Lower Extremity Anatomy

00:01 Okay, here we have the SI joint, also called the SIG or SIJ.

00:10 At the sacroiliac joint which bones articulating? The ilium and the sacrum.

00:15 We have an amphiarthrosis, which is a real joint with very little movement.

00:19 It's held together by very strong ligaments that allow only a few degrees of movement around three to five, to be specific.

00:29 The sacrum is wider at the top than at the bottom.

00:33 This means that when an axial loading force is applied downward, the sacrum forms a wedge between the right and left pelvic bones.

00:41 Since the ligaments are very strong, both anteriorly and posteriorly, the SI joint becomes even more tight during the load.

00:48 When you jump and land on your feet, and using this axial force, you can sometimes develop what's called an SI blockage if the jump was too high.

00:56 This can be very painful with symptoms that resemble sciatica.

00:59 Here we see the piriformis muscle.

01:02 It originates on the anterior sacrum as well as the pelvic facets.

01:08 It runs through the greater sciatic foramen and divides it into greater and lesser sciatic notches.

01:16 It then inserts onto the greater trochanter.

01:20 It functions in abduction because it's above the abduction axis and does external rotation because it comes from behind its longitudinal axis.

01:29 Here the sacral plexus exits posteriorly.

01:33 It lies on the piriformis muscle along its ventral aspect and then courses further posterior.

01:40 A good learning aid is to orient your hand like this.

01:42 The thumb above the greater sciatic notch represents the superior gluteal nerve and the four fingers below are the other four nerves are the sacral plexus.

01:50 So five nerves at the sacral plexus.

01:52 Above the superior gluteal nerve, below the inferior gluteal nerve.

01:57 Then there's a nerve that supplies sensation to the skin of the thigh.

02:01 The posterior femoral cutaneous nerve.

02:05 The thickest nerve, the sciatic nerve can be as thick as your pinky finger so that's easy to remember because it's the fifth finger.

02:12 We also have the pudendal nerve.

02:14 The pudendal nerve travels beneath the piriformis around the ischial spine, through the lesser sciatic notch, and then dives inside the fascia of the obturator internus muscle.

02:26 This muscle originates from inside the rim of the obturator foramen.

02:32 We now come to the motor and sensory innervation of these five sacral nerves.

02:36 The upper nerve, our thumb from the hand aid is the superior gluteal nerve running here.

02:41 It's purely the motor innervation of the gluteus medius, gluteus minimus, and the tensor fasciae latae muscles..

02:48 The tensor muscle travels from the anterior superior iliac spine, laterally into the iliotibial tract.

02:55 The inferior gluteal nerve exits from beneath the piriformis muscle.

03:01 It then supplies motor to the gluteus maximus muscle.

03:06 This whole area has sensation supplied by the cluneal nerves.

03:10 The superior cluneal nerves arises from the dorsal branches of the lumbar plexus of Levels L1 to L3.

03:18 The middle cluneal nerves arise from the dorsal branches of the sacral plexus, S1 to S3.

03:24 In the inferior cluneal nerve comes from both the posterior femoral cutaneous nerve and the dorsal femoral cutaneous nerve.

03:34 These nerves innervate the skin on the back of the thigh for sensation.

03:40 The pudendal nerve which runs around the ischial spine through the lesser sciatic foramen, then to the fascia from the obturator internus innervates the muscles of the pelvic floor and supply sensation to the skin on the perineum.

03:58 The sciatic nerve which runs down through the greater sciatic foramen, and remember, it's a very thick nerve.

04:03 In fact, it's the thickest nerve in the human body.

04:07 It then turns into the laterally located common fibular nerve which is also called the common peroneal nerve.

04:19 The medial portion of the sciatic then becomes the tibial nerve.

04:23 The lateral portion also innervates the lateral hamstring muscles.

04:32 These muscles originate from the ischial tuberosity and traveled to the lower thigh.

04:38 The tibial portion supplies the more medial hamstrings, which course medially as they descend down the leg.

04:43 The first muscle is called the semitendinosus muscle and insert on the pes anserinus superficialis.

04:49 The other is the semimembranosus muscle which inserts more proximally and deeply on the pes.

04:55 Remember: P for Proximal. P for Profundus.

04:59 The lateral portion of the nerve supplies the short head which is the lateral portion of the biceps femoris.

05:08 The long head starts in the ischial tuberosity, but is supplied by the tibial or medial portion of the sciatic nerve.

05:20 The common fibular nerve runs directly on the fibula and can be compressed with the lower leg cast.

05:32 Iit has both a superficial and deep branch.

05:35 The deep branch runs anteriorly into the lower leg extensors.

05:39 The superficial fibular nerve innervates the peroneal muscles, while the deep fibular nerve travels down further and supplies two muscles in the back of the foot.

05:55 It also provides sensation to the distal foot between the first and second toe and a small dorsal patch proximal to the toe space.

06:06 The superficial fibular nerve provides a larger area of sensation.

06:11 It provides the majority of this area with sensation where you often scratch your dorsal foot in the lateral lower leg when it itches.

06:24 These sensory nerves are called the intermediate dorsal cutaneous and the medial dorsal cutaneous nerve.

06:33 There's also a lateral dorsal cutaneous nerve, which is a terminal branch of the sural nerve.

06:42 The tibial nerve courses through the soleus muscle and runs between the fibula and the tibia.

06:50 Here you can see the soleal line.

06:53 The tibial nerve innervates the superficial and deep lower leg flexor groups.

06:58 The superficial ones include the medial and lateral heads of the gastrocnemius, which are joined by the soleus here by the Achilles tendon before it inserts on the calcaneal tubercle.

07:09 There is also the small plantaris longus muscle that's included in the superficial group.

07:16 The deep group would be the popliteus, the flexor digitorum longus muscle, the tibialis posterior muscle, and the flexor hallucis longus muscle.

