Canine Forelimb Flashcards
What are the basic functions of the canine forelimb?
- Bodyweight support for cranially positioned structures – anything in the thoracic region, head and neck.
- Involved in locomotion, particularly in directional control
- Object manipulation
Briefly state the innervation and supply to the canine forelimb.
- Innervation via structures of the brachial plexus
- Arterial supply via the axillary artery
- Venous drainage mainly via the external jugular vein
Describe the neurological input to the brachial plexus.
- Spinal nerves C6-T2
- Nerve roots converge and then diverge to innervate specific areas of the limb
- Complex neurological structure found in the axillary region
What are brachial plexus avulsion injuries?
When the forelimb has been pulled further away from the body than it normally would be, which damages and stretched out the structures of the brachial plexus and neurological inputs are prevented from coming through these nerves.
Name 6 important nerves of the brachial plexus.
Subscapular
Suprascapular
Musculocutaneous Axillary
Median
Ulnar
Radial
What is the location of the radial nerve?
Extends the elbow, carpus and digits. Runs caudomedially to humerus and then wraps cranially over brachialis to extensor muscles of cranial antebrachium.
Can be identified running medial to lateral between accessory head of triceps and brachialis.
What is the function of the radial nerve?
Important for weightbearing anti-gravity muscles.
What does the median nerve supply?
Provides sensory innervation to the palmaromedial paw
What does the ulnar nerve supply?
Provides sensory innervation to the caudal antebrachium, palmar paw and the lateral side of the 5th digit
What is similar between the radial and ulnar nerves?
Both median and ulnar nerves have the same motor innervation and provide all carpal and digital flexion supply to carpal and digital flexion muscles.
Define autonomous sensory zones.
The areas in the limb where only 1 nerve is supplying that region, there is no overlap of other nerves. Which means, if an animal is unable to feel in that region, there is a problem with the sensory nerve from that particular nerve.
State the autonomous sensory zones of the radial, ulnar and median nerves.
Radial – craniolateral antebrachium and dorsal paw
Ulnar – caudal antebrachium, palmarolateral paw and lateral 5th digit
Median – palmaromedial paw
Describe the blood supply to the canine forelimb.
- Axillary artery comes in through the axilla
- Branches to give off thoracodorsal artery
- Then becomes the brachial artery in the upper part of the limb
- Branches into ulnar and median arteries
- Also branches into an interosseous branch, which runs between the 2 distal limb bones of the limb
- Median artery branches to the palmar arteries just distal to the accessory carpal
Where can a palpable pulse be felt in the distal forelimb? Why is this important?
Median artery branches to the palmar arteries just distal to the accessory carpal and is a region where you can find a palpable pulse in the distal limb of the dog.
Peripheral pulses are important for checking peripheral circulation and patient monitoring.
Describe the venous drainage of the forelimb.
- Some blood returned to the body via the axillary vein but the majority of blood return is via the cephalic vein
- Cephalic vein runs up the dorsal side of the limb and is joined by venous return from the medial veins more palmarly via the median cubital vein, which crosses across the elbow joint
- Cephalic vein into the external jugular vein
Cephalic and accessory cephalic veins are important clinically for venepuncture in dogs and cats.
What is synsarcosis?
Forelimb is attached to the body by synsarcosis, a muscular sling supporting the torso between the forelimbs. If laid down and forelimbs where extended and straight, muscles such as the serratus ventralis would allow the ribcage to be sort of sling.
Why is synsarcosis useful?
Synsarcosis is useful in locomotion, as it allows craniocaudal translation across the thorax. Along with spinal extension and flexion, increases stride length in locomotion.
Distinguish extrinsic and intrinsic muscles.
Extrinsic muscles attach the limb to the body
Muscles with origin and insertion within the limb are intrinsic
Name the extrinsic musculature of the forelimb.
Trapezius
Omotransversarius
Brachiocephalicus
Latissimus dorsi
Pectorals
Describe the structure and function of trapezius.
Large triangular shaped muscles, 2 bellies, one cranially and one caudally. These attach from the scapula spine to cervical midline cranially and thoracic dorsal midline caudally.
Describe the position of omotransversarius.
Runs from distal scapula spine to transverse processes of C1-C2.
Describe the structure of brachiocephalicus.
Runs between the arm and head. Split into 2 portions at the clavicular intersection, the area where a clavicle would be if the animal had it and where you may find a vestigial clavicle, particularly on feline radiographs. 2 parts:
- Cleidobrachialis – goes to the arm
- Cleidocephalicus – going from the clavicular intersection to the head
Describe the structure and position of latissimus dorsi.
