equine distal limb

describe the bones in the distal limb (from carpus down to the hoof)

• metacarpal/metatarsal bone (cannon bone)

• proximal sesamoid bones

• proximal phalanx (long pastern)

• middle phalanx (short pastern)

• distal sesamoid bone (navicular)

• distal phalanx/ pedal bone (coffin)

describe the joints of the distal limb

• metacarpophalangeal/ metatarsophalangeal joint - MCP/MTP (fetlock)

• proximal interphalangeal joint (PIP)

• distal interphalagneal joint (DIP)

describe the hoof dermis

• dermis = corium

• five parts - perioplic, coronary, lamellar, solar, frog

• subcutis (coronary cushion and digital cushion)

• dermal laminae attaches skeleton to hoof

describe the ligaments in the distal hind limb

• broken down into collateral ligaments, palmar ligaments and sesamoidean ligaments

• diagnosis can be narrowed down by nerve blocking

describe the medial and lateral collateral ligaments of the MCP/PIP/DIP

• short ligaments individually crossing the MCP joint, PIP joint and DIP joint

describe the palmar ligaments

• palmar axial and abaxial ligaments (PIP)

• annular ligaments - form a ring around the joints - palmar (over MCP), proximal digital (over proximal P1), distal digital (over distal P1/pedal bone)

• keep flexor tendons in place

• tendon sheaths pass deep to the annular ligaments

name the proximal sesamoidean ligaments

• short - runs through MCP joint

• collateral - run round MCP joint to the front of the bone from the back

• oblique - run from MCP on the palmar side of the limb through to PIP

• cruciate - sit behind the oblique

• intersesamoidean - sit on the palmar side of metacarpal bone at the top

• straight - run on the palmar side from the MCP to the PIP

name the flexor tendons of the distal limb

• suspensory ligament (most deep)

• deep digital flexor tendon (DDFT) - with associated distal check ligament

• superficial digital flexor tendon (SDFT) - associated proximal check ligament

name the extensor tendons

• common and lateral digital extensor tendons

• common inserts on extensor process of distal phalanx

• same connections between flexors and extensors

describe the superficial digital flexor tendon (SDFT)

• closely associated with the DDFT

• inserts either side of proximal interphalangeal joint

• flattens and wraps around the DDFT at the proximal sesamoid bone (called the manica flexoria)

• divides and allows emergence of DDFT at mid level of proximal phalanx

describe the deep digital flexor tendon (DDFT)

• inserts upon palmar distal phalanx

• passes over palmar aspect navicular bone

• distal check ligament anchors tendon to proximal metacarpal joint - to prevent overflexing

describe the digital check ligament

• also called accessory ligament of the DDFT

• attaches the DDFT to the palmar carpal ligament

• stiffens the tendon

• less tension is placed of the DDF muscle

describe the suspensory ligament

• tendinous remnants of the interosseous muscle

• palmar aspect of metacarpal bone

• originates from distal row of carpal bones and proximal MC

• inserts upon abaxial aspect of proximal sesamoid bones

• extensor branches connect with common digital extensor

• most deep of all tendons

describe the bursae and sheaths

• cushions and sleaves - cavity lined with synovial membrane

• navicular bursa on palmar aspect of navicular bone

• DDFT/SDFT share the digital tendon sheath, digital sheath starts proximal to MCP and terminates mid-level of middle phalanx (potential site of damage/infection)

describe the structure and function of the navicular apparatus

• navicular bone, collateral sesamoidean ligaments, distal sesamoidean impar ligaments, navicular bursa, DDFT, distal digital annular ligament

• functions - navicular bone displaces DDFT away from DIP (increases leverage), bursa cushions both the DDFT and the navicular bone

• poor conformation can cause abnormal compression of navicular bone against the middle phalanx

describe the sensory innervation of the palmar aspect of the distal limb

• same in distal forelimb and hindlimb

• medial and lateral palmar nerves run alongside SDFT and branch at MCP into dorsal branches and palmar digital nerves

• palmar metacarpal nerves (from deep branch of lateral palmar nerve)

• palmar digital nerves (innervate the heel of the foot)

describe the sensory innervation of the dorsal aspect of the distal limb

• dorsal branches of digital nerves - innervate toe of foot

• additional dorsal foot innervation in hindlimb by dorsal metatarsal nerves

describe the different nerve blocks in a distal hindlimb

• palmar digital nerve block - blocks sensory info to the heel (done in the palmar groove of P3)

• abaxial sesamoid nerve block - blocks sensory info to the whole of the hoof up to the coronary band (done on medial and lateral side of fetlock)

• low 4 point nerve block - blocks entire foot/leg up to metacarpophalangeal joint (done on medial and lateral side just above the fetlock)