Lecture 6 - Standing Without Effort
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Transcript of Lecture 6 - Standing Without Effort
AAEP 56th Annual Convention: Baltimore, Maryland 2010
Standing without effort (mostly)
Dr.KathrynCarmalt,DVM,MSc,BA,AS
UNIVERSITY OF SASKATCHEWAN Saskatoon, Saskatchewan, Canada. www.usask.ca
Stifle
Hock
Suspensory Ligament
Cannon
Knee
Ergot
ElbowGaskin
Flexor tendons
Forearm
Point of Shoulder
Parts of the Horse Leg
Hoof
Shoulder
Point of hip
Pastern
Fetlock
Hip
Thigh
Chestnut
Special adaptations needed
As size doubles -> wt3, yet cross-sectional area2… which means the animal would have to have huge muscle mass to support its wt.
Evolutionary adaptations • Increase limb length • Restriction of range
of motion (osteology)
• Muscle replaced by tendons.
• Muscles located at proximal end of limb
Passive Stay Apparatus
Increase efficiency of locomotion as well as efficiency at rest.
Passive stay apparatus In the forelimb
• Syncarcosis • Biceps brachii • Lacertus fibrosis • Suspensory apparatus
In the hindlimb
• Stifle-locking mechanism • Reciprocal apparatus/
mechanism of stifle/hock • Suspensory apparatus
The forelimbs support 60%
of body weight
The Stay Apparatus
Adapted from Dyce, Sack and Wensing (2001)
The Stay Apparatus Fixing the Shoulder (3 parts)
Muscle mass of the shoulder – Extrinsic (1° serratus ventralis)
Adapted from Dyce, Sack and Wensing (2001)
The serratus group, trapezius group, rhomboid group, and pectorals suspend the trunk between the forelimbs and stabilizes the shoulder.
Extrinsic Muscle Mass of the Shoulder
From Dyce, Sack and Wensing (2001)
Rupture of the synsarcosis (mainly the serratus) is mercifully rare
When this fails!
Adapted from Dyce, Sack and Wensing (2001)
The Stay Apparatus Fixing the Shoulder
• Muscle mass of the shoulder • Tendon of the biceps brachii
Specimen, Tuskegee University
Craniolateral view of the shoulder joint
Lesser tubercle
Intermediate tubercle
Scapula
HumerusGreater tubercle
Superglenoid tubercle
Tendon of the biceps brachii
This is what it looks like in
the fresh state
Origin
Fibro-cartilaginous pad
Muscle belly Image courtesy of Peter Flood
Plastinated specimen, Tuskegee University
Tendon of origin of the biceps has a strong,
curved, fibro-cartilaginous pad with a depression on caudal surface that matches
the intermediate tubercle
When the tubercle and the depression are tightly engaged, the shoulder is fixed
Adapted from Dyce, Sack and Wensing (2001)
Locking of the shoulder joint is essential to fixation of the forelimb.
This line represents the biceps brachii
Simplified from Dyce, Sack and Wensing (2001)
Assume that the shoulder is locked and that it can no longer flex
In this case, the only action of the triceps is to extend the elbow holding it in the fully extended position
This action is opposed by the biceps
The Stay Apparatus Fixing the Elbow
• Long head of Triceps – Innervation? Why is this important?
Differential Diagnoses?
5.5 mm Cortical Screw (medium-size threads on screws)
6.5 Cancellous Screw (bigger threads on screws)
4.0 Locking Screws(smallest threads can hardly see here)
Tension band wire
Courtesy of Dr. James Carmalt
Adapted from Dyce, Sack and Wensing (2001)
The Stay Apparatus Fixing the Shoulder
• Muscle mass of the shoulder – Extrinsic
• Tendon of the biceps brachii • Lacertus fibrous
Lacertus fibrosus: a substantial structure in the horse (less so in ruminants, absent in small animals)
Biceps
Extensor carpi radialis
Lacertus fibrosus
Simplified from Dyce, Sack and Wensing (2001)
Continuous fibrous band from the scapula to the metacarpus: • Tendon running through biceps is
continued distally by the lacertus fibrosus to the tendon of insertion of the extensor carpi radialis
• Under tension in the standing horse - created by opposing forces of biceps and triceps
Thus, when the shoulder is fixed the carpus is held in full extension
• Superficial digital flexor tendon
• Deep digital flexor tendon
• Suspensory ligament – Aka interosseous ligament
• Sesamoidean ligaments
The Suspensory Apparatus of the Digit
Simplified from Dyce, Sack and Wensing (2001)
Imagine a horse landing from a jump . . . .
