Schedule

Lab 14 - Anterior Thigh & Leg

Suggested readings from
Gray's Anatomy for Students, 2nd ed.
Ch. 6: 555-599

Suggested readings from Langman's Medical Embryology

11th ed: Ch 9 pp 134-42 -- Ch 10 pp 147-54
12th ed: Ch 11 pp 145-50 -- Ch 12 pp 151-61

Prelab: Osteology of the Lower Limb

Lab 14 Primary Lab Objectives:

  1. Locate the anatomical surface landmarks on the hip, thigh, and leg.

  2. Remove the skin from the anterior thigh and leg to the ankle and locate and examine the great saphenous vein. Understand the role of the valves in the veins of the lower limb.

  3. Examine the iliopsoas and consider the muscles that fuse to form it.

  4. Examine the femoral triangle containing the femoral artery, vein, nerve (and its branches), and lymphatic channels. Transect and reflect the sartorius muscle, exposing the saphenous nerve and the femoral vessels in the subsartorial canal. Examine the quadriceps femoris and consider the muscles that form this group and their action on the patellar ligament on the tibia.

  5. Locate the profunda femoris branch of the femoral artery and consider the arterial supply of the adductor muscles.

  6. Identify the extensor and depressor compartments of the leg; trace the path of the fibular nerve, expose and examine the extensor musculature.

  7. Trace the motor branches of the tibial nerve to the gastrocnemius muscle, and appreciate this muscle's insertion and action at the calcaneal tendon. Trace the arterial supply to the leg and expose the flexor muscles deep to the intermuscular septum.

 

Dissection Instructions

1. SURFACE ANATOMY: ANTERIOR THIGH AND LEG

  1. Locate the medial and lateral epicondyles of the distal femur (they are less pronounced than at the elbow but still palpable; check a skeleton) on the cadaver.
  2. Locate the patella on the cadaver.
 

 

  1. Measure one hand's breadth posterior to the medial edge of the patella to locate the great saphenous vein on the cadaver.

Atlas Images:

 

  1. On the lateral side of the leg of your cadaver, palpate the bony prominence below the lateral femoral condyle and mark it as the head of the fibula.

Atlas Images:

FUNCTIONAL ANATOMY

Identifying the fibular head under the skin on the lateral side of the knee is important because this landmark represents the position where the common fibular nerve enters the anterior leg in a position vulnerable to injury. This nerve is injured commonly at this location by compression against the fibula.

 

  1. At the ankle of the cadaver, locate the medial malleolus of the tibia and the lateral malleolus of the fibula.
  2. Mark the location of the dorsalis pedis artery. The dorsalis pedis artery is the continuation of the anterior tibial artery on the dorsum of the foot between the medial and lateral malleoli. This artery is often used to evaluate peripheral pulses.

Atlas Images:

 

2. SKIN, FASCIA AND CUTANEOUS VESSELS

  1. Remove the skin of the the thigh and leg down to the ankle.

 

  1. Identify and dissect out the major cutaneous veins (especially the great saphenous vein) embedded in the superficial fascia.

 

  1. Cut the great saphenous vein about two inches below where it enters the femoral vein.
  2. Remove a six inch section of the great saphenous vein.

 

  1. Open the section of the great saphenous vein that you removed and wash it out in the sink to examine its valves.

FUNCTIONAL ANATOMY:
Veins have a limited muscular layer.  The valves in this and other veins in the lower limb prevent blood from pooling in the lower limb.  The great saphenous vein is often used for vascular bypass elsewhere in the body.

 

  1. Identify the deep fascia of the thigh: the fascia lata.
  2. Note that the iliotibial tract is continuous with the lateral intermuscular septum that marks the lateral boundary between the “elevators” and the “depressors” in the thigh.

HINT: You can locate the medial boundary between the elevators and depressors by lifting up the sartorius muscle.