07:25 See the muscles? The tibial nerve passes medially or around the medial malleolus and splits into the medial and lateral plantar nerves which are century for the plantar foot.

07:41 The medial nerve, like the median nerve of the hand does sensation for three and a half toes.

07:46 The lateral plantar nerve, like the ulnar nerve of the hand is sensation for one and a half toes.

07:52 Here we see the piriformis muscle, which from the front runs from the ventral sacrum through the greater sciatic foramen and divides the greater sciatic foramen into the greater and lesser notch.

08:04 The learning aid to remember this was, "thumbs up".

08:07 There's only one nerve to the top and the nerve was seen here, the superior gluteal nerve, which integrates the gluteus medius, minimus, and tensor fasciae latae muscles.

08:16 Then the four nerves coming down from below the piriformis out through the lesser sciatic notch.

08:21 The first is of course the inferior gluteal nerve, which we see here as it radiates into the gluteus maximus muscle.

08:31 There is the very thin posterior cutaneous nerve which we see here, which supplies sensitivity to the posterior thigh.

08:44 This is the pudendal nerve.

08:48 We can see it here passing beneath the piriformis then passing around the ischial spine through the lesser sciatic foramen, then here into the fascial fold of the internal obturator muscle.

09:05 It supplies the muscles of the pelvic floor below and the sensation to the skin on the perineum.

09:11 The perineum or regio perinealis is the area from the pubic symphysis to the anus.

09:18 The thickest and final nerve is the sciatic nerve.

09:21 To remember this we say, "It's as thick as the little finger." Though sometimes it's not really quite as thick in real life.

09:26 As it runs along here and then divides usually near the middle third of the thigh.

09:34 As we can see here, it was higher than this specimen as it gives off the more laterally located common fibular nerve or perineal nerve as well as the more medial tibial nerve that we can see here.

09:52 So again.

09:53 The pudendal nerve passes below the piriformis then through the lesser sciatic notch, then in into the ischioanal fossa.

10:02 And there it lies in the fascial fold of the obturator internus muscle, which forms the Alcock's canal.

10:07 So there's four places to remember: below the piriformis, lesser sciatic foramen, ischioanal fossa, and Alcock's canal.

10:18 Let's first look at the sensory innervation the tibial nerve and the common fibular nerve.

10:24 Here in the posterior area.

10:27 The fibular nerve we see here gives off the branch called the lateral sural nerve.

10:32 We will see the calf muscle innervation later.

10:34 The fibular nerve tracts laterally and gives rise to the lateral sural nerve.

10:39 The tibial nerve because it tracks medially gives off the medial sural nerve.

10:43 So the medial sural and the lateral sural nerve then combine and form a point of union.

10:48 And distally, they're referred to as just the sural nerve or the calf nerve.

10:53 The sural nerve then continues down here laterally before it terminates on the lateral dorsum of the foot.

11:01 At this point it becomes called the dorsal lateral cutaneous nerve.

11:07 So again, the medial sural nerve arises from the tibial nerve and the lateral sural nerve from the fibular nerve.

11:13 They then combine to form the sural nerve, which ultimately becomes the dorsal lateral cutaneous nerve.

11:20 This nerve innervates the skin on the side of the foot.

11:24 Now we come to the common fibular nerve.

11:26 It divides into two branches: the superficial and deep fibula nerve.

11:32 The superficial branch runs near the surface and to the back of the foot.

11:36 The deep fibular nerve on the other hand, it travels deep with the leg muscles.

11:40 The common fibular nerve lies directly under the skin at the fibular head and can be compressed by a short leg cast.

11:46 It can also be damaged by lying on the operating table without proper padding.

11:51 So nerve compression is a real concern in this area.

11:55 Here you can see the course of the superficial fibular nerve.

11:59 It runs laterally into the peroneal muscles, the peroneus longus, and the peroneus brevis and provides their motor innovation.

12:07 It then continues to course superficially as shown here, very close to the skin.

12:13 It proceeds to give off the medial dorsal cutaneous and middle dorsal cutaneous nerve.

12:22 This nerve is called the middle because the lateral dorsal cutaneous nerve is still running here.

12:28 For recall, it comes from the sural nerve, the posterior calf nerve.

12:32 The sural nerve was formed by the union of the medial cutaneous sural nerve from the tibial nerve and the lateral cutaneous sural nerve from the fibular nerve.

12:42 So again, the superficial fibular nerve provides motor for the peroneus, longus, and brevis than run superficial to the surface relatively early and supplies sensation to the skin there were one often scratches the dorsal foot or the lower leg.

12:56 These branches are called the dorsal cutaneous nerve and middle dorsal cutaneous nerve.

13:01 Again, the lateral dorsal cutaneous nerve is the terminal branch of the sural nerve.

13:07 The sural nerve runs along the back of the calf, and it was formed by the union of the medial and lateral sural cutaneous nerve from the tibial and fibular nerve respectively.

13:17 The deep fibular nerve, as the name suggests, then moves into the lower leg extensor group.

13:26 And if we look here, you can see the nerve.

13:32 It runs deeply and supplies motor to the lower leg extensor muscles.

13:37 And since it's called profundus, it stays deep only to surface at the very end.

13:45 We see that it emerges here between the toes to provide sensation.

13:49 Specifically, it innervates the skin area between the big toe and the second toe and a small patch of dorsal skin just proximal to this web space.

13:57 The terminal sensory branch is called the lateral hallucis nerve So don't forget the small patch of dorsal skin and the first web space between the first and second toes.

14:06 Now, we come to the tibial nerve.

14:08 The tibial nerve runs here in the popliteal fossa.

14:16 Through the soleus and deeply through the interosseous membrane.

14:19 The interosseous membrane runs between the fibula and the tibia.

14:23 At this point it can be compressed causing soleus compression syndrome.

14:26 It then runs distally between the superficial and deep lower leg flexor group and provides them with motor innervation.

14:33 It travels to the medial malleolus and runs beneath the flexor retinaculum along with the deep lower leg flexor tendons.

