≤11 ribs is associated with a number of congenital abnormalities and skeletal dysplasias, including:
Down syndrome (trisomy 21)
asphyxiating thoracic dysplasia (Jeune syndrome)
short rib polydactyly syndromes
chromosome 1q21.1 deletion...
18q-deletion syndrome is a rare chromosomal anomaly where there is a deletion of part of the long arm of chromosome 18. Associated symptoms and findings vary widely, as do their severity. Characteristic clinical features include short stature, intellectual disability, hypotonia, facial, and dist...
The 5th metacarpal pit refers to the normal exaggeration of the pit-like depression in the head of fifth metacarpal.
It should not be mistaken for a boxer fracture (old or new) or an erosion.
Abdominal hernias (herniae also used) may be congenital or acquired and come with varying eponyms. They are distinguished primarily based on location and content. 75-80% of all hernias are inguinal.
Content of the hernia is variable, and may include:
small bowel loops
mobile colon segments (s...
Abdominal surface anatomy can be described when viewed from in front of the abdomen in 2 ways:
divided into 9 regions by two vertical and two horizontal imaginary planes
divided into 4 quadrants by single vertical and horizontal imaginary planes
These regions and quadrants are of clinical imp...
Abdominal wall injuries comprise a set of injuries of the abdominal wall and include different forms of muscle injuries, traumatic hernias and injuries to the subcutaneous tissue. They are often overshadowed by the attention to associated “more severe” abdominal visceral injuries.
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 muscle, within the hypothenar eminence, and is one of the intrinsic muscles of the hand. Occasionally an accessory abductor digiti minimi muscle of the hand is present.
origin: pisiform, pisohamate ligament, and tend...
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 muscle is a thin subcutaneous muscle located laterally in the thenar eminence of the hand, and is one of the intrinsic muscles of the hand.
origin: mainly from the flexor retinaculum
few fibers originate from the tubercles of scaphoid and trapezium and ten...
The abductor pollicis longus (APL) muscle is 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. It is one of the ext...
The ABER position relates to MR arthrography of the shoulder joint and is a mnemonic for ABduction and External Rotation.
In this position, labral tears are made conspicuous by tightening the inferior glenohumeral labroligamentous complex (which are also the most important glenohumeral ligament...
The OMERACT ultrasound group published a consensus in 2005 of widely accepted definitions of abnormal ultrasound findings in rheumatological diseases:
erosion: an intra-articular discontinuity of the bone surface that is visible in two orthogonal planes 4
joint effusion: abnormal hypoechoic or...
Abscesses are focal confined collections of suppurative inflammatory material and can be thought of as having three components 1:
a central core consisting of necrotic inflammatory cells and local tissue
peripheral halo of viable neutrophils
surrounded by a 'capsule' with dilated blood vessel...
The absent bow tie sign represents the loss of the normal appearance of the menisci on parasagittal MRI images and is suggestive of meniscal injury.
Normally the medial and lateral menisci appear as low signal bow-tie-shaped structures between the femoral condyles and tibial plateaux. As the no...
An absent patella is a rare finding and can be found with an equally rare set of associations:
surgical removal of patella (patellectomy)
nail patella syndrome 2
popliteal pterygium syndrome
proximal focal femoral deficiency (PFFD)
Meier-Gorlin syndrome 3
An absent thumb can have many associations. They include:
Fanconi anemia (pancytopenia-dysmelia syndrome)
phocomelia (e.g. thalidomide embryopathy)
Poland syndrome (pectoral muscle aplasia and syndactyly)
Seckel syndrome ...
An accessory abductor digiti minimi (ADM) muscle is the commonest accessory muscle of the hypothenar eminence, found in 24% individuals. When present it is one of the intrinsic muscles of the hand.
antebrachial fascia passing anteriorly to Guyon canal
occasionally arises from...
The accessory anterior inferior tibiofibular ligament (accessory AITFL), also known as Bassett's ligament, is an anatomical variant present in many ankles. Pathological thickening of the accessory ligament is seen in the setting of inversion injury that causing the pain due to mild anterior inst...
