Lumbar Spine
Lumbar Spine
Vertebrae and facet joints -
L1-4 are typical, L5 is atypical.
The facet joints are diarthrodial planar joints where the joint surfaces are covered with articular cartilage and the joint is enclosed by a capsule. The facet joints form an articulation between the inferior articular process of the vertebrae above and the superior articular process of the vertebrae below. The facet joints are complex structures whose shape and orientation are not only difficult to define at any specific inter-segmental level but they also change as one moves in a cephalad to a caudad direction. In the upper lumbar segments they are vertical with a predominantly sagittal plane orientation, while in the lower lumbar segments they are somewhat less vertical and are approximately halfway between a sagittal and a coronal plane orientation.
Throughout all of the segmental levels the shape of the superior articular process is concave while the inferior articular process is correspondingly convex. In the upper lumbar spine the superior articular process faces medially while the inferior articular process faces essentially laterally. In the lower lumbar spine as the orientation of the joint gradually becomes closer to the coronal plane, the superior articular facet faces both posteriorly and medially while the superior articular facet faces anteriorly and laterally.
The joint capsule encloses the facet joints and is relatively tighter anteriorly and more lax posteriorly. The multifidus muscle attaches in part to the posterior capsule and may exert a tensioning effect on the capsule. The superior capsule has been shown to be stretched and may be injured with axial loads, especially with the spine in extension. Attached to the interior surface of the joint capsule at the level of the superior and inferior joint recesses are fibrofatty or fibrous structures. They have been described as meniscus like, and some authors believe that they may be a source of nociception if trapped between the joint surfaces.
The facet joints and capsule are richly innervated through branches from the posterior primary ramus as it exits from the intervertebral foramina. The posterior primary ramus at a given segmental level sends fibres to the facet joint at that level but also to the facet joints above and below the level of the nerve exit. The innervation of the facet joints and capsule appears to be through mechanoreceptors as well as nociceptors, and there appear to be substance P–containing nerve fibres present.
Biomechanics and Function of the Facet Joint
The function of the facet joints is to limit and guide the motion of the lumbar spine. The generally sagittal plane orientation of the facet joints markedly limits axial rotation in the lumbar spine. However, the relatively more coronal orientation at the L-5 to S- 1 junction may allow somewhat greater rotation to occur. Flexion of the lumbar spine can be influenced dynamically through the lumbar spine musculature and through the passive
restraint of connective tissue. It is interesting to note that in spite of the significant stature of the interspinous and supraspinal ligaments, the facet joints provide the greatest limitation to full flexion.
During full flexion, contact between the more anterior portions of the superior and inferior articular processes of the facet joints and tension in their joint capsules are the major restraint to motion. In full extension there is stretch applied to the superior aspect of the facet joint capsule, and there may be bottoming out of the inferior articular process on the laminae below.
In the absence of disk degeneration the joint capsule carries significant loads, while in the presence of disk degeneration a greater portion of the load may be borne by the articular surface (22).
As noted previously, the lumbosacral junction is subject to significant shear stresses because of the lumbar lordosis and the posterior angulation of the sacrum. The L-5 to S-1 facet joint bears significant shear stress loads. These shear stresses may in part play a role in the increased incidence of spondylolysis and secondary spondylolisthesis.
Info from:
http://anatomedunesa.weebly.com/uploads/1/8/7/1/1871495/general_considerations_of_pain_in_the_low_back_hips_and_lo.pdf
Ligaments
ALL - covers anterior surfaces of lumbar vertebral bodies and discs. Intimately attached to the anterior annular disc fibers. The ALL maintains the stability of the joints and limits extension.
PLL – in the vertebral canal over the posterior surface of the vertebral bodies and discs. It functions to limit flexion of the vertebral column. Not attached to discs, narrow and weak in the L-Sp.
Supraspinous ligament - Tip of SP to tip of SP from L1-L3. Weakly resists flexion & vertebral separation.
Interspinous ligament – Connects SP to Sp from root to apex. Weakly resists flexion & vertebral separation.
Ligamentum flavum (LF) – Connects lamina of adjacent vertebrae, attaching to the interspinous ligament medially and the facet capsule laterally (forming the posterior wall of the vertebral canal). Normally, the ligament is taut, stretching for flexion and contracting its elastin fibers in neutral or extension. It maintains constant disc tension.