14:42 Here it can also be compressed.

14:44 This is known as posterior tarsal tunnel syndrome.

14:47 The deep fibular nerve can be compressed anteriorly and this is called anterior tarsal tunnel syndrome.

14:56 The tibial nerve then divides into a medial plantar nerve which we can see here.

15:05 This nerve supply sensation to three and a half toes similar to the median nerve of the hand.

15:14 The other division is the lateral plantar nerve, which we can see here supplying plantar sensation to one and a half toes, just as the ulnar nerve supplies one and a half palmar fingers in the hand.

15:30 The medial and lateral plantar nerves also supply the small foot muscles with motor.

15:35 We come now to the outer hip muscles.

15:37 There are four large and four small ones.

15:39 The four large ones are the gluteus maximus (most distal), then the gluteus medius, which is covered by the gluteal fascia that has already been cut away here and is partially covered by the gluteus maximus.

15:54 Here we see the gluteus medius and minimus portions, which can no longer be clearly separated here.

16:00 And then we see the piriformis muscle, the inner hip muscles, and the greater and lesser sciatic foramen.

16:05 I will show these more clearly later on the other side.

16:09 The fourth of the large external hip muscles is thetensor fasciae muscle, which arises here from the ASIS, the Anterior Superior Iliac Spine.

16:19 And then runs below the fasciae latae into the band shaped reinforcement of the fasciae latae the iliotibial tract or IT band.

16:28 This runs laterally down the leg and counteracts bending forces of the thigh.

16:35 It inserts on the Gerdy's tubercle on the anterior proximal tibia.

16:45 Now onto the four outer small hip muscles.

16:48 Before discussing them, you have seen that these are not the external muscles, but the deep piriformis and here the obturator internus muscle.

16:57 These are on the outside, but those are on the inside.

17:00 So here is the piriformis muscle.

17:02 It actually starts at the front on the ventral side of the sacrum passes through the greater sciatic foramen, and then inserts on the tip of the greater trochanter.

17:14 Above it we have the greater sciatic notch and below the lesser sciatic notch.

17:20 Here we can see the obturator internus muscle.

17:22 It's also not an external small hip muscle, as its name internist suggests, it arises from the inside.

17:28 Specifically, it originates inside the obturator foramen and courses around the iliac spine, which it uses as a fulcrum to orient its contraction force.

17:37 And here we see its tendons and the superior gemellus as well as the inferior gemellus, the small external hip muscles.

17:46 If you go deep between the obturator internus and inferior gemellus, you will find the tendon of the obturator externus which originates outside of the obturator frame.

18:00 Below we can see the square shaped Quadratus Femoris muscle.

18:07 So the four small external muscles are the superior and inferior gemelli which arise from the tendons of the obturator internus muscle, then located between the obturator internus and the inferior gemellus the obturator externus can be found.

18:21 And at the very bottom the Quadratus Femoris muscle.

18:26 We now come to the details of the external major hip muscles.

18:29 Starting with the gluteus maximus muscle.

18:32 Its origin is at the dorsal sacrum as well as from the iliac crest and sacrotuberous ligament.

18:39 What we see here is that it inserts the ischial tuberosity.

18:44 The gluteus maximus muscle has a portion above and below the hip joint.

18:47 Therefore, it can adduct and abduct.

18:50 The upper portion abducts while the lower portion adducts.

18:53 It lies behind the flex x axis of the hip joint making it the strongest extensor and the hip joint along with the adductor magnus.

19:01 It is also the strongest external rotator in the hip joint.

19:05 Now, the gluteus medius and minimus can no longer be fully seen here.

19:09 But just know that only the gluteus medius is covered by a fascia, which we can see partially here and they have their origin on the gluteal lines laterally on the sacral ala.

19:22 Because of that, they have a distribution similar to the deltoid, with some being in front of and behind the flex x axis allowing for both external and internal rotation.

19:33 The lateral portion allows abduction while the posterior portion does the external rotation and extension in the hip.

19:43 Finally, the anterior portion allows flexion and internal rotation.

19:49 Here we come to the tensor fasciae latae muscle, the tensioner of the fasciae latae, the thigh fascia.

19:55 It originates on the ASIS and radiates into the fascia lata below, eventually becoming the IT band.

20:05 The IT band inserts on Gerdy's tubercle on the anterior tibia.

20:12 Its function is flexion in the hip joint, and it's sometimes called the sprinter muscle.

20:18 The iliopsoas is the strongest flexor.

20:21 But when this hit muscle fails the tensor can enlarge.

20:25 This can also happen in highly trained sprinters.

20:28 So it may enlarge without the other muscles failing.

20:31 In addition to flexion, it also does internal rotation in the hip.

20:35 So it does flexion, an internal rotation, which we cannot show so clearly here.

20:43 We come to the function of the four outer small hip muscles.

20:47 Here we see the obturator internus again, then the superior gemellus, the twin muscles pulling towards the obturator tendon.

20:56 The original the superior gemellus is at the top of the iliac spine, while the inferior gemellus below is from the ischial tuberosity.

21:04 The insertion is on the tendon of the obturator internus.

21:07 And the function is to help the external rotation of the obturator internus.

21:15 Below the obturator internus we don't really see it here.

21:20 But if we imagine it here, we will come across the tendon from the obturator externus.

21:25 The obturator externus also has an external rotation effect and in addition can do adduction as well.

21:34 Below that we have the Quadratus Femoris muscle.

21:37 The Quadratus Femoris originates on the ischial tuberosity as well and then inserts at the intertrochanteric crest.

21:43 Its function is also external rotation.

21:46 And since it's below the axis of abduction from the hip joint that causes adduction.

21:53 The two inner small hip muscles are the piriformis muscle and the obturator internus muscle.

21:59 The only big one is the iliopsoas muscle.

22:03 The piriformis muscle actually originates on the ventral sacral os.

