Dissector Answers - Leg, and Knee Joint

Learning Objectives:

Upon completion of this session, the student will be able to:

  1. Describe the arrangement, specializations and compartments of the fascia of the leg.
  2. Identify the muscles of the posterior compartment of the leg and give their functional significance in locomotion.
  3. Identify the vascular supply of the posterior compartment of the leg.
  4. Identify the nerves of the posterior compartment of the leg, the muscles and cutaneous regions supplied by them, so that given a functional and/or cutaneous loss one can predict the nerve and the probable level of injury.
  5. Identify the muscles of the anterior and lateral compartments of the leg and give their functional significance in locomotion.
  6. Identify the vascular supply of the anterior and lateral compartments of the leg.
  7. Identify the nerves of the anterior and lateral compartments of the leg, the muscles and cutaneous regions supplied by them, so that given a functional and/or cutaneous loss one can predict the nerve and the probable level of injury.
  8. Recall the general plan of the collateral circulation at the knee.
  9. Identify the bony, cartilagenous, ligamentous and membranous components of the knee joint.
  10. Correlate knee joint movements with the muscles producing these actions.
  11. Describe the functional capabilities and limitations of the knee based on its bony structure and ligaments.

 

Learning Objectives and Explanations:

1. Describe the arrangement, specializations and compartments of the fascia of the leg and foot. (W&B 608-610, TG3-02, TG3-03, TG3-32, TG3-45)

The crural fascia is a continuation of the fascia lata of the thigh. It is attached anteriorly to the patella, the patellar ligament and the tibial tuberosity. Medially and laterally, it attaches to the condyles of the tibia and to the head of the fibula. The fascia envelops the bones and soft parts of the leg blending with periosteum of the tibia. Distally, the crural fascia is attached to the medial and lateral malleoli and to the posterior surface of the calcaneus.

As mentioned in a previous lab, the crural fascia has the following specializations in the leg:

·       retinacula of the patella: formed by the attachments of the crural fascia to the medial and lateral condyles of the tibia and the head of the fibula. This also includes tendinous fibers from the vastus muscles. (Latin, retinacula = halter, cable)

·       anterior intermuscular septum: from the crural fascia to the anterior aspect of the fibula. It separates the anterior (extensor) muscles from the lateral (fibular) muscles. Also, one could say that it is the boundary between the anterior and lateral compartments.

·       posterior intermuscular septum: from the crural fascia to the posterior aspect of the fibula. It separates the posterior (flexor) muscles from the lateral (fibular) muscles. Also, one could say that it is the boundary between the posterior and lateral compartments.

·       transverse intermuscular septum: from the posterior intermuscular septum, around to the anteromedial aspect of the tibia. It separates the deep posterior muscles from the superficial posterior muscles.

·       popliteal fascia: two layers, superficial and deep, that cover the popliteal fossa. This fascia stretches with the movement of the knee joint, providing protection for the neurovascular structures traveling through the area.

In the ankle region, the crural fascia thickens to form five retinacula that hold tendons close to the bone, creating a sort of pulley sytem. They are listed here:

·       superior extensor retinaculum: superior to the ankle, on the anterior aspect of the leg

·       inferior extensor retinaculum: on the anterior aspect of the ankle. It is Y-shaped, extending onto the dorsum of the foot.

·       flexor retinaculum: on the posteromedial aspect of the ankle

·       superior & inferior fibular retinacula: associated with the tendons of the fibularis longus and brevis muscles.

2. Identify the muscles of the posterior compartment of the leg and give their functional significance in locomotion. (W&B 610-616, N512, N515, N516, N517, N518, N520, N522, N529, N531, N534, N535, N536, N541, N542, TG3-33, TG3-34, TG3-35)

 

The good news about this lab is that muscles are named for what they do, who they do it to, and what they look like. Extensors extend the digits or hallux (the big toe) and are on the front of the leg and foot. Flexors are on the back of the leg and sole of the foot. (Remember, we're talking about the toes being flexed and extended here, not the ankle.) Adduction means toward midline, which is defined as second toe in the foot. Abduction means motion away from midline. Inversion means that you direct the sole of your foot toward midline. Eversion means that you direct the sole of your foot laterally. Plantar flexion means pointing your toe (true flexion at the ankle). Dorsiflexion means bringing the top of the foot up toward the anterior surface of the leg (effectively extension at the ankle). "________ longus" means the muscle is long and you should expect a "_______ brevis", a short muscle that does the same thing. Hallucis means big toe, digitorum refers to the other four toes, and digiti minimi, though not named by Austin Powers, refers to the little toe.

