Identifying Muscles of the Lower Extremities - Anatomy

Sartorius, gracilis, semitendinosus make up the pes anserine group whose conjoined tendons insert onto the anteromedial surface of the proximal extremity of the tibia. They flex and medially rotate the leg at the knee joint.

The adductor magnus is innervated by both the sciatic nerve and the obturator nerve.

Gluteus maximus is an thigh extensor, additionally it laterally stabilizes the hip and knee, and laterally rotates and adducts the thigh. It's insertion is the gluteal tuberosity. It is innervated by the inferior gluteal nerve.

The superior gluteal nerve innervates the tensor fascia lata, gluteus medius, and gluteus minimus. It does not innervate gluteus maximus, which is innervated by the inferior gluteal nerve. The obturator nerve provides sensation to skin on the medial aspect of the thigh and innervates adductor muscles of the lower extremity. The sciatic nerve provides sensation to most of the skin on the leg, and it innervates muscles of the posterior thigh, leg, and foot.

The superior gluteal nerve innervates the tensor fascia lata, gluteus medius, and gluteus minimus. It does not innervate gluteus maximus, which is innervated by the inferior gluteal nerve.

Tensor fascia lata helps stabilize the knee, especially in extension, while gluteus medius and minimus abduct the thigh and help to medially rotate the thigh. Paralysis of these gluteal abductors leads to a characteristic limp called the Trendelenburg gait. The Trendelenburg can be described when a person shifts their body weight tot he affected side to keep from tripping over the other side.

The knee is the largest, most complex synovial joint in the body. It is primarily limited to flexion and extension, but allows for some minimal rotation. It is composed of the distal femur, proximal tibia, and patella. The knee is stabilized by the posterior cruciate ligament (PCL), anterior cruciate ligament (ACL), the medial collateral ligament (MCL), the lateral collateral ligament (LCL), and meniscus. The patella is held into place by the patellar ligament.

The sartorius originates from the anterior superior iliac spine (ASIS) and inserts near the tibial tuberocity, running laterally to medially along the anterior thigh. Because the sartorius crosses both the hip and the knee, contraction of the muscle is capable of flexing both the leg and thigh. By running laterally to medially, shortening of the muscle also causes lateral rotation and abduction of the thigh.

The gracillis muscle is thin and flat muscle at the medial side of the thigh; it is the most superficial muscle on the medial side of the thigh. It originates at the anterior margin of the symphysis pubis and the pubic arch. The muscle runs downward, ending in a tendon that passes behind the medial condyle of the femur and onto the medial condyle of the tibia where it inserts into the tibia below the condyle (as part of the pes anserinus).

The gracillis adducts, medially rotates, and flexes the hip, it also aids in knee flexion.

In weight-bearing, as is the case during walking, ankle dorsiflexion and plantarflexion cause the tibia to move anteriorly and posteriorly, respectively. This results in flexion or extension of the knee, respectively. Keeping this in mind, although the gastrocnemius is a plantarflexor, it is also a knee flexor, so weakness in this muscle would not contribute to knee buckling. Because of the effect of dorsiflexion during weight bearing, the tibialis anterior would actually promote knee buckling, not resist it. Although the tibialis posterior is a plantarflexor, its primary role in gait involves maintaining the shape of the medial longitudinal arch. The soleus is ankle plantarflexor that eccentrically resists knee flexion (anterior movement of the tibia during weight-bearing). Accordingly, soleus weakness would explain this patient's knee buckling.

The quadriceps muscle group is primarily responsible for the extension of the knee. This group includes the rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius. The biceps femoris part of the hamstring muscle group and is responsible for the flexion of the knee.

The semitendinosus, gracilis, and sartorius are the three muscles that make up the pes anserine group, coming from the posterior, medial, and anterior compartments of the thigh, respectively. The adductor longus, is not part of this group as it inserts on the linea aspera of the femur, rather than the pes anserinus, like the semitendinosus, gracilis, and sartorius.

No muscles attach to the talus directly. However, the extensor digitorum brevis comes close, via its attachment to one of the talocalcaneal ligaments.

The long head of the biceps femoris attaches to the ischial tuberosity, and has attachments to the sacrotuberous ligament. Through this attachment, it is thought that the long head of the biceps femoris helps stabilize the sacroiliac joint. Although the gluteus maximus attaches to the sacrotuberous ligament, the gluteus medius does not, and neither do the gemellus superior nor the adductor magnus.

The achilles tendon or calcaneal tendon inserts on the posterior side of the calcaneus. It is the largest tendon in the body and pulls the heel up to point the toes downward. This decreases the angle between the bottom of the foot and back of the leg. This is called plantar flexion.

The hamstring muscles consist of three posterior muscles and their tendons (semitendinosus, semimembranosus, and biceps femoris). The hamstring muscles are responsible for knee flexion and hip extension. The semitendinosus, semimembranosus, and the long head of biceps femoris all originate at the ischial tuberosity (having these muscles cross the hip joint), while the short head of biceps femoris originate at the linea aspera and the lateral supracondylar line of the femur.

The flexor digitorum brevis lies in the middle of the sole of the foot above the plantar aponeurosis. It arises from a tendon from the medial process of the calcaneus, it continues towards the toes and divides into four tendons, one for each of the four lesser toes. It is innervated by the medial plantar nerve. The tibialis posterior, extensor digitorum longus, and soleus all cross the ankle joint thus having leverage above it.

The biceps femoris muscle forms part of the hamstrings, and consists of a long and short head. Both heads perform knee flexion, and the long head is involved in hip extension as it originates in the pelvis.

Quadratus femoris is a strong external rotator and adductor of the thigh. Piriformis is a lateral rotator, and laterally rotates the femur, abducting it, during hip extension. The quadriceps consist of rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius. The quadriceps flex the hip and extend the knee.

The soleus is the correct answer. The gastrocnemius also inserts on the calcaneus, but it originates on the condyles of the femur. Th plantaris muscle also inserts at the calcaneus, but it also originates at the femur. The biceps femoris muscles are located on the posterior side of the thigh. The sartorius originates on the anterior superior iliac spine, and inserts on the anteromedial aspect of the tibia.

The psaos major and the iliacus muscles are distinct in the abdomen and unite at the level of the inguinal ligament to form the iliopsoas muscle in the thigh. The iliopsoas muscle crosses the hip joint and inserts on to the lesser trochanter of the femur. The iliopsoas is involved in flexion and lateral rotation of the thigh. It is the strongest of the hip flexors, and is important in standing, walking, and running.

The gluteus medius, gluteus minimus, and piriformis insert onto the greater trochanter.

The biceps femoris inserts on the lateral surface of the fibular head. The other muscles of the hamstring insert of the medial surface of the tibia.