Which of the following bones in the arm is more medial when standing in anatomical position?

Publisher Summary

Anatomical terminology for hominids refers to the body in what is called standard anatomical position. Standard anatomical position is that of a human standing, looking forward, feet together and pointing forward, with none of the long bones crossed from the viewer's perspective. All of the directional terms used here refer to the human body in standard anatomical position, but it is important to note that most of these terms are applicable to all mammals. A few terms may occasionally cause confusion when hominid and nonhominid bones are being compared because humans are orthograde (trunk upright) bipeds and most other mammals are pronograde (trunk horizontal) quadrupeds. This chapter discusses the general bone features that are classified under various biological names, such as superior, inferior, anterior, posterior, medial, lateral, and so on.

Proximal Row

From the radial side (the side defined by the radius: lateral in human anatomy using the standard anatomical position: see Chapter 2: Introduction to Anatomical Terminology) radiale, intermedium and ulnare. The proximal row in the rat comprises the scapho-lunate (fused scaphoid and lunate) and the triquetrum (or triquetral bone). It might be useful to note that though scaphoid is an adjective (meaning boat-shaped), as is lunate, (meaning shaped like a half-moon) the word is also used as a noun: the scaphoid bone or the scaphoid. The pisiform sits on the palmar surface of the triquetral bone and is a sesamoid bone (see below).

Clock Method

The clock method is one of the most common methods of wound measurement. The wound is considered as a face of a clock with the position of the wound based on the standard anatomical position of the patient (Figure 2-2). For wounds on the torso and extremities, the patient’s head is considered as the landmark for 12 o’clock and the feet are considered 6 o’clock, whereas for wounds located on the foot, the heel is considered 12 o’clock and the toes are 6 o’clock. Key characteristics that can be measured and described using the clock method are length, width, depth, and the presence of dead space. Dead space represents tissue damage that is not immediately evident when inspecting visible aspects of the wound. All forms of dead space must be properly addressed during local treatment of the wound to prevent the accumulation of pathogens and exudate. This can be prevented by using wound fillers, such as calcium alginate or amorphous hydrogel, or in deeper wounds using gauze strips. In addition, the use of wound fillers to occupy dead space ensures that the wound will heal from the base to the surface without abscess formation or opportunities for deeper infection and sepsis.

Categories of dead space include sinus formation, tunneling, and undermining. Tunneling is generally located in the wound bed or along the wound margins and can connect one wound to another or a wound to a body cavity. Tunnels can descend deeper into the wound or to the side of the wound bed. The deepest area of tunneling and its location on the clock should be recorded. Sinus formation may appear similar to tunneling but differs in that there is no exit point. Sinuses may extend beyond the visible margins of the wound and are often hidden beneath the surface of the skin. Both tunneling and sinus formation need to be carefully assessed due to possible infection, unrelieved pressure, or the presence of foreign bodies. Undermining is another category of dead space and can be described as a hidden shelf or ledge resting just beneath the wound margin but not visible from the surface of the skin. The presence of undermining can indicate shear or pulling at the wound bed and should be properly documented because the presence of preexisting damage to the subcutaneous tissues may later manifest as a visible increase in the length, width, or diameter of the wound. Undermining should be measured at each time of the clock, for example, 4 cm at 12 o’clock, 3 cm at 3 o’clock, 3 cm at 6 o’clock, and 2 cm at 9 o’clock.

1.6 Planes of Reference and Directional Terms

This section presents brief definitions of the planes of reference and directional terms that are essential in the description of the human skeleton. All definitions provided here assume that the human skeleton is in standard anatomical position, that is, standing erect, looking forward, with the feet close and parallel to each other, the arms at the sides, and the palms facing forward (Fig. 1.6.1).

The main planes of reference for the human skeleton are used to divide the body into sections (Fig. 1.6.1). The sagittal (or midsagittal) plane separates the right half from the left half of the body, whereas the coronal plane is perpendicular to the sagittal and separates the anterior half from the posterior half of the body. Finally, the transverse plane is perpendicular to the sagittal and coronal planes and it may be located at different heights.

