Anatomy of the Canine Front Limb

Original Editor - Ansi van der Walt Top Contributors -

This page introduces the anatomy of the canine front limb, also known as forelimb and thoracic limb.

Bones of the Canine Front Limb[edit | edit source]

Canine Skeleton

The bones of the front limb are:

  • Scapula
  • Humerus
  • Radius
  • Ulnar
  • Carpus
  • Metacarpals
  • Phalanges

Specific Features of the Canine Skeleton[1][edit | edit source]

  • While dogs do have a clavicle, it is a rudimentary structure within the brachiocephalicus muscle and it is rarely seen on x-ray
  • There is a narrow band of scapula cartilage along the dorsal border
  • Both dogs and cats have a supratrochlear foramen on their humerus. Nothing passes through this gap in dogs. In cats, the median nerve and brachial vessels pass through this foramen
  • There are no significant modifications of the radius and ulnar bones
  • There are seven carpal bones - the radial and intermediate carpal bones are fused, thus forming the canine “radial” carpal bone
  • The first metacarpal is significantly reduced - it has only two phalanges (P1 and P3) and is a non-weight bearing structure. It only has one associated sesamoid bone and is known as the “dew claw”
  • The distal phalanx carries the horny claw. The flexor process (palmar) is where the deep digital flexor tendon inserts. The extensor process (dorsal) is where the common digital extensor tendon inserts
  • The ungual process is a cone shaped process covered by the horny claw
  • Sesamoids
    • Proximal - pared articulating with MII dorsal. The axial surface is joined by a thick inter-sesamoidean ligament
    • Distal / navicular - boat-shaped, articulated with P2 and P3. Provides a bearing surface for the deep digital flexor tendon, which places it under significant compressive stress

The following videos describe the skeletal system of the canine front limb in detail. The second video discusses other animals as well. The front limb is discussed from 49:11 minutes to 59.37 minutes.

Joints of the Canine Front Limb[edit | edit source]

Scapulo-trunk (scapulo-thoracic)[1][edit | edit source]

  • Type
    • Synsarcotic joint with no attachments
  • Supporting structures
    • A series of muscles that sling the trunk from the scapula. This allows for shock absorption and increases range of motion
  • Joint motion and range
    • Cranial glide (NB: caudal, dorsal and ventral glide are described, but not quantified)
    • Winging, tipping and rotation are not described

Shoulder (glenohumeral)[1][edit | edit source]

  • Type
    • Ball and socket joint
    • Consists of glenoid cavity of the scapula and the head of the humerus
    • The glenoid fossa on the scapula is deepened by the glenoid labrum
  • NB: shoulder flexion (and extension) is not the same as limb flexion (and extension). Limb flexion (i.e. protraction) involves shoulder extension
  • The biceps tendon lies over the cranial aspect of the joint and it is held against the humerus by the transverse humeral ligament
  • Glenohumeral ligaments are thickenings of the joint capsule, not true ligaments
  • There are no other ligaments
  • The synovial sheath of the biceps brachii tendon is an extension of the joint capsule

[4]

Shoulder Joint Motion and Ranges[edit | edit source]

Joint Movement Normal ROM for Dogs
Shoulder Extension 30-40 degrees
Flexion 170 degrees
Abduction 40-50 degrees
Adduction 40-50 degrees
Medial rotation 40-50 degrees
Lateral rotation 40-50 degrees

Elbow (humeroradial, humeroulnar, proximal radioulnar)[1][edit | edit source]

  • Type
    • Hinge joint
    • Consists of the humeral condyle, the radius head and semilunar notch of the elbow
  • Ligaments
    • Medial and lateral collateral ligaments. These limit rotation when the elbow is flexed
    • Annular ligament of the radial head

Distal Radial-Ulnar Joint[1][edit | edit source]

  • Part of the antebrachiocarpal joint (shares a joint capsule)

Elbow Joint Range of Motion and Ranges[1][edit | edit source]

Joint Movement Normal ROM for Dogs
Elbow Flexion 25-40 degrees
Extension 170 degrees
Hyper- or over-extension
Radioulnar Pronation 40-50 degrees
Supination 80-90 degrees

