• The scaphoid fat stripe is one of the soft tissue structures that should be visible on all scaphoid images (see Figure 4-30). It is convex and located just lateral to the scaphoid in an uninjured wrist.

• To obtain an accurate PA axial (scaphoid) projection, abduct the humerus until it is positioned parallel with the IR and place the elbow in a flexed, lateral position. Then pronate the extended hand, place the wrist in ulnar deviation, and ensure the wrist is rotated medially approximately 25 degrees (Figure 4-44).

• The scaphotrapezium and scaphotrapezoidal joints are aligned at a 15-degree angle to the IR when the patient's hand is in full extension. These joints will be open when a 15-degree proximally angled central ray is used. If the hand is not extended so that the palm is placed flat against the IR, but rather is flexed, the second metacarpal is superimposed over the trapezoid and trapezium and closes the scaphotrapezium and scaphotrapezoidal joint spaces (see Image 55).

• To demonstrate the scaphoid without foreshortening, position the patient's wrist in maximum ulnar deviation; then direct a 15-degree proximal (toward the elbow) central ray angulation to the long axis of the scaphoid. Maximum ulnar deviation has been accomplished when the first metacarpal is aligned with the radius. In a neutral PA projection of the nondeviated wrist, the distal scaphoid tilts anteriorly approximately 20 degrees. This tilt results in foreshortening of the scaphoid on the PA axial projection (Figures 4-29 and 4-45). To offset some of this foreshortening and demonstrate more of the scaphoid, place the wrist in ulnar deviation. In ulnar deviation the distal scaphoid moves posteriorly, decreasing the degree of foreshortening by 5 degrees (see Figure 4-45).

    Adequate ulnar deviation and central ray angulation place the central ray perpendicular to the long axis of the scaphoid (Figure 4-46). Because 70% of the fractures occur at the waist, most scaphoid fractures should be visualized with this positioning and angulation (see Image 56).

• Compensating for inadequate ulnar deviation. Many patients with suspected scaphoid fractures are unable to achieve maximum ulnar wrist deviation. Without adequate ulnar deviation, the distal scaphoid is titled more anteriorly. To compensate for this increased anterior tilt, the central ray angulation should be increased to approximately 20 degrees to place the central ray and scaphoid long axis perpendicular to each other.

• Scaphoid elongation. The goal of the PA axial (scaphoid) projection is to demonstrate the scaphoid with the least amount of foreshortening or elongation. A slight amount of elongation of the scaphoid occurs on PA axial projections because the IR is not positioned parallel with the long axis of the scaphoid and the central ray is not aligned perpendicularly with the IR (Figure 4-46). Excessive elongation of the scaphoid results when the central ray is angled more than needed to align it perpendicularly to the long axis of the scaphoid.

• Mechanics of scaphoid fracture. The scaphoid is the most commonly fractured carpal bone. One reason for this is its location among the other carpal bones. Two rows of carpal bones exist, a distal row and a proximal row, with joint spaces between them that allow the wrist to flex. The long scaphoid bone, however, is aligned partially with both these rows, with no joint space. When an individual falls on an outstretched hand, the wrist is hyperextended, causing the proximal and distal carpal rows to flex at the joints, and a great deal of stress is placed on the narrow waist of the scaphoid. This stress may result in a fracture.

• Three areas of the scaphoid may be fractured: the waist, which sustains approximately 70% of the fractures; the distal end, which sustains 20% of the fractures; and the proximal end, which sustains 10% (Figure 4-47). Because scaphoid fractures can be at different locations on the scaphoid, precise positioning and central ray angulation are essential to obtain the optimum demonstration of this bone.

• Demonstrating fractures of distal and proximal scaphoid. When a fracture is suspected because of persistent pain and obliteration of the fat stripe but has not been demonstrated on routine images, it may be necessary to use different angles to position the central ray parallel with these fractures sites (Figure 4-48). A decrease of 5 to 10 degrees in central ray angulation better demonstrates the proximal scaphoid. Compare Figures 4-49 and 4-50. These PA axial projections demonstrate a proximal fracture. Figure 4-49 was taken with the typical 15-degree proximal angle, and Figure 4-50 was taken with a 5-degree proximal angle. Note the increase in fracture line visualization in Figure 4-50. Increase the central ray angle by 5 to 10 degrees, with a maximum of 25 degrees, to demonstrate a distal scaphoid fracture best (Figure 4-51). Angulations more than 25 degrees project the proximal second metacarpal onto the distal scaphoid, obscuring the area of interest (see Image 57).

• The scaphocapitate and scapholunate joints are open when the wrist is medially rotated approximately 25 degrees. This obliquity is accomplished somewhat naturally as the patient's wrist is ulnar-deviated, with the humerus abducted and positioned parallel with the IR, and the elbow placed in a flexed lateral projection. If the scaphocapitate joint space is closed and the capitate and hamate are demonstrated without superimposition, the degree of obliquity was insufficient (see Image 58). If the scapholunate joint space is closed and the capitate and hamate demonstrate some degree of superimposition, the wrist was rotated more than needed (see Image 59). Excessive external wrist obliquity often occurs when the humerus and forearm are not positioned on the same horizontal plane and the elbow is not placed in a lateral projection. On a PA axial projection, one can judge accurate humerus, forearm, and elbow positioning by evaluating the ulnar styloid. Accurate positioning places the ulnar styloid in profile medially. If the arm is not positioned accurately, the ulnar styloid is demonstrated distal to the midline of the ulnar head (see Image 60).

