Arthroplasty is a procedure that reconstructs or reforms the articular surface of a joint. There are numerous types of arthroplasty that range from complete replacement of all sides of the joint (total joint replacement) or one articular surface (hemiarthroplasty) with various combinations of me...
The articularis cubiti muscle lies 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...
Articular-sided rotator cuff tears are referred to as partial-thickness rotator cuff tears extending from the articular side into the rotator cuff.
Articular-sided rotator cuff tears commonly occur in athletes with overhead activity 1.
They are more common than bursal-sided tears...
First published in 2009 with a revised consensus in 2016, the Assessment in SpondyloArthritis International Society (ASAS) classification system utilizes imaging features of the sacroiliac joints on MR imaging to assist in characterizing the presence of sacroiliitis.
The ASAS classification is ...
Aseptic loosening is considered relatively common complication of hip joint replacements. It is usually considered a long-term complication and is often considered as the most common complication 3.
Aseptic loosening can occur as a result of inadequate initial fixation, mechanical lo...
Aseptic lymphocyte-dominant vasculitis-associated lesion (ALVAL) is a histological entity denoting a chronic inflammatory response to metal particles (cobalt and chromium ions) from a metal-on-metal prosthesis. The finding falls on the spectrum of adverse reactions to metal debris.
The American Spinal Injury Association Impairment Scale was developed by the American Spinal Injury Association (ASIA) in 2006, was revised in 2011, and remains the most widely used neurologic classification of spinal cord injury.
The scale divides spinal cord injuries into 5 ca...
Many signs in radiology have been inspired by astronomical phenomena:
comet tail (disambiguation)
comet tail artifact (ultrasound)
color comet tail artifact
comet tail sign (chest)
comet tail sign (phleboliths)
galaxy sign (chest)
loss of half-moon overlap sign
Atelosteogenesis refers to a heterogeneous group of lethal skeletal dysplasias that are characterized by aplasia/hypoplasia of the humeri, femora and spine.
atelosteogenesis type I (boomerang dysplasia)
atelosteogenesis type II
atelosteogenesis type III 4
Athletic pubalgia or groin pain in athletes is a clinical syndrome of chronic lower pelvic and groin pain, usually encountered in athletes. It is either a musculotendinous or osseous injury that involves the insertion of abdominal muscles on the pubis and the upper aponeurotic insertion of the a...
Atlanto-axial subluxation is a disorder of C1-C2 causing impairment in rotation of the neck. The anterior facet of C1 is fixed on the facet of C2. It may be associated with dislocation of the lateral mass of C1 on C2.
Down syndrome (20%)
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 0.08-3%) of the population 2-5,. It is thought to affect males and females equally.
Atlanto-occipital dissociation (AOD) injuries are severe and include both atlanto-occipital dislocations and atlanto-occipital subluxations.
The tectorial membrane and alar ligaments provide most of the stability to the atlanto-occipital joint, and injury to these ligaments results i...
The atlas (plural: atlases) 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. ...
The atlas of individual radiographic features in osteoarthritis (OARSI atlas) are publications about radiographic features of osteoarthritis in different joints. They provide a grading scheme for those features illustrated by imaging examples 1,2.
The original and revised version of the OARSI a...
Atraumatic fractures, as the name suggests, occur with no trauma or minimal trauma that would not normally be expected to result in a fracture 1. They can be:
atypical fractures, e.g. bisphosphonate-related proximal femoral fractures
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 anterior and posterior arches with lateral masses. Its superior articular surfaces articulate with the occiput at t...
Atypical femoral fractures, also known as bisphosphonate-related proximal femoral fractures, are an example of insufficiency fractures, although the direct causative link remains somewhat controversial 2. The atypical fracture pattern occurs in the femur shaft and may be unilateral or bilateral...
Atypical fibroxanthomas are well-circumscribed mesenchymal skin tumors that mainly manifest in the head and neck
Atypical fibroxanthomas are rapidly growing tumors associated with excessive sun exposure, i.e. UV exposure, and usually occur in elderly patients. There is also an ass...
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. Some authors however describe the second, tenth and eleventh ribs as atypical ribs also.
Of all ribs, the first is the strongest, broadest and most curved. Ribs eleven and twelve are unique, among other ...
Atypical spindle cell/pleomorphic lipomatous tumors or atypical spindle cell lipoma are benign adipocytic soft tissue neoplasms with a variable proportion of atypical spindle cells, pleomorphic cells adipocytes and other cells with no risk for dedifferentiation but a low risk of local recurrence...
T1 and T9 - T12 are considered atypical thoracic 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 Atzei classification of peripheral triangular fibrocartilage complex (TFCC) tears offers a more differentiated approach on a spectrum of peripherally located triangular fibrocartilage complex (TFCC) tears, which are classically summarized as “Palmer 1b” lesions 1-3.