A brachialis accessorius muscle or accessory brachialis muscle is a very rare accessory flexor of the elbow and a normal anatomical variant.
origin: anterior surface of the lower humeral diaphysis
course: variably medial or lateral to the brachialis muscle
insertion: variable, includ...
The accessory extensor digiti secundus muscle is a rare accessory muscle or tendon of the ankle and a normal anatomical variant.
origin: extensor hallucis longus tendon or muscle
insertion: the medial phalanx of the second toe second tendon of the extensor digitorum longus muscle
The accessory flexor carpi ulnaris (AFCU) is a rare accessory muscle of the forearm and wrist and a normal anatomical variant that can be found in addition to a normal flexor carpi ulnaris muscle.
The accessory flexor carpi ulnaris muscle is considered very rare 1,2.
The accessory flexor digitorum longus muscle is an accessory muscle in the deep posterior compartment of the leg with a reported prevalence of 6-8%. Unilateral muscles are more common although bilateral cases have been reported.
origin: variable; either the medial margin of the tibia a...
An accessory flexor digitorum superficialis indicis muscle is an unusual accessory muscle of the hand and wrist and a normal anatomical variant.
origin: flexor digitorum superficialis tendon near the transverse carpal ligament
insertion: metacarpal head of the index finger near the A1...
Accessory muscles are a form of anatomic variation that refers to supplementary discrete muscles that are found alongside the normal expected musculature. They have been described in the neck, pelvis, upper and lower limbs.
Accessory muscles of the ankle are normal muscular anatomical variants that are usually asymptomatic but rarely cause symptoms or might be encountered on imaging studies.
The following accessory muscles around the ankle have been described 1-4:
Accessory muscles of the forearm, wrist and hand are normal muscular usually asymptomatic anatomical variants that might be encountered on imaging studies and confused with pathologic conditions.
The following accessory muscles around the forearm wrist and hand have been described 1-6:
An accessory navicular is a large accessory ossicle that can be present adjacent to the medial side of the navicular bone. The tibialis posterior tendon often inserts with a broad attachment into the ossicle. Most cases are asymptomatic but in a small proportion it may cause painful tendinosis d...
Accessory navicular syndrome occurs when a type II accessory navicular becomes painful due to movement across the pseudo-joint between the ossicle and the navicular bone.
It can be inferred on musculoskeletal ultrasound if a patient's pain is located at a type...
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 centers that remain 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 occ...
Accessory ossicles of the feet are common developmental variants with almost 40 having been described. Some of the more common include 1-4:
os tibiale externum (accessory navicular)
os calcaneus secundaris
There are numerous named and unnamed accessory ossicles of the lower limb. These include:
ossicles of the hip
ossicles of the knee
ossicles of the foot
os tibiale externum
os calcaneus secundaris
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 ...
The accessory ossicles of the wrist can be easily recalled with the mnemonics:
O: os styloideum (carpal boss)
T: (os) triangulare
T: (os) trapezium secondarium
E: (os) epilunate
O: os hamuli proprium
H: (os) hamuli proprium
O: os tri...
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 phrenic nerve is an anatomical variant seen in a little over one third of patients (36%). It most commonly arises from the ansa cervicalis, or slightly less commonly, the subclavian nerve. It is unknown as to how much the accessory phrenic nerve contributes to diaphragmatic functio...
Accessory sacroiliac joints are a common finding, present on ~15% (range 13-17.5%) of CT studies, and may be unilateral or bilateral. They are an articulation between the medial aspect of the posterior superior iliac spine and the sacrum just lateral to the second dorsal sacral foramen. They may...
The accessory semimembranosus muscle is a rare accessory muscle of the posterior compartment of the thigh. It arises from the distal aspect of the semimembranosus muscle belly and courses through the popliteal fossa between it and the semitendinosus muscle medially and the biceps femoris lateral...
