The abdomen, when looking from in front, is divided into nine regions by imaginary planes (two vertical and two horizontal) forming abdominal surface anatomy. The nine regions are of clinical importance when examining and describing pathologies related to the abdomen. The horizontal planes are o...
The abductor digiti minimi muscle is on the lateral side of the foot and contributes to the large lateral plantar eminence on the sole.
origin: lateral and medial processes of calcaneal tuberosity, and band of connective tissue connecting calcaneus with base of metatarsal V
The abductor digiti minimi muscle overlies the opponens digiti minimi.
origin: pisiform, the pisohamate ligament, and tendon of flexor carpi ulnaris
insertion: 5th proximal phalanx
action: abducts 5th finger at metacarpophalangeal joint
arterial supply: ulnar artery
The abductor hallucis muscle forms the medial margin of the foot and contributes to a soft tissue bulge on the medial side of the sole.
origin: medial process of calcaneal tuberosity
insertion: medial side of base of proximal phalanx of great toe
action: abducts and flexes great toe ...
The abductor pollicis brevis is a thin subcutaneous muscle located laterally in the thenar eminence of the hand.
origin: mainly from the flexor retinaculum
few fibres originate from the tubercles of scaphoid and trapezium and tendon of abductor pollicis longus
accessory slips may ori...
The abductor pollicis longus (APL) is a muscle found in the deep layer of the posterior compartment of the forearm. As it descends, it becomes superficial and passes under the extensor retinaculum and through the 1st extensor compartment of the wrist before attaching distally.
The accessory ossicle of the anterior arch of the atlas is a normal variant and is best appreciated on a lateral cervical/sagittal study. It is observed as a circular and corticated osseous density that articulates with the inferior aspect of the anterior arch of the atlas.
It is not associate...
Accessory ossicles are secondary ossification centres that are separate from the adjacent bone. They are usually round or ovoid in shape, occur in typical locations and have well defined smooth cortical margins on all sides.
In most cases, they are congenital in origin, although they may occur ...
Accessory ossicles of the feet are common developmental variants with almost 40 having been described. The more common ones include:
os tibiale externum (accessory navicular)
os calcaneus secundaris
pars peronea met...
Accessory ossicles of the wrist are commonly seen on plain radiographs of the wrist and associated cross-sectional imaging. Over 20 were originally described 2, although the more common include 1:
lunula: between TFCC and triquetrum
os styloideum (carpal boss): on dorsal surface of 2nd or 3rd ...
Accessory peroneal muscles are a group of accessory muscles that can occur in the foot region as a normal variant in some individuals. The peroneal compartment is known as the lateral compartment of the leg.
Peroneus quartus muscle
Originally, several accessory muscles were distinguished in th...
The accessory soleus muscle is an anatomical variant characterised by an additional distinct muscle encountered along a normal soleus muscle. It is uncommon with a prevalence of ~3% (range 0.7-5.5%).
origin: fibula, soleal line of the tibia, or the anterior surface of the soleus muscle...
An accessory superior acetabular notch is a normal variant of the acetabulum, which can be seen on radiographs. It may lead to diagnostic confusion, especially in younger patients.
appear as bilateral symmetric fluid-filled pits in the roof of the acetabulum with sh...
The acetabular foramen is formed by the bony margins of the acetabular notch and completed by the transverse ligament of the hip. From its margins (both transverse ligament and acetabular notch) arises the ligamentum teres. Through it pass nutrient vessels to the femoral head epiphysis.
Acetabular labrum acts to deepen the acetabulum and increase contact between the pelvis and the femoral head. Its exact biomechanical role remains to be fully elucidated.
The acetabular labrum is a C-shaped fibrocartilaginous structure with an opening anteroinferiorly at the site...
The acetablar notch is a depression in the margin of the acetabulum located anteroinferiorly. It is bridged by the transverse ligament, and thus forms the acteabular foramen. The ligamentum teres has part of its origin from the acetabular notch.
The acetabulum (plural: acetabula) is the large cup-shaped cavity on the anterolateral aspect of the pelvis that articulates with the femoral head to form the hip joint.
All three bones of the pelvis (the ilium, ischium, and pubis) together form the acetabulum. The three bones ar...
The shape of the acromion had been initially divided into three types (which was known as the Bigliani classification) 3, to which a fourth has been added 2. They are useful as a standardised way of describing the acromion, as well as predicting to a degree the incidence of impingement.
The acromioclavicular (AC) joint is a plane synovial joint of the pectoral girdle.
