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    7 biomechanics of vertebral column   muscles 7 biomechanics of vertebral column muscles Presentation Transcript

    • 7.Biomechanics ofVertebral Column: Regional Structure & Function-Muscles of the Vertebral ColumnDr. D. N. BidSarvajanik College of Physiotherapy,Rampura, Surat – 395003.
    • The Craniocervical /Upper Thoracic Regions• The muscles of the craniocervical region servetwo primary roles:– to hold the head upright against gravity and– to infinitely position the head in space in order tooptimally position the sensory organs.• The muscles of the cervicothoracic region alsoserve two primary roles: again,– to position the head and neck in space and– to stabilize the head and neck to allow and producemovement of the scapula.6/14/2013 dnbid71@gmail.com 2
    • • The line of gravity in an upright standingposition passes anteriorly to the axis ofrotation in the cervical region, producing aflexion moment (Fig. 4-51).6/14/2013 dnbid71@gmail.com 3
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    • • The posterior muscles, along with the ligamentousstructures previously discussed, counter this flexionmoment.• The need to position the head for the special sensoryorgans often includes rapid, coordinated movements, suchas when a loud noise is heard and there is rapid turning ofthe head to locate the source of the sound.• The muscular structure and function are complex in orderto serve the demands for such great amounts of motionand yet provide sufficient stability to protect the spinal cordand allow for use of the upper extremities.6/14/2013 dnbid71@gmail.com 5
    • Posterior Muscles• We will examine the muscles from superficial to deep and beginwith the posterior muscles (Figs. 4-52 and 4-53).• The trapezius muscle is the most superficial of the posteriormuscles. The trapezius spans from the occiput to the lower thoracicspine and contains a prominent tendinous region over thecervicothoracic junction.• The trapezius belongs predominantly to the shoulder region;however, when the upper extremities are fixated, the trapezius canproduce extension of the head and neck. Acting unilaterally, theupper trapezius can produce ipsilateral lateral flexion andcontralateral rotation of the head and neck.6/14/2013 dnbid71@gmail.com 6
    • • The levator scapula is deep to the trapezius.• It runs from the root of the spine of the scapula andcourses superiorly, medially, and anteriorly to insert on thecervical transverse processes.• This muscle has a large crosssectional area.• The levator scapula is a scapular elevator and downwardrotator when the neck is stable, but if the upper extremityis stabilized, it will produce ipsilateral lateral flexion androtation of the cervical spine.6/14/2013 dnbid71@gmail.com 7
    • • In addition, the anterior inclination plays animportant role in the mechanics of the cervicalspine.• The levator scapula is optimally aligned toproduce a posterior shear force on the cervicalspine.6/14/2013 dnbid71@gmail.com 8
    • Figure 4-52■ Posterior back muscles. The superficial muscles have beenremoved on the right side to show the erector spinae.The anterior layer of the thoracolumbar fascia is intact on the leftside of the back.• Missing6/14/2013 dnbid71@gmail.com 9
    • • Porterfield and DeRosa likened the levator scapulae to the deeperector spinae of the lumbopelvic area, which will be discussedlater.• The cervical spine is subjected to constant anterior shear forcescaused by gravity and the lordotic position of the spine in thisregion.• The levator scapulae help resist these forces (Fig. 4-54).• An increase in the cervical lordosis, as is often seen in excessiveforward head posture, will further increase the anterior shearforces on the cervical vertebrae and may cause overactivity of thelevator scapula to resist these excessive anterior shear forces.6/14/2013 dnbid71@gmail.com 10
    • Figure 4-53■Erector spinae and deep back muscles. Theerector spinae muscle has been removed from the right side ofthe neck to show the deep back muscles.6/14/2013 dnbid71@gmail.com 11
    • Figure 4-54: The cervical spine is subjected to anterior shear forces as a resultof the lordosis and anterior line of gravity. The levator scapulae help resist theanterior shear forces by producing posterior shear.6/14/2013 dnbid71@gmail.com 12
