FEMUR

 

The femur or the thigh bone is the only bone in thigh. It is the longest, heaviest and the strongest human bone. The name of the bone is derived from the Latin word ‘femur’ meaning ‘thigh’. The proximal end of the femur fits into the socket in the pelvis called as hip joint, and the bottom of the femur connects to the tibia and patella to form the knee joint.

The femur length on an average is 26.74% of an individual height.

The proximal end has a pyramid shaped neck attaches the spherical head at the top and the cylindrical shaft at the bottom. There are two prominent bony protrusions, greater and lesser trochanter which attaches muscles that helps in the motion of both hip and knee joints. The angle between neck of the femur and the shaft is known as the inclination angle which is about 128 degrees in an average adult which decreases with the age. In general population without any severe tibiofemoral deformities, the femoral-tibial angle is almost about 175 degrees.

The head of the femur is directed medially upwards and slightly forwards. The shaft is directed obliquely downwards and medially so that the lower surfaces of the two femoral condyles lie in the same horizontal plane.

The femoral length is associated with a striding gait, strength, weight and muscular forces it is required to withstand. The femur supports all the body weight while standing or doing other activities like running, walking, jumping, etc., stability of the gait and is an essential component of the lower kinetic chain. The weight of the upper body rests on the femoral heads. The degree of the femoral obliquity varies between individuals but is greater in women than in men.

The femur is divided into three parts: Proximal, Shaft and Distal.

PROXIMAL FEMUR

The proximal femur contains head, neck, greater trochanter, lesser trochanter, Intertrochanteric line and intertrochanteric crest.

FEMORAL HEAD

It faces antero-supero-medially to articulate with the acetabulum. The head is of a spheroidal shape. Its smoothness is interrupted posteroinferior to its centre by a small, rough fovea which is an ovoid depression. The fovea is connected through the round ligament to the sides of the acetabular notch known as the ligamentum teres. The head of femur articulates with the acetabulum to form a ball and socket joint known as hip joint. The femoral head is intracapsular and is encircled distal to its middle line by the acetabular labrum. The articular margin is distinct except anteriorly, where the articular surface extends to the femoral neck.

NECK

The femoral head narrows considerably to form a cylindrical neck that connects the head with the shaft with an average angle of 127 degrees also known as angle of inclination or neck-shaft angle. The neck is almost 4-5 cm long. The angle of inclination provides movement at the hip joint, allows the limb to swing and also provides a lever for the action of the muscles at the hip joint. The angle is widest at the birth and diminishes gradually until the age of 10 years and is smaller in the females due to wider pelvis. It is strengthened by a thickening of bone called calcar femorale present along the concavity. The neck is laterally rotated with respect to the angle of anteversion which is almost 10-15° and this varies from person to person. The neck is rounded, upper surface is almost horizontal and slightly concave, while the lower surface is straighter, oblique, directed inferolaterally and backwards to the shaft near the lesser trochanter.

The neck has 2 borders and 2 surfaces. The upper border is concave and horizontal which meets the shaft at the greater trochanter. The lower border is straight and oblique which meets the shaft near the lesser trochanter. The anterior surface is flat and meets the shaft at the intertrochanteric line, which is entirely intracapsular. The posterior surface is convex from above downwards and concave from side to side and meets the shaft at the intertrochanteric crest.

GREATER TROCHANTER

The greater trochanter is large, irregular, box shaped apophysis present laterally and posteriorly and is the most lateral prominent of the femur. The highest point of the greater trochanter is higher than the neck of the femur and it reaches the midpoint of the femur. It can be palpated very easily. It has an upper border with an apex which is inturned posterior part of the posterior border. The greater trochanter also has three surfaces: Anterior, Medial and Lateral. The anterior border is rough in the lateral part. The medial surface has a rough impression above and a deep trochanteric fossa below which presents a tubercle. The lateral surface is crossed by an oblique ridge directed downwards and forwards, it is palpable when muscles are relaxed.

LESSER TROCHANTER

The lesser trochanter is a cone shaped extension of the lowest part of the femoral neck. It is smaller than the greater trochanter. It projects from the postero-medial side of the femur. The lesser trochanter is not palpable.

INTERTROCHANTERIC LINE

The intertrochanteric line is a prominent ridge at the junction of the anterior surface of the neck and shaft which descends medially from a tubercle on the upper part of the anterior aspect of the greater trochanter to a point on the lower border of the neck and anteriorly to the lesser tubercle. Distally this line is known as the pectineal line which serves as the anterior attachment of the hip joint capsule.

INTERTROCHANTERIC CREST

The intertrochanteric crest marks as a junction of the posterior surface of the neck with shaft of femur. It is a smooth rounded ridge, which starts above at the posterosuperior angle of the greater trochanter and ends at the lesser trochanter. The rounded elevation, a little above its middle is called as the quadrate tubercle (linea quadrata) which is almost 5cm in length.