Atlas Images:

 

3. HIP FLEXORS: ILIACUS, PSOAS MAJOR AND MINOR MUSCLES

FUNCTIONAL ANATOMY:
The iliopsoas muscle is composed of two separate bellies: the iliacus muscle has a fleshy origin from the iliac blade; the psoas major muscle originates from the vertebral column below the last rib. The two muscles pass over the rim of the pelvis, under the inguinal ligament, to a common insertion on the lesser trochanter of the femur. On the surface of the psoas major, you may be able to see the small psoas minor muscle (absent in about 40% of humans) running down to attach to the rim of the pelvis at the psoas major muscle's medial margin. Both the iliacus and psoas major muscles receive their innervation from the posterior divisions of the ventral rami L.2-4, which come together more laterally to form the femoral nerve.  The iliopsoas muscle is an important thigh flexor that helps initiate the swing of the limb.

  1. Locate the broad, fleshy fibers of the iliacus muscle on the inner surface of the ilium.
  2. Look for the longitudinal fibers of the psoas major muscle medially.
  3. Find the femoral nerve as it emerges from behind the psoas major muscle and runs down the surface of the iliacus muscle, enclosed within the iliac fascia.

A smaller nerve also running along the surface of the iliacus muscle, lateral to the much larger femoral nerve, is the lateral cutaneous nerve of the thigh.

Atlas Images:

 

  1. Follow the iliopsoas muscle towards its common insertion; here, you will find the femoral vessels.
  2. Push aside the femoral vessels and further expose the femoral nerve, which breaks up at this point into a cluster of motor branches to the extensors of the knee.

Atlas Images:

 

 

4. THE SARTORIUS AND QUADRICEPS GROUP: RECTUS FEMORIS, VASTUS LATERALIS, MEDIALIS, AND INTERMEDIUS MUSCLES

The femoral triangle is formed by the sartorius muscle laterally, the adductor muscles medially, and the inguinal ligament superiorly. Here, you will find three important structures passing under the inguinal ligament and into this triangle: the femoral artery and vein, and the femoral nerve.

  1. Identify the femoral artery and its branches superficial to the accompanying veins.
  2. Notice that fascia forms a femoral sheath around the artery and vein.
  3. Confirm that the femoral nerve is not contained in the sheath. Instead it runs around the inside of the pelvis superficial to the fascia of the iliacus muscle.

NOTE: the femoral nerve splits into many branches once it passes beneath the inguinal ligament. These include cutaneous sensory nerves as well as muscular branches going to the quadriceps group and pectineus.

 

 

  1. Identify the sartorius and rectus femoris muscles.
  2. Trace the sartorius muscle from origin to insertion, and compare its path with that of the rectus femoris muscle.
  3. Verify the actions of the sartorius muscle by pulling on it.
  4. Transect the sartorius muscle and reflect it to its attachments at either end.

FUNCTIONAL ANATOMY:
The sartorius muscle tends to rotate the femur laterally and flex the hip and the knee - bringing the hind limb into a position for sitting cross-legged on the ground. The origin and insertion of the sartorius (anterior superior iliac spine to the pes anserinus on the tibia) are close to those of the rectus femoris muscle (anterior inferior iliac spine to the tibia via the patellar tendon) but the course of sartorius takes it behind the axis of rotation at the knee joint. Therefore, it acts as a weak flexor of the knee. It is part of this muscle group with the quadriceps, and is innervated by the femoral nerve.

 

  1. Identify the muscles that form the quadriceps femoris muscle group: the rectus femoris, and vastus muscles.
  2. Transect the rectus femoris muscle at mid-thigh, reflect it, and identify the three vastus muscles.
  3. At this point you may wish to transect and reflect the tensor fascia lata and gluteus minimus muscles to examine their cross-section more thoroughly.

Atlas Images:

 

  1. Trace the rectus femoris muscle back to its tendon of origin.
  2. Find the patellar ligament through which the quadriceps femoris muscle group attaches to the tibia via the patella, and define its insertion.
  3. Examine the vastus lateralis and medialis muscles and consider their attachments to the patella. 
  4. Thinking about the mechanics of their action, consider how they will move the patella.   
  5. Separate the adductor muscles from the vastus medialis muscle and expose the femoral vessels and nerve.
  6. Find the profunda femoris branch (="deep femoral a.") of the femoral artery, and trace it into the adductor group.