The accessory soleus muscle is an anatomical variant characterized 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 angle is a radiographic measurement used when evaluating potential developmental dysplasia of the hip (DDH). It is most useful in patients who have started to ossify the epiphysis since ossification diminishes the usefulness of ultrasound.
The angle is formed by a horizontal lin...
Acetabular dysplasia is referred to as a shallow acetabulum, not being able to provide sufficient coverage for the femoral head and thus leading to instability of the hip joint.
Acetabular dysplasia is a form of developmental dysplasia of the hip (DDH) often referred to in the adol...
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.
The acetabular fossa, also known as the cotyloid fossa, is the central aspect of the medial wall of the acetabulum that hosts the ligamentum teres and the fibrofatty pulvinar. It is the nonarticular portion inside the U-shaped labrum that extends to the acetabular notch 1. The acetabular fossa i...
Acetabular fractures are a type of pelvic fracture, which may also involve the ilium, ischium or pubis depending on fracture configuration.
Acetabular fractures are uncommon. The reported incidence is approximately 3 per 100,000 per year. This study reported a 63% to 37% male to f...
The acetabular index also called acetabular roof angle or Tönnis angle is a radiographic measurement of femoral head bony coverage by the acetabulum. It is useful in assessing for developmental dysplasia of the hip (DDH) as well as pincer morphology in femoroacetabular impingement (FAI).
Acetabular labral calcification in the hip can be a finding detected on imaging studies. It has an association with osteoarthritis of the hip and may account for higher pain levels in individuals with a high degree of calcification independent of age and histological degeneration 2.
An acetabular labral sulcus is a type of normal variant seen as a cleft like appearance on imaging. It forms where the labrum meets the adjacent articular cartilage. Several sulci can be identified which include
several sublabral sulci
posterosuperior ~ 48%
anterosuperior ~ 44%
Acetabular labral tear, as the name implies, is a tear involving the acetabular labrum of the hip. It is defined as a defect in the labral surface, intralabral surface or chondrolabral junction 10.
With the increasing use of hip arthroscopy in orthopedic surgery since the 1970s pathologies of t...
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 acetabular notch is a depression in the margin of the acetabulum located anteroinferiorly. It is bridged by the transverse ligament, and thus forms the acetabular foramen. The ligamentum teres has part of its origin from the acetabular notch.
Acetabular protrusion, also known as protrusio acetabuli, is intrapelvic displacement of the acetabulum and femoral head, so that the femoral head projects medial to the ilioischial line. It should be differentiated from coxa profunda.
Acetabular protrusion is divided into primary an...
Acetabular retroversion denotes an abnormal posterior angulation of the superolateral acetabular rim, resulting in excessive coverage of the femoral head and metaphysis along the anterior border 1,2.
Acetabular retroversion is a common abnormality affecting 5 to 20% of the genera...
The acetabular sector angles are a set of angles, comprising the anterior acetabular sector angle (AASA), the posterior acetabular sector angle (PASA) and horizontal acetabular sector angle (HASA) and are used on cross-sectional imaging, especially pelvic CT, for the evaluation of acetabular cov...
The acetabular sourcil is a radiographic feature seen on plain radiographs of the hip and pelvis as well as coronal CT reformats and MR images. It refers to the roof or the weight-bearing area of the acetabulum and is characterized by an increased degree of sclerosis.
Its medial and lateral edg...
The acetabular version angle or acetabular anteversion angle is a measurement used on cross-sectional imaging especially pelvic CT for the assessment of acetabular morphology.
The acetabular version angle is influenced by pelvic obliquity and pelvic tilt, which might lead to measurement ...
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...
Acheiria refers to absence of one or both hands and can occur in a number of situations, including:
amniotic band syndrome: particularly if unilateral
Cornelia de Lange syndrome 1
fetal hydantoin syndrome 2
Rare defect occurring in 1:65 000 live births.
Achilles tendinopathy refers to a combination of pathological changes affecting the Achilles tendon usually due to overuse and excessive chronic stress upon the tendon. It can be seen both in athletes and non-athletes. It is hard to differentiate clinically from a paratendinopathy (which is most...
