APPENDICULAR SKELETON

The appendicular skeleton consists of the bones of the upper limbs, the lower limbs,
and the girdles. The term girdle, which means a belt or a zone, refers to the two
zones, pectoral and pelvic, where the limbs are attached to the body.

PECTORAL GIRDLE AND UPPER LIMB

PECTORAL GIRDLE
The pectoral girdle, or shoulder girdle, consists of two pairs of bones that attach the
upper limb to the body.
Each pair is composed of a scapula, or shoulder blade, and a clavicle, or collarbone.
Scapula
The scapula is a flat, triangular bone that can easily be seen and felt in a living person.
The base of the triangle, the superior border, faces superiorly; the apex, the inferior
angle, is directed inferiorly.
The large acromion process of the scapula, which can be felt at the tip of the
shoulder, has three functions:
 to form a protective cover for the shoulder joint,
 to form the attachment site for the clavicle,
 to provide attachment points for some of the shoulder muscles.
The scapular spine extends from the acromion process across the posterior surface of
the scapula and divides that surface into a small supraspinous fossa superior to the
spine and a larger infraspinous fossa inferior to the spine. The deep, anterior surface
of the scapula constitutes the subscapular fossa.
The smaller coracoid process provides attachments for some shoulder and arm
muscles.
A glenoid cavity, located in the superior lateral portion of the bone, articulates with
the head of the humerus.
Clavicle

The clavicle is a long bone with a slight sigmoid (S-shaped) curve. It is easily seen
and felt in the living human.

The lateral end of the clavicle articulates with the acromion process, and its medial
end articulates with the manubrium of the sternum. These articulations form the only
bony connections between the pectoral girdle and the axial skeleton. Because the
clavicle holds the upper limb away from the body, it facilitates the limb’s mobility.

UPPER LIMB

Arm

The arm, the part of the upper limb from the shoulder to the elbow, contains only one
bone, the humerus . The humeral head articulates with the glenoid cavity of the
scapula.

The greater tubercle is on the lateral surface, and the lesser tubercle is on the
anterior surface of the proximal end of the humerus, where both are sites of muscle
attachment.

The groove between the two tubercles contains one tendon of the biceps brachii
muscle and is called the intertubercular groove.

The deltoid tuberosity is located on the lateral surface of the humerus a little more
than a third of the way along its length and is the attachment site for the deltoid
muscle.

The articular surfaces of the distal end of the humerus exhibit unusual features where
the humerus articulates with thetwo forearm bones. The lateral portion of the articular
surface is very rounded, articulates with the radius, and is called the capitulum
(head-shaped).

The medial portion somewhat resembles a spool or pulley, articulates with the ulna,
and is called the trochlea (spool).

Proximal to the capitulum and the trochlea are the lateral and medialepicondyles,
which are points of attachment for the muscles of the forearm.

Right Humerus diagram

Forearm

The forearm has two bones. The ulna is on the medial side of the forearm, the side
with the little finger.

The radius is on the lateral, or thumb, side of the forearm.

The proximal end of the ulna has a C-shaped articular surface, called the trochlear
notch, or semilunar notch, that fits over the trochlea of the humerus. The trochlear
notch is bounded by two processes.

The larger, posterior process is the olecranon process. It can easily be felt and is
commonly referred to as “the elbow.

Posterior arm muscles attach to the olecranon process. The smaller, anterior process

is the coronoid process.

The distal end of the ulna has a small head, which articulates with both the radius and
the wrist bones . The head can be seen on the posterior, medial (ulnar) side of the
distal forearm. The posteromedial side of the head has a small styloid process, to
which ligaments of the wrist are attached.

The proximal end of the radius is the head. It is concave and articulates with the
capitulum of the humerus.
As the forearm rotates, the proximal end of the ulna stays in place and the radius
rotates. The radial tuberosity is the point at which a major anterior arm muscle, the
biceps brachii, attaches.