SHAFT

The shaft or the body of the femur is large, thick and almost cylindrical in form. It is little broader above than in the center, widest and somewhat flattened from before backward below. It is slightly arched hence it is convex in anterior side and concave in posterior side, where it is strengthened by a prominent longitudinal ridge known as linea aspera which divides proximally and distal as the medial and lateral ridge.

In the upper 1/3^rd of the shaft, two lips of linea aspera diverge to enclose an additional posterior surface. It has 4 borders: Medial, Lateral, Spiral line and Lateral lip of the gluteal tuberosity. It also has 4 surfaces: Anterior, Medial, Lateral and Posterior. The gluteal tuberosity is a broad roughened ridge on the lateral part of the posterior surface.

In the middle 1/3^rd shaft has 3 borders: Medial, Lateral and Posterior & 3 surfaces: Anterior, Medial and Lateral. The medial and lateral borders are rounded and ill-defined, but the posterior border is in the roughened ridge as linea aspera. The medial and lateral surfaces are directed more backwards than towards the sides. Its subjacent compact bone is augmented to withstand compressive forces which are concentrated here by the anterior curvature of the shaft. Nutrient foramina, directed proximally, appear in the linea aspera, varying in number and site, one usually near its proximal end, a second usually near its distal end.

In the lower 1/3^rd of the shaft the two lips of linea aspera diverge as supracondylar lines to accommodate popliteal surface. This part of the shaft also has 4 surfaces: Anterior, Medial, Lateral and Popliteal. Anterior surface is smooth and convex for most of the part. The upper portion of this surface has a roughened area called the patellar fossa. Posterior surface also known as popliteal surface is smooth and concave throughout most of its length. The linea aspera extends upwards from the upper two-thirds of the posterior surface and ends just above the condyles. Medial surface is relatively flat and smooth. Contains the adductor tubercle, a roughened area near the upper part of this surface for attachment of the adductor muscles, which pull the thigh towards the midline. The medial condyle, a rounded bony prominence, forms the lower part of the medial surface. Lateral surface is convex and smoother than the medial surface. The lateral condyle, a rounded bony prominence, forms the lower part of the lateral surface.

DISTAL END

The distal end of the femur is cuboid in form and widely expanded as a bearing surface for the transmission of the weight to the tibia. It has 2 condyles, medial and lateral. Anteriorly, the condyles are merging and continues into the shaft. The condyles are slightly prominent and are separated by a smooth shallow articular depression called patellar surface. Posteriorly, the condyles are separated by a deep intercondylar fossa or intercondylar notch and project beyond the plane of the popliteal surface. The distal end articulates with tibia and patella which forms the knee joint. The articular surface for knee joint is a broad area like an inverted U shape and has 2 surfaces, Tibial and Patellar.

PATELLAR SURFACE

The patellar surface extends anteriorly on both the condyles, especially the lateral then medial. It is transversely concave, vertically convex and grooved for the posterior patellar surface. The anterior border is therefore oblique and runs distally and medially, separated from the tibial surfaces by two small grooves that crosses the condyles obliquely. The lateral groove runs laterally and bit forwards from the front of the intercondylar fossa and expands to form a small triangular depression which rests on the anterior edge of the lateral meniscus when the knee is fully extended. The medial groove is restricted to the medial part of the medial condyle and rests on the anterior edge of the medial meniscus in full knee extension.

TIBIAL SURFACE

The tibial surface is divided by the intercondylar fossa but is anteriorly continuous with the patellar surface and is convex in all the directions. The medial part of the tibial surface is a broad strip on the convex infero-posterior surface of the medial condyle and is gently curved with a medial convexity. The lateral part of the tibial surface is broader and passes slightly back. Both the medial and lateral surfaces have dis-similar antero-posterior curvatures.

MEDIAL CONDYLE

The medial condyle is longer and when femur is held with its body perpendicular projects to a lower level. The condyle is convex medially, has a bulging and is easily palpable. Posterosuperior to the epicondyle there is projection known as the adductor tubercle. This tubercle is an important landmark as an epiphyseal line for the lower end of the femur passes through it. The lateral surface of the condyle is the medial wall of the intercondylar fossa. A curved strip which is 1cm wide and adjoining the medial articular margin, is covered by the synovial membrane and is inside the joint capsule.

LATERAL CONDYLE

The lateral condyle is more prominent and is broader both in its antero-posterior and transverse diameters. The condyle is thicker, stronger and flat laterally and is more in the line of the shaft of femur hence it takes greater part in the transmission of the body weight to the tibia. the popliteal grove just below the epicondyle has a deeper anterior part and a shallower posterior part.

