The pelvis is the keystone of the skeleton, a link between the weight forces from the trunk and upper body and the ground forces transmitted by the lower body. The structural strength of the pelvis is provided by its substantial osseous components and its relatively rigid ringlike architecture. Trauma to the pelvis requires great force, and fractures here are often associated with serious vascular and visceral complications.
The femur is the largest bone in the body. The proximal ends of the femurs articulate with the pelvic acetabula to form the hip joints. The hip joints have great structural and ligamentous stability yet permit a wide range of motion. The primary function of the hip joints is to transmit ground forces in the erect skeleton, allowing for maintenance of upright posture and ambulation. In radiology, the hip joints are most often evaluated to assess degenerative processes that manifest here as well as the fractures sustained here. Rehabilitation is important in the restoration of functional and ambulatory skills after the hip is compromised.
The pelvis consists of four bones in the adult: two coxal or innominate bones, the sacrum, and the coccyx.1–8 The ilium, ischium, and pubis make up each coxal bone. The fusion of these three components during childhood forms the cup-shaped acetabulum, which accepts the head of the femur to form the hip joint (Figs. 12-1 and 12-2).
Each innominate bone is formed by the fusion of the ilium, ischium, and pubis bones. The cup-shaped acetabulum is formed at the junction of these three components.
The superior portion of each coxal bone is the ilium. The flared, thin upper portion of the ilium is the ala, or wing. The upper margin of the ala is the iliac crest, extending from the anterosuperior iliac spine (ASIS) to the posterosuperior iliac spine (PSIS). Less prominent landmarks include the anteroinferior iliac spine (AIIS), inferior to the anterosuperior iliac spine, and the posteroinferior iliac spine (PIIS), inferior to the posterosuperior iliac spine. The inferior portion of the ilium is the body, which includes the upper two-fifths of the acetabulum.
The ischium is the inferior and posterior portion of each coxal bone. The upper portion of the ischium is the body; it forms the posterior two-fifths of the acetabulum. The lower portion is the ramus, ending caudally at the ischial tuberosity.
The pubis is the inferior ...