The distal end of the radius, which articulates with the ulna and the carpal bones, is
somewhat broadened, and a styloid process to which wrist ligaments are attached is
located on the lateral side of the distal radius.

WRIST

The wrist is a relatively short region between the forearm and the hand; it is composed
of eight carpal bones arranged into two rows of four each.

The proximal row of carpal bones, lateral to medial, includes the scaphoid, which is
boat-shaped; the lunate, which is moon-shaped; the three-cornered triquetrum; and
the pea-shaped pisiform, which is located on the palmar surface of the triquetrum.
The distal row of carpal bones, from medial to lateral, includes the hamate, which has
a hooked process on its palmar side, called the hook of the hamate; the head-shaped
capitat; the trapezoid; and the trapezium, which

Hand

Five metacarpal bones are attached to the carpal bones and constitute the bony
framework of the hand. They are numbered one to five, starting with the most lateral
metacarpal bone, at the base of the thumb.

The metacarpal bones form a curve so that, in the resting position, the palm of the
hand is concave. The distal ends of the metacarpal bones help form the knuckles of
the hand.

The spaces between the metacarpal bones are occupied by soft tissue.

The five digits of each hand include one thumb and four fingers.
Each digit consists of small long bones called phalanges (sing. phalanx).

The thumb has two phalanges, called proximal and distal. Each finger has three
phalanges, designated proximal, middle, and distal.

One or two sesamoid bones often form near the junction between the proximal
phalanx and the metacarpal bone of the thumb.
 PELVIC GIRDLE AND LOWER LIMB

PELVIC GIRDLE

The right and left hipbones join each other anteriorly and the sacrum posteriorly to
form a ring of bone called the pelvic girdle.

The pelvis includes the pelvic girdle and the coccyx. Each hipbone consists of a large,
concave, bony plate superiorly, a slightly narrower region in the center, and an
expanded bony ring inferiorly, which surrounds a large obturator foramen.

A fossa called the acetabulum is located on the lateral surface of each hipbone and is
the point where the lower limb articulates with the girdle (the hip socket).

The pelvic girdle serves as the place of attachment for the lower limbs, supports the
weight of the body, and protects internal organs.

Because the pelvic girdle is a complete bony ring, it provides more stable support but
less mobility than the incomplete ring of the pectoral girdle.

In addition, the pelvis in a woman protects a developing fetus and forms a passageway
through which the fetus passes during delivery.

Each hipbone (pelvis) is formed by the fusion of three bones during development: the
ilium, the ischium, and the pubis’All three bones join near the center of the
acetabulum.

The superior portion of the ilium is called the iliac crest. The crest ends anteriorly as
the anterior superior iliac spine and posteriorly as the posterior superior iliac
spine.

The greater sciatic notch is on the posterior side of the ilium, just inferior to the
posterior inferior iliac spine. The sciatic nerve passes through the greater sciatic notch.
The auricular surface of the ilium joins the sacrum to form the sacroiliac joint. The
medial side of the ilium consists of a large depression called the iliac fossa.

Each sacroiliac joint is formed by the junction of the auricular surface of a hipbone
and one articular surface of the sacrum. The sacroiliac joints receive most of the
weight of the upper body and are strongly supported by ligaments.

The ischium possesses a heavy ischial tuberosity, where posterior thigh muscles
attach and on which a person sits.

The pubis has a pubic crest medially where abdominal muscles attach and a pubic
tubercle laterally where the inguinal ligament attaches.

The pubic crest can be felt anteriorly. Just inferior to the pubic crest is the point of
junction, the symphysis pubis, between the two hipbones.

The pelvis is subdivided into a true pelvis and a false pelvis. The opening to the true
pelvis is the pelvic inlet, and the inferior opening of the true pelvis is the pelvic
outlet.

The false pelvis is formed by muscle overlying bone of the true pelvis.

Thigh

The thigh, like the arm, contains a single bone, the femur.

The femur has a prominent, rounded head, where it articulates with the acetabulum,
and a well-defined neck; both are located at an oblique angle to the shaft of the femur.

