Bones of the Proximal Forelimb and the Shoulder Joint

Evolutionarily, what has happened to the pectoral skeleton and the limbs in domestic species compared to humans? (Cursorial Adaptations)

Cursorial Adaptations - speed or endurance. Most cursorials are either predators or medium - large sized herbivores. 

1.Reduced pectoral skeleton - narrower and deeper

• More cranial/ caudal movement

• Clavicle absent / vestigial (Present in cats)

• Deep, narrow chest

2.Elongation at proximal end of limb

• Scapula lies lateral and vertical

3.Elongation at distal end of limb

• long metacarpals, walk on toes or

• hooves (increased leg length)

Describe the main regions of the forelimb.

Omo (shoulder)

Brachium (arm) - from shoulder to elbow

Antebrachium (forearm) - from elbow to carpus

Carpus (wrist)

Manus (hand) - distal to carpus

Digit (toe)

How is the scapula oriented in domestics?

• Why is it orientated this way?

• How is it attached to the rest of the musculoskeletal system?

• Vertical orientation

  • Shoulder joint relatively lower in limb

  • Increases limb length → increasing stride length → more ground covered

  • Restricted lateral movement (abduction/adduction)

• Absent / vestigial clavicle

• Muscular attachment between forelimb & trunk

What lateral surfaces of the scapula are palpable?

Lateral surface:

• Dorsal border - palpable

• Cranial border - palpable

• Caudal border - difficult to palpate / not palpable

• beneath muscle

• Scapular spine - palpable, divides scapula into two portions

• Supraspinous fossa

• Infraspinous fossa

• Acromion process - palpable

• Guide for location of shoulder joint

What key features and attachment sites are found on the ventral and lateral aspects of the scapula?

Ventral surface:

• Glenoid cavity :

• Concave

• smooth subchondral / articular surface for shoulder joint

• Supraglenoid tubercle

• Attachment of biceps brachii muscle

What structures are found on the medial / costal surface of the scapula?

• Flat - scapular glide (Scapula gliding across the surface of the rib-cage)

• Rough bone - muscle attachment

  • Serratus ventralis muscle (dorsal)

  • Subscapularis muscle (ventral)

How does the scapula in a cat compare to a dog?

Cats:

• More rounded cranial angle than dog

• Suprahamate process

• proximal to acromion process

How does the scapula appear in large species?

Large species:

• Tuber on spine

• Cartilage extension to dorsal border

• Horse specifically does not have acromnion process

What are the centers of ossification in the scapula?

• What potential issue may result?

• 2 centres of ossification:

• Body

• Supraglenoid tubercle

Potential issue:

- origin of tendon of biceps brachii m.

- Physis weak point = avulsion fracture - as it is near the growth plates

What are key features of the proximal end of the humerus?

• Describe the surface of the head and any tubercules

• Head

• articular surface, convex and smooth surface (for shoulder joint)

• articulates with glenoid cavity of scapula

• Greater tubercle - palpable (lateral)

• Location of shoulder joint, palpation can help locate

• Lesser tubercle (medial)

• Intertubercular groove (Between the tubercles)

• Passage of biceps tendon through it

• Smooth surface

What structures are found on the distal end of the humerus?

• Distal end called the condyle

• Medial epicondyle (ME) - palpable

• Lateral epicondyle (LE)- palpable

• Trochlea *

• Is a central depression

• Is a smooth articular surface for elbow joint

• Ulnar / olecranon fossa

• Caudal aspect

• Radial fossa

• Cranial aspect

• Supratrochlear foramen:

• Nothing passes through, it is a mechanical foramen, in some dogs it provides a hook or stability to elbow joint

• May not be present in short legged (chondrodystrophic) dogs

• Absent in larger species eg. horse

Is the supratrochlear foramen present in cats?

NO

• No supratrochlear foramen, instead have Supracondyloid foramen

• Brachial artery & median nerve pass through

• Vulnerable in fractures

What are the areas of ossification in the humerus?

Development:

• 5 Centres of ossification:

• Proximal epiphyses

• Body

• Condyle:

• Medial epicondyle

• Medial half

• Lateral half

Describe the anatomic location of the shoulder joint capsule or bicipital bursa.

