Difference between revisions of "Canine Forelimb - Anatomy & Physiology"

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<big><center>[[Musculoskeletal System - Anatomy & Physiology|'''BACK TO MUSCULOSKELETAL ANATOMY AND PHYSIOLOGY''']]</center></big>
 +
<big><center>[[Forelimb - Anatomy & Physiology|'''BACK TO FORELIMB''']]</center></big>
 +
 
 
==Structures of the Proximal Forelimb and Shoulder==
 
==Structures of the Proximal Forelimb and Shoulder==
  
−
===[[Forelimb - Anatomy & Physiology#Scapula|Scapula]]===
+
===Scapula===
  
−
The Scapula forms the basis of the shoulder region, providing points of attachment of extrinsic and intrinsic muscles. It is held in place by a synsarcosis of muscles and does not form a conventional articulation with the trunk. The spine culminates in the '''acromion'''. The scapular cartilage is comprised of only a very narrow rim.
+
The Scapula forms the basis of the shoulder region, providing points of attachment of extrinsic and intrinsic muscles. It is held in place by a synsarcosis of muscles and does not form a conventional articulation with the trunk.
 +
*The spine culminates in the '''acromion'''.
 +
*The articular surface of the glenoid cavity and continues round onto the supraglenoid tubercle.
 +
*The scapular cartilage comprises of only a very narrow rim.
  
−
===[[Forelimb - Anatomy & Physiology#Clavicle|Clavicle]]===
+
===Clavicle===
  
−
In the cat, a remnant of bone may remain embedded in the fibrous intersection in the brachiocephalicus, which may prove misleading in radiographic images.
+
In the dog and cat, a remnant of bone may remain embedded in the fibrous intersection in the brachiocephalicus, which may prove misleading in radiographic images.
  
−
===[[Forelimb - Anatomy & Physiology#Humerus|Humerus]]===
+
===Humerus===
  
−
The Humerus is the long bone of the forearm, articulating with the scapula to form the shoulder and the radius and ulna to form the elbow. In situ, it lies obliquely along the ventral thorax and is more horizontal in larger species. The greater tubercle is not separated into two parts like in other species. In dogs and cats, it articulates with the ulna medially via a '''trochlea''' and the radius laterally via a '''capitulum'''.
+
The Humerus is the long bone of the forearm, articulating with the scapula to form the shoulder and the radius and ulna to form the elbow. In situ, it lies obliquely along the ventral thorax and is more horizontal in larger species.
  
−
===[[Forelimb - Anatomy & Physiology#Radius|Radius]]===
+
*The greater tubercle is not seperated into two parts like in other species
 +
*In dogs and cats, it articulates with the radius medially via a trochlea and the ulna laterally via a '''capitulum'''
  
−
A radial tuberosity provides a site of attachment for brachialis and biceps brachii mm. This roughened area is very variable in size in dogs and can be non-existent.
+
===Radius===
  
−
===[[Forelimb - Anatomy & Physiology#Ulna|Ulna]]===
+
*A radial tuberosity provides a site of attachment for brachialis and biceps brachii. This roughened area is very variable in size in dogs and can be non-exsistent.
  
−
The ulna shaft tapers distally, lying oblique to the radius, i.e. the proximal end lies medial and the distal end lateral to the radius. There is a distinct gap between it and the radius, which is filled by the pronator quadratus muscle. The distal styloid process is blunt and articulates with the ulnar carpal bone, accessory carpal bone and ulnar notch of the radius.
+
===Ulna===
 +
 
 +
The Ulna's greatest contribution to functional anatomy is in the formation of the '''Olecranon''', or the point of the elbow, which gives rise to the attachment of the '''triceps'''. The olecranon articulates with the humerus via its anconeal process.  Distally (where unfused), the '''lateral styloid process''' articulates with the '''ulnar carpal bone'''.
  
 
==Joints of the Proximal Forelimb==
 
==Joints of the Proximal Forelimb==
−
===[[Forelimb - Anatomy & Physiology#Shoulder Joint|Shoulder Joint]]===
+
===Shoulder Joint===
−
 
 
−
The joint capsule barely extends past the areas of articulation, except where it continues distally into the intertubercular groove of the humerus. This provides cushioning and synovial support for the bicipital tendon. The bicipital tendon and the joint capsule pouch are held in place by the '''transverse humeral retinaculum''', which lies between the greater and lesser tubercles of the humerus.
 
  
−
===[[Forelimb - Anatomy & Physiology#Elbow Joint|Elbow Joint]]===
+
The shoulder joint links the humerus and the scapula at the '''glenoid cavity''', which is much smaller than the head of the humerus.  While structually it is a [[Joints - Anatomy & Physiology#Types of Joints|'''ball and socket''']] joint, it functions as a [[Joints - Anatomy & Physiology#Types of Joints|'''hinge joint''']] due to extensive muscling around the articulation.  The joint capsule is enlarged and extends under the tendon of the biceps, acting as a synovial sheath to protect the tendon.
  
