13 Posterior Lower Extremity
Learning Objectives:
By the end of this lab, students will be able to:
- Identify the muscles of the gluteal region, posterior thigh, superficial and deep posterior compartments of the leg, plantar layers of the foot, and name their actions.
- Using the muscle charts as a guide, identify the action, origin, insertion, and innervation for the muscles of the gluteal region, posterior thigh, superficial and deep posterior compartments of the leg, and plantar layers of the foot.
- Describe how structure governs function and provide examples based on muscle orientation and actions.
- Identify the sacroiliac joint, pubic symphysis, and hip joints, including ligaments and capsules.
Terms to Know
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Muscles of the Lower Extremity
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Intrinsic muscles of the foot
Joints of the Lower Extremity Part I
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Introduction
Today you will explore the muscles of the gluteal region, posterior thigh, posterior leg, and plantar layers of the foot. You will use videos from the digital atlas, lower extremity dissections, and image slideshows to explore the muscles of the gluteal region, posterior thigh, and plantar layers of the foot.
Here are a few important tips before learning about these muscles:
- You should know the origins, insertions, actions, and innervations presented in the muscle charts for these and all muscles of the lower extremity. The muscle chart is color-coded, and the information about what we expect you to know from the muscle table is described in the chart document itself. Please read that information. We will ask you questions about the function, attachment site, and/or innervation of muscles on the exam.
- As you are studying, I recommend using landmarks to understand the attachment sites, action, and sometimes the innervation. Follow the muscle to its attachment site if it is visible. Notice the joint the muscle crosses and the side of the joint it is on, and that will give you information about the muscle’s action. In some cases, you can see the nerve go to or even through the muscle it innervates. These visual cues can help you remember the information from the muscle tables.
Lab Activities
Activity 1: Gluteal Region and posterior thigh
- Explore the Sacroiliac joint and pubic symphysis: The sacroiliac joint is the joint between the sacrum and ilium. It is a highly-stable joint capable of only a small amount of gliding movement. This is where the lower extremity meets the spinal column. The pubic symphysis is located between the right and left pubic bones. There is a thick fibrocartilaginous disc between the two pelvic bones at this location.
- Explore the Coxal (hip) joint: First, observe the iliofemoral, ischiofemoral, and pubofemoral ligaments. Be sure to notice which bone of the pelvis they are attaching to, as this will tell you which ligament you are viewing. These ligaments all contribute to the capsule of the hip joint. Also, observe the ligamentum teres, or ligament to the head of the femur. This ligament contains the artery to the head of the femur. The acetabulum is the “socket” of the “ball-and-socket” joint. It is made up of all three bones of the os coxae.
- Explore muscles of the gluteal region: In the gluteal region, first, observe the gluteus maximus. This is the largest and most superficial of the gluteal muscles. Just deep to this is the gluteus medius. The gluteus minimus is the deepest and smallest of the gluteal muscles. The piriformis is an important lateral rotator of the hip. There are 5 other small lateral rotator muscles of the hip. While they are listed in the muscle chart, you will not be asked to identify these muscles in class.
- Explore the muscles of the posterior thigh. The posterior thigh muscles are collectively called the hamstring muscles. The hamstring muscles originate on the ischial tuberosity. Two muscles travel to the medial aspect of the knee. The semimembranosus has a thicker muscle belly and a shorter tendon. The semitendinosus has a thinner muscle belly and a longer tendon. It sits just superficial to the semimembranosus. The biceps femoris has two heads. The long head of biceps femoris originates on the ischial tuberosity, but the short head of biceps femoris originates on the femur. The two heads merge into a common tendon and insert onto the fibular head.
Activity 2: Posterior Leg
The leg can be divided into four compartments. The compartments are separated by a thick, fibrous layer of tissue. Each compartment has an associated nerve, artery, and muscles.
- Superficial posterior compartment of the leg: The most superficial posterior leg muscle is the gastrocnemius. It has a medial and lateral head that cross the knee to insert on the femur. This muscle aids knee flexion and is the primary plantarflexor of the foot. The soleus sits deep to the gastrocnemius and originates on the tibia. The gastrocnemius and soleus tendons merge to form the calcaneal (Achilles) tendon. The plantaris is a small muscle with a tiny muscle belly deep to the gastrocnemius and a long, thin tendon that extends toward the calcaneus. This muscle is not present in all individuals.