Intertransverse ligament – TP-to-TP, resists side bending of the trunk.
Iliolumbar ligament - Tip of the L5 TP to posterior part of the inner lip of the iliac crest. It helps stabilise the LS.
Lumbosacral ligament – L5 to ala of Sacrum. Very closely linked to L5 nerve root.
Muscles
Extensors - 3 layers.
i. Erector Spinae (The largest group of intrinsic back muscles and primary extensor). Upper L-Sp has 3 groups – Iliocostalis (lateral), longissimus (middle & largest) & spinalis (medial & smallest). Common attcahment on Sacrum, L-Sp SP’s & Iliac Crest. In lower L-Sp they blend as 1 muscle
ii. Transversospinal group (Deep to LES) 3-layered fasciculated muscle. Attaches to mamillary processes & post sacral foramina to lamina & SP’s and adjacent vertebra. . Extend & rotate.
iii. Interspinales and Intertransversarii. Deepest group, postural & proprioceptive.
Flexors
Iliothoracic (extrinsic) group - Abdominal wall muscles: rectus abdominis, external abdominal oblique, internal abdominal obliquus, and the transversus abdominis.
Femorospinal (intrinsic) group - Psoas major and Iliacus muscles.
Lateral Flexors (combination of side bending and rotation)
Ipsilateral contraction of the oblique and transversus abdominal muscles and quadratus lumborum.
Quadratus Lumborum can produce lateral flexion on its own with unilateral contraction.
Rotators
Rotation of the lumbar spine is brought about by the unilateral contraction of muscles that follow an oblique direction of pull; the more oblique the course, the more important the rotational effect. Most of the extensors and lateral flexors follow an oblique course and produce rotation when their primary component has been neutralized by antagonist muscle groups.
Transversospinal muscle group, when contracting unilaterally, rotate contralaterally.
They are divided into 3 groups: Semispinalis, Multifidus, and Rotatores Lumborum muscles.
There are some good images on this site:
http://emedicine.medscape.com/article/1899031-overview
Might be worth a read….
http://www.painphysicianjournal.com/2003/july/2003%3B6%3B361-368.pdf
Vertebrae and facet joints -
L1-4 are typical, L5 is atypical.
The facet joints are diarthrodial planar joints where the joint surfaces are covered with articular cartilage and the joint is enclosed by a capsule. The facet joints form an articulation between the inferior articular process of the vertebrae above and the superior articular process of the vertebrae below. The facet joints are complex structures whose shape and orientation are not only difficult to define at any specific inter-segmental level but they also change as one moves in a cephalad to a caudad direction. In the upper lumbar segments they are vertical with a predominantly sagittal plane orientation, while in the lower lumbar segments they are somewhat less vertical and are approximately halfway between a sagittal and a coronal plane orientation.
Throughout all of the segmental levels the shape of the superior articular process is concave while the inferior articular process is correspondingly convex. In the upper lumbar spine the superior articular process faces medially while the inferior articular process faces essentially laterally. In the lower lumbar spine as the orientation of the joint gradually becomes closer to the coronal plane, the superior articular facet faces both posteriorly and medially while the superior articular facet faces anteriorly and laterally.
The joint capsule encloses the facet joints and is relatively tighter anteriorly and more lax posteriorly. The multifidus muscle attaches in part to the posterior capsule and may exert a tensioning effect on the capsule. The superior capsule has been shown to be stretched and may be injured with axial loads, especially with the spine in extension. Attached to the interior surface of the joint capsule at the level of the superior and inferior joint recesses are fibrofatty or fibrous structures. They have been described as meniscus like, and some authors believe that they may be a source of nociception if trapped between the joint surfaces.
The facet joints and capsule are richly innervated through branches from the posterior primary ramus as it exits from the intervertebral foramina. The posterior primary ramus at a given segmental level sends fibres to the facet joint at that level but also to the facet joints above and below the level of the nerve exit. The innervation of the facet joints and capsule appears to be through mechanoreceptors as well as nociceptors, and there appear to be substance P–containing nerve fibres present.