22:10 It passes through the greater sciatic foramen, dividing it into the greater and lesser notch.

22:16 It's insertion is at the top of the greater trochanter.

22:20 Because it lies above the abduction axis it does abduction in the hip joint.

22:24 And because it comes from posterior to the longitudinal axis of rotation, like all hip muscles, it does external rotation.

22:31 So abduction plus external rotation.

22:35 Now, let's go into more detail about the obturator internus muscle.

22:38 It originates on the inside edge of the obturator foramen and the obturator membrane.

22:44 Then it travels around the ischial spine under the sacral spinal ligament here it uses the ischial spine as a deflection point before inserting onto the trochanteric fossa.

22:58 The superior and inferior gemelli, the two small outer hip muscles run with it.

23:03 Its function is only external rotation.

23:06 It's neither above nor below the adduction axis and it comes from behind the longitudinal axis of rotation.

23:12 So it only causes external rotation like all other hip muscles.

23:16 We come to the ventral thigh muscles which are innervated here by the femoral nerve.

23:21 The muscles are the sartorius also called, "the tailor's muscle." Then the quadriceps femoris muscle with its foreheads, the rectus femoris, vastus intermedius, vastus medialis, and vastus lateralis.

23:44 The vastus muscles literally envelope the entire thigh and go to the back of the roof line of the linea aspera.

23:54 The sartorius has its origin on the ASIS, the anterior superior iliac spine, as well as the tensor muscle of the external hip muscles.

24:06 Then it moves diagonally down to the pes anserinus.

24:13 The most superficial of the three claws.

24:16 The others being the gracilis, and the semitendinosus muscle, which also insert here.

24:27 So the semitendinosus first, then the gracilis, and finally the sartorius.

24:38 They come together to form the distal pes anserinus.

24:41 There's also the proximal pes profundus, which is further P - Profundus.

24:46 P as in further proximal.

24:48 From the semimembranosus of the issue of cruel muscles, you can see the adductors.

24:52 The age remember the function of the sartorius is to remember it's called the Taylor's muscle.

24:56 So hip flexion like when sitting cross legged, adduction, and external rotation.

25:05 In the knee, as when sitting cross legged, it flexes.

25:09 And if the knee is flexed, it can rotate the knee internally.

25:15 Let's now take the sartorius away and look at the quadriceps femoris muscle.

25:19 Its rectus femoris is the only one of the foreheads that crosses two joints.

25:24 So it still acts at the hip joint because it's origin is below the anterior superior iliac spine on the anterior inferior iliac spine.

25:35 It travels down here and then has a tendon which unites with the vastus medialis, the vastus intermedius, and the vastus lateralis to form the quad tendon.

25:46 Then the patella, which is the largest sesamoid bone is embedded in the tendon.

25:50 Below the patella and inserting to the tibial tuberosity we find the patellar tendon.

26:00 The function of the rectus femoris is flexion in the hip because it lies in front of the flex x axis.

26:06 And like the entire quadriceps femoris the primary function is extension of the knee joint.

26:13 Let's look at the vastus muscles.

26:15 The vastus medialis, lateralis, and intermedius envelop the femur.

26:21 So it runs up to the back of the linea aspera, in here on the side of the femur going up to the greater trochanter, and here going upwards medially on the femur.

26:36 They unite distally to form the quad tendon.

26:39 There's another special feature that causes the vastus medialis with its lower oblique part to become an important muscle.

26:46 Because we often have patella subluxation laterally this muscle can be trained to prevent lateral dislocation.

26:57 The vastus muscles only do extension in the knee joint.

27:01 Another special feature is the vastus medialis and adductor magnus here form a channel into which the femoral nerve runs.

27:12 Here we can see the femoral nerve.

27:14 You can remember IVAN.

27:16 I for Inside Out, V for Vein, Artery, and N for Nerve.

27:20 I-V-A-N, Ivan.

27:22 Here the femoral nerve travels down and supplies the motor to the ventral thigh muscles.

27:26 And its sensation branch, the saphenous nerve travels down here with the femoral artery.

27:36 You can see that runs into the adductor canal, the hunter canal.

27:40 The canal is formed by a membrane between the vastus medialis and the adductor magnus.

27:45 The saphenous nerve passes anterior to the membrane.

27:48 The femoral artery runs deep and goes into the popliteal fossa and continues to form the popliteal artery in the back of the knee.

27:56 The end of the hunter canal is called the adductor hiatus.

28:01 We come now to the medial adductors sometimes called the equestrian muscles of the thigh.

28:08 They are innervated by the obturator nerve, which travels in the obturator canal and through the obturator foramen.

28:16 These muscles include the pectineus, the adductor longus, the adductor brevis, the adductor magnus, and the gracilis.

28:36 The gracilis is the only one that crosses two joints.

28:41 All the others act only on the hip joint.

28:45 But the knee joint does see action by the gracilis, the longest of all muscles.

28:51 Now more detail.

28:53 The pectineus originates up here at the superior pubic ramus and inserts behind the femur, which is not visible here on the pectineal line.

29:05 In the adductor longus muscle has its origin here at the front of the pubic symphysis.

29:13 It inserts to the linea aspera and the medial labrum because it comes from the medial side.

29:22 Under it lies the adductor brevis muscle, which originates from the inferior pubic ramus.

29:31 It extends to the medial labrum more proximately on the femur.

29:37 The adductor magnus muscle is for this back.

29:40 It originates from the ischial of ramus and ischial tuberosity and is very strong.

29:46 It inserts for this down and it's not visible here.

29:54 Here, you can see it just slightly and it ends here with an attachment to the adductor tubercle.

30:02 The gracilis muscle also starts at the inferior pubic ramus.

30:05 before it travels distally to insert together with the sartorius muscle, and the semitendinosus muscle on the pes anserinus medially on the tibia.

30:26 The function of the adductors as the name suggests is abduction of the hip joint.