The main directions for parts of the body are superior, inferior, anterior, posterior, medial, and lateral, whereas the terms proximal and distal are more appropriate for the limbs (Figs. 1.6.1 and 1.6.2). Superior is toward the head, inferior toward the feet, anterior toward the front of the body, posterior toward the back of the body, medial toward the sagittal plane, and lateral away from the sagittal plane. For the limbs, proximal lies toward the trunk of the body, and distal lies away from the trunk. Terms that are often used for the hands and feet include palmar, which is the palm side of the hand; plantar, which is the sole side of the foot; and dorsal, that is, the top side of the foot or the back side of the hand. Note that when the terms right and left are used, they refer to the sides of the individual being studied and not to the sides of the observer.

ANATOMICAL POSITION

Anatomical position is the specific alignment of the body used as the position of reference for describing the anatomical planes and axes. Although there are many possible ideal positions and postures, there is only one standard anatomical position. In anatomical position the body is erect with the head and torso upright. The arms are at the sides of the torso with the shoulders in neutral rotation, elbows extended, the cubital fossae of the elbow and the palms face forward, the fingers are extended, and the thumbs are adducted with the pad of each thumb facing forward. The lower extremities are straight and parallel, with the second toe facing straight forward (Fig. 4-3). From the anatomical position, three planes and three axes may be used to describe position, alignment, and motion of the body. In addition, the positions of the joints in anatomical position are considered the zero position for measurements of joint ROM for most joints.4

2.3.1 General

a.

Flexion: generally, a bending movement that decreases the angle between body parts. When a hand is clenched into a fist there is strong flexion of the phalanges on the metacarpal heads. By convention, flexion at the shoulder or hip joint refers to a ventral (forward) movement of the limb.

Extension: opposite of flexion; a straightening movement that increases the angle between body parts. The classic karate chop is made by a rigid hand in which the fingers are extended. By convention, extension at the shoulder or hip joint is a dorsal (backward) swing of the limb.

Abduction: movement of a body part, usually a limb, away from the sagittal plane. When the arm is raised to the side from standard anatomical position, abduction of the arm occurs. For the special case of fingers and toes, abduction is movement of the digit away from the midline of the hand or foot (spreading the digits).

Adduction: opposite of abduction; movement of a body part, usually a limb, toward the sagittal plane. Bringing the arm down to slap the side of the thigh is adduction. For the special case of fingers and toes, adduction is movement of the digit toward the midline of the hand or foot (closing the digits).

Circumduction: a combination of abduction and adduction, as well as flexion and extension, that results in an appendage being moved in a cone-shaped path. When the driver of a slow vehicle signals someone behind him to pass, this “waving on” is often done by circumducting the arm.

Rotation: motion that occurs as one body part turns on an axis. The movement of the head of the radius on the distal humerus is an example of rotation.

Opposition: motion in which body parts are brought together. Opposition of the thumb and finger tips allows us to grasp small objects.

2.4 Skeletal anatomy

Study of the anatomical features of the skeleton requires the use of standard nomenclature that represents a common language used by anatomists, anthropologists, and medical practitioners. After growth and development is complete and all epiphyses have fused, the mature adult human skeleton consists of approximately 206 bones (Figure 2.7). All of the bones of the human skeleton (except the hyoid) articulate with at least one other bone of the skeleton, forming the highly integrated system of skeletal structures. The following sections outline and define some of the anatomical terms, bone names, and features that are important in forensic anthropological analyses.

Anatomical directions and planes are used in reference to bones, body parts, their portions, and their relative positions. All of these terms are relative to a standard anatomical position, which for humans is standing upright, facing with the feet pointing forward, the palms of the hands facing forward, and the thumbs pointed laterally (see Figures 2.8 and 2.9 and Table 2.2). In anatomical position, none of the bones are crossed when the body is viewed from the front. Some of these terms may differ somewhat for humans versus other animals, since humans are bipeds while most others are quadrupeds, and body parts are therefore in different positions relative to each other. When the terms left and right are used, they refer to the left and right sides of the individual or bone being studied with respect to anatomical position, not from the perspective of the observer.

Table 2.2. Anatomical planes of reference and directions

(Modified from White et al., 2011.)

Bones have many generalized external structures and features that are often examined and utilized in forensic anthropological analyses. Bones can be categorized as being long bones (which are characterized by being mostly tubular, such as limb bones), flat bones (such as those of the cranium), or irregular (such as the bones of the vertebral column, wrist, and ankle). Bones are integrated with the muscular, vascular, nervous, and other bodily systems, and their surface morphology reflects this interconnectivity. This can be seen in their various projections, depressions, and foramina, which serve as the attachment sites for muscles, the passage of blood vessels and nerves, and other reflections of adjacent anatomy. Some of these general feature terms are defined in Table 2.3.