Carpal Joint[1][edit | edit source]

  • Hinge joint
  • Radiocarpal (RC) - consists of the trochlear of the radius and carpals
  • Midcarpals (MC) - proximal and distal carpals
  • Carpometacarpals (CMCs) - carpal bones (II-IV) and metacarpals (II to IV)
  • Intercarpals (IC) - carpals of the same row
  • Ligaments of the carpal joint
    • Medial and lateral collateral ligaments
    • Intercarpals
    • Palmar carpal ligament (fibrocartilage)
    • Flexor retinaculum
  • Carpal canal
    • Formed by the accessory carpal bone (laterally), the palmar carpal ligament (cranially) and the flexor retinaculum (palmar)
    • Structures passing through the carpal tunnel include:
      • Tendons and synovial sheaths of the superficial and deep digital flexor tendons
      • Ulnar and median nerves
      • Arteries and veins

Carpus Joint Range of Motion and Ranges[1][edit | edit source]

Joint Movement Normal ROM for Dogs
Carpus Flexion 20-30 degrees
Hyper-extension 10-15 degrees
Radial or medial deviation 15-20 degrees
Ulnar or lateral deviation 15-20 degrees

Muscles of the Canine Front Limb[edit | edit source]

Extrinsic Muscles of the Shoulder[1][edit | edit source]

Muscle Origin Insertion Action Nerve
Cutaneous trunci Superficial fascia of the dorsal, lateral and ventral walls of the thorax and abdomen Medial side of the forelimb Twitches the skin over the scapular and shoulder area Lateral thoracic nerve
Trapezius (cervical part) Median or mid-dorsal raphe of the neck and supraspinous ligament Dorsal aspect of the spine of the scapula Elevates the scapula cranially and dorsally; abducts the forelimb Accessory spinal nerve (CNXI)
Trapezius (thoracic part) Supraspinous ligament and dorsal spinous processes of T2-T8 or T9 Middle part of the spine of the scapula Elevates the scapula caudally and dorsally; abducts the forelimb Accessory spinal nerve (CNXI)
Omotransversarius Distal end of the spine of the scapula Transverse process of the atlas Advances the forelimb Accessory spinal nerve
Latissimus Dorsi Thoracolumbar fascia from spinous processes of most caudal 7 or 8 thoracic and lumbar vertebrae; most caudal 2 or 3 ribs Teres major tuberosity on the humerus and teres major tendon; joins tip of the cutaneous trunci muscle laterally Flexes the shoulder, draws the trunk cranially in weight bearing; adducts the shoulder; supports the trunk Thoracodorsal
Rhomboid (capital part) Nuchal crest of the occipital bone Cranial dorsal border of the scapula Elevates the scapula and forelimb; pulls the scapula to the trunk Dorsal branches of the spinal nerves
Rhomboid (cervical part) Median fibrous raphe of the neck, spinous processes of T1-T3 Caudal (base) of the scapula medially and laterally As above As above
Rhomboid (thoracic part) Spinous processes of T4-T7 Caudal (base of the scapula medially and laterally) As above As above
Brachiocephalicus (cleidocephalicus) Dorsal aspect of the clavicle Cranial half; mid-dorsal fibrous raphe and nuchal crest of the occipital bone Draws the head to the side; extends the neck Accessory nerve; ventral rami of cervical spinal nerves
Brachiocephalicus (cleidobrachialis) Ventral aspect of the clavicle Cranial surface, distal third of the humerus, between the biceps brachii medially and the brachialis laterally Extends the shoulder; advances the forelimb As above
Serratus ventralis Raises thorax; shifts weight to contralateral limb Long thoracic
Serratus ventralis (cervical part) Transverse processes of C3-C7 and ventral ribs 1-7 or 8 Medial scapula, dorsal third Carries the trunk and shoulder forward and back; supports the trunk; depresses the scapula Ventral rami of cervical spinal nerves, long thoracic nerves
Superficial pectoral (descending portion) Ventral sternum, most cranial aspect (ventral to the transverse pectoral muscle) All but the most distal part of the crest of the greater tubercle of the humerus Adducts the shoulder, prevents abduction in weight-bearing; extends the shoulder; draws the trunk sidewards Cranial pectoral
Superficial pectoral (transverse portion) Ventral sternum, cranial half; dorsal to the descending pectoral muscle As above As above, but also flexes or extends the shoulder depending on the position of the shoulder As above
Superficial pectoral (deep or ascending pectoral) Ventral aspect of the sternum, dorsal to the superficial pectoral muscles cranially Major portion; lesser tubercle of humerus, aponeurosis to the greater tubercle and crest of humerus; caudal portion, medial brachial fascia Flexes the shoulder; moves the trunk cranially during weight-bearing; supports the trunk with the serratus ventralis Caudal pectoral nerves

