Pelvis AnatomyEdit

The pelvis is the central, ring-like structure at the base of the spine that bears weight, anchors the legs, and houses and protects a suite of vital organs. It forms a durable yet flexible bridge between the upper body and the lower limbs, enabling upright posture and bipedal locomotion while accommodating the functions of the bladder, bowel, and, in females, the reproductive system. The pelvis is traditionally divided into two regions: the greater or false pelvis, which lies above the pelvic brim, and the lesser or true pelvis, which lies below and forms the birth canal in females. The pelvic floor, a muscular diaphragm spanning the pelvic outlet, provides support for pelvic viscera and contributes to continence and posture. The structure is built from a set of bones, joints, ligaments, nerves, and vessels that work in concert to keep weight-bearing, movement, and organ function aligned.

Anatomy and components are often described at multiple levels—from the bony framework to the soft-tissue supports and the contained organs. The pelvic girdle consists of paired hip bones, each formed by fusion of the ilium, ischium, and pubis, articulating with the sacrum at the sacroiliac joint. The two hip bones contribute to the ring that encircles the pelvic cavity. The acetabulum, a socket on each hip bone, accepts the head of the femur, forming the hip joint. The posterior boundary is formed by the sacrum and coccyx. This bony ring encloses the pelvic cavity, which contains organs and structures essential to urinary, digestive, and reproductive functions. See the detailed sections below for the relationships between these parts and their clinical significance.

Anatomy overview

The pelvis comprises bones, joints, ligaments, muscles, nerves, and vessels that together create a strong, load-bearing ring. The left and right pelvic bones each include the three main components: the ilium, the ischium, and the pubis. See ilium, ischium, and pubis for the main subunits; these three elements fuse in adulthood to form each hip bone. The acetabulum is the hip socket formed where the pubis, ischium, and ilium meet, and it articulates with the femoral head to create the hip joint. The sacrum and coccyx complete the posterior portion of the ring. See sacrum and coccyx for the central axial elements.
The pelvis is divided by the pelvic brim into two regions: the greater pelvis (above) and the lesser pelvis (below). The boundary between them is a key landmark for obstetric and surgical planning; it is sometimes discussed in terms of its diameters, such as the obstetric conjugate. See pelvic brim and pelvic inlet for related concepts.
Joints at the back of the pelvis include the two sacroiliac joints and the anterior pubic symphysis that unite the two hip bones. The sacroiliac joints transmit axial loads between the spine and the lower limbs, while the pubic symphysis allows slight movement to accommodate childbirth and gait. See sacroiliac joint and pubic symphysis.
The pelvic ring is reinforced by ligaments such as the sacrotuberous ligament and the sacrospinous ligament, which help stabilize the sacrum and coccyx and shape the pelvic outlet. See sacrotuberous ligament and sacrospinous ligament.
The pelvic cavity houses pelvic organs and is lined by peritoneum in many regions. In females, the uterus, ovaries, fallopian tubes, and related structures are contained within; in males, the bladder and portions of the reproductive tract are situated within proximity to the pelvis. See uterus, ovaries, fallopian tubes, prostate, and bladder for organ specifics.
The pelvic floor forms the pelvic diaphragm, a muscular shelf that supports pelvic viscera and resists intra-abdominal pressure. The principal muscles belong to the levator ani group (including the pubococcygeus, puborectalis, and iliococcygeus) and the coccygeus. See pelvic floor, levator ani, and coccygeus.
Innervation and blood supply reflect the pelvis’s dual role in locomotion and autonomic function. The nerves of the lumbosacral plexus, including the pudendal nerve, provide motor and sensory input for the pelvic organs and perineum. The internal iliac artery and its branches supply pelvic viscera and walls. See pudendal nerve and lumbosacral plexus; see internal iliac artery.
The pelvic organs, pelvic muscles, and the supporting ligaments collectively contribute to continence, reproduction, and core stability. The bladder, rectum, and, in females, the uterus and cervix sit within or adjacent to the pelvic cavity; in males, the prostate and seminal vesicles reside in close proximity. See bladder, rectum, uterus, cervix, prostate, and seminal vesicles for organ-level detail.