Atlas Images:

 

 

5. THE ADDUCTOR GROUP: ADDUCTOR LONGUS, BREVIS, AND MAGNUS, GRACILIS AND PECTINEUS MUSCLES

  1. Locate the saphenous nerve between the adductor and quadriceps muscle groups. The saphenous nerve is a major cutaneous branch of the femoral nerve traveling down the thigh in company with the femoral vessels.

HINT: To follow the saphenous nerve you will have to trace it through some muscular spaces. The saphenous nerve continues down and becomes cutaneous just below the knee. The vessels pass through a gap, called the adductor hiatus, between the insertions of the adductor and hamstring parts of the adductor magnus muscle to enter the popliteal fossa behind the knee.

Atlas Images:

  1. Beginning within the pelvis, trace the obturator nerve from the lumbar plexus through the obturator foramen and canal into the adductor muscle group. The artery accompanying the nerve is the obturator artery.

Atlas Images:

  1. In the medial thigh, identify the adductor longus muscle - This is the most superficial of the adductors.
  2. Look for the profunda femoris artery where it passes backward between the adductor longus and the pectineus muscles.
  3. Locate the perforating branches of the profunda femoris artery supplying the muscles attached to the linea aspera.

Branches of the profunda femoris artery supply the quadriceps muscle group, and the muscles on the back of the thigh.

  1. Sever the adductor longus muscle and reflect it to expose the adductor brevis and magnus muscles.

HINT: The insertion site on the femur of adductor brevis is directly beneath that of pectinus. Both are deep to adductor longus.

Atlas Images:

 

  1. Idenfiy the gracilis muscle (the most medial adductor) the long, strap-like muscle along the inner thigh.
  2. Note the medial fibers of the adductor magnus muscle inserting into the adductor tubercle just above the medial epicondyle of the femur.

Atlas Images:

FUNCTIONAL ANATOMY:
The nervous innervation of the muscles found in the thigh can be confusing.  We take a moment here to reflect on a couple of the “odd” ones before we move on to the leg. You reviewed the hamstrings in the last lab.  But it may be worth reminding yourself that the hamstrings are depressor musculature (roughly corresponding to the biceps brachii muscle in the arm). They receive motor branches from the tibial portion of the sciatic nerve. The hamstrings can flex the knee and extend the hip joint. In this context, one might ask why the part of adductor magnus that does not cross the knee is innervated like a hamstring?  Despite the fact that it cannot act on the knee, the bundle of adductor magnus muscle fibers inserting into the adductor tubercle is developmentally part of the hamstring muscle group, and thus receives motor innervation from the tibial component of the sciatic nerve.

The innervation of the pectineus can also be confusing.  Although the pectineus muscle receives most of its innervation from the femoral nerve and is not far removed from the psoas major muscle in its course and attachments, its medial edge commonly receives some motor fibers from the obturator nerve. In some mammals, the femoral and obturator parts of the pectineus muscle are separate muscles. The human pectineus muscle may be a mosaic of functions; both the adductor and iliopsoas muscle components. Here we will treat pectineus as part of the adductor group, but it could just as easily be classified with the iliopsoas muscle.

The biceps femoris muscle raises interesting issues with innervation as well. As you remember from last lab, the short head of biceps femoris is not really a hamstring.  It might be best considered as an isolated elevator muscle that inserts with the long head of biceps femoris. The short head is therefore innervated by the posterior-division fibers from the fibular portion of the sciatic nerve.

 

6. EXTENSOR COMPARTMENT OF THE LEG: TIBIALIS ANTERIOR, EXTENSOR HALLUCIS LONGUS, EXTENSOR DIGITORUM LONGUS, FIBULARIS TERTIUS, LONGUS, AND BREVIS MUSCLES

The elevator musculature in the leg lies within the extensor compartment, which is subdivided into an anterior and a lateral (or fibular) compartment. You may also occasionally see the fibular compartment and fibularis muscles referred to as the peroneal compartment or peroneus muscles.