30:36 In addition, of course, because they insert towards the posterior femur, they can also apply an external rotation at the hip joint.

30:44 In relation to flexion and extension, the muscles are in front of the flex x axis, for example, the pectineus, the adductor longus, and the adductor brevis all allow flexion.

30:58 The gracilis lies at the level of the flex x axis, so it does not make any flexion from the neutral hip position, which is the straight position when standing with arms drooping.

31:12 The adductor magnus is behind the flex x axis because it originates from the ischial ramus.

31:17 and it is the only one that does extension of the hip joint So flexion with the longus, the pectineus, and the brevis.

31:26 The gracilis does neither in the adductor magnus does extension.

31:33 That gracilis is the only one which has an effect on both the knee and hip joints.

31:38 All muscles that attach to the pes anserinus whether the superficial or profundus always flex the knee joint and if the knee is flexed do internal rotation at the knee.

31:47 So the gracilis has flexion and internal rotation at the knee joint.

31:53 Here we see the hamstring muscles called the ischial curl muscles because they run from the ischial tuberosity down to the crus or lower leg.

32:02 These are the muscles.

32:04 There are two medial, the semitendinosus muscle which is called the half tendon because it's tendon is in the lower third and the muscle is in the proximal portion.

32:15 And the semimembranosus muscle, which is the opposite.

32:19 It has a membrane in the proximal portion and then becomes a muscle distally.

32:22 The semimembranosus is above as a membrane, the semitendinosus below is a tendon.

32:27 Both are medial structures.

32:29 Both originate from the ischial tuberosity and run distally.

32:32 The biceps femoris also originates at the ischial tuberosity but only the long head.

32:37 This is often related to the semitendinosus muscle.

32:40 Here's the long end of the biceps femoris which runs down towards the fibula and it's called the biceps because as we see here, it has two heads.

32:49 The short head runs completely to the side of the femur and then also tracks towards the fibula.

32:56 So the semitendinosus, the semimembranosus have their origin above with the long head of the biceps femoris.

33:06 The short head originates on the lateral femur and travels laterally towards the fibula.

33:13 The semitendinosus inserts on the so called pes anserinus.

33:20 The garcilis muscle also inserts here, as well as the sartorius muscle.

33:31 The pes anserinus has called "the goosefoot" because they resemble the three toes of a goosefoot.

33:38 The semimembranosus muscle inserts proximately to the pes anserinus alone.

33:43 Remember, P for Proximal, and P for Profundus.

33:46 Because it lies further deep for the posterior and further approximately.

33:50 It's three parts attach here to the lateral collateral ligaments of the tibia.

33:55 They're not visible here behind the fascia of the popliteus muscle and the posterior capsular ligaments of the knee, the oblique ligament.

34:05 The semimembranosus functions as an important stabilizer on the medial side of the knee joint.

34:16 The biceps femoris muscle has an attachment of the long and short head onto the head of the fibula.

34:23 The function of these muscles at the hip because they're all behind the flex x axis at the hip joint is extension.

34:30 They all lie like this.

34:31 They are medially oriented to the abduction axis.

34:34 therefore they all do adduction like the other adductor muscle group.

34:38 Only the biceps femoris with its long head can be contracted and cause an additional external rotation at the hip joint.

34:48 Now let's discuss further their function at the knee joint.

34:51 The two that insert medially the semimembranosus and the semitendinosus behave like the biceps femoris.

34:57 They all flex because they lie behind the flex x axis of the knee joint.

35:02 Those who inserted medially the naturally do internal rotation and the lateral insertions allow the knee external rotation.

35:09 So the biceps femoris does the external rotation, while the semitendinosus and semimembranosus do the internal rotation.

35:17 Now, I welcome you to the lower leg extensors.

35:20 There are three muscles from medial to lateral.

35:22 The tibialis anterior for this medial, the extensor hallucis longus, and laterally, the extensor digitorum longus.

35:32 They are all innervated by the deep fibula nerve, which you can see very deeply here as it travels in the lower leg extensor compartment until it becomes superficial at the distal foot.

35:41 This is where it supplies the skin between the first and second toes and medially on the dorsum of the foot.

35:48 Remember, this nerve is called the lateral hallucis nerve.

35:56 The origin is up here on the tibia, the interosseous membrane, and on the fibula.

36:00 The tibialis anterior which importantly travels in front of the flex x axis and the upper ankle which allows dorsiflexion.

36:07 It's important to remember that it runs medially around the ankle, so it allows for supination.

36:12 It's the strongest supinator in this group.

36:15 It inserted the medial cuneiform and the base of the first metatarsal.

36:23 The extensor hallucis longus lying next to it inserts into the dorsal aponeurosis of the hallux, the big toe.

36:31 It also does dorsiflexion in the ankle and allows slight supination but less than the tibialis anterior.

36:41 The extensor digitorum longus which inserts of the dorsal aponeurosis of toes two through five allows dorsiflexion in the ankle joint but also it does pronation want.

36:54 It lies to the side of the axis of pronation and supination.

36:57 This axis runs from the anterior ankle medially through the sustentaculum tali, which cannot be shown here exactly but looks something like that.

37:05 And downwards, laterally, to the calcaneal tuberosity.

37:08 That's why it does pronation.

37:11 Here we see the two retinacula.

37:13 The reinforcements of the lower leg fascia which prevent the tendons from both stringing during dorsiflexion.

37:21 The proximal one runs transversely and it's called the transverse ligament.

37:25 The lower one here is y-shaped or cross shaped and it's called the cruciform ligament.

37:36 This ligament can compress the deep fibular nerve causing anterior tarsal syndrome.

37:43 Now we come to the superficial lower leg flexor muscles.

37:46 This includes the gastrocnemius, which joins the Achilles tendon to the calcaneal tuberosity.

37:51 There are three heads.

37:52 These include the medial and lateral heads of the gastrocnemius muscle and the soleus muscle.

