SSN ANATOMY
Workshop 4: Lower Extremity
If you need a leg to stand on, we’ve got your back…
1. On your medicine rotation third year, a patient is admitted who is suspected of having
bacterial meningitis, and you are asked to do a lumbar puncture. Before you do so, the
resident pimps you on all of the structures the needle will pass through before it reaches the
CSF. Without even blinking an eye, you answer…..
In order: skin, superficial fascia, SUPRAspinous ligament, INTERspinous ligament,
ligamentum flavum, epidural space (containing the internal vertebral venous [Batson’s]
plexus), dura mater then finally arachnoidCSF
(NOTE: same structures for a spinal block/intrathecal anaesthesia, BUT only to the epidural
space for epidural anaestesia)
2. Which levels of the cervical spine are responsible for….
Flexion/extension: atlantooccipital joint
Rotation: atlantoaxial joint
Lateral flexion (abduction): between C2-C7
Circumduction: combination of flexion/extension and abduction
3. Label the regions of the spinal cord (April 151-2).
4. IPSIlateral spinal cord crush injury—Brown-Sequard syndrome (April 153)
Pathway affected
Where does it cross?
Clinical sequelae
MOTOR—lateral
corticospinal tract, which
Lower brain stem
Paralysis on IPSIlateral
controls voluntary
side
movement below the neck
SENSORY—dorsal
columns (fasciculus
2nd order neuron decussates IPSIlateral anaestesia below
cuneatus, gracilis), which
in the brain stem
the level of injury
carry touch, proprioception
SENSORY—lateral
2nd order neuron cell body
Loss of pain and
spinothalamic tract, which
resides in lamina of the
temperature sense on
conveys sharp pain and
dorsal horn and decussates CONTRAlateral side below
temperature
through the ant. Commisure level of injury
Mnemonic for dorsal columns: “Your ass is grass”—the fasciculus GRACilis carries sensory
(touch, proprioception) information from the LOWER extremities, and remember that the
sensory neurons add on to the dorsal columns laterally as you go up the spinal cord; the f.
gracilis are therefore medial, and the f. cuneatus are lateral.
5. What is the highest corresponding vertebral level of the iliac crests, and why is this
clinically relevant?
(April 149, 155, 472) L4—landmark for spinal tap/epidural and spinal anaestesia—the low
level on the vertebral canal ensures that the spinal cord has already terminated inferiorly;
also the spinous processes of the lumbar vertebrae are more horizontal, improving access to
the vertebral canal.
Remember that the vertebral column outgrows the spinal cord after the fourth fetal month,
resulting in the cauda equina (“law of descent”—spinal nerves still emerge from
corresponding level of vertebral column).
6. Where in the vertebral column is disc herniation most likely to occur? In which direction
does the disk go, and what happens?
(April 140) The L4-L5 and L5-S1 disks are most likely to herniate, and they do so
POSTEROLATERALLY, where the annulus fibrosis is NOT reinforced by ligamentous or
bony structures. The NEXT LOWER vertebral level spinal nerve is compressed (L5 or S1,
respectively), causing symptoms (referred pain down buttocks, back of legs, etc.) related to
the dermatome and myotome supplied by that nerve, as well as local pain from the stretched
annulus fibrosis (painful spasms of back muscles).
7. What is the strongest joint in the body? What type of joint is it? Are there any changes
this joint experiences throughout life? Name the five ligaments that support it.
(April 163, 165) Sacroiliac joint—articulation of alar plate of sacrum with ilium. The SI
joint is a diarthrosis (synovial joint); the joint usually fuses by age 50, and also the supportive
ligaments become relatively lax in pregnancy. The five supportive ligaments are: dorsal SI
ligaments, ventral SI ligaments, iliolumbar ligaments, sacrospinous ligament, sacrotuberous
ligament.
8. What are the differences between intracapsular and extracapsular fractures of the hip joint?
What are the capsular ligaments? Speaking of trauma, what is the most common type of
dislocation of the hip joint? What nerve is at risk for injury?
(April 164, 167) Intracapsular fractures (FEMORAL NECK) endanger blood supply to
proximal fragment (the femoral head), resulting in AVN; extracapsular fractures are more
likely to heal without problems, due to a more abundant collateral blood supply (medial and
lateral circumflex arteries).
Capsular ligaments are the iliofemoral (Y ligament of Bigelow), the ischiofemoral, and the
pubofemoral ligaments.
POSTERIOR dislocation is the most common—the hip joint is least stable in the flexed
position, and dislocation can occur when the flexed thigh comes into violent contact with a
dashboard for instance, placing the SCIATIC n at risk. The patient presents with the head of
the femur posterior to the iliofemoral ligament and the lower limb is flexed at the hip joint,
adducted, medially rotated, and shorter than the uninjured limb.