The suspensory apparatus.
Superficial digital flexor Medial view
Single origin from medial epicondyle
Adapted from Ellenberger Baum (1912)
Strong accessory (“check”) ligament above the carpus on the medial side
Inserts on proximal end of middle phalanx
Deep digital flexor Medial view
Three heads
Strong accessory (“check”) ligament below the carpus
Inserted on distal phalanx just as in the hindlimb
Adapted from Ellenberger Baum (1912)
And if the system fails:
Bowed tendons and related conditions
Interosseus and sesamoidean ligaments
Interosseus arising from palmar surface of the third metacarpal bone (between MC 2 & 4)
Sesamoidean ligaments
Extensor branch
Adapted from Ellenberger Baum (1912)
What about the hind limb?
Adapted from Robert Kainer in Adams’ Lamness in Horses (1987)
Sacroiliac joint
Hip (flex)
Stifle (flex)
Fetlock (over extend)
Hock (flex)
Effect of body weight on joints of the hind limb
You can’t use muscle to defy gravity for
very long
The Reciprocal Apparatus & Patella Lock
Adapted from Robert Kainer in Adams’ Lamness in Horses (1987)
Superficial flexor
musculotendon unit
Peroneus tertius
The Reciprocal Apparatus
Gastrocnemius mm
Adapted from Robert Kainer in Adams’ Lamness in Horses (1987)
Hip
Stifle
Fetlock
Hock
The Reciprocal Apparatus
The hock and stifle MUST flex together
Which of these limbs has a reciprocal apparatus?
With rest, recovery is spontaneous and complete
Ruptured peroneus tertius
The horse can still bear weight in the limb
Falls in which the distal hindlimb is forcibly retracted
From Adams’ Lamness in Horses (1987)
Wrinkles
Failure of the Reciprocal Apparatus
Gastrocnemius rupture Peroneus tertius rupture
The Stay Apparatus Fixing the hip & pelvis
• Muscle mass of the hip • Locking of the stifle
Adapted from Robert Kainer in Adams’ Lamness in Horses (1987)
The Stay Apparatus Fixing the Stifle
Adapted from Robert Kainer in Adams’ Lamness in Horses (1987)
• The “patella lock” – The patella is brought proximal and
lateral by quadriceps and tensor fascaie latae
– Medial patellar ligament “catches” over medial trochlear ridge of distal femur
• The “patella unlock” – Quadriceps bring patella proximal and
medial into normal position
Patella
Middle patellar ligament
Left equine stifle,
cranial view
Medial patellar ligament Lateral
patellar ligament
Medial ridge of trochlea
Quadriceps insert onto patella VIA the patellar ligaments
Patella
Medial miniscus
Left equine stifle, medial
view
Medial collateral ligament
Medial patellar ligament
Medial ridge of trochlea
Articular surface of the patella
Medial miniscus
Left equine stifle, cranio-medial view
Medial patellar ligament
Medial ridge of trochlea
Lateral ridge of trochlea
The condition can recur so probably restablishment of the ligament
Inability to release the locked patella
Cutting the medial patellar ligament gives immediate relief
Young horses in poor condition
From Adams’ Lamness in Horses (1987)
Adapted from Robert Kainer in Adams’ Lamness in Horses (1987)
Just a little more detail needed
Fixation of the hock
Trochlea of talus
Calcaneus
Right equine hock, lateral
view
3rd metatarsus
Calcanean tuber
Collateral ligament
Plantar ligament
4th metatarsus
Trochlea of talus
Calcaneus
Right equine hock, medial
view 3rd metatarsus
Calcanean tuber
Collateral ligament
Plantar ligament
2nd metatarsus
Groove for deep digital flexor tendon
Medial tendon of insertion of
the cranial tibial muscle
Equine hock, medial view
Calcanean tuber covered by superficial
flexor
Plantar ligament
Deep digital flexor tendon
The Suspensory Apparatus of the Hind Limb
• Same basic components as front limb
• No superior check in hind limb
Adapted from Robert Kainer in Adams’ Lamness in Horses (1987)
Straight sesamoid ligaments
Sesamoid ligaments
Superficial flexor insertion
Sesamoid bones embedded in fibrocartilage
Interosseus muscle!
Oblique sesamoid ligaments
Deep flexor insertion
Passive stay apparatus In the forelimb
• Syncarcosis • Biceps brachii • Lacertus fibrosis • Suspensory apparatus
In the hindlimb
• Stifle-locking mechanism • Reciprocal apparatus/
mechanism of stifle/hock • Suspensory apparatus