Autologous chondrocyte implantation (ACI) is a cell-based cartilage reconstruction or replacement method where hyaline articular cartilage is directly administered and retained. It can be used for larger chondral lesions, where the subchondral bone plate remains intact.
Autosomal dominant osteopetrosis is the less severe type of osteopetrosis and should be considered and compared with the other subtype autosomal recessive osteopetrosis. The autosomal dominant (AD) type is less severe than its autosomal recessive (AR) mate. Hence, it is also given the name "beni...
Infantile autosomal recessive osteopetrosis is a subtype of osteopetrosis, a bone disease of dysfunctional osteoclasts that results in the overgrowth of bone. It is a more severe form that tends to present earlier. Hence, it is referred to as "infantile" and "malignant" compared to its autosomal...
Mnemonics for the causes of avascular necrosis (AVN) or more correctly osteonecrosis:
Most common causes:
S: steroids, SLE
T: trauma (e.g. femoral neck fracture, hip dislocation, scaphoid fracture, slipped capital femoral epiphysis 2)
Avascular necrosis of the hip is more common than other sites, presumably due to a combination of precarious blood supply and high loading when standing.
The most common presenting symptom is a pain in the region of affected hip, thigh, groin, and buttock. Although few p...
Aviator astragalus is an antiquated reference to a pattern of isolated fracture/dislocation injury of the talus. Fractures included under this name include compression fractures of the talar neck, fractures of the body, posterior process or fracture-dislocation injuries.
More specifically the t...
Avulsion fracture of the 5th metatarsal styloid, also known as a pseudo-Jones fracture or a dancer fracture, is one of the more common foot avulsion injuries and accounts for over 90% of fractures of the base of the 5th metatarsal.
Despite what should be a simple entity, controversy exists, as ...
Avulsion fractures of the knee are numerous due to the many ligaments and tendons inserting around this joint. They include 1:
anterior cruciate ligament avulsion fracture
posterior cruciate ligament avulsion fracture
avulsion of the medial collateral ligament
origin of MCL avulsion fracture...
Avulsion injuries or fractures occur where the joint capsule, ligament, tendon or muscle attachment site is pulled off from the bone, usually taking a fragment of cortical bone. Avulsion fractures are commonly distracted due to the high tensile forces involved. There are numerous sites at which ...
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 thorax, which permits the passage of major neurovascular structures.
The axilla is pyramidal in shape with its apex opening superiorly towards the base of the neck between the subclavius muscle, first rib, superior border o...
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 (or dens), which is embryologically the body of the atlas (C1) 1,2. ...
Baastrup disease/syndrome (also referred to as kissing spines) is a cause of low back pain characterized by interspinous bursitis and other degenerative changes of the bones and soft tissues where adjacent spinous processes in the lumbar spine rub against each other.
It tends to b...
Babcock triangle is a relatively radiolucent triangular area seen in the subcapital region of the femoral neck on an anteroposterior radiograph of the hip. In this region, the trabeculae are loosely arranged and surrounded by more radiodense normal bony trabeculae groups. It may be the initial s...
Bacillary angiomatosis is an infective complication in those with the acquired immunodeficiency syndrome (AIDS) 3. Amongst other widespread multi-organ manifestations, the infection causes skin lesions which can be similar to those of Kaposi sarcoma.
Characterized by a non-neoplastic...
The Bado classification is one of the more widely used classifications for Monteggia fracture-dislocations and mainly focuses on the radial component. Four types are recognized and are generally based on the principle that the direction in which the apex of the ulnar fracture points is the same ...
Baker cysts, or popliteal cysts, are fluid-filled distended synovial-lined lesions arising in the popliteal fossa between the medial head of the gastrocnemius and the semimembranosus tendons via a communication with the knee joint. They are usually located at or below the joint line.
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 etiology has been debated with two theories p...
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...
Bamboo spine is a pathognomonic radiographic feature seen in ankylosing spondylitis that occurs as a result of vertebral body fusion by marginal syndesmophytes. It is often accompanied by fusion of the posterior vertebral elements as well.
A bamboo spine typically involves the thoracolumbar an...
A banana fracture refers to a complete, horizontally oriented pathological fracture seen in deformed bones affected by Paget disease. This term is often used to describe incremental fractures that occur in Paget disease as well, which represent a type of insufficiency fracture.
The former of th...
Bankart lesions are injuries specifically at the anteroinferior aspect of the glenoid labral complex and represent a common complication of anterior shoulder dislocation. They are frequently seen in association with a Hill-Sachs lesion.
Strictly speaking, a "Bankart lesion" refers...
