≤11 ribs is associated with a number of congenital abnormalities and skeletal dysplasias, including:
asphyxiating thoracic dysplasia (Jeune syndrome)
short rib polydactyly syndromes
chromosome 1q21.1 deletion syndrome
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 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...
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 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
joint effusion: abnormal hypoechoic or a...
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 n...
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 anaemia (pancytopenia-dysmelia syndrome)
phocomelia (e.g. thalidomide embryopathy)
Poland syndrome (pectoral muscle aplasia and syndactyly)
Accessory navicular syndrome occurs when a type II accessory navicular (or "os tibiale externum") becomes painful due to movement across the pseudojoint between the ossicle and the navicular bone.
It can be inferred on musculoskeletal ultrasound if a patient's...
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 ossicles of the wrist can be easily recalled with the mnemonic:
O: os styloideum (carpal boss)
T: (os) triangulare
T: (os) trapezium secondarium
E: (os) epilunate
O: os hamuli propriu
Another useful mnemonic is HOTELS
H: (os) hamuli propr...
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 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 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...
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 fractures are a pelvic fracture, which may also involve the ilium, ischium, and/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 fema...
Acetabular labral tears, as the name implies, are tears involving the acetabular labrum of the hip.
With the increasing use of hip arthroscopy in orthopaedic surgery since the 1970s pathologies of the acetabular labrum as a possible cause of chronic hip and groin pain have become more familia...
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...
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 (weekend warriors). It is hard to differentiate clinically from a paratendinop...
Achilles tendon ossification (ATO) 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 aetiology is unknown but Achilles tendon ossification i...
Achilles tendon tears are the most common ankle tendon injuries, and are most commonly seen secondary to sports-related injury, especially squash and basketball.
There is strong male over-representation presumably as a result of the predominantly sport related aetiology. Patients ...
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 xanthomas are painless soft tissue masses occurring most commonly at the distal one-third of the tendon and are usually bilateral and symmetrical.
It is characterised by localised accumulation of lipid-laden macrophages, inflammatory cells and giant cells secondary to...
Achondrogenesis refers to a group of rare and extreme skeletal dysplasias.
The estimated incidence is 1:40,000 with no recognised 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.
The growth plate cartilage completely la...
Achondrogenesis type Ib, also known as Parenti-Fraccaro subtype, is a subtype of achondrogenesis and is an extremely rare skeletal dysplasia (chondrodysplasia).
Undersulphation has a pronounced effect on the composition of the extracellular matrix of cartilage, and this has been sh...
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...
Acrocephalopolysyndactyly (ACPS) syndrome is comprised of a rare group of disorders collectively characterised 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) is a rare group of disorders collectively characterised 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 majo...
Acrodysostosis is a rare skeletal dysplasia characterised by growth retardation, nasal hypoplasia, brachydactyly, midfacial deficiency, mental retardation and deafness.
Most cases are sporadic. Few cases with autosomal dominant transmission have been reported. It is believed to occur...
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).
It is most commonly diagn...
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 standardised way of describing the acromion, as well as predicting to a degree the incidence of impingement.
Acromioclavicular joint injuries are common and range from a mild sprain to complete disruption of the acromioclavicular joint (ACJ) and injury to surrounding structures.
Acromioclavicular joint injuries usually occur from a direct blow or following a fall onto the shoul...
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 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...
The acromioclavicular (AC) joint radiographic series is a used to evaluate the acromioclavicular joint and the distal clavicle.
AC radiographs are performed for a variety of indications including:
direct blows to the should region
following a fall onto adducted ...
Acromiohumeral interval is a useful and reliable measurement on AP shoulder radiographs and when narrowed is indicative of rotator cuff tear or tendinopathy.
Measurements of the acromiohumeral interval in the following intervals are suggestive of pathology 1,2:
>12 mm: shoulder dis...
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...
Acro-osteolysis refers to resorption of the distal phalanx. The terminal tuft is most commonly affected but the shaft of the distal phalanx can also be affected in a few conditions. It is associated with a heterogeneous group of pathological entities and, some of which can be remembered by using...
The causes of acro-osteolysis can be remembered using the mnemonic:
I: injury, e.g. thermal burn, frost bite
N: neuropathy, e.g. diabetes, 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.
Is one of the more common manifestations of Fabry disease (more common than...
Adamantinomas are rare primary malignant bone tumours that in the vast majority of cases occur in the tibia of young patients.
In the past, ameloblastomas, which are benign, locally aggressive bone tumours of the mandible, were also known as adamantinomas of the mandible. The two e...
The Adams forward bend test is clinical test to assess the presence of a scoliosis.
Exclusion of a limb length discrepancy is considered important prior to performing the test. The patient is asked to bend forward with feet together, arms hanging and knees extended until the back bec...
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
Adhesive capsulitis of the shoulder, also known as frozen shoulder, is a condition characterised by thickening and contraction of the shoulder joint capsule and surrounding synovium. Adhesive capsulitis can rarely affect other sites such as the ankle 8.
The incidence in the genera...
The ADIR (ADduction and Internal Rotation) position relates to MR arthrography of the shoulder joint.