Large fan shaped muscle from teres major tuberosity on caudal humerus to the thoracolumbar fascia and last 2-3 ribs.
Describe the position of the pectorals.
Across the thorax more ventrally.
- Superficial pectoral – runs from 1st 2-3 sternebrae to the great tubercle of the humerus
- Deep pectoral – runs from lesser tubercle and brachial fascia
Name the deep extrinsic musculature of the forelimb.
Rhomboideus
Serratus ventralis
Describe the position and function of the rhomboideus.
Dorsal midline, and the capital, cervical and thoracic regions, to the proximomedial border of the scapula.
Holds scapula against the body wall.
Describe the position and function of the serratus ventralis.
Lateral thoracic wall/neck ventrally to the medial surface of the scapula and acts as a sling for the limb.
What is the function of the glenohumeral joint?
Primarily acts in flexion and extension. Minimal abduction and adduction.
What is the structure of the glenohumeral joint?
- Joint capsule supported by lateral and medial glenohumeral ligaments
- Medial is larger and y-shaped muscles provide significant support
What happens when the glenohumeral joint is torn?
Helps to keep abduction of limb to 25 degrees. When torn, abduction can get to around 70 degrees.
What do the muscles that act on the glenohumeral joint do?
- Provide support laterally and medially
- Have flexors caudally
- Have extensors cranially
Describe the muscles of broad scapula origin.
Lateral support superior to the spine from the supraspinatus and inferior to the spine, from the infraspinatus.
Medial support from the subscapularis. In some dissections and diagrams, you may see the coracobrachialis, which is functionally insignificant.
Describe the muscles of broad scapula origin.
Lateral support superior to the spine from the supraspinatus and inferior to the spine, from the infraspinatus.
Medial support from the subscapularis. In some dissections and diagrams, you may see the coracobrachialis, which is functionally insignificant.
Describe the muscles of broad scapula origin’s innervation.
Supplied by nerves in the brachial plexus: lateral by suprascapular nerve and medial by subscapular nerve.
Name and describe the 2 shoulder flexors.
Deltoideus – lateral and has 2 heads, superficial to the infraspinatus. Acromion and scapular spine to deltoid tuberosity.
Teres major – medial. Caudal scapular margin to medial humeral diaphysis.
Both supplied by axillary nerve from brachial plexus.
Describe the structure of the biceps brachii.
- Origin on supraglenoid tubercle, insertion on proximal radius and ulna
- Proximal tendon prone to tendon strains
- Bi-articular muscle – crosses 2 joints and can move both of them
What is the function of the biceps brachii?
Minimal action in shoulder extension, primary action is elbow flexion.
What is the similarity between supraspinatus and biceps brachii?
Supraspinatus is also a weak shoulder extensor.
Both flexors of the elbow so are innervated by musculocutaneous nerve.
What is the function of the canine elbow joint?
- Hinge joint for flexion and extension
- Limited pronation and supination
Most common forelimb joint involved in canine lameness
What are the 3 ligaments that support the canine elbow joint?
Lateral collateral – lateral epicondyle to lateral radial head and lateral ulna
Medial collateral – medial epicondyle to medial radial head
Annular – encircles radial head and attached to the coronoid process
What are the 3 main articulation in the canine elbow joint?
- Humeroradial – bears most weight
- Humeroulnar – resists lateral movement
- Proximal radioulnar – allows rotational movement of antebrachium
How can the canine elbow joint be divided into compartments?
All 1 synovial space. Can be divided into medial and lateral compartments by trochlear notch. The medial compartment is the most problematic as many things can happen to the medial coronoid process.
What are the 3 main areas of elbow joint incongruence?
- Trochlear notch misshapen doesn’t fit the humeral trochlea
- Radius/ulna length discrepancy
- Radial incisure – radius and ulna do not fit together neatly
What happens when an incongruency occurs at the canine elbow?
Coronoid process sticks out and so is likely to get damaged when humerus moves through flexion and extension. Medial coronoid process is prone to problems due to an un-equal load sharing between radius and ulna due to incongruency. Leads to:
- Stress fractures of medial coronoid process
- Osteochondrosis dissecans of humeral head
- Lameness
- Leading cause of elbow osteoarthritis
What occurs in elbow osteoarthritis?
Wear and damage to the articular cartilage, replacement with fibrocartilage. Production of osteophytes. Increased joint fluid volumes and increased water content.
Name the 2 elbow extensors.
Triceps brachii
Anconeus
Describe the structure of triceps brachii.
