Muscles of the Posterior Trunk Myology Muscles of the Posterior Trunk

Latissimus Dorsi Fibers of the latissimus dorsi twist in such a way that the superior fibers attach distally on the humerus and the inferior fibers attach proximally. Sometimes the latissimus blends with the teres major The spinal and pelvic attachments are all via thoracolumbar fascia. Since it has an attachment onto the inferior angle of the scapula, it can move the scapula. When trunk is fixed, it can depress, retract and downwardly rotate the scapula. If the arm is fixed, the lat can elevate the trunk at the shoulder joint toward the humerus (as in a “pull up”). The latissimus dorsi and pectoralis major are both large powerful muscles which attach trunk to the arm. The both adduct and medially rotate the humerus.

Latissimus Dorsi latissimus = wide dorsi = back O: Thoracolumbar aponeurosis, posterior sacrum, posterior iliac crest, lower 3 or 4 ribs, and inferior angle of the scapula I: Medial lip of the Bicipital Groove of the humerus A: Extends, medially rotates, adducts the arm (handcuff position) ** Reversed muscle action bilaterally causes anterior tilt of the pelvis. Unilateral contraction causes elevation of the pelvis, contralateral rotation of the trunk, and lateral deviation of the trunk. N: Thoracodorsal nerve Palpation: Page 207

Rhomboids They are deep to the trapezius Rhomboid minor is superior to rhomboid major. Rhomboid minor attaches to the scapula, inferior to the levator scapulae. Deep to the rhomboids are the splenius capitis, splenius cervicis, serratus posterior superior and erector spinae They also cause downward rotation of the scapula. Are sometimes called Christmas Tree muscles due to their shape. Rounded Shoulders is a common condition in which scapulae are protracted (abducted) and depressed and the humeri are medially rotated. When rhomboids are weak, the can contribute to this condition. This is especially true if the protractors (pecs) are tight.

Rhomboid Major and Minor O: Rhomboid Major: Sp’s T2-T5 Rhomboid Minor: Sp’s C7-T1 I: Medial border of the scapula from the root of the spine of the scapula to the inferior angle of the scapula A: Retracts, elevates, and downwardly rotates the scapula. **Reversed muscle action: Unilaterally causes contralateral rotation of the trunk N: Dorsal scapular nerve Palpation: Page 212

Serratus Anterior Majority of this muscle lies deep to the scapula and lats posteriorly and pecs anteriorly. Lowest 4-5 slips of costal attachments interdigitate with external oblique. Lies next to (anterior to) the subscapularis. Serrated appearance comes from attaching onto separate ribs, which creates the notched look of a serrated knife. Prime mover of protraction, upward rotation, & medial tilt of scapula. Required during forceful protraction of scapula i.e. reaching, pushing, punching, throwing.

Serratus Anterior O: Outer borders of the 1st through 9th ribs I: Anterior surface of the entire medial border of the scapula A: (PUSS) Protracts, upwardly rotates, and stabilizes the scapula N. Long thoracic nerve (of Bell) Palpation: Page 215

Serratus Posterior Superior Thin, quadrilateral shaped muscle Important for respiration specifically inspiration since it elevates ribs 2-5 increasing the size of the thoracic cage (Boyle’s Law). Lies deep to the rhomboids

Serratus Posterior Superior O: SP’s of C7-T3 I: Superior borders of Ribs 2-5 (deep to the rhomboids) A: Elevation of ribs 2-5 N: intercostal nerves Palpation: Page 219

Serratus Posterior Inferior O: SP’s of T11-L2 I: Inferior borders of Ribs 9-12 A: Depression of ribs 9-12 N: subcostal & intercostal nerves Palpation: Page 221

The Erector Spinae Group Name tells us that these muscles make the spine erect. Lie deep in the back and neck In lumbar region, this group is deep to the lat and serratus posterior inferior. In thoracic region, deep to trap, lats, rhomboids, serratus posterior superior, splenius capitis & splenius cervicis. In cervical region, deep to trap, splenius cap/cerv, and SCM In trunk, erector spinae are superficial to transversospinalis group, QL, and ribcage. In neck erector spinae group is superficial to suboccipitals. Spinalis, longissimus, and iliocostalis make up erector spinae group. From medial to lateral the acronym SLI name the muscle of the group