Bannayan–Riley–Ruvalcaba syndrome (BRRS or BRR syndrome) is a very rare autosomal dominant hamartomatous disorder caused by a mutation in the PTEN gene. It is considered in the family of hamartomatous polyposis syndrome.
There are no formal diagnostic criteria for this disease, but characterist...
Bannayan-Zonana syndrome, also known as Bannayan-Riley-Ruvalcaba syndrome, is a rare hamartomatous disorder.
Male predominance is reported 1.
Bannayan-Zonana syndrome is characterized by:
Other findings that...
Bare area is a term that may apply to:
bare area of the liver
bare area of the spleen
glenoid bare area
bare area of a joint where synovium is in direct contact with bone, the site of marginal joint erosion in some inflammatory arthritides
Barton fractures are fractures of the distal radius. It is also sometimes termed the dorsal type Barton fracture to distinguish it from the volar type or reverse Barton fracture.
Barton fractures extend through the dorsal aspect to the articular surface but not to the volar aspect. Therefore, i...
A basal cell carcinoma (BCC) is one of the commonest non-melanocytic types of skin cancer.
Typically present in elderly fair skinned patients in the 7th to 8th decades of life. There may be an increased male predilection.
Multiple basal cell carcinomas may be prese...
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 - from anterior to posterior:
Baumann angle, also known as the humeral-capitellar angle, is used for the evaluation of the displacement of pediatric supracondylar humeral fractures. It is measured on a frontal radiograph, with elbow in extension.
This angle is formed by the humeral axis and a straight line through the epi...
Baxter neuropathy is a nerve entrapment syndrome resulting from the compression of the inferior calcaneal nerve (Baxter nerve).
heel pain with maximal tenderness over the course of the inferior calcaneal nerve (on the plantar medial aspect of the foot and anterior to the ...
Bayonet deformity is a term used to describe the shape of the wrist in certain conditions:
hereditary multiple exostosis with pseudo-Madelung deformity
retarded bone growth of the distal ulna with outward bowing of the radius with distal radioulnar joint subluxation
Becker muscular dystrophy (BMD) is a dystrophinopathy that is considered to be a milder form of Duchenne muscular dystrophy.
It may be present in 3 to 6 per 100,000 male births. The condition is extremely rare in females due to its inheritance pattern, as discussed below.
Benign fibrous histiocytoma is closely related to fibroxanthoma of bone, is a rare lesion usually occurring in the skin where it is known as dermatofibroma.
Typically presents with pain, and most often in the third decade.
Only a few case reports have been pub...
Benign lytic bone lesions encompass a wide variety of entities. A useful starting point is the FEGNOMASHIC mnemonic.
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A mnemonic to remember five benign lytic lesions that rarely occur in patients over 30 years old
S: simple bone cyst
A: aneurysmal bone cyst
N: non-ossifying fibroma (including fibrous cortical defect)
E: eosinophilic granuloma
In a patient old...
Benign notochordal cell tumors are vertebral lesions that are usually asymptomatic and discovered incidentally on imaging of the head or spine. As this is a poorly-recognized entity, it can often be confused with aggressive vertebral lesions, such as a chordoma, when it is seen on imaging.
A Bennett fracture is a fracture of the base of the thumb resulting from forced abduction of the first metacarpal. It is defined as an intra-articular two-part fracture of the base of the first metacarpal bone.
two piece fracture of the base of the thumb...
Bennett lesions of the shoulder, also called thrower's exostosis refers to the mineralization of the posterior band of the inferior glenohumeral ligament.
The abnormality is more prevalent in overhead throwing athletes.
It is associated with posterior labral tears,...
Bent bone dysplasias are a class of dysplasia included in a 2010 classification of genetic skeletal disorders 1.
kyphomelic dysplasias, a diverse class, including
congenital bowing of the long bones
cartilage-hair hypoplasia (CHH; metaphyseal d...
Berndt and Harty classification is used for osteochondral lesions of the talus.
stage I: subchondral bone compression (marrow edema)
stage IIa: subchondral cyst
stage IIb: incomplete separation of fragment
stage III: complete separation but no displacement
Bernese periacetabular osteotomy, also known as Ganz osteotomy, is an orthopedic procedure involving osteotomy surrounding the acetabulum and subsequent angulation to improve coverage of the femoral head by the acetabulum. It is performed in the context of hip dysplasia. There is an osteotomy th...
Bertolotti syndrome refers to the association between lumbosacral transitional vertebrae and low back pain.
Although it may be a consideration in younger patients, the entity is considered controversial and has been both supported and disputed since the Italian radiologist Mario Bertolotti (187...
The beta angle is a measurement used in the ultrasonographic assessment of developmental dysplasia of the hip (DDH).
It is defined as the angle formed between the vertical cortex of the ilium and the triangular labral fibrocartilage (echogenic triangle) and thus reflects the femoral head cartil...