−
The radius articulates with the capitulum and lateral trochlear surface of the humeral condyle. Whilst the medial part articulates with the trochlear notch of the ulna. To allow the radius to rotate slightly the radial head has a marginal band of cartilage making the articular circumference. It faces the radial notch of the ulna between the medial and lateral coronoid processes. The joint capsule runs from just proximal to the articular surface of the condyle of the humerus to the periphery of the olecranon fossa; it pouches between the ulna and radius, and under the tendinous attachments of some muscles.
+
===Elbow Joint===
  
−
'''Collateral ligaments''' are paired and lie medially and laterally. They both attach proximally to the epicondyle and distally to the tuberosities of the radius and ulna.
+
Movement of the elbow joint is restricted to the [[Planes and Axes - Anatomy & Physiology|sagittal plane]].  It is bounded medially and laterally by collateral ligaments betweek the humerus and radius, caudally by the olecranon ligament between the humerus and olecranon, and further enforced by the annular radial ligament.  The elbow is a compound joint including:
 +
*The [[Joints - Anatomy & Physiology#Types of Joints|'''hinge joint''']] between the humerus and the radius and ulna
 +
*The [[Joints - Anatomy & Physiology#Types of Joints|'''pivot joint''']] between the radius and ulna
 +
*The point of the elbow, or the '''olecranon''' is formed by the anconeal process of the ulna inserting into the olecranon fossa of the humerus
  
−
'''Annular ligament''' of the radius attaches to the sides of the coronoid process of the ulna. This runs deep to the collateral ligaments and forms a ring for the radial head to turn in during pronation and supination.
 
  
−
The radius and ulna are joined mid-shaft by the '''interosseous ligament''', the remainder is filled by the interosseous membrane.
 
  
 
==Structures of the Distal Forelimb==
 
==Structures of the Distal Forelimb==
  
−
===[[Forelimb - Anatomy & Physiology#Carpal bones|Carpal Bones]]===
+
===Carpal bones===
  
 
Carpal bones comprise two rows:
 
Carpal bones comprise two rows:
 +
*Proximally, (mediolaterally), radial, intermediate, ulnar and accessory bones
 +
**The accessory bone serves as a landmark for palpation
 +
*Distally, bones are numbered 1-5, though 5 is always fused with 4
 +
*A small [[Bones and Cartilage - Anatomy & Physiology#Types of Bone|'''sesamoid''']] bone embedded in the medial tissues of the joint can sometimes be mistaken as a chip fracture
 +
 +
===Metacarpal bones===
  
−
Proximally - the radial and intermediate bones are fused to form the '''radial''' carpal bone. The accessory carpal bone articulates with both the ulnar carpal bone and the distal ulna.
+
The number of metacarpals varies widely among species, as the demand for their function changes: '''plantigrade''', or flat-footed, animals requiring the full complement of five metacarpal bones; the number is reduced in the upright stature of '''digitigrade''' animals such as the dog and cat, and shows the extreme in '''unguligrades''' like the horse, who depends entirely on the third metacarpal bone for its stature.
 +
*Colloquially, the third metacarpal of the horse is known as the '''canon''' bone, and the vestigial 2 and 4 as '''splint bones'''
  
−
Distally -  bones I-IV are present.
+
==Joints of the Distal Forelimb==
 +
===Carpal Joint===
  
−
===[[Forelimb - Anatomy & Physiology#Metacarpal bones|Metacarpal Bones]]===
+
The carpal joint is a compound joint composed of:
 +
*The '''antebrachiocarpal joint''' between the radius/ulna and the proximal carpal bones
 +
*The '''middle carpal joint''' between the two rows of carpal bones
 +
*The '''carpometacarpal joint''' between the distal carpal bones and the proximal metacarpals
  
−
These are covered in detail in the [[Canine Phalanges - Anatomy & Physiology|canine phalanges]] section.
+
The joint is a synovial joint, comprised of a common outer fibrous capsule and three inner synovial pouches, one for each joint.  Numerous ligaments add to the stability of the joint and ensure movement is largely limited to the [[Planes and Axes - Anatomy & Physiology|sagittal plane]], although no collateral ligaments exist in the dog between the radius and the proximal metacarpals.  This allows a very small amount of rotation.
  
−
==Joints of the Distal Forelimb==
+
===Metacarpal Joint===
  
−
===[[Forelimb - Anatomy & Physiology#Carpal Joint|Carpal Joint]]===
+
The metacarpal joint is defined by the presence of palmar [[Bones and Cartilage - Anatomy & Physiology#Types of Bone|'''sesamoids''']], which allow the flexor tendons to pass over the sharp change in angle presented by the joint.  These are paired on each digit, with the exception of the first digit where it exists.
  
−
The '''synovial membranes''' form three compartments corresponding to each joint. The proximal is the largest whilst the middle carpal and carpometacarpal sacs communicate and extend into the intermetacarpal articulations. The fibrous joint capsule is common to all three joints and attaches to the individual bones and various intercarpal ligaments. The '''extensor retinaculum''' is fibrous collagenous tissue on the dorsal aspect that allows passage of the extensor tendons. On the palmar aspect lies the '''palmar carpal fibrocartilage''', that provides attachment for some metacarpal bones. Paired '''collateral ligaments''' bridge the sides of the three main articulations.
 
  
−
The  '''flexor retinaculum''' is the carpal fascia on the palmar aspect, and lies between the accessory carpal bone and the medial aspect of the carpus. This with the joint capsule and medial surface of the accessory carpal bone, makes up the '''carpal canal'''. It houses just the deep digital flexor tendon in the dog. The intermetacarpal joints, are tight joints between the proximal ends of the metacarpals. The joint capsules are continuous with that of the carpal joint. They are held together by the '''interosseous metacarpal ligaments'''.
 