The acromioclavicular joint is between the small facets of the convex distal clavicle and flat medial acromion. The articular surfaces are lined with hyaline cartilage 4. A fibrocartilaginous wedge...
There is much variation in acromioclavicular (AC) joint configuration which may be confused with pathology.
The relationship of the acromion to the distal clavicle at the AC joint can be described in the coronal plane as 1, 2, 3:
low lying: associated with shoulder impinge...
The acromion, also known as the acromial process, is a small section of the scapula that extends anteriorly from the spine of the scapula.
It forms the acromioclavicular joint with the lateral third of the clavicle, and also connects with the coracoid process via the coraco-acro...
The adductor brevis is a muscle in the medial compartment of the thigh that lies immediately deep to the pectineus and adductor longus.
origin: external surface of body of pubis and inferior pubic ramus
insertion: posterior surface of proximal femur, linea aspera, medial supracondylar...
The adductor canal is a muscular tunnel in the thigh. It commences at the inferior end of the femoral triangle and terminates at the adductor hiatus.
anteriorly: sartorius muscle
posteromedially: adductor longus and adductor magnus muscles
laterally: vastus mediali...
The adductor hallucis muscle arises by two heads, an oblique and transverse head. It is responsible for adducting the big toe.
transverse head: ligaments associated with metatarsophalangeal joints of lateral three toes
oblique head: bases of metatarsals II to IV and from sheat...
The adductor longus is a muscle in the medial compartment of the thigh that lies anterior to the adductor magnus.
origin: external surface of body of pubis (triangular depression inferior to pubic crest and lateral to pubic symphysis)
insertion: linea aspera on middle one-third of sh...
The adductor magnus is the largest and deepest of the muscles in the medial compartment of the thigh. Like the adductor longus and brevis muscles, the adductor magnus is a triangular or fan shaped muscle anchored by its apex to the pelvis and attached by its expanded base to the femur.
The adductor pollicis is a large triangular muscle anterior to the plane of the interossei that crosses the palm.
transverse head: 3rd metacarpal
oblique head: capitate and bases of 2nd and 3rd metacarpals
insertion: base of proximal phalanx and extensor hood of thumb
Amphiarthroses are a functional class of joint that permit a small amount of movement under normal conditions.
symphyses (secondary cartilaginous joints)
The anal sphincter is divided into an internal and external anal sphincter. It surrounds the anal canal.
Internal anal sphincter
continuation of inner rectal muscle
thickened, circular muscle fibres, up to 5 mm thick
composed of visceral muscle
External anal sphincter
The anatomical snuff box is a surface anatomy feature. It appears as a triangular depression on the lateral surface of the wrist on full extension of the thumb.
medial: tendons of the extensor pollicis longus
lateral: tendons of the
extensor pollicis brevis
The anatomy curriculum is one of our curriculum articles and aims to be a collection of articles that represent the core anatomy knowledge for radiologists and imaging specialists.
Head and neck anatomy
Abdominal and pelvic anatomy
The anconeus is a small muscle in the posterior compartment of the arm at the lateral aspect of the elbow. It has little functional significance but should be differentiated from the variably present anconeus epitrochlearis at the medial aspect of the elbow.
origin: lateral epicondyle ...
Anconeus epitrochlearis is an accessory muscle at the medial aspect of the elbow. It is also known as the accessory anconeus muscle and should not be confused with the anconeus muscle which is present at the lateral aspect of the elbow.
The muscle may be unilateral but has been f...
The angle of the longitudinal arch is one of the angles drawn on the weightbearing lateral foot radiograph. The angle is formed between the calcaneal inclination axis and a line drawn along the inferior edge of the 5th metatarsal.
The normal angle is 150-170°.
In pes cavus, as the height of th...
The ankle joint forms the articulation between the foot and the leg. It is a primary hinge synovial joint lined with hyaline cartilage.
The ankle joint is comprised of the tibia, fibula, talus, and calcaneus as well as the supporting ligaments, muscles and neurovascular bundles. ...
The annulus fibrosus surrounds the nucleus polposus and together they form the intervertebral disc.
The annulus comprises 15 to 20 collagenous (type I) laminae which run obliquely from the edge of one vertebra down to the edge of the vertebra below. The direction of the fibres al...
The anterior abdominal wall forms the anterior limit of the abdominal viscera and is defined superiorly by the xiphoid process of the sternum and costal cartilages and inferiorly by the iliac crest and pubic bones of the pelvis.
The anterior abdominal wall has seven layers (from ...
Anterior angulation of the coccyx may be a normal variant but poses a diagnostic challenge for those considering coccygeal trauma.
