Along with the sacrum, the hip bone or the Innominate bone forms a bony ring around the pelvic structures. Each hip bone is formed by the Ilium, the ischium and the pubis, which are fused at the acetabulum anteriorly to form a single bone.
The hip bone articulates with the sacrum, the femur and its opposite counterpart. It is responsible for movements in all three planes and is therefore prone to injury if its supporting structures fail to function well.
Ossification of the hip bone
It is ossified from eight ossification centers: three primary and five secondary centers. The three primary centers – one each for the Ilium, ischium and the pubic bone – unite around a Y- shaped tri-radiate cartilage around puberty. Around this time, secondary centers or epiphyses appear in that cartilage and also in the anterior inferior iliac spine, the iliac crest, ischial tuberosity and the pubic symphysis. These eventually unite about the twenty-fifth year.
Ilium consists of a body and an ala (or wing) which is demarcated internally by the curved arcuate line and externally by the acetabular margin. The body of the Ilium forms the superior two-fifths of the acetabular fossa and fuses with the ischium and the pubis.
The inner surface of the body forms the wall of the lesser pelvis and provides attachment to the obturator internus muscles fibers. The superior border of the body is called the iliac crest and is easily palpable. The anterior superior iliac spine forms the anterior limit of the iliac crest, while the posterior superior iliac spine forms the posterior limit.
The ilioinguinal ligament connects the anterior superior iliac spine to the pubic symphysis and separates the thigh from the anterior abdominal wall. The iliac crest has an outer and an inner lip which provides attachment to several muscles.
The ala of the ilium is an expanded wing-like part with an internal or medial, external or lateral surface, the sacropelvic surface, a crest and an anterior and posterior border. The external or lateral or gluteal surface is concave posteriorly and convex anteriorly. It is bounded by the crest above and by the upper border of the acetabulum below. The external surface has the anterior, posterior and inferior gluteal lines.
The gluteus maximus muscle is attached to a semilunar surface behind the posterior gluteal line; the gluteus medius is attached to the intervening space between the anterior and posterior gluteal lines, while the gluteus minimus is attached to the surface of the bone between the anterior and inferior gluteal lines.
The internal or medial surface has the iliac fossa, which forms a part of the lateral pelvic wall. The sacropelvic surface, posterior to the iliac fossa, has a rough ligamentous area, the iliac tuberosity and the auricular surface which forms the sacro-iliac joint.
The anterior superior iliac spine is the site where the anterior border of the ilium begins, then continues to the anterior inferior spine located superior to the acetabulum and ends at the junction of the ilium and the pubis forming the iliopubic eminence. The posterior border, on the other hand, starts at the posterior superior iliac spine and then continues to form the greater sciatic notch.
This bone forms the postero-inferior aspect of the hip bone. It consists of two rami (the superior and inferior) and a body. The body forms more than two-fifths of the acetabulum and has an internal and an external surface. The internal surface forms a part of the pelvic wall and the obturator internus originates from it.
Along its posterior border, there is a triangular, pointed eminence called the ischial spine, which provides attachment to the gemellus superior, the coccygeus, levator ani and the pelvic fascia. The sacrospinous ligament is attached to the pointed tip of the ischial spine.
Superior to the spine is the greater sciatic notch through which passes the piriformis muscle, the superior and the inferior gluteal vessels, nerves, the sciatic and posterior femoral cutaneous nerves, the internal pudendal vessels and nerve and the nerves to the obturator internus and quadratus femoris.
The lesser sciatic notch lies inferior to the ischial spine and is converted into a foramen by the sacrospinous and sacrotuberous ligaments. It transmits the obturator internus, its nerve and the internal pudendal vessels and nerve.
The gluteus maximus muscle obscures the ischial tuberosity on hip extension, but the tuberosity is palpable when the thigh is flexed. The two rami of the ischium and the pubis form the inferior aspect of the obturator foramen. The external surface of the superior ramus provides attachment to the obturator externus, the quadratus femoris and the adductor magnus.
