Hip Bones and Lower Limb Anatomy: Pelvic Girdle to the Foot

Short summary

In this video, anatomy experts explain the hip bones that form the pelvic girdle and the bones of the free lower limb, highlighting the ilium, ischium, pubis, acetabulum, sacroiliac joint, pubic symphysis, and hip joint, followed by the femur, tibia, fibula, patella and foot bones.

• Key structures of the pelvic girdle include the ilium, ischium, pubis, acetabulum, sacroiliac joint and pubic symphysis
• Lower limb bone anatomy covered in detail for the femur, tibia, fibula and patella
• Foot bones organized into the tarsus, metatarsus and phalanges

Pelvic Girdle and the Lower Limb Overview

This video presents a detailed anatomy lesson on the pelvic girdle and the bones of the free lower limb. It begins with the pelvic ring, a bony circle formed by the right and left hip bones and the sacrum, which is shared with the axial skeleton. Each hip bone is a fusion of the ilium, ischium and pubis and articulates with the sacrum at the sacroiliac joint, with the other hip bone at the pubic symphysis, and with the head of the femur to create the hip joint. The lower limb then includes the femur, tibia, fibula, patella and the bones of the feet. The long bones of the leg and foot are explained with emphasis on their articular surfaces, attachments and weight bearing roles.

Pelvic Girdle: Structure and Joints

The pelvic girdle forms a ring called the pelvic ring. It is comprised of the ilium, ischium and pubis from each side, joined at the midline by the pubic symphysis and connected to the sacrum. The acetabulum is the large socket formed where the three bones contribute to articular surface for the head of the femur. The acetabular notch marks the incomplete inferior rim, and the acetabular fossa lies in the floor. The sacroiliac joints connect the hip bones to the sacrum, providing stability for weight transfer from the trunk to the lower limbs. The obturator foramen closes with a membrane that allows attachment for multiple muscles and reduces bone weight. The iliac crests and several gluteal lines show where the gluteal muscles attach, while the anterior and posterior borders of the ilium provide insertion points for ligaments and muscles that support the hip and trunk. The hip joint is formed where the head of the femur articulates with the acetabulum, and the hip joint capsule is reinforced by ligaments including the iliofemoral ligament.

Ilium: Landmarks and Attachments

The ilium is the largest and most superior part of the hip bone. It is divided into a body and a wing or ala. The ala has a lateral and a median surface, a crest and anterior and posterior borders. The iliac crest runs from the anterior superior iliac spine to the posterior superior iliac spine, with an internal and external lip that serves as a major muscle and deep fascia attachment site. The lateral surface of the ala features three gluteal lines for gluteal muscle attachment. The medial surface forms the iliac fossa for iliacus muscle attachment, while the auricular surface on the posteromedial portion forms the sacroiliac joint with the sacrum. The iliac crest also hosts the anterior superior iliac spine where the inguinal ligament and sartorius attach, and the anterior inferior iliac spine where the straight head of the rectus femoris and the iliofemoral ligament attach. The posterior border bears the posterior superior iliac spine where the oblique sacroiliac ligaments and the multifidus attach, and the greater sciatic notch lies inferior to the ischial spine. The ala continues inferiorly to join the body at the acetabulum, where the acetabulum is formed by contributions from the ilium, ischium and pubis.

Ischium and Pubis: Roles in the Pelvic Ring

The ischium contributes to the posterior inferior part of the hip bone. Its posterior border forms the inferior margin of the greater sciatic notch, and the ischial spine is a key feature for sacrospinous ligament and superior gemellus muscle attachment. The lesser sciatic notch lies below the spine, separated from the greater notch by the sacrospinous ligament. The ischial tuberosity is a thick rough prominence that bears weight during sitting and serves as the attachment site for the inferior gemellus muscle and the hamstrings. The ramus of the ischium joins the inferior ramus of the pubis to form the ischiopubic ramus, which forms part of the obturator foramen’s border. The pubis forms the anterior medial portion of the hip bone. Its body bears the symphyseal surface for the pubic symphysis, a cartilaginous joint joining the pubic bones at their rami. Anterosuperiorly, the pubis presents the pubic crest and tubercle, with the pubic tubercle marking the distal attachment point of the inguinal ligament. The superior ramus participates in the acetabulum and the pectineal line, which helps form the iliopectineal line with the ilium. The inferior ramus joins the ramus of the ischium, completing the ischiopubic ramus that defines part of the obturator foramen.

