Muscles and Tendons of the Distal Limb

What are the general features of muscles found in the antebrachium?

• Affect joints of carpus and digits

• Originate epicondyles of humerus

• Muscle belly located in antebrachium

• Tendons of insertion - are distal to carpus

Describe the following features of the extensor carpi radialis muscle:

• Origin

• Insertion

• Function

• Nerve Supply

• Useful landmark

• Extensor carpi radialis muscle

•  O = lateral epicondyle of humerus

•  I = Metacarpal bones

• Location:

• Cranial aspect of antebrachium

• Function:

• Crosses dorsal aspect carpus

• Carpal EXTENSOR

• Nerve supply

• Radial nerve

• Oblique muscle

  • Crosses at level of carpus

  • Useful landmark

Describe the following features of the common digital extensor muscle.

• Origin

• Insertion

• Function

• Nerve Supply

Common digital extensor muscle

• O = lateral epicondyle of humerus

• I = all digits

• distal phalanx - extensor process

• Location:

• Cranio-lateral aspect of antebrachium

• Function:

• Crosses dorsal aspect carpus

  • Carpal EXTENSOR

• Crosses dorsal aspect metacarpo-phalangeal joints & interphalangeal joints

  • Digital EXTENSOR

• Nerve Supply:

• Radial nerve

How does the branching of the common digital extensor muscle differ between species?

• Dogs

  • 4 branches (+1 to the dew claw if present)’

• Horse

  • 1 branch, attaches dorsal aspect of phalanges and protected by joint capsules'

  • Receives branches of the suspensory ligament

Describe the following features of the extensor carpi ulnaris / ulnaris lateralis muscle.

• Origin

• Insertion

• Function

• Nerve Supply

extensor carpi ulnaris / ulnaris lateralis muscle

• O = lateral epicondyle of humerus

• I = Metacarpal bone + ACB

• Location:

• Lateral aspect of antebrachium

• Function:

• Crosses lateral aspect carpus

• Carpal EXTENSOR & FLEXOR

  • Depends on position of limb

• Nerve supply:

• Radial nerve

Describe the following features of the flexor carpi ulnaris muscle. 

• Origin

• Insertion

• Function

• Nerve Supply

flexor carpi ulnaris muscle

• O = medial epicondyle

• O = Olecranon process of ulna

• I = ACB

• Location:

• Caudal aspect of antebrachium

• Function:

• Crosses caudal aspect carpus

• Carpal FLEXOR

• Nerve supply

• Median & Ulnar nerves

Describe the following features of the superficial digital flexor muscle. 

• Origin

• Insertion

• Function

• Nerve Supply

superficial digital flexor muscle

• O = medial epicondyle

• I = all digits (middle phalanx)

• Location:

• Caudal aspect of limb

• Function:

• Crosses palmar aspect carpus

  • Carpal FLEXOR

• Crosses palmar aspect of Metacarpo-phalangeal joints & Proximal interphalangeal joints

  • Digital FLEXOR

• Nerve Supply:

• Median & Ulnar nerves

Describe species differences in the branching of the superficial digital flexor muscle.

• Dog:

• 4 branches (+1 to dew claw)

• Horse:

• 1 branch

• Receives Accessory Check ligament (ACL) from radius

  • Proximal to carpus

  • Limits length of tendon / protects muscle belly from over-stretching

• Both:

• Splits to allow passage of DDFT -

  • Inserts middle phalanx

Describe the following features of the deep digital flexor muscle. 

• Origin

• Insertion

• Function

• Nerve Supply

deep digital flexor muscle

• O = medial epicondyle

• O=radius & ulna

• I = all digits(palmar process distal phalanx)

• Location:

• Caudal aspect of limb

• Function:

• Crosses palmar aspect carpus

  • Carpal FLEXOR

• Crosses palmar aspect Metacarpo-phalangeal joints & both interphalangeal joints

  • Digital FLEXOR

• Nerve Supply:

• Median & Ulnar nerves

Describe species differences in the branching of the deep digital flexor muscle. 