INTERCONDYLAR FOSSA OR NOTCH

The intercondylar fossa separates both the condyles distally and behind. The fossa is intracapsular but moreover extracapsular. The distal border of the patellar surface limits the fossa in front and at back intercondylar line limits the fossa separating from the popliteal surface. Its lateral wall, the medial surface of the lateral condyle, bears a flat posterosuperior impression that spreads to the floor of the fossa near the intercondylar line for the proximal attachment of the anterior cruciate ligament. The medial wall of the fossa, i.e. the lateral surface of the medial condyle, bears a similar larger area, but far more anteriorly, for the proximal attachment of the posterior cruciate ligament. Both impressions are smooth and largely devoid of vascular foramina, whereas the rest of the fossa is rough and pitted by vascular foramina. A bursal recess between the ligaments may ascend to the fossa. The capsular ligament and, laterally, the oblique popliteal ligament are attached to the intercondylar line. The infrapatellar synovial fold is attached to the anterior border of the fossa.

Attachments on the Femur

1. Fovea: Attachment for ligamentum teres.
2. Greater Trochanter:
• Piriformis at apex.
• Gluteus minimus on anterior surface.
• Obturator internus and gemelli on medial surface.
• Obturator externus in trochanteric fossa.
• Gluteus medius on lateral surface; trochanteric bursa behind it.
3. Lesser Trochanter:
• Psoas major on apex and anterior surface.
• Iliacus on base and below.
• Bursa covers posterior surface.
4. Intertrochanteric Line:
• Capsular ligament attachment.
• Iliofemoral ligament upper and lower bands.
• Vastus lateralis and medialis origin from ends of the line.
5. Quadrate Tubercle: Quadratus femoris insertion.
6. Shaft:
• Medial head of gastrocnemius on popliteal surface.
• Vastus intermedius from anterior and lateral surfaces.
• Articularis genu below vastus intermedius.
• Suprapatellar bursa related to lower anterior surface.
• Vastus lateralis from greater trochanter and linea aspera.
• Vastus medialis from intertrochanteric line and linea aspera.
• Gluteus maximus, adductors, and pectineus insertions detailed along linea aspera.
7. Lateral Condyle:
• Fibular collateral ligament attachment.
• Popliteus origin in popliteal groove.
8. Medial Condyle:
• Tibial collateral ligament attachment.
• Adductor tubercle receives adductor magnus insertion.
9. Intercondylar Notch:
• Cruciate ligaments attached to condyles.
• Capsular and oblique popliteal ligament attachments.

Nutrient Artery: From second perforating artery, enters via foramen on linea aspera.

This summary maintains the original description’s essence while being more concise for easier reference.

BLOOD SUPPLY

1. Deep Femoral Artery: Supplies blood to the shaft and distal portion of the femur.

2. Medial and Lateral Circumflex Femoral Arteries: Supplies blood to the head and neck of the bone.

3. Obturator Artery: Supplies blood to the femoral head.

4. Foveal Artery: Supplies blood to the femoral head.

 

OSSIFICATION

The femur, the long bone in your thigh, has distinct growth regions at its ends called epiphyses. These epiphyses are capped with cartilage and separated from the main shaft (diaphysis) by growth plates (physes). Understanding these regions is important for various reasons, including bone development, forensic analysis, and proper imaging techniques.

Structure and Fusion:

• Upper end: There are three epiphyses at the top of the femur:
• The head (capital epiphysis) forms the ball-shaped joint with the hip socket.
• The greater trochanter, a large bony prominence for muscle attachment.
• The lesser trochanter, a smaller ridge on the posterior aspect.
• Lower end: A single epiphysis exists at the lower end of the femur.

These fuse with the shaft at different times: * Upper epiphyses (lesser trochanter, greater trochanter, head): Fuse around 18 years old. * Lower epiphysis: Fuses around 20 years old.

Ossification and Forensic Importance:

The presence of an ossification center (bone formation starting point) in the lower femoral epiphysis of a newborn found dead indicates the child was viable, meaning it could have survived independently outside the womb.

Growth and Development:

• The lower end of the femur is the primary growth region during childhood and adolescence.
• The lower epiphyseal line (growth plate) interestingly passes through the adductor tubercle, a bony bump for muscle attachment.
• In contrast, the upper head epiphysis is entirely cartilaginous in infants and not visible on standard X-rays. Ultrasound is preferred for early visualization.
• The growth plate of the head starts ossifying around 10 years old. Initially, it has a horizontal orientation, incorporating the inferomedial part of the articular surface (joint surface) into the neck region.
• Over time, the medial part of the epiphysis grows down, covering this previously neck-related articular surface. This process transforms the head into a hollow cup shape sitting atop the femoral neck.
• Notably, the epiphyseal line of the head generally follows the articular margin, except for a superior non-articular area allowing blood vessel passage into the head.

