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.
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...
Avascular necrosis (AVN), or more correctly osteonecrosis, is a generic term referring to the ischaemic death of the constituents of bone. AVN has a wide variety of causes and can affect nearly any bone in the body. Most sites of involvement have an eponym associated with avascular necrosis of t...
Mnemonics for the causes of avascular necrosis (AVN) or more correctly osteonecrosis:
Most common causes:
T: trauma (e.g. femoral neck fracture, hip dislocation, scaphoid fracture)
A: alcohol abuse
S: sickle cell dise...
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. The talar neck is the mo...
An aviator fracture is a coronal-plane fracture of the neck of the talus resulting from forced dorsiflexion of ankle. It is the second most common talar fracture, after talar dome fractures.
In 20% of cases a fracture of the medial malleolus is also present 1.
These fractures are at risk of av...
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, where a portion of cortical bone is ripped from the rest of the bone by the attached tendon, are common among those who participate in sports, and there are numerous sites at which these occur. Being familiar with them is important as chronic injuries can appear aggressive.
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...
Baastrup syndrome (also referred to as kissing spines) results from adjacent spinous processes in the lumbar spine rubbing against each other and resulting in hypertrophy and sclerosis with focal midline pain and tenderness relieved by flexion and aggravated by extension.
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.
Characterised 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 recognised 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 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...
Bamboo spine is a 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 and/or lumbosacr...
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 a common complication of anterior shoulder dislocation and are frequently seen in association with a Hill-Sachs lesion.
They result from detachment of the anterior inferior labrum from the underlying glenoid as a direct result of the anteriorly dislocated humeral ...
Bannayan-Zonana syndrome is a rare hamartomatous disorder.
Inheritance is by autosomal dominant transmission with few reported sporadic cases. Male predominance is reported. 1
Bannayan-Zonana syndrome characterised by :
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...
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):
Baumann angle, also known as the humeral-capitellar angle, is used for the evaluation of the displacement of paediatric 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 ep...
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 of age.
S - simple bone cyst
C - chondroblastoma
A - aneurysmal bone cyst
N - non-ossifying fibroma
E - eosinophilic granuloma
In a patient older than 30 years of age th...
A Bennett fracture-dislocation is a fracture of the thumb resultant of forced abduction of the first metacarpal. Defined as an intra-articular two-part fracture of the base of the first metacarpal bone.
two piece fracture dislocation of the base of the t...
A Bennett lesion (of the shoulder) refers to a mineralisation of the posterior band of the inferior glenohumeral ligament .
More prevalent in overhead throwing athletes.
Patients may have pain during the cocking and follow-through phases of throwing. There...
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 osteotomy, also known also Ganz osteotomy, is an orthopaedic 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 through the su...
Bertolotti syndrome refers to the association between lumbosacral transitional vertebrae (LSTV) and low back pain, and can be an important cause in young patients.
It is considered controversial and has been both supported and disputed since Mario Bertolotti first described it in 1917. Some st...
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
A biceps brachii rupture can occur at either superior or inferior end but most commonly involves the long head at its proximal attachment to superior glenoid labrum.
The biceps tendon has a fibrous covering (the lacertus fibrosus) that can clinically feel similar to an intact tendon even though...
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.
long head: medial facet of the ischial tuberosity
short head: lateral line...
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.
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”.
Anatomy of Biceps Pulley:
The biceps pulley or “sling” is a complex capsuloligamentous structur...
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 whi...
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 ribs are uncommon. They are thought to occur in ~0.2% of the population and there may be a female as well as right-sided predilection 2.
Usually asymptomatic, they may cause musculoskeletal pain or intercostal nerve entrapment. A bifid first rib is an unco...
The bifurcate ligament arises from the anterior process of the calcaneus as a single band and divides into calcaneocuboid (lateral) and calcaneonavicular (medial) parts forming a Y-shape.
A bilateral facet dislocation is a flexion distraction type of dislocation of the cervical spine, often a result of buckling force.
It has been thought to result from hyperflexion, however, recent studies suggest a buckling force to be the cause 1.
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 aetiology is unknown but is thought to be an age-r...
A bipartite medial cuneiform is an anatomical variant where there are two ossification centres 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 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
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 recognised increased incidence with high birth weight babies, forceps delivery and shoulder dyst...
Birth trauma relates to those conditions caused by both physical/mechanical and hypoxic injuries.
Birth trauma occurs in ~5 per 1000 births 2.
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 proximal third of the femur, typically subtrochanteric, and may be unilateral or bilatera...
Bizarre parosteal osteochondromatous proliferation (BPOP) (also known as a Nora lesion) is a benign exophytic osteochondral lesion which has an appearance similar to an osteochondroma, and is typically seen in the hands and feet.
BPOPs are continuous with the underlying cortex, but usually wit...
The Blackburne-Peel ratio is an alternative to Insall-Salvati ratio and is used to assess patellar height, and determine the presence of patella baja or patella alta.
A lateral radiograph of the knee with 30 degrees of flexion is obtained, and a horizontal line at the level of the tibial platea...
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...