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    • • The splenius capitis and splenius cervicis muscles aredeep to the levator scapulae.• The splenius muscles are large, flat muscles runningfrom the spinous processes of the cervical and thoracicspine and the ligamentum nuchae to the superiornuchal line, the mastoid process, and the cervicaltransverse processes (see Fig. 4-52).6/14/2013 dnbid71@gmail.com 14
    • • These muscles serve as prime movers of the headand neck as a result of their large cross-sectionalarea and the large moment arm.• They produce extension when working bilaterallyand ipsilateral rotation when working unilaterally.• However, these muscles show littleelectromyographic activity in normal stance.6/14/2013 dnbid71@gmail.com 15
    • • The splenius capitis and splenius cervicis muscles are deepto the levator scapulae.• The splenius muscles are large, flat muscles running fromthe spinous processes of the cervical and thoracic spine andthe ligamentum nuchae to the superior nuchal line, themastoid process, and the cervical transverse processes (seeFig. 4-52).• These muscles serve as prime movers of the head and neckas a result of their large cross-sectional area and the largemoment arm.• They produce extension when working bilaterally andipsilateral rotation when working unilaterally.However, these muscles show little electromyographicactivity in normal stance.6/14/2013 dnbid71@gmail.com 16
    • • Porterfield and DeRosa likened the function of thesemispinalis group to that of the multifidus muscles inthe lumbar region in that they have optimal alignmentand moment arm for increasing the lordosis of thecervical and lumbar regions, respectively (Fig. 4-55).• It is important to note that the greater occipital nervepierces the semispinalis capitis muscle on its way toinnervate the skull.• This can be a site of nerve irritation and entrapmentwhen the semispinalis capitis is overactive orshortened as in a forward head posture. Occipitalregion headaches can result.6/14/2013 dnbid71@gmail.com 17
    • • The longissimus capitis and longissimus cervicis aredeep and lateral to the semispinalis group (see Fig. 4-53).• Their deep position places them close to the axis ofrotation for flexion and extension, rendering themineffective extensors because of the small momentarm.• They do, however, produce compression of the cervicalsegments.• The lateral position allows them to produce ipsilaterallateral flexion when working unilaterally, and whenworking bilaterally, they serve as frontal planestabilizers of the cervical spine.6/14/2013 dnbid71@gmail.com 18
    • • The suboccipital muscles are the deepest posterior musclesand consist of the rectus capitus posterior minor andmajor, inferior oblique, and superior oblique muscles.• As a group, they run between the occiput and C2, allowingindependent movement of the craniovertebral region onthe lower cervical spine. Together, they produce occipitalextension.• Unilaterally, they produce ipsilateral rotation and lateralflexion.• Given the small cross-sectional area of these muscles, someauthors have questioned their ability to generate force andproduce movement; rather, they may serve primarily aproprioceptive role and produce small movements in orderto fine-tune motion.6/14/2013 dnbid71@gmail.com 19
    • Figure 4-55■Function of the semispinalis capitis in comparison with the lumbar multifidus muscle. Thesemispinalis capitis has an optimal lever arm for cervical extension. M, multifidus muscle; SE, semispinaliscapitis muscle.(From Porter, JA, and DeRosa, C; Mechanical Neck Pain. Saunders/ Elsevier, 1995, with permission.)6/14/2013 dnbid71@gmail.com 20
    • Lateral Muscles• The scalene muscles are located on the lateral aspect of thecervical spine and serve as frontal plane stabilizers alongwith the longissimus muscles posteriorly when they areacting as a group.• In the sagittal plane, the anterior scalene muscles, whichrun from the first rib to the anterior tubercles of thetransverse processes of C3 to C6, work with the levatorscapulae to provide stability (Fig. 4-56).• The anterior scalene muscles, when working bilaterally, willflex the cervical spine and produce an anterior shear.• Unilaterally, the anterior scalene muscles will produceipsilateral lateral flexion and contralateral rotation to thecervical spine.6/14/2013 dnbid71@gmail.com 21
