Pes region, Nerves & Blood Supply

Nerves & Blood Supply of the Distal Hindlimb

1. Components and Movements of Pes

   • Understand the structure and functionalities of the pes (metatarsus and phalanges).

2. Extensors and Flexors

   • Describe the groups and arrangements of tendons and ligaments over the hock joint and digits.

3. Nerve Supply

   • Explain the origin and formation of the lumbosacral plexus and major nerve supplies to hindlimb.

4. Blood Supply and Lymphatic Drainage

   • Describe major blood supply and lymphatic drainage of the hindlimb.

Pes (Metatarsus and Phalanges)

• Similar structure as MANUS (forelimb)

• Absence of stopper/carpal pad

• Dew claw: variable in dogs; less common than in the fore leg, absent in cats.

Tissues

• Dorsal CT

• Plantar CT

Hock Flexor Muscles

• Standing Position: Indicates extension of the hock.

• Hock Flexion: Involves muscles that run cranially/dorsally to the limb.

• Peroneal/Fibular Nerve: A branch of the Sciatic nerve.

• Cranial Tibial Muscle:

  • Origin: Lateral tibia

  • Insertion: Metatarsal bones

Group of Hock Flexor Muscles

• Peroneus Longus/Long Fibular Muscle:

  • Origin: Lateral tibia & fibula

  • Insertion: Plantar aspect of tarsus

• Peroneus Brevis/Short Fibular Muscle:

  • Origin: Tibia & fibula

  • Insertion: 5th Metatarsal bone

• Peroneus Tertius/Third Fibular: Absent in dogs and cats.

Muscular Innervation

• Innervated primarily by the Peroneal/Fibular Nerve, a branch of the Sciatic nerve.

Hock Flexor/Digital Extensor Muscles

• Long Digital Extensor Muscle:

  • Origin: Extensor fossa (femur)

  • Incorporates tendon into stifle joint capsule for lateral collateral support.

  • Insertion: All digits (4 branches) to distal phalanx (extensor process).

• Lateral Digital Extensor Muscle:

  • Origin: Lateral aspect tibia

  • Insertion: Fuses with branches of long digital extensor, affecting few digits (4th, 5th, possibly 3rd).

Hock Extensor Muscles

• Common Calcanean Tendon (Achilles Tendon):

  • Inserts at calcanean tuberosity of calcaneus.

  • Acts as a lever for the distal limb.

  • Convergence of 3 main components:

    1. Biceps femoris

    2. Semitendinosus

    3. Gracilis (medial muscle)

  • Also involves Gastrocnemius (iv) and Superficial Digital Flexor (V).

Hock Extensor/Digital Flexor Muscles

• Superficial Digital Flexor Muscle:

  • Origin: Lateral popliteal fossa femur (associated with gastrocnemius).

  • Insertion: Calcaneus via common calcanean tendon, branching to all digits (middle phalanx).

• Innerated by Tibial Nerve (branch of sciatic nerve).

Deep Digital Flexor Muscle (2 Heads)

• Origin: Tibia

  1. Lateral Head (Flexor Hallucis Longus):

     • Runs over sustentaculum tali of calcaneus, reinforced by fibrocartilage in the joint capsule.

  2. Medial Head (Flexor Digitorum Longus):

     • Runs over medial aspect of tarsus.

• Merges and divides into 4 branches to all digits (distal phalanx).

• Innervation by Tibial Nerve (branch of sciatic nerve).

Clinical Considerations

• Clinical examples of chronic injuries affecting hindlimb function, such as tendon avulsions leading to changes in typical stance.

• Conditions like plantigrade stance from chronic avulsion of the Achilles and gastrocnemius tendon rupture.

Hindlimb Nerves Supply

• Major spinal nerves involved include L5, L6, L7, S1, S2.

• Dorsal branches supply dorsal structures; ventral branches contribute to the lumbosacral plexus, emerging as peripheral nerves to hindlimb muscles.

• Key peripheral nerves:

  • Gluteal: (cranial + caudal)

  • Obturator:

  • Femoral:

  • Sciatic: divides into Tibial & Fibular/Peroneal nerves.

Specific Nerves Overview

• Gluteal Nerve: Motor only, supplies hindlimb abductors and TFL.

• Obturator Nerve: Motor only, provides motor function to adductors (e.g., Gracilis, Adductor).

• Femoral Nerve: Mixed motor & sensory function, controls hip flexors and stifle extensors.

  • Patellar reflex: assessed through quadriceps; includes saphenous branch for sensory nerves.

• Sciatic (Ischiatic) Nerve: Mixed motor & sensory, affecting caudal thigh muscles (hip extensors/stifle flexors).

• Tibial Nerve: Branch of Sciatic nerve, primarily innervates caudal crural muscles (e.g., gastrocnemius).

• Fibular/Peroneal Nerve: Motor for cranial crural muscles and sensory for cranial/dorsal aspects.

Sciatic Nerve Damage

• Conditions like hip trauma/surgery leading to loss of supply to affected muscle groups, resulting in impaired function and sensory loss, except medial aspects of the limb.

Blood Supply

• Follow flexor surfaces from External Iliac Artery as it bifurcates into Femoral Artery.

  • Saphenous artery provides superficial supply to the paw, while the femoral artery continues as the Popliteal Artery that further divides into Cranial Tibial Artery aiding deep supply to the paw.

Venous Drainage

• Comprised of both deep and superficial venous systems:

  • Lateral and Medial Saphenous Veins provide access to systemic circulation.

  • These veins drain into the Femoral Vein, crucial for blood return from the pelvic limb.

Lymphatic Drainage

• Main node: Popliteal lymph node (caudal to stifle).

  • Enlarged due to infection, useful for differentiating localized vs. generalized diseases, significant in meat inspection for food-producing animals.

Questions

• Instructor emphasizes the importance of engaging with any queries discussed during the class or through the discussion board.