9. You are on your third year rotations and you happen to be in the ER. A patient comes in
who needs a cannula inserted, and you are told to do so. You panic, being that you’ve never
done one before, but then you remember your anatomy. Where is a good place to insert a
cannula? Which nerve are you going to try really hard not to damage?
(April 235, 239) Great saphenous vein, anterior to the medial malleolus. The saphenous
nerve (terminal branch of the femoral n) can be damaged, causing pain on the medial side of
the dorsal foot.
10. On same day, a patient comes in who is complaining of a pain and pin-prick sensation on
his lateral thigh. The patient is a middle-aged man who is markedly obese. The intern didn’t
go to P&S and therefore didn’t take Clinical Anatomy, and he’s too busy to find his copy of
Netter, so he asks you what you think. What’s going on?
(April 233) The lateral femoral cutaneous nerve (L2-3 off the lumbar plexus) is being pinched
by the obese abdomen between the inguinal ligament and the iliopubic ramus.
11. What are the muscles that insert onto the greater trochanter of the femur? The lesser?
Greater troch—piriformis, obturator internus and externus, superior and inferior gemelli (all
lateral rotators of thigh), and gluteus medius and gluteus minimus muscles (aBductors of
thigh)
Lesser troch—iliopsoas muscle ONLY (major flexor of hip joint)
12. What are the SIX muscles that act across BOTH the hip and knee joints?
SARTORIUS (hip and knee flexion)
TENSOR FASCIA LATA (disconcerting sinking feeling—flexes hip and flexed knee, extends
extended knee)
GLUTEUS MAXIMUS (same as TFL since it inserts onto the fascia lata),
GRACILIS (flexes hip and knee)
RECTUS FEMORIS (flexes hip, extends knee)
BICEPS FEMOIS—LONG HEAD (extends hip, flexes knee)
13. What are the boundaries of the femoral triangle? What are its contents?
(April 192-3) Boundaries: inguinal ligament, sartorius muscle, and adductor longus muscle.
Contains: femoral ring (which contains lymphatics that drain inguinal lymph nodes), femoral
artery, nerve, and vein (NOTE: great saphenous vein joins femoral vien here—good spot for
a saphenous cutdown)
14. What about the popliteal fossa and its contents?
(April 195) Boundaries: superolaterally by the biceps femoris, superomedially by the
semitendinosus, and inferiorly by the lateral and medial heads of the gastroc; the popliteal
muscle forms the floor.
Contains: tibial nerve, common peroneal nerve, popliteal artery (when femoral artery
emerges from adductor canal into popliteal fossa, it is then the popliteal artery), popliteal
vein, small saphenous vein
15. On your orthopedics rotation third year, you see an 18 yo patient who had broken his
proximal fibula and lateral tibial condyle after a kick from an opponent in a karate match. He
has healed the fractures, but is still walking abnormally—specifically, he has to “high-step,”
meaning he raises his foot higher than normal so his toes don’t scrape the ground, and his foot
makes a “clop” sound as it hits the floor. What is wrong?
He probably damaged the common peroneal nerve as it swings around the neck of the fibula,
and now has a foot drop.
16.
What nerve….
Superior gluteal (L4-S1
posterior)
Inferior gluteal (L5-S2
posterior)
Femoral (L2-L4 posterior)
Obturator (L2-L4 anterior)
Tibial (L4-S3)
Common peroneal/fibular
(L4-S2)
Innervates these muscles?
What happens w/nerve
damage?
Gluteus medius and
Abductor lurch
minimus, Tensor fascia lata (Trendelenburg gait)—no
ability to pull the ipsilateral
pelvis down when walking;
no abduction of thigh
Gluteus maximus
Inability to rise from a
chair or climb stairs
Iliacus, sartorius, 4
Weakened flexion of thigh,
quadriceps femoris muscles, extension of leg is lost,
and pectineus
ALSO sensory loss over
anterior thigh and medial
leg and foot
Adductors longus, brevis,
Adduction of thigh lost,
and anterior part of magnus, some sensory loss medial
gracilis, pectineus
thigh
Posterior part of adductor
Loss of plantar flexion and
magnus, gastroc, soleus,
flexion of toes, weakened
plantaris, popliteus, flexors inversion of foot, sensory
digitorum and hallucis
loss on sole of foot, no
longus, tibialis posterior,
Achilles reflex; NOTE: Pt
intrinsic muscles of plantar with tibial n. KO’d will
foot
present with
calcneovalgocavus—
opposing muscles dorsiflex
and evert foot
Short head of biceps
Loss of eversion and
femoris, peroneus
dorsiflexion of foot, loss of
longus/brevis/tertius,
extension of toes (NOTE:
extensor hallucius and
FOOT DROP—Pt presents
digitorum longus, tibialis
in equinovarus—plantar
anterior, intrinsic muscles
flexion and inversion of
of dorsal foot
foot), and sensory loss over
anterolateral leg and dorsal
foot
17. The next patient you see on your orthopedics rotation is the running back for Columbia’s
football team. He took a really hard hit in the knee in the homecoming game against Harvard,
in which Columbia stomped over their opponent and made the alumni proud (obviously a
fictional tale). Still, he insists that you watch the tape of the game he brought with him, and
you see that his knee was flexed and his foot was planted as he was hit on the lateral side of
the distal femur. You examine him and note that his knee locks, makes popping noises on
movement, and cannot reach terminal extension, and he exhibits an anterior drawer sign but
no posterior drawer sign. What do you think is going on here?