Fusion Timeline:

• Lesser trochanter: Fuses shortly after puberty.
• Greater trochanter: Fuses after the lesser trochanter.
• Capital epiphysis (head): Fuses around 14 years in females and 17 years in males.
• Distal epiphysis (lower end): Fuses around 16 years in females and 18 years in males.
• Distal epiphyseal plate: Notably, this growth plate runs through the adductor tubercle.

Ossification Process:

The femur has one primary ossification center in the shaft that appears between the 5th and 7th week of fetal development. Secondary ossification centers then emerge at different times:

• Distal end: 9th month of fetal development
• Head: 6th month after birth
• Greater trochanter: 4th year
• Lesser trochanter: 12th to 14th years

 

RADIUS

The radius or radial bone is one of the two large bones of the forearm, the other being the ulna. It extends from the lateral side of the elbow to the thumb side of the wrist and runs parallel to the ulna. The ulna is usually slightly longer than the radius, but the radius is thicker. Therefore, the radius is considered to be the larger of the two. It is a long bone, prism-shaped and slightly curved longitudinally.

The word radius is Latin for "ray". In the context of the radius bone, a ray can be thought of rotating around an axis line extending diagonally from center of capitulum to the center of distal ulna. While the ulna is the major contributor to the elbow joint, the radius primarily contributes to the wrist joint.

The radius is named so because the radius (bone) acts like the radius (of a circle). It rotates around the ulna and the far end (where it joins to the bones of the hand), known as the styloid process of the radius, is the distance from the ulna (center of the circle) to the edge of the radius (the circle). The ulna acts as the center point to the circle because when the arm is rotated the ulna does not move.

The radius is part of two joints: the elbow and the wrist. At the elbow, it joins with the capitulum of the humerus, and in a separate region, with the ulna at the radial notch. At the wrist, the radius forms a joint with the ulna bone.

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

GENERAL FEATURES 

Upper End

Head is disc shaped and is covered with a Hyaline cartilage. It has a superior concave surface which articulates with the capitulum of the humerus at the elbow joint. The circumference of the head is smooth; it is broad medially where it articulates with the radial notch of the ulna, narrow in the rest of its extent and then embraced by the annular ligament thus forming a superior radioulnar joint which provides supination and pronation movement.

Neck is enclosed by the narrow lower margin of the annular ligament. The head and neck are free from capsular attachment and can rotate freely with the socket

Tuberosity lies just below the medial part of the neck. It has a rough posterior and a smooth anterior part.

Shaft

The shaft of radius is prismoid in form, narrower above than below, and slightly curved, so as to be convex lateralward. It presents three borders and three surfaces.

Borders 

1. Anterior or Volar border extends from the lower part of the tuberosity above to the anterior part of the base of the styloid process below and separates the volar from the lateral surface. It is oblique in the upper half of the shaft and vertical in the lower half. The oblique part is called the anterior oblique line and lower part is crest like.

2. Posterior border begins above at the back of the neck and ends below at the posterior part of the base of the styloid process; it separates the posterior from the lateral surface. is indistinct above and below, but well-marked in the middle third of the bone.

3. Medial or Interosseous border is the sharpest of the three borders which extends from the radial tuberosity above to the posterior margin of the ulnar notch below. The interosseous membrane is attached to its lower 3/4th. In its lower part it forms the posterior margin of an elongated triangular area.

Surfaces 

1. Anterior surface lies between the anterior and interosseous borders. A nutrient foramen opens in its upper part which is directed upwards. Nutrient artery is a branch of the anterior interosseous artery.

2. Posterior surface lies between posterior and interosseous borders.

3. Lateral surface lies between the anterior and posterior borders.

Lower End

The lower end is the widest part of the bone. It has 5 surfaces:

1.The anterior surface is in the form of a thick prominent ridge. The radial artery is palpated against this surface.

2.The posterior surface presents four grooves for the extensor tendons. The dorsal tubercle (of Lister) lies lateral to an oblique groove.

3.The medial surface is occupied by the ulnar notch for the head of the ulna.

4.The lateral surface is prolonged downwards to form the styloid process.

5.The inferior surface bears a triangular area for the scaphoid bone, and a medial quadrangular area for the lunate bone. This surface takes part in forming the wrist joint.

ATTCHMENTS TO MUSCLES & LIGAMENTS AND JOINTS

The lateral ligaments of the elbow are collectively named the lateral collateral ligament complex, which is composed of four ligaments that are difficult to separate. First, the lateral collateral ligament (a.k.a. "radial collateral ligament") attaches from the lateral epicondyle of the humerus to the annular ligament. The lateral collateral ligament joins the radius to the humerus and protects the antebrachium against varus stress. The annular ligament attaches from anterior to the posterior radial notch of the ulna encircling the radial head allowing pronation and supination. The lateral ulnar collateral ligament attaches from the lateral epicondyle of the humerus to the ulnar supinator crest. The lateral ulnar collateral ligament helps protect the antebrachium against valgus stress. Finally, the accessory lateral collateral ligament attaches from the supinator crest to the inferior margin of the annular ligament, providing further stability to the joint.