    • • The middle scalene muscles run from the first rib to theanterior tubercles of the transverse processes of C3 to C7.• The middle scalene muscles are more laterally placed thanare the anterior scalene muscles, and their line of pullmakes them excellent frontal plane stabilizers.• The posterior scalene muscles run from the second rib tothe posterior tubercles of the transverse processes of C3 toC7.• The posterior scalene muscles predominantly laterally flexthe neck.6/14/2013 dnbid71@gmail.com 22
    • • The anterior and middle scalene muscles form atriangle through which the brachial plexus andthe subclavian artery and vein pass (Fig. 4-57).• This can be a site for compression on theneurovascular structures by the anterior scalenemuscle: scalenus anticus syndrome, described byCailliet.• This can produce pain, numbness, and tingling tothe arm.6/14/2013 dnbid71@gmail.com 23
    • • The sternocleidomastoid muscle runs from the6/14/2013 dnbid71@gmail.com 24
    • Figure 4-57: The brachial plexus and the subclavian artery andvein pass between the anterior and middle scalene muscles.6/14/2013 dnbid71@gmail.com 25
    • • The sternocleidomastoid muscle runs from thesternum, distal clavicle, and acromion to the mastoidprocess. The angle of inclination is posterior, medial, andsuperior.• It is unique in that, because of this orientation, it liesanterior to the axis of rotation in the lower cervicalspine, producing flexion when acting bilaterally butposterior to the axis at the skull, producing extension of thehead on the neck.• Acting unilaterally, the sternocleidomastoid muscle willproduce ipsilateral lateral flexion and contralateral rotationof the head and neck.6/14/2013 dnbid71@gmail.com 26
    • Anterior Muscles• The longus capitis run from the anteriortubercles of the cervical transverse processesto the occiput.• The longus colli run from the thoracicvertebral bodies to the anterior tubercles ofthe cervical transverse processes and craniallyfrom the anterior tubercles of the transverseprocesses to the atlas.6/14/2013 dnbid71@gmail.com 27
    • • These two muscles lie close to the vertebralbodies and therefore are relatively close to theaxis of rotation. Although they do have sufficientmoment arm to produce flexion, they alsoproduce a fair amount of compression.• The longus capitis and longus colli work insynergy with the trapezius to stabilize the headand neck to allow the trapezius to upwardlyrotate the scapula (Fig. 4-58).6/14/2013 dnbid71@gmail.com 28
    • • Given that muscles always contract from bothends, were it not for the longus capitis andlongus colli, the trapezius would extend thehead and neck rather than upwardly rotatethe scapula, in view of the vastly greaterweight and moment arm of the upperextremity in comparison with the head.6/14/2013 dnbid71@gmail.com 29
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    • • The rectus capitis anterior and rectus capitislateralis are able to produce flexion as a resultof their line of pull;however, as with the suboccipital muscles,the small cross-sectional area and momentarms probably render them capable ofserving a greater proprioceptive functionrather than prime mover.6/14/2013 dnbid71@gmail.com 31
    • Figure 4-58: In thesagittal plane, thetrapezius, longuscapitis, and longuscolli work insynergy to elevatethe scapula.6/14/2013 dnbid71@gmail.com 32
    • Lower Thoracic/Lumbopelvic Regions• Muscles of the lower spine regions serve theroles of producing and controlling movementof the trunk and stabilizing the trunk formotion of the lower extremities.• The muscles also assist in attenuating theextensive forces that affect this area.6/14/2013 dnbid71@gmail.com 33
    • Posterior Muscles• Again, we will examine the muscles from superficial todeep and begin with the posterior muscles.• The thoracolumbar fascia is the most superficialstructure. As discussed previously, several majormuscle groups of this region are associated with thethoracolumbar fascia.• The fascia gives rise to the latissimus dorsi, the gluteusmaximus, the internal and external abdominaloblique, and the transversus abdominis.• In addition, the fascia surrounds the erector spinae andthe multifidus muscles of the lumbar region.6/14/2013 dnbid71@gmail.com 34
