Axial Skeleton

Question 1

How is the musculoskeletal system assessed in a clinical examination?

Answer 1

• Observation – lame? Cause of lameness? Describe it?
• Palpation – pain, heat or swelling? Where? Muscle wastage? Group of muscles? Why? Consequence of this?
• Manipulation – range in motion, what joint is affected? What part of the joint? Why?
• Mechanical tests and clinical imaging – cranial drawer test, tibial thrust test and ortolani test. Radiography, ultrasonography, MRI and CT.

Question 2

What are some examples of active muscle control?

Answer 2

Muscles to maintain body posture = antigravity extensor muscles of the limbs and spine.

To move limb joints = flexor and extensor muscles

To move jaw = muscles of mastication/trigeminal muscles

Shape the lips = muscles of facial expression

Move food into GI tract = palatine and pharyngeal muscles

Support abdominal organs = abdominal muscles

Question 3

What is biomechanics?

Answer 3

The study of the mechanical laws relating to the movement or structure of living organisms. Forces loads and levers. Application of basic biomechanical principles is fundamental to understanding the function of the locomotor system.

Question 4

Describe the function of levers in biomechanics.

Answer 4

Muscles can only deliver so much force and levers can change the force required to move a set mass, or can increase the speed of movement for a given force, they do this by altering the lengths of the lever arms.

Question 5

Describe the function of muscle distribution in biomechanics.

Answer 5

More muscle mass is found proximally, as proximal muscles tend to be larger, better adapted to more powerful movements and have longer fascicles. Distal muscles tend to be smaller and better adapted to develop force and have shorter fascicles and longer tendons, which store elastic energy or pulling on distal structure to help decrease mass in the distal limb.

Question 6

Describe the function of tendons in biomechanics.

Answer 6

Tendons that act as strings tend to be thinner relative to length and tendons that act as springs tend to be thicker relative to length. Spring tendons have greater elastic components and for them to act like springs the attached muscle fibres need to develop force so that the tendon can be stretched. Reduced muscle fibre content reduces this need for energy.

Question 7

Describe the 2 ends of a muscle attachment.

Answer 7

Origin - typically proximal and generally moves less

Insertion - typically distal and generally moves more

Question 8

Define translation.

Answer 8

Moving 2 structures relative to one another across a plane.

Question 9

Define varus and valgus.

Answer 9

Varus – 2 distal structures are more medially placed than a more proximal structure.

Valgus – 2 distal structures are more laterally placed than a more proximal structure.

Question 10

Define luxation and subluxation.

Answer 10

Luxation or subluxation describe versions of dislocations. Subluxation means a smaller dislocation.

Question 11

Define avulsion.

Answer 11

Avulsion fractures are when a piece of bone has broken away from a larger bone structure. Happens when a muscle and a tendon have pulled on that piece of bone on that insertion point.

Question 12

Define transection.

Answer 12

Describes how you would cut across bone or muscle in surgery or dissection

Question 13

What are the 4 functions of the vertebral column?

Answer 13

• Provide support to body weight
• Allow force transfer
• Be flexible to allow movement
• Protect the spinal cord and nerves

Question 14

What is the structure of intervertebral discs?

Answer 14

• Round discs of tissue that sit between the bodies of the vertebrae
• Has an annulus fibrosis tough ring and a nucleus pulposus soft centre. Annulus is thinner dorsally
• Fibrocartilaginous

Question 15

What is the function of intervertebral discs?

Answer 15

Provides most stability of all support structures by resisting compression and absorbing shock.

Most common cause of spinal problems in dogs.

Question 16

What are articular facet joints and their function?

Answer 16

Articular facet joints in between individual bones. They are synovial joints that can get osteoarthritis and cause chord/spinal compression.

Question 17

What are flaval ligaments and their function?

Answer 17

Flaval ligaments are yellow and sit between facet joints. They are very elastic and help return the vertebral column to the neutral position after flexion.

Question 18

What are supraspinous ligaments and their function?

Answer 18

Run all the way along. They resist hyper flexion of the vertebral column and run lumber to thoracic and continues as the nuchal ligament.

Question 19

What are dorsal longitudinal ligaments and their function?

Answer 19

Dorsal longitudinal ligaments are dorsal to the bodies of the vertebrae and resist hyper flexion.

Question 20

What are ventral longitudinal ligaments and their function?

Answer 20

Ventral longitudinal ligaments are ventral to the bodies of the vertebrae and resist hyper extension.

Question 21

What is intervertebral disc extrusion?

