ILIUM

 

The Ilium or the flank forms the upper extended plate-like part of the hip bone. It has upper and lower parts and three surfaces. The upper end is called the iliac crest which forms the two-fifths of the acetabulum and the lower end which is smaller than upper end is fused with pubis and ischium at the acetabulum. The upper part is much expanded, and has gluteal, sacropelvic and iliac (internal) surfaces. The posterolateral gluteal surface is an extensive rough area; the anteromedial iliac fossa is smooth and concave; and the sacropelvic surface is medial and posteroinferior to the fossa, from which it is separated by the medial border.

Ilium

Ilium

 

Iliac crest

The iliac crest is the superior border of the ilium. It is broad and convex upwards but sinuous from side to side, being internally concave in front and convex behind. Its ends project as anterior and posterior superior iliac spines. The anterior superior iliac spine is palpable at the lateral end of the inguinal fold; the lateral end of the inguinal ligament is attached to the anterior superior iliac spine. The posterior superior iliac spine is not palpable but is often indicated by a dimple, approximately 4 cm lateral to the second sacral spinous process, above the medial gluteal region.

The iliac crest has ventral and dorsal segments. The ventral segment occupies slightly more than the anterior two-thirds of the iliac crest. It has internal and external lips and a rough intermediate zone that is narrowest centrally. The dorsal segment, which occupies approximately the posterior 1/3^rd in humans. It has two sloping surfaces separated by a longitudinal ridge ending at the posterior superior spine. The tubercle of the iliac crest projects outwards from the outer lip approximately 5 cm posterosuperior to the anterior superior spine. The summit of the iliac crest, a little behind its midpoint, is level with the 4^th lumbar vertebral body in adults and with the 5^th lumbar vertebral body in children aged 10 years or less.

Anterior border

The anterior border descends to the acetabulum from the anterior superior spine. Superiorly it is concave forwards. Inferiorly, immediately above the acetabulum, is a rough anterior inferior iliac spine, which is divided indistinctly into an upper area for the straight head of rectus femoris and a lower area extending laterally along the upper acetabular margin to form a triangular impression for the proximal end of the iliofemoral ligament.

Posterior border

The posterior border is irregularly curved and descends from the posterior superior spine, at first forwards, with a posterior concavity forming a small notch. At the lower end of the notch is a wide, low projection known as the posterior inferior iliac spine. Here the border turns almost horizontally forwards for approximately 3 cm, then down and back to join the posterior ischial border. Together these borders form a deep notch, the greater sciatic notch, which is bounded above by the ilium and below by the ilium and ischium. The upper fibres of the sacrotuberous ligament are attached to the upper part of the posterior border. The superior rim of the notch is related to the superior gluteal vessels and nerve. The lower margin of the greater sciatic notch is covered by piriformis and is related to the sciatic nerve.

Medial border

The medial border separates the iliac fossa and the sacropelvic surface. It is indistinct near the crest, rough in its upper part, then sharp where it bounds an articular surface for the sacrum and finally rounded. The latter part is the arcuate line, which inferiorly reaches the posterior part of the iliopubic ramus, marking the union of the ilium and pubis.

• Gluteal surface

Gluteal surface is the outer surface of the ilium, which is convex in front and concave behind, like the iliac crest. It is rough and curved, convex in front, concave behind, and marked by three gluteal lines which divides into four areas. The posterior gluteal line is shortest, descending from the external lip of the crest approximately 5 cm in front of its posterior limit and ending in front of the posterior inferior iliac spine. Above, it is usually distinct, but inferiorly it is poorly defined and frequently absent. The anterior gluteal line, the longest, begins near the midpoint of the superior margin of the greater sciatic notch and ascends forwards into the outer lip of the crest, a little anterior to its tubercle. The inferior gluteal line, seldom well marked, begins posterosuperior to the anterior inferior iliac spine, curving posteroinferiorly to end near the apex of the greater sciatic notch. Between the inferior gluteal line and the acetabular margin is a rough, shallow groove. Behind the acetabulum, the lower gluteal surface is continuous with the posterior ischial surface.