Table 2.3. Gross anatomical features of bones

(Modified from White et al., 2011.)

The skeleton can be divided into several major sections. The cranial skeleton refers to the bones of the skull, while the postcranial skeleton (or infracranial skeleton) refers to everything below the skull. The postcranial skeleton can be further subdivided into the axial skeleton, which consists of bones along and near the body’s midline, and the appendicular skeleton, which consists of the bones of the limbs as well as their supporting structures where they connect with the axial skeleton.

The skull consists of the entire bony head including the bones of the cranium (Figures 2.10 and 2.11) and the mandible (Figure 2.12) for a total of 28 bones. These include the frontal, two parietals, two temporals [each of which contain three auditory ossicles: the malleus, incus, and stapes (Figure 2.13)], the occipital, the sphenoid, two maxillae, two palatines, two inferior nasal conchae, the ethmoid, the vomer, two lacrimals, two nasals, two zygomatics, and the mandible. The bones of the cranium can be divided into two groups: the cranial vault or neurocranium, consisting of the bones that form the sides, top, and back of the brain case, and the splanchnocranium or facial skeleton, consisting of the bones of the face. Several of the bones of the cranium contain sinuses (or paranasal sinuses), which are air pockets that are linked to the nasal cavity. Sinuses can be found in the frontal bone, the maxillae, the ethmoid, and the sphenoid, and the mastoid processes of the temporal bone contain sinus-like air cells. While the functions of the sinuses are not well understood, the frontal and maxillary sinuses have proven useful in anthropological assessments of identification. Tables 2.4 to 2.5 describe the bones and selected features of the skull.

Table 2.4. Bones and features of the skull

(Modified from White et al., 2011.)

Table 2.5. Sutures and other features of the skull

(Modified from White et al., 2011.)

The axial skeleton refers to bones on or near the body’s midline including the skull as well as and the thorax or trunk. Bones of the thorax include the hyoid, sternum, vertebrae, and ribs, and these bones and some of their features are described in Table 2.6. The hyoid (Figure 2.14) is the only bone in the body that does not articulate with any other bone. It is located in the anterior neck and serves as a connection point for various structures of the neck and throat. The sternum or breastbone (Figure 2.15) anchors the anterior ends of ribs 1–7 via costal cartilage and also connects with the shoulder girdle. It consists of three major portions: the manubrium (the most superior portion), the body or corpus sterni (the central portion), and the xiphoid process (the most inferior portion).

Table 2.6. Bones and features of the axial skeleton

(Modified from White et al., 2011.)

The vertebrae provide support for the central part of the body, anchor various muscles of the back, and serve as a protective passageway for the spinal cord. There are 24 moveable (unfused) vertebrae of three different types in different regions of the vertebral column or spinal column (Figure 2.16). The seven cervical vertebrae are the most superior, forming the neck. The 12 thoracic vertebrae make up the upper and middle back, and the five lumbar vertebrae make up the lower back. Vertebrae are typically referred to by their type and number counting from superior to inferior. For example, cervical vertebra number 5, or C5, is the fifth of the cervical vertebra from the top; thoracic vertebra number 10, or T10, is the tenth of the thoracic vertebrae; and lumbar vertebra number 3, or L3, is the third of the lumbar vertebrae. All vertebrae have a central foramen called the vertebral foramen through which the spinal cord passes.

Cervical vertebrae (Figure 2.17) are the smallest of the moveable vertebrae and are characterized by small vertebral bodies and a foramen through each of their transverse processes (called transverse foramina). The first two vertebrae are especially distinctive (Figure 2.18). The first cervical vertebra (also called the atlas) is ring-shaped, lacks a body, and has large superior facets for articulation with the occipital bone. The second cervical vertebra (also called the axis) is characterized by a superior projection called the dens (also called the odontoid process) which allows the head to pivot on the spine.

Thoracic vertebrae make up the middle portion of the spinal column and can be distinguished by their facets for articulation with the ribs, one on each side of the vertebral body, and one on each transverse process (Figure 2.19). Though the typical number of thoracic vertebrae is 12, accessory thoracic vertebrae (usually accompanied by accessory ribs) are not uncommon. Lumbar vertebrae are the most inferior of the moveable vertebra and are characterized by large vertebral bodies due to their greater weight-bearing function (Figure 2.20).