Answer 21

Intercalated discs have annulus fibrosis that is thinner dorsally than ventrally so if the nucleus pulposus becomes herniated out of the intervertebral disc, it will likely escape dorsally and put pressure on the spinal cord in an intervertebral disc extrusion. This could have effects on the signals running to and from the brain.

Question 22

What are intercapital ligaments and their function?

Answer 22

Links the heads of rib pairs ventral to the spinal cord and dorsal to the intervertebral discs (tether rib pairs together dorsally).

Their presence from T2-10 makes discs extrusion uncommon in this region.

Question 23

Describe epaxial musculature and their function.

Answer 23

• Musculature on the dorsal aspect of the transverse processes
• Extension of the spine or lateral movement if engaged on one side
• Dorsal branches of spinal nerves
• 3 parallel columns

Question 24

Describe the hypaxial musculature and their function.

Answer 24

• Ventral to the transverse processes
• Flexion of the spine
• Ventral branches of spinal nerves
• Includes thoracic and abdominal wall musculature
• Also called sublumbar muscles in lumbar region

Question 25

Why can radiographs not be used to view the spinal cord?

Answer 25

Bone is radio opaque and appears white on radiographs. Soft tissues are less radio dense and appear grey. The bones of the spinal column can be visualised on plain radiographs but the spinal cord cannot.

Question 26

What imaging modalities can be used to assess conditions of the spine?

Answer 26

Myelography
MRI
CT

Question 27

Describe myelography.

Answer 27

An imaging technique that shows the passage of contrast medium in the subarachnoid space highlighting the spinal cord. Requires aseptic injection of contrast media under general anaesthesia.

It has now largely been replaced by MRI.

Question 28

How does an MRI work?

Answer 28

• Hydrogen/protons of water molecules in the body have a charge and a magnetic field.
• When in an MRI, magnetic fields align protons in the same direction.
• Short bursts of radio waves are sent to certain area of the body, knocking protons out of alignment.
• When the radio waves are turned off, the protons realign. This sends out radio signals, which are picked up by receives.
• A computer can generate a picture which distinguish between the various types of tissue in the body, because the protons in the different types of tissue realign at different speeds and produce distinct signals.

Question 29

What is intervertebral disc disease?

Answer 29

IVDD result in reduced shock-absorbing ability and often leads to disc herniation and subsequent spinal cord compression.

Question 30

Name the bony landmarks of the body.

Answer 30

Tuber sacrale
Tuber coxae
Tuber ischium
Calcaneus
Xiphoid
Olecranon
Manubrium

Question 31

What action do epaxial muscles have on the spinal column when they contract bilaterally?

Answer 31

Extend the spine.

Question 32

What action do hypaxial muscles have on the spinal column when they contract bilaterally?

Answer 32

Flexion of the spine.

Question 33

In relation to the spinal cord, where does the dorsal longitudinal ligament lie?

Answer 33

Ventral.

Dorsal longitudinal ligament refers to its location in relation to the vertebral body, which sits ventral to the spinal cord, and so lies ventral to the spinal cord.

Question 34

Describe the cranial cervical vertebrae.

Answer 34

Specialised for attachments to the head (atlas) ad rotational movement (axis).

Question 35

Describe the caudal cervical vertebrae.

Answer 35

Have a short dorsal spinous process and include modified transverse processes and transverse foraminae lateral to the vertebral foramen which allow passage of the vertebral arteries.

Question 36

Describe the thoracic vertebrae.

Answer 36

Have elongated dorsal spinal processes and modified/almost absent transverse processes to facilitate the attachment of the ribs. These transverse processes are adapted to form an articulation with the tubercle of the rib. Ther vertebral body of the thoracic vertebrae have indentations both caudal and cranial, called the cranial and caudal costal foveas, to allow the head of the rib to articulate with the intervertebral space.

Question 37

Describe the lumbar vertebrae.

Answer 37

Have moderate dorsal spinous processes and no costal foveas or transverse foraminae.

Question 38

Describe the sacral vertebrae.

Answer 38

Are fused in the dog to form the sacrum and form a trapezoidal shaped bone with a narrowing vertebral foramen and segmental spinal foramen laterally for the segmental spinal nerves.

Question 39

Describe the coccygeal vertebrae.

Answer 39

Are smaller narrow tubular vertebrae with short vertebral processes which become more simple with no vertebral foramen or processes towards the caudal tip of the tail.

Question 40

What type of joint is the intervertebral disc referred to as?

Answer 40

Fibrocartilagenous

Question 41

What is the name of the process of ossification in foetal long bones?

Answer 41

Endochondral ossification