Study Guide for Test # 2 HE 270
About test #2: 1.No essays or short answer this time 2.All the questions are on this study guide (in some form). Your text is excellent resource if you do not understand some of the bullet points. 3.The CD is also an excellent resource for understanding the muscles and how they attach to different structures. 4. If you do not understand an area or topic I would advise first referencing your Text, your lecture notes and my powerpoint slides. If this does not help, please reference one of the TA’s or me. 5. Finally, this test will be worth 100 points so if you did not do well on the last test you can make up for lost points with this test! And, there will be extra credit question on one of our celebrity pictures.
FORCES SUSTAINED AT THE LUMBOSACRAL JUNCTION (transitional zone) Lumbosacral junction is prone to injury, including disc lesions and spondylolisthesis. Loads on the joint contribute to pathology. Or, we can think of it as posture. Simplified model predicts muscle loads of 112% of body weight and compressive load of 240% and shear forces of 0.70% body weight. Magnitude of compressive and shear forces is affected by size of load being lifted and orientation of the pelvis. LOADS IN THE LUMBOSACRAL REGION DURING BENDING AND LIFTING • Estimated compressive loads range from 270 to 1,236 lb, and peak anterior shear from 90 to 270 lb. • Estimates depend on assumptions used in model. • Understanding the effects of posture and lifting techniques on anterior shear forces will help clinicians to develop effective treatment and prevention strategies Sacroiliac Joint Forces from the Literature • • • • Loads from 0.85 and 1.1 times body weight reported during static single-limb stance. Walking appears to generate larger loads at the sacroiliac joint. Lumbar lordosis with the lordosis of the cervical region and kyphosis of the thoracic regions enhances the load-bearing capacity of the spine. Transition zones between adjacent regions are sites of frequent injury.
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Articular tripod helps provide stability and mobility in lumbar region. Arising from the neural arch are seven bony projections --2 superior and inferior articular processes --2 tranverse processes --1 spinous process • • Neural arch and IVDs sustain most of the torsional loading. Vertebral bodies and intervertebral discs (IVDs) sustain most of the compressive loading.
VERTEBRAL BODIES • • • • • • • Sustain 80–90% of compressive load in erect standing Cancellous bone supported by blood and hematopoietic tissue Best at sustaining compressive loads, less capable of sustaining rotational stress Cartilaginous endplates cover superior and inferior surfaces. Articular processes lie close to sagittal plane, allowing flexion and extension but limiting rotation and side-bending. Spinous processes are thick and palpable. Long transverse processes (longest at L3 and thickest at L5) provide attachments for important stabilizing structures.
VERTEBRAL FORAMINA • House lowest part of spinal cord in upper portion and the cauda equina in the inferior region
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Intervertebral foramina are formed by vertebral body and anulus fibrosus, pedicles, ligamentum flavum, and anterior aspect of the facet joint capsule. • Ratio between size of vertebral foramen and the size of the exiting nerves is typically large. • Area of intervertebral foramen increases with flexion and decreases with extension. Ligamentous Support of the Lumbar Spine • • • • Ligamentum flavum is elastic to prevent buckling into vertebral foramen. Iliolumbar ligament supports lower lumbar region in all directions. Ligaments may act as important motion sensors. Muscles provide important additional stability to the lumbar spine.
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Thoracolumbar Fascia • • May provide important dynamic stabilization by connecting the spine to abdominal muscles and the upper extremity with large hip muscles.
STRUCTURE OF THE JOINTS OF THE LUMBAR SPINE • • The joint system of the lumbar spine comprises the large symphysis joint (the intevetebral joint) anteriorly and the paired synovial joints posteriorly (facet joints/apophyseal joints) Articular tripod provides dynamic stability.