The articular capsule is attached to an area adjoining the acetabular margin, most of which is covered by gluteus minimus. Posteroinferiorly, near the union of the ilium and ischium, the bone is related to piriformis.

• Iliac fossa

The iliac fossa, the internal concavity of the ilium, faces anterosuperiorly. It is limited above by the iliac crest, in front by the anterior border and behind by the medial border, separating it from the sacropelvic surface. It forms the smooth and gently concave posterolateral wall of the greater pelvis. Below it is continuous with a wide shallow groove, bounded laterally by the anterior inferior iliac spine and medially by the iliopubic ramus.

• Sacropelvic surface

The sacropelvic surface, the posteroinferior part of the medial iliac surface, is bounded posteroinferiorly by the posterior border, anterosuperiorly by the medial border, posterosuperiorly by the iliac crest and anteroinferiorly by the line of fusion of the ilium and ischium. It is divided into iliac tuberosity and auricular & pelvic surfaces. The iliac tuberosity, a large, rough area below the dorsal segment of the iliac crest, shows cranial and caudal areas separated by an oblique ridge and connected to the sacrum by the interosseous sacroiliac ligament. The sacropelvic surface gives attachment to the posterior sacroiliac ligaments and, behind the auricular surface, to the interosseous sacroiliac ligament. The iliolumbar ligament is attached to its anterior part. The auricular surface, immediately anteroinferior to the tuberosity, articulates with the lateral sacral mass. Shaped like an ear, its widest part is anterosuperior, and its ‘lobule’ posteroinferior and on the medial aspect of the posterior inferior spine. Its edges are well defined but the surface, though articular, is rough and irregular. It articulates with the sacrum and is reciprocally shaped. The anterior sacroiliac ligament is attached to its sharp anterior and inferior borders. The narrow part of the pelvic surface, between the auricular surface and the upper rim of the greater sciatic notch, often shows a rough pre-auricular sulcus (that is usually better defined in females) for the lower fibres of the anterior sacroiliac ligament. The pelvic surface is anteroinferior to the acutely curved part of the auricular surface, and contributes to the lateral wall of the lesser pelvis. Its upper part, facing down, is between the auricular surface and the upper limb of the greater sciatic notch. Its lower part faces medially and is separated from the iliac fossa by the arcuate line. Anteroinferiorly, it extends to the line of union between the ilium and ischium. Though usually obliterated, it passes from the depth of the acetabulum to approximately the middle of the inferior limb of the greater sciatic notch.

Muscle attachments

The attachment of sartorius extends down the anterior border below the anterior superior iliac spine.

The iliac crest gives attachment to the anterolateral and dorsal abdominal muscles, and to the fasciae and muscles of the lower limb.

The fascia lata and iliotibial tract are attached to the outer lip and tubercle of its ventral segment.

Tensor fasciae latae is attached anterior to the tubercle. The lower fibres of external oblique and, just behind the summit of the crest, the lowest fibres of latissimus dorsi are attached to its anterior two-thirds. A variable interval exists between the most posterior attachment of external oblique and the most anterior attachment of latissimus dorsi, and here the crest forms the base of the lumbar triangle through which herniation of abdominal contents may rarely occur.

Internal oblique is attached to the intermediate area of the crest.

Transversus abdominis is attached to the anterior two-thirds of the inner lip of the crest, and behind this to the thoracolumbar fascia and quadratus lumborum. The highest fibres of gluteus maximus are attached to the dorsal segment of the crest on its lateral slope.

Erector spinae arises from the medial slope of the dorsal segment.

The straight head of rectus femoris is attached to the upper area of the anterior inferior spine.

Some fibres of piriformis are attached in front of the posterior inferior spine on the upper border of the greater sciatic foramen.

The gluteal surface is divided by three gluteal lines into four areas. Behind the posterior line, the upper rough part gives attachment to the upper fibres of gluteus maximus and the lower, smooth region to part of the sacrotuberous ligament and iliac head of piriformis. Gluteus medius is attached between the posterior and anterior lines, below the iliac crest, and gluteus minimus is attached between the anterior and inferior lines.

