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Anatomy & biomechanics
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Anatomy & biomechanics

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  • Functional Anatomy & Biomechanics of the Distal Forelimb Presented by: Mitch L. Taylor, CJF The Kentucky Horseshoeing School “Excellence Through Education”
  • The equine limb and boot have evolved into a highly specialized appendage to maximize speed, endurance and efficient locomotion. The horse’s lower limb design is referred to as unguligrade . This means that he is standing on the very tip of his toe with only one bone for the foundation of the limb. This arrangement maximizes efficiency but has low tolerances for error in its various planes of balance. In comparison, the human which is referred to as plantigrade, or the dog and cat which are referred to as digitigrade, have several bones in the foot as the foundation of the limb resulting more surface area per unit weight of body mass thus allowing for more stability.
  • The horse has developed over time as a highly specialized locomotor machine adapted for travel over long distances at moderate rates of speed with the additional capability of high rates of speed for shorter distances. The elongated Third Metacarpal and Metatarsal bones have been combined with a grouping of muscles at the proximal end of the limb to provide a long lever arm with powerful drivers. The long lever provides a longer stride per unit of muscle work than in the animal with shorter legs. These long lever arms, however, are not well adapted for developing force or stability, and the large draft horse, for example, has to depend on it’s great weight to move loads in a quite inefficient mechanical manner. Consequently, a number of muscles have been reduced in size and others are connected to tendoligamentis structures which subserve a marked degree of automacity in lower leg function. The so-called Check and Suspensory ligaments are examples. A knowledge of the detailed anatomy, both osteological and tendoligamentis, is essential for a proper understanding of correct footcare and lamenesses of the feet and limbs.
  • As a result of the specialized design features of the horse, it has evolved into a highly athletic animal with great power speed and agility able to compete in a variety of athletic endeavors.
  • As we know, bones of the appendecular skeleton are best suited to resist the forces of compression although there are many specialized bones in the distal limb of the horse that have additional functions. The Distal Sesamoid bone functions to increase the mechanical advantage of the Deep Flexor tendon which results in a constant angle of insertion for the tendon.
  • The Proximal Sesamoid bones act as a pulley and move the fulcrum of the Fetlock joint farther away from its center of rotation which maximizes tendon strength. Because they don’t resist compression, these bones are particularly subject to injury in racing due to the tensile forces they must resist from the Suspensory ligament and the Sesamoidian ligaments.
  • The Splint bones, or 2 nd and 4 th Metacarpal/Metatarsal bones, are attached to the Canon bone (3 rd Metacarpal/Metatarsal) by way of the Interosseus ligaments which ossify at skeletal maturity. Because the distal ends of the bones do not communicate in a joint the compressive forces are taken by the Interosseus ligaments. The function of the Splint bones is to increase the surface area of the floor of the Carpus.
  • A close-up view of the very strong and fibrous Interosseus ligament.
  • The Coffin bone weighing 3-4 ounces in the mature horse is considered a modified cuboidal bone. Its seemingly fragile architecture is strengthened by the engorgement of blood that is trapped in the hoof capsule. The Coffin bone is subject to a high degree of remodeling during development as is indicated by the different medial and lateral angles.
  • This Coffin bone of a 3-year old racehorse shows how the bone has remodeled due to chronic over-trimming of the sole.
  • This sagittal section of the Coffin bone shows the large medullary cavity including the Central Terminal Arch and the relatively thin outer Cortical bone. Notice the thickening of the Cortical bone at the insertion of the Deep Flexor tendon.
  • The Hyaline cartilage of the Coffin bone is approximately twice as thick as the cartilage on other joint surfaces.
  • Joints of the distal limb do not generally articulate in one plane, but rather, around a slight radius as indicated by the break in straight line of the cannon bone and long pastern bone.
