Lumbosacral Biomechanics
Original Editors Bert Lasat
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Search Strategy[edit | edit source]
First I searched for books about lumbosacral biomechanics in the library of the University of Brussels. After I read the literature, I searched on multiple scientifically sites like PubMed, Web of Knowledge,… for information about the lumbosacral biomechanics.
Then I had enough information and I started to write this publication.
Definition/Description[edit | edit source]
Mechanics, the study of forces and their effects, when applied to humans, is called biomechanics. Logically means ‘lumbosacral biomechanics’ the study of forces and their effects at the level of the lumbosacral region.Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title(Gail M. 1980 (D))
Clinically Relevant Anatomy[edit | edit source]
The lumbosacral transition is at the level of L5 - S1.
The lumbar spine has normally 5 vertebrae (normal range 4-6), while the sacrale spine consists of a series of 3 – 5 fused sacral vertebrae. Both the lumbar and the sacrale vertebrale bodies are separated by a discus intervertebralis.
The intervertebral disk is a unique articular structure, part of a component load-bearing system consisting of disks, vertebrae, ligaments, and muscles.
The disk, which is the most important component, absorbs the load and distributes the
forces applied to the vertebral spine. The structures that allows this shock-absorbing, force-distributing ability are the nucleus pulposus, the annulus fibrosis and the cartilaginous end-plates.
The nucleus pulposus consists of a gelatinous mucoprotein and mucopolysaccharide. Those molecules are responsible for the fact that the nucleus is consisted out 70-90% water. The annulus fibrosus consist of concentric rings of fibrocartilaginous fibers. This structure is encapsulating the nucleus. The last component of the intervertebral disk is the endplate. This plate is a thin layer of cartilage tissue situated between the vertebral body and the disk.
The lumbar vertebrae are great because they need to bear a large part of the body weight. L5 has a wedge-shaped vertebrae body and is connected to the sacrum, so that the lumbar spine and pelvis are always in relation to one another. Typical for the lumbar column is that the nucleus pulposus is located posterioly, between the cartilaginous end plates and is surrounded by the annulus fibrosis.Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title(Gail M. 1980 (D))Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title
The sacrum is a triangular bone with a concave and convex surface, the facies pelvina, the facies dorsalis and an apex. On the anterior surface of the sacrum the superior and inferior edges of the vertebral bodies correspond as transverse ridges. The sacral vertebrae are finally connected to the coccyx.Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive titleCite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title
Biomechanics of the lumbar spine and sacrum (L4-L5 L5-S1)[edit | edit source]
The four main movements in the spine and sacrum are flexion, extension, rotation and lateral bending.
There are different forces acting on the lumbar spine and sacrum: compressive force, tensile force, shear force, bending moment and torsional moment.Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title
Compressive force is a force or pressure that attempts to flatten or squeeze a material, in this case the intervertebral disk. With the term tensile force they mean the ability of a material to resist forces that attempt to pull it apart or stretch it.
Shear force is a force which acts parallel to the intervertebral disc. Shear force is more commonly from gravity acting on the body and so there’s a greater force on the lumbar spine where the disc’s lay in a steep angle to the horizontal (90°) and in bending postures. A definition of bending moment could be: the internal load generated within a bending element whenever a pure moment is reacted, or a shear load is transferred by beam action from the point of application to distant points of reaction. At last torsional moment means: the algebraic sum of the couples or the moments of the external forces about the axis of twist or both in a body being twisted.Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title
Not only forces act on the spine and sacrum, also the mass, body weight, stress and displacement have their influences. The vertebral bodies and their discs form a column that permits movements, they resist compression and resist the body weight and forces of the thorax and upper limbs. Forward bending (flexion) is possible because each intervertebral disc compresses, anteriorly and is resisted by tension developed in the posterior part of the annulus fibrosus. Backward bending (extension) and lateral bending are possible because of the actions of the contralateral elements in the opposite direction.
In the normal position the sacrum is bending forward so that the upper surface is below horizontal at an angle of 50°. The L5-S1 intervertebral disc is wedge-shaped, by about 16° (between sacrum and bottom of L5). The inferior processi articulares of L5 connect with the sacrum so the sacrum can not slide forward. The mobility in the sacrum contains 2°.Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title
The differences in range of motion between L4-L5 and L5-S1 in the three movements are:Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title
- More flexion in L4-L5
- More extension in L5-S1
- More lateral bending in L4-L5
- More rotation in L4-L5
The differences in stiffness are:
- More compression in L5-S1
- More shear forces lat and ant/post in L4-L5
- More bending in L5-S1
- More rotation in L4-L5
Mechanism of Injury / Pathological Process[edit | edit source]
- Compression and tension stresses: normal - gegenerated lumbar disk
When a normal lumbar disc is subjected to a compressive force, it will absorb some of the stress. Under the same compressive load, the nucleus of a degenerated disk will not absorb some of the stress and transfer the remainder to the annulus and end-plates; instead, the increased load is distributed to the annulus. Under these conditions the outer annulus fibers receive a large tensile stress without the fiber mechanism to absorb
the stress or the hydrostatic nucleus to distribute the forces radially. Consequently, the inner fibers receive a large compressive stress with all consequences.
Common diseases in the lumbar spine and sacrum are:
- Facet joint syndrome
- Disc herniation
- Instability
- Cauda equine syndroomCite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title(Gail M. 1980 (D))Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive titleCite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title
Outcome Measures[edit | edit source]
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Examination[edit | edit source]
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Key Research[edit | edit source]
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Resources
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Clinical Bottom Line[edit | edit source]
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Recent Related Research (from Pubmed)[edit | edit source]
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References[edit | edit source]
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