  
 
==Muscles of the Forelimb==
 
==Muscles of the Forelimb==
 +
===Extrinsic Musculature===
  
−
===[[Forelimb - Anatomy & Physiology#Extrinsic Musculature|Extrinsic Musculature]]===
+
These muscle are responsible for joining tht forelimb to the trunk, forming a synsarcosis rather than a conventional joint. Collectively, they act to transfer the weight of the body to the forelimbs as well as stabilize the scapula.
−
 
 
−
These muscle are responsible for joining the forelimb to the trunk, forming a synsarcosis rather than a conventional joint. Collectively, they act to transfer the weight of the body to the forelimbs as well as stabilize the scapula.
 
  
−
'''''Trapezius''''':
+
'''''Trapezius''''': Accessory n.
−
:Innervated by: Accessory n.
+
*Origin: mid-dorsal raphe and supraspinous ligament
−
:Origin: mid-dorsal raphe and supraspinous ligament
+
*Insertion: spine of the scapula
−
:Insertion: spine of the scapula
+
*Body: two parts, cervical and thoracic separated by aponeurosis
−
:Body: two parts, cervical and thoracic separated by aponeurosis
+
*Action: raises scapula against the trunk and swings cranially to advance the limb
−
:Action: raises scapula against the trunk and swings cranially to advance the limb.
 
  
−
'''''Brachiocephalic m.''''':
+
'''''Brachiocephalic m.''''': Accessory n.
−
:Innervated by: Accessory n.
+
*Two parts separated by the clavicle where it exists
−
:There are two parts separated by the clavicle.
+
*Origin: clavicle or vestigial fibrous intersection
−
:Origin: clavicle
+
*Insertion: several places on the head and neck
−
:Insertion: median raphe of the neck and the occipital bone. The ventral part attaches to the mastoid process.
+
*Actions:  
−
:Actions: advances the limb and extends the shoulder joint when the limb is in motion; draws the head and neck ventrally when the limb is fixed.
+
**advances the limb and extends the shoulder joint when limb is in motion
 +
**draws head and neck ventrally when limb is fixed
  
−
'''''Omotransversarius''''':
+
'''''Omotransversarius''''': Accessory n.
−
:Innervated by: Accessory n.
+
*Origin: transverse processes of the atlas
−
:Origin: transverse processes of the atlas
+
*Insertion: acromion and adjacent scapula
−
:Insertion: acromion and distal spine of the scapula
+
*Action: advancing the limb
−
:Action: advancing the limb
+
*Innervation
  
−
'''''Latissimus dorsi''''':
+
'''''Latissimus dorsi''''': local branch of brachial plexus
−
:Innervated by: local branch of brachial plexus
+
*The '''broadest muscle of the back'''
−
:It is the broadest muscle of the back.
+
*Origin: thoracolumbar fascia  
−
:Origin: thoracolumbar fascia
+
*Insertion: teres tuberosity of the humerus
−
:Insertion: teres tuberosity of the humerus
+
*Actions: antagonist to the brachiocephalic m.
−
:Actions: antagonist to the brachiocephalic m. It retracts the free limb and flexes the shoulder joint. It also draws the trunk forward over the fixed limb.
+
**cranial fibers strap scapula to the chest
 +
**retracts free limb and flexes shoulder joint
 +
**draws trunk forward over the fixed limb
  
−
'''''Pectoral mm.''''':
+
'''''Pectoral mm.''''': brachial plexus
−
:Innervated by: brachial plexus
+
*Two superficial parts, cranial and caudal
−
:Two superficial parts; cranial and caudal
+
**Origin: cranial sternum
−
:Origin: cranial sternum
+
**Insertion:
−
:Insertion: Cranial ('''descending'''): crest of the humerus distal to the deltoid tuberosity. Caudal ('''transverse'''): covers the elbow joint to insert on the medial fascia of the forearm.
+
***cranial ('''descending'''): crest of the humerus distal to the deltoid tuberosity
−
:Action: adduct the forelimb, assist in protraction and retraction.
+
***caudal ('''transverse'''): covers elbow joint to insert on the medial fascia of the forearm
−
:One deep part ('''pectoralis profundus'''), with cranial and caudal parts.
+
**Action: adduct the forelimb, assist in protraction and retraction
−
::Origin: ventral sternum and adjacent cartilage
+
*One deep part ('''pectoralis profundus'''), with cranial and caudal parts
−
::Insertions: Cranial (subclavius): supraspinatus m., Caudal (pectoralis ascendens): lesser tubercle of the humerus.
+
**Origin: ventral sternum and adjacent cartilage
−
::Actions: slinging trunk between forelimbs, may also retract free limbs. It draws the trunk forward when the limb is fixed.
+
**Insertions:
 +
***cranial (subclavius): supraspinatus m.
 +
***caudal (pectoralis ascendens): lesser tubercle of the humerus
 +
**Actions:  
 +
***slinging trunk between forelimbs
 +
***may also retract free limbs
 +
***draw trunk forward when limb is fixed
  
