The lower extremity or lower limb refers to the part of the body that extends from hips to toes. That includes the thighs, knees, legs and ankles. A study of the cross-sectional anatomy allows to have a clear understanding of the structural organization of this area. That will permit an unique representation of the positions, sizes, shapes, and relationships of the structures present in the upper extremity of a human body.
Anatomy of the hip and thigh
The hip region connects the axial skeleton with the lower extremity. It is formed from the articulation of the head of the femur with the acetabulum of the hip bone that is formed from the fusion of the ilium, ischium and pubis. The thigh is the region of the free lower limb that lies between the hip and knee joints. Its skeletal framework is formed solely of the femur bone.
The hip muscles are the tensor fasciae latae, iliacus, iliopsoas, psoas minor, gluteus maximus, gluteus medius, gluteus minimus, piriformis, quadratus internus and gemellus muscles. The thigh muscles are divided into three compartments. The anterior compartment includes the sartorius and the large quadriceps femoris muscles, while the posterior compartment includes the semitendinosus, semimembranosus and biceps femoris muscle. The medial compartment is comprised of the gracilis, pectineus, adductor longus, adductor brevis, adductor magnus, and obturator externus muscles.
Knee and Leg
The knee joint articulates the thigh region with the leg. The leg region lies between the knee and ankle joints. Its bony framework is made up of the tibia and fibula. The leg is also separated into three compartments. The anterior compartment includes the tibialis anterior, extensor hallucis longus, extensor digitorum longus and fibularis tertius muscles. The medial compartment, which is formed by the fibularis longus and brevis. The posterior compartment includes the gastrocnemius, soleus, plantaris, flexor hallucis longus, flexor digitorum longus, tibialis posterior, and popliteus muscles.
Ankle and Foot
The ankle and foot skeleton consists of seven tarsals (talus, calcaneus, navicular, cuboid and the lateral, intermediate, and medial cuneiform bones), metatarsals (I-V), and phalanges. Each toe has three phalanges (proximal, middle and distal), except for the great toe, which only has two.
The muscles seen in a foot and ankle cross sections are the extensor digitorum brevis, extensor hallucis brevis, dorsal interosseous, plantar interosseous, flexor digitorum brevis, quadratus plantae and lumbrical muscles. Other muscles, which belong to the big toe are the flexor hallucis brevis, abductor halluces and adductor halluces, while those of the little toe are the abductor digiti minimi, flexor digiti minimi and opponens digiti minimi.
The blood supply of the lower extremity is mainly provided by continuations and branches of the femoral artery. The superficial veins found in this area are the great and small saphenous, while the deep veins present correspond to their arteries and bear their name. The nerves located in the lower extremity are branches from both the lumbar and sacral plexuses.
X-rays are usually the imaging modality of choice when it comes to evaluating the lower extremity region. However, computed tomography (CT) angiography has shown to be ideal for detecting vascular injuries like dissections, occlusions, aneurysms, fistulas and focal stenosis. Magnetic resonance imaging (MRI) is also recommended when examining the major joints of the lower extremity. Both of the scans mentioned above depend on the cross-sectional analysis of the anatomic structures present in this region and play a vital role in clinical practice.