The fourth area, below the inferior line, contains vascular foramina. The reflected head of rectus femoris attaches to a curved groove above the acetabulum.

Iliacus is attached to the upper two-thirds of the iliac fossa and is related to its lower one-third. The medial part of quadratus lumborum is attached to the anterior part of the sacropelvic surface, above the iliolumbar ligament.

Piriformis is sometimes partly attached lateral to the pre-auricular sulcus, and part of obturator internus is attached to the more extensive remainder of the pelvic surface.

Vascular supply Branches of the iliolumbar artery run between iliacus and the ilium; one or more enter large nutrient foramina lying posteroinferiorly in the iliac fossa. The superior gluteal, obturator and superficial circumflex iliac arteries contribute to the periosteal supply. The obturator artery may supply a nutrient branch. Vascular foramina on the ilium underlying the gluteal muscles may lead into large vascular canals in the bone. Innervation The periosteum is innervated by branches of nerves that supply muscles attached to the bone, the hip joint and the sacroiliac joint.

OSSIFICATION

Ossification is by three primary centers: one each for the ilium, ischium and pubis. The iliac centre appears above the greater sciatic notch prenatally at about the 9^th week and the pubic centre in its superior ramus between the 4^th and 5^th months. The pubis is often not recovered from prenatal remains due to its size and fragility and because it is the last of the hip bones to begin ossification (Scheuer and Black 2004). At birth the whole iliac crest, the acetabular floor and the inferior margin are cartilaginous. Gradual ossification of the three components of the acetabulum results in a triradiate cartilaginous stem extending medially to the pelvic surface as a Y-shaped epiphysial plate between the ilium, ischium and pubis, and including the anterior inferior iliac spine. Cartilage along the inferior margin also covers the ischial tuberosity, forms conjoined ischial and pubic rami and continues to the pubic symphysial surface and along the pubic crest to the pubic tubercle. The ossifying ischium and pubis fuse to form a continuous ischiopubic ramus at the 7^th or 8^th year. 

Secondary centres, other than for the acetabulum, appear at about puberty and fuse between the 15^th and 25^th years. There are usually two for the iliac crest (which fuse early), and single centres for anterior inferior iliac spine (although it may ossify from the triradiate cartilage) and symphysial surface of the pubis (the pubic tubercle and crest may have separate centres). Progression of ossification of the iliac crest in girls is an index of skeletal maturity and is useful in determining the optimal timing of surgery for spinal deformity. Between the ages of 8 and 9 years, three major centres of ossification appear in the acetabular cartilage. The largest appears in the anterior wall of the acetabulum and fuses with the pubis, the second in the iliac acetabular cartilage superiorly, fusing with the ilium, and the third in the ischial acetabular cartilage posteriorly, fusing with the ischium. At puberty, these epiphyses expand towards the periphery of the acetabulum and contribute to its depth. Fusion between the three bones within the acetabulum occurs between the sixteenth and eighteenth years. Delaere et al have suggested that ossification of the ilium is similar to that of a long bone, possessing three cartilaginous epiphyses and one cartilaginous process, although it tends to undergo osteoclastic resorption comparable with that of cranial bones. During development, the acetabulum increases in breadth at a faster rate than it does in depth. Avulsion fractures of pelvic apophyses may occur from excessive pull on tendons, usually in athletic adolescents. The most frequent examples of such injuries are those to the ischial tuberosity (hamstrings) and anterior inferior iliac spine (rectus femoris).

Complied & written by Dr. Palak Shah.

 

ULNA

The ulna is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. It runs parallel to the radius, the other long bone in the forearm. The ulna is usually slightly longer than the radius, but the radius is thicker.

The ulna has a bony process, the olecranon process, a hook-like structure that fits into the olecranon fossa of the humerus. This prevents hyperextension and forms a hinge joint with the trochlea of the humerus. There is also a radial notch for the head of the radius, and the ulnar tuberosity to which muscles attach.