4 heads, all insert on olecranon
- Long – caudal scapula
- Lateral – lateral humerus
- Accessory – neck of humerus
- Medial – medial humerus
What is the structure and function of anconeus?
Olecranon to lateral condylar ridge. Supports elbow joint.
Rank each level of the carpus in its range of motion.
Antebrachiocarpal joint – greatest
Intercarpal – moderate
Carpometacarpal – minimal
Which joint spaces of the carpus communicate?
Intercarpal and carpometacarpal
Name the ligaments of the carpus.
Medial collateral ligament
Short dorsal carpal ligaments
Lateral collateral ligament
Flexor carpi ulnaris tendon
Distal accessory carpal ligaments
What is the palmar carpal fibrocartilage and its function?
A big smooth sheet of fibrocartilage that helps keep things in place and is smooth to allow muscles and tendons to slide over it.
What are the characteristics of the muscles of the craniolateral antebrachium?
- All originate on the lateral humeral epicondyle/ridge
- All innervated by radial nerve
- Mostly extensors
Name the craniolateral muscles of the antebrachium.
Ulnaris lateralis - carpal flexor and abductor
Lateral digital extensor
Common digital extensor
Extensor carpi radialis
What are the characteristics of the caudomedial muscles?
All originate on the medial humeral epicondyle, at least in part
Innervated by the median and ulnar nerve
Name the 4 caudomedial muscles and their insertions.
Flexor carpi ulnaris – 2 heads and inserts on the accessory carpal bone
Superficial digital flexor – inserts on the 2nd digital phalanx of the digits
Deep digital flexor – 3 heads and inserts on 3rd digital phalanx of the digits
Flexor carpi radialis – inserts of radial side of the carpus
Name the 3 rotator muscles.
Supinator
Pronator teres
Abductor pollicis longus
What is the position and innervation of the supinator muscle?
Lateral humeral epicondyle to radius. Innervated by radial nerve (as do all that attach to LHE)
What is the position and innervation of the pronator teres?
Medial humeral epicondyle to radius. Innervated by median nerve (as so all that attach to MHE)
What is the position and innervation of the abductor pollicis longus?
Lateral ulna to medial digit I. Tendon runs over extensor carpi radialis tendon distally, only for abduction of 1st digit (pollux)
Describe digital extensors at the carpus.
- Common digital extensor tendons sits in the extensor groove on lateral craniodistal radius
- Lateral digital extensor sits between radius and ulna at level of radio-carpal joint
- Extensor retinaculum restrains tendons
- Arthrocentesis between tendons
Describe the dorsal digital extensors at the phalanges.
- The tendons of the common and lateral digital extensors fuse prior to insertion on the 3rd distal phalanx of their respective digit.
- Canine P2-3 has elastic ligament to partially retract the claw
- Felines have paired dorsal elastic ligaments for full claws retraction
Describe the structure of the flexor tendons in the palmar foot, the manica flexoria.
- Superficial digital flexor tendon inserts on P2
- Deep digital flexor tendon inserts on P3
- Superficial and deep digital flexors held up against the bone by flexor retinaculum to stop them going out
- SDFT makes a tube through which DDFT runs
- SDFT splits and inserts as 2 slips on each P2 and DDFT becomes visible between the 2 slips
- More fine motor control as a result
Describe the digital palmar muscles.
- Interosseous muscles for balance and object manipulation
- Proximal palmar metacarpal to proximal P1 of each digit
- Paired sesamoids distally over metacarpophalangeal joints – allow for superficial and deep digital flexor tendons to run between sesamoids in a groove, so they are not crushed when an animal puts weight on the ground.
- Significantly modified in the horse
Describe the canine digital pads.
Thickened, cornified epithelium is highly keratinised and resists abrasion and prevents the skin on palmar surface wearing away.
Fatty pad of subcutaneous has increased elastic and collagenous fibre for shock absorption to prevent damage to digits and modulate forces up the limbs.
What is elbow arthroscopy?
Another form of diagnostic imaging that can also serve as treatment. The joints and cartilage surfaces can be assessed for disease whilst also removing damaged fragments which cause pain.
Which muscles form the synsarcosis?
Serratus ventralis
Trapezius
Rhomboideus
Pectoral muscles
Which nerve innervates the muscles which flex the digits?
Median/ulnar nerves
What nerve is affected is cutaneous sensation to the medial aspect of the canine antebrachium is deficient?
Musculocutaneous
If a dog is unable to extend its carpus or digits, what nerves are likely to be affected?
Radial nerve
It innervates the carpal and digital extensor and innervates the elbow extensors making it very important for weight bearing.