The internal surface of the superior ramus provides attachment to the transversus perinaei and the ischiocavernosus muscles. The inferior aspect of the superior ramus has the ischial tuberosity which provides attachment to the semimembranosus, the long head of the biceps femoris and the semitendinosus.
The outer surface of the inferior ramus is uneven and provides attachment to the obturator externus and the adductor magnus. The medial border of its inner surface is everted and rough to form the pelvic outlet, and provides attachment to the inferior fascia of the urogenital diaphragm and the deep layer of the superficial perineal fascia.
This forms the anterior part of the hip bone and consists of the body, a superior and an inferior ramus. The body of the pubis forms one fifth of the acetabulum. The bodies of the two sides meet at the pubic symphysis in the median plane. The symphysial surface of the body is covered by cartilage, while the pelvic surface supports the bladder.
The rough femoral surface of the body provides attachment to muscles. The pubic tubercle on the anterior aspect of the body is an important anatomical landmark which can be found 3 cm from the median plane by tracing the tendon of the adductor longus muscle superiorly.
The spermatic cord crosses the pubic tubercle, which is a guide to the superficial inguinal ring, the femoral ring and the saphenous opening. The pectineal line extends from the pubic tubercles along the superior pubic ramus to the iliopubic eminence.
The pubic tubercle and the pectineal line together form a part of the linea terminalis. The superior ramus has a pelvic surface, an obturator surface and the obturator crest on its inferior aspect. The obturator surface has an obturator groove conveying the obturator nerve and vessels. The inferior pubic ramus joins the ischial ramus.
Acetabulum and obturator foramen
Ilium, ischium and pubis together form the acetabulum which forms the socket for the femoral head. Its articular surface is called the lunate surface, while its non-articular surface is called the acetabular fossa. The rim of the acetabulum, that is deficient inferiorly, provides attachment to the acetabular labrum, which deepens the hip socket. The ischium, the pubis and their rami form boundaries of the obturator foramen which is closed by the obturator membrane except at the obturator groove.
This is also known as the thigh bone and is the longest and the strongest bone in the human body. Extremely strong forces are required to cause femur fractures. The femur connects the hip to the knee. It has a body and two extremities. The upper extremity consists of the head, a neck, a greater and a lesser trochanter, while the lower extremity consists of the patellar surface, the medial and the lateral condyle.
The head of the femur articulates with the innominate or hip bone at the acetabulum to form the hip joint. The greater and lesser trochanters are bony projections near the superior aspect of the head. Several hip and groin muscles like the iliopsoas, the gluteus medius and the adductor longus, are attached to the greater and lesser trochanters of the femur.
The body of the femur is cylindrical, convex anteriorly and concave posteriorly. The linea aspera is a longitudinal ridge on its concave posterior aspect.
The lower extremity of the femur has the medial and lateral condyles, which articulate with the tibia to form the knee joint. The intercondylar fossa is a small depression between the two condyles, which provides attachment to the anterior and posterior cruciate ligaments. These ligaments stabilize the knee joint in the anterior-posterior axis. The patellar surface of the femur adjoins the patella.
Tibia or the shin bone is a long bone which forms the knee joint and connects the femur to the ankle bones. The tibia takes part in forming four joints – the knee joint, the ankle joint and the superior and inferior tibiofibular joint. Its parts include its upper extremity, the body and its lower extremity.
The upper extremity of the tibia has the medial and lateral condyle. The superior, flat surfaces of the condyles articulate with the femur to form the weight bearing part of the tibiofemoral or knee joint. The cruciate ligaments and the menisci are attached in the intercondylar area between the two condyles. The patellar ligament is attached to the tibial tuberosity, which is a bony prominence inferior to the condyles.
The body of the tibia is triangular and has three borders. The lower extremity of the tibia is narrower than its upper extremity. It forms the ankle joint along with the fibula and the talus.
This is the thin bone on the lateral aspect of the leg, parallel to the tibia. It stabilizes the ankle. The fibular head articulates with the tibia to form the proximal tibiofibular joint.
