Changes in the position of the talar and calcaneal axes relative to one another in the
(A) pes planovalgus,
(B) rectus,
(C) and pes cavus foot.
Initially, this entails a general overview of the foot and is assessed with the planar views, i.e., dorsoplantar (anteroposterior) and lateral views. Sit back and gain an overall impression of the foot type. Appreciate the position of each bone relative to the remaining structures (i.e., "Eyeballing a Biomechanical Evaluation"). The axis of each bone has a characteristic position in the foot relative to neighboring bones. Primarily, the angulation between the two bones is assessed and compared to the rectus ("normal") foot. For example, in the dorsoplantar view, the talar axis is mildly adducted (or, angulated medially) relative to the calcaneal axis in the rectus foot, greatly adducted in the pes planovalgus foot, and nearly parallel to the calcaneal axis in the pes cavus foot:
| A |
B |
C |
Changes in the position of the talar and calcaneal axes relative to one another in the (A) pes planovalgus, (B) rectus, (C) and pes cavus foot. |
The position of adjacent articular surfaces is also assessed. There normally should be 100% apposition between the two surfaces. Partial apposition is a sign of subluxation, and 0% apposition represents dislocation:
A  |
B  |
Position: apposition between two articular surfaces. (A) partial apposition (subluxation of the first and second metatarsal-cuneiform joints), and (B) 0% apposition (dislocation of the second toe proximal interphalangeal joint). |
Positioning terminology is especially useful when describing the position of a fracture fragment relative to another. Alignment conveys the degree of parallelism of the two fragments . Angulation refers to a lack of alignment or parallelism of the two segments and can be described in two fashions: by the tilt of the distal segment relative to the proximal segment, or, by the direction the apex formed between the two segments points . The degree of bony contact (touching) between the two fracture fragments is referred to as apposition . If there is total (or, 100%) apposition, there is no displacement. Displacement exists if there is partial or no apposition between the two fragments:
 |
Fracture position: angulation and displacement. The dorsoplantar radiograph of this rock singer demonstrates three different examples of fracture position in the transverse plane. Second metatarsal: there is no angulation nor displacement of the distal segment relative to the proximal segment. Third metatarsal: The distal segment is displaced laterally (50% apposition) and angulated medially. Fourth metatarsal: the distal segment is displaced laterally (75% apposition) but there is no apparent angulation. |
Positional terms must be described in two perpendicular planes to fully appreciate three-dimensional position:
A  |
B  |
Fracture position: two perpendicular planar views of a fifth metatarsal diaphyseal fracture. (A) Dorsoplantar view: the distal fracture segment is displaced medially and slightly angulated medially relative to the proximal segment. (B) Lateral view: the distal segment is displaced superiorly and angulated inferiorly. |
Assess for abnormalities or variations of the form or shape and size of each bone, including girth, tubulation, length, contour, and growth. The form of identifiable soft tissue shadows (the Achilles tendon, for example) should also be evaluated. The girth of a short tubular bone (such as the metatarsal or phalanx) is affected by subperiosteal remodeling: apposition increases the girth, resorption decreases it. Decreased girth or overtubulation of short tubular bones, for example, is seen with the variant spool-shaped phalanx and pathologic states such as osteogenesis imperfecta:
A  |
B  |
Form: overtubulation (decreased girth). (A) Osteogenesis imperfecta. (B) Skeletal variation of the proximal phalanges. |
Increased girth is frequently secondary to periosteal apposition of bone, though undertubulation may be a variation of skeletal development:
A  |
B  |
Form: undertubulation (increased girth). (A) Periosteal bone apposition of the second, third, and fourth metatarsals (unknown etiology). (B) Skeletal variation affecting all metatarsals. |
Increased and decreased bone length should also be noted:
A  |
B  |
Form: increased and decreased bone length. (A) Elongated third metatarsal. (B) Short fourth metatarsal. |
Irregularity or deformity of the bone's contour may be caused by periosteal apposition, an exostosis along the outer aspect of a bone, or by an internal "expansile" lesion:
A  |
B  |
Form: bone deformity. (A) Exostosis at the fifth metatarsal tuberosity. (B) Expansile lesion (first metatarsal). |
Density refers to the degree of blackness seen on the radiograph. It is a relative term; that is, increased or decreased density depends upon the blackness of surrounding structures. Differing degrees of subject radiodensity are what constitute the radiographic image. Therefore, some decreased densities are normal findings, others are abnormal:
A  |
B  |
Examples of normal and abnormal decreased bone density. (A) The decreased density (arrow) seen in the medial aspect of the fifth metatarsal head is a normal finding. (B) The decreased density in the medial aspect of the first metatarsal head is an abnormal finding secondary to intraosseous deposition of gouty tophi. |
The same holds true for increased densities:
A  |
B  |
Examples of normal and abnormal increased bone density. (A) The linear, transverse increased density seen in the talar body (arrow) corresponds to the superimposed ridge along the medial surface of the talar body for insertion of the deltoid ligament. (B) The ill-defined increased density viewed in the fourth metatarsal head (arrow) is a stress fracture approximately two weeks old. |
It is necessary to become familiar with the normal radiographic anatomy of all soft tissue and osseous structures before one can differentiate between normal and abnormal radiodensities.
