Equine Forelimb Flashcards
(88 cards)
1
Q
What are the characteristics of the equine forelimb, as a highly specialised cursor?
A
- More proximal muscle distribution
- Long limbs relative to body mass
- Large, high powered hip muscles
- Forelimb braking and hindlimb propulsive
- Well developed supporting ligaments and tendons restricting joint motions
- Reduced digits – no need for manipulation/fine motor control
- Thicker tendons and more elastic storage mechanisms
2
Q
What is passive stay apparatus?
A
A set of anatomical structures in forelimb and hindlimb that contribute to helping the limb stay relatively columnar and locks into position when the animals are quiet standing. This prevents the animal from having to put in a lot of muscular effort to keep themselves upright.
3
Q
What are the forelimb passive stay apparatus?
A
- Extra tendinous support to prevent hyperextensions
- Shoulder held stiff
- Body weight directed backward over elbow joint
4
Q
What are the hindlimb passive stay apparatus?
A
- Extra tendinous support to prevent hyperextension
- Patellar locking mechanism at stifle
- Reciprocal apparatus in distal limb – fibularis (peroneus) longus and superficial digital flexor
5
Q
Link the equine digit to the pentadactyl limb.
A
Digits have been lost or reduced. Metacarpals 2 and 4 are remnants either side of metacarpal 3.
6
Q
What is the structure of the equine carpus?
A
Radial, intermediate and ulnar carpal bones
Accessory carpal bone
Carpal bone II, III and IV
Metacarpal II, III and IV
7
Q
Why is the metacarpus and phalanges the most commonly injured region in the horse?
A
- Large forces transferred through singular bones
- Digit III weight bearing
- Modified P3 for weight bearing
8
Q
What is the clinical relevance of the equine forelimb?
A
Kicks in the field – nerve damage
Running into stable door frames – shoulder injuries
9
Q
What is the difference between the extrinsic muscles of the proximal forelimb of the dog and horse?
A
- Very similar to canine, except, only horses contain the subclavius muscle, which acts similarly to the pectorals.
- Omotransversarius except it inserts on the clavicular intersection (and not the scapular spine like in dogs)
- Bracheiocephalicus – forms the border of the jugular groove
10
Q
Where is the subclavius located?
A
Deep to trapezius, omotransversarius and brachiocephalicus. Once considered part of the pectorals.
11
Q
Where does support at the glenohumeral joint come from in the dog and horse?
A
Dog - glenohumeral ligaments
Horse - lateral and medial muscles
12
Q
What are the synovial structures of the equine shoulder joint?
A
Shoulder/scapulohumeral joint is separate from biceps tendon bursa.
Small bursa under infraspinatus tendon on caudal part of greater tubercle.
13
Q
Name the lateral muscles of the equine shoulder.
A
Supraspinatus
Infraspinatus
Deltoideus - no acromial head in horse
14
Q
Name and state the function of the medial muscles of the equine shoulder.
A
Subscapularis - medial support
Teres major - flexor
Coracobrachialis - Medial support
15
Q
Describe the innervation of the equine shoulder muscles.
A
Same as in the dog:
- Flexors – axillary nerve
- Extensors – musculocutaneous nerve
- Lateral – suprascapular nerve
- Medial – subscapular nerve
16
Q
Distinguish the canine and equine elbow joints.
A
- Trochlear notch is made up of ulnar and the radius in front.
- Horse has a little bit of a trochlear notch but most of the weight of the horse is going down through the radius.
- Less likely in horses that there will be an issue therefore between the radius and ulnar and the humerus rotating through the notch, as in dogs.
17
Q
Name the supporting structures in the equine elbow.
A
- Radial head bears most weight
- Humeroulnar articulation much smaller
- Collateral ligaments are very strong and palpable
- Annular ligament is poorly developed
- Joint capsule is a single compartment
18
Q
What are the muscles at the elbow?
A
Triceps brachii - has 3 heads in equine: long, lateral and medial.
Tensor fascia antebarchii - thin sheet of muscle and pulls fascia of the antebrachia used to pull things tight.
19
Q
Describe the location of the equine biceps brachii.
A
- Starts at supraglenoid tubercle, crossing over the shoulder joint and heading down to cross the elbow joint and insert on the radius.
- At proximal end, it moulds over the bicipital groove either side of the intermediate tubercle.
20
Q
What is the function of the biceps brachii?
A
Prevents glenohumeral joint flexing:
- Internal tendon runs the length of the muscle and resists shoulder flexion when standing
- Detaches a branch called the lacertus fibrosus, which blends with epimysium of the extensor carpi radialis. This limits carpal flexion when weight bearing and prevents buckling over of carpus when standing.
