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2 | P a g e
Structures under the cover of Gluteus Maximus:
1-Bones: Ileum, Femur (Head, greater trochanter and gluteal
tuberosity), Ischium (ischial tuberosity).
2- Ligaments: Sacrotuberous ligament and Sacrospinous ligament.
3- Muscles: gluteus medius, gluteus minimus, lateral rotators:
(Piriformis, Obturator Internus, Superior & Inferior Gemellus,
Quadratus Femoris).
4- Vessels: Superior & Inferior Gluteal Vessels (go through greater
sciatic foramen), Internal pudendal vessels.
5- Nerves: Sciatic nerve, Posterior cutaneous nerve of the thigh, Nerve
to Obturator internus, Nerve to Quadratous, Superior & Inferior
Gluteal nerves, Pudendal nerve.
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Clinical application: *Sciatic nerve goes through greater sciatic foramen
under the Piriformis muscle.
This is important to know when giving intramuscular injection, and we
already know how to divide the gluteal region into 4 parts. So according
to the picture below we give injection in the upper lateral part to be far
from the sciatic nerve, so we don’t damage it, since it’s so important and
supplies too many muscles.
Another way to determine the injection site is by putting your thumb on
the posterior superior spine, hand on iliac crest and stretch your hand
then inject right below your hand.
*This injection is given mainly in the gluteus medius (safer because it’s
far from sciatic nerve), sometimes given in the g. maximus because it’s
bigger and has more vessels (less safe because it’s closer to sciatic n.).
Posterior compartment of the thigh
Muscles: 1- Biceps Femoris (Short & long heads). 2-Semitendinosus. 3-
Semimembranosus. 4- Hamstring (or ischial) part of Adductor
Magnus.
Nerve Supply: ALL supplied by Sciatic nerve.
*Sciatic nerve divides into 2 nerves: Tibial nerve & Common peroneal
(fibular) nerve.
All 4 previous muscles are supplied by Tibial nerve, EXCEPT short head of
biceps femoris which is supplied by common fibular nerve.
4 | P a g e
*Make a connection in your mind between the position of the biceps
femoris which is lateral and the position of common fibular nerve which
is also lateral, and because of that part of the biceps (short head) is
supplied by this nerve.
Origin: All muscles originate from Ischial
tuberosity, EXCEPT short head of biceps
femoris (because it’s short, it originates
from the lateral supracondylar line on
the femur).
Insertion: 1- Biceps femoris: Inserts on
the fibula (head/styloid process).
2- Semitendinosus: Inserts on SGS
(upper part of medial surface of tibial
head).
3- Semimembranosus: Inserts on the
posterior part of medial condyle of the
tibia.
4- Adductor magnus: Inserts on
adductor tubercle on the femur.
Action: All of them cross 2 joints: hip joint and
knee joint. So, the action for these muscles will
be flexion of the knee & extension of the hip.
EXCEPT 2 muscles: Short head of biceps femoris
& adductor magnus.
Short head only crosses the knee joint, so it only
helps with flexing the knee.
Adductor magnus only crosses hip joint so the
hamstring part helps with extension of the hip.
In addition to that, medial muscles
(Semitendinosus & semimembranosus) do medial
rotation of the leg, and biceps femoris do lateral
rotation.
5 | P a g e
Ischial tuberosity
Ischial tuberosity divides into 2 parts: upper & lower parts, and every
part divids into another 2 parts.
^Origins of ischial tuberosity-originated muscles that mentioned in the
picture are important.
Lower triangular (medial) part has no muscles, but it has subcutaneous
bursa (a sac contains synovial fluid) and when we sit we sit on it, so it
helps in preventing direct connection
between the bone and the skin when
sitting.
Sciatic Nerve
Originates from the sacral plexus (L4, L5, S1,
S2, S3).
Course: From sacral plexus to greater sciatic
foramen (below the piriformis), then goes to
the middle of the thigh, there, gives 2
branches: common peroneal and tibial
nerve. Sciatic nerve gives its branches in
6 | P a g e
different sites from person to another.
You can determine the surface anatomy of sciatic nerve by two points.
The first one is the middle point between posterior superior iliac spine
and the ischial tuberosity. The second one is the middle point between
ischial tuberosity and greater trochanter.
Posterior cutaneous nerve of the thigh
Originates from sacral plexus (S1, S2, S3), then enter the gluteal region
through the greater sciatic foramen below the piriformis.
It supplies the posterior skin of the thigh, upper posterior part of the leg
and medial lower part of the gluteal region.
Popliteal fossa
The back of the knee. Have 4 borders: 2 upper & 2 lower borders.
1- Upper medial: Semitendinosus, Semimembranosus.
2- Upper lateral: Biceps femoris (long head).
3- Lower medial: medial head of gastrocnemius.
4- Lower lateral: lateral head of gastrocnemius (and plantaris, but
maybe absent).
7 | P a g e
Floor: Upper part is femur, lower is
tibia, and capsule of knee joint
between them.
Roof: skin, superficial fascia and
deep fascia.
Contents:
1- vessels: Popliteal artery (most
deep, closest to the bone),
popliteal vein (posterior to
popliteal artery, continue as
femoral vein), small saphenous
vein (drain into popliteal vein).
2- nerves: tibial nerve (From the
upper angle to the lower angle),
common fibular nerve (from upper angle to lateral angle).
3- lymph nodes: from lateral side of the foot and leg.
8 | P a g e
*Common fibular nerve turns around the neck of the fibula then divides
into 2 nerves: Superficial fibular nerve & deep fibular nerve.
*Common fibular nerve gives 2 branches: Lateral cutaneous nerve of
the calf (supplies the upper lateral side of the leg & the anterior lateral
side of the leg & the posterior lateral side of the leg) and Sural
communicating branch.
Tibial nerve gives a branch called Sural nerve (supplies the back of the
leg and lateral side of the foot.
Sural nerve goes along with small saphenous vein posterior to the lateral
malleolus.
Clinical case: If a patient was complaining of a mass on the popliteal
fossa what can the cause possibly be?
First thing you think about is the content of this fossa, and you see from
what the mass is arising. If it’s arising from the skin it could be sebaceous
cyst or lipoma, if it’s from the popliteal artery it could be aneurysm, and
it could be from the lymph node, or a tumor in the femur. (What the
doctor meant by this example is that we have many causes of swelling in
the popliteal fossa and it could be any on of them because of the variety
of the content).