Extremities Lab 5.1

Lab 5.1: Thigh and Knee

Learning objectives:

Understand the flow of blood both from and to the lower extremity
Identify the muscles and neurovasculature in the anterior, medial, and posterior compartments of the thigh
Identify the ligaments and structures within the knee

Short List of Structures - 5.1

Hip and Gluteal Region Review

We’ll begin with a review of the posterior body wall and the gluteal region. This dissection was initially done as part of the pelvic region, but because many of the structures in this region continue into the thigh they will be included as part of the lower limb dissection as well.

Psoas m. - is made up of a psoas major m. and psoas minor m., though we will refer to them collectively as the psoas m.

Iliacus m. - sits in the iliac fossa, just lateral to the psoas m.

Iliopsoas m. - formed by the union of the iliacus m. and psoas m. A flexor of the hip.

Femoral n. - The femoral n. runs between the iliacus m. and the psoas m. It exits the pelvis as it passes deep to the inguinal ligament with the femoral a. and femoral v. and supplies motor innervation to the anterior compartment of the thigh.

Femoral a. - the continuation of the external iliac a., it changes names when it passes deep to the inguinal ligament with the femoral n. and femoral v.

Femoral v. - the continuation of the external iliac v., it changes names when it passes deep to the inguinal ligament with the femoral n. and femoral a.

Obturator n. - The obturator n. runs medial to the psoas m., and passes through the obturator canal to supply motor innervation to the muscles of the medial compartment of the thigh.

Gluteus maximus m. - a large muscle, broadly attached to the ilium, sacrum, and coccyx. Was reflected during dissection of the pelvis.

Gluteus medius m. - deep to the gluteus maximus, helps stabilize the pelvis during swing phase (prevents Trendelenberg sign)

Gluteus minimus m. - deep to the gluteus medius.

Lateral rotators of the hip, deep to the gluteal muscles:

Piriformis m. - most superior of the lateral rotators of the hip.

Just inferior to the piriformis m. is a trio of small lateral rotators. The superior gemellus m. and the inferior gemellus m. run together, and sandwiched between them is the tendon of the obturator internus m.

Inferior to the gemellus mm. is the quadratus femoris m.

The tendon of the obturator externus m. can be found between the inferior gemellus m. and the quadratus femoris m., but it is very deep in that space, you’ll have to dig for it.

Nerves and vessels of the gluteal region:

On either side of the piriformis m. you will find the cut remains of the nerves and vessels that serve the gluteal mm.

The superior gluteal n. , superior gluteal a., and superior gluteal v. form a bundle that emerge superior to the piriformis m. The superior gluteal n. innervates the gluteus medius and gluteus minimus mm.

The inferior gluteal n., inferior gluteal a., and inferior gluteal v. form a bundle that emerges inferior to the piriformis m. The inferior gluteal n. innervates the gluteus maximus.

The sciatic n. emerges from underneath the inferior border of the piriformis m. It passes into the posterior thigh, and provides motor and sensory innervation to the posterior thigh, and everything below the knee. You’re also likely to see the smaller posterior cutaneous nerve of the thigh running with the sciatic n.

Dissection of the thigh

Deep fascia and compartments of the lower limb:

As you remove the skin and superficial fascia of the thigh and leg, you’ll see that the muscles are enclosed in a heavy connective tissue, the deep fascia of the thigh. You encountered similar deep fascia in the upper limb, but the fascia in the lower limb is even thicker. You’ll have to remove most of this deep fascia to see the muscles, nerves, and vessels of the thigh. There are a few things to be aware of as you deal with this deep fascia:

In the lateral aspect of the thigh there is an especially thick region of the deep fascia that forms the iliotibial tract or iliotibial band (IT band). The IT band is the tendon of the tensor fascia lata m. (TFL in the image), and also serves as a tendon of the gluteus maximus m. Be aware that the IT band is a thickened region of the fascia, so it will not appear as discrete as it does in the image until you cut away the rest of the deep fascia. Preserve the IT band.