  • In order to maintain soundness the horse has developed a highly orchestrated sequence of events that occurs during athletic movement that are referred to as the phases of the stride. The phases of the stride are: Heel Strike or ground impact Slide phase Loading phases Heel lift-off and breakover Swing phase. The impulsion generated for heel lift-off and breakover is initiated by the suspensory apparatus at mid stance. As the foot leaves the ground, the lower limb flexes and muscles of the proximal limb protract the limb forward. The velocity of the foot at this point is greater than the velocity of the body. At the end of the protraction phase, the foot extends and the limb is retracted to the ground. As the limb is retracting, the joints are pulled into the close packed position getting ready for ground impact. During this retraction phase, the velocity of the limb is decelerated.
  • Tendons and Ligaments of the Distal Liimb
  • Origin of the Superficial Flexor Tendon and the Superior Check Ligament
  • A posterior view of the Superficial Flexor tendon and the Superior Check ligament. The function of this check ligament is to aid in supporting the Fetlock joint under load so that a reduced muscle mass can result.
  • The Superficial Flexor tendon inserts at the medial and lateral aspect of the distal long and proximal short Pastern bones.
  • A close up view of the medial insertion point of the superficial flexor tendon.
  • A view of the palmar fibro cartilage, the axial pastern ligament, and the straight sesamoidian ligament after dissection of the superficial flexor tendon.
  • Origins of the Deep Flexor Tendon The Deep Flexor Tendon has 3 separate muscle originations
  • Orientation of the Deep Flexor Tendon A lateral view of the Deep Flexor Tendon and its accessory check ligament The Inferior Check Ligament originates at the most distal row of carpal bones and inserts mid-cannon to the Deep Flexor Tendon, its function is to aid in supporting the tensions of the Deep Flexor Muscle. Additionally, the inferior check ligament prevents the knee from flexing under load at muscle fatigue.
  • There are multiple insertions of the Deep Flexor Tendon The photo on the left shows the chondronavicular ligament and the branch to the fibro-cartilage of the navicular bone The photo on the right shows the navicular bursae and the superficial sesamoidian ligament
  • Insertions of the Deep Flexor Tendon The photo on the left shows a palmar view of the superficial Flexor and Deep Flexor Tendons when the digital annular ligaments are dissected away The photo on the right shows the chondronavicular ligament as the Deep flexor tendon makes connecton to the ungular cartilage
  • Insertions of the Deep Flexor Tendon from a palmar view
  • The lateral extensor tendon originates on the lateral extensor muscle on the lateral aspect of forearm and inserts on to the proximal lateral aspect of P1.
  • The main extensor tendon originates at the main extensor muscle and has four insertions. A soft tissue insertion on the capsular ligament of the fetlock joint. The middle of the long pastern The middle of the short pastern The extensor process of the pedal bone.
  • Digital Annular Ligaments
  • View of: Palmar Annular Ligament, a true annular ligament. Originates at the medial sesamoid and inserts at the lateral sesamoid bone Proximal Digital annular ligament, a pseudo annular ligament as its function is closer to a check ligament than that of an annular ligament. Originates at the medial and lateral proximal aspect of P1 and the medial and lateral distal aspect of P1 and inserts on to the superficial flexor tendon body. The distal digital annular ligament is also a pseudo annular ligament in that it serves a check ligament function as well as an annular ligament function. Originates at the medial and lateral mid P1 and inserts onto the deep flexor tendon.
  • A second view of the proximal and distal digital annular ligaments.
  • The distal digital annular ligament has multiple functions. Because it originates from a bone and inserts onto a tendon, the proximal and distal digital annular ligaments serve as distal check ligaments as well as maintaining a tight connection of the flexor tendons to the palmar aspect of the pastern.
