Introduction

In this lab, you will explore the muscles of the anterior thigh, medial thigh, lateral thigh; anterior compartment of the leg; lateral compartment of the leg; and the dorsal aspect foot. Use the muscle tables to guide your learning of the origin, insertion, action, and innervation.

Dynamic vs. Static stability of the Knee Joint

An interesting clinical point to consider is the dynamic vs. static stability of the knee joint. Static stability comes from all the non-contractile elements of a joint (e.g., bone shape, ligaments, cartilage, capsule) and gives us many structure governs function examples. Dynamic stability refers to joint stability provided by muscle actions. The knee provides two great examples: The action of the quad muscle directly support the PCL ligament (a ligament designed to protect posterior translation of the tibia on the femur), and the hamstrings directly support the ACL ligament (a ligament designed to protect anterior translation of the tibia on the femur).

Lab Activity 1:  Visible Body Digital Atlas–Muscles of the Anterior, Medial, and Lateral Thigh and the Knee Joint

While you are looking at the muscles of the lower extremity, you can select the individual muscles, then click the red attachment icon. When you have clicked the attachment icon, videos will often pop up to demonstrate the motion of the muscles you have selected. You can also go to the Muscle Actions icon from the home page and scroll down to see the motions of the leg and foot. Explore the various movements at the knee and ankle joints in relation to the muscle actions responsible for those movements. You should also review these muscle actions from your muscle tables.

• Explore muscles of the thigh: Click on the Systems icon, then under Muscular System Views, click on 18. Knee. Explore the muscles of the anterior, medial, and lateral thigh provided in the list of terms. As you navigate through, highlight the various muscles, and use your muscle charts to study the origins, insertions, and actions of these muscles with the images. Remember to explore the various movements at the knee joint and the muscles responsible for those movements. You should also review these muscle actions from your muscle charts.
• Explore the Knee joint:  Click on the Systems icon, then under Skeletal System Views, click on 1. Full Skeleton.
  • To see the medial and lateral menisci, zoom into the knee, then hide the femur. Now, rotate the image, so you are looking at it from a superior to inferior view. The menisci function as cushions and shock absorbers for the knee joint. The lateral meniscus is more “O” shaped, while the medial meniscus is more “C” shaped.
  • Reset the view to the full skeleton, zoom into the knee, and observe the medial collateral ligament. This ligament protects against valgus forces at the knee, in which the knee bends inward in the coronal plane and opens the medial joint space. For example, a valgus force could occur when a football player hits the lateral aspect of another player’s knee during a tackle. Now, look at the lateral collateral ligament. This ligament prevents varus forces, resulting in the knee bending out laterally in the coronal plane and opening the lateral joint space.
  • To see the cruciate ligaments deep in the knee joint in the intercondylar space, you should first hide the patella and the patellar tendon. You may also need to hide the femur. Make sure to rotate around the image to appreciate these ligaments from an anterior and posterior view. The posterior cruciate ligament, or PCL, runs from the inner surface of the medial femoral condyle to the posterior intercondylar area of the tibia. It prevents the tibia from moving posteriorly on the femur. The anterior cruciate ligament, or ACL, is commonly injured. It runs from the inner surface of the lateral femoral condyle, wraps around the PCL, and inserts onto the anterior intercondylar area of the tibia. This ligament prevents anterior movement of the tibia on the femur, and it is crucial to the integrity and proper function of our knee. Many activities we do biomechanically involve forces that push our tibia anteriorly: walking, running, jumping, and more. If this ligament is damaged, it can feel as if our knee is “giving out.” Forceful movements such as jumping without this ligament are difficult and can damage other structures in the knee.
  • You will NOT be able to observe the infrapatellar fat pad just deep and inferior to the patella. This fat pad helps to cushion the joint. You can observe some bursae or fluid-filled sacs around the knee, but you will not be tested on these.

• Explore the muscles of the anterior and lateral leg: Use the right leg to view the anterior and lateral leg muscles. Use finger gestures, rotation, zoom, and highlight tools to explore the muscles in the list of terms. Reference the muscle charts for origin, insertion, and innervation information. You will need to hide or remove the superficial muscles to see the deeper muscles of the anterior and lateral leg.
• Explore the muscles on the dorsal aspect of the foot: Use the right leg to view the muscles on the dorsal aspect of the foot. There are only two muscles on the dorsal aspect.
• Explore the Talocrural (ankle) joint and joints of the foot: Click on the Systems icon and then Muscular System Views. Go to 19. Ankle and Foot. Use the left foot to see the ligaments of the ankle, or talocrural, joint. The talocrural joint occurs between the tibia, fibula, and talus. Notice how the fibula projects more inferiorly than the tibia at this joint. This is why we have a greater range of motion with inversion of our ankle (pointing the bottom of the foot inwards) than with eversion (pointing the bottom of our foot outwards). When our foot is at a 90-degree angle to our lower leg, as in standing in anatomical position, our talus is locked into a more stable position between the fibula and tibia. However, when we plantarflex our foot or point our toe, the talus moves out of this position, and we are more vulnerable to ankle sprains in this position. To better visualize the ligaments, hide the extensor and flexor retinaculum. Observe the deltoid ligament on the medial aspect of the ankle. The app shows different parts of this ligament. You do not need to know the different parts of the ligament, just that those medial ligaments together comprise the deltoid ligament. Anteriorly, observe the anterior tibiofibular ligament running from the distal tibia to the distal fibula. When a patient incurs a high ankle sprain, the tibia and fibula are forced apparat, and this ligament is injured. On the anterolateral aspect, observe the anterior talofibular ligament (ATF). This ligament runs from the talus to the fibula, and it is commonly injured with eversion ankle sprains. Finally, view the calcaneofibular ligament, which runs from the fibula to the calcaneus.