The muscles of the leg are divided into groups, just like the leg is divided into compartments, by the intermuscular septa described above. These are the anterior, lateral, superficial posterior, and deep posterior groups (compartments).

The three muscles of the superficial posterior compartment:

Muscle

Origin

Insertion

Action

Innervation

gastrocnemius

femur; medial head: above medial femoral condyle; lateral head: above lateral femoral condyle

dorsum of calcaneus via calcaneal (Achilles') tendon

flexes leg, plantarflexes foot

tibial nerve

plantaris

above lateral femoral condyle (above lateral head of gastrocnemius)

dorsum of calcaneus medial to calcaneal tendon

flexes leg, plantarflexes foot

tibial nerve

soleus

posterior surface of head & upper shaft of fibula, soleal line of tibia

dorsum of calcaneus via the calcaneal (Achilles') tendon

plantarflexes foot

tibial nerve

·       Blood supply to the superficial posterior compartment depends on the muscle. The soleus muscle receives the posterior tibial artery, the gastrocnemius muscle gets the posterior tibial artery and sural arteries (the ones that are not genicular arteries), and the plantaris, since it is superior, gets blood via the popliteal artery.

·       The four muscles of the deep posterior compartment:

Muscle

Origin

Insertion

Action

Innervation

popliteus

lateral condyle of femur (via a round tendon)

posterior surface of tibia above soleal line

flexes and rotates leg medially (with foot planted, rotates thigh laterally)

tibial nerve

flexor hallucis longus

lower two/thirds of posterior surface of fibula

base of distal phalanx of hallux

flexes metatarsophalangeal and proximal interphalangeal joints of hallux; plantarflexes foot

tibial nerve

flexor digitorum longus

middle half of posterior surface of tibia

bases of distal phalanges of digits 2-5

flexes metatarsophalangeal, proximal interphalangeal and distal interphalangeal joints of digits 2-5; plantarflexes foot

tibial nerve

tibialis posterior

interosseous membrane, posteromedial surface of fibula, posterolateral surface of tibia

tuberosity of navicular & medial cuneiform, metatarsals 2-4

plantarflexes foot and inverts foot

tibial nerve

·       Blood supply to the deep posterior compartment goes by muscle. The popliteus muscle receives the popliteal artery, the flexor hallucis longus and tibialis posterior muscles use the posterior tibial artery and fibular artery, and the flexor digitorum longus muscle only gets the posterior tibial artery.

·       (If you are looking at the remaining three muscles around mid calf, then the tibialis posterior muscle is in the middle, the flexor digitorum longus muscle is medial, and the flexor hallucis longus muscle is lateral. The order of the tendons at the medial malleolus, however, is different - Tom, Dick, and Harry.)

·       Summary of actions:

The muscles of the superficial posterior compartment
raise the heel against the weight of the body in walking. In standing these muscles draw back on the leg, stabilizing the ankle joint and preventing dorsiflexion of the foot. Muscles of the deep posterior compartment assist the muscles of the superficial compartment in plantar flexion and inversion of the foot at the ankle, but their important functions are elsewhere. The tibialis posterior muscle acts powerfully in adduction and inversion of the foot. It also distributes weight among the metatarsals, reducing flat foot, and shifts body weight to the lateral side. The flexor hallucis longus muscle flexes the distal phalanx of the big toe and shows its greatest activity at push off during walking. The flexor digitorum longus muscle similarly flexes the distal phalanges of the lateral four toes.

3.     Identify the vascular supply of the posterior compartment of the leg. (W&B 618-620, TG3-38)

·       The popliteal artery is the continuation of the femoral artery in the popliteal fossa. It descends across the popliteus muscle and at its lateral border, divides into the anterior and the posterior tibial arteries. The anterior tibial artery punches forward above the interosseous membrane and into the anterior compartment of the leg.

The
posterior tibial artery gives off the fibular (peroneal) artery and then descends in the deep posterior compartment of the leg, accompanied by the tibial nerve. It passes behind the medial malleolus of the ankle and into the sole of the foot where it divides into the medial and lateral plantar arteries. (Similarly, the tibial nerve divides into medial and lateral plantar branches here.)