Between the medial border of the radius and the lateral border of the ulna resides the interosseous membrane which divides the anterior and posterior compartments of the antebrachium. The interosseus membrane serves as an attachment site for muscle while allowing for force distribution across the forearm. When the forearm supinates, the interosseous membrane fibers become taught, stabilizing distal and proximal joints. Like the lateral collateral ligament complex, the composition of the interosseous membrane is of multiple ligaments that are difficult to separate. The five ligaments of the interosseous membrane are the proximal oblique cord, accessory band, central band, dorsal oblique accessory cord, and the distal oblique bundle.

The distal radioulnar articulation is composed of the palmar radioulnar ligament (volar radioulnar ligament) that attaches the anterior radius to the anterior ulna, the dorsal radioulnar ligament (posterior radioulnar ligament) which attaches the posterior radius to the posterior ulna, and the articular disc which lies between the distal ulna and radius. These structures allow for load distribution and allow the second pivot during pronation and supination of the forearm.

The distal radius is attached to the lunate bone via two ligaments, the long and short radiolunate ligaments. These ligaments prevent hyperextension of the lunate bone during wrist extension. The distal radius is attached to the scaphoid via the radial collateral ligament of the wrist, and the radioscaphocapitate ligament attaches the volar aspect of the radius to the scaphoid and capitate carpal bones. Lastly, the dorsal radiotriquetral ligament is a wide ligament, which connects the dorsal radius to the dorsal scaphoid, lunate, and triquetrum.

The muscles of the forearm divide into two compartments - posterior and anterior. The posterior compartment is composed primarily of muscles that allow for wrist extension, finger extension, and forearm supination. The anterior compartment contains mostly the muscles involved in wrist flexion, finger flexion, and forearm pronation. 

The anterior compartment subdivides into the superficial, intermediate, and deep layers. The muscles of the superficial layer are the flexor carpi ulnaris, palmaris longus, flexor carpi radialis, and pronator teres. The intermediate layer contains a single muscle, the flexor digitorum superficialis. The deep anterior layer is composed of the flexor digitorum profundus, the flexor pollicis longus, and the pronator quadratus.

The posterior compartment of the forearm subdivides into superficial and deep layers. The muscles of the superficial layer are the brachioradialis, extensor carpi radialis brevis, extensor carpi radialis longus, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, and anconeus muscles. The muscles of the posterior layer are supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis muscles.

BLOOD SUPPLY, LYMPHATICS AND NERVES

The blood supply to the proximal radius is provided primarily by the radial and radial recurrent arteries. The radial recurrent artery travels proximally to anastomose with the radial collateral artery. Blood supply to the middle and distal radius is through the radial, posterior interosseous, and anterior interosseous arteries.

Lymph from the radius drains via the deep lymphatic vessels which follow the deep veins such as the brachial, ulnar, and radial veins.  These vessels drain into the humeral axillary lymph nodes.

The nerves of the brachial plexus provide motor and sensory innervation to the antebrachium. 

The radial nerve provides sensory innervation for the posterior forearm and motor innervation to the brachioradialis, extensor carpi radialis brevis, extensor carpi radialis longus, supinator, extensor carpi ulnaris, abductor pollicis longus, abductor pollicis brevis, extensor pollicis longus, extensor pollicis brevis, extensor indicis, extensor digitorum, and extensor digiti minimi muscles. 

The medial and lateral antebrachial cutaneous nerves provide sensory innervation to the anteromedial and anterolateral forearm respectfully.

The musculocutaneous nerve is the source of motor innervation to the biceps brachii.

The median nerve provides motor innervation to the pronator teres, flexor carpi radialis, palmaris longus, flexor digitorum superficialis, flexor pollicis longus, pronator quadratus, and the lateral half of the flexor digitorum profundus muscles.

The ulnar nerve supplies motor innervation to the flexor carpi ulnaris and flexor digitorum profundus muscles.

EMBRYOLOGY AND OSSIFICATION

The development of the radius occurs through endochondral ossification and begins with lateral plate mesoderm - the origin of all long bones. Endochondral ossification is the replacement of hyaline cartilage with bone. Mesoderm-derived mesenchymal cells become chondrocytes, which proliferate rapidly and form a bone template. 

Chondrocytes near the center of the model begin laying down collagen and fibronectin to the matrix which allows for calcification. Around week six of gestation, the calcification prevents nutrients from reaching the chondrocytes. The chondrocytes eventually undergo apoptosis. Blood vessels proliferate through the spaces vacated by the chondrocytes and eventually form the medullary cavity. Around the 12th week of gestation, osteoblasts create a thick area of compact bone in the diaphysis called the periosteal collar which becomes the site of primary ossification. Epiphyseal plates (growth plates) at either end of the bone contain proliferating chondrocytes, that continue to elongate the bone, until puberty. During puberty, sex hormones cause secondary ossification centers to form, and the epiphyseal plates ossify in a congruent fashion as the diaphysis.