(Recall that subject radiodensity depends on the thickness, atomic number, and compactness of the tissue being imaged. An area of increased radiodensity, such as cortical bone, is radiopaque –absorbs x-rays– and will appear white in the radiograph. Air, on the other hand, is radiolucent –transmits x-rays– and appears blacker. In contrast, optical density, also known as radiographic or film density, refers to the overall blackening of the finished radiograph . A blacker film has increased optical density and is therefore opaque–absorbs light; a lighter film is lucent–transmits light– and demonstrates decreased optical density.)
Abnormal radiodensity may be either an isolated finding (local), distributed in one extremity or a segment of the extremity (regional), or found throughout the entire skeleton (diffuse). The finding is primarily described as an increased or decreased density; applicable adjectives should be used when appropriate. For example, in bone, an ill-defined decreased density may have a permeative or motheaten (spotty or mottled) appearance; a well-defined, localized decreased density that has form (or, sharply delineated margins) can be described as being geographic:
A  |
B  |
Examples of adjectives used to describe decreased bone density. (A) Mottled (acute osteopenia affecting all metatarsals). (B) Geographic (solitary bone cyst). |
An abnormal decreased density seen in soft tissues is air (especially gas produced by some anaerobic bacteria). It also may be localized or regional:
A  |
B  |
Decreased density in soft tissue: air produced by gas-forming bacteria. (A) Localized. (B) Regional (gas gangrene). |
Increased soft tissue densities may be related to ectopic calcification or ossification:
 |
Increased density in soft tissue: vessel calcification. |
The earliest finding of a periosteal reaction is a localized increased density at the interface between the bone's outer margin and adjacent soft tissue:
 |
Increased soft tissue density along the outer margin of a bone: periosteal reaction. |
Joint effusion will appear as a fairly well-defined increased soft tissue density adjacent to an articulation:
 |
Increased soft tissue density at a periarticular location: joint effusion. |
Several terms are used interchangeably to describe subject radiodensity in the radiograph. Sclerotic, eburnation, and radiopaque have been used to denote increased bone density. Abnormal increased density in bone usually indicates reactive new bone or tumor bone formation. Nomenclature synonymous with decreased bone density are osteopenia, radiolucency, and rarefaction. The terms osteoporosis, demineralization, undermineralization, and deossification should not be used for describing relative radiodensities because they imply specific etiologies .
The radiodensity of anatomical structures on the radiograph can also be influenced by the film's optical density, which is highly dependent upon technical factors. For example, increased or decreased kilovoltage (kVp), milliampere-seconds (mAs), and processing time and temperature, to name a few, can result in an overall blacker or less black radiograph, respectively. These factors can impair not only the quality of the image but give the wrong impression of subject density.
Generalized loss of bone density is a feature of the metabolic bone diseases (for example, osteoporosis). Unfortunately, diffuse decreased bone density can easily be misjudged in the plain x-ray film. Its appearance is quite subjective and dependent on several factors, such as the superimposition of other tissues, bone position, and, most importantly, exposure and processing techniques. It is, therefore, recommended that the interpreter not rely on the appearance of diffuse decreased bone density alone for evaluating osteopenia. Examination of architectural features is useful for assessing osteopenia and is more objective (see Architecture, below).
Each bone has its own characteristic appearance or structure. The architecture of each bone viewed in a radiograph can be divided into external and internal aspects. The outer margin is the bone's external architecture. It consists of the subperiosteal surface of the cortex, entheses (where tendon, muscle, and joint capsule insert), and the subchondral bone plate. The internal architecture consists of multiple textures, including cortex, spongiosa, and the shadows of normal osteologic landmarks. In the pediatric patient, the metaphysis, zone of provisional calcification, physis, and epiphysis are additional aspects of internal architecture.