The
fibular (peroneal) artery is the muscular artery of the fibular side of the leg. It descends near the fibula, within the substance of hallucis longus muscle, in the deep posterior compartment. It also serves as a large collateral vessel, for near the ankle it is connected by a horizontal communicating branch with the posterior tibial artery and by a perforating ramus with the anterior tibial artery.

4.      Identify the nerves of the posterior compartment of the leg, the muscles and cutaneous regions supplied by them, so that given a functional and/or cutaneous loss one can predict the nerve and the probable level of injury. (W&B 581, 621-622, TG3-39, TG3-66AB, TG3-67, TG3-68)

·       All of the muscles of the posterior compartment are innervated by the tibial nerve. Don't confuse this with the tibial arteries. There are no anterior and posterior tibial nerves!

5.     Identify the muscles of the anterior and lateral compartments of the leg and give their functional significance in locomotion. (W&B 610-616, TG3-36, TG3-37)
The muscles of the leg are divided into groups, just like the leg is divided into compartments, by the intermuscular septa described above. These are the anterior, lateral, superficial posterior, and deep posterior groups (compartments).

The four muscles of the anterior compartment:

Muscle

Origin

Insertion

Action

Innervation

tibialis anterior

lateral tibial condyle and upper lateral surface of tibia

medial surface of medial cuneiform and 1st metatarsal

dorsiflexes and inverts foot

deep fibular (peroneal) nerve

extensor hallucis longus

middle half of anterior surface of fibula & interosseous membrane

base of distal phalanx of hallux

extends metatarsophalangeal & interphalangeal joints of hallux

deep fibular (peroneal) nerve

extensor digitorum longus

lateral condyle of tibia, anterior surface of fibula, lateral portion of interosseous membrane

dorsum of lateral 4 toes via extensor expansions (central slip inserts on base of middle phalanx, lateral slips on base of distal phalanx)

extends metatarsophalangeal, proximal interphalangeal and distal interphalangeal joints of lateral 4 toes

deep fibular (peroneal) nerve

fibularis (peroneus) tertius

distal part of anterior surface of fibula

dorsum of shaft of 5th metatarsal bone

everts foot

deep fibular (peroneal) nerve

Blood supply to the anterior compartment is via the anterior tibial artery.

(The anterior compartment can also be remembered, in order, as "Tom, Harry, Dick AND Fred". That is, medial to lateral you have: Tibialis anterior muscle, extensor Hallucis longus muscle, extensor Digitorum longus muscle, anterior tibial Artery, deep fibular Nerve, and Fibularis tertius muscle.)

The two muscles of the lateral compartment:

Muscle

Origin

Insertion

Action

Innervation

fibularis (peroneus) longus

upper two/thirds of lateral surface of fibula

after crossing plantar surface of foot deep to intrinsic muscles, it inserts on medial cuneiform and base of 1st metatarsal

plantarflexes and everts the foot

superficial fibular (peroneal) nerve

fibularis (peroneus) brevis

lower one third of lateral surface of fibula

tuberosity of base of 5th metatarsal

plantarflexes and everts the foot

superficial fibular (peroneal) nerve

Blood supply to the lateral compartment is via the fibular artery.

(The fibularis brevis muscle is deep to the fibularis longus muscle. Also note that, though the blood supply is via the fibular artery, the fibular artery does not live in the lateral compartment.)

Summary of actions:

Muscles of the anterior compartment
of the leg dorsiflex and invert the foot at the ankle. The tibialis anterior muscle is powerful in this action; with the foot on the ground, it draws the tibia forward (as in walking). The extensor hallucis longus muscle dorsiflexes the great toe, while the extensor digitorum longus muscle dorsiflexes toes two through five.
Muscles of the lateral compartment
evert and abduct the foot, and also assist in its plantar flexion.

6. Identify the vascular supply of the anterior and lateral compartments of the leg. (W&B 618-620, TG3-38, TG3-39A, TG3-39B)

The popliteal artery is the continuation of the femoral artery in the popliteal fossa. It descends across the popliteus muscle and at its lateral border, divides into the anterior and the posterior tibial arteries. The anterior tibial artery punches forward above the interosseous membrane and into the anterior compartment of the leg. The artery descends on top of the membrane, joined by the deep fibular nerve, and crosses the ankle midway between the lateral and medial malleous. It enters the dorsum of the foot as the dorsalis pedis.