The proximal shaft exhibits two projections: a greater trochanter lateral to the neck
and a smaller, lesser trochanter inferior and posterior to the neck.

Both trochanters are attachment sites for muscles that fasten the hip to the thigh.

The greater trochanter and its attached muscles form a bulge that can be seen as the
widest part of the hips.
The distal end of the femur has medial and lateral condyles, smooth, rounded
surfaces that articulate with the tibia. These condyles allow us to bend at the knees.
Located proximally to the condyles are the medial and lateral epicondyles, important
sites of ligament attachment.

An adductor tubercle, to which muscles attach, is located just proximal to the medial
epicondyle.

The patella, or kneecap, is a large sesamoid bone located within the tendon of the
quadriceps femoris muscle group, which is the major muscle group of the anterior
thigh.

The patella articulates with the patellar groove of the femur to create a smooth
articular surface over the anterior distal end of the femur.

The patella holds the tendon away from the distal end of the femur and thereby
changes the angle of the tendon between the quadriceps femoris muscle and the tibia,
where the tendon attaches.

Leg

The leg is the part of the lower limb between the knee and the ankle. Like the forearm,
it consists of two bones: the tibia, or shinbone, and the fibula. The tibia, by far the
larger of the two, supports most of the weight of the leg.

A tibial tuberosity, which is the attachment point for the quadriceps femoris muscle
group, can easily be seen and felt just inferior to the patella. The anterior crest forms
the shin.

The proximal end of the tibia has flat medial and lateral condyles, which articulate
with the condyles of the femur.

The distal end of the tibia is enlarged to form the medial malleolus, which helps form
the medial side of the ankle joint.
The fibula does not articulate with the femur but has a small proximal head where it
articulates with the tibia. The distal end of the fibula is also slightly enlarged as the
lateral malleolus to create the lateral wall of the ankle joint. The lateral and medial

Foot

To continue our comparison of the lower limb with the upper limb, the proximal

foot is relatively much larger than the wrist. It consists of seven tarsal bones.

Three of these bones—the talus, the calcaneus, and the navicular—are proximal in the
foot but do not form a row. The talus, or ankle bone, articulates with the tibia and the
fibula to form the ankle joint. It also articulates with the calcaneus and navicular
bones.

The calcaneus (heel), the heel bone, is the largest and strongest bone in the foot. It is
located inferior to the talus and supports that bone. The calcaneus protrudes
posteriorly, is the important attachment point for the large calf muscles, and can be
easily felt as the heel of the foot.

The navicular, which is boat-shaped, lies between the talus posteriorly and the
cuneiforms anteriorly.

The metatarsal bones and phalanges of the foot are arranged in a manner very
similar to that of the metacarpal bones and phalanges of the hand, with the great toe
comparable to the thumb.

Small sesamoid bones often form in the tendons of muscles attached to the great toe.
The ball of the foot is the junction between the metatarsal bones and the phalanges.
form a row. The three medial, wedge-shaped bones are the medial cuneiform, the
intermediate cuneiform, and the lateral cuneiform, collectively called the
cuneiforms

The cuboid, which is cube-shaped, is the most lateral of the distal row.
 STRUCTURAL AND FUNCTIONAL CLASSIFICATION OF JOINTS

Definition

A joint is defined as a connection between two bones in the skeletal system.

The anatomical definition of a joint (articulation) is the location where two or more
bones, or any rigid parts of the skeleton, connect with each other. It forms a
mechanical support to the skeleton and allows a variety of movements in different
ranges between the rigid skeletal elements.

Some joints, such as the sutures between cranial bones, allow very little or no

movement. Other joints, such as the shoulder and hip joints, allow free movement in a
large range.

Classification of Joints

Joints can be classified by the type of the tissue present (fibrous, cartilaginous or
synovial), or by the degree of movement permitted (synarthrosis, amphiarthrosis or
diarthrosis).