In both the thigh and the leg there are extensions of the deep fascia that run between muscles, all the way to the bones of the limb. These extensions divide the thigh and leg into fascial compartments. The thigh is divided into an anterior, posterior, and medial compartment. The leg is divided into an anterior, posterior, and lateral compartment. The compartments contain muscles that have similar functions and are innervated by the same nerve. Therefore, the compartments serve as useful tools for organizing your study of the lower limb.

Figure 1.4 Fascial compartments of the thigh

Figure 1.3 Lateral thigh.

In the superficial fascia (adipose) between the skin and the deep fascia, you’ll find cutaneous nerves and superficial veins. These are similar to the cutaneous nerves and veins you’ve seen in other regions of the body, and ultimately they’ll be removed as you dissect the deeper structures of the limb. The one superficial vein to take note of is the great saphenous v. This vein runs from the femoral triangle (just inferior to the inguinal ligament) all the way to the medial aspect of the ankle and out into the foot. The great saphenous v. is often used for coronary artery bypass surgery.

Anterior compartment of the thigh, muscles:

The anterior compartment of the thigh contains muscles that flex the hip and extend the knee, with the quadriceps being the main muscles. Innervation of the anterior compartment is by the femoral n., and blood supply is from the femoral a.

The 4 main muscles of the anterior compartment of the thigh are collectively called the quadriceps femoris muscle group: rectus femoris m., vastus lateralis m., vastus medialis m., and vastus intermedius m. The 4 muscles of the quadriceps group have different origins, but all insert together through the quadriceps tendon and patellar ligament into the tibial tuberosity.

The most superficial of the anterior compartment muscles is the sartorius m., a long, thin strap muscle that runs from the ASIS to the medial surface of the superior tibia.

The most lateral of the anterior compartment muscles is the fascia lata m., which was referred to earlier in relation to the IT band.

In the superior thigh are the iliopsoas m. and the pectineus m. To follow the iliopsoas muscle out from the pelvis you’ll have to remove the overlying inguinal ligament and fascia associated with the ligament. That will also give you a better view of the pectineus m., which is deep and medial in the anterior compartment.

Medial compartment of the thigh, muscles:

The medial compartment of the thigh is the adductor compartment; it contains muscles that mainly function to adduct the thigh at the hip.

Moving medially from the anterior compartment, the first of the medial compartment muscles you’re likely to see is the adductor longus m. Use blunt dissection to separate the adductor longus from the underlying adductor magnus m. To find the small adductor brevis m. you’ll have to separate the adductor longus and adductor magnus and look between the two musles and superiorly. The adductor brevis will be tucked up into the interval between the longus and magnus.

The most medial of the medial compartment muscles is the gracilis m., a long, thin strap muscle. Follow the tendon of the gracilis inferiorly, and you’ll see that it inserts on the tibia in the same region as the sartorius m.

The pectineus m. (introduced on the previous page) may be considered either a medial compartment or anterior compartment muscle. Its action is both adduction and flexion of the hip, and although it is usually innervated by the femoral n., it is sometimes innervated by the obturator n. (which innervates the other medial compartment muscles).

Note that in the second figure the adductor longus, pectineus, and iliopsoas have been cut to view the deeper muscles.

The far left figure shows only the muscle attachments, and then from left to right the figures show the medial compartment muscles from most anterior to most posterior.

The Femoral Triangle:

The femoral triangle is the region in the superior thigh where you will find the femoral n., femoral a., and femoral v. as they pass under the inguinal ligament and into the thigh. The borders of the femoral triangle are the sartorius m. (anterior compartment), the adductor longus m. (medial compartment), and the inguinal ligament. You can also get a good idea of where to find the structures of the femoral triangle by following the femoral n., external iliac a., and external iliac v. out of the pelvis and into the thigh.

It’s important to know that the roof of the femoral triangle will be covered with heavy fascia, and there will be adipose within the triangle, so you’ll have to clean it out to see the nerve and vessels. The femoral a. and femoral v. are also covered in the femoral sheath, so the connective tissue that forms the sheath will also have to be incised and removed. Be careful as you search for these structures, do not scalpel blindly into the femoral triangle.