Blade plates (or angled blade plates) are a type of orthopaedic hardware used for reconstructing subtrochanteric femoral fractures, including therapeutic fractures during derotational osteotomies.
Blade plates were an advance on earlier fixation nails such as the Y nail or the Zicker nail. Alth...
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.
hemivertebrae/absent vertebra above or below block leve...
Bloom syndrome is a rare autosomal recessive disorder characterized by short stature, brachydactyly, malar hypoplasia and facial telangiectasia, erythema and cafe au lait spots. Affected individuals have an increased risk of developing malignancies.
There is extreme chromosomal fragi...
Blount disease refers to a local disturbance of growth of the medial proximal tibial epiphysis that results in tibia vara. The condition is commonly bilateral.
There is no recognised inheritance pattern.
Clinically, the child often presents with leg bowin...
Blow out bone metastases or expansile bone metastases are typically only encountered in a relatively small number of primary malignancies, including 1:
renal cell carcinoma
Occasionally the sclerotic metastases of prostate cancer may also be expansile a...
Blumensaat line is the line drawn along the roof of the intercondylar notch of the femur as seen on lateral radiograph of the knee joint. It can been used for:
indicating the relative position of the patella as normally this line intersects the lower pole of the patella
suggesting ACL injury a...
A Bochdalek hernia is a form of congenital diaphragmatic hernia. They occur posteriorly and are due to a defect in the posterior attachment of the diaphragm when there is a failure of pleuroperitoneal membrane closure in utero. Retroperitoneal structures may prolapse through the defect, e.g. ret...
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...
Böhler angle, also written as Bohler angle or Boehler angle, is also called the calcaneal angle or tuber joint angle 1, and is the angle between two lines tangent to the calcaneus on the lateral radiograph. These lines are drawn tangent to the anterior and posterior aspects of the superior calca...
Bone age assessment is an important part of the diagnostic and management pathway in children with growth and endocrine disorders. It is helpful in the diagnosis of various growth disorders and can provide a prediction of final height for patients presenting with short stature.
Bone age can als...
Bone (marrow) contusion (bone bruising or bone marrow oedema) is an osseous injury which may result from compression of bone structures.
Bone contusions represent microfractures with haemorrhage and can progress to osteochondritis dissecans 2. They typically appear within 48 hours of...
A mnemonic for bony cortical lesions is:
O: osteoid osteoma
S: stress fracture
Conditions associated with bone deformity from softening includes:
bowing of long bones
biconcave vertebral bodies / codfish vertebra
Bone-forming tumours are a subset of bone tumours that are characterised by their propensity to form excess osteoid. They can be further subdivided into benign and malignant tumours.
bone island (enostosis)
Bone infarction is a term used to refer to osteonecrosis within the metaphysis or diaphysis of a bone. Necrosis is a type of cell death due to irreversible cell injury, which can be recognised microscopically by alterations in the cytoplasm (becomes eosinophilic) and in the nucleus (swelling, py...
There are several bony lesions that can involve or depict a sequestrum.
brodie abscess: osteomyelitis
certain soft tissue tumours (with bony extension)
malignant fibrous histiocytoma
metastasis (especially from breast ca...
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:
Normal bone marrow is divided into red and yellow marrow, a distinction made on the grounds of how much fat it contains.
Red marrow is composed of:
reticulum (phagocytes and undifferentiated progenitor cells)
scattered fat cells
a rich ...
Bone mineral density (BMD) is defined as amount of mineral (calcium hydroxyapatite) per unit of bone.
BMD can be measured by various methods:
gamma rays: replaced by radiographic methods
single-energy photon absorptiometry (SPA) was superseded by the introduction of sin...
Bone scans are a nuclear medicine (scintigraphic) study that makes use of Technetium 99m (commonly Tc99m-methylene diphosphonate (MDP)) as the active agent.
The study has three phases which follow intravenous injection of the tracer. Sometimes a fourth (delayed/delayed) phase is performed.
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 ...
There are a bewildering number of bone tumours with a wide variety of radiological appearances:
bone island / enostosis
Bone within a bone is a descriptive term applied to bones that appear to have another bone within them. There are numerous causes including:
thoracic and lumbar vertebrae (neonates and infants)
growth recovery lines (after infancy)
cortical splitting and new periostitis
sickle cell d...
A useful mnemonic to remember the possible aetiologies of a bone within a bone appearance is:
G: growth arrest lines
H: heavy metal, hypoparathryoid, hypothyroid
S: sickle cell anaemia, scurvy, syphilis
T: thalassamia, tuberculosis
D: disease of Caf...
Bony humeral avulsion of the glenohumeral ligament (BHAGL) lesion is just like its slightly shorter relative HAGL lesion, except as the name suggests a bony avulsion fracture is seen at humeral insertion of the inferior glenohumeral ligament.
It is often associated with a subscapularis tear, an...
A mnemonic to help remember bony lesions that have no pain or periostitis is:
F: fibrous dysplasia
U: unicameral bone cyst
N: non-ossifying fibroma
If periostitis or pain is present (assuming no trauma, which can be a foolhardy assumption), you can exclude E-...
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...