When added to a neutral-position shoulder protocol, MR arthrography in the ADIR position facilitates the diagnosis of labroligamentous lesions in patients with recurrent shoulder dislocations, ...
Adult-onset Still disease is a rare multisystem inflammatory disorder.
Still disease in adults is rare affecting around 1.5 per 100,000 people, it occurs in a bimodal distribution with one peak around the age of 15-25 years old and another around the age of 35-45 years old 1. It a...
Adventitial bursae are those bursae that develop later in life in response to pressures developed as a result of acquired bony prominences or deformities 1. These bursa can become inflamed resulting in adventitious bursitis.
Adventitious or adventitial bursitis refers to inflammation associated with adventitious bursae.
Adventitious bursae are not permanent native bursae. They can develop in adulthood at sites where subcutaneous tissue becomes exposed to high pressure and friction.
Aggressive angiomyxomas are rare tumours that arise in the pelvis and typically cross the levator ani muscles. Despite its name, it is essentially a benign tumour and the term "aggressive" is given due to a predilection for local recurrence. Only rarely does it metastasise.
It is ...
Aggressive fibromatosis is a type of musculoskeletal fibromatosis. While it is a non-metastasising fibrous lesion, it is thought to be a true neoplasm that arises from the fascial and musculoaponeurotic coverings, sometimes at the site of a traumatic or post-surgical scar.
Aggressive granulomatosis post hip replacement is a potential complication of a hip joint replacement. Some authors use the same term for particle disease - if you are an expert on this we would love your help.
Aggressive granulomas consist of well organised connective tissue contain...
This classification was proposed by Ahlback et al. in 1968.
According to Ahlbäck system, knee joint osteoarthritis is classified as:
grade 1: joint space narrowing (less than 3 mm)
grade 2: joint space obliteration
grade 3: minor bone attrition (0-5 mm)
grade 4: moderate bone attrition (5-1...
Ainhum ("dactylolysis spontanea") is a rare cutaneous condition in which a hyperkeratotic band partially or totally encircles a digit. The constriction thins the underlying bone, which is then prone to fracture. Some cases result in autoamputation.
Some have suggested that the dis...
Allen and Ferguson classification is used for research purposes to classify subaxial spine injuries. It is based ofn the mechanism of injury and position of the neck during injury. This classification was proposed by Allen and Ferguson in 19823 and at the time of writing (July 2016) remains the ...
Alpha angle can refer to two different musculoskeletal measurements:
alpha angle (developmental dysplasia of the hip)
alpha angle (femoroacetabular impingement)
The alpha angle is a measurement used in the ultrasonographic assessment of developmental dysplasia of the hip (DDH).
The angle is formed by the acetabular roof to the vertical cortex of the ilium and thus reflects the depth of the bony acetabular roof. This is a similar measurement to the acet...
Alternating radiolucent and radiodense metaphyseal lines can be seen with a number of conditions and the differential diagnosis is wide:
growth arrest lines
rickets: especially those on prolonged treatment, e.g. vitamin D dependent rickets
Alveolar rhabdomyosarcomas are a type of rhabdomyosarcoma and account for 20-40% of all rhabdomyosarcomas 1-2.
Unlike embryonal rhabdomyosarcomas, which are more common, these tumours occur in slightly older individuals, typically 10-25 years of age 1.
Alveolar soft part sarcomas are rare, highly vascular, deep soft tissue malignancy that is classically seen in the lower extremities of young adults. They account for <1% of all soft tissue sarcomas.
There is a slight female predilection in patients less than 30 years old 1.
The American Academy of Orthopedic Surgeons classification of periprosthetic hip fractures divides the femur into three separate regions:
level I: proximal femur distally to the lower extent of the lesser trochanter
level II: 10 cm of femur distal to level I
level III: femur distal to level...
Amniotic band syndrome (ABS) comprises of a wide spectrum of abnormalities, all of which result from entrapment of various fetal body parts in a disrupted amnion. Due to the randomness of entrapment, each affected individual has the potential to form a unique deficit.
Amphiarthroses are a functional class of joint that permit a small amount of movement under normal conditions.
symphyses (secondary cartilaginous joints)
The term amputation refers to the disconnection of all or part of a limb from the body. Specifically amputation is defined as removal of the structure through a bone. This is in contrast to disarticulation, which is removal of the structure through a joint.
When due to trauma, trau...
The Amsterdam wrist rules are validated clinical decision rules for determining which patients require radiographic imaging (wrist radiography) for acute wrist pain following trauma. The initial study evaluated 882 patients and were published in 2015 1. The decision rules assessed different clin...
Amyloid arthropathy is the extracellular deposition of the fibrous protein amyloid within the skeletal system. It is a skeletal manifestation of amyloidosis and may involve either the axial skeleton (especially the cervical spine) or the appendicular skeleton.
Amyoplasia congenita is a syndrome characterized by multiple specific congenital joint contractures, associated with substitution of muscular tissue by fibrosis and adipose tissue.
The estimated incidence is at 1: 10000 live births. There may be a higher prevalence with twin preg...
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
An anaplastic rhabdomyosarcoma is a subtype of embryonal rhabdomyosarcoma, characterised by extensive anaplastic cells seen throughout the tumour 1.