At the inferior end of the vertebral column is the sacrum, which is formed of 4–6 fused vertebral segments (Figure 2.21). This bone also serves as the posterior portion of the pelvis. Inferior to the sacrum is the variably fused coccyx, which represents the vestigial human tail and consists of 3–5 variable fused segments.

There are 12 ribs on each side (24 in total) which form the rib cage (Figure 2.22). Each rib articulates posteriorly with the vertebrae, and the first ten ribs (ribs 1–10) articulate anteriorly with costal cartilage connected to the sternum. Ribs 11–12 do not connect to the sternum in this way, and are therefore sometimes referred to as “floating ribs.” Most ribs are characterized by being long, slender, and curved bones. Ribs 1 and 2 can be distinguished because they are flatter and more tightly curved. Sequentially, ribs 1–7 increase in length, and then decrease in length from ribs 8–12. Also, with each sequential rib, the angle becomes more obtuse.

The appendicular skeleton consists of the bones of the arms (or upper limbs) and legs (or lower limbs) as well as their supporting structures where they articulate with the axial skeleton. The supporting structure of the upper limb is referred to as the shoulder girdle, consisting of the clavicle and scapula, which connects the trunk to the arm (Figure 2.23). The upper limb consists of the arm, wrist, and hand. The bones of the arm include the humerus (Figure 2.24), which makes up the upper arm, and the radius (Figure 2.25) and ulna (Figure 2.26), which make up the forearm. The wrist consists of eight small irregular bones called carpals. The hand consists of five metacarpals, one for each digit or ray. The metacarpals are numbered 1–5 counting from lateral (the thumb side) to medial (the little finger side). The fingers consist of bones called manual phalanges (phalanx, singular); the first digit (the thumb) consists of two phalanges (a proximal and a distal), while digits 2–5 each consist of three (a proximal, intermediate, and distal) (Figure 2.27). Often, accessory bones of the hand and wrist occur and are called sesamoid bones. Some features of the upper limb are described in Table 2.7.

Table 2.7. Bones and features of the upper limb

(Modified from White et al., 2011.)

The pelvic girdle, consisting of the two innominates (also called ossa coxae) along with the sacrum, connects the trunk to the lower limb (Figure 2.28). The innominates form from three fused portions called the ilium, ischium, and pubis (Figure 2.29). The lower limb consists of the leg, ankle, and foot. The bones of the leg include the femur (Figure 2.30), which makes up the upper leg, the patella or kneecap (Figure 2.31), and the tibia (Figure 2.32) and fibula (Figure 2.33), which make up the lower leg. The ankle consists of seven irregular bones called tarsals. The foot consists of five metatarsals, one for each digit. The first toe (the “big toe”) consists of two pedal phalanges, while digits 2–5 consist of three. Sesamoid bones may also occur in the ankle and foot (Figure 2.34). Some features of the lower limb are described in Table 2.8.

Table 2.8. Bones and features of the lower limb

(Modified from White et al., 2011.)

1.4 Significance of the anatomical variations

As stressed by Standring [56], the language of anatomy is fundamental to medicine. An unambiguous description of thousands of anatomical structures would not be possible without extensive, specialized terminology, the use of which must be subject to strict rules. To avoid ambiguity, all anatomical descriptions have been gradually standardized and now refer to the appropriate arrangements of individual body parts in space, called standard anatomical positions. With centuries of progress in anatomical knowledge, the human body itself underwent a kind of standardization, resulting in the establishment of a general textbook description of how organs and systems should appear. Such descriptions are idealized images of the “perfect body”. There is nothing wrong with such an abstract “norm” as long as it is treated only as a general outline or very approximate estimate. “Normality” understood in this way is a model, a useful fiction. It allows us to predict, generally, features that could require investigation or medical intervention [7]. However, clinicians (and students and teachers) should pay attention to individual anatomical characteristics, including different manifestations of variability. The broad role of individualization was stressed by Chadwick [23]. It should be accepted that anatomical variations are not “unnatural”, and awareness of them is essential for successful medical practice. Contemporary authors rightly emphasize that anatomical variability constitutes a kind of medical routine and should therefore be taught at medical schools and kept in mind by clinicians [5–7]. Bergman et al. [5] said that variants “are » normal « even though they may differ from the mean or usual. They are found in »normal « long-lived individuals, and they are statistically (for the most part) predictable”.

2.6 Cone beam computed tomography (CBCT)