The dorsalis pedis
has many branches, and eventually becomes the deep plantar artery. This artery dives to the sole of the foot (between the 2 heads of the 1st dorsal interosseous muscle, between the 1st and 2nd toes). It unites with the lateral plantar artery to form the plantar arterial arch.

The
posterior tibial artery gives off the fibular (peroneal) artery and then descends in the deep posterior compartment of the leg, accompanied by the tibial nerve. It passes behind the medial malleolus of the ankle and into the sole of the foot where it divides into the medial and lateral plantar arteries. (Similarly, the tibial nerve divides into medial and lateral plantar branches here.) The medial plantar artery runs in the groove between the medial and central compartments.

7. Identify the nerves of the anterior and lateral compartments of the leg, the muscles and cutaneous regions supplied by them, so that given a functional and/or cutaneous loss one can predict the nerve and the probable level of injury. (W&B 581, 621-622, TG3-39A, TG3-39B, TG3-39A, TG3-68)

With respect to specific muscles, the nerves are listed above in #1. In general, they are divided thus:

·       anterior compartment - deep fibular (peroneal) nerve

·       lateral compartment - superficial fibular (peroneal) nerve

·       posterior compartment - tibial nerve

 

Cutaneous nerve distribution in the leg and foot:

·       saphenous nerve (from femoral nerve, L2 through L4): does skin of medial leg and foot. The dermatome curves around the medial side of the foot just to the metatarsals.

·       superficial fibular nerve (from the common fibular nerve, L4 through S2, which is from the sciatic nerve): does the distal 1/3 of the anterior leg, the dorsum of foot (excluding the web between the big toe and the second toe), and the distal interphalangeal segments of all toes.

·       deep fibular nerve (from the common fibular nerve, L4 through S2, which is from the sciatic nerve): does skin of web between big toe and the second toe

·       sural nerve: the union of medial sural nerve and a communicating branch of the lateral sural nerve. It does skin of lower leg posteriorly and the lateral side of the foot, curving under to the sole of the foot.

·       medial calcaneal branches of the tibial nerve (S1 and S2): do the posterior sole of the foot

·       medial plantar nerve (from the tibial nerve, L4 and L5): does medial side of the plantar surface from big toe to 1/2 of the 4th toe

·       lateral plantar nerve (from the tibial nerve, S1 and S2): does the lateral side of the plantar surface from little toe to 1/2 of the 4th toe

8.      Knee Joint: (TG3-56A, TG3-56B, TG3-57A, TG3-57B, TG3-58A, TG3-58B, TG3-58C, TG3-59AB, TG3-59CD) The knee joint is basically a hinge type of joint, allowing flexion and extension. The hinge movements are combined with some gliding and rolling and with some rotation about a vertical axis. This allows free motion in one primary plane combined with decent stability. The fibrous capsule is deficient in a few areas to allow tendons to pass through to the outside. The synovial membrane lines the fibrous capsule and attaches to the periphery of the patella and the edges of the menisci. (Latin, patella = shallow dish, Greek, meniskos = moon, crescent). It reflects onto the cruciate ligaments and also reflects between the tibia and fibula, covering the infrapatellar fat pad. This technically separates the fat pad and the cruciate ligaments from the joint cavity. The knee joint is relatively weak and depends on several things to strengthen it. First, its area of weight distribution is two or three times larger than either the tibia or the femur, which reduces the overall pressure. Furthermore, a strong fibrous capsule, the medial patellar and lateral patellar retinacula, patellar tendon, iliotibial tract (lateral side), and longitudinal fibers of fascia lata (medial side) all serve to strengthen the joint. Finally, two groups of important ligaments help add stability:

collateral ligaments: capsular and extracapsular. They become taut in extension and prevent hyperextension, also prevent abduction and adduction. The medial collateral ligament, at its midpoint, firmly attaches to the medial meniscus. It is the weaker of the two, so injuries are more common here and, moreover, will usually involve the medial meniscus. The lateral collateral ligament is separated from the lateral meniscus by the tendon of the popliteus. Other extracapsular ligaments that strengthen the knee are the patellar ligament, the oblique popliteal ligament and the arcuate popliteal ligament.

cruciate ligaments:
intracapsular. The anterior cruciate ligament (ACL) is weaker than the posterior cruciate ligament (PCL). They both prevent movement of the tibia forward or backward under the femoral condyles. They become taut in all positions of flexion but mostly with full extension and full flexion. (cruciate = cross-shaped)

·      What is the difference between the two collateral ligaments in the knee joint?