Within the femoral triangle the femoral n. branches repeatedly to innervate the muscles of the anterior compartment. You’ll see these branches, but you will not see a single femoral n. as you did in the pelvis.

The great saphenous v. joins the femoral v. in the femoral triangle.

Figure 1.7 The femoral triangle.

Path and branches of the femoral a.:

The femoral a. and its many branches provide the main blood supply to the lower limb. Within the femoral triangle the artery gives off its main branches to the thigh.

The deep artery of the thigh (profunda femoris, deep femoral) branches from the femoral artery. It courses posterior (deep) to the femoral a., and runs through the medial compartment of the thigh. It gives off approximately 4-5 perforating arteries that pass into the posterior compartment of the thigh to supply blood to that region.

The lateral circumflex a. is a branch of either the deep artery of the thigh or of the femoral a. It passes anterior to the tendon of the iliopsoas and anterior to the femur, and divides into 3 branches; descending, transverse, and ascending.

The medial circumflex a. is a branch of either the deep artery of the thigh or of the femoral a. It passes posterior to the femur.

“Muscular branches” of the femoral and deep femoral aa. are simply branches that provide blood to the muscles of the thigh. There are many of them and they are variable.

“Perforating branches” of the deep femoral a. pass though (perforate) the attachment of the adductor magnus to enter the anterior compartment of the thigh.

The femoral a. becomes more posterior as it descends, and eventually passes through an opening in the adductor magnus called the adductor hiatus. At that point the artery changes its name to the popliteal a., and will be found in the popliteal fossa posterior to the knee.

Anterior view of the femoral a. and its branches.

Posterior view of the femoral and deep femoral aa.

Obturator nerve and artery:

The obturator n. and the obturator a. pass through the obturator foramen to enter the medial compartment of the thigh.

The obturator n. innervates the adductor longus m., adductor brevis m., adductor magnus m., gracilis m., obturator externus m., and sometimes the pectineus m.

The obturator n. splits into an anterior and posterior division. The anterior division runs anterior to the adductor brevis m., between the adductor brevis m. and the adductor longus m. The posterior division runs posterior to the adductor brevis, between the adductor brevis m. and the adductor magnus m.

The obturator a. supplies blood to the muscles of the medial compartment of the thigh, though it is not the sole blood supply to those muscles (branches of the femoral a. also supply blood to muscles of the medial compartment). Branches of the obturator a. accompany the branches of the obturator n.

Figure 1.8 Obturator nerve

Posterior compartment of the thigh, muscles and nerve:

The posterior compartment of the thigh contains the muscles that are collectively called the hamstring muscles. There are 3 hamstring muscles, though one of those muscles has two heads (biceps femoris m.), and one of those heads is not technically a hamstring muscle. The hamstring muscles extend the hip and flex the knee.

The biceps femoris m. is the lateral hamstring muscle. It is composed of two heads, a long head that originates from the ischial tuberosity, and a short head that originates from the posterior surface of the femur. Technically a hamstring muscle originates from the ischial tuberosity, so the short head is not considered a true hamstring muscle.

Medially there are two hamstring muscles, the semitendinosus m. and the semimembranosus m. The semitendinosus m. is the thinner of the two muscles, and has a long, cord-like tendon of insertion. The semimembranosus is the broader of the two muscles, and has a broad, membranous tendon of origin.

The innervation of the hamstring muscles is the sciatic n., specifically the tibial branch of the sciatic n., with the exception of the short head of the biceps femoris m., which is innervated by the fibular branch of the sciatic n.

The Knee

Dissection of the knee will require that you cut many structures, because of that, we do not want most of the groups in lab to dissect the knee. There is often a prosection of the knee in lab, so make sure you are able to see that. If you want to cut into the knee joint of your cadaver, please call a faculty member over and they will let you know if you can.

The knee is primarily a hinge type of synovial joint, allowing flexion and extension. The knee joint consists of three articulations:

Two femorotibial articulations between the lateral and medial femoral and tibial condyles.
One intermediate femoropatellar articulation between the patella and the femur.