−
'''''Serratis ventralis''''':
+
'''''Serratis ventralis''''': branch of brachial plexus
−
:Innervated by: branch of brachial plexus
+
*Origin: C4 to 10th rib
−
:Origin: C4 to 10th rib
+
*Insertion: medial scapula and scapular cartilage
−
:Insertion: medial scapula and scapular cartilage
+
*Action: supporting the weight of the trunk
−
:Action: supporting the weight of the trunk. It is reinforced by strong fascia. The cervical portion can retract the limb and the caudal portion can advance the limb.
+
**reinforced by strong fascia
 +
**cervical portion can retract the limb
 +
**caudal portion can advance the limb
  
−
'''''Rhomboids''''':
+
'''''Rhomboids''''': brachial plexus, although in some species, dorsal spinal nerves can innervate
−
:Innervated by: brachial plexus
+
*Origin: median connective tissue from poll to withers, lying deep to the trapezius
−
:Origin: nuchal ligament, 4th - 6th thoracic spine
+
*Insertion: dorsal border and adjacent scapula
−
:Insertion: dorsal border and adjacent scapula
+
*Action: retracting the limb, may also raise limb
−
:Action: retracting the limb, may also raise limb.
 
−
 
 
−
===[[Forelimb - Anatomy & Physiology#Intrinsic Musculature|Intrinsic Musculature]]===
 
  
 +
===Intrinsic Musculature===
 
====Muscles of the Shoulder====
 
====Muscles of the Shoulder====
−
 
 
These muscles are grouped:
 
These muscles are grouped:
 +
*Lateral:'''Supraspinatus ''' and '''Infraspinatus''', Suprascapular n. of the brachial plexus
 +
**Origin: the fossae of the scapula
 +
**Insertion: both tubercles of the humerus
 +
**Action: brace the shoulder
 +
**Clinical significance: bursa between the tendon of the infraspinatus and lateral tubercle of the humerus can be the site of inflammation
 +
*Medial:
 +
**'''Supscapularis''': Subscapular n. from the brachial plexus
 +
***Origin: Deep surface of the scapula
 +
***Insertion: medial tubercle of the humerus
 +
***Action: braces medial shoulder joint, potential adductor
 +
**'''Coracobrachialis''': Musculocutaneous n. of the brachial plexus
 +
***Origin: medial supraglenoid tubercle
 +
***Insertion: proximal shaft of the humerus
 +
***Action: fixator
 +
*Caudal (Flexors): Axillary n. of the brachial plexus
 +
**'''Deltoids'''
 +
***Origin: caudal border and spine of the scapula
 +
****One head in the horse and two in species with an acromion (site of second origin)
 +
***Insertion: deltoid tuberosity on the humerus
 +
**'''Teres Major'''
 +
***Origin: dorsal part of the caudal scapula
 +
***Insertion: teres tuberosity midway down humerus
 +
**'''Teres Minor'''
 +
*There are no defined extensors of the shoulder.  Those involved (brachiocephalic m., biceps brachii, supraspinatus, and ascending pectorals) have other, more primary roles.
  
−
<u>'''Lateral'''</u>
+
====Muscles of the Elbow====
−
 
+
''Extensors'': Radial n. from the brachial plexus
−
'''''Supraspinatus''''' and '''''Infraspinatus''''':
+
*'''Triceps brachii''': Three heads, four in the dog
−
:Innervated by: Suprascapular n. of the brachial plexus
+
**Long head: caudal margin of the scapula
−
:Origin: the fossae of the scapula
+
**Lateral, medial, and accessory heads: shaft of the humerus
−
:Insertion: both tubercles of the humerus
+
**Insertion: olecranon, proteced by tricipital bursa against the bone and subcutaneous bursa against the skin
−
:Action: brace the shoulder
+
*'''Tensor fasciae antebrachii'''
−
:Clinical significance: the bursa between the tendon of the infraspinatus and lateral tubercle of the humerus, can be the site of inflammation.
+
**Overlies triceps extending from scapula to olecranon
−
 
+
*'''Anconeus'''
−
<u>'''Medial'''</u>
+
**Origin: distal humerus
−
 
+
**Insertion: lateral olecranon
−
'''''Supscapularis''''':
 
−
:Innervated by: Subscapular n. from the brachial plexus
 
−
:Origin: Deep surface of the scapula
 
−
:Insertion: medial tubercle of the humerus
 
−
:Action: braces medial shoulder joint, potential adductor
 
−
 
 
−
'''''Coracobrachialis''''':
 
−
:Innervated by: Musculocutaneous n. of the brachial plexus
 
−
:Origin: medial supraglenoid tubercle
 
−
:Insertion: proximal shaft of the humerus
 
−
:Action: fixator
 
−
 
 
−
<u>'''Caudal (Flexors)'''</u>
 
−
 
 
−
'''''Deltoids''''':
 
−
:Innervated by: Axillary n. of the brachial plexus
 
−
:Origin: acromion, the length of the scapular spine
 
−
:Insertion: deltoid tuberosity on the humerus, fascia of the lateral arm
 
−
:Action: Flexor of Shoulder, Abductor and outward rotator of the arm
 
−
 
 
−
'''''Teres Major''''':
 
−
:Innervated by: Axillary n. of the brachial plexus
 
−
:Origin: dorsal part of the caudal scapula
 
−
:Insertion: teres tuberosity midway down humerus
 
−
 
 
−
====[[Forelimb - Anatomy & Physiology#Muscles of the Elbow|Muscles of the Elbow]]====
 
−
 
 
−
<u>1. '''Extensors''' </u>
 
−
 
 
−
'''''Triceps brachii''''':  
 