The long, narrow medullary cavity of the ulna is enclosed in a strong wall of cortical tissue which is thickest along the interosseous border and dorsal surface. At the extremities the compact layer thins. The compact layer is continued onto the back of the olecranon as a plate of close spongy bone with lamella parallel. From the inner surface of this plate and the compact layer below its trabecula arch forward toward the olecranon and coronoid and cross other trabecula, passing backward over the medullary cavity from the upper part of the shaft below the coronoid. Below the coronoid process there is a small area of compact bone from which trabecula curve upward to end obliquely to the surface of the semilunar notch which is coated with a thin layer of compact bone. The trabecula at the lower end has a more longitudinal direction.

The ulna has an upper end, shaft and a lower end.

GENERAL FEATURES

Upper End

It presents the olecranon and coronoid processes and the trochlear and radial notches.

1. Olecranon process projects upwards from the shaft. It has 5 surfaces. Anterior surface is articular which forms the upper part of the trochlear notch. Posterior surface forms a triangular subcutaneous area which is separated from the skin by bursa. Inferiorly it is continuous with the posterior border of the shaft of the ulna and upper part forms the point of the elbow. Medial surface is continuous inferiorly with the medial surface of the shaft. Lateral surface is smooth and Superior surface in its posterior part shows a roughened area.

2. Coronoid process projects forwards from the shaft just below the olecranon and has 4 surfaces. Superior surface forms the lower part of the trochlear notch. Anterior surface is triangular and rough & its lower corner forms the ulnar tuberosity. Lateral surface upper part is marked by radial notch for the head the radius. Annular ligament is attached to the anterior and posterior margins of the notch. Lower part forms a depressed area to accommodate the radial tuberosity. It is limited behind by a ridge called supinator crest. Medial surface is continuous with the medial surface of the shaft.

3. Trochlear notch forms an articular surface which articulates with trochlea of the humerus to form the elbow joint.

4. Radial notch articulates with the head of the radius to form the superior radioulnar joint.

Shaft

The shaft of the Ulna at its upper part is prismatic in form and curved so as to be convex behind and lateralward; its central part is straight; its lower part is rounded, smooth, and bent a little lateralward. It tapers gradually from above downward and has three borders and three surfaces.

Borders

1.The interosseous or lateral border is sharpest in its middle two-fourths. Inferiorly, it can be traced to the lateral side of the head. Superiorly, it is continuous with the supinator crest.

2.The anterior border is thick and rounded. It begins above on the medial side of the ulnar tuberosity, passes backwards in its lower one-third, and terminates at the medial side of the styloid process.

3.The posterior border is subcutaneous. It begins, above, at the apex of the triangular subcutaneous area at the back of the olecranon and terminates at the base of the styloid process.

Surfaces

1.The anterior surface lies between the anterior and interosseous borders. A nutrient foramen is seen on the upper part of this surface. It is directed upwards. The nutrient artery is derived from the anterior interosseous artery.

2.The medial surface lies between the anterior and posterior borders.

3.The posterior surface lies between the posterior and interosseous borders. It is subdivided into three areas by two lines. An oblique line divides it into upper and lower parts. The lower part is further divided by a vertical line into a medial and a lateral area.

Lower End 

The lower end of the ulna presents an articular surface, part of which, of an oval or semilunar form, is directed downward, and articulates with the upper surface of the triangular articular disc which separates it from the wrist-joint; the remaining portion, directed lateralward, is narrow, convex, and received into the ulnar notch of the radius.

Near the wrist, the ulnar, with two eminences; the lateral and larger is a rounded, articular eminence, termed the head of the ulna; the medial, narrower and more projecting, is a non-articular eminence, the styloid process.

The head presents an articular surface, part of which, of an oval or semilunar form, is directed downward, and articulates with the upper surface of the triangular articular disk which separates it from the wrist-joint; the remaining portion, directed lateralward, is narrow, convex, and received into the ulnar notch of the radius. 

The styloid process projects from the medial and back part of the bone; it descends a little lower than the head, and its rounded end affords attachment to the ulnar collateral ligament of the wrist joint.