Complied & Written by Dr. Palak Shah

SCAPULA

The scapula also known as the shoulder bone, shoulder blade, wing bone or blade bone, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on either side of the body being roughly a mirror image of the other. The name derives from the Classical Latin word for trowel or small shovel, which it was thought to resemble.

The scapula forms the back of the shoulder girdle. In humans, it is a flat and thin bone, roughly triangular in shape, placed on a posterolateral aspect of the thoracic cage.

GENERAL FEATURES

SURFACES: There are two surfaces costal and dorsal.

1. Costal surface or subscapular fossa is concave and directed medially and forwards. It is marked by 3 longitudinal ridges and one more thick ridge joins the lateral border which is almost rod - like. At the upper part of the fossa is a transverse depression, where the bone appears to be bent on itself along a line at right angles to and passing through the center of the glenoid cavity, forming a considerable angle, called the subscapular angle; this gives greater strength to the body of the bone by its arched form, while the summit of the arch serves to support the spine and acromion.

COSTAL SURFACE

2. Dorsal surface gives attachment to the spine of scapula which divides the surface into smaller supraspinatous fossa and a larger infraspinatous fossa. These two are connected by spinoglenoid notch which lateral to the root of the spine.

DORSAL SURFACE

BORDERS:

1. Superior border is the shortest and thinnest; it is concave and extends from the superior angle to the base of the coracoid process. It is referred to as the cranial border in animals. At its lateral part is a deep, semicircular notch, the scapular notch, formed partly by the base of the coracoid process. This notch is converted into a foramen by the superior transverse scapular ligament and serves for the passage of the suprascapular nerve; sometimes the ligament is ossified. The adjacent part of the superior border affords attachment to the omohyoideus.

Red line is Superior Border

2. Axillary border (or "lateral border") is the thickest of the three. It begins above at the lower margin of the glenoid cavity, and inclines obliquely downward and backward to the inferior angle. At the upper end it presents the infragleniod tubercle. It is referred to as the caudal border in animals.

Lateral Border

3. Medial border (also called the vertebral border or medial margin) is the thinnest and is the longest of the three borders and extends from the superior angle to the inferior angle. In animals it is referred to as the dorsal border.

Medial Border

ANGLES

1. Superior angle of the scapula or Medial angle is covered by the trapezius muscle. This angle is formed by the junction of the superior and medial borders of the scapula. The superior angle is located at the approximate level of the second thoracic vertebra. The superior angle of the scapula is thin, smooth, rounded, and inclined somewhat lateralward, and gives attachment to a few fibers of the levator scapulae muscle.

Superior angle of Scapula

2. Inferior angle of the scapula is the lowest part of the scapula and is covered by the latissimus dorsi muscle. It moves forwards round the chest when the arm is abducted. The inferior angle is formed by the union of the medial and lateral borders of the scapula. It is thick and rough, and its posterior or back surface affords attachment to the teres major and often to a few fibers of the latissimus dorsi. The anatomical plane that passes vertically through the inferior angle is named the scapular line.

Inferior angle of Scapula

3. Lateral angle of the scapula or glenoid angle also known as the head of the scapula is the thickest part of the scapula. It is broad and bears the glenoid cavity on its articular surface which is directed forward, laterally and slightly upwards, and articulates with the head of the humerus. The inferior angle is broader below than above and its vertical diameter is the longest. The surface is covered with cartilage in the fresh state; and its margins, slightly raised, give attachment to a fibrocartilaginous structure, the glenoidal labrum, which deepens the cavity. At its apex is a slight elevation, the supraglenoid tuberosity, to which the long head of the biceps brachii is attached.

Lateral angle of Scapula

PROCESSES

1. Spine or spinous process is a triangular plate of bone with 3 borders and 2 surfaces.   It divides the dorsal surface of the scapula into the supraspinatus and infraspinatus   fossae. Its posterior border is called the crest of the spine. The crest has upper and   lower lips.