The lateral is stronger and does not attach to the meniscus, while the medial is weaker and does attach to the meniscus. (TG3-58A, TG3-58B, TG3-58C)

·      What is the function of the patella?

The patella is a large sesamoid bone that developed in the tendon of the quadriceps femoris muscle. It pushes against the anterior articular surface of the femur's inferior surface, and, by holding the tendon off the lower end of the femur, improves the angle of approach of the tendon to the tibial tuberosity.

·      With what does the patella articulate?

·      See above. (TG3-56)

·      What are the actions of the cruciate ligaments?

They stabilize the knee joint by preventing the movement of the tibia forward or backward, with the anterior cruciate ligament preventing anterior displacement and the posterior cruciate ligament preventing posterior displacement. (TG3-59AB, TG3-59CD)

·      What are the "drawer sign" and the "terrible triad"?

The anterior drawer sign, movement of the tibia anteriorly when the flexed leg is pulled anteriorly, indicates anterior cruciate ligament rupture. The posterior drawer sign, movement of the tibia posteriorly when the flexed leg is pushed, indicates posterior cruciate rupture. The terrible triad is a tearing of the medial collateral ligament, the medial meniscus, and the anterior cruciate ligament all at the same time.

·       The "genicular anastomosis" in the region of the knee is also very important. It involves ten vessels. Two from above (the descending branch of the lateral circumflex femoral artery and the descending genicular branch (highest genicular) of the femoral artery), five from the popliteal artery, and three from below, usually branches of the anterior tibial artery. This system can help supply blood to the leg in the event of an obstruction of the femoral artery below the branching-off of the deep femoral artery.

·       http://www.med.umich.edu/lrc/coursepages/m1/anatomy2010/html/images/knee_collateral.gif

9. - 11. Describe the functional capabilities and limitations of the knee based on its bony structure and ligaments.

Images from "Anatomy of the Human Body" by Henry Gray are provided by:

Knee Joint: (TG3-56A, TG3-56B, TG3-57A, TG3-57B, TG3-58A, TG3-58B, TG3-58C, TG3-59AB, TG3-59CD) The knee joint is basically a hinge type of joint, allowing flexion and extension. The hinge movements are combined with some gliding and rolling and with some rotation about a vertical axis. This allows free motion in one primary plane combined with decent stability. The fibrous capsule is deficient in a few areas to allow tendons to pass through to the outside. The synovial membrane lines the fibrous capsule and attaches to the periphery of the patella and the edges of the menisci. (Latin, patella = shallow dish, Greek, meniskos = moon, crescent). It reflects onto the cruciate ligaments and also reflects between the tibia and fibula, covering the infrapatellar fat pad. This technically separates the fat pad and the cruciate ligaments from the joint cavity. The knee joint is relatively weak and depends on several things to strengthen it. First, its area of weight distribution is two or three times larger than either the tibia or the femur, which reduces the overall pressure. Furthermore, a strong fibrous capsule, the medial patellar and lateral patellar retinacula, patellar tendon, iliotibial tract (lateral side), and longitudinal fibers of fascia lata (medial side) all serve to strengthen the joint. Finally, two groups of important ligaments help add stability:
collateral ligaments: capsular and extracapsular. They become taut in extension and prevent hyperextension, also prevent abduction and adduction. The medial collateral ligament, at its midpoint, firmly attaches to the medial meniscus. It is the weaker of the two, so injuries are more common here and, moreover, will usually involve the medial meniscus. The lateral collateral ligament is separated from the lateral meniscus by the tendon of the popliteus. Other extracapsular ligaments that strengthen the knee are the patellar ligament, the oblique popliteal ligament and the arcuate popliteal ligament.

cruciate ligaments: intracapsular. The anterior cruciate ligament (ACL) is weaker than the posterior cruciate ligament (PCL). They both prevent movement of the tibia forward or backward under the femoral condyles. They become taut in all positions of flexion but mostly with full extension and full flexion. (cruciate = cross-shaped)

 

 

Updated 9 Nov 2011