−
:Innervated by: Radial n. from the brachial plexus
 
−
:Has four heads in the dog
 
−
:Origin:
 
−
::Long head: From the caudal border of the scapula
 
−
::Lateral, medial, and accessory heads: From the shaft of the humerus
 
−
:Insertion: olecranon, protected by tricipital bursa against the bone, and subcutaneous bursa against the skin
 
−
 
 
−
'''''Tensor fasciae antebrachii''''':
 
−
:Innervated by: Radial n. from the brachial plexus
 
−
:Origin: tendon and lateral surface of the latissimus dorsi
 
−
 
 
−
<u>2. '''Flexors'''</u>
 
−
 
 
−
'''''Biceps brachii''''':
 
−
:Innervated by: Musculocutaneous n. from the brachial plexus
 
−
:Origin: supraglenoid tubercle of the scapula
 
−
:Insertion: medial tuberosity of proximal radius and adjacent ulna
 
−
:Runs through the intertubercular groove of the humerus
 
  
−
'''''Brachialis''''':  
+
''Flexors'': Musculocutaneous n. from the brachial plexus
−
:Innervated by: Musculocutaneous n. from the brachial plexus
+
*'''Biceps brachii'''
−
:Origin: proximocaudal humerus
+
**Origin: supraglenoid tubercle of the scapula
−
:Insertion: spirals to insert just proximal to biceps
+
**Insertion: medial tuberosity of proximal radius and adjacent ulna
 +
**Runs through the intertubercular groove of the humerus
 +
*'''Brachialis'''
 +
**Origin: proximocaudal humerus
 +
**Insertion: spirals to insert next to biceps
  
−
====[[Forelimb - Anatomy & Physiology#Muscles of Supination and Pronation|Muscles of Supination and Pronation]]====
+
====Muscles of Supination and Pronation ====
 +
''Supinators'': Radial n. from the brachial plexus
 +
*'''Brachioradialis'''
 +
**Origin: lateral epicondyle of the humerus
 +
**Insertion: distal medial forearm within superficial fascia
 +
**Prominent in the cat but nearly absent in the dog
 +
*'''Supinator'''
 +
**Deep to extensor muscles,  passing from lateral humeral epicondyles to upper medial radius
  
−
<u>1. '''Supinators'''</u>
+
''Pronators'': Median n. from the brachial plexus
 +
*'''Pronator teres''': only functional in cat and dog
 +
**Origin: medial epicondyle of the humerus
 +
**Insertion: supinator
 +
*'''Pronator quadratus''': only found in carnivores
 +
**Origin: shaft of the ulna
 +
**Insertion: shaft of the radius
  
−
'''''Brachioradialis''''':  
+
====Muscles of the Carpal and Digital Joints====
−
:Innervated by: Radial n. from the brachial plexus
+
''Extensors'': Radial n. from the brachial plexus
−
:Origin: lateral epicondyle of the humerus
+
*Craniolateral position on the forearm
−
:Insertion: distal part of the medial radius
+
*Almost all originate from the lateral epicondyle of the humerus
−
:Often much reduced, and sometimes absent
+
*'''Extensor carpi radialis''': most medial, inserts on 2nd/3rd metacarpal bone
 +
*'''Ulnaris lateralis''': most lateral, inserts on accessory carpal bone
 +
*'''Extensor carpi obliquus''': aka '''abductor pollicis longus'''
 +
**Origin: cranial radius
 +
**Insertion: most medial metacarpal bone
 +
*Last two may also serve in medial deviation of the paw
 +
*'''Common Digital Extensor'''
 +
**Insertion: extensor process of the distal phalanx of each digit
 +
**Sends a medial branch to dewlcaw and medial digits in all but horse and cat
 +
*'''Lateral Digital Extensor'''
 +
**Insertion: dorsal proximal phalanx
  
−
'''''Supinator''''':  
+
''Flexors'': Median or Ulnar n. of the brachial plexus
−
:Innervated by: Radial n. from the brachial plexus
+
*Caudal position on the forearm
−
:Deep to the extensor muscles, passing from the lateral humeral epicondyles to the upper medial radius
+
*Originate from the caaudal medial epicondyle of the humerus
 +
*'''Flexor carpi radialis''': most medial, inserts on upper 2nd/3rd metacarpal bone
 +
*'''Flexor carpi ulnaris''': most lateral, inserts on the accessory carpal bone
 +
*'''Superficial Digital Flexor'''
 +
**Branches according to the number of digis and inserts in proximal interphalangeal joint
 +
*'''Deep Digital Flexor'''
 +
**Passes through carpal canal before branching and continues to palmar distal phalanges
  
−
<u>2. '''Pronators'''</u>
+
''Interosseus muscles''
 +
*Support metacarpophalnageal joints
 +
*Arise from palmar proximal metacarpal bones and insert on sesamoid bones within the joints, continued by ligaments to phalanges
  
−
'''''Pronator teres''''':
 
−
:Innervated by: Median n. from the brachial plexus
 
−
:Origin: medial epicondyle of the humerus
 
−
:Insertion: dorsal surface and medial border of radius
 
−
 
−
'''''Pronator quadratus''''':
 
−
:Innervated by: Median n. from the brachial plexus
 
−
:Origin: palmar surface of radius and interosseous ligament
 
−
:Insertion: interosseous border of the ulna
 
−
 
−
====[[Forelimb - Anatomy & Physiology#Muscles of the Carpal and Digital Joints|Muscles of the Carpal and Digital Joints]]====
 
−
 
−
<u>1.'''Extensors'''</u>
 
−
 
−
They are located at the craniolateral position on the forearm. They almost all originate from the lateral epicondyle of the humerus and are all innervated by the radial n. from the brachial plexus.
 
