Normal Radiographic Anatomy: Elbow and Arm

Vocabulary flashcards covering normal radiographic anatomy, lines of measurement, fat pads, secondary ossification centres, and common normal variants and abnormalities of the elbow and upper arm.

Routine Projections of the Elbow

The standard radiographic examination of the elbow consisting of the Anteroposterior (AP) and Lateral views to assess alignment, articular surfaces, and adjacent soft tissues.

Routine Projections of the Humerus

The standard radiographic views consisting of the Anteroposterior (AP) and Lateral projections, which visualize the humeral shaft and ideally include both the shoulder and elbow joints.

Anterior Humeral Line

A radiographic alignment line drawn down the anterior cortical margin of the humeral shaft on a true lateral elbow radiograph; it should normally transect the middle third of the capitellum.

Radiocapitellar Line

A line drawn through the longitudinal center of the radial neck that should intersect the capitellum on every radiographic projection, where non-intersection indicates radial head dislocation.

Normal Elbow Fat Pads

Intracapsular, extrasynovial adipose structures where the anterior fat pad sits within the coronoid fossa (normally visible as a thin radiolucent stripe) and the posterior fat pad sits within the olecranon fossa (normally invisible).

Sail Sign

Elevation and triangular displacement of the anterior fat pad away from the humerus caused by joint effusion, commonly indicating a radial head fracture in adults or a supracondylar fracture in children.

Posterior Fat Pad Sign

The radiographic visualization of the posterior fat pad displaced from the olecranon fossa on a lateral projection, indicating joint distension usually due to an occult non-displaced radial head fracture in adults or a supracondylar fracture in children.

CRITOE

A mnemonic describing the sequence and ages of appearance of the six secondary ossification centres of the pediatric elbow: Capitellum ($1\text{ year}$), Radial head ($3\text{ years}$), Internal (medial) epicondyle ($5\text{ years}$), Trochlea ($7\text{ years}$), Olecranon ($9\text{ years}$), and External (lateral) epicondyle ($11\text{ years}$).

Elbow Ossification Sequence Rule

The clinical radiographic principle specifying that the trochlea ossification centre must never appear prior to the internal (medial) epicondyle ossification centre.

Olecranon Foramen

A normal anatomical variant (also called septal aperture or supratrochlear foramen) resulting from failed ossification of the bony septum between the coronoid and olecranon fossae, visible as an oval lucency in the distal humerus.

Radioulnar Synostosis

An abnormal bony union across the proximal radius and ulna obliterating the interosseous space and restricting pronation and supination; can be post-traumatic or congenital (associated with syndromes such as Klinefelter, Apert, Holt-Oram, or Cornelia de Lange).

Supracondylar Process of the Humerus

A congenital bony spur present in approximately $1\%$ of individuals, pointing distally and anteromedially from the humeral metadiaphysis roughly $5\,\text{cm}$ superior to the medial epicondyle.

Struthers Ligament

A fibrous band extending from a supracondylar spur of the humerus to the medial epicondyle, which can compress the brachial artery or median nerve.

Radial Head Fracture

A break of the proximal radius commonly caused by indirect force transmitted through a fall onto an outstretched hand (FOOSH) with elbow flexion; often occult on initial radiographs, necessitating careful evaluation of joint fat pad displacement.

Radial Tuberosity Pseudocyst

A normal variant displaying an ovoid, cyst-like radiolucency at the proximal radius on lateral elbow projections, produced by localized trabecular rarefaction in a low-stress biomechanical zone.

Humeral Head Pseudocyst

A "do not touch" normal variant presenting as a lucent lesion within the greater tuberosity of the humerus with a well-defined inferior curvilinear margin, caused by a local abundance of cancellous bone.

Prominent Deltoid Insertion

Localized cortical thickening along the lateral midshaft of the humerus at the deltoid tuberosity that mimics periostitis or neoplasm.

Os Supratrochlear Dorsale

An accessory ossicle situated in the olecranon fossa of the humerus that may cause impingement symptoms during elbow extension, requiring differentiation from an intra-articular loose body.

Patella Cubiti

A rare sesamoid bone positioned within the distal tendon of the triceps brachii that mimics the appearance of a patella on lateral radiographs; differential diagnoses include an ununited olecranon fracture or persistent olecranon epiphysis.

CT Arthrography of the Elbow

An imaging technique combining intra-articular contrast injection with computed tomography, specifically tailored for the evaluation of traumatic or degenerative lesions of the articular cartilage and subchondral bone plate.