First Year Anatomy Nicholas Urbanek, BVMS, MRCVS The Fetlock and Foot First Year Anatomy Nicholas 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 Lateral Lateral 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 bone B: Proximal phalanx C: Medial proximal sesamoid bone D: Lateral proximal sesamoid bone E: Metacarpo(tarso)-phalangeal joint 1: Sagittal ridge 3: Palmar process of proximal phalanx/Lateral palmar tubercle (eminence) 6: Medial condyle of third MC/MT bone DLPMO Dorsal Palmar/Pl Medial Lateral

DMPLO A: Third MC/MT bone B: Proximal phalanx C: Medial proximal sesamoid bone D: Lateral proximal sesamoid bone E: Metacarpo(tarso)-phalangeal joint 1: Sagittal ridge 2: Lateral condyle of third metacarpal/tarsal bone 3: Palmar process of proximal phalanx DMPLO Dorsal Palmar/Pl Medial Lateral

Fetlock Forelimb vs Hindlimb Bulging  The MT is convex at its distal aspect DP view - Hindlimb DP view - Forelimb The proximal sesamoid bones are higher The proximal sesamoid bones are more triangular

Foot or Distal Limb Composed of four bones Multiple views obtained 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 phalanx B: Third phalanx C: Navicular bone 1: Proximal interphalangeal joint 2: Distal interphalangeal joint 3: Extensor process 4: Dorsal surface 5: Palmar process

Dorsopalmar(plantar) view A: Middle phalanx B: Distal phalanx C: Navicular bone 6: Proximal interphalangeal joint 7: Distal interphalangeal joint R 6 A 7 C B

Dorsoproximal-palmar(pl)odistal oblique view 6 5 2 7 B A A: Middle phalanx B: Third phalanx C: Navicular bone 1: Proximal interphalangeal joint 2: Distal interphalangeal joint 3: Extensor process 4: Dorsal surface 5: Palmar process 6: Vascular channel 7: Solar margin R “Upright pedal” “High coronary” Dorsoproximal-palmar(plantar)odistal oblique view

Palmaro(plantar)oproximal-palmar(plantar)odistal oblique view “Skyline Novicular” C: Navicular bone 3: Articular surface 8: Palmar aspect of middle phalanx 9: Nutrient foramen 10: Sagittal ridge 11: Articulation between navicular bone and middle phalanx