(2) A prominent longitudinal ridge or crest, the linea aspera, presenting an
inner and an outer lip, mark the posterior surface of the shaft. The inferior or lower
extremity presents two condyles, the lateral and medial, and the patellar facet. The
condyles are separated on the posterior surface by the intercondylar fossa. Each
condyle is surmounted by an elevation, the lateral and medial epicondyles. Above the
condyles and the intercondylar fossa on the posterior aspect is a triangular area called
the popliteal surface.
b. The Patella. The patella, or kneecap, is a sesamoid bone developed in the
extensor tendon of the knee and is situated on the front of the knee joint. It is
somewhat triangular in shape, with its pointed apex directed inferiorly, and its broad
base superiorly. The posterior surface presents a smooth, oval, articular surface for
articulation with the patellar surface and the condyles of the femur. The anterior surface
is convex and rough. The knee joint is shown in figure 1-13.
2-13. THE PELVIC GIRDLE OR PELVIS
a. General. The pelvic girdle (figure 2-14), or pelvis, is a complete bony girdle
made up of the two os coxae bones laterally and in front, and the sacrum and coccyx
behind. The two os coxae bones are joined anteriorly at the symphysis pubis.
Posteriorly, the iliac portions of the os coxae are joined to the sacrum at the sacroiliac
joints. The pelvis is divided by an oblique plane, which passes through the prominence
of the sacrum (sacral promontory), the arcuate lines, and the superior plane of the pubic
or pubes bones. Above this plane is the greater (false) pelvis, and below is the lesser
(true) pelvis. The circumference of this plane is termed the pelvic brim or ring. The
interior diameter of the female true pelvis is important in prenatal pelvimetry.
b. The Os Coxa. The os coxa consists of three parts: the ilium, ischium, and
pubic (figures 2-15 and 2-16). These are three separate, distinct bones in the young
subject, but are fused and consolidated in the adult. The bodies of these three portions
meet and unite in and around a large cup-shaped socket, the acetabulum (figure 2-16),
which is situated near the middle of the lateral surface of the bone. The ilium, or flank
bone, is the upper expanded portion of the bone and its body forms the upper two-fifths
of the acetabulum. The ischium forms the lower and back part of the bone; its body also
contributes about two-fifths to the acetabulum. The pubis forms the anterior and inferior
portion of the bone and its body contributes one-fifth to the acetabulum.