2. Acromion has 2 borders, 2 surfaces and a facet.

3. Coracoid process is directed forwards and slightly laterally.

ATTACHMENTS

MUSCLES

• Subscapularis arises from the medial 2/3rds of the subscapular fossa.
• Supraspinatus arises from medial 2/3rds of supraspinous fossa including upper surface of the spine
• Infraspinatus arises from medial 2/3rds of infraspinous fossa, including lower surface of spine.
• Deltoid arises from lower border of the crest of spine and from lateral border acromion.
• Latissimus Dorsi lower fibres originate from inferior angle of scapula.
• Trapezius is inserted into the upper border of the crest of the spine and into medial border of the acromion.
• Serratus anterior is inserted along the medial border of costal surface; 1 digitation from the superior angle to the root of the spine, 2 digitations to the medial border, 5 digitations to the inferior angle.
• The long head of biceps brachii arises from supraglenoid tubercle and the short head from the lateral part of the tip of the coracoid process.
• Coracobrachialis arises from medial part of tip of the coracoids process
• Pectoralis minor is inserted into the medial border and superior surface of coracoid process.
• The long head of triceps arises from infraglenoid tubercle
• Teres minor arises from upper 2/3rds of rough strip on the dorsal surface along the lateral border.
• Teres major arises from lower 1/3rd of rough strip on the dorsal aspect of lateral border
• Levator scapulae is inserted along the dorsal aspect of the medial border, from superior angle up to root of spine
• Rhomboideus minor is inserted into medial border (dorsal aspect) opposite to root of spine
• Rhomboideus major is inserted into the medial border (dorsal aspect) between the root of spine and inferior angle
• Inferior belly of omohyoid arises from upper border near suprascapular notch.
  

LIGAMENTS

• The margin of glenoid cavity gives attachment to the capsule of shoulder joint and to the glenoid labrum
• The margin of the facet on the medial aspect of the acromion gives attachment to the capsule of the acromioclavicular joint
• The coracoacromial ligament is attached to the lateral border of the coracoids process and to the medial side of the tip of the acromion process
• The coracohumeral ligament is attached to the root of the coracoids process.
• The coracoclavicular ligament is attached to the coracoid process; the trapezoid part on the superior aspect, and the conoid part near the root. The coracoclavicular ligament is made up of 2 bands: the conoid and the trapezoid, both of which provide vertical stability. The coracoacromial ligament connects the coracoid process to the acromion.
• The suprascapular ligament bridges across the suprascapular notch and converts it into a foramen which transmits the suprascapular nerve. The suprascapular ligament lies above the ligament.
• The spinoglenoid ligament bridges the spinoglenoid notch. The suprascapular vessels and nerve pass to it.
• The acromioclavicular ligament connects the distal end of the clavicle to the acromion and provides horizontal stability
  

BURSAE

1. Scapulothoracic Bursa, between the serratus and the thorax, and
2. Subscapularis Bursa, between the subscapularis and the serratus.

OSSIFICATION

The scapula is ossified from 7 or more centers: one for the body, two for the coracoid process, two for the acromion, one for the vertebral border, and one for the inferior angle. Ossification of the body begins about the second month of fetal life, by an irregular quadrilateral plate of bone forming, immediately behind the glenoid cavity. This plate extends to form the chief part of the bone, the scapular spine growing up from its dorsal surface about the third month. Ossification starts as membranous ossification before birth. After birth, the cartilaginous components would undergo endochondral ossification. The larger part of the scapula undergoes membranous ossification. Some of the outer parts of the scapula are cartilaginous at birth and would therefore undergo endochondral ossification.

At birth, a large part of the scapula is osseous, but the glenoid cavity, the coracoid process, the acromion, the vertebral border and the inferior angle are cartilaginous. From the 15th to the 18th month after birth, ossification takes place in the middle of the coracoid process, which as a rule becomes joined with the rest of the bone about the 15th year.

Between the 14th and 20th years, the remaining parts ossify in quick succession, and usually in the following order: first, in the root of the coracoid process, in the form of a broad scale; secondly, near the base of the acromion; thirdly, in the inferior angle and contiguous part of the vertebral border; fourthly, near the outer end of the acromion; fifthly, in the vertebral border. The base of the acromion is formed by an extension from the spine; the two nuclei of the acromion unite and then join with the extension from the spine. The upper third of the glenoid cavity is ossified from a separate center (sub coracoid), which appears between the 10th and 11th years and joins between the 16th and the 18th years. Further, an epiphysial plate appears for the lower part of the glenoid cavity, and the tip of the coracoid process frequently has a separate nucleus. These various epiphyses are joined to the bone by the 25th year.

Failure of bony union between the acromion and spine sometimes occurs (see os acromiale), the junction being affected by fibrous tissue, or by an imperfect articulation; in some cases of supposed fracture of the acromion with ligamentous union, it is probable that the detached segment was never united to the rest of the bone.

Complied & Written by Dr. Palak Shah

CARTILAGE

Cartilage is a connective tissue composed of cells and fibres embedded in a firm, gel-like matrix which is rich in a mucopolysaccharide. it is more elastic than bone.

• Cartilage doesn't have blood supply nor it has lymphatics.it's nutrition diffuses through the matrix.
• It doesn't have nerves hence it is insensitive.
• Cartilage is surrounded by a fibrous membrane known as perichondrium which is similar to the periosteum in both structure and function. The articular cartilage doesn't have perichondrium so it's regeneration after injury is inadequate. 
• When cartilage dies, it forms into a bone like tissue.

