Download Anatomy Description Posterior Leg Anatomy

Posterior Leg Anatomy Questions Things to Consider
Sciatic Nerve
1. Sciatic nerve
a. Combination of two nerves
i. Preaxial Tibial
ii. Postaxial Common Peroneal or Fibular
b. Arises form L4 to S3
i. Tibial from Anterior branches of L4 to S3
ii. Common Peroneal or Fibular from posterior branches of L4 to S2
c. The Path of the Sciatic Nerve
i. Leaves the pelvis through the Greater Sciatic Foramen
ii. Inferior to the Piriformis Muscle
iii. Descends over
1. Internal Obturator Tendon and Gemellus Muscles
2. Quadratus Femoris muscle Between the Greater Trochanter
and Ischial Tuberosity
3. Adductor Magnus
4. Crossed obliquely by the Long Head of the Biceps Femoris
Muscle
d. Branches of the Sciatic Nerve in the thigh are
i. from the Tibial portion of the nerve and arise from the medial side
ii. Articular Branches to the hip joint
iii. Muscular Branches to the hamstring Muscles
1. Semitendinosis Muscle
2. SemiMembranosis Muscle
3. Biceps Femoris
a. Long head by the Tibial
b. (Short Head is by a branch of the Common Peroneal
or Fibular Nerve which is also articular to the Knee
in company with Genicular Arteries)
4. Adductor Magnus: Ischial portion
a. The rest is innervated by the Obturator Nerve
b. This is the portion that continues to the knee as the
Tendon of the Adductor forming the Adductor
Hiatus through which travel the Femoral Artery and
Vein as they become the Popliteal Artery and Vein
2. Tibial Nerve
a. In the Popliteal Fossa the Tibial Nerve separates from the Common
Peroneal or Fibular Nerve
b. Path of the Tibial nerve
i. Passes between the heads of the gastrocnemius and
ii. under the Soleus muscle
c. Branches
i. Three articular branches follow the genicular arteries to the knee
ii. Medial Sural nerve
iii. Muscular branches to the muscles of the calf
3. Common Peroneal or Fibular nerve
a. Having given off the branch to the Short head of the biceps femoris
b. Follows the tendon of the long Head of the biceps femoris
c. Gives off the Lateral Sural Cutaneous Nerve
d. Wraps around the neck under the head of the fibula
e. Passes deep to the Peroneus (Fibularis) Longus
f. Divides into
i. Superficial Peroneal or Fibular
ii. Deep Peroneal or Fibular
iii. Muscular branch to the short head of the bicpes femoris
iv. Articular to the knee with braches the follow the Genicular
Arteries
4. Sural Nerve
a. Formed by the union of two nerves
i. Medial Sural Cutaneous (Tibial)
1. Arises from the Tibial Nerve in the popliteal fossa
2. Descends under the deep fascia in the groove between the
two heads of the gastrocnemius muscle
3. ;ierces the deep fasica above it to join the Peroneal or
Fibular Communicating Branch (from the Lateral Sural
Nerve) to form the Sural Nerve
4. in 20% of cases there is on union so the distribution of the
sural is divided between the Medial and Latera Sural nerves
where the Medial Sural nerve continues on to innervate the
heel and foot
ii. Lateral Sural Cutaneous (Common Peroneal or Fibular)
1. Arises from the Common Peroneal or Fibular Nerve in the
popliteal fossa
2. Pierces the deep fascia over the lateral head of the
gastrocnemius muscle
3. Distributes to the lateral part of the back of the leg for its
proximal two thirds
4. Gives off the Peroneal or Fibular Communicating Branch
that eventually joins with the Medial Sural Cutaneous nerve
b. The Sural Nerve descends in company with the Lesser Saphenous Vein
c. Between Lateral Malleolus and Calcaneal Tendon
d. Cutaneous to the
i. Lateral side and back of the distal one third of the lower leg
ii. Ankle
iii. Heel
e. On the side of the foot it is known as the Lateral Dorsal Cutaneous Nerve
i. Supplies the lateral aspect of the foot and the little toe
ii. Articular branches to the ankle and Tarsal Joints
iii. Communicates with the Superficial Peroneal or Fibular Nerve
through its Intermediate Dorsal Branch
5. Branches of the Sacral Plexus
a. Posterior Femoral Cutaneous Nerve
i. Descends as a sensory nerve in the back of the thigh
ii. At the lower border of the gluteus maximus a perineal branch
arises and runs medially across the origin of the hamstring muscles
near the ischial tuberosity and goes toward the perineum
iii. A mixed nerve formed by posterior branches of S! and S2 and
Anterior Branches of S2 and S3
iv. Leaves the pelvis below the Piriformis Muscle
v. Lies alongside the sciatic Nerve
vi. At the lower border of the gluteus maximus gives rise to the
Gluteal and Perineal branches
1. Gluteal Branches are the Inferior Cluneal Nerves
a. Supply the lower half of the buttock
b. Laterally to as far as the greater trochanter
c. Medially to near the coccyx
2. Perineal Branches cross the ischiopubic ramus to the
perineum
vii. Descends deep to the fascial lata, gives off branches medially and
laterally, as it distributes to the skin of the back of the thigh and
finally to the area of skin over the popliteal fossa
b. Pudendal Nerve
i. Formed from the anterior branches of S2, S3 and S4
ii. Crosses the spine of the ischium and the sacrospinous ligament
with the internal pudendal vessels and enters the pudendal canal
c. Muscular branches to the Internal Obturator, Superior Gemellus muscles
and the Quadratus Femoris
d. Perforating Cutaneous Nerve to the skin over the medial part of the fold of
the buttock
6. Important Landmark
a. Piriformis Muscle
i. Flat triangular
ii. Arises from the pelvic surfaces of the second, third and fourth
sacral vertebrae between and lateral to the pelvic sacral foramina
iii. The muscle is directed toward the greater Sciatic Foramen
iv. Its rounded tendon inserts into the upper border and medial side of
the greater trochanter of the femur
v. The sacral plexus is formed on the pelvic surface of the piriformis
b. Important landmark for Anaotmy
i. The superior gluteal vessels and nerve emerge above the piriformis
ii. The Sciatic and other nerves of the sacral plexus and the ingerior
gluteal and internal pudendal vessels emerge at it slower border
iii. The muscle can be pierced by the Common Peroneal Nerve in
variation of formations of the Sciatic Nerve
iv. Innervated by the first and second sacral nerves
v. Lateral rotator of the thigh
c. Important Landmark for Anesthesia and the Classic approach to the
Sciatic Nerve
i. Labat’s line drawn from the PSIS to the Greater Trochanter defines
the superior border of the piriformis
ii. Winnie’s modification drawn from the Greater trochanter to the
sacral hiatus defines the inferior border of the pirifomis
iii. The line drawn from the midpoint of the Labat line for 4 cm and
that intersects the Winnie modification line is where the Sciatic
Nerve emerges from underneath the piriformis
________________________
Woodburne pages 607 to 608, Sciatic, Tibial, Common Peroneal Nerves
Woodburne pages 583 to 584 for Sural
Posterior Femoral Cutaneous Nerve page 521, 560 fig 8-21, 561, 580
Piriformis Muscle page 564