38:01 The soleus muscle body looks like a fish fillet, hence its name.

38:08 All three converge to form the Achilles tendon the strongest tendon in the human body, which inserts onto the calcaneal tuberosity.

38:16 The plantaris muscle also belongs to the superficial lower leg flexor group.

38:20 The tendon of which very often joins into the medial head of the gastrocnemius or inserts directly to the calcaneal tubercle.

38:29 The medial and lateral gastroc heads flex at the knee joint as does the plantaris longus.

38:40 The soleus starts the arcus tendinous through which the tibial nerve runs.

38:48 The tibial nerve innervates the superficial and deep lower leg flexor groups.

38:54 Here the tibial nerve can be compressed at the arcus of the soleus between the tibia and fibula.

39:01 These muscles allow plantar flexion and supination.

39:06 The supination effect is not understandable at first because the Achilles tendon appears to just be coming down here.

39:12 But since the pronation and supination access to the foot runs from anterior superior medially to posterior inferior laterally, the Achilles tendon attachment is thus medial to the axis of pronation and supination.

39:26 It is the strongest supinator of the foot through the Achilles.

39:32 In the knee joint, the lateral head of the gastrocnemius can do internal rotation.

39:38 And the medial head can do external rotation.

39:45 The plantaris longus which runs down here just like the lateral head does internal rotation in a similar fashion.

39:56 We now come to the deep group.

39:57 And there we have the popliteus muscle.

39:59 It functions just like the lateral head, like the plataris longus muscle.

40:03 All three together do internal rotation of the knee joint.

40:08 When you put your fingers in the back of your knees like this, you will then understand when there's contraction and internal rotation is performed in the knee joint.

40:17 We come to the four deep lower leg flexor muscles.

40:21 Only one lies in the popliteal fossa of the knee, the popliteus muscle.

40:26 It runs if we put our right index finger in the right hollow the knee.

40:33 Then the three remaining muscles we have the furthest lateral, which travels the furthest medial to the hallux.

40:39 (ie) the flexor hallucis longus.

40:44 We see the flexor hallucis longus when we remove the plantar aponeurosis, here.

40:49 remove the middle flexor digitorum brefis.

40:52 Then we see the flexor hallucis longus tendon running here.

40:55 It's crossed by the flexor digitorum longus muscle at the plantar chiasm.

41:01 In addition to the flexor hallucis longus, which is the most lateral, there's also the tibialis posterior.

41:07 And then there's the flexor digitorum longus, which is the furthest medial.

41:11 The flexor digitorum longus crosses the tibialis posterior and then it runs down here along the medial malleolus.

41:19 Crosses the flexion hallucis longus and finally appears as the flexor digitorum brevis muscle in front.

41:30 The flexor digitorum brevis extends to the middle phalanx.

41:33 The flexor digitorum longus extends to the terminal phalanx.

41:36 So just as the flexor digitorum superficialis was pierced in the hand by the flexor digitorum profundus.

41:43 The flexor digitorum brevis is worked up to the middle phalanx and is pierced by the flexor digitorum longus, which then extends beyond it to the terminal phalanx.

41:51 The flexor digitorum longus is the perforans muscle and the flexor digitorum brevis muscle is again the perforatus muscle.

41:59 There are also two muscles, namely: here, the quadratus plantae, the middle group of intrinsic foot muscles runs towards the tendon from the flexor digitorum longus.

42:09 And then the lumbricals which run away from its tendons.

42:14 They look like an earthworm in this specimen.

42:16 So the flexor digitorum longus has five properties.

42:20 It has a chiasm on the lower leg, where the flexor digitorum longus muscle crosses the tibialis posterior.

42:27 She has a plantar chiasm where the flexor digitorum longus crosses the flexor hallucis longus.

42:34 It appears is the flexor digitorum brevis, which is the third property, and fourth and fifth have to do with muscles.

42:40 The quadratus plantar pulls towards its tendon while the lumbrical muscles pull away from its tendon.

42:48 As for functions, the popliteus muscle does flexion and internal rotation.

42:52 Here it runs from the lateral upper condyle medial to the tibia.

42:56 The other three are doing plantar flexion in the ankle, and because they travel medial to the medial malleolus they also do supination.

43:07 In addition, we have a ligament on the medial malleolus.

43:11 The retinaculum of the deep lower like flexors.

43:14 This can lead to posterior tarsal tunnel syndrome, where the tibial nerve is compressed under the retinaculum.

43:21 We now come to the lateral muscles of the lower leg, the so called fibular or peroneal muscle group.

43:28 It consists of two muscles: the fibularis longus and brevis.

43:33 The longus originates more proximally and inserts more distal people.

43:39 The peroneus brevis originates more distal and inserts more proximal.

43:45 There's a third a rare splitting off of the extensor digitorum communis muscle, the peroneus tertius muscle, shown here, which is inconsistently present.

43:56 Now let's discuss the peroneus longus and the peroneus brevis.

44:01 First the brevis.

44:02 It starts here, originating laterally on the middle third of the fibula, and on the two septa which are covered by the fascia that envelope the lower leg under the skin.

44:11 It runs downwards as the intramuscular septum.

44:17 Like the longus it runs behind the lateral malleolus thus causing plantar flexion.

44:24 Then it runs laterally on the calcaneus under the perineal trochlea before inserting on the tuberosity of the base of the fifth metatarsal.

44:43 Since it's coursing here, it pronates on contraction.

44:48 Certainly pull on the peroneus, we can clearly see it causes pronation.

44:55 We come down to the longus.

44:56 Remember, the longus is longer at the top and longer at the bottom.

45:00 That means its origin is at the head of the fibula and at the intermuscular septum and it runs down laterally here lying behind the brevis.

45:08 A good learning aid is brevis B, like belly in the belly and the belly is further anterior, the longus is for the posterior.

45:15 Then the longus runs under the lateral malleolus and exactly the same way as the brevis.

45:20 It runs along the perineal trochlea.