• Dog

• 4 branches (+ 1 to dew claw) *

• Horse:

• 1 branch

• Receives Accessory check ligament

  • Extension of carpal joint capsule

  • Distal to carpus

  • Limits length of tendon / protect muscle belly

• Both:

• Pass through split in SDFT to insert

• Insert distal phalanx

• Horse - runs over distal sesamoid

Summarize the muscles of the distal forelimb, dividing them into the:

• Extensors

  • Origin

  • Location

  • Nerve Supply

• Flexors

  • Origin

  • Location

  • Nerve Supply

What regions of the equine distal limb are the extensor and flexor tendons found?

• Where do they run?

• Carpus:

• Extensor tendons - dorsal aspect

• Flexor tendons - palmar aspect

• Run through carpal canal

What are the boundaries of the carpal canal?

• Boundaries of carpal canal:

• Dorsal - Palmar aspect of carpal joint capsule

• Lateral - ACB

• Palmar - palmar / flexor retinaculum (Compression band or sleeve of fibrous tissue encasing)

What are the contents of the equine carpal canal?

• How about the carnivore carpal canal?

• Contents of carpal canal in equines:

• Deep digital flexor tendon (DDFT)

• Superficial digital flexor tendon (SDFT)

• Blood vessels & nerves

In Carnivores:

• SDFT runs OUTSIDE the carpal canal

• DDFT inside

What are the purpose of tendon sheaths in the equine distal limb.

• What effect can inflammation have in this location?

• Tendon Sheath:

• Fluid filled

• Protect tendons where pass through confined spaces

• Inflammation:

• increased fluid volume / pressure

• bulges proximally & distally

What other supportive structures are found in the distal equine limb?

• Consider dorsal aspect

• And palmar aspect

• Dorsal aspect limb:

• CDE held in place by retinaculum-

• Palmar aspect limb:

• SDFT & DDFT held in place by

  • Carpal canal

• Annular ligaments

• Fetlock & pastern regions

• Length limited by check ligaments

• Accessory Check Ligaments

• Provide palmar support for carpus & all distal limb joints

• Protected by tendon sheaths

Summarize the type of tendons on the:

• Dorsal Aspect

• Palmar Aspect

• Dorsal aspect = extensor tendons

• Palmar aspect =

• Skin

a. SDFT

b. DDFT

c. Check ligament (Fuses with DDFT)

d. Suspensory ligament (Splits into 2 branches)

What are “chestnuts” on the equine limb?

• Chestnuts are vestigial structure found on the medial aspect of the antebrachium, thought to be remnant of 1st metacarpal bone

• Vestigial horn pad

What are “ergots” on the equine limb?

• Lump in skin found on palmar aspect of MCP joint hidden by feathers

• Thought to be remnant of metacarpal pad

What is the purpose of the equine stay apparatus?

A mechanism for passive weight bearing, allowing horses to sleep while standing, stand without effort.

• Most of weight is borne on the forelimb, hindlimb is more fore propulsion

HOW does the stay apparatus work?

• Requirements:

• Maintenance of all joints in weight- bearing extension

• Proximal limb joints:

• Prevention of flexion in shoulder and elbow

• Carpus:

• Prevention of flexion

• Prevention of hyperextension

• Distal limbs joints:

• Prevention of hyperextension

What key muscles are important parts of the equine stay apparatus and what actions or purpose does each have?

• Serratus ventralis

• Suspends weight of body between forelimbs, acting like a sling

• Proximal limb joints & carpus:

• Prevention of flexion:

• Shoulder:

  • Biceps brachi, maintains shoulder in extension, preventing collapse

• Elbow:

• Collateral ligaments (caudal location)

• Alignment of bones

• Carpus:

• Lacertus fibrosis, fibrous extension of biceps

How do the carpus and distal limb joints prevent hyperextension in the equine stay apparatus?

• Carpus:

• Palmar fibrocartilage joint reinforcement at level of the carpus

• SDFT and check ligament

• Retinaculum

• MCP, PIP & DIP joints:

  • DDFT & SDFT

    • Check ligaments

    • Annular ligaments

• MCP / Fetlock joint :

• Suspensory ligament

• Common digital extensor

• Proximal sesamoids

• Distal sesamoidean ligaments

  • (short, cruciate, oblique & straight)