The head is separated from the styloid process by a depression for the attachment of the apex of the triangular articular disk, and behind, by a shallow groove for the tendon of the extensor carpi ulnaris.

PARTICULAR FEATURES:

MUSCLES

The ulna serves as the attachment site for numerous muscles with a myriad of actions. The following are organized in terms of the direction and where on the ulna is the attachment of the muscle’s fibers.

The following muscles insert into the ulna:

Triceps brachii – posterior section of the superior surface of the olecranon Anconeus – olecranon Brachialis – the volar surface of the coronoid process

The following muscles originate from the ulna:

• Pronator teres – the medial surface of the coronoid process
• Flexor carpi ulnaris – olecranon process
• Flexor digitorum superficialis – coronoid process
• Flexor digitorum profundus – anteromedial surface
• Pronator quadratus – distal anterior shaft
• Extensor carpi ulnaris – posterior border
• Supinator – proximal ulna
• Abductor pollicis longus – posterior surface
• Extensor pollicis longus – dorsal shaft
• Extensor indicis – posterior distal shaft
  

Blood vessels and Lymphatics

The main blood supply of the ulna originates from the ulnar artery or the ulnar recurrent artery. The ulnar artery then branches into a common interosseous artery that then further subdivides into the posterior and anterior interosseous vessels. These vessels are vital for the nutrients of the ulnar diaphysis. The ulnar metaphysis is supplied by the end branches of the anterior interosseous artery, while the head of the ulna receives its supply from small divisions off of the ulnar artery proper.

The lymphatics of the ulna drain either to the supratrochlear lymph node or directly travel to the adjacent cluster of axillary lymph nodes.

Nerves

Three main nerves run in the forearm in the proximity of the ulna: the median, ulnar, and radial nerves. The median nerve runs anterolaterally and innervates the muscles responsible for flexion of the wrist and the fingers (digits 1 to 3 and radial aspect of the fourth). The ulnar nerve is positioned more anteromedially, running in between the flexor digitorum superficialis and flexor digitorum profundus. This nerve is also involved in flexion of the wrist and fingers (the ulnar aspect of 4th and all of the 5th) but also is responsible for spanning the fingers. A major branch of the median nerve is the anterior interosseous nerve. Impingement or entrapment of the anterior interosseous nerve results in the characteristic clinical finding of weakness related to the "pincer" movement. The radial nerve extends posteriorly to the ulna and the radius and is the sole nerve involved in the muscles responsible for extension of the forearm, wrist, and fingers.  The posterior interosseous nerve is a branch of the radial nerve with both motor and sensory functions. Posterior interosseous nerve impingement or entrapment occurs in the region of the radial tunnel resulting in weakness related to the extension of the digits.

EMBRYOLOGY AND OSSIFICATION

The ulna develops from the induction of the lateral plate mesoderm. From this, it differentiates into the somatic mesoderm, which, in turn, gives rise to all of the bones, ligaments, connective tissue, and blood vessels of the extremities. Endochondral ossification allows for the induction of bone from previously laid hyaline cartilage. The ulna itself is ossified in three sections. First, it commences at the body of the ulna. Around week eight of gestation, the chondrocytes in the middle of the ulna lay down collagen and fibronectin to appropriately calcify the bone template. At the time of birth, the ends of the bone are still cartilaginous and not ossified. Around age four, an ossification center arises in the middle of the ulnar head and then encompasses into the styloid process. At age ten, a subsequent center appears in the olecranon, which is then met by the growth of the epiphysis at approximately age sixteen. The ossification centers about the elbow occur in a predictable order and understanding/knowledge of these stages of development is essential for identifying traumatic injuries about the elbow

CLAVICLE

The clavicle is a sigmoid-shaped long bone with a convex surface along its medial end when observed from cephalad position. It connects axial and appendicular skeleton. It supports shoulder so that arm can swing clearly away from the trunk. Clavicle transmits weight of the limb to the sternum. 

 It receives its name from the Latin clavicula ("little key"), because the bone rotates along its axis like a key when the shoulder is abducted. Clavicle has a shaft and two ends.

SHAFT

The shaft is further divided in lateral one-third & medial two-thirds. 

