Skeletal structure of the Equine Forelimb

University of Liverpool,
School of Veterinary Science

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Created by
Mr P P Tomlinson
Liverpool Veterinary Student

Welcome to “Skeletal Structure of the Equine
Forelimb” this resource has been created as
part of the “Online Veterinary Anatomy
Museum” (OVAM) in conjunction with
Liverpool Vet School.
It aims to provide a detailed guide to the
relevant bony landmarks present on the equine
forelimb (Chapter One) and also highlight
certain ligaments and tendons, particularly in
reference to the joints (Chapter Two).

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 Forelimb Overview  Distal Phalanx: Dorsal View
 Scapula: Lateral View  Distal Phalanx: Cranial View
 Scapula: Medial View  Distal Phalanx: Ventral View
 Humerus: Lateral View  Distal Phalanx: Caudal View
 Humerus: Medial View  Hoof: Dorsal View
 Humerus: Cranial View  Hoof: Ventral View
 Humerus: Caudal View  Information Slides
 Radius and Ulna: Lateral View  Scapula Information
 Radius and Ulna: Medial View  Humerus Information
 Radius and Ulna: Cranial View  Condyle: Cranial View
 Radius and Ulna: Caudal View  Condyle: Caudal View
 Carpus  Radius and Ulna Information
 Carpal Bones  Carpus Information
 Manus Overview  Metacarpal Region Information
 Below the Carpus  Proximal Phalanx Information
 Metacarpal Region  Middle Phalanx Information
 Proximal Paired Sesamoids  Navicular Bone Information
 Proximal Phalanx  Distal Phalanx Information
 Middle Phalanx
 Navicular Bone

Chapter Two Start

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For Condyle
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Note: The proximal and distal
parts of the ulna are fused to the
radius. The lateral styloid process
is the fused distal portion of the
ulna. The body of the ulna is
absent.


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• The equine scapula has no acromion process
• Due to the position of the scapular spine there is a
large infraspinous fossa
• There is a central tuberosity on the scapular spine
• Well developed supraglenoid tubercle and coracoid
process
• The supraglenoid tubercle is separate from the
glenoid cavity
• Extensive scapular cartilage when compared to other
species

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• The equine humerus is quite horizontal in
comparison to that of the dog and cat
• The greater tuberosity is split into a larger cranial
portion and a smaller caudal portion
• The musculospiral groove is relatively deep
• The deltoid tuberosity is large
• Well-developed epicondyles
• Unlike the dog/cat, the horse has no supratrochlear/
supracondylar foramen
• The Presence of an intermediate tubercle results in
the formation of a double inter-tubercular groove

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Note: The olecranon
fossa receives the
anconeal process of
the ulna when the
elbow joint is
extended

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• Prominent tuberosities on the radius allow for the
• The proximal quarter ligaments and the biceps muscle
insertion of collateral of the radius is held to the ulna by
ligaments, beyond this the two bones are fused
• Grooves for the extensor tendons are present on the
• The distal third/half of the ulna fails to form apart from
cranial portion of the distal extremity of the radius
the lateral styloid process
• Fusion of the radius and ulna result in a lack of pronation
• The lateral styloid process(Unlike distal extremity of the
or supination at this level (fused the dog and cat where
ulna) will appear in foals as a secondary ossification
the interosseus space allows for a large amount of
centre
pronation and supination)
• There is a small interosseus space at the proximal
radio-ulnar notch through which blood vessels pass.
Beyond this the ulna is either fused with the radius or
fails to develop

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• There is a two row arrangement
• The proximal row comprises of the ulnar carpal
bone, intermediate carpal bone, radial carpal bone
and the accessory carpal bone.
• The distal row comprises of the 4th carpal bone, 3rd
carpal bone and 2nd carpal bone. The 1st carpal bone
is generally absent, however, if present it will be very
small and easy to mistake for a fracture
• The accessory carpal bone articulates with both the
radius and the ulnar carpal bone

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• The third metacarpal is the functional weight bearing
bone of this region. The second and fourth metacarpal
bones are also present in the form of splint bones
• MC3 articulates proximally with the carpal bones and
distally with the proximal sesamoids and proximal
phalanx
• Splint bones also articulate with the carpal bones but
taper to a point (known as the button) approximately two
thirds down MC3
• The buttons are a useful landmark for nerve blocks
• The junction between MC2 and MC3 is a common location
forsplints. Splints are a typical ailment of the equine
forelimb
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• The proximal phalanx is often referred
to as P1 or the long pastern
• Collateral ligaments insert onto
palpable tubercles on P1’s surface
• The caudal surface is V-shaped to
accommodate the oblique sesamoidean
ligaments

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• The middle phalanx is often referred to as P2 or the
short pastern
• Approximately half of P2 is buried in the hoof
• Lateral hoof cartilages lie on both the medial and
lateral sides of P2
• The superficial digital flexor tendon (SDF) inserts on
the proximal edge of P2
• P2 articulates with both the distal phalanx and the
Navicular bone

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• An unpaired boat-shaped bone that articulates with both
P2 and P3
• The deep digital flexor tendon runs over its palmar
surface
NAVICULAR DISEASE
• Navicular disease is a complex condition with a wide
variety of suspected causes
• Ultimately it is a long term degenerative condition of both
the navicular bone and bursa
• It is the most common causes of long term forelimb
lameness

