Lumbar Study Notes

PT805: Lumbar Spine Notes

Content Organization

• Overview of presentation layout:

  • I. Anatomical Units

  • II. Functional Units

  • III. Collective Function

Lumbar Spine: Introduction

• Low Back Pain (LBP)

  • Leading cause of activity limitation and work absence worldwide.

  • Statistics (WHO, Aug 2013):

  • Point prevalence: $12\%$

  • 1-month prevalence: $23\%$

  • Reference: Hoy et al., 2012.

• Importance of understanding anatomy for effective treatment and intervention.

• Functionality of Lumbar Spine:

  • Supports the superincumbent weight of the trunk.

  • Large vertebral bodies and intervertebral discs facilitate support and movement.

  • L5-S1 identified as a critical transitional segment allowing and limiting trunk movement.

Basic Structural Components of the Vertebra

• Nutrient Foramina:

  • Located on the posterior aspect of vertebral bodies.

  • Transmit nutrient arteries and basivertebral veins.

• Pedicles:

  • Connect anterior and posterior aspects of the vertebrae.

  • Contribute to the anterior-posterior (A-P) dimension of the vertebral foramen.

Anatomical Variants of the Lumbar Spine

• Commonly contains 5 vertebrae but variations can occur:

  • Sacralization: L5 fused with sacrum, resulting in only 4 vertebrae.

  • Lumbarization: S1 not fused, resulting in 6 vertebrae.

  • Transitional vertebrae observed in 20-25% of the population.

Osteology of the Lumbar Spine

• L1-L4 Body Height:

  • Anterior height is equal to posterior height.

• L5 Characteristics:

  • Wedge-shaped with anterior height greater than posterior.

• Vertebral Body Composition:

  • Primarily composed of cancellous bone, contains vertical and horizontal trabeculae.

  • Surrounded by a shell of cortical bone.

Trabecular Structure and Functionality

• Trabecular System:

  • Composed of vertical and horizontal struts, providing support against compressive forces.

  • Horizontal trabeculae prevent bending or buckling of vertical struts.

• Ring Apophysis:

  • Raised rim on vertebral body, acting as a secondary ossification center.

• Transverse Processes (TPs) & Spinous Processes (SPs):

  • Large to accommodate muscle attachments.

Lumbar Spine: Facet Joint Orientation

• Facet Orientation:

  • Primarily in the sagittal plane.

  • Motion capabilities:

  • Best allows flexion and extension.

  • Least allows rotation.

• Superior Articular Process:

  • Forms a facet joint with a concave orientation facing posteromedially.

• Inferior Articular Process:

  • Creates a facet joint with a convex orientation facing anterolaterally.

• Zygapophyseal (Facet) Joints:

  • Comprised of:

  • Superior facet (from inferior articular process of the superior vertebra).

  • Inferior facet (from superior articular process of the inferior vertebra).

Intervertebral Disc Structure and Characteristics

• Disc Composition:

  • Nucleus Pulposus (NP): Thick, gelatinous core surrounded by lamellae of the annulus fibrosus (AF).

  • Unique posterior concavity in lumbar discs.

• Size and Behavior:

  • Vertebrae and discs in lumbar region are the largest, providing significant passive resistance to movement.

• Intervertebral Foramen Boundaries:

  • Formed by pedicle notches, posterior disc, posterior bodies, articular processes, Z-joint & capsule.

  • Contains spinal nerves, vascular structures, connective and nerve tissues, typically occupying 30-40% of the foramen with common variations.

Lumbar Spine Motion and Mechanics

• Vertebra vs. Segment:

  • Vertebral mechanics involve 3 joints (body-disc-body plus 2 Z-joints) and interposed ligaments.

• Segmental Mechanics:

  • Flexion:

  • Facet joint mechanics: The inferior facet of the superior vertebra glides superiorly on the superior facet of the inferior vertebra.

  • Tension occurs in the joint capsule, compression occurs in the disc anteriorly, and tensioning occurs in the annulus fibrosus posteriorly.

  • Foramen Effect: In flexion, the intervertebral foramen enlarges, providing more space for nerve roots.

  • Spinal Canal Effect: Total canal space increases.

  • Limitations of Flexion:

  • Joint capsules, annulus fibrosus, ligamentum flavum, supraspinous ligament, interspinous ligament, posterior longitudinal ligament.

• Extension Mechanics:

  • Z-Joints exhibit inferior gliding of superior facets.

  • Joint surfaces approximate, causing disc compression posteriorly and tension anteriorly on the NP.

  • Foramen & Canal Effects: Extension reduces available space in the intervertebral foramen and decreases canal space cumulatively, especially with age-related changes.

  • Limitations of Extension:

  • Affected by anterior longitudinal ligament, annulus fibrosus, static tension from anterior muscles, and approximation of spinous processes.