Lateral one-third: It is flattened from above downwards. It has 2 borders and 2 surfaces.

The anterior border is concave forwards which gives origin to Deltoid muscle and Posterior border is convex backwards which gives origin to Trapezius muscle.

The superior surface is subcutaneous and the inferior surface has a ridge called the trapezoid line and a tubercle; the conoid tubercle for attachment with the trapezoid and the conoid ligament, part of the coracoclavicular ligament that serves to connect the collarbone with the coracoid process of the scapula.

Medial two-thirds: It is rounded and said to have 4 surfaces. The Anterior is convex forwards, Posterior has smooth surface, Superior surface is rough in medial part and & Inferior surface has a rough oval impression at the medial end.The lateral half of this surface has a longitudinal subclavian groove in which nutrient foraman lies.

LATERAL END & MEDIAL END

The lateral end is also known as the acromial end. It is flat from above downward. It bears a facet that articulates with the shoulder to form the acromioclavicular joint. The area surrounding the joint gives an attachment to the joint capsule. The anterior border is concave forward and posterior border is convex backward.

It is also known as the sternal end. The medial end is quadrangular and articulates with the clavicular notch of the manubrium of the sternum to form the sternoclavicular joint. The articular surface extends to the inferior aspect for articulation with the first costal cartilage.

Right clavicle - Superior aspect

      Right Clavicle - Inferior aspect

SIDE DETERMINATION

The side to which a clavicle belongs can be determined from the following characters:

1. The lateral end is flat, and the medial end is large and quadrilateral.

2. The shaft is slightly curved, so that it is convex forwards in its medial two-thirds, and concave forwards in its lateral one-third.

3. The inferior surface is grooved longitudinally in its middle one-third.

SEX DETERMINATION

1. In females, the clavicle is shorter, lighter, thinner, smoother, and less curved than in males.

2. The midshaft circumference and the weight of the clavicle are reliable criteria for sexing the clavicle.

3. In females, the lateral end of the clavicle is a little below the medial end; in males, the lateral end is either at the same level or slightly higher than the medial end.

DEVELOPMENT AND OSSIFICATION

The collarbone is the first bone to begin the process of ossification (laying down of minerals onto a preformed matrix) during development of the embryo, during the fifth and sixth weeks of gestation. However, it is one of the last bones to finish ossification at about 21–25 years of age. Its lateral end is formed by intramembranous ossification while medially it is formed by endochondral ossification. It consists of a mass of cancellous bone surrounded by a compact bone shell. The cancellous bone forms via two ossification centres, one medial and one lateral, which fuse later on. The compact forms as the layer of fascia covering the bone stimulates the ossification of adjacent tissue. The resulting compact bone is known as a periosteal collar.

Even though it is classified as a long bone, the collarbone has no medullary (bone marrow) cavity like other long bones, though this is not always true. It is made up of spongy cancellous bone with a shell of compact bone. It is a dermal bone derived from elements originally attached to the skull.

MUSCLES AND LIGAMENTS ATTACHMENT

   1.At the lateral end the margin of the articular surface for the acromioclavicular joint gives attachment to the joint capsule.

   2.At the medial end the margin of the articular surface for the sternum gives attachment to:

(a) the fibrous capsule all round

(b) the articular disc posterosuperiorly

(c) the interclavicular ligament superiorly.

   3.Lateral one-third of shaft

(a)The anterior border gives origin to the deltoid.

(b)The posterior border provides insertion to the trapezius.

(c) The conoid tubercle and trapezoid ridge give attachment to the conoid and trapezoid parts of the coracoclavicular ligament.

   4. Medial two-thirds of the shaft

(a)The anterior surface gives origin to the pectoralis major.

(b)The rough superior surface gives origin to the clavicular head of the stemocleidomastoid.

(c)The oval impression on the inferior surface at the medial end gives attachment to the costoclavicular ligament.

(d)The subclavian groove gives insertion to the subclavius muscle. The margins of the groove give attachment to the clavipectoral fascia.

The nutrient foramen transmits a branch of the suprascapular artery.