Classification by type of tissue: Classification by degree of movement:

 Fibrous – bones connected by fibrous  Synarthrosis – immovable.

tissue.
 Amphiarthrosis – slightly moveable.
 Cartilaginous – bones connected by
 Diarthrosis – freely moveable.
cartilage.

 Synovial – articulating surfaces

enclosed within fluid-filled joint
Classification by type of tissue: Classification by degree of movement:

capsule.

FIBROUS JOINTS

A fibrous joint is where the bones are bound by a tough, fibrous tissue. These are
typically joints that require strength and stability over range of movement.

Fibrous joints can be further sub-classified into sutures, gomphoses and syndesmoses.

i. Sutures

Sutures are immovable joints (synarthrosis), and are only found between the flat,
plate-like bones of the skull.

There is limited movement until about 20 years of age, after which they become fixed
and immobile. They are most important in birth, as at that stage the joints are not
fused, allowing deformation of the skull as it passes through the birth canal.

ii. Gomphoses

Gomphoses are also immovable joints. They are found where the teeth articulate with
their sockets in the maxilla (upper teeth) or the mandible (lower teeth).

The tooth is bound into its socket by the strong periodontal ligament.

iii. Syndesmoses

Syndesmoses are slightly movable joints (amphiarthroses).

They are comprised of bones held together by an interosseous membrane. The

middle radioulnar joint and middle tibiofibular joint are examples of a syndesmosis
joint.
CARTILAGINOUS

In a cartilaginous joint, the bones are united by fibrocartilage or hyaline cartilage.

There are two main types: synchondroses (primary cartilaginous) and symphyses
(secondary cartilaginous).

i. Synchondroses

In a synchondrosis, the bones are connected by hyaline cartilage. These joints are
immovable (synarthrosis). An example of a synchondrosis is the joint between the
diaphysis and epiphysis of a growing long bone.

ii. Symphyses

Symphysial joints are where the bones are united by a layer of fibrocartilage. They
are slightly movable (amphiarthrosis). Examples include the pubic symphysis, and
the joints between vertebral bodies.

SYNOVIAL

A synovial joint is defined by the presence of a fluid-filled joint cavity contained

within a fibrous capsule. They are freely movable (diarthrosis) and are the most
common type of joint found in the body. Synovial joints can be sub-classified into
several different types, depending on the shape of their articular surfaces and the
movements permitted:

i. Hinge – permits movement in one plane – usually flexion and extension.

o E.g. elbow joint, ankle joint, knee joint.

ii. Saddle – named due to its resemblance to a saddle on a horse’s back. It is

characterised by opposing articular surfaces with a reciprocal concave-convex
shape.

o E.g. carpometacarpal joints.

iii. Plane – the articular surfaces are relatively flat, allowing the bones to glide
over one another.

o E.g. acromioclavicular joint, subtalar joint.

iv. Pivot – allows for rotation only. It is formed by a central bony pivot, which is
surrounded by a bony-ligamentous ring

o E.g. proximal and distal radioulnar joints, atlantoaxial joint.

v. Condyloid – contains a convex surface which articulates with a concave

elliptical cavity. They are also known as ellipsoid joints.

o E.g. wrist joint, metacarpophalangeal joint, metatarsophalangeal joint.

vi. Ball and Socket – where the ball-shaped surface of one rounded bone fits into
the cup-like depression of another bone. It permits free movement in numerous
axes.

o E.g. hip joint, shoulder joint.

The different types of synovial joint.
ANATOMICAL TERMS OF MOVEMENT

Anatomical terms of movement are used to describe the actions of muscles upon the
skeleton. Muscles contract to produce movement at joints, and the subsequent
movements can be precisely described using this terminology.

The terms used assume that the body begins in the anatomical position. Most
movements have an opposite movement – also known as an antagonistic movement.
We have described the terms in antagonistic pairs for ease of understanding.

i. Flexion and Extension

Flexion and extension are movements that occur in the sagittal plane. They refer to
increasing and decreasing the angle between two body parts:

Flexion refers to a movement that decreases the angle between two body parts.
Flexion at the elbow is decreasing the angle between the ulna and the humerus. When
the knee flexes, the ankle moves closer to the buttock, and the angle between the
femur and tibia gets smaller.

