F I G U R E 4 - 9 Tibialis posterior.
F I G U R E 4 - 1 0 Flexor digitorum longus.
F I G U R E 4 - 8 Gastrocnemius.
Now, let’s show the tibial nerve-innervated muscles. First, indicate the superfi cial posterior compartment muscles:
gastrocnemius and soleus, supplied by S1, S2. Both mus-cles provide foot plantar fl exion: we test gastrocnemius with the knee extended and soleus with the knee fl exed.
Next, show the deep posterior compartment muscles:
tibialis posterior and fl exor digitorum longus and fl exor hallucis longus, supplied by L5, S1, primarily. Note that some texts indicate that L4 also innervates tibialis poste-rior and some texts indicate that S2 also innervates the fl exor digitorum and hallucis muscles. Tibialis posterior provides foot inversion; fl exor digitorum longus fl exes the toes (except the great toe); and fl exor hallucis longus fl exes the great toe.
Now, add the lesser muscles that the tibial nerve innervates: popliteus and plantaris. Popliteus unlocks the knee at the beginning of knee fl exion and plantaris acts in concert with gastrocnemius.
Finally, let’s begin to address the sensory innervation of the leg and foot. First, show that the common peroneal nerve derives a common sensory trunk that produces
both the lateral sural cutaneous nerve and also the sural communicating branch. Show that the tibial nerve pro-duces the medial sural cutaneous nerve, which joins the sural communicating branch to form the sural nerve.
Th en, show that when the sural nerve passes through the ankle, it produces both the lateral calcaneal nerve branch and also the lateral dorsal cutaneous nerve. Th e lateral calcaneal branch is the lateral corollary of the medial cal-caneal branch, which we will draw in a moment. But fi rst, show another important anatomic region, the tarsal tunnel, which is the medial entry zone of the tibial nerve through the ankle into the foot.
Th e medial malleolus and medial calcaneus form the superior and inferior boundaries of the tarsal tunnel, respectively, and the fl exor retinaculum forms its roof.
Show that within the tarsal tunnel, the tibial nerve divides into the plantar nerves (medial and lateral) and also the medial calcaneal sensory nerve. Th e plantar nerves inner-vate the plantar intrinsic foot muscles, supplied by S1–S3, and the plantar nerves and medial calcaneal nerve pro-vide sensory coverage to the sole of the foot. 1 – 4 , 6 – 8
Common peroneal nerve
Tibial nerve
Sural nerve (cutaneous)
Sciatic nerve (L4 - S3)
Superficial peroneal nerve
Deep peroneal nerve
Peroneus longus & peroneus brevis (L5, S1)
Thigh Leg
Fibular neck
Lateral calcaneal branch &
lateral dorsal cutaneous nerves
Tibialis anterior (L4, L5)
Ext. digit. longus, ext. hallucis longus,
& peroneus tertius (L5, S1)
Deep m. - tibialis post., flexor digit. longus,
& flexor hallucis longus (L5, S1) Medial sural cutaneous nerve Lateral sural cutaneous nerve
Plantar instrinsic foot muscles (S1- S3)
Foot
Medial and lateral plantar nerves Tarsal
tunnel Popliteal fossa
Ext. digit. brevis &
ext. hallucis brevis (L5, S1)
Sural communicating branch
Medial calcaneal branch (cutaneous)
Superficial m. - gastrocnemius & soleus (S1, S2)
(additional m. - popliteus and plantaris)
D R AW I N G 4 - 4 Th e Leg & Foot — Complete
The Thigh
Here, we will draw the innervation of the thigh. To local-ize each form of femoral, sciatic, or obturator nerve injury, learn at least one muscle from each muscle group.
First, label across the top of the page from left to right:
abdomen and pelvis, thigh, and leg. Th e thigh divides into three compartments: anterior, medial, and poste-rior, which supply the extensor, adductor, and fl exor muscles, respectively. In accordance with the “one compartment — one nerve” principle, indicate that the femoral nerve innervates the anterior compartment, which the L2–L4 nerve roots supply; the obturator nerve innervates the medial compartment, which is also supplied by L2–L4; and the sciatic nerve innervates the posterior compartment, which, again, is supplied by L4–S2. Note, though, that the tibial division of the sci-atic nerve receives additional supply from S3 for its innervation of the foot.
Now, let’s show the innervation of each compart-ment’s primary muscle groups. First, indicate that proximally, the femoral nerve innervates the iliopsoas muscle, which comprises iliacus and the psoas major and
minor muscles. Iliopsoas is the primary hip fl exor and attaches within the "iliac region;” when it is weak, patients have diffi culty climbing upstairs or rising from a low chair. Next, indicate that distally, the femoral nerve innervates the quadriceps femoris muscles, which are rectus femoris and the vastus muscles: vastus medialis, vastus intermedius, and vastus lateralis. Th e quadriceps femoris muscles provide knee extension, and when they are weak, patients have diffi culty walking downstairs.
Next, show that the obturator nerve innervates the adductor muscles, which are adductor longus, adductor brevis, and adductor magnus; note that adductor magnus is also supplied by the sciatic nerve, as we will later show.
We test the adductor muscles through hip adduction but these muscles provide a variety of actions intrinsic to gait and stability.
Now, show that the sciatic nerve innervates the ham-strings muscles, which are semimembranosus, semiten-dinosus, and the short and long heads of the biceps femoris muscle. Th e hamstrings muscles provide knee fl exion and hip extension.
F I G U R E 4 - 1 1 Iliopsoas. F I G U R E 4 - 1 2 Quadriceps femoris.
F I G U R E 4 - 1 3 Adductor muscles. F I G U R E 4 - 1 4 Hamstrings.
Abdomen & pelvis Thigh
Iliopsoas
Leg
Quadriceps femoris: rectus femoris, vastus medialis, vastus intermedius, & vastus lateralis
Adductor muscles: longus, brevis, (magnus)
Hamstrings: semimembranosus, semitendinosus, biceps femoris (short and long heads)
Femoral nerve (L2 - L4)
Anterior compartment
Obturator nerve (L2 - L4)
Medial compartment
Sciatic nerve (L4 - S2)
Posterior compartment
D R AW I N G 4 - 5 Th e Th igh — Partial