The fibula is not involved in the knee joint. The stability of the knee joint depends on the strength and actions of surrounding muscles and ligaments connecting the femur and tibia. Of these supports, the muscles are most important, particularly the quadriceps femoris muscle group of the anterior thigh.

Within the fibrous joint capsule, the medial and lateral menisci are crescentic plates of fibrocartilage on the tibial condyles that deepen the articular surfaces and play a role in shock absorption. The menisci are thicker at their external margins and taper to thin, unattached edges in the interior of the joint.

Also within the fibrous joint capsule are the cruciate ligaments, which strengthen the knee. The cruciate ligaments join the femur and tibia, crisscrossing within the joint capsule. The crossing-over point of the cruciate ligaments serves as the pivot for rotatory movements at the knee. In every position, one cruciate ligament, or parts of one or both ligaments, is/are tense. The anterior cruciate ligament (ACL) is the weaker of the two cruciate ligaments. It arises from the anterior surface of the tibia and prevents anterior displacement of the tibia on the femur. The posterior cruciate ligament (PCL) is the stronger of the two cruciate ligaments. It arises from the posterior surface of the tibia and prevents posterior displacement of the tibia on the femur.

Externally, the fibrous joint capsule is reinforced by several strong ligaments. The patellar ligament is the distal part of the quadriceps femoris tendon. It is a strong, thick fibrous band passing from the patella to the tibial tuberosity of the tibia. The collateral ligaments of the knee include the medial (tibial) and lateral (fibular) collateral ligaments (MCL and LCL, respectively) on either side of the joint capsule. These are taut when the knee is fully extended. During flexion, they become increasingly slack, permitting some rotation at the knee. The MCL is firmly attached to the medial meniscus, whereas the LCL is not attached to the lateral meniscus.

Flexion and extension are the main knee movements but some rotation occurs when the knee is flexed. When the leg is fully extended with the foot on the ground, the knee passively “locks” because of medial rotation of the femur on the planted tibia. This position makes the lower limb a solid column and more adapted for weight bearing. When the knee is locked, the thigh and leg muscles can relax briefly without making the knee joint too unstable. To unlock the knee, a small muscle called the popliteus m. contracts, rotating the femur laterally about 5 degrees on the tibial plateau so that flexion of the knee can occur.

The Popliteal Fossa (Posterior Knee)

The popliteal fossa is the diamond-shaped region on the posterior aspect of the lower limb, posterior to the inferior thigh and knee. The nerves and blood vessels that pass from the thigh into the leg (calf) and foot all pass through the popliteal fossa. As usual, the contents of the popliteal fossa will be enveloped in adipose and connective tissue. Work your way carefully through this connective tissue to find the nerves and vessels (do not scalpel blindly in the popliteal fossa).

The superior borders of the popliteal fossa are the biceps femoris m. and the semimembranosus m. The inferior borders of the popliteal fossa are the medial and lateral heads of the gastrocnemius m. (the superficial muscle of the calf). As you work your way into the popliteal fossa it will be helpful to spread the two heads of the gastrocnemius m.

Within the popliteal fossa, the sciatic n. divides into the tibial n. and the common fibular n. (fibular and peroneal are synonymous). There’s a lot of variation in the location of the split, sometimes it’s more superior in the thigh, and sometimes the two branches are separate throughout the course of the nerve.

As you remove more fascia you’ll find the sheath that contains the popliteal a. and popliteal v. (continuation of the femoral). The artery and veins will be tightly adhered to one another, it will take some work to separate them.

Look for the superior lateral geniculate a. and the superior medial geniculate a., branches of the popliteal a. that sit on the posterior femur. These arteries anastomose with the inferior lateral geniculate a. and the inferior medial geniculate a., which are inferior to the knee.

Boundaries of the popliteal fossa.

Branches of the sciatic n. within the popliteal fossa.

Look for the superior geniculate aa. on the posterior surface of the femur.

Clinical Correlations

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