Facet Joints Multifidus has capsular attachment • •
Facets guide motion, resist anterior shear and torsion. Bear approximately 18–20% of compressive loads, more with increased lordosis
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Intervertebral Joint VERTEBRAL ENDPLATE • • • Provides portal for nutrients between vertebral body and disc Can rupture or pull away from body Acts as a boundary between the IVD and the vertebra
INTERVERTEBRAL DISC • Nuclear region is less distinct from anulus fibrosus, and distinction decreases with degeneration.
ANULUS FIBROSUS • Several layers of fibrocartilage, collagen fibers lying oblique to fibers in adjacent layers • Posterior concavity increases posterior strength. • Outer layer has abundance of mechanoreceptors. NUCLEUS PULPOSUS • • • 70–90% water but concentration decreases with age Structure is hydrophilic and behaves hydraulically. Hydrostatic and osmotic pressures allow fluid to move in and out of disc
MECHANICAL PROPERTIES OF THE IVD • Hydraulic behavior allows the disc to absorb and transmit forces. • Sustains compression, tension, bending, and rotation Compression • • • • Compression forces are transformed into circumferential tensile forces. Radial expansion of nucleus pulposus is resisted by anulus fibrosus. Stores energy Dehydration or removal of nucleus pulposus subjects anulus fibrosus to larger loads.
Bending • Nucleus tends to migrate in the direction opposite to trunk motion.
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Rotation • Only some collagen fibers are stressed during rotation; other fibers are on slack.
IVD Pressures during Activities of Daily Living Intradiscal pressures increase with flexion of the spine.
Gross Motion of the Lumbar Spine • • Motion depends on facet joint orientation and disc height. Degeneration of discs can alter joint motion.
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LUMBAR FLEXION • • Limited by posterior anulus fibrosus and posterior ligaments abdominal muscles appear to be underestimated.why??
30% decrease because scans are taken in the supine position Abdominal contents collapse in the posterior position, under gravity-not real life. Moment arm and muscle pull are different when one is standing because of the visceral contents. MUSCLE GROUPS Rotatores and Intertransversarii Small PCSA and moment arms, so unlikely to contribute significant torque May serve as length transducers and position sensors (highly enriched muscle spindles). Extensors of the Spine Longissimus, Iliocostalis, and Multifidus Groups Longissimus thoracis and iliocostalis lumborum each have thoracic and lumbar segments. Longissimus thoracis pars thoracis and iliocostalis lumborum pars thoracis are predominantly slow-twitch fibers, attach to ribs and vertebral components, have long tendons and relatively short fibers, and run parallel to the spine. See page 570-Attach to the thoracic region are the most efficient lumbar extensors, since they have the longest moment arms as they course the lumbar spine The bulk of the contractile fibers lie in the thoracic spine, tendons pass over the lumbar spine and therefore have the greatest mechanical advantage. Longissimus thoracis pars lumborum and iliocostalis lumborum pars lumborum have more even distribution of fiber types, attach to each lumbar vertebra, and run obliquely to the lumbar spine, exerting a posterior shear and extensor moment on the superior vertebra Multifidi Multifidi span only a few segments and run parallel to the compression axis. There forces only effect specific areas of the spine RECTUS ABDOMINIS Major trunk flexor Sections prevent buckling of muscle during trunk flexion. Obliques transmit force to rectus abdominis. Participate in twisting, side-bending, and lumbar stabilization. Play a role in stabilization exercises
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Page 573
Special Case of the Quadratus Lumborum and Psoas Major • Psoas major appears to be primarily a hip flexor, with little role in lumbar stabilization. • Psoas major disperses bending stresses across the whole lumbar spine during hip flexion. • Quadratus lumborum appears to be important as lumbar stabilizer. Functional Consideration for the Interspinous and Supraspinous Ligaments Supraspinous ligaments are parallel to the compressive axis. Importance of ligaments in resisting flexion appears to be overstated. Supraspinous ligament appears to be most important ligamentous restraint to flexion.
Interspinous ligaments are oblique to the compressive axis of the spine, perhaps providing restraint to flexion throughout the ROM.