Achilles tendon ossification is an uncommon condition that consists of characteristic bone formation within the substance of the Achilles tendon.
Achilles tendon ossification is more common in males 4.
The etiology is unknown but Achilles tendon ossification is seen ...
Achilles tendon tears are the most common ankle tendon injuries, with microtears to full thickness tendon tears of the Achilles tendon and are most commonly seen secondary to sports-related injury, especially squash and basketball.
There is strong male over-representation presumab...
Achilles tendon thickening can occur for a number of reasons.
The Achilles tendon has an average AP diameter of 6 mm 1. Thickening of the tendon is when it exceeds 8 mm in AP diameter and can result from:
Achilles tendon xanthomata are painless soft tissue masses occurring most commonly at the distal portion of the tendon and are usually bilateral and symmetrical.
Characterized by localized accumulation of lipid-laden macrophages, inflammatory cells and giant cells secondary to choles...
Achondrogenesis refers to a group of rare and extreme skeletal dysplasias.
The estimated incidence is 1:40,000 with no recognized gender predilection.
It is classified as an osteochondrodysplasia, meaning deficiency of both bone and cartilage development.
Achondrogenesis type Ia, also known as the Houston-Harris subtype, is a subtype of achondrogenesis. It is an extremely rare lethal skeletal dysplasia (chondrodysplasia) with a characteristic severe disarrangement of endochondral ossification.
Some of the common clinical f...
Achondrogenesis type Ib, also known as Parenti-Fraccaro subtype, is a subtype of achondrogenesis and is an extremely rare skeletal dysplasia (chondrodysplasia).
The fetuses frequently present in breech position. The physical appearance is strikingly abnormal and charact...
Achondroplasia is a congenital genetic disorder resulting in rhizomelic dwarfism and is the most common skeletal dysplasia. It has numerous distinctive radiographic features.
It occurs due to sporadic mutations in the majority of cases but can be inherited as an autosomal dominan...
Achondroplasia is the most common cause of short-limb dwarfism. (For a general discussion, see the generic article on achondroplasia.)
As the skull base forms by endochondral ossification whereas the skull vault by membranous ossification, there is a marked discrepancy in relative size as the s...
Acquired lipodystrophy is defined by the loss of body fat, insulin resistance and metabolic profile derangement. Subtypes include Barraquer-Simons syndrome, localized lipodystrophy and Lawrence syndrome. Lipodystrophy is illustrated as a complete or partial loss of adipose tissues from the body....
Acral fibromyxomas are benign mesenchymal proliferations prone to recurrence usually found in the subungual and periungual sites of the digits.
Superficial acral fibromyxoma or digital fibromyxoma are other acceptable names, the term cellular digital fibroma is no longer recommende...
Acrocephalopolysyndactyly (ACPS) syndrome is comprised of a rare group of disorders collectively characterized by:
calvarial anomalies: e.g. craniosynostoses
digital anomalies: syndactyly and polydactyly
While there can be some overlap in features, they can be primarily classified into the fo...
Acrocephalosyndactyly syndromes (ACS) are a rare group of disorders collectively characterized by:
calvarial anomalies, e.g. craniosynostoses
digital anomalies, e.g. syndactyly
While there can be some overlap in features, they can be primarily classified into the following maj...
Acrodysostosis is a rare skeletal dysplasia characterized by growth retardation, nasal hypoplasia, brachydactyly, midfacial deficiency, intellectual disability and deafness.
Most cases are sporadic. Few cases with autosomal dominant transmission have been reported. It is believed to ...
Acromegaly is the result of excessive growth hormone production in skeletally mature patients, most commonly from a pituitary adenoma. The same excess of growth hormone in individuals whose epiphyses have not fused will result in gigantism (excessively tall stature).
Acromial apohysiolysis is a finding on shoulder MRI that may be encountered in patients with an unfused acromial apophysis. It is associated with athletes in throwing sports.
