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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 dorsallateral 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.