• What ligaments holds the tendon of the bicep in place

• Forms part of joint capsule extends into intertubercular groove which envelopes the tendon, contains fluid and protects it from wear and tear

• between greater & lesser tubercles

• Wraps around tendon of origin of Biceps brachii

• (originates on supraglenoid tubercle)

• Tendon held in place by Transverse ligament

What are the main lateral support muscles in the shoulder joint?

• Note Origin

• Insertion

• Nerve supply

• Lateral support:

• Supraspinatous muscle *

• O= Supraspinous fossa

• Infraspinatous muscle +

• O = Infraspinous fossa

• | = proximal lateral humerus

• Nerve supply = suprascapular nerve

What are the main medial support muscles in the shoulder joint?

• Note Origin

• Insertion

• Nerve supply

• Medial support:

• Subscapularis muscle X

• O = Subscapular fossa

• I = proximal medial humerus

• Nerve supply = subscapular nerve

How is skeletal muscle arranged?

How do they usually originate and insert?

• Fibres arranged in parallel bundles

• Encased in fibrous tissue

• Attached to rigid structures - usually bone

• Origin - usually proximal

• Insertion - usually distal

How do muscles attach to bones?

Attachments:

• Directly to bone

• Rough surface area

• Bony bumps / tubercles

• Via aponeurosis

• Sheets of fibrous tissue

• Areas of restricted access

• Via tendons

What are the functions of muscle, how do they work when movement occurs?

• Muscle fibres contract - muscle belly shortens

• Points of attachment pulled closer together

• Effect depends on location of origin & insertion

What does antagonistic pairs mean?

opposite actions

Action of muscles depends on what factors?

• Action depends on:

• Specific joints) crossed

• Aspect of joints) crossed

• Note: a muscle has no effect on a joint if it doesn't cross it!

Reminder** Where do extrinsic muscles originate and insert?

• What four movements of the limb relative to the trunk can occur?

• Origin on axial skeleton

• Insertion in appendicular skeleton

• Movement of limb relative to trunk:

• Protraction (limb moves cranially)

• Retraction (limb moves caudally)

• Adduction (medially)

• Abduction (laterally)

Reminder** Where do intrinsic muscles originate and insert?

• What movements can occur here?

• Origin & insertion within appendicular skeleton

• Movement limited to within limb

• Flexion / Extension

• Rotation

• Flexion - reduced flexor angle

• non weight bearing position

• Extension - increased flexor angle

• weight bearing position

What is the origin and insertion of the brachiocephalic muscle?

• What is its movement function?

• Origin = cervical vertebrae & skull

• Insertion = humerus

• Located cranial to the limb

• Forelimb PROTRACTOR

• Shoulder EXTENSOR

What species is the clavicle present in and what does it allow in a diagnostic setting?

• Clavicle

• Bony remnant in muscle cranial to shoulder

• Present in cats

• Absent in dogs

• Allows differentiation on radiographs

What is the origin and insertion of the latissimus dorsi?

• Origin = thoracic vertebrae

• Insertion = humerus

• Located caudal to the limb

• Function:

• Forelimb RETRACTOR

• Also propulsion

• Shoulder FLEXOR

What are the origins and insertions of the serratus ventralis muscle?

• As well as its functions

• Origins:

• Thoracic wall (ribs)

• Cervical vertebrae

Insertions

• proximal scapula (medial aspect) - proximal to pivotal point, which is the region where the scapula can rotate

• Located between forelimb and trunk

• Function (relating to locomotion):

• Cranial portion (black arrows)- Protracts

• Caudal portion (orange arrows) - Retracts

What are the origins and insertions of the trapezius muscle?

• As well as its functions

• Origin = cervical & thoracic vertebrae

• Insertion = proximal scapular spine

• 2 parts - cranial and caudal

• Located proximal to limb

• Proximal to pivotal point

• Function :

• ABDUCTION of the limb

• ( Also protraction)

What are the origin and insertion points of the pectoral muscles?

• What about the function?

Pectoral muscles

• Origin = sternum

• Insertion = humerus

• Two heads: Deep & superficial groups

• Located medial to limb

• Distal to pivotal point

• Function:

• ADDUCTION of the limb

Which forelimb muscles are innervated by the brachial plexus?

• Which are not?

• NOT = brachiocephalic and trapezius

Are innervated

• Latissimus dorsi

• Serratus ventralis

• Pectoralis