Erector Spinae Group (Overview of entire group) O: Pelvis I: Spine, ribcage, head A: Bilateral Contraction: causes Extension of the trunk, neck, and head; anterior pelvic tilting. Unilateral contraction: causes lateral flexion and Ipsilateral rotation of the trunk, head, and neck; elevation of the pelvis N: Dorsal rami of the spinal nerves

Individual Erector Group Muscles Iliocostalis Subdivided into lumborum, thoracis, and cervicis Most lateral of the three Longissimus Subdivided into thoracis, cervicis, and capitis Longest & largest of the three with most superior attachments. Spinalis Most medial of the three

Iliocostalis O: Iliocostalis Lumborum: Medial iliac crest and sacrum Iliocostalis Thoracis: angles of ribs 7 – 12 Iliocostalis Cervicis: angles of ribs 3-6 I: Iliocostalis Lumborum: angles of ribs 7 – 12 Iliocostalis Thoracis: angles of ribs 1-7 and C7 TP Iliocostalis Cervicis: TP’s of C4 – C6 A: Bilateral contraction: Extends the trunk and neck and anteriorly tilts the pelvis. Unilateral contraction: Lateral flexion and ipsilateral rotation of the trunk and neck; elevation of the pelvis at the lumbosacral joint. N: Dorsal rami of the cervical, thoracic, and lumbar spinal nerves Palpation: Page 227

Longissimus O: Longissimus Thoracis: Medial iliac crest, posterior sacrum, and TP’s of L1 – L5 Longissimus Cervicis: TP’s of T1 – T5 Longissimus Capitis: TP’s of T1 – T5 and the AP’s of C5 - Ct I: Longissimus Thoracis: TP’s of all thoracic vertebrae and the 9 lower ribs Longissimus Cervicis: TP’s of C2 – C6 Longissimus Capitis: Mastoid process A: Bilateral contraction: Extends the trunk and neck and anteriorly tilts the pelvis. Unilateral contraction: Lateral flexion and ipsilateral rotation of the trunk, neck, and head; elevation of the pelvis at the lumbosacral joint. N: Dorsal rami of the cervical, thoracic, and lumbar spinal nerves Palpation: Page 230

Spinalis O: Spinalis Thoracis: SP’s of T11 – T12 Spinalis Cervicis: Inferior nuchal ligament and SP of C7 Spinalis Capitis: Usually considered to be part of the semispinalis capitis I: Spinalis Thoracis: SP’s of T4 – T8 Spinalis Cervicis: SP of C2 Spinalis Capitis: Usually considered to be part of the semispinalis capitis A: Bilateral contraction: Extends the trunk and neck. Unilateral contraction: Lateral flexion and ipsilateral rotation of the trunk, neck, and head N: Dorsal rami of the cervical, thoracic, and lumbar spinal nerves Palpation: Page 233

Transversospinalis Group (Overview of entire group) O: Pelvis I: Spine & head A: Bilateral contraction: Extension of the head, neck, and trunk and Anterior tilting of the pelvis Unilateral contraction: Lateral flexion of the head, neck, and trunk; Contralateral rotation of the neck and trunk N: Dorsal rami of the cervical, thoracic, and lumbar spinal nerves

Transversospinalis Group Very deep in the back and lie in the laminar groove (over the laminae between the SPs/TPs) In trunk, directly deep to the erector spinae group In neck, deep to trap, SCM, & splenius capitis. Name tells us that this group attaches from TP (transverso) to SP (spinalis). The transverse process attachment is inferior with the spinous process attachment superior. Subdivided, superficial to deep into: semispinalis, multifidus, and rotatores. Semispinalis attaches superiorly to vertebrae 5 or more levels above Multifidus attaches superiorly 2-4 levels Rotatores attach superiorly 1-2 levels. Only multifidus attaches onto pelvis. Only semispinalis attaches onto head. The term paraspinal musculature is used to describe erector spinae and transversospinalis groups.