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
Biceps brachii rupture can occur at either superior or inferior attachment but most commonly involves the long head at its proximal origin at the superior glenoid labrum. Rupture of the distal biceps rupture causes weakness when supinating the forearm. It is therefore associated with significant...
Biceps chondromalacia is an attritional lesion of the humeral head caused by repeated abrasion by the intra-articular segment of the long head of biceps tendon.
The long head of biceps brachii arises from the supraglenoid tubercle of the glenoid fossa and has an intra- and extra-arti...
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.
Its medial border forms the superolateral border of the popliteal fossa.
The biceps pulley is a capsuloligamentous complex that stabilizes the long head of biceps tendon within the bicipital groove. It comprises the coracohumeral ligament, superior glenohumeral ligament, and distal attachment of the subscapularis tendon. It is located within the rotator interval betw...
Biceps pulley injuries can be challenging and difficult to diagnose. They can be missed during open and arthroscopic examination, and therefore have sometimes been referred to as a “hidden lesions”.
Anterior extension of supraspinatus tendon tears may involve the rotator interval cap...
The bicipital groove (also known as the intertubercular sulcus or sulcus intertubercularis) is the indentation between the greater and lesser tuberosities of the humerus that lodges the biceps tendon.
The bicipital groove is typically 4-6 mm deep 1. It contains the tendon of the ...
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...
Bicipitoradial bursitis refers to inflammation of the bicipitoradial bursa.
The bicipitoradial bursa surrounds the biceps tendon in supination. In pronation, the radial tuberosity rotates posteriorly, which compresses the bicipitoradial bursa between the biceps tendon and the radial cortex, wh...
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 ...
Bifid or forked or bifurcated rib is a congenital skeletal abnormality of the rib cage with the cleaved sternal end into two. They are thought to occur in ~0.2% of the population and there may be a female as well as right-sided predilection 2.
Bifid ribs can be seen ...
The bifurcate ligament is one of the ligaments of the midtarsal joint, connecting the calcaneus with the navicular and the cuboid bone.
The bifurcate ligament arises from the anterior process of the calcaneus (distal to the origin of the extensor digitorum brevis). It consists of...
Biker's nodule refers to a mass in the perineum that occur in cyclists.
In keeping with bicycling being a male dominated recreational activity, the pathology is most commonly found in young-middle aged males, more commonly during first 6 to 12 months of taking up the sport.
A bilateral facet dislocation is an unstable flexion distraction type of dislocation of the cervical spine, often a result of buckling force. Occasionally, the bilateral facet dislocation has been named a 'doubly-locked' vertebral injury giving the impression of stability. However, due to comple...
Bilateral thinning of the parietal bones, also known as biparietal osteodystrophy, is an uncommon, slowly progressive acquired disease of middle-aged people with slight female predilection. It is typically an incidental finding.
The etiology is unknown but is thought to be an age-re...
A bipartite medial cuneiform is an anatomical variant where there are two ossification centers involving the medial cuneiform. In many cases, the overall shape of the medial cuneiform is conserved, although the size of the two combined bones is larger than that of a normal medial cuneiform.
A bipartite patella (two-part patella) is a patella with an unfused accessory ossification center, typically 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. Bipartite...
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
Birth fractures of the clavicle occur in 0.5-1% of vaginal deliveries and are the most frequent birth-related fracture. They are most commonly seen following normal, uncomplicated births but there is recognized increased incidence with high birth weight babies, forceps delivery and shoulder dyst...
Birth trauma (a.k.a. birth injury) relates to those conditions caused by both physical/mechanical and hypoxic injuries.
Birth trauma occurs in ~5 per 1000 births 2.
Bizarre parosteal osteochondromatous proliferations (BPOP), also known as Nora lesions, are benign exophytic osteochondral lesions which have an appearance similar to an osteochondroma and are typically seen in the hands and feet. On imaging, BPOPs are shown to be continuous with the underlying ...
The Blackburne-Peel ratio is an alternative to Insall-Salvati ratio and is used to assess patellar height including patella alta and baja.
The Blackburne-Peel ratio has higher interobserver reliability compared to the Insall-Salvati ratio and can also be used when the tibial tuberosity ...
The black line sign refers to a linear finding of the articular cartilage on magnetic resonance imaging initially seen the trochlear groove 1-3.
These lesions have been found also in all other regions of articular cartilage in the knee and not only on T2 weighted images but also in other sequen...
The blade of grass sign, also called the candle flame sign, refers to the lucent leading edge in a long bone seen during the lytic phase of Paget disease of bone.
The blade of grass sign is characteristic of Paget disease of bone. This is akin to osteoporosis circumscripta cranii seen in the s...