    • • These attachments are significant in that tensile forces can beexerted on the thoracolumbar fascia through muscle contraction ofthese muscles.• Tension on the thoracolumbar fascia will produce a force that exertscompression of the abdominal contents.• Along with contraction of the abdominal muscles, this compressionis similar to that of an external corset.• The coupled action of the latissimus dorsi, contralateral gluteusmaximus, and tension through the thoracolumbar fascia willcompress the lumbosacral region and impart stability (Fig. 4-59).6/14/2013 dnbid71@gmail.com 35
    • • The erector spinae consist of the longissimus and iliocostalis musclegroups.• In general, these muscles are identified as extensors of the trunk.• Bogduk examined the function of the longissimus thoracis and theiliocostalis lumborum and further described these muscles as eachhaving a lumbar portion (pars lumborum) and a thoracic portion(pars thoracis).• The longissimus thoracis pars thoracis and the iliocostalis lumborumpars thoracis form the more superficial layer and the longissimusthoracis pars lumborum and the iliocostalis lumborum parslumborum form a deeper layer.6/14/2013 dnbid71@gmail.com 36
    • • Anatomically and functionally, therefore, it is easier togroup the muscles together as the superficial layer andthe deep layer.• The superficial layerruns from the ribs and thoracictransverse processes to form muscle bellies that arelaterally located in the thoracic region.• The muscles have long tendons that join together toform the ESA, which inserts into the spinous processesof the lower lumbar spine, sacrum, and iliac crest (Fig.4-60).6/14/2013 dnbid71@gmail.com 37
    • Figure 4-59: Coupled action of the latissimusdorsi, contralateral gluteus maximus, and tensionthrough the thoracolumbar fascia will compress andstabilize the lumbosacral region.6/14/2013 dnbid71@gmail.com 38
    • • This superficial layer, with its long moment armand excellent line of pull, produces extension ofthe thoracic and lumbar regions when actingbilaterally.• These muscles are considered to be the primaryextensors of the trunk (Fig. 4-61).• Acting unilaterally, they are able to laterally flexthe trunk and contribute to rotation. During trunkflexion from a standing position, the erectorspinae are responsible for contractingeccentrically to control the motion.6/14/2013 dnbid71@gmail.com 39
    • • The gravitational moment will produceforward flexion, but the extent and rate offlexion are controlled partially by eccentriccontractions of the extensors with the ESA andpartially by the thoracolumbar fascia andposterior ligamentous system.6/14/2013 dnbid71@gmail.com 40
    • • The erector spinae act eccentrically until approximatelytwo thirds of maximal flexion has been attained, atwhich point they become electrically silent.• This is called the flexion-relaxationphenomenon, which is thought to occur at the pointwhen stretched and deformed passive tissues are ableto generate the required moment.• However, the extensor muscles may be relaxed only inthe electrical sense because they may be generatingforce elastically through passive stretching.6/14/2013 dnbid71@gmail.com 41
    • • According to Gracovetsky, control of flexionbecomes the responsibility of the passive elasticresponse of the ESA, the thoracolumbarfascia, and the posterior ligamentous system.• The posterior ligaments (supraspinous andinterspinous ligaments) have longer momentarms than do the extensor muscles and thus havea mechanical advantage over the extensors.6/14/2013 dnbid71@gmail.com 42
    • Figure 4-60■Thesuperficial erectorspinae with theerector spinaeaponeurosis (ESA).IL, iliocostalislumborum parsthoracis;LT, longissimusthoracispars thoracis.6/14/2013 dnbid71@gmail.com 43