Move to the foot and observe the intertarsal (the app will define these, you do not need to know each one individually), tarsometatarsal, metatarsophalangeal (the app will show the capsules of these joints), and interphalangeal joints. Note that interphalangeal joints are found in both the hand and foot. Like the hand, toes 2-5 have proximal and distal interphalangeal joints, while the great toe, like the thumb, only has an interphalangeal joint.

Lab Activity 3:  Lower Extremity Cadaveric Tissue-Muscles of the anterior, medial, and lateral thigh

Reminder: Never touch the plastinated specimens with wet gloves! Also, though you can turn the plastinated specimens to view different structures, you should try to handle these as little as possible. 

• Anterior thigh
  • Observe the psoas major, iliacus, or iliopsoas muscles. The psoas major originates on the lumbar vertebrae, and it merges with the iliacus to form the iliopsoas. These muscles flex the hip.
  • Observe the sartorius. This long, thin muscle runs across the anterior thigh from the ASIS to the pes anserine insertion on the tibia. This is the longest muscle in the body.
  • Now observe the four muscles that make up the quadriceps muscle group. The rectus femoris is the superficial muscle located on the midline of the thigh. It crosses both the knee and hip joints. The vastus lateralis and vastus medialis are located just lateral and medial to the rectus femoris, respectively. The vastus intermedius is deep to the rectus femoris.
• Medial thigh
  • First, observe the gracilis. This muscle is long and thin, and it inserts at the pes anserine insertion of the proximal medial tibia.
  • Observe the adductor magnus. This large muscle has both hamstring and adductor parts. The adductor portion inserts just superior to the medial condyle of the femur at the adductor tubercle.
  • Observe adductor longus, adductor brevis, and pectineus. The adductor longus is thinner, longer, and anterior to the adductor brevis.  Pectineus is also deep to adductor longus.
  • The medial thigh muscles appear somewhat fanned out along the medial thigh. All medial thigh muscles have an attachment to the pubis. They insert on the femur (except gracilis), in the following order from superior to inferior: Pectineus, adductor brevis, adductor longus, adductor magnus, and gracilis, which inserts onto the tibia at the pes anserine insertion.
• Lateral thigh
  • Near the hip, observe the tensor fasciae latae (TFL) on the lateral aspect of the thigh. The TFL anteriorly and gluteus maximus posteriorly attach to a long, flat, tendon-like, thick fascial layer called the iliotibial tract (IT band). The IT band inserts at Gerdy’s tubercle on the lateral aspect of the proximal tibia.

On the deep dissection, the knee has been opened. Lift the patella and quadriceps tendon and observe the deep aspect of the patella. There is evidence of osteoarthritis on the medial facet. It should be smooth and shiny. Also, observe the femoral condyles. There is significant osteoarthritis and bone spurs here, particularly on the medial condyle.

• Observe the tibial plateau and the medial and lateral menisci. Though you can’t see the whole meniscus on either side, you can see the location and anatomy of these structures.
• The collateral ligaments are difficult to see because they blend into the capsule. The medial collateral ligament (MCL) has been isolated on the medial aspect of the knee. However, the lateral collateral ligament (LCL) has not been isolated.
• Deep in the knee, observe the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL). Notice how the ACL inserts into the anterior aspect of the tibial plateau, while the PCL inserts onto the posterior aspect of the tibial plateau. Therefore, these ligaments cross each other. The ACL prevents anterior translation of the tibia on the femur. If an ACL tear is suspected, you can test this ligament by performing a Lachman’s Test. You are encouraged to perform this test on the deep dissection, as the “end point” feels the same as it would with an intact ACL in a living person. To perform this test, place one hand around the proximal tibia with the palm on the posterior aspect of the tibia. Place the other hand around the distal femur, with the palm on the anterior aspect of the femur. Slightly bend the knee (about 10 degrees). Stabilize the femur while somewhat quickly pulling the tibia anteriorly. You should feel a hard endpoint as the ACL prevents the tibia from moving anteriorly. Be sure to watch the ACL in action as you are performing this test.

• Anterior compartment of the leg: Observe the muscle that appears to be tightly adhered to the lateral aspect of the anterior tibia. This is the tibialis anterior, and it is the primary dorsiflexor of the foot. Just lateral to it is the extensor digitorum longus. The tendons of this muscle extend to digits 2-5. Unlike the upper extremity, there are two “extensor digitorum” muscles, so it is critical to include “longus” in the name when referring to this muscle. Deep to tibialis anterior is extensor hallucis longus. “Hallucis” means “great (1^st) toe. You may not be able to see the entire muscle belly, but you will be able to see the tendon of this muscle extending to the great toe. Finally, observe the peroneus (fibularis) tertius. This muscle is very small, and it either is not present in our tissue or is blended in with the extensor digitorum. You can see this muscle in other images.
• Lateral compartment of the leg: There are two muscles of the lateral compartment of the leg. Peroneus (fibularis) longus is superficial to peroneus brevis and sends its long tendon under the arch of the foot to insert on the base of the first metatarsal. You can pull on the tendon near the base of the first metatarsal on the deep wet specimen and see the tendon move on the lateral aspect of the foot. Peroneus (fibularis) brevis has a shorter tendon that inserts at the base of the 5^th metatarsal on the lateral aspect of the foot. These muscles act to evert the foot.
• Muscles on the dorsal aspect of the foot: The extensor digitorum brevis muscle extends digits 2-4, while extensor hallucis brevis extends the great toe.

Lab Activity 6:  Radiology of the Lower Extremity

Use the computers to view a tutorial on radiology of the gluteal region, thigh, and knee. The MRI images will have a few more structures listed than what you need to know for this lab. Focus on the list of terms to know from above.