−
 
−
'''''Extensor carpi radialis'''''
 
−
:The most medial, inserts on middle metacarpal bone.
 
−
 
−
'''''Ulnaris lateralis'''''
 
−
:The most lateral, inserts on accessory carpal bone and 5th metacarpal.
 
−
 
−
'''''Extensor carpi obliquus''''' (aka '''''abductor pollicis longus''''')
 
−
:Origin: cranial radius
 
−
:Insertion: 1st metacarpal
 
−
 
−
Last two may also serve in medial deviation of the paw.
 
−
 
−
 
−
'''''Common Digital Extensor'''''
 
−
:Insertion: extensor process of the distal phalanx of each digit
 
−
:Sends a medial branch to the dew caw.
 
−
 
−
'''''Lateral Digital Extensor'''''
 
−
:Inserts on the dorsal proximal phalanges of the 3rd to 5th digit.
 
−
 
−
 
−
<u>2. '''Flexors'''</u>
 
−
 
−
They are at the caudal position on the forearm, originate from the caudal medial epicondyle of the humerus and all are innervated by the median or ulnar n. of the brachial plexus.
 
−
 
−
'''''Flexor carpi radialis'''''
 
−
:The most medial, inserts on the upper 2nd/3rd metacarpal bone.
 
−
 
−
'''''Flexor carpi ulnaris'''''
 
−
:The most lateral, inserts on the accessory carpal bone.
 
−
 
−
'''''Superficial Digital Flexor'''''
 
−
:It divides into four branches, which insert on the middle phalanges of all digits.
 
−
 
−
'''''Deep Digital Flexor'''''
 
−
:Passes through the carpal canal before branching, and continues to the palmar distal phalanges.
 
−
 
−
'''''Interosseus muscles'''''
 
−
:Support the metacarpophalnageal joints. They arise from the palmar proximal metacarpal bones, and insert on the sesamoid bones within the joints. They are continued by ligaments to the phalanges.
 
  
 
==Vasculature of the Forelimb==
 
==Vasculature of the Forelimb==
 +
*'''[[Arteries of the Forelimb - Anatomy & Physiology|Arteries of the Forelimb]]'''
 +
*'''[[Veins of the Forelimb - Anatomy & Physiology|Veins of the Forelimb]]'''
 +
*'''[[Lymphatics of the Forelimb - Anatomy & Physiology|Lymphatics of the Forelimb]]'''
  
−
'''[[Arteries of the Forelimb - Anatomy & Physiology|Arteries of the Forelimb]]'''
+
==Innervation of the Forelimb==
−
 
 
−
'''[[Veins of the Forelimb - Anatomy & Physiology|Veins of the Forelimb]]'''
 
−
 
 
−
'''[[Lymphatics of the Forelimb - Anatomy & Physiology|Lymphatics of the Forelimb]]'''
 
−
 
 
−
 
 
−
{{Learning
 
−
|dragster = [[:Category:Canine Thoracic Limb Dragster|Canine muscular anatomy]]
 
−
|CAL = [[Canine Radiographic Anatomy resource|Canine Radiographs programme, look at complete canine skeleton]]
 
−
|OVAM = [http://www.onlineveterinaryanatomy.net/content/muscle-flashcards-forelimb-extrinsics-quicktime Muscle flashcards - extrinsic musculature of the canine forelimb]<br>[http://www.onlineveterinaryanatomy.net/content/muscle-flashcards-shoulder-quicktime Muscle flashcards - muscles of the canine shoulder]<br>[http://www.onlineveterinaryanatomy.net/content/muscle-flashcards-elbow-quicktime Muscle flashcards - muscles of the canine elbow]<br>[http://www.onlineveterinaryanatomy.net/content/muscle-flashcards-antebrachium-quicktime Muscle flashcards - muscles of canine antebrachium]
 
−
}}
 
−
 
 
−
==Webinars==
 
−
<rss filterout="equine horse feline">https://www.thewebinarvet.com/orthopaedics/webinars/feed</rss>
 
−
 
 
−
 
 
−
[[Category:Musculoskeletal System - Anatomy & Physiology]][[Category:Dog - Musculoskeletal System]]
 
−
[[Category:A&P Done]]
 

Revision as of 10:31, 25 August 2008

BACK TO MUSCULOSKELETAL ANATOMY AND PHYSIOLOGY
BACK TO FORELIMB

Structures of the Proximal Forelimb and Shoulder

Scapula

The Scapula forms the basis of the shoulder region, providing points of attachment of extrinsic and intrinsic muscles. It is held in place by a synsarcosis of muscles and does not form a conventional articulation with the trunk.

  • The spine culminates in the acromion.
  • The articular surface of the glenoid cavity and continues round onto the supraglenoid tubercle.
  • The scapular cartilage comprises of only a very narrow rim.

Clavicle

In the dog and cat, a remnant of bone may remain embedded in the fibrous intersection in the brachiocephalicus, which may prove misleading in radiographic images.

