The Trunk – Axial Skeleton and joints, muscles of the trunk

Learning & Test Objectives

  1. Structural composition of the axial skeleton as a whole and as subdivided units.
  2. Structure of bones individually, ligaments attachments and joints.
  3. Fasciae and compartmentation.
  4. The function of:
    • Vertebral column as a functional unit.
    • Rib cage as a functional unit.  
    • Pelvic diameters and planes.
    • Arrangement of muscles within their functional groups.
  5. Origin and insertion, innervation, and function of muscles, vesseles and nerves of the trunk. 
  6. Topographical spaces of the trunk musculoskeletal system. Abdominal wall, inguinal canal, and herniae.
  7. Identifying and drawing structures observed on cross-sections and radiographs.

Topographical spaces:

  • Abdominal wall layers and rectus sheath
  • Trunk – Trigonum clavipectorale, Spatium intercostale, Diaphragma, Canalis inguinalis, Trigonum suboccipitale – borders and contents
  • Back – Trigonum lumbale superius et inferius – borders only


Description of the test

This test is in written format and follows the general rules of written tests (see Continuous Testing – Organisation).

The test is focused on the bones and joints of the axial skeleton, the origins, insertions, functions, innervations and groups of the muscles of the back, thorax, abdomen and pelvic floor. Apart from the suboccipital muscles, it is not required to know the precise origins and insertions of the deep back muscles (e.g. m. semispinals- O: transvers process; I: spinous process. is sufficient, no need to know the levels as in T6-T10..etc nor which subpart of the transverse and spinous processes). For all other muscles it is required to know the precise origin and insertion, the innervation and function.  Students are required not only to know the individual features of each bone of the axial skeleton (vertebrae, sacrum, ribs and sternum), but also how they are interconnected and how the vertebral column functions as a single unit. The bones of the skull are not included in this test, but the craniovertebral joints are. Other topics in this test include the pelvis, pelvic diameters and planes. The test may also contain questions on general myology, fasciae, the topographic space listed above and various radiological images of the bones and joints of the skull and axial skeleton. Additionally, students are required to know the spinal segments that give rise to the phrenic nerve. 

Radiological images may be tested, hey can be found here.  At the end of the test, students will be required to draw and describe one of the required pictures (see list of required pictures).


Clinical notes

Scoliosis is a sideways curvature of the spine. It occurs most often during the growth spurt just before puberty.

Hyperlordosis and hyperkyphosis are pathological conditions caused by excessive anteroposterior curvatures of the vertebral column. Loss of the natural lower curvature of the spine is called flat back or flat back syndrome.

Vertebrobasilar insufficiency is usually caused by decreased blood flow in the vertebral arteries. This is most commonly due to atherosclerosis, although it may also be caused by disorders of the cervical spine, leading to compression of the vertebral arteries. Vertebrobasilar insufficiency is characterised by a constellation of various symptoms depending on which part of the brain is affected. Symptoms include fatigue, headache, vertigo, tinnitus and unconsciousness.

Fracture of the dens axis with posterior dislocation causes immediate death by compression of the medulla oblongata. This is the mechanical principle of death caused by hanging.

Sandberg projection is an X-ray picture of the dens axis taken from the front with an open mouth.

The dens axis is approached surgically through the posterior pharyngeal wall.

Thoracocentesis (also known as a pleural tap) is performed above the upper edge of a rib in order to prevent injury of intercostal vessels and nerves running in the costal groove.

Coccygeal syndrome is caused by shortening of the muscles that insert on the coccyx. These muscles are the levator ani and the ischiococcygeus.
This leads to a variety of symptoms, some of which develop in other parts of body. Symptoms include premenstrual pain, headache, neck pain and pain during walking.

A sternal puncture is performed by sticking a needle into the bone marrow cavity of the sternum. It is typically used for the diagnosis of haematological disorders.

Single rib fractures may be very painful but usually do not require treatment. Multiple rib fractures lead to a condition called flail chest, which is characterised by paradoxical breathing. In paradoxical breathing, the fracture fragments move in the opposite direction to the normal movements of the chest.
Multiple rib fractures require intensive treatment.

Cervical ribs are an anatomical abnormality occurring unilaterally or bilaterally on vertebra C7.  Although cervical ribs are usually asymptomatic, they may encroach on surrounding structures.

