Tarsus Anatomy

Dane Tatarniuk, DVM

Bones

• Talus b.• Calcaneus b.• Central tarsal b.• 1st & 2nd (fused) tarsal b.• 3rd tarsal b.• 4th tarsal b.

• Proximally: Tibia• Distally: 2nd, 3rd, 4th metatarsal b.

Dorsal-Plantar Lateral-medial

DLPMO DMPLO

PMDLO PLDMO

Plantar-Dorsal

Joints

• Tarsocrural• Talocalcaneal• Proximal Intertarsal• Talocalcaneal-Centroquatral

• Distal Intertarsal– Centrodistal

• Tarsometatarsal

Tarsocrural

• Ginglymus Joint– Hinge-like joint, direction in only one plane– Deep grooves in cochlear surface of distal tibia,

and trochlea of the talus• Articulation– 12 to 15 degrees to the sagittal plane, in dorsal-

lateral direction

PIT / DIT / TMT

• Plane joints• Only a very limited gliding movement

Joint Capsule

• Proximal: attaches to distal aspect of the tibia• Distal: attaches to metatarsal bones• Joint Pouch Effusion:– Dorsal-medial aspect of joint capsule, at level of

medial trochlea– Proximal aspect of plantar joint capsule, at level of

talus and distal tibia, both medial/lateral side

Ligaments

• Lateral Long Collateral Ligament– Superficial– Originate: Caudal aspect of lateral malleolus of

distal tibia– Inserts: Fourth tarsal b., third metatarsal b., fourth

metatarsal b.– Forms canal for lateral digital extensor tendon

Ligaments

• Lateral Short Collateral Ligament– Deep to long collateral– Originates: Cranial aspect of lateral malleolus of

the distal tibia– Runs caudally– Insertion: Lateral aspect of calcaneus

Ligaments

• Medial Long Collateral Ligament– Originates: Caudal aspect of medial malleolus of

distal tibia– Insertion: Second metatarsal b., third metatarsal

b., medial aspect third tarsal b.

Ligaments

• Medial Short Collateral Ligament– Deep to medial long collateral– Originates: Cranial aspect of the medial malleolus

of distal tibia– Insertion: Medial aspect of the calcaneus and

sustentaculum tali

Ligaments

• Long Plantar Ligament – Strong, flat band– Originates: Proximal plantar aspect of calcaneus– Insertion: Fourth metatarsal b., fourth tarsal b.

Ligaments

• Dorsal tarsal ligament– Originates: Distal tuberosity of the talus– Insertion: Central tarsal b., third tarsal b., proximal

third metatarsal b.

Muscle/Tendons

• Cranial-lateral– Tibialis cranialis• Flexor of hock• Originates from lateral condyle of tibia• Tendon passes through split in peroneus tertius• Tibialis cranialis tendon then splits itself• Insertion:

– Dorsal branch, proximal third metatarsus– Medial branch, crosses the medial long collateral ligament and

inserts on the fused 1st & 2nd tarsal bone

• Innervated by peroneal nerve

Muscle/Tendons

• Cranial-lateral– Peroneus tertius• Originates from distal femur• Courses alongside the long extensor muscle• Bifurcates at the dorsal tarsus• Lateral branch inserts on calcaneous b. and fourth

tarsal b.• Dorsal branch inserts on the proximal third metatarsal• Links the flexion of hock and stifle• Innervated by peroneal nerve

Muscle/Tendons

• Cranial-lateral– Long digital extensor• Originates from distal femur• Inserts on the extensor process of third phalanx• Lateral extensor tendon joins into long at level of

proximal metatarsus• Tendon sheath present as it crosses the dorsal tarsus• Held in place by 3 retinacula• Synovial sheath present• Flexes the hock, extends the digit• Innervated by peroneal nerve

Muscle/Tendons

• Cranial-lateral– Lateral digital extensor

• Originates lateral collateral ligament of stifle• Inserts (joins) into the long extensor tendon• Held in place by retinaculum• Synovial sheath present• Innervated by peroneal nerve

– Extensor digitalis brevis• Small, short digital extensor tendon between the angle of

the long and lateral digital extensor tendons

Muscle/Tendons

• Caudal– Gastrocnemius• Originates from 2 heads on the supracondylar

tuberosities of the femur, superficial to SDFT• Inserts on the points of the calcaneus, deep to

superficial digital flexor tendon• Extends the hock• Innervated by tibial nerve

Muscle/Tendons

• Caudal– Superficial digital flexor• Originates from the supracondylar fossa of femur, deep

to gastrocnemius• Twists medially to become superficial to gastrocnemius• Medial and lateral aspects insert on the point of the

calcaneus• Remainder of SDFT continues down plantar aspect of

distal limb, inserts on first and second phalanx• Innervated by tibial nerve

Muscle/Tendons

• Caudal– Deep digital flexor tendon

• Originates from three heads– Lateral digital flexor & Tibialis caudalis

» Originates from caudal tibia» Become joined, pass through the sustentaculum tali» Tarsal sheath

– Medial digital flexor» Originates from lateral condyle of tibia» Passes within groove on medial malleolus and medial

collateral ligament

• Innervated by tibial nerve

Tendon Sheaths

• All the tendons coursing over the hock, with exception of superficial digital flexor tendon, have a concurrent tendon sheath

Bursas

• Cunean Bursa– Directly deep to the

cunean tendon• Calcaneal Bursa (2)– Subcutaneous– Subtendinous

Nerves & Vessels

Nerves & Vessels

References• Dr. Alexander zur Linden, http://vetmed.iastate.edu/limbanatomy/horse.html• Horowitz A., Berg R., “Anatomy of the Horse”, 5th ed.• Moyer, “Equine Joint Injection and Regional Anesthesia”, 3rd ed.