  • Suspensory Apparatus Those bones, tendons and ligaments that support the fetlock under load. Farriers must have a thorough understanding of the biomechanics of the suspensory apparatus in order to properly balance the limb and foot. Because farriers are the mechanics of the system, we commonly alter foot lengths and angles. We must have a complete understanding of what, or how other structures are effected when we raise or lower heels beyond normal physiological limits Many therapeutic or corrective shoeing techniques, effect the suspensory apparatus
  • Structures that makeup the suspensory apparatus: Deep flexor tendon Superficial flexor tendon Superior and inferior check ligaments Suspensory ligament and its extensor branches Sesamoidian ligaments Proximal and distal digital annular ligaments Proximal and distal sesamoid bones
  • Because of the insertion area of the superficial flexor tendon it only influences the fetlock joint. Therefore, the photo on the left demonstrates the position in which the superficial flexor tendon is under maximum strain. Because the insertion of the deep flexor tendon is on the coffin bone, there are two joints that influence its mechanics. The photo on the right demonstrates the position of the leg when the deep flexor tendon is under maximum strain. The actions of the coffin joint allow for some degree of protection of the deep flexor tendon.
  • Flexor tendon tension differences throughout the loading phase. This slide demonstrates in a diagrammatic manner the tempo and degree of tendon tension during the loading phases of the stride.
  • The suspensory ligament, which is the main supporting structure of the suspensory apparatus, originates at the proximal palmar aspect of the metacarpal bones.
  • The ink denotes the origination of the suspensory ligament.
  • After dissection of the fibro-cartilage of one sesamoid bone, the insertion of the main body of the suspensory ligament is apparent.
  • A palmar view of the fetlock joint showing the fibro cartilage dissected from one sesamoid bone, the cruciate ligament and short sesamoidian ligaments that attach the sesamoid bones to the proximal palmar aspect of P1.
  • A lateral view of the suspensory ligament showing one extensor branch of the suspensory ligament
  • A lateral view of one of extensor branches of the suspensory ligament
  • A frontal view of the medial and lateral extensor branches of the suspensory ligament when they make their connection to the main extensor tendon
  • Sectioning the suspensory ligament reveals the muscle fibers imbedded within the main body of the ligament
  • An oblique view of the main or straight sesamoidian ligament originating from the fibro-cartilage of the sesamoid bones and inserting onto the palmar fibro-cartilage of the short pastern bone, notice the two smaller axial pastern ligaments which help support the pastern joint during dorsopalmar articulation. The grouping of ligaments known as the sesamoidian ligaments are made up of the short sesamoidian, the cruciate or deep sesamoidian, the oblique or middle sesamoidian ligament and the straight or superficial sesamoidian ligament provide an opposing resistance to the upward pull from the main body of the suspensory ligament.
  • A rear view of the straight sesamoidian ligament and the pair of axial pastern ligaments
  • A side view of the straight sesamoidian ligament and deep flexor tendon
  • A view of the oblique and cruciate sesamoidian ligaments
  • The oblique sesamoidian ligament is unusual because it inserts along the entire palmar surface of the short pastern bone
  • A palmar view of the fetlock showing the short and cruciate sesamoidian ligaments
  • A view of the short sesamoidian ligaments
  • A side view of the digit with the skin and facia removed, the tools are pointing out the co-lateral ligament of the coffin joint and the suspensory ligament of the navicular bone.
  • This palmar view of the foot shows the flexor surface of the navicular bone and one branch of the suspensory ligament of the navicular bone.
  • An enlarged view of the bones and ligaments of the coffin joint showing the tension placed on the suspensory ligament of the navicular bone and the co-lateral ligament of the distal interphalangeal joint at heel lift off
  • The blue markings of this photo depict the insertions of the suspensory ligament of the navicular bone
  • The impar ligament originates at dorsal aspect of the navicular bone and inserts onto the coffin bone
  • This photo shows the impar ligament
  • When reflecting the navicular bone back one can see some adhesions of the impar ligament to the deep flexor tendon which are common on speed horses.