45:23 And now it's running to the plantar aspect.

45:25 We're going to look at that from below.

45:29 Now we see the view from the plantar aspect.

45:32 Here's the peroneus longus and it runs deep into the groove of the cuboid.

45:38 Another learning aid is to remember in front of the large calcaneus is the large cuboid.

45:43 CC - Calcaneus Cuboid.

45:46 It then runs diagonally on the foot, thus tightening the longitudinal and transverse arches.

45:51 It has its insertion at the medial cuneiform and at the base of the first metatarsal.

45:56 Exactly where the tibialis anterior muscle also runs from the lower leg extensors.

46:03 So the peroneus longus and the tibialis anterior have a shared insertion.

46:10 Namely, on the medial cuneiform and the base of the first metatarsal.

46:14 However, these are sometimes referred to as anatomical stapes muscles.

46:18 Next, we come to the two small muscles of the back foot.

46:21 We see here the extensor hallucis brevis, and the extensor digitorum brevis.

46:26 They lie deep to the lower leg extensors which are of the same name.

46:29 Here is the extensor hallucis longus.

46:32 And here is the extensor digitorum longus.

46:35 The origin of the extensor hallucis brevis and extensor digitorum brevis, is here on the calcaneus and they radiate into the dorsal aponeurosis of the toes.

46:43 Their function is toe extension.

46:49 They're innovated by the deep fibular nerve which we cannot see now like the lower leg extensors.

46:55 If we look beneath the extensor digitorum longus muscle and the extensor digitorum brevis, we will find the dorsal interossei between the metatarsals.

47:09 Now to the layers of the plantar foot.

47:11 Once the skin has been taken off, then comes the plantar aponeurosis, which can be thickened in disease patients, much like the palmar aponeurosis of the hand.

47:21 An example of this would be in cirrhosis of the liver where thickening occurs on the ulnar side of the aponeurosis.

47:26 This can cause a strong contraction of the connective fibers.

47:29 The plantar aponeurosis can also be aggravated in ledderhose disease.

47:33 Below the plantar aponeurosis we see the flexor digitorum brevis muscle.

47:37 It belongs to the middle group and does not exist on the hand.

47:40 It's pierced by the flexor digitorum longus muscle the deep lower leg flexor.

47:47 The longest passes through the brevis.

47:49 The brevis is thus Y-shaped like the flexor digitorum superficialis on the hand.

47:55 flexor digitorum longus muscle is similar to the flexor digitorum profundus on the hand with tendon that pierces the other tendon.

48:05 The brevis is therefore called the perforatus and the longus is the perforans.

48:11 We see here that the second small foot muscle in the middle group, which is also not found on the hand, connects to the tendons of the flexor digitorum longus.

48:19 This is the small Quadratus Plantae muscle.

48:22 It's also called the flexor accessory because it pulls on the tendon of the flexor digitorum longus and therefore also supports flexion.

48:32 The middle group also includes the lumbrical muscles.

48:34 We see them here originating from the tendons of the flexor digitorum longus.

48:39 It can flex at the proximal and extend in the middle and distal joints just like the palmar and dorsal interossei.

48:51 If we now fold away the flexor digitorum longus we see the adductor hallucis muscle.

48:56 The transverse head cannot be seen.

48:59 The oblique heads windowed so to speak It can be seen here more approximately in distal.

49:05 The abductor hallucis brevis muscle with its oblique head and the transverse head which cannot be seen here is only found on the hallux.

49:14 The big toe and little toe muscles have in both cases and abductor.

49:19 The abductor hallucis brevis and the abductor digiti minimi are most lateral.

49:25 There's also the flexor hallucis brevis, with a medial and lateral head not seen here, and a flexor digitorum minimi.

49:32 There's an opponent's muscle to counteract those.

49:35 However, only digiti minimi has this and there's no opponents hallucis.

49:39 We don't have a saddle joint here in the foot so we don't have an opposing muscle either.

49:43 On the hand, we do have a saddle joint and an opponent.

49:46 We also have an opponent on the little finger muscle.

49:48 Although there's no saddle joint here either, but as a learning aid where there's no saddle joint, namely at the bottom of the foot, you will not find an opponent's below.

49:56 I have a saddle joint at the top of my thumb and there I have the opponent's pollicis brevis muscle.

50:01 The innervation of the foot muscles are as follows.

50:04 Just like the median nerve on the hand, we have the medial plantar nerve.

50:07 It takes care of the middle group, the flexor digitorum brevis and the adductor from the big toe group.

50:17 but only the medial head of the flexor.

50:19 The lateral head is then supplied by the lateral plantar nerve and the abductor with its transverse and oblique heads, which cannot be seen here is also supplied by the lateral plantar nerve.

50:31 The learning aid, the big toe is brought laterally through the adductor.

50:35 Therefore, it's still innervated by the lateral plantar nerve.

50:39 In addition, the medial plantar nerve supplies the lumbricals 1 and 2.

50:43 Lumbricals 3 and 4 and all interossei are supplied by the lateral plantar nerve.

50:49 Just like the ulnar nerve of the hand supplies all the interossei muscles and the lumbricals 3 and 4.

50:57 Here you see the external iliac artery.

51:00 It runs under the inguinal ligament, the ligamentum inguinale, and through the vascular lacuna.

51:05 We have the medial lacuna vasorum and the lateral muscular lacuna.

51:09 From the middle of the inguinal ligament runs the iliopectineus which is the same as the iliopubisisus down to an iliopubic tract.

51:17 This separates the lateral muscular lacuna where the iliopsoas and femoral nerve travel from the lacuna vasorum containing the vessels.

51:27 In the order from medial to lateral, remember, IVAN.

51:30 I - Inside Out, V for Vein, A for Artery, N for Nerve.

51:36 And then we discuss the small genital femoral nerve, which provides sensory and the great saphenous vein which joins the femoral vein.