Four types of coccyx have been described:
type I: the coccyx is curved slightly forward, with its apex pointing caudally (~70%)
type II: the coccy...
The anterior compartment of the arm is one of the two compartments of the arm.
A sheath of deep fascia surrounds the arm, the brachial fascia. Two intermuscular septa (medial and lateral) extend from it to attach to the humerus at the medial condylar ridge and lateral supracondylar ridge, respe...
The forearm is divided into the anterior compartment and the posterior compartment by the deep fascia, lateral intermuscular septum and the interosseous membrane between the ulna and radius.
The eight muscles located in the anterior compartment of the forearm can be divided into three...
The anterior compartment of the leg is one of the four compartments in the leg between the knee and foot. Muscles within this compartment primarily produce ankle dorsiflexion and toe extension.
The leg is separated into anterior, lateral, superficial posterior and deep posterior compartments by...
The anterior compartment of the thigh is one of the three compartments in the thigh. Muscles within this compartment primarily produce hip flexion and knee extension.
The thigh is separated into anterior, posterior and medial (adductor) compartments by intermuscular septa and surrounded by the ...
Anterior cruciate ligament (ACL) is one of the two cruciate ligaments that stabilise the knee joint.
The ACL arises from the anteromedial aspect of the intercondylar area on the tibial plateau and passes upwards and backwards to attach to the posteromedial aspect of the lateral ...
The anterior humeral circumflex artery is a vessel arising from the axillary artery at the proximal part of the arm. It is smaller in size relative to the posterior humeral circumflex artery.
origin: branch of the axillary artery at the proximal part of the arm
location: proximal arm...
The anterior humeral line is key to demonstrating normal elbow alignment and should be used whenever reading a paediatric elbow radiograph to exclude a subtle supracondylar fracture.
A line drawn down the anterior surface of the humerus should intersect the middle third of the capitel...
The anterior inferior iliac spine (AIIS) is bony prominence on the anterior border of the ilium forming the superior border of the acetabulum.
Attachments include the Iliacus, origin of straight head of the rectus femoris, and also the the proximal ileofemoral ligament (Y-ligament or ligament o...
The anterior interosseous nerve also known as the volar interosseous nerve arises from the median nerve in the forearm, and supplies the flexor pollicis longus, pronator quadratus and the lateral portion of flexor digitorum profundus.
The anterior interosseous nerve conti...
There are three anterior knee fat pads 1:
infrapatellar fat pad (of Hoffa)
fills the space between the patella ligament and the anterior intercondylar area of the tibia 2
posterior suprapatellar (prefemoral or supratrochlear) fat pad
anterior suprapatellar (quadriceps) fat pad
fills the spa...
The anterior lateral malleolar artery is the counterpart to the anterior medial malleolar artery, supplies the lateral aspect of the ankle.
Origin and course
branch of anterior tibial artery
runs posterior to the tendons of extensor digitorum longus and fibularis tertius to th...
The anterior longitudinal ligament (ALL) arises from the anteroinferior basilar portion of occipital bone, traverses the entire length of the spine, and ends on the anteriosuperior portion of the sacrum.
The ALL runs along the anterior surface of the vertebral bodies (firmly united to the perio...
Anterior medial malleolar artery is the counterpart to the anterior lateral malleolar artery, and supplies the medial aspect of the ankle.
Origin and course
branch of anterior tibial artery
arises approximately 5 cm proximal to the ankle
passes posterior to the tendons of exte...
The anterior capsular insertion, unlike the posterior aspect of the shoulder joint capsule which has a constant scapular attachment along the margins of the glenoid labrum, inserts a variable distance from the labrum.
The capsular insertions are classified as follows:
type I: at or very near t...
The anterior superior iliac spine is an important bony surface landmark and is the prominence is the most anterior part of the ilium. It can be palpated at the lateral end of the inguinal fold. Attachments include the inguinal ligament, tensor fasciae latae and sartorius.
Clinically, as an easi...
The anterior talofibular ligament (ATFL) is part of the lateral collateral ligament complex of the ankle. Its role is to stabilise the talus. It is also the weakest of the lateral collateral ankle ligaments.
The ATFL is an intra-capsular flat two-banded ligament that arises from...
The anterior tibial veins, continuations of the venae comitantes of the dorsalis pedis artery, leave the anterior compartment between the tibia and fibula and pass through the proximal end of the interosseous membrane. They unite with the posterior tibial veins to form the popliteal vein at the ...