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• The distal phalanx is also known as P3 or the coffin bone,
it articulates with P2 and the navicular bone to form the
coffin joint
LAMINITIS
•Laminitis involves inflammation of the sensitive lamina that
secure the bones of the distal limb extremity to the hoof wall
• This inflammation leads to separation of the sensitive lamina
from the interdigitating insensitive lamina
• The distal phalanx will then rotate due to the pull of the deep
digital flexor. The tip of the distal phalanx will eventually
penetrate the soft horn of the sole

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• The hoof covers and protects the distal extremity of the digit
• The hoof is formed from keratinized epithelium secreted by the modified
dermis covering the distal extremity of the digit
• Expansion of the hoof dissipates pressure helping to prevent concussive
damage on impact
• The join between skin and hoof is called the coronet
• The sole of the hoof lies between the wall and the frog
• The white line is the junction between the sole and the wall of the hoof,
shoe nails are driven into the outer edge of this line
• The concave surface means that only the frog and wall make contact with
the ground
• The frog is a wedge-shaped projection into the sole, with its base set
between the two heels. The caudal end of the frog extends over the heel
and is known as the heel bulb, and the groove between the frog, bar and
the sole is called the paracuneal groove

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 Joints of the Forelimb Overview  Information Slides
 Shoulder Joint  Shoulder Joint Information
 Elbow Joint  Elbow Joint Information
 Carpal Joints  Carpal Joint Information
 Fetlock Joint  Fetlock Joint Information
 Ligaments of the Fetlock/Pastern Joints  Pastern Joint Information
 Coffin Joint  Coffin Joint Information
 Annular Ligaments  Annular Ligaments Information

Chapter One Start

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• Although a ball and socket joint,the shoulderactually
functions more like a hinge joint
• The tendons of supraspinatus and infraspinatus act as
collateral ligaments supporting the joint
• Supraspinatus tendon splits forming attachments with the
lesser tuberosity and the cranial portion of the greater
tuberosity.
• Bicepsbrachii originates from the supraglenoid tubercle
by way of a grooved cartilaginous tendon. This tendon is
supported by the intertubercular bursa (biceps bursa)
• Bursa and tendon are held in place by the transverse
humeral ligament and then overlaid with the aponeurosis
of the deep pectoral muscle

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• Typically described as a “snap” joint, where while
standing the joint is very stable but on flexion
becomes more movable.
• This is due to two specific anatomical features:
• The humeral condyles have unequal curvature,
this means the radius of the central portion is
greater than the radius of the cranial and
caudal parts (highlighted in previous slide)
• The medial and lateral collateral ligaments
have eccentric insertions on the humerus

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•
• A common outer fibrous capsulejoint comprises of:
As a compound joint, the carpal surrounds the
overall joint and each individual joint is surrounded
by an innerradiocarpal (antebrachiocarpal) joint,
• The synovial pouch
which is between the radius and the proximal
• Collateral ligaments The present on the medial and
carpal bones. are majority of the movement
lateral occurs here
surfaces extending from the radius to the
metacarpals
• The intercarpal (middle carpal) joint, which is
• The carpal canal is occupied by the superficial and
between the two rows of carpal bones
deep digital flexor tendons surrounded by a common
• The carpometacarpal joint between the distal
synovial sheath
carpal bones and the metacarpals. Here
• The accessory carpalminimal palmar carpal
movement is ligament,
ligament and flexor retinaculum all oppose over
extension of the carpus

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• The joint between metacarpal three, the proximal phalanx and
the proximal palmar sesamoids
• The main ligaments of this joint are shown on the previous
slide
• Of particular importance is the proximal extension of the thick
palmar ligament. This approximately 2cm enlargement serves
a number of functions
• Increases the bearing surface for the flexor tendons
• Supports the flexor tendons during over extension of
the fetlock
• Prevents bone to bone contact during flexion of the
fetlock when the sesamoids move up along the
condyles of MC3

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• The joint between the long pastern (P1) and the short
pastern (P2)
• This particular joint has fairly restricted movement
• Paired axial and paired abaxial palmar ligaments
extend from P1 to the fibrocartilage of P2
• These ligaments oppose over extension of the joint,
the straight sesamoidean ligament also aids this

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• The coffin joint involves P2, P3 and the
navicular bone
• There is very little movement at this joint
• The collateral ligaments between P2 and P3
are short and thick
• The navicular bone is held in place by
collateral navicular ligaments, a proximal
navicular ligament and a distal navicular
ligament

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• The annular ligaments hold the flexor tendons in place
• They are formed from localized thickened fascia

• The palmar annular ligament attaches the abaxial
borders of the sesamoids to the superficial digital
flexor tendons
• The proximal digital annular ligament is X-shaped
when seen in a palmar view
• The distal digital annular ligament is U-shaped when
seen in a palmar view. It arises from the proximal
phalanx and covers the collateral navicular ligament. It
also separates the deep digital flexor tendon from the
digital cushion

Resource Map

Skeletal structure of the Equine Forelimb

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