51:47 The great saphenous vein, let's see where it comes from.

51:54 From from the medial big toe.

51:56 The great saphenous vein like the great big toe.

51:59 The big toe is also called the magna saphena.

52:02 The great saphenous vein runs along the lower leg with the saphenous nerve, the sensory branch of the femoral nerve.

52:08 Then it runs along the medial side of the thigh and flows down into the femoral vein at the so called saphenous hiatus.

52:17 Suppose a bull's horn rammed into the thigh and injured the femoral artery in an emergency you can press your fist here against the superior pubic ramus and thus initiate hemostasis.

52:35 Two or three liters of blood are lost very quickly and the patient bleeds to death from hypovolemic shock.

52:41 Second, the puncture the femoral vein for a central line could be important.

52:45 We feel the femoral artery and then you go medially with the cannula and hope to get into the femoral vein.

52:50 This sometimes needs to be done when they're unable to perform the vena puncture on the arm.

52:55 Here we see the femoral artery as it progresses.

52:58 It travels up here in the iliopectineal fossa, through the pectineus of the abductors and the iliopsoas muscles of the internal hip muscles.

53:06 The femoral triangle is bounded by the inguinal ligament, the sartorius, and the gracilis.

53:19 This triangle is seen here and if we look deeply in the bottom of the iliopectineal fossa you can see the iliopsoas and pectineus.

53:27 So here we find the femoral artery which continues downward, then lies partially under the sartorius muscle.

53:35 Then we see it down here moving into the hunter canal.

53:41 Together with the femoral vein, we now see the saphenous nerve, the sensory branch of the femoral nerve.

53:47 The hunter canal is formed by the vastus medialis muscle, the quadriceps group of the ventral thigh muscles and connective tissue fibers running to the adductor magnus muscle.

53:59 The femoral artery and vein extend into the canal with the saphenous nerve.

54:03 The vessels that emerge in the popliteal fossa.

54:06 It's only the artery and vein now as the popliteal artery and vein the do this.

54:10 The saphenous nerve on the other hand, breaks the membrane beforehand and joins the descending genicular artery.

54:24 Here the saphenous nerve can be compressed on the abductor membrane in a pathology known as Hunter's compression syndrome.

54:30 We see the vessels in the popliteal fossa the hollow of the knee.

54:34 Here we see at the exit of the hunter's canal, the canalis adductorius, how the femoral artery becomes the popliteal artery.

54:43 Here lies the popliteal artery next to the popliteal vein, the tibial nerve and the common fibula nerve which can be seen here.

54:53 A good learning aid.

54:54 The tingling P-N-V-A from lateral dorsal to medial ventral.

55:04 This is how the structures lie in the hollow of the knee.

55:07 So the furthest lateral tingling P like Perineal nerve, then N for tibial nerve, and VA for vein and artery.

55:17 This is important.

55:18 The popliteal artery can have an aneurysm in the back of the knee.

55:21 You have to know on the magnetic resonance image, which vessel is which? So, the tingling P-N-V-A from dorsal lateral to ventromedial.

55:32 Here we see the saphenous vein opening into the popliteal vein.

55:38 The little one is called parva because it comes from the little toe and here it runs together with the sural nerve.

55:44 The small saphenous vein is cut away here but it will come from the little toe running here with the sural nerve.

55:51 And then in the depth of the popliteal fossa flows into the popliteal vein.

55:56 The learning aid is the parva goes P like the popliteal vein.

56:02 Here we see the popliteal artery.

56:04 For this ventromedial and the popliteal fossa and now continues under the Arcus tendinosis of the soleus muscle.

56:13 It flows into the posterior tibial artery.

56:17 The posterior tibial artery runs distally in the deep group of lower leg flexors.

56:24 And then gives off a lateral branch the perineal artery.

56:30 One might think that because of the name it runs in the fibular or peroneal muscle group.

56:35 It doesn't.

56:36 Like the posterior tibial artery it runs in the deep group of lower leg flexors.

56:41 The posterior tibial artery then continues downward and then comes to rest here on the medial malleolus where the pulse of the posterior tibial artery can be felt.

56:53 Then it splits up like the medial and lateral plantar nerve into the medial and lateral plantar artery.

57:04 This is important because the lateral artery then runs downwards here and forms the arcus plantaris at the bottom.

57:13 There's only one arterial arch on the foot in contrast to the hand.

57:17 Where we have a superficial and deep palmar arch.

57:19 Here we have only one plantar arch and it's formed by the lateral plantar artery.

57:25 The learning aid is A-L-A.

57:29 A for the Arcus, and then L A for Lateral Artery.

57:32 Lateral Plantar Artery.

57:38 Here, to be honest, the anterior has to come forward passing through the interosseous membrane between the tibia and fibula and passes through it and now runs anteriorly.

57:50 Let's now turn the leg over.

57:52 Here the anterior tibial artery of the lower leg extensors reappears.

57:58 It then continues on the dorsum of the foot to the dorsalis pedis artery whose pulse can be palpated here on the side of the tendon of the extensor hallucis longus muscle.

58:07 The extensor hallucis longus muscle is a key muscle for the L5 spinal cord segment because it is mainly over 90% motor innervated by the spinal cord segment L5.

58:17 So to the side of the tendon of the extensor hallucis longus the L5 indication muscle you can find the pulse of the dorsalis pedis artery.

58:26 You must always assess this pulse when suspecting an injury or during any internal examination.

58:31 Another special feature, here is the tibialis anterior muscle located in its compartment of the lower leg extensors.

58:37 If you walk a lot or have trauma, the muscle may swell causing the artery to become compressed resulting in ischemia.

58:44 The pain receptors are irritated by the lack of oxygen caused by the ischemia and this can go as far as causing muscle necrosis due to the lack of oxygen.

58:54 So you have to cut the fascia of the lower leg extensors.

58:57 This procedure is called a fasciotomy.

58:59 And this pathology is called compartment syndrome.