The Fetlock and Foot

First Year AnatomyNicholas Urbanek, BVMS, MRCVS

What is the Fetlock?• Fetlock is the common name for the

metacarpophalangeal and metatarsophalangeal joints (MCPJ and MTPJ) of the horses.

• It is formed by the junction of the third metacarpal (forelimb) or metatarsal (hindlimb) bones (cannon bones) proximally and the proximal phalanx (pastern bone) distally.

• Paired proximal sesamoid bones articulate with the palmar or plantar distal surface of the third metacarpal or metatarsal bones and are rigidly fixed to the proximo-palmar /-plantar edge of the proximal phalanx.

Common Views

LateralLateral DMPLO

DP DLPMO

Lateral View• A: Third MC/MT bone• B: Proximal phalanx (P1)

• 1: Sagittal ridge• 3: Palmar process of

proximal phalanx• 4: Condyles of third

metacarpal bone• 5: Proximal sesamoid

bones

Dorso-palmer/-plantar (DP)• A: Third MC/MT bone• B: Proximal phalanx• C: Medial proximal

sesamoid bone• D: Lateral proximal

sesamoid bone• E: Metacarpo(tarso)-

phalangeal joint• J: Depression for medial

collateral ligament attachment

• 1: Sagittal ridge

Obliques – A Review

• The view is named for the projection of the beam.• Typically taken at 45 degree angles off the sagittal axis

of the limb.• Markers must be in place, otherwise unable to

distinguish medial from lateral side.• Dorsomedial-palmarolateral (plantar)oblique (DMPLO)• Dorsolateral-palmaromedial (plantar)oblique (DLPMO)

DLPMO

A: Third MC/MT boneB: Proximal phalanxC: Medial proximal sesamoid boneD: Lateral proximal sesamoid boneE: Metacarpo(tarso)-phalangeal joint1: Sagittal ridge3: Palmar process of proximal phalanx/Lateral palmar tubercle (eminence)6: Medial condyle of third MC/MT bone

DLPMO

Dorsal

Palmar/Pl

MedialLateral

DMPLO

A: Third MC/MT boneB: Proximal phalanxC: Medial proximal sesamoid boneD: Lateral proximal sesamoid boneE: Metacarpo(tarso)-phalangeal joint1: Sagittal ridge2: Lateral condyle of third metacarpal/tarsal bone3: Palmar process of proximal phalanx

Dorsal

Palmar/Pl

MedialLateral

DMPLO

Forelimb vs Hindlimb

DP view - Forelimb DP view - Hindlimb

The proximal sesamoid bones are higher

Bulging

• The MT is convex at its distal aspect

The proximal sesamoid bones are more triangular

Fetlock

Foot or Distal Limb• Composed of four bones

– Proximal, middle, distal (first, second, and third) phalanx– Navicular bone

• Multiple views obtained– Lateral– Dorsopalmar(plantar) view– Dorsoproximal-palmar(plantar)odistal oblique

• “Upright Pedal” or “High coronary”– Palmar(plantar)oproximal-palmar(plantar)odistal

• “Skyline Novicular”– Other oblique views

• The foot should have no shoe, be trimmed, and sulci should be packed with Play-Doh

• Marker always to the lateral side…can not tell laterality otherwise

Lateral view

A: Middle phalanxB: Third phalanxC: Navicular bone1: Proximal interphalangeal joint2: Distal interphalangeal joint3: Extensor process4: Dorsal surface5: Palmar process

Dorsopalmar(plantar) view

A: Middle phalanxB: Distal phalanxC: Navicular bone6: Proximal interphalangeal joint7: Distal interphalangeal joint

R

A

BC

6

7

Dorsoproximal-palmar(pl)odistal oblique view

A: Middle phalanxB: Third phalanxC: Navicular bone1: Proximal interphalangeal joint2: Distal interphalangeal joint3: Extensor process4: Dorsal surface5: Palmar process6: Vascular channel7: Solar margin

6

55

2

7

B

Dorsoproximal-palmar(plantar)odistal oblique view

R

“Upright pedal”

“High coronary”

A

C: Navicular bone3: Articular surface8: Palmar aspect of middle phalanx9: Nutrient foramen10: Sagittal ridge11: Articulation between navicular bone and middle phalanx

Palmaro(plantar)oproximal-palmar(plantar)odistal oblique view

“Skyline Novicular”