Semispinalis O: Semispinalis Thoracis: TP’s T6-T10 Semispinalis Cervicis: TP’s T1 – T5 Semispinalis Capitis: TP’s of C7 – T6 and the AP’s of C4 – C6 I: Semispinalis Thoracis: SP’s of C6 – T4 Semispinalis Cervicis: SP’s of C2 – C5 Semispinalis Capitis: Occiput A: Bilateral contraction: Extension of the head, neck, and trunk Unilateral contraction: Lateral flexion of the head, neck, and trunk; Contralateral rotation of the neck and trunk N: Dorsal rami of the cervical, thoracic, and lumbar spinal nerves Palpation: page 240

Multifidus O: Posterior sacrum, PSIS, L5-C4 I: SP’s 2-4 levels superior to inferior attachment A: Bilateral contraction: Extension of the neck and trunk ; Anteriorly tilts the pelvis. Unilateral contraction: Lateral flexion of the neck, and trunk; Contralateral rotation of the neck and trunk; Elevates the pelvis. N: Dorsal rami of the cervical, thoracic, and lumbar spinal nerves Palpation: page 243

Rotatores O: TP’s of the lumbar, thoracic, and cervical vertebrae I: Lamina of the vertebrae one to two levels above A: Bilateral contraction: Extension of the neck and trunk; Unilateral contraction: Contralateral rotation of the neck and trunk N: Dorsal rami of the cervical, thoracic, and lumbar spinal nerves Not palpable

Quadratus Lumborum Refer to as QL Very deep and forms part of posterior abdominal wall Majority deep to erector spinae Must be accessed with palpation from lateral to medial (i.e. come in from the side). Can elevate the pelvis. Often the term “hiking the hip” is used to describe the action.

Quadratus Lumborum O: Rib 12, L1-4 TPs I: Posterior Iliac Crest. A: Bilateral contraction: Extension of trunk; anterior tilting of the pelvis Unilateral contraction: Lateral trunk flexion; “hiking” up of the hip; depression of the 12th rib N: Lumbar plexus Palpation: page 248

Interspinals Paired muscles that are located on either side of the interspinous ligaments between the apices of the SPs of adjacent vertebrae. Located deep to supraspinous ligament (nuchal ligament in cervical region). Not located throughout entire spine. Primarily found in cervical & lumbar regions. May be important at fixating the spine.

Interspinals O: From a SP I: SP directly superior (not well developed or absent in the thoracic spine) A: Extension of neck and trunk N: Dorsal rami of the cervical, thoracic, and lumbar spinal nerves Palpation: page 251

Intertransversarii Located between TPs and very deep. Attach onto anterior tubercles and posterior tubercles of TPs in cervical spine. Do not exist in thoracic region since levator costarum and intercostals take their place. Important as fixators of spine (stabilize)

Intertransversarii O: From a TP of a vertebrae I: TP directly superior (in the thoracic region these muscles are found between T10 and L1) A: Lateral flexion of neck and trunk N: Dorsal rami of the cervical, thoracic, and lumbar spinal nerves Not palpable

Levator Costarum O: TP’s of C7-T11 I: Rib 1-12 (inferiorly) A: Elevation of ribs (primary action). In addition contributes to extension of the trunk when contracting bilaterally and lateral flexion of the trunk when contracting unilaterally N: Dorsal rami of the thoracic spinal nerves Not palpable

Which muscle of the deep spinal group performs rotation? interspinalis intertansversari rotatores deep spinal

Levator Costarum Name tells us that the elevate the ribs Attach from vertebrae TP and run inferolaterally on to rib directly inferior. Controversy as whether they are respiratory muscles that move ribs or move/fixate spinal joints

Subcostales Usually well developed in lower thoracic region. Lie deep to the ribcage and superficial to the plural membrane. Thought to be respiratory muscles which depress the ribs for forced expiration.

Subcostales I: Rib 8-10 O: Ribs 10-12 A: Depression of ribs 8-10 N: Intercostal nerves 8 -11 Not palpable