    • • Bogduk and others identified the deep layer of the erectorspinae as being entirely separate from the superficial layerand consisting of individual fascicles with commontendinous insertions.• Bogduk reported that the fascicles arise from the ilium atthe PSIS and just lateral on the iliac crest and coursesuperiorly, medially, and anteriorly to insert on the lumbartransverse processes (Fig. 4-62).• Some debate remains, however, inasmuch as Daggfeldt etal. reported some attachment to the ESA (and therefore notindependent function) of the upper lumbar fascicles.• Porterfield and DeRosa described these deep erectorspinae as similar in orientation and function to the levatorscapulae in the cervical region.6/14/2013 dnbid71@gmail.com 44
    • • These muscles lie close to the axis of rotation and therefore do nothave sufficient moment arm to be the prime movers into extension.• Their oblique orientation, however, allows the muscles to exert aposterior shear force to the vertebrae. In addition to posteriorshear, they also exert compressive forces (Fig. 4-63).• Because of their oblique line of action and ability to produceposterior shear, these muscles provide an extremely importantdynamic resistance to the constant anterior shear forces of thelumbar region caused by the lordotic position and the forces ofgravity and ground reaction forces combined.6/14/2013 dnbid71@gmail.com 45
    • • These muscles, then, have great clinicalsignificance.• McGill reported, however, that with lumbar spineflexion, these muscles lose their obliqueorientation and therefore lose their ability toresist anterior shear forces.• A flexed spine, therefore, is unable to dynamicallyresist anterior shear forces, which can causedamage.6/14/2013 dnbid71@gmail.com 46
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    • Figure 4-61■Sagittal view ofthe force vectors ofthe superficialerectorspinae, demonstrating the excellentline of pull andlarge moment armfor extension.6/14/2013 dnbid71@gmail.com 48
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    • Figure 4-3■ Sagittalview of the forcevectors of the deeperectorspinae, demonstrating thecompression andposterior shearcomponents.6/14/2013 dnbid71@gmail.com 50
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    • • The multifidus muscles of the spine are complex anddemonstrate segmental and regional differences.• In the lumbar region, the multifidus muscles are not trulytransversospinales, as most anatomy texts depict.• They run generally from the dorsal sacrum and the ilium inthe region of the PSIS to the spinous processes of thelumbar vertebrae.• They also have separate fascicles that run from themamillary processes to the spinous process of the cranialvertebrae. The line of pull in the lumbar region is morevertically oriented.• In the thoracic region, the multifidus muscles aretransversospinales, inasmuch as they are more laterallyoriented with an oblique line of pull.6/14/2013 dnbid71@gmail.com 53
    • • They run from the transverse process of thevertebra to the spinous processes of the morecranial vertebrae covering one to three segments.• The lumbar multifidus muscles are deep to theESA only below L3.• They are a thick mass that fills the area of thesacral sulcus and are easily palpable here.6/14/2013 dnbid71@gmail.com 54
    • • As the multifidus muscles in the lumbar region have agreater cross-sectional area and more verticallyoriented fibers than those of the thoracic region, itappears that they are better suited to produceextension.• The thoracic multifidus muscles are better suited toproduce rotation.• The lumbar multifidus muscles are arranged insegmental fascicles, which suggests that their principleaction is on focal lumbar segments.6/14/2013 dnbid71@gmail.com 55
    • • The fibers of the lumbar multifidus muscles becomeincreasingly more vertical in a caudal direction.• The line of action will produce extension by increasing thelumbar lordosis (see Fig 4-55).• In so doing, the fibers will add compressive loads to theposterior aspect of the interbody joints.• The role of the lumbar multifidus muscles in rotation is towork in synergy with the abdominal muscles by opposingthe flexion moment that the abdominal muscles produce.6/14/2013 dnbid71@gmail.com 56
    • • McGill suggested that the role of the lumbar multifidusmuscles is to produce extensor torque to allowcorrection of individual segments that are the foci ofstress.• Rotatores and intertransversarii muscles are frequentlydescribed as producing lateral flexion androtation, respectively.• Because of small cross-sectional areas and smallmoment arms, however, it appears likely that thesemuscles serve more of a proprioceptive role.6/14/2013 dnbid71@gmail.com 57