The distal tibiofibular joint is formed at the medial malleolus with the tibia and the lower end of the fibula. It also forms the ankle joint with the tibia and the talus. Several muscles are attached to the fibula – the peroneus muscles, the soleus, flexors and extensors of the toes at its distal end, while the biceps femoris is inserted on its head.
The fibula is often a source for bone grafts to reconstruct bone defects in other parts of the body.
The tarsus consists of seven bones: the talus, navicular and the three cuneiforms medially, the calcaneus and the cuboid laterally. In addition, several sesamoid bones may exist e.g. the os trigonum at the posterior aspect of the talus, the os tibiale externum near the navicular tuberosity and the fibular sesamoid.
The talus and the calcaneus start to ossify in fetal life, while the ossification of the cuboid starts immediately after birth. During childhood, epiphyseal centers begin to appear for the calcaneal tuberosity and the talar posterior tubercle.
The talus does not have muscular attachments. It has a superior projection called the trochlea which articulates with the medial malleolus of the tibia and the lateral malleolus of the fibula to form the ankle joint. The talus articulates inferiorly with the calcaneus or the heel bone.
There are several tubercles, of which the lateral tubercle is called the os trigonum. The tarsal sinus is a deep depression inferior to the neck of the talus and above the calcaneus. The talus and the calcaneus together form the posterior aspect of the transverse tarsal joint.
The calcaneus is responsible for transmitting the body weight from the talus to the ground. It has a prominent bony extension medially called the sustentaculum tali, which supports the talus medially. The calcaneal tuberosity provides attachment to the calcaneal tendon posteriorly and to the short muscles of the sole and the plantar aponeurosis inferiorly. On its anterior aspect, the calcaneus articulates with the cuboid.
The cuboid bone articulates with the calcaneus anteriorly, with the fourth and the fifth metatarsals posteriorly and with the lateral cuneiform and occasionally with the navicular laterally. A groove on its inferior surface may be occupied by the fibularis longus.
The navicular bone lies between the talus and the three cuneiform bones. The tuberosity of the navicular bone provides insertion for the tibialis posterior tendon and its posterior aspect forms the medial part of the transverse tarsal joint.
The three wedge shaped cuneiform bones (medial, intermediate and the lateral cuneiform) are located between the navicular bone anteriorly and the first three metatarsals posteriorly. The cuneiforms together form the transverse curvature of the foot.
The metatarsus connects the tarsus to the phalanges. Medial to laterally, the metatarsus are numbered 1 to 5. Each metatarsal bone consists of a base, a shaft and a head and has its own individual feature e.g. the first metatarsal is short and thick, while the fifth metatarsal bone has a palpable lateral tuberosity.
Unlike the metacarpals, the metatarsal bones are thinner and longer. The metatarsal bones articulate with the proximal phalanx of each toe forming the metatarsophalangeal joint. The anterior ball of the foot is formed by the heads of the metatarsal bones.
During fetal life, the shaft of the metatarsal bones begins to ossify. Postnatally, ossification centers for the heads of the metatarsal bones begin to appear. While the first metatarsal may have separate ossification centers for its head and base, the fifth metatarsal may have its own separate ossification center which fails to fuse and can be confused with a fracture.
There are five phalanges: the proximal, middle and the distal. Each phalange consists of a base, a shaft and a head. Often, the great toe (or hallux) and the little toe have two phalanges each, while the others have one each. The joint between two adjacent phalangeal bones is called the interphalangeal joint.
In the little toe, the middle and the distal phalanges are often fused. During fetal life, the phalanges begin to ossify and postnatally ossification centers appear at their bases.
Flexion and extension, internal and external rotation, abduction/adduction and circumduction. Movements are limited compared to those at the shoulder.
This is a synovial joint which permits flexion, extension and some medial and lateral rotation.
The ankle joint is a simple hinge joint and is capable of dorsiflexion, plantar flexion, eversion and inversion.