The anterolateral ligament of the knee (ALL) is a ligament that is thought to aid with rotational stability of the knee joint. Some think that its presence (or reconstruction) may result in better outcomes from ACL stabilisation surgery 2. The ligament has also been implied in Segond fractures 3...
The apophysis (pl: apophyses) is a normal bony outgrowth that arises from a separate ossification centre and fuses with the bone in course of time. The apophysis is a site of tendon or ligament attachment, as compared to the epiphysis which contributes to a joint.
When unfused, they can easily ...
The apophysis of the proximal 5th metatarsal lies laterally and is oriented longitudinally parallel to the shaft.
Apophysis of the fifth metatarsal base appears on plain radiographs at age 12 for boys and 10 for girls. Fusion of the apophysis to the metatarsal base usually occurs within the fol...
The appendicular skeleton is the portion of the bony skeleton that includes and supports the limbs (the appendages). It includes the pectoral girdle and the bony pelvis, connected to the axial skeleton centrally and is composed of 126 bones in total.
Appendicular bones form from cartilage, by ...
The arcade of Frohse (pronounced "\ Frəʊs \" to rhyme with "crows") is also known as the supinator arch.
The arcade is formed by a fibrous band between the two heads of the supinator muscle. The deep branch of the radial nerve passes beneath the arcade accompanied by vessels known as the leash ...
The arcuate foramen (foramen arcuale atlantis, ponticulus posticus or posterior ponticle, or Kimerle anomaly) is a frequently encountered normal variant of the atlas and is easily appreciated on a lateral plain film of the cranio-cervical junction.
It develops by calcification of the posterior ...
The arcuate ligament is part of the posterolateral ligamentous complex of the knee that is variably present, being found in ~65% (range 47.9-71%) of knees. It is a Y-shaped thickening of the posterolateral capsule, which arises from the fibular styloid and divides into two limbs:
medial limb: c...
The arcuate line is located at roughly one-third of the distance from the pubic crest to the umbilicus. It is the demarcation where the internal oblique and transversus abdominis aponeuroses of the rectus sheath start to pass anteriorly to the rectus abdominis muscle, leaving only the transversa...
The arm is part of the upper limb below the pectoral girdle and above the forearm, comprising the humerus.
The elbow joint is inferior and the glenohumeral joint is superior. Arm flexion, extension, abduction, adduction, internal rotation and external rotation occur at the shoulder.
The articularis cubiti is a muscle in the posterior compartment of the arm:
origin: posterior surface of the distal humerus
insertion: posterior surface of the elbow joint capsule
innervation: radial nerve
action: tenses the posterior elbow joint capsule during elbow extension
The articularis genu is a small flat muscle of the anterior knee. During knee extension it acts to tighten the synovial membrane superiorly thereby preventing impingement of the synovial folds between the femur and the patella.
origin: anterior distal femoral shaft
insertion: knee joi...
Atlanto-occipital assimilation is the fusion of the atlas (C1) to the occiput and is one of the transitional vertebrae.
Atlanto-occipital assimilation occurs in approximately 0.5% (range 0.25-1%) of the population 2-4.
Atlanto-occipital is typically asymp...
The atlas is the first cervical vertebra, commonly called C1. It is an atypical cervical vertebra with unique features. It articulates with the dens of the axis and the occiput, respectively allowing rotation of the head, and flexion, extension and lateral flexion of the head. Unlike the rest o...
Of the cervical vertebrae, the atlas (C1), axis (C2) and vertebra prominens (C7) are considered atypical cervical vertebrae.
The atlas (C1) lacks a body or spinous process. It has an anterior and posterior arches with lateral masses. Its superior articular surfaces articulate with the occiput a...
Of the five lumbar vertebrae, L5 is considered atypical due to its shape. The remaining lumbar vertebrae are largely typical.
For a basic anatomic description of the structure a generic vertebra, see vertebrae.
Owing to their features, the first, eleventh and twelfth ribs are considered atypical ribs.
Of all ribs, the first is the strongest, broadest and most curved. Ribs eleven and twelve are unique, among other reasons, by not being attached to the sternum.
T1 and T9 to T12 are considered atypical vertebrae. T1 bears some resemblance to low cervical vertebrae. T9 has no inferior demifacet. T10 often, but not always, shares features with T11 and T12.
For a basic anatomic description of the structure a generic vertebra, see vertebrae.
The axial skeleton is the central portion of the bony skeleton comprising the head, neck and trunk (80 bones in total). It has many functions including housing and protecting the central nervous system as well as the organs of the chest, abdomen and pelvis. It enables movement and supports the u...