Intrinsic Muscles of the Shoulder[1][edit | edit source]

Muscle Origin Insertion Action Nerve
Deltoid (spinous head) Scapular spine, blending with the infraspinatus The 2 parts of the deltoid blend near the shoulder joint and attach to the deltoid tuberosity Axillary
Deltoid (acromial head)

NB this is very large in large dogs

Acromion As above Shoulder abduction Axillary
Supraspinatus Supraspinatus fossa Greater tubercle of the humerus by a thick tendon Extends the shoulder; stabilises and prevents the collapse of the shoulder Suprascapular
Infraspinatus Infraspinatus fossa Lateral side of the greater tubercle of the humerus Shoulder flexion or extension depending on the position of the shoulder; shoulder abduction and lateral rotation; stabilises the lateral shoulder Suprascapular
Teres minor Infraglenoid tubercle Infraglenoid tuberosity of the humerus Shoulder flexion and lateral rotation Axillary
Biceps brachii Supraglenoid tubercle of the humerus

NB has only 1 head, but 2 tendons

Ulnar tuberosity on the proximal cranial ulna; radial tuberosity on the proximal cranial radius by way of the biceps brachii tendon Shoulder extension and elbow flexion; some passive stability in weight-bearing, prevents shoulder flexion Musculocutaneous
Coracobrachialis Coracoid process of the scapula Crest of the lesser tubercle of the humerus, proximal to the teres major tuberosity Shoulder adduction and extension Musculocutaneous
Teres major Caudal angle and border of the scapula and caudal subscapularis Teres major tuberosity of the humerus Shoulder flexion and medial rotation Axillary
Subscapularis Subscapular fossa Lesser tubercle of the humerus Adducts, extends and stabilises the shoulder medially Subscapular
Triceps brachii (long head) Caudal border of the scapula Olecranon tuberosity Elbow extension and shoulder flexion Radial
Triceps brachii (lateral head) Tricipital line of the humerus Olecranon tuberosity, to the long head Elbow extension As above
Medial head Crest of the lesser tubercle near the teres major tuberosity Olecranon tuberosity As above As above
Accessory head Neck of the humerus Olecranon tuberosity, between the lateral and medial heads) As above As above

Muscles of the Elbow[1][edit | edit source]

Muscle Origin Insertion Action Nerve
Brachialis Proximal third of the lateral humerus Ulnar tuberosity on the proximal cranial ulna; radial tuberosity on the proximal cranial radius by way of the biceps brachii tendon Elbow flexion Musculocutaneous
Anconeus Lateral supracondylar crest; lateral and part of the medial epicondyles of the humerus Lateral surface, proximal end of the ulnar Elbow extension; helps to tense the antebrachial fascia Radial
Extensor carpi radialis Lateral supracondylar crest; double tendon throughout the distal third Small tuberosities on the dorsal bases of the metacarpal bones II and III Carpal extension and elbow flexion Radial
Tensor fasciae antebrachii Fascia covering the latissimus dorsi Olecranon and the medial fascia of the forearm Elbow extension, chief tensor of the antebrachial fascia Radial

Muscles of the Distal Limb[1][edit | edit source]