Humerus

The Humerus is the long bone of the forearm, articulating with the scapula to form the shoulder and the radius and ulna to form the elbow. In situ, it lies obliquely along the ventral thorax and is more horizontal in larger species.

  • The greater tubercle is not seperated into two parts like in other species
  • In dogs and cats, it articulates with the radius medially via a trochlea and the ulna laterally via a capitulum

Radius

  • A radial tuberosity provides a site of attachment for brachialis and biceps brachii. This roughened area is very variable in size in dogs and can be non-exsistent.

Ulna

The Ulna's greatest contribution to functional anatomy is in the formation of the Olecranon, or the point of the elbow, which gives rise to the attachment of the triceps. The olecranon articulates with the humerus via its anconeal process. Distally (where unfused), the lateral styloid process articulates with the ulnar carpal bone.

Joints of the Proximal Forelimb

Shoulder Joint

The shoulder joint links the humerus and the scapula at the glenoid cavity, which is much smaller than the head of the humerus. While structually it is a ball and socket joint, it functions as a hinge joint due to extensive muscling around the articulation. The joint capsule is enlarged and extends under the tendon of the biceps, acting as a synovial sheath to protect the tendon.

Elbow Joint

Movement of the elbow joint is restricted to the sagittal plane. It is bounded medially and laterally by collateral ligaments betweek the humerus and radius, caudally by the olecranon ligament between the humerus and olecranon, and further enforced by the annular radial ligament. The elbow is a compound joint including:

  • The hinge joint between the humerus and the radius and ulna
  • The pivot joint between the radius and ulna
  • The point of the elbow, or the olecranon is formed by the anconeal process of the ulna inserting into the olecranon fossa of the humerus


Structures of the Distal Forelimb

Carpal bones

Carpal bones comprise two rows:

  • Proximally, (mediolaterally), radial, intermediate, ulnar and accessory bones
    • The accessory bone serves as a landmark for palpation
  • Distally, bones are numbered 1-5, though 5 is always fused with 4
  • A small sesamoid bone embedded in the medial tissues of the joint can sometimes be mistaken as a chip fracture

Metacarpal bones

The number of metacarpals varies widely among species, as the demand for their function changes: plantigrade, or flat-footed, animals requiring the full complement of five metacarpal bones; the number is reduced in the upright stature of digitigrade animals such as the dog and cat, and shows the extreme in unguligrades like the horse, who depends entirely on the third metacarpal bone for its stature.

  • Colloquially, the third metacarpal of the horse is known as the canon bone, and the vestigial 2 and 4 as splint bones

Joints of the Distal Forelimb

Carpal Joint

The carpal joint is a compound joint composed of:

  • The antebrachiocarpal joint between the radius/ulna and the proximal carpal bones
  • The middle carpal joint between the two rows of carpal bones
  • The carpometacarpal joint between the distal carpal bones and the proximal metacarpals

The joint is a synovial joint, comprised of a common outer fibrous capsule and three inner synovial pouches, one for each joint. Numerous ligaments add to the stability of the joint and ensure movement is largely limited to the sagittal plane, although no collateral ligaments exist in the dog between the radius and the proximal metacarpals. This allows a very small amount of rotation.

Metacarpal Joint

The metacarpal joint is defined by the presence of palmar sesamoids, which allow the flexor tendons to pass over the sharp change in angle presented by the joint. These are paired on each digit, with the exception of the first digit where it exists.


Muscles of the Forelimb

Extrinsic Musculature

These muscle are responsible for joining tht forelimb to the trunk, forming a synsarcosis rather than a conventional joint. Collectively, they act to transfer the weight of the body to the forelimbs as well as stabilize the scapula.

Trapezius: Accessory n.

  • Origin: mid-dorsal raphe and supraspinous ligament
  • Insertion: spine of the scapula
  • Body: two parts, cervical and thoracic separated by aponeurosis
  • Action: raises scapula against the trunk and swings cranially to advance the limb

Brachiocephalic m.: Accessory n.

  • Two parts separated by the clavicle where it exists
  • Origin: clavicle or vestigial fibrous intersection
  • Insertion: several places on the head and neck
  • Actions:
    • advances the limb and extends the shoulder joint when limb is in motion
    • draws head and neck ventrally when limb is fixed

Omotransversarius: Accessory n.

  • Origin: transverse processes of the atlas
  • Insertion: acromion and adjacent scapula
  • Action: advancing the limb
  • Innervation

Latissimus dorsi: local branch of brachial plexus

  • The broadest muscle of the back
  • Origin: thoracolumbar fascia
  • Insertion: teres tuberosity of the humerus
  • Actions: antagonist to the brachiocephalic m.
    • cranial fibers strap scapula to the chest
    • retracts free limb and flexes shoulder joint
    • draws trunk forward over the fixed limb

Pectoral mm.: brachial plexus

  • Two superficial parts, cranial and caudal
    • Origin: cranial sternum
    • Insertion:
      • cranial (descending): crest of the humerus distal to the deltoid tuberosity
      • caudal (transverse): covers elbow joint to insert on the medial fascia of the forearm
    • Action: adduct the forelimb, assist in protraction and retraction
  • One deep part (pectoralis profundus), with cranial and caudal parts
    • Origin: ventral sternum and adjacent cartilage
    • Insertions:
      • cranial (subclavius): supraspinatus m.
      • caudal (pectoralis ascendens): lesser tubercle of the humerus
    • Actions:
      • slinging trunk between forelimbs
      • may also retract free limbs
      • draw trunk forward when limb is fixed