Presents with superior shoulder tenderness in a patient <25 years old, often in a young throwing ...
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 used as a standardized way of describing the acromion, as well as predicting to a degree the incidence of impingement.
Acromioclavicular joint (AC) injuries are characterized by damage to the acromioclavicular joint and surrounding structures. Almost invariably traumatic in etiology, they range in severity from a mild sprain to complete disruption.
Acromioclavicular joint injuries can occur at any...
The acromioclavicular joint (ACJ) is a planar diarthrodial synovial joint of the pectoral girdle.
The acromioclavicular joint is between the small facet of the convex distal clavicle and flat anteromedial acromion. The articular surfaces are lined with fibrocartilage (like the st...
The acromioclavicular AP view is a single projection assessing the patency of the acromioclavicular joint.
See also, acromioclavicular joint injuries.
The AP view of the acromioclavicular joint is often requested when the referrer either knows about or highly suspects an acromiocl...
The acromioclavicular joint AP weight-bearing view, often performed together with the normal non-weight-bearing AP view, helps in ruling out joint displacement when it is suspected but not confirmed on the frontal image.
This view is used in the assessment of possible acromioclavic...
There is much variation in acromioclavicular 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 1-3:
low-lying: associated with shoulder impingement (unfo...
Acromioclavicular joint (ACJ) injections under image guidance ensure precise delivery of an injectate into the joint. Ultrasound allows for real time visualization of the needle and administration of the injectate. Fluoroscopy is an alternative method of image guidance.
pain - art...
Acromioclavicular joint (ACJ) osteoarthritis (OA) is a common degenerative condition of the shoulder.
Acromioclavicular joint osteoarthritis accounts for ~20% (range 12.7-24%) of patients with shoulder pain. It most commonly presents in the fourth decade 3.
The acromioclavicular (AC) joint radiographic series is used to evaluate the acromioclavicular joint and the distal clavicle.
AC radiographs are performed for a variety of indications including:
direct blows to the shoulder region
following a fall onto an adduct...
Acromiohumeral interval is a useful and reliable measurement on AP shoulder radiographs and when narrowed is indicative of subacromial impingement +/- rotator cuff tear or tendinopathy.
The shortest distance is measured.
true AP shoulder radiograph
The acromion (plural: acromia), also known as the acromial process, is a small projection of the scapula that extends anteriorly from the spine of the scapula.
It forms the acromioclavicular joint (ACJ) with the lateral third of the clavicle and also connects with the coracoid p...
The acromion process is the lateral projection of the scapula spine that extends anteriorly. Fractures of the scapula are uncommon injuries and account for ~3% of all shoulder fractures 1,2 while isolated acromion fractures occur rarely and account for only 9% of all scapular fractures 3.
Acro-osteolysis (plural: acro-osteolyses) refers to resorption of the distal phalanx. The terminal tuft is most commonly affected. It is associated with a heterogeneous group of pathological entities and, some of which can be remembered by using the mnemonic PINCH FO.
When there is linear bone ...
The causes of acro-osteolysis can be remembered using the mnemonic:
I: injury, e.g. thermal burn, frost bite
N: neuropathy, e.g. diabetes mellitus, leprosy
C: collagen vascular disease, e.g. scleroderma, Raynaud disease
Acroparesthesia refers to tingling, pins-and-needles, burning or numbness or stiffness in the hands and feet, particularly the fingers and toes 1. Occasionally episodic pain is also present, which can be very severe 1.
It is one of the more common manifestations of Fabry disease (more common t...
Acute abdominal pain is a common acute presentation in clinical practice. It encompasses a very broad range of possible etiologies and diagnoses, and imaging is routinely employed as the primary investigative tool in its modern management.
A subgroup of patients with acute abdomina...
Acute calcific periarthritis is an acutely painful monoarticular condition characterized by the juxta-articular deposition of calcium hydroxyapatite crystals and local inflammation.
Affects both males and females over a wide age range, however, occurs more frequently in females t...