7.5: Bones of the Pelvic Girdle and Lower Limb
Describe the location, structural features, and functions of the bones of the pelvic girdle
Compare and contrast the adult male and female pelvic bones
Describe the location, structural features, and functions of the bones of the leg, ankle, and foot
1. Location, Structural Features, and Functions of the Pelvic Girdle
The pelvic girdle (or hip girdle) serves as the attachment point for the lower limbs to the axial skeleton. It is composed of two pelvic bones (also known as coxal bones or os coxae).
General Structure:
The two pelvic bones articulate posteriorly with the sacrum at the sacroiliac joints.
Both bones meet anteriorly at the pubic symphysis, where they are joined by a fibrocartilage disc.
The pelvis as a whole consists of the pelvic girdle plus the sacrum and coccyx.
Acetabulum: A deep, lateral socket where the femur articulates. It is formed by the fusion of the three constituent bones of the os coxae.
The pelvic girdle and sacrum form the pelvic inlet, the ridge surrounding it is the pelvic ridge
The greater pelvis (false) is superior to the pelvic brim, while the lesser pelvis (true) is inferior to the brim
The Three Fused Bones:
Ilium: The largest and most superior portion. Features include iliac crest (superior border), the ala (superior surface), the anterior superior iliac spine (ASIS; termination site of the ilia crest), and the greater sciatic notch (allows passage for the sciatic nerve; is just below posterior inferior iliac spine). The iliac fossa is the smooth anterior part, the rough posterior side is the auricular surface, which the line between the two is the arcuate line
Ischium: The posteroinferior portion of the pelvic bone.
It consists of an ischial body (posterior; along with ilium and pubis form part of the acetabulum) and an ischial ramus (anterior; along with pubis forms part of obturator foramen).
Ischial spine: A bony projection located posterior to the acetabulum; the lesser sciatic notch is located just inferior to it; ligament from sacrum attaches; inferior to which is the lesser sciatic notch which also has nerves passing through.
Ischial tuberosity: Posteroinferior side; The thick, roughened area that serves as the "sitting bone," supporting the body's weight when seated and providing an attachment point for the hamstring muscles.
The ischial ramus extends anteriorly to join the inferior pubic ramus.
Pubis: The most anterior and inferior portion of the pelvic bone.
It consists of a pubic body, a superior pubic ramus (contributes to the acetabulum, and both rami form part of the obturator foramen boundary), and an inferior pubic ramus.
Pubic symphysis: The joint where the two pubic bodies meet anteriorly.
Pubic tubercle: A small projection on the lateral end of the pubic crest that serves as an attachment site for the inguinal ligament.
Pubic crest: The medial ridge on the superior surface of the pubic body.
Obturator foramen: The large opening through which nerves and blood vessels pass; it is enclosed by the rami of both the pubis and the ischium.
Functions:
Supports and protects the pelvic organs (bladder, reproductive organs).
Connects the lower limbs to the trunk.
Transmits the weight of the upper body to the lower limbs.
2. Comparison of the Adult Male and Female Pelvic Bones
The female pelvis is biologically adapted for childbearing, leading to several key morphological differences compared to the male pelvis:
General Shape: The female pelvis is wider, shallower, and lighter. The male pelvis is narrower, deeper, and heavier with more prominent bone markings.
Pelvic Inlet and Outlet:
The pelvic inlet in females is wider and more oval-shaped; in males, it is heart-shaped.
The pelvic outlet in females is wider, with the ischial tuberosities positioned further apart.
Pubic Arch (Subpubic Angle): In females, this angle is broad, typically greater than 90∘. In males, it is narrower, typically less than 90∘.
Female Acetabula are far apart and point anteriorly, giving them a “swaying“ gait
Greater Sciatic Notch: Broad and shallow in females; narrow and deep in males.
Sacrum and Coccyx: The female sacrum is wider, shorter, and less curved. The female coccyx is more flexible and oriented more posteriorly to allow for the passage of a fetus.
Ischial tuberosities females tend to have them point laterally, while males’ point medially
Sex differences in pelvic bones are significant due to functional demands (especially childbirth in females):
General Structural Differences
Feature
Female Pelvis
Male Pelvis
Pelvic inlet shape
Wider, more oval/round
Narrower, more heart-shaped
Subpubic angle
Wider (≈ > 80°)
Narrower (≈ < 70°)
Pelvic outlet
Larger and broader
Smaller
Sacrum
Shorter, wider, less curved
Longer, narrower, more curved
Greater sciatic notch
Broader
Narrower and deeper
Overall shape
Broader and shallower
Taller and deeper
3. Location, Structural Features, and Functions of the Lower Limb
The Thigh (Femur)
Location: Extends from the hip to the knee.
Structural Features:
Head: Articulates with the acetabulum; contains the fovea capitis for ligament attachment.
Neck: The weakest part of the femur and a common fracture site.
Trochanters: The greater and lesser trochanters serve as major sites for muscle attachment; connected by the intertrochanter line, continuing posteriorly as the intertrochanteric crest
Posterior the femur is the linea aspera, splitting into two lines that lead to 2 projections: the epicondyles
Condyles: The epicondyle then tapers into the medial and lateral condyles articulate with the tibia to form the knee joint.
Intercondylar fossa: posterior indentation between the two condyles, anterior to it is the smooth patellar surface
Patella: articulates with the patellar surface of the femur
is a sesamoid bone (embedded within tendon or muscle)
the patellar ligament is a continuation of the quadriceps tendon, which inserts into the tibia and secures the patella
proximal end is base, and distal is the apex
The Leg (Tibia and Fibula)
Tibia: The medial, larger bone of the leg. It is the only weight-bearing bone of the leg. Notable features include the tibial tuberosity (anterior site for patellar ligament attachment) and the medial malleolus (the inner ankle bump). proximal end has medial and lateral condyles (separated by a ridge, the intercondylar eminence) to articulate with femoral condyle. Anterior crest of the tibia is the shin, which terminates at the medial malleolus.
Fibula: The lateral, thinner bone. It does not bear weight but serves as a site for muscle attachment and stabilizes the ankle. Its distal end is the lateral malleolus (the outer ankle bump).
United by an interosseous membrane, and articulate distally and proximally at the tibiofibular joints, allowing for little movement and more stability
The Ankle and Foot
Tarsals: There are 7 tarsal bones in the ankle. The talus articulates with the tibia and fibula, while the calcaneus (the heel bone) is the largest and provides the point of attachment for the Achilles (Calcaneal) tendon. Distally, the talus articulates with the navicular
The distal for tarsal bones from medial to lateral are: medial cuneiform, intermediate cuneiform, lateral cuneiform, and cuboid
All cuneiforms articulate with the navicular, while the cuboid articulates posteriorly with the navicular
Metatarsals: 5 bones (II-VV) forming the sole/instep of the foot.
Phalanges: The toes consist of 14 bones. The hallux (great toe) has 2 phalanges (proximal and distal), while the other four toes have 3 phalanges each (proximal, middle, and distal).
The Hallux also has 2 sesamoid bones
The phalanges do not rest on the ground due to these ligaments and muscles:
Medial longitudinal arch: runs along medial side of foot, from calcaneus to metatarsals 1-3
Lateral longitudinal arch: extends from lateral side of calcaneus to metatarsals 4-5
Transverse arch: runs along middle foot and involves distal tarsals and the bases of all 5 metatarsals