Acetabulum and Foramina: The Hip Socket and Passages

The acetabulum is the large socket of the lateral face of the hip bone that articulates with the head of the femur to form the hip joint. Its boundaries are defined by the superior rim from the ilium, the posterior boundary from the ischium, and the anterior boundary from the pubis. The acetabular notch creates a “cup with a broken rim,” and the acetabular fossa sits in the floor. The lunate surface forms the smooth crescent-shaped articular surface that articulates with the femoral head. The obturator foramen is the large opening bounded by the pubis and ischium and the rami, which is normally closed by the obturator membrane. The membrane provides a broad area for the attachment of internal and external obturator muscles and contains a small canal for the obturator nerve and vessels.

Lower Limb Bones: From Femur to Foot

The femur is the longest bone in the body and is oriented obliquely, directed inferior and medial as it extends downward. The proximal end features a spherical head that forms the hip joint with the acetabulum, a neck, and the greater and lesser trochanters. The neck is narrow near the head and broad at the base where it transitions into the shaft. The greater trochanter is the attachment site for abductors and rotators, while the lesser trochanter is where the iliopsoas attaches. Between the trochanters lies the intertrochanteric line on the anterior surface, and the intertrochanteric crest on the posterior surface. The iliofemoral ligament attaches near the intertrochanteric line, and the vastus medialis attaches near the crest. The femur’s shaft features the linea aspera on the posterior surface, a prominent ridge where thigh adductor muscles attach. The distal femur consists mainly of the medial and lateral femoral condyles, which articulate with the tibia and the menisci to form the knee joint, and a patellar surface that articulates with the patella. The knee is stabilized by the medial and lateral epicondyles and the adductor tubercle situated above the medial epicondyle for adductor magnus insertion. The patella, or kneecap, is a large sesamoid bone that increases the leverage of the quadriceps during extension and has anterior and posterior surfaces, a superior base, and an inferior apex, divided posteriorly into medial and lateral articular facets to track within the intercondylar groove.

The Tibia and Fibula: Support and Weight Transfer

The tibia lies medially and is the main weight bearing bone of the leg. Its proximal end forms the tibial plateau with medial and lateral articular surfaces separated by the intercondylar eminence, which is formed by the medial and lateral intercondylar tubercles. The tibial plateau articulates with the femoral condyles and is followed by the tibial condyles on the proximal end. The tibial shaft has an anterior border that can be felt along the leg, the interosseous border for the interosseous membrane, and the soleal line on the posterior surface where several muscles attach. The distal tibia forms the medial malleolus that articulates with the talus to complete part of the ankle joint, while the fibula lies posterolateral to the tibia and forms the proximal and distal tibiofibular joints. The fibula ends in the lateral malleolus, which extends distally and helps in ankle stability. The fibula provides muscle attachment sites but does not bear weight.

The Foot: Tarsus, Metatarsus and Phalanges

The foot is organized into three sections. The tarsus contains seven bones with the talus forming the superior ankle joint with the leg bones and articulating anteriorly with the navicular. The calcaneus or heel lies below the talus and forms the subtalar and calcaneocuboid joints. The navicular sits anterior to the talus and articulates with the three cuneiform bones and the cuboid articulates with the talus and surrounding bones. The metatarsus consists of five metatarsals numbered medially, with the bases bearing prominent tuberosities for tendon attachments; the first and fifth bases are particularly notable for tendon insertions. The head of the first metatarsal bears sesamoid bones on the plantar surface. The phalanges are the toe bones, with the great toe containing two phalanges while the other four toes have three. Each phalanx has a proximal base, a shaft and a distal head. Together these bones enable weight bearing, balance and locomotion across the foot.

Closing Thoughts

The video emphasizes that the hip bones are formed by the fusion of the ilium, ischium and pubis, with the ilium being the superior portion, the ischium forming the posterior inferior portion and the pubis contributing to the anterior medial part of the hip bone. It then traces the proximal and distal features of the femur, tibia and fibula and ends with a complete tour of the bones of the foot, including the tarsus, metatarsus and phalanges. The content is presented in a way intended to help current and future clinicians focus, learn, retain and thrive by understanding the structural relationships and attachment sites of these bones and joints.