The axilla is a space located between the upper limb and the neck and thorax, which permits the passage of the major neurovascular structures.
The axilla is pyramidal in shape with its apex opening superiorly into the base of the neck between the subclavius muscle, first rib and ...
The axillary nerve is one of five terminal branches of the brachial plexus, supplying motor and sensory branches to the shoulder.
origin: posterior cord of the brachial plexus
course: passes out of axilla through the quadrangular space to the upper arm
major branches: superior later...
The axis is the second cervical vertebra, commonly called C2. It is an atypical cervical vertebra with unique features and important relations that make it easily recognisable. Its most prominent feature is the odontoid process, which is embryologically the body of the atlas (C1) 1,2. It plays a...
A ball and socket ankle joint is a variant affecting the ankle where there is a rounded or spherical configuration to the talar dome with the corresponding concavity of the tibial plafond. The distal fibula may or may not be involved.
The aetiology has been debated with two theories ...
Ball and socket joints are a type of synovial joint where the spheroid articular surface of one bone sits within a cup-like depression of another bone.
The ball and socket configuration allows for movement with 3 degrees of freedom, which is more than any other type of synovial joint...
The base of the skull (or skull base) forms the floor of the cranial cavity and separates the brain from the structures of the neck and face.
The base of the skull is a bony diaphragm composed of a number of bones including (from anterior to posterior):
The biceps brachii muscle (also known simply as biceps) is a two-headed muscle in the anterior compartment of the arm that flexes at the elbow and supinates the forearm.
short head: coracoid process of the scapula
long head: supraglenoid tubercle of the scapula
The biceps femoris is one of the large muscles in the posterior compartment of the thigh and a component of the hamstrings. It has a long and a short head, each with different functions and innervation.
long head: tuberosity of the ischium
short head: linea aspera on the poste...
Biceps pulley refers to a complex capsuloligamentous structure which provides stability and hold the long head of biceps tendon within the bicipital groove. It comprises of the coracohumeral ligament, superior glenohumeral ligament, and distal attachment of the subscapularis tendon.
The bicipitoradial bursa is located between the distal biceps brachii tendon and the tuberosity of the radius. The bursa partially or completely wraps around the biceps tendon. It ensures frictionless motion between the biceps tendon and the proximal radius during pronation and supination of the...
The median nerve may divide into two nerve bundles in
the distal forearm and appear as a bifid median nerve in the carpal tunnel. It has an incidence of ~3%.
The median nerve usually divides into two or three branches after exiting the distal edge of the transverse carpal ligament that covers...
The bifurcate ligament arises from the calcaneus as a single band and divides into calcaneocuboid (lateral) and calcaneonavicular (medial) parts forming a Y-shape.
A bipartite patella (two-part patella) is a patella with an unfused accessory ossification center at the superolateral aspect.
The superolateral accessory ossification center of the patella is usually present by 12 years of age and may persist into adult life. Prevalence of a bipa...
A bipartite scaphoid is a rare example of a divided carpus. There is controversy whether this condition is congenital (i.e. normal variant) or post-traumatic. Bipartite scaphoids may be unilateral or bilateral.
Diagnostic criteria have been proposed 3:
no history of traumatic injury
Block vertebra is a type of vertebral anomaly where there is a failure of separation of two or more adjacent vertebral bodies.
In a block vertebra, there is partial or complete fusion of adjacent vertebral bodies.
there is a frequent association with hemivertebrae/abse...
The body of the sphenoid bone is the midline cubical portion of the sphenoid bone, hollowed by the sphenoid air sinuses.
The body has superior, inferior, anterior, posterior, and lateral surfaces.
The superior surface features:
ethmoidal spine: prominent spine that articulates...
Bone macroscopic structure allows a bone to be divided into regions based on position or morphology. This is important for a number of reasons including how growth may be affected by injury.
Bones can be separated into:
The bones in the upper limb can be divided into those within the arm and pectoral girdle (3), forearm (2) and wrist and hand (27). There are also a number of accessory ossicles, predominantly occurring at the wrist.
Bones of the arm and pectoral girdle
Bones of the...
There are many types of bone within the body:
long bones (longer than they are wide)
short bones (not long bones)
sesamoid bones (for within a tendon)
irregular bones (don't fit into a category)
The majority of the bones of the appendicular skeleton are long bones. However, the ...
The bony pelvis is formed by the sacrum and coccyx and a pair of hip bones (os coxae or innominate bones), comprising the ischium, pubis and ilium and are part of the appendicular skeleton.
Its primary function is the transmission of forces from the axial skeleton to the lower limbs as well as...