    • Lateral Muscles• The quadratus lumborum is deep to the erector spinae andmultifidus muscles.• The quadratus lumborum, when acting bilaterally, serves asan important frontal plane stabilizer (Fig. 4-64A).• Porterfield and DeRosa also described the quadratuslumborum as serving an important role in stabilization inthe horizontal plane as well.• When acting unilaterally, the quadratus lumborum canlaterally flex the spine and attachments to the lumbartransverse processes, allowing it to control rotationalmotion as well (see Fig. 4-64C).6/14/2013 dnbid71@gmail.com 58
    • • If lateral flexion occurs from erect standing, the forceof gravity will continue the motion, and thecontralateral quadratus lumborum will control themovement by contracting eccentrically.• If the pelvis is free to move, the quadratus lumborumwill “hike the hip” or laterally tilt the pelvis in thefrontal plane (see Fig. 4-64B).6/14/2013 dnbid71@gmail.com 59
    • Anterior Muscles• The rectus abdominis is the prime flexor of thetrunk.• It is contained within the abdominal fascia, whichseparates the rectus abdominis into sections andattaches the rectus abdominis to the aponeurosisof the abdominal wall.• The abdominal fascia also has attachment to theaponeurosis of the pectoralis major.6/14/2013 dnbid71@gmail.com 60
    • • McGill and Porterfield and DeRosa discussedthe importance of these fascial connections asthey transmit forces across midline andaround the trunk.• Tension on this fascial system will providestability in a corset type of manner around thetrunk.6/14/2013 dnbid71@gmail.com 61
    • Figure 4-64■A. The illustration shows the attachments of the right andleft quadratus lumborum muscles.B. A unilateral contraction of the left quadratus lumborum muscle willlift and tilt the left side of the pelvis and hike the hip when the trunk isfixed and the pelvis and leg are free to move.C. A unilateral contraction of the left quadratus lumborum muscle whenthe pelvis and left leg are fixed will cause ipsilateral trunk flexion.6/14/2013 dnbid71@gmail.com 62
    • • The abdominal wall consists of the external oblique, theinternal oblique, and the transversus abdominis muscles.• These muscles together form what McGill called the“hoop” around the entire abdomen with the abdominalwall as the anterior aspect and the thoracolumbar fasciaand its muscle attachments as the posterior aspect (see Fig.4-44).• This hoop plays an important role in stability of thelumbopelvic region.• The transversus abdominis has been shown to mechanicallycontrol the SIJ through significant compressive forces dueto the transverse (perpendicular) orientation of the muscleto the SIJ.6/14/2013 dnbid71@gmail.com 63
    • • Richardson et al. demonstrated that contraction of thetransversus abdominis decreased laxity at the SIJ.• Cholewicki et al. demonstrated that in a neutral spineposture in standing, there is trunk flexor-extensor musclecoactivation at a low level.• Furthermore, they measured this activation level toincrease with an external load and with decreased spinalstiffness, which supports the hypothesis that this “hoop”can provide stability to the lumbopelvic region and thatincreased muscle activity can compensate for loss ofstiffness in the spinal column caused by injury.6/14/2013 dnbid71@gmail.com 64
    • • The psoas major runs from the lumbar transverseprocesses, the anterolateral vertebral bodies of T12 toL4, and the lumbar intervertebral disks to the lessertrochanter of the femur.• It courses inferiorly and laterally, and the distal tendonmerges with that of the iliacus. The primary role of thepsoas major is flexion of the hip.• McGill reported that it is active only when there is activehip flexion. The iliacus runs from the iliac crest over thepubic ramus to the lesser trochanter with the tendon of thepsoas major.6/14/2013 dnbid71@gmail.com 65
    • • The primary role of the iliacus is also hip flexion.• The role of the psoas major at the lumbar spine appears tobe to buttress the forces of the iliacus, which, whenactivated, cause anterior ilial rotation and thus lumbarspine extension.• The psoas major also provides stability to the lumbar spineduring hip flexion activities by providing great amounts oflumbar compression during activation.• Some anterior shear is also produced when it is activated.6/14/2013 dnbid71@gmail.com 66
