Download Posterior thigh

Posterior thigh & popliteal fossa (18)
Posterior
thigh
-functions to flex the knee & extend the thigh
-occupied primarily by a group of 3 muscles known collectively as the
hamstrings
*biceps femoris is located laterally & consists of a long head and short
head
*semimembranosus & semitendinosus are located medially 
semimembranosus is located immediately deep to semitendinosus
-origin of hamstrings is the ischial tuberosity (with one exception)  short
head of biceps femoris originates on the linea aspera of the femur
INSERTIONS
-biceps femoris inserts on the head of the fibula
-semitendinosus inserts on the medial surface of the superior tibia
-semimembranosus inserts on the posterior part of the media condyle of
the tibia
ACTIONS
-approaching full knee flexion, hamstrings have been shortened to the
point here hip extension is NOT possible
-when the hip is extended, the hamstring have been shortened to the point
where full knee flexion is NOT possible
-if lower limbs are fixed, the hamstrings help extend the trunk
-mildly rotate the legs when he knees are flexed- semitendinosus &
semimembranosus rotate medially, while biceps femoris rotates laterally
GAIT & POSTURE
-hamstrings help maintain a relaxed standing posture by preventing
forward-falling
*any trunk action that takes the center of gravity in front of the hips
strongly activates the hamstrings in order to restore balance
-during gait, hamstrings are most active when they are contracting
eccentrically in order to decelerate hip flexion and knee extension 
terminal swing
Hamstrin
gs injury
-strains about as twice as common as quadriceps strains
*proper warm up? Strength imbalance? Slight hyperextension of
hamstrings in resting position?
-strains most often occur in sports requiring rapid, or violent muscular
exertion (sprinting)  most occur when muscle is thrown into rapid
lengthening during terminal swing
-with hamstring fully lengthened (thigh flexed & leg extended) an avulsion
fx may occur
Motor
-sciatic nerve (L4-S3) passes through gluteal region but supplies NO
muscles there  supplies all posterior thigh muscles, all leg & foot muscles,
and most of the skin of the leg & foot
-one exception  hamstrings are innervated by the tibial division of the
sciatic nerve – the short head of the biceps femoris is innervated by the
fibular division of the sciatic nerve
Cutaneous
-most via the posterior femoral cutaneous nerve (S1-S3)
*supplies more skin than any other cutaneous nerve
*lateral aspect of posterior thigh is supplied by lateral femoral cutaneous
nerve (L2-L3- from lumbar plexus)
-main part of nerve is deep to fascia lata w/only terminal branches piercing
through the skin
Blood
supply
-NO major artery exclusive to the compartment – served indirectly by major
arteries
-internal iliac artery gives rise to the inferior gluteal artery  supplies
superior part of hamstrings
-profunda femoris gives rise to the medial circumflex femoral artery &
perforating arteries
-perforating arteries  unusual in that they have a transverse,
intercompartmental course
*these large arteries must be detected during surgery
lymphatics
-parallel the major route of venous drainage, femoral vein
-most drainage converges on the superficial inguinal lymph nodes and then
proceeds to the external iliac nodes
Popliteal
fossa
-important area of transition
-mostly fat-filled, diamond shaped, intermuscular space on the posterior
aspect of the knee
*visible when the knee is flexed
-poplitis means ham of the knee  note that in the extended leg, this
“ham” provides protection for fossa contents
-superior border semimembranosus & semitendinosus medially & biceps
femoris laterally
-inferior border  medial & lateral heads of gastrocnemius
*in a living person, the inferior triangle of the diamond is non-existent
until the two heads of the gastrocnemius are retracted from one another
-roof  skin & popliteal (deep) fascia which is continuous with fascia lata
and crural fascia
*fascia provides protection to fossa contents & serves as a weak
retinaculum for hamstrings tendons
-floor  femur, knee joint capsule, and popliteus muscle
Nerves
-sciatic nerve usually ends at the superior angle of the popliteal fossa by
dividing into the tibial & common fibular nerves
*tibial nerve bisects the popliteal fossa, while the common fibular nerve
follows the tendon of biceps femoris
-skin supplied by posterior cutaneous nerve of the thigh
-in the fossa, the tibial nerve gives rise to the medial sural cutaneous nerve,
while the common fibular nerve gives off the lateral sural cutaneous nerve
*lateral sural cutaneous nerve gives off the sural communicating branch
which joins the medial sural cutaneous nerve to form the sural nerve
Vasculature
-inferior border  posterior tibial veins form popliteal vein which in turn
becomes the femoral vein at the adductor hiatus
-on posterior aspect of the leg, small/short saphenous vein pierces the
popliteal fascia to drain into the popliteal vein
*surgical approaches to posterior knee, the small/short saphenous serves
as a superficial landmark (along with the medial sural cutaneous nerve) that
makes it easier to find the tibial nerve
-adductor canal  long, narrow passageway in the middle third of the
thigh, which extends the apex of the femoral triangle to the adductor hiatus
– an opening in the tendon of adductor magnus
*provides an intermuscular passage for the femoral artery & vein, the
nerve to vastus medialis (branch of femoral nerve), and saphenous nerve
-popliteal artery  continuation of the femoral artery; begins at the
adductor hiatus, ends at the inferior border of popliteus where it passes
deep to the tendinous arch of the soleus and divides into anterior &
posterior tibial arteries
*deepest structure in fossa but it can be palpated when compressed
against the tibia in the lower part of the fossa
*gives rise to multiple arterial branches which fall into 2 categories 
muscular branches & genicular branches
-genicular branches supply the capsule & ligaments of the knee joint & are
heavily involved in anastomosis, which provides extensive collateral
circulation around the knee
*5 branches  medial genicular arteries (superior & inferior) lateral
genicular arteries (superior & inferior) and middle genicular artery
Lymphatics
-superficial popliteal lymph nodes lie in the subcutaneous tissue
-deep nodes (~6-7) are located around the blood vessels
-usu. there is one node associated with the small saphenous vein, where it
drains into the popliteal vein
-drainage follows femoral vessels to deep inguinal nodes
Clinical
-popliteal fascia overlying the fossa is strong & resistant to expansion,
consequently the presence of tumors, abscesses, or any disease process
resulting in swelling usually leads to severe pain
-Baker’s (popliteal) cyst  protrusion of the bursa between
semimembranosus tendon and the medial head of gastrocnemius into the
fossa
*usu. result of chronic effusion from the knee joint
*tx  includes aspiration, but also arthroscopy, as intra-articular
pathology is usu. an underlying cause for the cyst
-arteriovenous fistula  combined injury of an artery & vein in close
proximity (as they are in the popliteal fossa) can result in an arteriovenous
fistula (AVF)
*such an injury may occur during procedures involving the knee joint,
such as intracapsular ligament reconstruction (though this is rare)
*in popliteal AVF blood is mostly shunted from artery to vein- with little
flow distally to the knee- necrosis of the leg and foot is possible