Hip Bones to Foot: An In-Depth Anatomy Guide of the Pelvic Girdle and Lower Limb

This Osmosis video provides a thorough tour of the pelvic girdle and the bones of the free lower limb, tracing how the hip joint forms and how the leg bones connect to the foot. It explains how the ilium, ischium and pubis fuse to form the hip bone, how the acetabulum accepts the head of the femur, and how the leg bones connect to the foot. The narration then details the femur, tibia, fibula, patella, and the seven tarsal bones that form the ankle and foot, including key landmarks and muscle and ligament attachments. The aim is to show how structure supports movement and weight bearing in daily life.

Introduction

This accompanying analysis provides a comprehensive overview of the pelvic girdle to the bones of the lower limb, focusing on bone morphology, landmarks, articulations, and functional relationships that underpin movement and weight distribution.

The Pelvic Girdle and Hip Bones

The hip bone is formed by the fusion of three primary bones: the ilium, ischium, and pubis. These components assemble into a bony ring known as the pelvic ring, connecting the lower limb to the axial skeleton. The sacrum is shared by the pelvic girdle and the axial skeleton, and the ring is completed anteriorly by the pubic symphysis. The pelvic girdle transfers weight from the spine to the legs and provides attachment points for muscles and deep fascia, while maintaining three main articulations: the sacroiliac joints posteriorly, the pubic symphysis anteriorly, and the hip joints with the femur laterally.

Key landmarks of the ilium include a body and ala (wing), with the iliac crest running from the anterior superior iliac spine to the posterior superior iliac spine. The crest has an internal and external lip and serves as an important attachment site for muscles and deep fascia. The gluteal lines on the lateral surface mark attachment points for gluteal muscles, and the iliac fossa on the medial surface houses the iliacus muscle. The auricular surface on the posteromedial part articulates with the sacrum to form the sacroiliac joint. Anteriorly, the anterior superior iliac spine and anterior inferior iliac spine provide attachment sites for the inguinal ligament, sartorius, straight head of the rectus femoris, and iliofemoral ligament. Posteriorly, the posterior superior and inferior iliac spines and the greater sciatic notch serve as attachment and passage regions for ligaments and muscles, including the multifidus and the sacrospinal components.

"First, there's the acetabulum, which is a large socket of the lateral face of the hip bone that articulates with the head of the femur to form the hip joint." - Osmosis Presenter

The Ischium and Pubis

The ischium forms the posterior inferior part of the hip bone. Its posterior border contributes to the inferior margin of the greater sciatic notch, while the ischial spine marks the origin of the sacrospinous ligament and the superior gemellus muscle. The lesser sciatic notch lies below the spine, separated from the greater notch by the sacrospinous ligament. The ischial tuberosity serves as the weight-bearing support when sitting and is the attachment site for several muscles. The pubis forms the anterior medial part of the hip bone, with the pubic symphysis a cartilaginous joint that joins the bodies of the left and right pubis by the ramus. The superior ramus forms part of the acetabulum, and the pectineal line, or pectin pubis, runs along the iliopectineal line to join the arcuate line of the ilium. The ischiopubic ramus completes the inferior border of the obturator foramen.

"The acetabular notch and depression, are surrounded by the thick and smooth lunate surface of the acetabulum, the articular surface on which the head of the femur slides." - Osmosis Presenter

The Femur

The femur is the longest bone in the body. Its proximal end features a head (2/3 of a sphere), a neck, and the greater and lesser trochanters. The fovea capitis is a small depression on the head where the ligament of the head of the femur attaches. The neck is trapezoidal, connecting the head to the shaft. Trochanters anchor major muscle groups: the lesser trochanter for the iliopsoas, and the greater trochanter for the abductors and rotators. A trochanteric fossa at the base of the greater trochanter marks insertions for several tendons, and along the shaft, the intertrochanteric line and crest provide additional sites for muscle attachments, including the iliofemoral ligament and parts of the vastus medialis. The shaft bears the linea aspera, a posterior rough ridge where thigh adductors attach, and its superior continuation includes the gluteal tuberosity and the spiral line leading to the lesser trochanter. Distally, the femur ends in medial and lateral condyles that articulate with the tibia and the menisci, with the patellar surface forming the kneejoint’s anterior articulation. The distal femur is aligned such that the femoral condyles sit on a common horizontal plane when weight is distributed, a feature described as the knee’s valgus angle.

The Patella

The patella, or kneecap, is a triangular, sesamoid bone that sits on top of the femoral condyles. Its anterior surface is smooth, while the posterior surface bears articular cartilage and is divided by a vertical ridge into medial and lateral articular surfaces. The patella acts to increase the leverage of the quadriceps during knee extension and to keep the tendon aligned in the intercondylar groove.

"The patella acts as the largest sesamoid bone in the body." - Osmosis Presenter

Tibia, Fibula, and Ankle

The tibia is the larger, weight-bearing bone of the lower leg, located medially and anteriorly relative to the fibula. Its proximal end forms the tibial plateau with medial and lateral articular surfaces separated by the intercondylar eminence. The tibial tuberosity marks the attachment of the patellar ligament, and the interosseous border anchors the interosseous membrane that connects the tibia to the fibula. The fibula, slender and lateral, articulates with the tibia at the proximal and distal tibiofibular joints and with the talus to contribute to the ankle joint. The distal tibia forms the medial malleolus, which interacts with the talus to stabilize the ankle, while the fibular malleolus forms the lateral side of the ankle mortise.

The Foot: Tarsus, Metatarsus and Phalanges

The foot comprises three segments: the tarsus, metatarsus, and phalanges. The talus sits superiorly as the ankle’s primary bone, articulating with the tibia and fibula above and the calcaneus below, while the navicular, cuboid, and three cuneiforms compose the midfoot. The calcaneus, or heel bone, bears a fibular trochlea for the fibularis muscles and hosts the sustentaculum tali for ligament and muscle attachments. The navicular articulates with the three cuneiforms and the talus, and the cuboid sits laterally adjacent to the calcaneus and navicular. The metatarsals form the foot’s arches proximal to the toes, and the toes themselves consist of proximal, middle, and distal phalanges, except the great toe which has only proximal and distal phalanges.

"The foot can be divided into three parts. The tarsus, metatarsus, phalanges." - Osmosis Presenter

Recap: From Pelvis to Toes

Having traced the pelvic girdle to the lower limb, this overview highlights how the hip joint, thigh, leg, and foot bones integrate structurally and functionally. Landmarks, joints, and muscular attachments all contribute to balanced weight transfer and coordinated movement, illustrating why bone anatomy matters for everyday activities and clinical understanding.