Biomechanics and Function of the Facet Joint
The function of the facet joints is to limit and guide the motion of the lumbar spine. The generally sagittal plane orientation of the facet joints markedly limits axial rotation in the lumbar spine. However, the relatively more coronal orientation at the L-5 to S- 1 junction may allow somewhat greater rotation to occur. Flexion of the lumbar spine can be influenced dynamically through the lumbar spine musculature and through the passive
restraint of connective tissue. It is interesting to note that in spite of the significant stature of the interspinous and supraspinal ligaments, the facet joints provide the greatest limitation to full flexion.
During full flexion, contact between the more anterior portions of the superior and inferior articular processes of the facet joints and tension in their joint capsules are the major restraint to motion. In full extension there is stretch applied to the superior aspect of the facet joint capsule, and there may be bottoming out of the inferior articular process on the laminae below.
In the absence of disk degeneration the joint capsule carries significant loads, while in the presence of disk degeneration a greater portion of the load may be borne by the articular surface (22).
As noted previously, the lumbosacral junction is subject to significant shear stresses because of the lumbar lordosis and the posterior angulation of the sacrum. The L-5 to S-1 facet joint bears significant shear stress loads. These shear stresses may in part play a role in the increased incidence of spondylolysis and secondary spondylolisthesis.
Info from:
http://anatomedunesa.weebly.com/uploads/1/8/7/1/1871495/general_considerations_of_pain_in_the_low_back_hips_and_lo.pdf
Ligaments
ALL - covers anterior surfaces of lumbar vertebral bodies and discs. Intimately attached to the anterior annular disc fibers. The ALL maintains the stability of the joints and limits extension.
PLL – in the vertebral canal over the posterior surface of the vertebral bodies and discs. It functions to limit flexion of the vertebral column. Not attached to discs, narrow and weak in the L-Sp.
Supraspinous ligament - Tip of SP to tip of SP from L1-L3. Weakly resists flexion & vertebral separation.
Interspinous ligament – Connects SP to Sp from root to apex. Weakly resists flexion & vertebral separation.
Ligamentum flavum (LF) – Connects lamina of adjacent vertebrae, attaching to the interspinous ligament medially and the facet capsule laterally (forming the posterior wall of the vertebral canal). Normally, the ligament is taut, stretching for flexion and contracting its elastin fibers in neutral or extension. It maintains constant disc tension.
Intertransverse ligament – TP-to-TP, resists side bending of the trunk.
Iliolumbar ligament - Tip of the L5 TP to posterior part of the inner lip of the iliac crest. It helps stabilise the LS.
Lumbosacral ligament – L5 to ala of Sacrum. Very closely linked to L5 nerve root.
Muscles
Extensors - 3 layers.
i. Erector Spinae (The largest group of intrinsic back muscles and primary extensor). Upper L-Sp has 3 groups – Iliocostalis (lateral), longissimus (middle & largest) & spinalis (medial & smallest). Common attcahment on Sacrum, L-Sp SP’s & Iliac Crest. In lower L-Sp they blend as 1 muscle
ii. Transversospinal group (Deep to LES) 3-layered fasciculated muscle. Attaches to mamillary processes & post sacral foramina to lamina & SP’s and adjacent vertebra. . Extend & rotate.
iii. Interspinales and Intertransversarii. Deepest group, postural & proprioceptive.
Flexors
Iliothoracic (extrinsic) group - Abdominal wall muscles: rectus abdominis, external abdominal oblique, internal abdominal obliquus, and the transversus abdominis.
Femorospinal (intrinsic) group - Psoas major and Iliacus muscles.
Lateral Flexors (combination of side bending and rotation)
Ipsilateral contraction of the oblique and transversus abdominal muscles and quadratus lumborum.
Quadratus Lumborum can produce lateral flexion on its own with unilateral contraction.
Rotators
Rotation of the lumbar spine is brought about by the unilateral contraction of muscles that follow an oblique direction of pull; the more oblique the course, the more important the rotational effect. Most of the extensors and lateral flexors follow an oblique course and produce rotation when their primary component has been neutralized by antagonist muscle groups.
Transversospinal muscle group, when contracting unilaterally, rotate contralaterally.
They are divided into 3 groups: Semispinalis, Multifidus, and Rotatores Lumborum muscles.
There are some good images on this site:
http://emedicine.medscape.com/article/1899031-overview
Might be worth a read….
http://www.painphysicianjournal.com/2003/july/2003%3B6%3B361-368.pdf