  • The hoof capsule design and sensitive structures Human architecture often imitates patterns found in nature. In engineering terms, the hoof capsule is referred to as a truncated cone which resembles some of the oldest buildings still standing on earth. The arch design, still used today, is one of the strongest design elements in construction due to its efficient load distribution characteristics.
  • Notice structural design differences between the front and of the back ½ of the foot Upright bars Frog stay Co-lateral cartilages Anchor for the sensitive laminae in this area Function to provide resiliency Digital cushion that is infused with fibro-cartilage
  • Coffin bones of front and hind feet
  • Periople is the junction between the skin and the horn of the wall
  • A view of the perioplic papilla, coronary groove, coronary papilla and the stratum internum of the capsule.
  • By properly trimming the periople of the frog one can define the true heel
  • Vasculature Generally in mammals there is almost a 1:1 ratio of veins and arteries in tissue. Since the blood of the horses foot provides a structural and energy dissipating function in addition to its nutritive function, there are more veins than arteries present. Medial and lateral digital arteries branch off to form the coronary plexus, the branch to the digital cushion and anastomis with each other at the terminal arch within the coffin bone. Radial arteries then penetrate the parietal surface of the coffin bone perfusing the micro vasculature of the sensitive laminae. The dorsal artery and the radial arteries penetrating the distal surface of the coffin bone form the circumflex artery which perfuses the sole coria.
  • A dissected specimen of the digital neuro vascular bundle. Notice all of the veins of the venus plexus surrounding the ungular cartilage.
  • A diagrammatic illustration of the papilla of the coria
  • The coronary papilla and sensitive lamina
  • The epidermal sockets of the bulbar papilla
  • A section of the laminar bed. Notice the secondary epidermal lamina, unique to the equine.
  • An electron micrograph of three primary lamina and their secondary laminar leaves.
  • Under load, the boney column descends slightly within the capsule to aid in dissipating concussion. This is a function of the unique architecture of the equine capsule and laminar bed. Research has shown that more than 60% of the concussion of ground impact is dissipated before it gets to the knee Some think that the laminar attachment is the primary mechanism for this but all of the structures of a healthy foot must work in concert to achieve maximum energy dissipation
  • Normal front foot of a young Thoroughbred before dissection.
  • This view shows normal anatomical bone and healthy coria position.
  • These two slides show before and after removal of the coronary and laminar coria.
  • Normal position of the coffin bone within the capsule. Notice the heel contact is behind the wing of the coffin bone.
  • Typical 3-year old Thoroughbred racehorse foot sectioned for sole and wall removal.
  • After the sole is removed, the solar papilla and laminar coria of the bars are exposed. Notice the significant mid dorsal notch and resultant seedy toe in the white line.
  • This foot demonstrates a zero palmar angle of P3
  • The insensitive sole. Take notice of the linear arrangement of the bars.
  • A solar view of the coffin bone, plantar cushion, and ungular cartilages of the previous foot.
  • The side view of the ungular cartilage and its relation to P3
  • “reassembled” P3, ungular cartilage & digital cushion
  • Front Foot Types Upright and underslung, respectively. Notice the greater volume of cartilage in the upright foot versus the underslung foot.
  • Sagittal sections of an upright and underslung foot. Notice the relative positions of the navicular bones the position and mass of the digital cushions. Upright feet generally have significantly more ungular cartilage mass than underslung feet.
  • Bottom view of an underslung and upright foot. The blue marks indicate the point of heel contact and frog bridge of the underslung foot
  • Note the distance between the coffin bone and the quarters between this underslung foot on the left and the upright foot on the right.
  • The coffin bone is positioned behind the point of contact of the heels in the underslung foot but well in front of the heels in the upright foot
  • Normal heel and bone position and underslung heel and bone position
  • An oblique view of the foot showing the chondrocoronal ligament
  • A view of the coffin joint showing the chondronavicular ligament
  • the following photos demonstrate the normal hoof mechanism from the sagittal plane
  • Why is the incidence of ringbone higher in upright feet?