Muscle Origin Insertion Action Nerve
Common digital extensor Lateral epicondyle of the humerus Extensor processes of the distal phalanges of digits II-IV Extension of digits II-V and carpal extension Radial
Lateral digital extensor Lateral epicondyle of the humerus Proximal ends of phalanges III-V, extensor processes of distal phalanges of III-V Extends digits III-V and carpal extension Radial
Ulnaris lateralis Lateral epicondyle of the humerus Lateral aspect of metacarpal bone V, accessory carpal bone Carpal ulnar deviation or abduction and weak carpal flexion Radial
Flexor carpi ulnaris (ulnar head) Olecranon Accessory carpal bone Carpal flexion and abduction Ulnar
Flexor carpi ulnaris (humeral head) Medial epicondyle of the humerus As above
Flexor carpi radialis Medial epicondyle of the humerus Medial border of the radius between the middle and proximal thirds Flexes the carpus Median
Pronator teres Medial epicondyle of the humerus Medial border of the radius between the middle and proximal thirds Pronation and elbow flexion Median
Superficial digital flexor Medial epicondyle of the humerus Palmar surface, base of the middle phalanges of II-V Proximal interphalangeal and metacarpophalangeal flexion of digits II-V and carpal flexion Median
Deep digital flexor (humeral head) Medial epicondyle of the humerus; radial, deep and medial bellies Palmar surface of the base (proximal end) of the distal phalanx of digits II-V and a weak tendon to digit I Flexion of the digits and carpal flexion Median nerve to deep and medial parts of the humeral head
Deep digital flexor (radial head) Middle third, medial border of the radius As above As above Median
Deep digital flexor (ulnar head) As above As above As above Ulnar

Nerves of the Canine Front Limb[1][edit | edit source]

Suprascapular (C6, C7)

  • Muscular innervation - supraspinatus and infraspinatus
  • Cutaneous innervation - nil
  • Damage to this nerve results in atrophy (a condition known as Sweeny)[5]

Subscapular (C6, C7)

  • Muscular innervation - subscapular
  • Cutaneous innervation - none

Musculocutaneous (C7, C8 and sometimes C6)

  • Muscular innervation - biceps brachii, brachialis
  • Cutaneous innervation - dorso-medial aspect of upper arm

Axillary (C7, C8)

  • Muscular innervation - deltoid, teres major and minor
  • Cutaneous innervation - dorso-lateral aspect of upper arm

Radial

  • Muscular innervation - extensors of elbow, carpus and digits
  • Cutaneous innervation - limited lateral forearm
  • If this whole nerve is damage, the dog will be unable to weight-bear, and will display a dropped elbow, flexed carpus and digits

Median / Ulnar (C8, T1, T2)

  • Muscular innervation - flexors of carpus and digits
  • Cutaneous innervation - caudal aspects of the limb
  • Damage to this nerve results in loss of sensation in the dog's foot. It has little affect on motor function

Metacarpal and digital nerves

  • Muscular innervation - nil
  • Cutaneous innervation - medial and lateral palmar nerves, medial and lateral palmar digital nerves supply two-thirds caudal from the foot

[6]

References[edit | edit source]

  1. 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 Van der Walt A. Managing Disorders of the Canine Front Limb Course. Physioplus, 2021.
  2. Pinoy Vet Anatomist. Skeletal System (Part 4) - Bones of the thoracic limb. Available from: https://www.youtube.com/watch?v=7fZoAHK02n0 [last accessed 28/2/21]
  3. Burnsie's RVT Vids. Skeletal Anatomy Dogs, Cats, Horses, Cows (VETERINARY TECHNICIAN EDUCATION). Available from: https://www.youtube.com/watch?v=6OoFyLHqjLM [last accessed 28/2/21]
  4. Priya Streram. *LEARN* Applied Anatomy of the Canine Shoulder. Available from https://www.youtube.com/watch?v=En4dLdmR4O8 [last accessed 28/2/21]
  5. Washington State University College of Veterinary Medicine Undergraduate Programs. Lab 5: thoracic limb: suprascapular nerve. Available from: https://undergraduate.vetmed.wsu.edu/courses/vph-308/gross/lab-5-gross-thoracic-limb-1/nerves-of-the-thoracic-limb/suprascapular-nerve (accessed 28 February 2021).
  6. Veterinary Anatomy. Innervation of the Thoracic Limb in the Dog. Available from: https://www.youtube.com/watch?v=T0etuvJUxwM [last accessed 28/2/21]