Compression of the brachial plexus and subclavian artery causes thoracic outlet syndrome; a disorder characterized by sensory disturbances in the ipsilateral arm.

Spinal disc herniation occurs when the anulus fibrosus tears and the nucleus pulposis protrudes through the tear. The herniating disc can impinge the spine nerve roots causing radiculopathy.

The descending part of the trapezius may be overloaded by carrying heavy luggage.

Upper crossed syndrome is caused by a muscular imbalance with the accentuated thoracic kyphosis and cervical lordosis (descending part of the trapezius, levator scapulae and sternocleidomastoid, and inferior part of the major pectoralis are shortened; the nuchal muscles, rhomboids and superior part of the major pectoralis are weakened).

The erector spinae is typically overloaded and hypertonic in the thoracolumbar and lumbosacral regions.

Hiccups (singultus) are caused by reflexive contractions of the diaphragm. They can be stopped by post-isometric relaxation of the diaphragm. This can be achieved by elevating the arm while holding the breath in inspiration.

Trigger points in the rectus abdominis are situated just above the pubic symphysis. The rectus abdominis is typically overloaded in its upper part between the xiphoid process and umbilicus. It is usually weakened from the umbilicus to the pubic symphysis. The linea alba may be split in extremely obese patients and in a pregnancy. This is called diastasis.

In the areas where the abdominal wall is thinner it is possible for the abdominal structures to go through (prolapse). Hernia is an outpouching of the parietal peritoneum through a preformed or secondarily established opening. A hernia defect is a canal or ring between the abdominal wall and the hernial sac, formed by the parietal peritoneum and pathological connective tissue. Hernia can contain the intestines, omentum and other abdominal organs.

The direct inguinal hernia passes directly through the medial inguinal fossa (inguinal triangle of Hesselbach) to the superficial inguinal ring. It is an acquired condition and thus is not seen at birth. It is possible to feel the pulse of the inferior epigastric artery laterally to the hernia.

The indirect inguinal hernia passes through the lateral inguinal fossa to the superficial inguinal ring via the inguinal canal. It can be congenital or acquired. It is not possible to feel the pulse of the inferior epigastric artery laterally to the hernia. In men, it may extend into the scrotum, in which case it is called a scrotal hernia.

Other types of herniae: femoral, umbilical, epigastric, obturator, hiatal sliding, etc.


Other interesting points

Kyphoses of the vertebral column are partially developed at birth. Lordoses are formed after birth when the baby activates and fully uses the muscles of the back. This occurs through lifting the head, which forms the cervical lordosis, and by erecting the trunk and walking, which forms the lumbar lordosis.

Abbreviations used for transitions points in the vertebral column:
AO – atlanto-occipital joint
CT – cervicothoracic transition
TL – thoracolumbar transition
LS – lumbosacral transition

Vertebra prominens is the clinical term for vertebra C7. It has an accentuated non-bifurcated spinous process with a spherical end. It is an orientation point used during palpation of the vertebral column.

Accentuated spinous processes can also be found on vertebra C6 and even T1. When palpating spinous processes, the patient's head must be in dorsiflexion. The first palpable vertebra going in a craniocaudal direction is C7. The other cervical spinous processes are not palpable.

We describe rotational movements of the individual vertebrae. However, the term torsion is used for when the whole spine rotates. Torsional movements require the vertebral segments to move in opposite directions to each other.

The rhomboid major and minor are responsible for stabilisation of the cervicothoracic transition. These muscles tend to weaken and it is important to stretch and exercise them together with the pectoral muscles. However, the weak rhomboid muscles often contain painful trigger points.

The erector spinae is a muscular complex alongside the vertebral column which is formed by (in a lateromedial direction): iliocostalis, longissimus and spinalis.

The inguinal ligament is the strengthened caudal margin of the aponeurosis of the external oblique. It is stretched between the superior anterior iliac spine and pubic tubercle.

The pelvic floor muscles work as a one complex unit. They support and protect organs against herniation and work as antagonists of the diaphragm.


Pictures to draw

  • Transverse section of the ventrolateral abdominal wall.
  • Transverse section of the ventrolateral abdominal wall with differences above and below umbilicus.
  • Transverse section of the posterior trunk wall showing the thoracolumbar fascia. 


Radiographical images

Radiolographs of the bone and joints of the axial skeleton

Created: 4. 10. 2017 / Modified: / Responsible person: MUDr. Azzat Al-Redouan