  • Why is a detailed knowledge of anatomy important? Front feet should have a resemblance to front feet not hind feet
  • To maximize foot function
  • And to better understand our limits for rehabilitation
  • Understand the results of your actions.
  • And…. Have some fun.

Anatomy & biomechanics Presentation Transcript

  • 1. FUNCTIONAL ANATOMY &BIOMECHANICS OF THE DISTAL FORELIMB Presented by: Mitch Taylor, CJF The Kentucky Horseshoeing School“Excellence Through Education”
  • 2. The equine limb and foot have evolved into a highly specializedappendage to maximize speed, endurance and efficient locomotion
  • 3. Similar angles ofinsertion with thenavicular bone 105° 105°Angles of insertionchange without thenavicular bone 135° 95°
  • 4.
  • 5. *
  • 6. Deep FlexorMuscle Grouphas 3 heads
  • 7. Inferior checkligament Main body of DFT
  • 8. Superficial or straight sesamoidian ligament DFTView of coffin joint including DFT navicular bone Lateral view of coffin joint
  • 9. Palmar views Superficial and deep flexors withannular ligaments dissected away
  • 10. Insertion(s) of the Deep Flexor Tendon Palmar or solar view of P3
  • 11. Distal Digital Annular LigamentPalmar AnnularLigament Proximal Digital Annular Ligament
  • 12. Distal Digital Annual Ligament Proximal Digital Annular Ligament
  • 13. Those bones, tendons and ligaments that support the fetlock under loadFarriers must have a thorough understanding of the biomechanics of the suspensory apparatus in order to properly balance the limb and foot
  • 14. Deep flexor tendonSuperficial flexor tendonSuperior and inferior check ligamentsSuspensory ligament and its extensor branchesSesamoidian ligamentsProximal and distal digital annular ligamentsProximal and distal sesamoid bones
  • 15. Flexor Tendon Tension Differences Throughout the Loading Phase = SFTTendon tension = DFT Loading phases of the stride
  • 16. Front half of foot Back half of foot
  • 17. P3 of Hind Foot P3 of Front Foot
  • 18. Under load, the boney column descends slightlywithin the capsule to aid in dissipatingconcussion. This is a function of the uniquearchitecture of the equine capsule and laminar bed
  • 19. Foot types have characteristic shapes
  • 20. Underslung and normal bone positionrelative to heel position
  • 21. * .
  • 22. .
  • 23. The importance of medio/lateral balanceand its results on the demineralization of P3
  • 24. Bone sinking to medial sideM.T. SavoldiEquine Research CenterShandon CA. 117
  • 25. M.T. SavoldiEquine Research CenterShandon CA. 118
  • 26. M.T. SavoldiEquine Research CenterShandon CA. 119
  • 27. Flare developing to lateral sideM.T. SavoldiEquine Research CenterShandon CA. 120
  • 28. M.T. SavoldiEquine Research CenterShandon CA. 121
  • 29. M.T. SavoldiEquine Research CenterShandon CA. 122
  • 30. M.T. SavoldiEquine Research CenterShandon CA. 123
  • 31. M.T. SavoldiEquine Research CenterShandon CA. 124
  • 32. M.T. SavoldiEquine Research CenterShandon CA. 126
  • 33. M.T. SavoldiEquine Research CenterShandon CA. 127
  • 34. M.T. SavoldiEquine Research CenterShandon CA. 128
  • 35. M.T. SavoldiEquine Research CenterShandon CA. 129
  • 36. M.T. SavoldiEquine Research CenterShandon CA. 130
  • 37. M.T. SavoldiEquine Research CenterShandon CA. 131
  • 38. M.T. SavoldiEquine Research CenterShandon CA. 132
  • 39. M.T. SavoldiEquine Research CenterShandon CA. 133
  • 40. Same foot before and after shoeing