Serratis ventralis: branch of brachial plexus

  • Origin: C4 to 10th rib
  • Insertion: medial scapula and scapular cartilage
  • Action: supporting the weight of the trunk
    • reinforced by strong fascia
    • cervical portion can retract the limb
    • caudal portion can advance the limb

Rhomboids: brachial plexus, although in some species, dorsal spinal nerves can innervate

  • Origin: median connective tissue from poll to withers, lying deep to the trapezius
  • Insertion: dorsal border and adjacent scapula
  • Action: retracting the limb, may also raise limb

Intrinsic Musculature

Muscles of the Shoulder

These muscles are grouped:

  • Lateral:Supraspinatus and Infraspinatus, Suprascapular n. of the brachial plexus
    • Origin: the fossae of the scapula
    • Insertion: both tubercles of the humerus
    • Action: brace the shoulder
    • Clinical significance: bursa between the tendon of the infraspinatus and lateral tubercle of the humerus can be the site of inflammation
  • Medial:
    • Supscapularis: Subscapular n. from the brachial plexus
      • Origin: Deep surface of the scapula
      • Insertion: medial tubercle of the humerus
      • Action: braces medial shoulder joint, potential adductor
    • Coracobrachialis: Musculocutaneous n. of the brachial plexus
      • Origin: medial supraglenoid tubercle
      • Insertion: proximal shaft of the humerus
      • Action: fixator
  • Caudal (Flexors): Axillary n. of the brachial plexus
    • Deltoids
      • Origin: caudal border and spine of the scapula
        • One head in the horse and two in species with an acromion (site of second origin)
      • Insertion: deltoid tuberosity on the humerus
    • Teres Major
      • Origin: dorsal part of the caudal scapula
      • Insertion: teres tuberosity midway down humerus
    • Teres Minor
  • There are no defined extensors of the shoulder. Those involved (brachiocephalic m., biceps brachii, supraspinatus, and ascending pectorals) have other, more primary roles.

Muscles of the Elbow

Extensors: Radial n. from the brachial plexus

  • Triceps brachii: Three heads, four in the dog
    • Long head: caudal margin of the scapula
    • Lateral, medial, and accessory heads: shaft of the humerus
    • Insertion: olecranon, proteced by tricipital bursa against the bone and subcutaneous bursa against the skin
  • Tensor fasciae antebrachii
    • Overlies triceps extending from scapula to olecranon
  • Anconeus
    • Origin: distal humerus
    • Insertion: lateral olecranon

Flexors: Musculocutaneous n. from the brachial plexus

  • Biceps brachii
    • Origin: supraglenoid tubercle of the scapula
    • Insertion: medial tuberosity of proximal radius and adjacent ulna
    • Runs through the intertubercular groove of the humerus
  • Brachialis
    • Origin: proximocaudal humerus
    • Insertion: spirals to insert next to biceps

Muscles of Supination and Pronation

Supinators: Radial n. from the brachial plexus

  • Brachioradialis
    • Origin: lateral epicondyle of the humerus
    • Insertion: distal medial forearm within superficial fascia
    • Prominent in the cat but nearly absent in the dog
  • Supinator
    • Deep to extensor muscles, passing from lateral humeral epicondyles to upper medial radius

Pronators: Median n. from the brachial plexus

  • Pronator teres: only functional in cat and dog
    • Origin: medial epicondyle of the humerus
    • Insertion: supinator
  • Pronator quadratus: only found in carnivores
    • Origin: shaft of the ulna
    • Insertion: shaft of the radius

Muscles of the Carpal and Digital Joints

Extensors: Radial n. from the brachial plexus

  • Craniolateral position on the forearm
  • Almost all originate from the lateral epicondyle of the humerus
  • Extensor carpi radialis: most medial, inserts on 2nd/3rd metacarpal bone
  • Ulnaris lateralis: most lateral, inserts on accessory carpal bone
  • Extensor carpi obliquus: aka abductor pollicis longus
    • Origin: cranial radius
    • Insertion: most medial metacarpal bone
  • Last two may also serve in medial deviation of the paw
  • Common Digital Extensor
    • Insertion: extensor process of the distal phalanx of each digit
    • Sends a medial branch to dewlcaw and medial digits in all but horse and cat
  • Lateral Digital Extensor
    • Insertion: dorsal proximal phalanx

Flexors: Median or Ulnar n. of the brachial plexus

  • Caudal position on the forearm
  • Originate from the caaudal medial epicondyle of the humerus
  • Flexor carpi radialis: most medial, inserts on upper 2nd/3rd metacarpal bone
  • Flexor carpi ulnaris: most lateral, inserts on the accessory carpal bone
  • Superficial Digital Flexor
    • Branches according to the number of digis and inserts in proximal interphalangeal joint
  • Deep Digital Flexor
    • Passes through carpal canal before branching and continues to palmar distal phalanges

Interosseus muscles

  • Support metacarpophalnageal joints
  • Arise from palmar proximal metacarpal bones and insert on sesamoid bones within the joints, continued by ligaments to phalanges


Vasculature of the Forelimb

Innervation of the Forelimb

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