Definition and continuity are two important attributes to consider when evaluating a bone's external architecture. The margins of the subperiosteal and subchondral surfaces should be well-defined and continuous. Discontinuity and/or loss of definition of the subperiosteal aspect of the cortex is an abnormal finding; it can represent fracture or bone resorption (erosion):
A  |
B  |
External architecture abnormality. (A) Discontinuity (fracture). (B) Ill-defined (loss of definition): erosion. |
Periosteal new bone formation may present as an ill-defined thickening of the involved margin. Entheses, though they may appear irregular, should be well-defined and continuous. Erosion and/or calcification/ossification may occur at these sites:
A  |
Mixed erosive (arrowhead) and spur-like enthesopathy, calcaneal medial tuberosity. |
Discontinuity of the subchondral bone plate is seen with joint disorders:
 |
External architecture: subchondral bone plate. Erosion (rheumatoid arthritis). |
A "dot-dash" appearance or "skip" pattern of the bone plate is considered to be a pre-erosive finding and is associated with inflammatory joint disorders:
 |
External architecture: dot-dash or "skip" pattern in patient with rheumatoid arthritis. |
Generalized subperiosteal bone resorption throughout the skeleton is characteristic of hyperparathyroidism:
 |
External architecture: phalangeal subperiosteal bone resorption. |
The periosteum is defined as "a specialized connective tissue covering all bones of the body, and possessing bone forming potentialities" . This connective tissue membrane envelopes all bones except at entheses and where they are covered by cartilage . The periosteum is only a few cell layers thick. The adult periosteal sheath is thinner in the adult and more firmly bound to the underlying bone than in the child. It also is quite vascular.
Anything that physically lifts the periosteum from the underlying bone can result in the formation of periosteal new bone formation. Examples include blood, pus, and tumor cells. Other terms synonymous with periosteal new bone formation include periostitis and periosteal reaction. Its presentation is highly variable:
 |
 |
External architecture: variable presentation of periostitis. (A) Ill-defined increased soft tissue density, (B) solid, continuous, |
 |
 |
(C) solid, lamellated, and (D) complex [(D) courtesy of Louis P. Zulli, D.P.M., Philadelphia, PA] |
Initially it may only appear as an ill-defined increased density adjacent to the cortex. As it remodels, it can deform the contour of the bone. In either case, periosteal reaction is best appreciated while examining the continuity and definition of the external bone margin.
Cortical bone and spongiosa constitute the greater part of internal architecture. The cortex normally is radiopaque and homogeneous. Linear radiolucent striations within the cortex of a long bone that run parallel to its long axis suggest intracortical tunneling, a finding associated with osteopenia:
A  |
B  |
C  |
Internal architecture: cortex. (A) Normal, (B) intracortical tunneling, and (C) endosteal resorption. |
The endosteal margin of the cortex should be well-defined. A scalloped appearance or loss of definition along the endosteal margin and subsequent thinning of the cortex indicate bone resorption (C above). Cancellous bone (spongiosa) consists of a honeycomb-like mesh of trabeculae. Trabeculae can be subdivided into primary and secondary trabeculae. The primary trabeculae are found along the lines of stress and are easily identified; secondary trabeculae run at angles to the lines of stress and have a fine appearance, giving an overall mesh-like appearance to normal spongiosa. Resorption of secondary trabeculae leave the primary trabeculae to stand out in relief with osteopenic conditions. Subsequent compensatory apposition of new bone onto the remaining primary trabeculae may occur, appearing as trabecular coarsening or thickening:
A  |
B  |
Internal architecture: trabecular bone resorption. (A) Normal metatarsal head. (B) Osteopenia. |
It has been suggested that the appearance of calcaneal trabecular patterns provides an index for assessing osteoporosis . However, controversy exists as to whether or not these trabecular patterns correlate with actual bone density .
The superimposed shadows of osseous landmarks and adjacent tissues compose the remainder of the internal architecture of a given bone. These shadows can easily be mistaken for abnormal findings:
 |
Internal architecture: misinterpretation. The radiolucency (arrow) in the talar body represents the superimposed fibular notch, not a solitary bone lesion. |
The metaphysis, zone of provisional calcification, physis, and epiphysis must additionally be assessed in the pediatric patient:
 |
The normal growing long bone. (m=metaphysis; z=zone of provisional calcification; p-=physis; e=epiphysis) |
The metaphysis, found at the end of the diaphysis of a tubular bone, primarily consists of spongiosa and has a characteristic density. The zone of provisional calcification is located at the junction of the metaphysis and physis (or, growth plate). It may be smooth or irregular (but well-defined) in contour and is sclerotic relative to the neighboring metaphysis. The physis is wholly cartilaginous and appears radiolucent. It separates the metaphysis and zone of provisional calcification from the epiphysis. The epiphysis has a well-defined sclerotic margin its entire circumference. Centrally, it is composed of spongiosa and has a characteristic density.
© Copyright 1998, Robert A. Christman, D.P.M.
These articles and figures may not be published, reposted, or redistributed without permission from Dr. Christman.
This page was updated May 5, 1998.