(April 183-7) Based on the locking, popping, and the anterior drawer sign, he probably has
the “unhappy/terrible triad”—medial meniscal tear, MCL and ACL tear/rupture, which can
happen with violent abduction and lateral rotation of the semiflexed fixed leg.
Remember that the medial meniscus is attached to the MCL, whereas the lateral meniscus is
not attached to the lateral collateral ligament. Also remember that the medial meniscus is C
shaped and the lateral meniscus is O-shaped.
The medial meniscus is well-attached to the knee joint (via the short internal collateral and
coronary ligaments), and has restricted movement, making it prone to tears. The lateral
meniscus is relatively free to move (attached to the meniscofemoral and coronary
ligaments)—it slides anteriorly with the lateral femoral condyle in the terminal phase of
extension.
Also remember the “finger-crossing” mnemonic for the orientation of the ACL and PCL in
the knee joint.
18. What structures are contained within the flexor retinaculum (tarsal tunnel)?
(April 215) From medial to lateral: tibialis posterior m., flexor digitorum m., posterior tibial
artery and nerve, and flexor hallucius longus.
Mnemonic: Tom Dick ANd Harry
19. What are the possible sequelae of a severe inversion of foot?
(April 204) Inversion sprains, which can tear the lateral collateral ligaments, in increasing
order of severity of the sprain: anterior talofibular ligament, calcaneofibular ligament, and
posterior talofibular ligament.
Also can end up with avulsion fractures, where the tuberosity of the fifth metatarsal (insertion
of the peroneus brevis m) breaks off.
20.
Reflex
Cremasteric
Patellar
Hamstring (April 199)
Achilles
21. Foot Musculature
DORSAL
Muscle
Extensor digitorum brevis
Extensor hallucius brevis
Spinal level
L2-L3
L2-L4
L5
S1
Muscle Group
Cremaster
Quadriceps femoris
Hamstrings
Posterior crural
compartment
Innervation
Deep peroneal n., some superficial
peroneal n.
Deep peroneal n., some superficial
peroneal n.
PLANTAR
It may be helpful to think of the dorsum of the foot having four LAYERS of muscles….
See plates 497-501 in Netter for diagrams.
After removal of the plantar aponeurosis, getting DEEPER as you go, you have the…
First layer
Muscle
Abductor hallucis (brevis) NOTE: no
longus
Flexor digitorum brevis
Abductor digiti minimi
Second layer
TENDONS of flexor hallucis/digitorum
longus mm.
Lumbricals
Quadratus plantae
Third layer
Flexor hallucis brevis (2 HEADS—med
and lateral)
Adductor hallucis (2 HEADS—transverse,
oblique—shaped like a “7”)
Flexor digiti minimi brevis
Innervation
Medial plantar n.
Medial plantar n.
Lateral plantar n.
None—just the tendons
Lateral plantar n.
Lateral plantar n.
Medial plantar n.
Lateral plantar n.
Lateral plantar n.
Fourth layer
Plantar interossei (three of them)
Lateral plantar n.
Dorsal interossei (four of them)
Lateral plantar n.
Mnemonic: Bring the plants IN in the winter—the plantar interossei ADDUCT the digits.
22. Mnemonic for lumbosacral plexus:
23. As you are finishing up your third year, you’re on your final rotation, pediatrics. You
have been asked to give an IM injection in the gluteals to a screaming four-year-old with an
equally anxious mother. Before you administer the shot, the mom asks you if there is a
chance you will hit any nerves. You confidently shake your head no, and go on to explain to
her that three of the four quadrants of the gluteal regions contain nerves which potentially
could be damaged. Which is the safe quadrant and what are the nerves in the remaining
three?
(April 177)
Superolateral quadrant—safe
Inferolateral quadrant—inferior gluteal nerve
Superomedial quadrant—superior gluteal nerve
Inferomedial quadrant—sciatic nerve