• Lateral Flexion Mechanics:

  • Z-Joints show gliding movements and tensioning of joint capsules during lateral flexion.

  • Limitations of Lateral Flexion: Anulus fibrosus, facet joint capsules, iliolumbar ligaments, and intertransverse ligaments.

• Rotation Mechanics:

  • Z-joint apposition and slackening of annulus fibers differentiate between ipsilateral and contralateral movements.

  • Limitations of Rotation: Governed by anulus fibrosus, facet surfaces approximation, supraspinous ligament, and interspinous ligament.

Lumbar Spine Coupling

• Lateral Flexion and Rotation:

  • At L1-4: Coupled movements typically contralateral.

  • At L4-S1: Coupled movements tend to be ipsilateral. Variations in patterns are common, necessitating caution in rigid interpretations.

Lumbar Stability Contributions

• Intrinsic Ligaments:

  • Anterior longitudinal ligament, posterior longitudinal ligament, interspinous ligament, supraspinous ligament, and ligamentum flavum.

• Dynamic Mechanisms:

  • Contributing musculature and thoracolumbar fascia play key roles in lumbar stability.

• Anulus Fibrosus Function:

  • Acts as a ligamentous container for NP and aligns through concentric layers of obliquely oriented fibers.

• Facet Joint Capsules & Structure:

  • Primary limiter of segmental flexion; sagittal plane orientation limits rotational movement due to approximation.

Lumbosacral Angle and Mechanics

• Defined by the angle between the superior aspect of S1 and a horizontal reference line, averaging approximately 30 degrees depending on lordosis.

• L5-S1 Z-Joints:

  • Adapted for biplanar motion to limit rotation and anterior translation of L5, countering its tendency to move anteriorly.

Myology of the Lumbar Spine

• Flexors:

  • Typically inactive during quiet stance; eccentrically control trunk flexion from a standing position against gravity.

  • Important flexors include rectus abdominis, internal and external oblique, and possibly psoas major.

• Extensors:

  • Include the extensor spinae group (erector spinae: iliocostalis, longissimus, spinalis) which help counter flexion forces during stance and maintain stability.

• Lateral Flexion Contributors:

  • Quadratus lumborum and psoas major facilitate lateral bending and stabilization.

• Lumbopelvic Rhythm:

  • Refers to the combined movements of the lumbar spine and pelvis during forward bending (lumbar flexion followed by anterior pelvic tilt with hip flexion); returns through reversing this pattern. Individual variability is notable.

Activity-Related Range of Motion (AROM)

• Data reflecting lumbar spine AROM as a percentage of maximum:

  • Pick Up From Floor: Flexion (73%), Lateral Flexion (28%), Rotation (24%).

  • Putting On Pants: Flexion (47%), Lateral Flexion (26%), Rotation (23%).

  • Tying Shoes: Flexion (38%), Lateral Flexion (21%), Rotation (19%).

  • Sit to Stand: Flexion (37%), Lateral Flexion (13%), Rotation (13%).

  • Shower: Flexion (34%), Lateral Flexion (32%), Rotation (23%).

  • Putting On Jacket: Flexion (19%), Lateral Flexion (30%), Rotation (46%).

  • Reference: Codian et al., 2013.

Lumbar Spine Pathologies

• Common conditions to consider:

  • Spondylolysis:

  • Stress reaction or fracture at the pars interarticularis without displacement, commonly due to shear forces.

  • Spondylolisthesis:

  • Fracture at the pars interarticularis with forward and inferior displacement, potentially harming the disc and risking neural encroachment.

• Lumbar Disc Herniation:

  • Types include protrusion, extrusion, and sequestration.

  • Population prevalence of spondylolysis and spondylolisthesis: $7-11\%$.

  • Herniation prevalence increases to $60-70\%$ in individuals over 40-50 years, most of whom remain asymptomatic.

Intervertebral Foramen and Nerve Root Relationships

• Boundaries:

  • Composed of pedicle notches, posterior disc, posterior bodies, and articular processes together with Z-joint and capsule.

  • Anatomical understanding is critical to address potential nerve root compression.

• Spinal Nerve Root:

  • Each lumbar level corresponds to specific nerve roots, e.g., the sciatic nerve, which consists of roots from L4 to S3, yielding tibial and fibular (peroneal) nerves.

• Dermatomes and Myotomes:

  • Review of lower quadrant neurological influences through dermatomal spiral patterns and myotomal functions continues through practical lab sessions.

Conclusion

• Comprehensive understanding of lumbar anatomy, biomechanics, and pathological conditions is crucial in functional anatomy practice, with practical applications in the assessment and rehabilitation of patients with lumbar spine disorders.