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Interspinous ligaments protect against posterior shear forces of the superior vertebra on the inferior vertebra. Forward-bending with a flexed spine increases the shear forces on the spine because of stretch of the interspinous ligaments and the superincumbent weight. Extensor muscles that can prevent anterior shear on superior vertebrae are silent when lumbar spine flexion is far enough to void protection against shear.
Twisting disables half of the collagen fibers in the anulus fibrosus. Injuries to the anulus require the spine to be fully flexed.
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Lumbopelvic rhythm • • • •
Lumbopelvic rhythm describes motion of lumbar spine and pelvic tilt. Coordinated movement of lumbar spine and pelvis is important for normal total movement. What happens to the pelvis with flexion? Extension?
LUMBAR EXTENSION • • Less motion than flexion, limited by anterior anulus fibrosus and spinous processes Limited posterior pelvic rotation may result in increased lumbar lordosis and increased loads on posterior structures of lumbar vertebrae.
LUMBAR ROTATION AND SIDE-BENDING • • • Rotation is limited by facet joint alignment at most lumbar segments. Side-bending is less restricted than rotation but more restricted than sagittal plane motion. Side-bending and rotation are coupled.
Neutral spine
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Neutral spine refers to normal lumbar lordosis • Motion that occurs at single motion segment • Osteokinematics describes rotations at joints. • Arthrokinematics describes displacement at joint surfaces. • Osteokinematics gross movements of bones at joints • • • • flexion / extension abduction / adduction internal rotation / external rotation
Arthrokinematics small amplitude motions of bones at joint surface • • • roll glide (or slide) spin
http://moon.ouhsc.edu/dthompso/namics/arthkin.htm
OSTEOLOGY OF PELVIC AND ASSOCIATED STRUCTURES • Pelvis consists of two innominate bones that exhibit symmetrical and asymmetrical motion with respect to the sacrum and a lumbopelvic rhythm with respect to the femurs.
Sacrum page 599 LATERAL PART • Ala (wing) formed by fused transverse processes APEX Articulates with first coccygeal segment Coccyx • Three to five segments • Sites of attachment for muscles and ligaments • Union of ilium, ischium, and pubis, fusing at about 25 years of age • Shelters and supports viscera and provides muscle attachment
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ILIUM • Largest of three • Consists of ala and body • Several important landmarks Lumbosacral Junction-pg 611 & 612 • • • • General components of articulation consistent with other lumbar joints Stabilized by trunk musculature and several ligaments Iliolumbar ligament provides important support that develops after birth. Orientation of facet joints protects against anterior shear of L5 on S1, increased because of sacral inclination.
LUMBOPELVIC RHYTHM • • • Movement of pelvis and lumbar spine as a unit on the femurs Similar to the scapulothoracic rhythm Review pg-620
Herniations occur in younger spines with good hydration of the disc. Why? Disc herniations are associated with cyclic loading. Hx of Herniations are associated with sitting and sedentary occupations Preventing Injury: What Does the Patient Need to Know? Don’t do too much of any one thing. Avoid end-range lumbar motion that can injure disc. Vary work positions.-ergonomics Allow time for tissues to return to their pre-stressed length following prolonged positions that would induce creep. Avoid too much sitting. Keep loads close to low back. Endurance appears to be a prerequisite for strength training. AEROBIC EXERCISE Important for reducing incidence and treating low back pain Curl-ups primarily activate the rectus abdominis. Sit-ups and leg raises increase psoas major activity and compressive loads on low back. Horizontal support increases activity of other abdominal muscles with little activity of psoas major. Should Abdominal Belts Be Worn? Evidence does not support use for exercise Notes for Exercise Prescription
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Frequency from three times per week to daily Avoid pain. Aerobic exercise Avoid full range movement with loads shortly after rising from bed. (why Hint: hydration) Emphasize endurance exercise over strengthening exercise. Improvement takes time.
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