TYPES OF CARTILAGE

1. HYALINE CARTILAGE: It is the most common form of cartilage. Hyalos is the Greek word for glass which describes the appearance of the tissue which is translucent, blueish-white and shiny. The cartilage is usually only 2-4mm thick. It is the embryonic form of cartilage. It is found in ribs, joints, nose. layrnx and trachea. Hyaline cartilage collagen fibres are primarily type II, extremely thin, invisible to microscope due to similar refractory properties to the matrix itself.

2. FIBROCARTILAGE: It is found where tendons and ligaments meet the bone, at the Pubic Symphysis, the Sternoclavicular joint and Annulus Fibrosus. The fibrocartilage is a very strong and pliable connective tissue. It is reinforced with collagen fibre bundles that run parallel to each other, allowing a low level stretch. Because of the abundance of collagen fibres, fibrocartilage is white in colour. It lacks a perichondrium and is composed of type II and type I collagen fibres. 

3. ELASTIC CARTILAGE: It is found in the external ear (auricle or pinna), the Eustachian tube and Epiglottis. Elastic's cartilage main role is purely structural, offering flexibility and resilience due to mixture of elastic fibres and type II collagen fibres. It is yellow in appearance without the organized structure of fibrocartilage when viewed under microscope.

COMPOSITION OF CARTILAGE

Cartilage is made up of highly specialized cells called chondrocytes and chondroblasts (chondro refers to cartilage), and other extracellular material which forms the cartilage matrix.

All connective tissue types within the human body are derived from the embryonal mesoderm. Bone, the strongest of the connective tissues, is the last to form and can remain in cartilage form well after birth. Increased cartilage to bone ratio enables a flexible and pliable new-born to exit the birth canal. A new-born has 300 bones, as opposed to the 206 of the normal adult, and all of these originate from cartilage.

From the 7th week of embryonic life, the process of ossification or osteogenesis slowly replaces cartilage with bone. This process continues into early childhood. Cartilage grows in two ways. In interstitial growth, chondrocytes proliferate and divide, producing more matrix inside existing cartilage throughout childhood and adolescence. In appositional growth, fresh layers of matrix are added to existing matrix surface by chondroblasts in the perichondrium. The perichondrium is a dense layer of connective tissue which surrounds most cartilage sites. Its outer layer contains collagen-producing fibroblasts, while the inner layer houses large numbers of differentiated fibroblasts called chondroblasts.

Chondroblasts: As long as they are free to move, chondroblasts produce the elements of the extracellular matrix (ECM). This cell type first forms a matrix of hyaluronic acid, chondroitin sulphate, collagen fibers, and water during embryonal development. Chondroblasts eventually become immobile after becoming surrounded by the matrix, and are then referred to as chondrocytes.

Chondrocytes: They are the immobile form of chondroblasts. They are surrounded by the matrix and contained within allotted spaces called lacunae. A single lacuna can contain one or more chondrocytes. Chondrocytes have varying roles according to the type of cartilage they are found in. In articular cartilage, found in the joints, chondrocytes increase joint articulation. At growth plates, chondrocytes regulate epiphyseal plate growth. While chondroblasts are ECM manufacturers, chondrocytes maintain the existing ECM and are a less active form of the same cell.

Fibroblasts: It is found in all types of connective tissue. In cartilage, these cells produce type I collagen. In certain situations, fibroblasts transform into chondrocytes.

Extracellular Matrix: There is significantly more matrix than cells in cartilage structure, as the low oxygen environment and lack of vasculature do not allow for larger numbers. Because of this, there is little metabolic activity, and little to no new growth in cartilage tissue – one of the reasons the elderly commonly suffer from degenerative joint pain. Cartilage does continue to grow slowly, however. This can be seen in the larger ears and noses of older individuals.

The ECM of cartilage contains three characteristic elements:

• Collagen

A protein-based collagen matrix gives form and strength to cartilage tissue through a mesh-like structure of fibrils. Although there are many different forms of collagen in the human body, the collagen found in cartilage is primarily type II, with an attached FACIT (short for fibril-associated collagen with interrupted triple helix) XIV collagen which determines the diameter of these fibers.

• Proteoglycans

Proteoglycans are large molecules that bind with water, providing flexibility and cushioning qualities. Proteoglycan monomers bond to hyaluronic acid by way of link proteins, as is the case with the large proteoglycan Aggrecan (chondroitin sulphate proteoglycan 

• Collagen and aggrecan in hyaline cartilage

The high numbers of negative charges such constructions provide, together with a large surface area, make it possible for proteoglycans to bind to large amounts of water. This creates high osmotic pressure, increases load-bearing, and constitutes the gel-like consistency of the ECM.

• Noncollagenous Proteins

Noncollagenous elements of the ECM are small in number and supposed to play a role in maintenance and organization of the cartilage structure on a macromolecular level.

Complied and written by Dr. Palak Shah