Pelvic bones and landmarks

Hip bones: Each hip bone is a fusion of the ilium, ischium, and pubis. These three components form the acetabulum, the socket for the femoral head, and contribute to the anterior and lateral aspects of the pelvis. See ilium, ischium, and pubis.
Iliac features: The iliac crest marks the superior border of the ilium and serves as an important attachment site for abdominal and thigh muscles. The anterior superior iliac spine (ASIS) is a notable landmark used in clinical assessment and imaging references.
Pelvic ring and outlets: The pelvic brim differentiates the true pelvis from the false pelvis, and the pelvic outlet is bounded by the pubic arch, ischiopubic rami, sacrotuberous ligament, and coccyx. See pelvic brim and pelvic outlet.
Obturator foramen: A large opening in the hip bone closed by a membrane and covered by soft tissues; it transmits nerves and vessels to the thigh. See obturator foramen.

Pelvic joints and ligaments

Sacroiliac joints: These joints link the sacrum to the iliac bones and transfer load between the spine and pelvis. They are reinforced by strong ligaments and are subject to age-related and activity-related changes. See sacroiliac joint.
Pubic symphysis: A cartilaginous joint at the front of the pelvis that provides limited movement and contributes to pelvic stability. See pubic symphysis.
Pelvic ligaments: The sacrospinous and sacrotuberous ligaments shape the pelvic outlet and stabilize the sacrum. See sacrospinous ligament and sacrotuberous ligament.

Pelvic organs and the pelvic floor

Pelvic organs: The bladder sits anteriorly to the reproductive tract, while the rectum lies posteriorly. In females, the uterus, ovaries, and fallopian tubes occupy the pelvic cavity; in males, the prostate and seminal vesicles are present in the pelvic region. See bladder, rectum, uterus, ovaries, fallopian tubes, prostate, and seminal vesicles.
Pelvic floor: The pelvic diaphragm, comprising the levator ani group (including the pubococcygeus, puborectalis, and iliococcygeus) and the coccygeus, forms a muscular sling that supports pelvic viscera and resists intra-abdominal pressure during coughing, lifting, and childbirth. See pelvic floor and levator ani.
Perineal region: The region at the outlet of the pelvis includes nerves, vessels, and muscular structures that contribute to continence and sexual function.

Muscular and neural support

Pelvic floor muscles: The levator ani group provides the majority of support to the pelvic viscera, while the coccygeus adds posterior support. These muscles help maintain continence and stabilize the pelvic ring during movement. See levator ani and coccygeus.
Nerves and vessels: The lumbosacral plexus gives rise to nerves that innervate pelvic muscles and organs, including the pudendal nerve, which carries motor and sensory information to the perineum. Vascular supply largely comes from the internal iliac artery and its branches, meeting the demands of pelvic organs and walls. See pudendal nerve and lumbosacral plexus; see internal iliac artery.

Variation, development, and evolution

Sex-based differences: The pelvis shows notable sexual dimorphism, with generally broader pelvic inlet shapes and wider subpubic angles in females, reflecting obstetric function. The degree of variation, however, is influenced by genetics, nutrition, and lifestyle. See sexual dimorphism and pelvic morphology.
Population and adaptation: Across populations, pelvic dimensions vary, reflecting evolutionary pressures for locomotion and reproduction. These differences have been discussed in anthropological and clinical literature, with emphasis on functional constraints rather than simplistic racial categorizations. See anthropology.
Aging and pathology: With age or disease, bone density and joint stability can change, affecting the pelvis’s capacity to bear load or withstand stress. Conditions such as osteoporosis can influence pelvic integrity and fracture risk. See osteoporosis and pelvic fracture.

Clinical relevance and controversies

Obstetric implications: The size and shape of the pelvis can influence childbirth and obstetric outcomes. Clinicians assess pelvic dimensions to anticipate delivery challenges and to plan interventions when necessary. See obstetric conjugate and diagonal conjugate for related measurements.
Injury and repair: Pelvic fractures and sacroiliac dysfunction are clinically significant due to their impact on mobility and organ function. Treatment requires careful consideration of weight-bearing, stability, and the surrounding neurovascular structures. See pelvic fracture and sacroiliac joint.
Controversies and debates: In discussions about pelvic anatomy, some contemporary critiques emphasize that biology interacts with environment, culture, and social factors in shaping health outcomes. A traditional view stresses observable, measurable relations between structure and function (for example, how pelvic dimensions relate to childbirth and gait). Critics of “biological determinism” argue for broader accounts of how social factors influence health, while proponents of anatomically grounded explanations maintain that functional constraints are real and relevant for clinical practice. Proponents of a biologically informed view might contend that measurable differences in pelvic dimensions can reflect genuine, practical differences in obstetric risk and hip biomechanics. See obstetric conjugate and pelvic fracture for clinical examples; for methodological debates, see evidence-based medicine and biomedical ethics.