- Deep posterior compartment of the leg: There are four muscles of the deep posterior compartment of the leg. The tibialis posterior runs along the posterior aspect of the tibia and acts to plantarflex and invert the foot. Flexor digitorum longus tendons extend to digits 2-5 and flexes these digits. Flexor hallucis longus originates on the posterior fibula, and it’s tendon wraps around the medial aspect of the ankle before it reaches the distal great toe. This long path gives the muscle a mechanical advantage and makes it a powerful flexor of the first digit. The muscles Tibialis posterior, flexor Digitorum longus, and flexor Hallucis longus usually travel in a specific order around the medial malleolus. You can remember the order of these tendons using the mnemonic Tom, Dick, an Harry; “an” stands for posterior tibial Artery and tibial Nerve. Tibialis posterior is most anterior/superior, and flexor hallucis is most posterior/inferior.
The last muscle of the posterior compartment of the leg is the popliteus. This muscle is difficult to see on the tissue, but you can see part of it on the deep dissections. It sits on the superior aspect of the tibia and crosses the knee joint. It functions to medially rotate the tibia and “unlock” the knee from full extension in the first few degrees of flexion.
activity 3: Plantar layers of the foot
Explore the muscles of the foot.
- Intrinsic muscles of the foot: The intrinsic muscles of the foot are muscles that act on the foot and are entirely located within the foot. The muscles that we just examined in the leg would be considered extrinsic muscles of the foot. The plantar aspect can be divided into four layers containing a total of ten muscles or categories of muscles. The layers are just a way to organize the information. We will not ask you to identify which muscle is in which layer.
- Plantar fascia: This thick layer of fascia is superficial to the muscles of the plantar aspect of the foot. It has been cut in both wet specimens, but you can observe how it would attach to the calcaneus in anatomical position. This fascia can become inflamed with plantar fasciitis.
- Plantar muscles layer 1: The flexor digitorum brevis muscle is deep to the plantar fascia and flexes digits 2-4. The abductor hallucis is the large muscle on the medial aspect of the great toe. It abducts the great toe. Likewise, the abductor digiti minimi is located on the lateral aspect of the 5th digit and abducts that digit.
- Plantar muscles layer 2: The muscles of this layer attach to the tendon of flexor digitorum longus. Quadratus plantae runs from the calcaneus to the tendons of flexor digitorum longus to adjust the angle of pull of these tendons. Because the flexor digitorum longus runs around the medial malleolus, without the adjustment from quadratus plantae, this muscle would cause the toes to flex in a medial direction. The quadratus plantae aligns these tendons so that the toes flex within the sagittal plane. The lumbricals of the foot are similar to those of the hand. They insert on to the flexor digitorum longus tendons distally and flex the MP and extend the PIP and DIP joints.
- Plantar muscles Layer 3: The adductor hallucis is similar to the adductor pollicis of the hand. It is “7” shaped, with transverse and oblique heads, and it adducts the great toe. The flexor hallucis brevis and flexor digiti minimi muscles flex the great toe and 5th digit, respectively. These muscles can be observed on the deep dissection.
- Plantar muscles layer 4: The deepest layer of muscles on the plantar aspect of the foot is composed of the dorsal and plantar interossei. Like the hand, the Dorsal interossei Abduct the toes, while the Plantar interossei Adduct the toes (DAB and PAD). However, be sure not to mix up the name of these muscles with those of the hand! In the foot, the interossei that adduct are called the plantar interossei, while in the hand, they are the palmar interossei. These muscles cannot be seen on the dissected tissue, but they can be observed in other images.
Wrap up and clinical connection
For today’s clinical connection, you will see two videos discussing injuries to muscles of the posterior leg. The first video discusses hamstring injuries, and the second video reviews an injury to the Achilles tendon. Use your understanding of origins, insertions, and innervation to help you answer questions on the slideshow.