21
Q
Name the elbow extensor muscles and their innervation.
A
Radial nerve
- Triceps brachii – only 3 heads and no accessory
- Anconeus
- Tensor fascia antebrachia
22
Q
Name the elbow flexors and their innervation.
A
Musculocutaneous nerve
- Biceps brachii
- Brachialis
23
Q
What is the clinical relevance of teh equine distal forelimb?
A
- The distal limb of the horse is a common site of injury: tendinopathies, fractures, wounds and infections, laminitis
- Racehorses – radial carpal fractures in hyperextension
- Nerve blocks
- Diagnostic imaging
24
Q
Describe 3 different types of metacarpal III bone fractures.
A
- Metacarpal distal condylar fractures are quite common. Fatigue fracture aetiology. Occurs in mostly training and racing horses.
- Medial and lateral condyles are different sizes and shapes. Lateral is narrower and thus more susceptible to injury.
- Articular fractures are more serious and affect joint function.
25
Describe carpal bone fragments.
Fatigue fractures and osteochondritis dissecans. Can affect antebrachiocarpal intercarpal joint.
26
What are the carpus support structures?
- Flexor carpi ulnaris and ulnaris lateralis tendons, which insert on accessory carpal
- Collateral ligament on either side
- Distal accessory carpal ligaments, which prevent dislocation
- Palmar fibrocartilage/ligament, which also prevent carpal bones dislocating
27
Name the carpal joint pouches and their ranges of motion?
Total range of motion = 135˚
Antebrachiocarpal = 90˚
Intercarpal = 45˚
Carpometacarpal = 0˚
28
What is the carpal joint access?
Flexed carpus open the dorsal aspect of the joint and makes needle insertion much easier.
29
Describe metcarpophalangeal joint.
- A hinge joint
- Keel on distal metacarpal III fits into groove on proximal phalanx I. this limits movement to flex and extend. Strong collaterals ligaments.
- Joint capsule – palmer pouch extends proximally between sesamoids and distal metacarpal III
30
Name the sesamoid ligaments.
Interosseus/suspensory ligament
Collateral sesamoidean ligament
Oblique sesamoidean ligament
Straight sesamoidean ligament
Palmar ligaments of the pastern
31
Give the location of the collateral sesamoidean ligaments.
From each sesamoid to the distal end of metacarpal III
32
Give the location of the oblique sesamoidean ligament.
Lateral sides of the sesamoids
33
Give the location of the straight sesamoidean ligament.
From most distal portion of the sesamoids to the proximal ends
34
Give the location of the palmar ligaments of the pastern.
Go across the pastern joint
35
Name the deep sesamoidean ligaments.
- Intersesamoidean ligaments and fibrocartilage
- Cruciate sesamoidean
- (as well as oblique sesamoidean)
36
Describe the structure of the proximal interphalangeal joint.
- Similar structure to the metacarpophalangeal joint
- Strong collateral ligaments
- No large palmar pouch in joint capsule
- Palmar support from superficial deep flexor tendon, straight sesamoidean and palmar ligaments of the pastern
37
Describe the characteristics of carpal and digital extensors.
- All have origin on lateral humeral epicondyle. Some have additional origins and the extensor carpi obliquus is an exception, with origin on the radius only.
- No muscle tissue distal to the carpus, only tendons
- Secured by extensor retinaculum
- All innervated by radial nerve
38
Name the carpal and digital extensors.
From cranial to caudal:
Extensor carpi radialis
Common digital extensor
Lateral digital extensor
Ulnaris lateralis
39
What is the extensor carpi obliquus?
- Loops over the extensor carpi radialis tendon
- Minor carpal extensor
- Analogous to abductor pollicus longus in the dog
40
What is the extensor reticulum?
- Dorsal carpus
- Restrains all extensor tendons
41
What are the sites of carpal joint access?
Medial to the extensor carpi radialis tendon and lateral to the extensor carpi obliquus tendon.
42
What are the characteristics of carpal/digital flexors?
- All have origin on medial hmeral epicondyle. Some have additional origins on the ulna and radius, for example.
- All pass medial to the accessory carpal bone
- All innervated by median/ulnar nerves
43
Name the carpal/digital flexors from superficial to deeper.
Flexor carpi ulnaris
Flexor carpi radialis
Superficial digital flexor
Deep digital flexor
44
What is the function of check ligaments?
Prevent hyperextension
45
What are the functions of the superficial and deep digital flexors?
Superficial digital flexor prevents carpus hyperextending at the metacarpophalangeal joint and proximal interphalangeal joint.
Deep digital flexor supports and prevents hyperextension at metacarpophalangeal joint, proximal interphalangeal joint and interphalangeal joint.