Extension refers to a movement that increases the angle between two body parts.
Extension at the elbow is increasing the angle between the ulna and the humerus.
Extension of the knee straightens the lower limb.
 ii. Abduction and Adduction

Abduction and adduction are two terms that are used to describe movements towards
or away from the midline of the body.

Abduction is a movement away from the midline – just as abducting someone is to

take them away. For example, abduction of the shoulder raises the arms out to the
sides of the body.

Adduction is a movement towards the midline. Adduction of the hip squeezes the
legs together.
In fingers and toes, the midline used is not the midline of the body, but of the hand
and foot respectively. Therefore, abducting the fingers spreads them out.

iii. Medial and Lateral Rotation

Medial and lateral rotation describe movement of the limbs around their long axis:

Medial rotation is a rotational movement towards the midline. It is sometimes

referred to as internal rotation. To understand this, we have two scenarios to imagine.
Firstly, with a straight leg, rotate it to point the toes inward. This is medial rotation of
the hip. Secondly, imagine you are carrying a tea tray in front of you, with elbow at 90
degrees. Now rotate the arm, bringing your hand towards your opposite hip (elbow
still at 90 degrees). This is internal rotation of the shoulder.

Lateral rotation is a rotating movement away from the midline. This is in the
opposite direction to the movements described above.
 iv. Elevation and Depression

Elevation refers to movement in a superior direction (e.g. shoulder shrug),

depression refers to movement in an inferior direction.

v. Pronation and Supination

This is easily confused with medial and lateral rotation, but the difference is subtle.
With your hand resting on a table in front of you, and keeping your shoulder and
elbow still, turn your hand onto its back, palm up. This is the supine position, and so
this movement is supination.

Again, keeping the elbow and shoulder still, flip your hand onto its front, palm down.
This is the prone position, and so this movement is named pronation.

These terms also apply to the whole body – when lying flat on the back, the body is
supine. When lying flat on the front, the body is prone.

vi. Dorsiflexion and Plantar flexion

Dorsiflexion and plantar flexion are terms used to describe movements at the ankle.
They refer to the two surfaces of the foot; the dorsum (superior surface) and the
plantar surface (the sole).

Dorsiflexion refers to flexion at the ankle, so that the foot points more superiorly.
Dorsiflexion of the hand is a confusing term, and so is rarely used. The dorsum of the
hand is the posterior surface, and so movement in that direction is extension.
Therefore we can say that dorsiflexion of the wrist is the same as extension.

Plantarflexion refers extension at the ankle, so that the foot points inferiorly.
Similarly there is a term for the hand, which is palmarflexion.
 vii. Inversion and Eversion

Inversion and eversion are movements which occur at the ankle joint, referring to the
rotation of the foot around its long axis.Inversion involves the movement of the sole
towards the median plane – so that the sole faces in a medial direction.

Eversion involves the movement of the sole away from the median plane – so that the
sole faces in a lateral direction.

viii. Opposition and Reposition

A pair of movements that are limited to humans and some great apes, these terms
apply to the additional movements that the hand and thumb can perform in these
species.

Opposition brings the thumb and little finger together.

Reposition is a movement that moves the thumb and the little finger away from each
other, effectively reversing opposition.

ix. Circumduction

Circumduction can be defined as a conical movement of a limb extending from the

joint at which the movement is controlled.

It is sometimes talked about as a circular motion, but is more accurately conical due to
the ‘cone’ formed by the moving limb.

x. Protraction and Retraction

Protraction describes the anterolateral movement of the scapula on the thoracic wall
that allows the shoulder to move anteriorly. In practice, this is the movement of
‘reaching out’ to something.

Retraction refers to the posteromedial movement of the scapula on the thoracic wall,
which causes the shoulder region to move posteriorly i.e. picking something up.