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    • Injury Prevention with Lifting Tasks:Squat Lift versus Stoop Lift• The prevalence of back problems in thegeneral population and the difficulties ofresolving these problems has generated agreat deal of research both to explain themechanisms involved in lifting and todetermine the best method of lifting so thatback injuries can be prevented.6/14/2013 dnbid71@gmail.com 70
    • • A great deal of focus has been on the squatversus stoop lift (Fig. 4-66).• During a stoop lift, trunk flexion is achievedprimarily by thoracolumbar flexion, and there islittle to no knee flexion.• During a squat lift, the spine remains as erect aspossible and trunk flexion is achieved primarily byhip and knee flexion.6/14/2013 dnbid71@gmail.com 71
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    • • Other, less controversial critical factors in lifting in anyposture appear to be the distance from the body to theobject to be lifted, 74 the velocity of the lift, and thedegree of lumbar flexion.• The farther away the load is from the body, the greateris the gravitational moment acting on the vertebralcolumn.• Greater muscle activity is required to perform thelift, and consequently greater pressure is created in thedisk.6/14/2013 dnbid71@gmail.com 77
    • • The higher the velocity of the lift is, the greater is theamount of weight that can be lifted, but the higher isthe load on the lumbar disks.• The relative spinal load and applied erector spinaeforce increase significantly with the velocity of trunkextension.6/14/2013 dnbid71@gmail.com 78
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    • Muscles of the Pelvic Floor6/14/2013 dnbid71@gmail.com 82
    • Structure• Although the levator ani andcoccygeusmuscles neitherplay a major supporting role for the vertebral columnnor produce movement of the column, these musclesare mentioned here because of their proximity to thecolumn and possible influence on the linkages thatform the pelvis.• The levator ani muscles comprise two distinctparts, the iliococcygeus and the pubococcygeus, whichhelp to form the floor of the pelvis and separate thepelvic cavity from the perineum.6/14/2013 dnbid71@gmail.com 83
    • • The left and right broad muscle sheets of the levatorani form the major portion of the floor of the pelvis.• The medial borders of the right and left muscles areseparated by the visceral outlet, through which passthe urethra, vagina (in the female), and anorectum.• The pubococcygeal part of the muscle arises from theposterior aspect of the pubis and has attachments tothe sphincter, urethra, walls of the vagina (in thefemale), and the pineal body and rectum (in bothgenders).• The iliococcygeal portion, which arises from theobturator fascia, is thin.6/14/2013 dnbid71@gmail.com 84
    • • Its fibers blend with the fibers of theanococcygeal ligament, form a raphe, and attachto the last two coccygeal segments.• The coccygeus muscle arises from the spine ofthe ischium and attaches to the coccyx and lowerportion of the sacrum.• The gluteal surface of the muscle blends with thesacrospinous ligament (Fig. 4-67).6/14/2013 dnbid71@gmail.com 85
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    • Function• Voluntary contractions of the levator ani muscleshelp constrict the openings in the pelvic floor(urethra and anus) and prevent unwantedmicturition and defecation (stress incontinence).• Involuntary contractions of these muscles occurduring coughing or holding one’s breath when theIAP is raised.• In women, these muscles surround the vagina andhelp to support the uterus.6/14/2013 dnbid71@gmail.com 87
    • • During pregnancy the muscles can be stretchedor traumatized, which can result in stressincontinence whenever the IAP is raised.• In men, damage to these muscles may occur afterprostate surgery.• The coccygeus muscle assists the levator ani insupporting the pelvic viscera and maintaining IAP.6/14/2013 dnbid71@gmail.com 88
    • Thank you……..,,,End of Part - 76/14/2013 dnbid71@gmail.com 89