46
Describe the arrangements of the superficial and deep digital flexor tendons.
- Superficial deep flexor tendon forms a sheath around the DDFT at the level of the proximal sesamoids.
- Splits at middle of PI so SDF attaches to distal tubercles of PI and fibrocartilage of PII.
47
Define tendon bursae/sheaths.
Synovial structures forms as separations within fascia around tendons under regions of pressure.
- Can be on 1 side of tendon
- Can encircle most of tendon with mesotendon attachment and include multiple separate tendons.
48
Describe carpal tendon sheaths.
- Most major structures over the carpus have tendon sheaths
- Carpal flexor sheath is largest and encompasses the DDFT and SDFT.
- This is well protected in palmar carpal tunnel and surrounds both tendons, extends from to proximal to joint to just distal.
49
What is the function of tendon sheaths?
Tendon sheaths and bursae make the equine distal limb quite complex because they are pockets where infection can set in and trails infection can track along.
50
Describe digital flexor tendon sheaths.
- Extends from just proximal t metacarpophalangeal joint to just proximal to the navicular bone
- Separate to metacarpophalangeal and proximal interphalangeal synovial compartments
51
Describe the location of the interosseous ligament.
- Runs along the caudal border, along the palmar border of the limb
- Runs form up near carpus down onto the proximal sesamoid bones
52
Describe the structure of the interosseous ligament.
Thick and highly tendinous. Extensor branches of the interosseous loop round medially and laterally around the digit. These interact with the common digital extensor and lateral digital extensor tendons and fuses on the dorsal surface.
53
What is the function of the interosseous ligament?
- Palmar support
- Important to passive stay apparatus
- Suspensory desmitis common in working horses
- Ultrasound and joint blocks diagnostic
54
What is the clinical relevance of the equine foot?
Very common site of clinical problems, such as laminitis, penetrating injuries and solar abscesses.
55
What are the anatomical and lay terms for structures of the distal equine forelimb?
- Metacarpal III, proximal sesamoids = cannon bone
- Metacarpophalangeal joint = fetlock
- Phalanx I = long pastern
- Proximal interphalangeal joint = pastern joint
- Phalanx II – short pastern
- Distal interphalangeal joint = coffin joint
- Distal sesamoid = navicular bone
- Phalanx III = coffin bone
56
Describe the ungual/hoof cartilages.
Inside the hoof:
- Lateral extensions to the caudal tips of P3
- Elastic to allow expansion of heel bulbs with locomotion
- Can become ossified with age or if overworked, causing a lack for elasticity and causing lameness.
57
Describe the structure of the interphalangeal joint.
- Joint itself I completely encased in the hoof wall
- Joint capsule protrudes dorsally and palmarly. Can access at this point for joint injections, most common dorsally.
- Has lower range of motion than the metacarpophalangeal and proximal interphalangeal joints.
- No sagittal ridge in joint surfaces
- Dorsal surface of navicular forms palmar aspect of joint
58
How is the distal interphalangeal joint supported?
- Supported by the common digital extensor in the forelimb
- Supported by the long digital extensor in the hindlimb dorsally
- Palmar and plantar support from the deep digital flexor tendon and navicular bone
- Collateral ligaments laterally and medially
59
What is the navicular bone and bursa?
- Distal sesamoid bone at distal interphalangeal joint
- Navicular bursa between bone and fatty heel pad
- Not continuous with the distal interphalangeal joint but important in foot lameness
60
Describe the position, structure and function of the subcutis/fatty digital pad?
- Connects the dermis to P3, tendons and hoof cartilages
- Thickened to form coronary cushion and digital cushion via increased collagen and elastin fibres
- Acts as a pump to move blood from the toe while walking
- Compression and relaxation helps to pump blood back up the limb and from the foot during walking.
61
What structure are affected by penetrating wound, for example, the common presentation of a street nail?
Deep structures to be concerned about:
- Navicular bone/bursa
- Deep digital flexor tendon sheath
- Coffin joint
- Digital cushion
62
How is the skin of the hoof modified and why?
- Solid structure of heavily keratinised epidermis over less stiff modified dermis.
- Protects underlying soft tissues.
- Dermal layer held to soft tissues via lots of interdigitating laminae.
- Wall bears majority of the weight and force is transmitted between the hoof wall and P3 via the laminae.
63
Describe how the foal hoof grows?
- Deciduous hoof capsule in utero protects the mother’s organs
- Young foals lean back on their heel s
- Foal hoof growth is fast and a cease in the hoof wall denotes the change in mechanical circumstances after birth
- Hoof grows faster proximally – distal hoof horn has been compressed by repeated loading
64
Name the layers of the hoof wall.