  1. On the lateral side of the leg, find the posterior intermuscular septum (the lateral boundary between the elevators and depressors).
  2. Anterolaterally, locate the anterior intermuscular septum which divides the elevator compartment into anterior and lateral (fibular) compartments.

Posterior division motor fibers are carried from the sciatic nerve into the extensor (anterior and lateral) compartments of the leg as the common fibular nerve.

 

  1. Find the common fibular nerve.
  2. Trace its path as it winds around the side of the fibular head between the attachment of the biceps femoris muscle and the origins of the ankle plantar flexors.
  3. Note where the common fibular nerve divides into deep and superficial branches.
  4. Trace the superficial fibular branch into the lateral compartment, and the deep fibular branch down into the anterior compartment.
 

 

  1. Find the tibialis anterior muscle arising from the anterior surface of the tibia.

The tibialis anterior muscle is found in the anterior component of the elevator compartment. It dorsiflexes the ankle and inverts the foot.

  1. Consult an articulated skeleton to locate its insertion into the base of the first metatarsal and the medial cuneiform.
  2. Open the deep fascia on the front of the leg and lift the tibialis anterior muscle to follow the deep fibular branch of the common fibular nerve.
  3. Lateral to the tibialis anterior muscle, separate out the extensor mass, which originates from the front of the fibula.

Both edges of this digital extensor mass are specialized. They have separate tendons and names of their own: the extensor hallucis longus muscle to the first digit and the fibularis tertius muscle to the fifth digit. The fibularis tertius is the only muscle which both everts and dorsiflexes the foot. The extensor digitorum longus muscle, located between these two specialized portions, also contributes a tendon to the 5th digit, along with tendons to digits 2, 3, and 4.

 

 

  1. Trace the anterior tibial artery down to the point at which it becomes the dorsalis pedis artery.
 

 

  1. Locate the lateral (fibular) compartment and distinguish the fibularis longus from fibularis brevis muscles. 

FUNCTIONAL ANATOMY:
The tibialis anterior and fibularis longus muscles form a sling or stirrup underneath the foot. This sling can be tightened to lend additional support to the arches as the heel leaves the ground during locomotion. The tibialis anterior muscle is also needed to hold the toes clear of the ground as the foot is brought forward during the swing phase of gait.

 

7. FLEXOR COMPARTMENT OF THE LEG: GASTROCNEMIUS, PLANTARIS, POPLITEUS, SOLEUS, FLEXOR HALLLUCIS LONGUS, FLEXOR DIGITORUM LONGUS AND TIBIALIS POSTERIOR MUSCLES

FUNCTIONAL ANATOMY:
The muscles in the flexor or posterior compartment of the leg comprise two sheet-like layers:

  1. A superficial layer that raises the heel (the two heads of the gastrocnemius, the soleus, and the plantaris muscles).
  2. A deeper layer containing a small muscle just behind the knee (the popliteus muscle) and three digital flexors that reach the sole by passing around the medial side of the heel (the flexor hallucis longus, flexor digitorum longus, and tibialis posterior muscles). 

At some point above the knee, the sciatic nerve ends by dividing into (1) its depressor (anterior-division) component, the tibial nerve, and (2) its elevator (posterior­division) component, the common fibular nerve. The tibial nerve runs down the leg between the superficial sheet and deeper sheets of the flexor muscles, sending motor branches to the muscles in both layers.

 

  1. Within the popliteal fossa, locate the point at which the sciatic nerve divides into its two major branches: the tibial and common fibular.
  2. Trace the motor branches of the tibial nerve to the two heads of the gastrocnemius muscle.

 

  1. Separate the proximal part of the gastrocnemius muscle from the underlying soleus muscle.
  2. Transect the two heads of the gastrocnemius muscle a hand's breadth below their origins and reflect the muscle (black dotted line below).

