Pre-lab Exercise: Surface Anatomy of the Thigh and Leg
Lab 15 Primary Lab Objectives:
Locate the surface landmarks on the hip, thigh, and leg.
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.
Examine the iliopsoas and consider the muscles that fuse to form it.
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.
Locate the profunda femoris branch of the femoral artery and consider the arterial supply of the adductor muscles.
Identify the anterior and lateral compartments of the leg; trace the path of the fibular nerve and expose and examine the extensor musculature.
1. SURFACE ANATOMY: ANTERIOR THIGH AND LEG
- 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.
- Locate the patella on the cadaver.
- Measure one hand's breadth posterior to the medial edge of the patella to locate the great saphenous vein on the cadaver.
- 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.
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.
- At the ankle of the cadaver, locate the medial malleolus of the tibia and the lateral malleolus of the fibula.
- 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.
2. SKIN, FASCIA AND CUTANEOUS VESSELS
- Remove the skin of the the thigh and leg down to the ankle.
- Identify and dissect out the great saphenous vein embedded in the superficial fascia.
- Cut the great saphenous vein about two inches below where it enters the femoral vein.
- Remove a six inch section of the great saphenous vein.
- Open the section of the great saphenous vein that you removed and wash it out in the sink to examine its valves.
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 coronary artery bypass, although its valves need to be removed before it can be used.
- Identify the deep fascia of the thigh: the fascia lata.
- Note that the iliotibial tract is continuous with the lateral intermuscular septum that separates muscular compartments in the thigh.
HINT: You can locate the medial boundary between the flexor compartment and the medial compartment of the thigh by lifting up the sartorius muscle.
3. HIP FLEXORS: ILIACUS, PSOAS MAJOR AND PSOAS MINOR MUSCLES
The iliopsoas muscle is composed of two separate muscles: the iliacus muscle has a broad origin from the iliac blade; the psoas major muscle originates from the vertebral bodies, transverse processes, and intervetebral discs of the lumbar vertebrae. 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 pubis. 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.
- Locate the fibers of the iliacus muscle on the inner surface of the ilium.
- Look for the longitudinal fibers of the psoas major muscle medially.
- 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.
- Follow the iliopsoas muscle towards its insertion; here, you will find the femoral artery, vein, and nerve in the femoral triangle.
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.
- Identify the femoral artery and its branches superficial to the accompanying veins.
- Notice that fascia forms a femoral sheath around the artery and vein.
- 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.
- Identify the sartorius and rectus femoris muscles.
- Trace the sartorius muscle from origin to insertion, and compare its path with that of the rectus femoris muscle.
- Transect the sartorius muscle near the middle of the thigh and reflect it to its attachments at either end.
The sartorius muscle rotates the femur laterally and flexes the hip and the knee - bringing the hind limb into a position for sitting cross-legged on the ground. The course of sartorius (anterior superior iliac spine to the pes anserinus on the tibia) 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 the muscle group of the anteior thigh with the quadriceps, and is innervated by the femoral nerve.
- Identify the muscles that form the quadriceps femoris muscle group: the rectus femoris, vastus medialis, vastus lateralis, and vastus intermedius.
- Transect the rectus femoris muscle at mid-thigh, reflect it, and identify the three vastus muscles.
- Trace the rectus femoris muscle back to its tendon of origin.
- Find the patellar ligament through which the quadriceps femoris muscle group attaches to the tibia.
- Examine the vastus lateralis and medialis muscles and consider their attachments to the patella.
- Thinking about the mechanics of their action, consider how they will move the patella.
- Separate the adductor muscles from the vastus medialis muscle and expose the femoral vessels and nerve.
- 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.
5. THE ADDUCTOR GROUP: ADDUCTOR LONGUS, BREVIS, AND MAGNUS, GRACILIS AND PECTINEUS MUSCLES
a. 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, which is a branch of the anterior division of the internal iliac artery.
- In the medial thigh, identify the adductor longus muscle. This is the most superficial of the adductor muscles.
- Look for the profunda femoris artery where it passes between the adductor longus and the pectineus muscles.
- Locate the perforating branches of the profunda femoris artery on the anterior surface of the adductor magnus, 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.
- Cut the adductor longus muscle near the middle of the muscle and reflect it to expose the deeper 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.
- The adductor magnus muscle has an adductor portion and a hamstring portion. Its adductor portion originates from the ischiopubic ramus and inserts onto the linea alba. The hamstring portion originates from the ischial tuberosity and inserts onto the adductor tubercle located just above the medial epicondyle of the femur.
- Identify the gracilis muscle (the most medial adductor) the long, strap-like muscle along the inner thigh. Notice the origin of the gracilis on the ischiopubic ramus, and its insertion of the pes ansurinus.
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. 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 adductor portion of adductor magnus is innervated by the obturator 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.
6. EXTENSORS OF THE ANKLE AND TOES: TIBIALIS ANTERIOR, EXTENSOR HALLUCIS LONGUS, EXTENSOR DIGITORUM LONGUS, FIBULARIS TERTIUS, FIBULARIS LONGUS, AND FIBULARIS BREVIS MUSCLES
The extensor muscles of the leg are 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.
- On the lateral side of the leg, find the posterior intermuscular septum.
- Anterolaterally, locate the anterior intermuscular septum which divides the extensors 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.
- Find the common fibular nerve and 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.
- Note where the common fibular nerve divides into deep and superficial branches.
- Trace the superficial fibular branch into the lateral compartment of the leg, and the deep fibular branch into the anterior compartment of the leg.
- Find the tibialis anterior muscle arising from the anterior surface of the tibia.
The tibialis anterior muscle is found in the anterior compartment. It dorsiflexes the ankle and inverts the foot.
- Consult an articulated skeleton to locate its insertion into the base of the first metatarsal and the medial cuneiform.
- Open the deep fascia on the front of the leg and move aside the tibialis anterior muscle to follow the deep fibular branch of the common fibular nerve.
- Lateral to the tibialis anterior muscle, separate out the remaining anterior compartment muscles, which originate 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.
- Trace the anterior tibial artery down the front of the leg to the point at which it crosses the ankle and becomes the dorsalis pedis artery. You will examine the dorsalis pedis artery in another lab.
- Locate the lateral (fibular) compartment and distinguish the fibularis longus from fibularis brevis muscles.
- Find the superficial branch of the fibular nerve in the lateral compartment of the leg.
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.
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.