1. Stratum externum
2. Stratum medium
3. Stratum internum – white line
65
What is the peripole?
Soft rubbery horn that grows over the top of the coronary band. Forms a thin outer layer of hoof and is thicker over heel bulbs.
66
Describe the position of the stratum externum.
Produced over the perioplic dermis, just proximal to the coronary dermis.
67
Describe the stratum medium.
- Usually pigmented
- Consists of horn tubules embedded within intertubular horn
- Stratum medium slides over the dermis and is worn away by ground contact
68
Describe the stratum internum.
- Non pigments laminar horn
- 600 primary keratinised lamellae, each with 150 secondary lamellae
69
Explain the link between interdigitation and laminitis.
- Strong bond
- Constantly forming and reforming
- Can be compromised allowing the pedal bone to rotate
- Laminitis – inflammation of dermis of hoof, causing breakdown of digital lamellae and causing pain and rotation and sinking of P3
70
Describe the blood supply to the laminae.
- Medial digital artery and vein
- Dorsal branch of digital artery and vein
- Ventral branch of digital artery and vein
- Palmar digital arteries anastomose within P3
71
Describe the neurovasculature of the equine forelimb.
Subclavian artery > axillary artery > suprascapular and subscapular branches of the axillary artery
Axillary artery > brachial artery > median artery > median and lateral palmar and digital artery branches
Veins are mostly satellite except cephalic vein.
72
Describe sensory innervation of the equine forelimb.
Axillary – lateral shoulder region
Musculocutaneous – medial antebrachium
Radial – lateral antebrachium
Median/ulnar nerves – caudal antebrachium
73
Where is radial sensory innervation in the equine limb?
Radial sensory innervation does not go past the carpus in horses: only median/ulnar nerves supply past the carpus.
74
What are the median and ulnar nerves?
Main sensory input from the median and ulnar also contributes. In order to desensitise the distal limb, both must be blocked.
75
What are the medial and lateral palmar nerves?
Medial and lateral palmar nerves from the median nerve, between sensory ligaments and flexor tendons
76
What are the medial and lateral metacarpal nerves?
Medial and lateral palmar metacarpal nerves from lateral palmer nerve and palmar branch of ulnar nerve. Deeper, they descend on axial surface of splint bones.
77
What are the median and lateral palmar digital nerves?
Medial and lateral palmar digital nerves from medial and lateral palmar. Run with palmar digital vessels. Dorsal branches from nerve around level of fetlock supply the dorsal 1/3 of foot.
78
What can nerve blocks be used for?
Nerve blocks can be performed in a series to test for site of pain.
79
Describe nerve blocking the palmar digit.
- Blocks navicular bone and palmer first 2 thirds of the foot
- Injection sites for the medial and lateral digital nerves are just above the heel bulbs, where the neurovascular bundles can be palpated.
80
Describe nerve blocking the abaxial sesamoid.
- Blocks whole foot and most of pastern, but dorsal pastern may remain sensitive.
- Includes dorsal rami supplying dorsal foot and pastern.
- Injection sites for the medial and lateral digital nerves are abaxial to the sesamoids where the neurovascular bundles can be palpated.
81
Describe the low 4 point metacarpal block.
- Medial and lateral palmar nerves are medial and lateral to flexor tendons
- Medial and lateral palmar metacarpal nerve can be palpated at the end of the metacarpal II and IV
- Blocks whole fetlock joint and distal to it, except perhaps the dorsal pouch of fetlock joint
82
What are the injection sites for a high 4 point metacarpal block?
Palmar metacarpal nerves can be palpated at proximal splint bones and injected axial to these.
Medial and lateral palmar nerves can be injected medial and lateral to the SDFT and DDFT.
Blocks everything distal to injection sites.
83
What landmark of the scapula is present in dogs but not horses?
The acromion process – the horse does not have an acromial head of the deltoideus muscle.
84
What limits the ability for the antebrachium to pronate and supinate in horses?
The radius and ulna are fused to each other and cannot move independently.
85
What nerves supplies the carpal and digital extensors?
Radial nerve supplies the carpal and digital extensors.
86
If the navicular bursa has been penetrated and infected, is the distal interphalangeal joint likely to be affected too?
No. the navicular burse and distal interphalangeal joint do not communicate, so infections between these spaces are spread only when the separation is disrupted by trauma or inflammation.
87
With equine laminitis, which layer of the hoof wall becomes inflamed initially? What happens to the distal phalanx in chronic laminitis?
Lamellar dermis. The tip rotates palmarally within the foot.
88
Which if any joint compartments communicate in the equine carpus?
Intercarpal and carpometacarpal joint compartments.
