the facet is a diarthrodial synovial joint, cartilage covers the sliding surfaces and ligamentous capsules guide, couple, and limit the relative translations and rotations of adjacent vertebrae. 

Broadly, the facet joint is made up of a variety of hard and soft tissues: the bony articular pillars of the lateral mass provide the opposing surfaces that are covered by cartilage, the synovium which is a connective tissue lining that

maintains lubrication for the articular surfaces and enables their frictionless motion, and a ligamentous capsule that envelops the entire joint [17–20]. 

The bony articular pillars support compressive loads and the facet capsular ligament resists tensile forces that are developed across the joint when it undergoes rotations and translations [1,6,21]. Together, this collection of tissues

functions to transfer the different loads across the joint during a variety of loading modes for the spine. Here, we provide a more detailed presentation of the facet anatomy in order to describe the response to mechanical loading for each of the soft and hard tissues composing the facet joint.

2.1 Bony Articular Pillars. The articular pillars are the bony

protuberances that extend superiorly and inferiorly from the lamina

of each vertebra along the long-axis of the spine (Fig. 1(a)).

They are located at the junction between the lamina and the lateral

masses in the cervical region of the spine; whereas, in the thoracic

and lumbar regions, they are joined to the vertebral body via the

bony pedicles. At each intervertebral joint along the spine, the adjacent

articular pillars are aligned to establish two postero-lateral

columns that provide mechanical support for axial loading along

the spine, together with the anterior column comprised of the vertebral

bodies joined by their interconnected intervertebral discs

[22,23]. In general, the inclination angle of the articular surfaces

of the facet joint in the sagittal plane ranges from 20–78 in the

cervical region, 55–80 in the thoracic region, and 82–86 in the

lumbar region (angle b in Fig. 1(a)). The angle between the articulating

surfaces in the axial plane range from 70–96, 85 –120,

and 15–70 off of the midline in the cervical, thoracic, and lumbar

regions, respectively (angle a in Fig. 1(b)), with increasing

orientation angles moving towards the lower levels in the lumbar

spine [24–27]. Lastly, the superior articular surfaces transition

from having a postero-medial orientation in the cervical region to

a more postero-lateral orientation in the thoracic region, although

asymmetrical orientations have also been reported [26].

The facet joint is formed by two adjacent vertebrae with the inferior

facet of the superior vertebra meeting the superior facet of

the inferior vertebra (Fig. 1(a)). As such, each articular pillar of a

vertebra has both a superior and an inferior articulating surface.

The surfaces of the pillars that form the articulation of the joint

have elliptically-shaped faces that are covered by cartilage (Fig.

2). The morphometry of these surfaces also differs between the

regions of the spine, as well as at each vertebral level [26,28–32].

The superior facet of the inferior vertebra is rather flat in the cervical

and thoracic regions and more convex in the lumbar region

[26]. The opposing inferior facet of the superior vertebra is concave

and forms an arch with its apex pointing towards the vertebral

body [20,33–36] (Fig. 2). Articular surfaces are more

horizontally-oriented in the cervical and upper thoracic spinal

regions [26,36], which enables the great degree of coupling of

axial rotation and lateral bending that exists in the cervical spine

[37–39]. In the lower thoracic and lumbar regions of the spine the

facets gradually become more vertically-oriented [25], which also

limits the flexibility of the spine in both lateral bending and rotation

in these regions. But, this decrease in flexibility protects the

intervertebral discs and spinal cord from nonphysiological kinematic

and kinetic exposures that could cause injury and/or create

pathological conditions [6].

2.2 Cartilaginous Articular Surfaces. An avascular layer of

hyaline cartilage, with varying thickness across spinal regions and

the genders, covers the articulating surfaces of each facet [19,40].

The cartilage is thinner at the edges of the opposing surfaces and

gradually increases to its thickest (1 mm) towards the center of

the articulating joint, in both the antero-posterior and medio-lateral

regions of the joint [41]. Based on experimental studies, the

thickness of cervical facet cartilage has been described to have a

half sinusoidal shape with a maximum thickness (tmax) at its center

and thinning out along its radius (r) towards the facet perimeter

(rperim), according to Eq. (1) [41]:

t . tmax cosk r

rperim

p

2

(1)

where both the maximum thickness and the shape coefficient (k,

ranging 0.38–0.63) were both determined by minimizing the difference

between the experimental and theoretical thickness distributions

[41].

Further, reports have found that the bony extremity of the pillars

is not always completely covered by a cartilage layer, leaving a

region of exposed subchondral bone at the outermost edges of the

bony pillar [19,41]. Yoganandan et al. [19] reported the gap of