Atlas Images:

 

  1. Note the bursa underlying the medial origin of the gastrocnemius muscle. 
  2. Locate the popliteus muscle running from the medial condyle of the tibia to the lateral femoral condyle as it crosses the knee joint.

The tendon calcaneus or Achilles' tendon is formed from the tendons of three muscles: 1) the gastrocnemius muscle, 2) the tiny plantaris muscle (both originating from the femur and thus crossing the knee joint), and 3) the soleus muscle (the largest of the three, arises from the tibia and fibula).

  1. Sever the calcaneal tendon, the plantaris tendon, and the tibial origin of the soleus muscle (blue dotted line in image above), and reflect the entire layer of plantar flexor muscles laterally.

The layer of deep fascia between the muscles that form the Achille’s tendon and the long digital flexors is called the intermuscular septum. The major vessels and nerves of the flexor (depressor) compartment plunge between the two heads of the soleus muscle to get into this layer of fascia, and run down the leg.

 

 

  1. Between the two insertions of the adductor magnus muscle, follow the femoral artery and vein into the flexor compartment of the leg. Note that at this point, their names change to the popliteal artery and vein.
  2. Clean the vein and artery and define the gap through which they pass.

As the popliteal artery crosses the popliteus muscle, it gives off the anterior and posterior tibial arteries.

  1. Follow the popliteal artery into the leg and find its anterior and posterior tibial branches.
  2. Trace the anterior tibial artery into the extensor or anterior compartment.
  3. Trace the posterior tibial artery down the back of the leg and locate its fibular branch.

The fibular artery supplies the fibular side of the posterior compartment of the leg, but also sends branches to the lateral compartment.

  1. Continue following the posterior tibial artery around the medial side of the ankle into the foot.

Atlas Image:

 

 

Three muscles lie deep to the intermuscular septum in the leg. The digital flexors, like the deep layer of digital flexors in the forearm, comprise two parallel muscles: one to the great toe (or hallux) and one to the other four digits. Peculiarly enough, the two muscles originate on the "wrong" sides; the long flexor of the hallux (the flexor hallucis longus muscle) arises from the fibula, while the long digital flexor (the flexor digitorum longus muscle) arises from the tibia. The third muscle, the tibialis posterior muscle, divides into a fan of tendons inserting on the tarsal and metatarsal bones, and does not move any of the digits.

  1. On your cadaver, study the origins of the two digital flexors in the leg – the flexor digitorum longus and flexor hallucis longus muscles.
  2. Note that the flexor hallucis longus muscle arises partly from the fascia of the underlying tibialis posterior muscle.
  3. Free the medial edge of the flexor hallucis longus muscle enough to pull it laterally and see the origins of the tibialis posterior muscle.

Atlas Imges:

 

 

Clinical correlations

1. Vascular bypass using the great saphenous vein

The great saphenous vein is used for various kinds of vascular bypasses, especially those in which many grafts are required, such as triple and quadruple coronary bypasses. It is also used for bypasses in peripheral arteries since it maintains patency well over the long term. Veins can be turned so that the valves do not impede blood flow, or can be stripped out using a device called a valvulotome.

2. Compartment syndrome

The muscular groupings bordered by the deep fascia of the leg, the tibial, fibular and deep posterior compartments of the calf, are inexpansible. Pressure buildup within these compartments can cause ischaemia (a restriction in blood supply) as the low pressure blood vessels (veins and capillaries) are compressed, causing tingling and numbness as intracompartmental nerves are compromised. Ischaemia also causes muscle damage leading to further swelling, and if untreated the compartment contents may die. Compartment syndrome can also be caused by blood leaking into the tissues via traumatic injury, or as a reperfusion injury. Capillaries become more permeable when deprived of blood flow, hence if flow is suddenly returned the compartment will swell. A fasciotomy (making a cut in the deep fascia covering the compartment) can be used before returning circulation to prevent pressure from building up.

 

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