• The distal radial carpal articular surface is concave and slants approximately 11 degrees from posterior to anterior when the forearm is positioned parallel with the IR. On a PA projection without a central ray angulation, the posterior radial margin is demonstrated slightly distal to the anterior margin if the forearm is placed parallel with the IR. When a 15-degree proximal central ray angulation is used for the PA axial (scaphoid) projection, the posterior margin is projected slightly proximal to the anterior margin (Figure 4-52). To demonstrate an open radioscaphoid joint, the anterior and posterior margins of the distal radius should be superimposed. This superimposition is accomplished by elevating the proximal forearm very slightly (2 degrees) above the distal forearm.

• To place the scaphoid at the center of the collimated field, center the central ray with the scaphoid. In ulnar deviation, the scaphoid can be palpated halfway between the first metacarpal base and the radial styloid. After the central ray is centered, open the longitudinal collimation to include the first through fourth metacarpal bases and the distal radius. Transversely collimate to within 0.5 inch (1.25 cm) of the wrist skin line.

    Avoid collimating too tightly. It is difficult to determine how to reposition the patient when an image reveals poor positioning if key anatomic structures are not included.

• Half of an 8- × 10-inch (18- × 24-cm) detailed screen-film or computed radiography IR placed crosswise should be adequate to include all the required anatomic structures.

Posteroanterior Axial (Scaphoid) Projection Analysis

• The tangential, inferosuperior carpal canal wrist projection is accomplished by placing the distal forearm and wrist on the IR in a PA projection, and then hyperextending (dorsiflexing) the wrist until the long axis of the metacarpals are close to vertical while the wrist remains in contact with the IR. To obtain adequate wrist hyperextension, have the patient grasp his or her fingers with the opposite hand and gently pull them posteriorly (Figure 4-54).

• The tangential, inferosuperior carpal canal projection is used to evaluate the carpal canal for the narrowing that results in carpal canal syndrome and demonstrate fractures of the pisiform and hamulus of the hamate. The carpal canal is a passageway formed anteriorly by the flexor retinaculum, posteriorly by the capitate, laterally by the scaphoid and trapezium, and medially by the pisiform and hamate (Figure 4-55). Fractures of the pisiform and hamulus process are best demonstrated when they are seen without superimposition. This is accomplished by rotating the patient's hand 10 degrees internally (toward the radial side) until the fifth metacarpal is aligned perpendicularly to the IR. If the hand is not internally rotated, the pisiform will be superimposed over the hamulus process on the resulting image (see Image 61).

• To show the carpal canal and demonstrate the carpals with only slight elongation, the patient's hand is positioned vertically, and the central ray is angled proximally (toward the palmar surface). The degree of central ray angulation that is needed will depend on how vertical the patient can bring the hand. To determine the angle to use, adjust the central ray proximally until it is aligned at a 15-degree angle with the palmar surface (Figure 4-56). The most common tube angle used is 25 to 30 degrees.

• Immaculate angle. If the angle between the central ray and palmar surface is too great, the carpal canal will not be fully demonstrated and the carpal bones will be foreshortened (see Image 62). If the angle between the central ray and palmar surface is too small, the bases of the hamulus process, pisiform, and scaphoid are obscured by the metacarpal bases (see Image 63).

• Insufficient wrist extension. When imaging a patient who is unable to extend the wrist enough to place the palmar surface even close to vertical, the resulting image will demonstrate adequate visualization of the carpal bones and carpal canal, although there will be increased elongation as the angle between the central ray and IR becomes more acute (see Image 64).

• The carpal canal is positioned in the center of the collimated field by centering the central ray to center of the palm of the hand. After the central ray is centered, open the longitudinal and transverse collimations to within 0.5 inch (1.25 cm) of the wrist skin line.

• Half of an 8- × 10-inch (18- × 24-cm) detailed screen-film or computed IR placed crosswise should be adequate to include all the required anatomic structures.

Tangential, Inferosuperior Carpal Canal Wrist Projection Analysis

• Anode heel effect. To use the anode heel effect to obtain uniform density across the forearm, position the thinner wrist (distal forearm) at the anode end of the tube and the thicker elbow (proximal forearm) at the cathode end. Set an exposure (mAs) that will adequately demonstrate the midpoint of the forearm.

• Aligning the long axis of the forearm with the long axis of the collimated field enables you to collimate tightly without clipping the distal or proximal forearm.

• A perpendicular central ray is centered to the midpoint of the forearm to place it in the center of the image.

• When the wrist and elbow joints are included on the image, the degree of radiation beam divergence used to image a long body part needs to be considered (Figure 4-58).

• IR length for the forearm. Choose an IR that is long enough to allow at least 1 inch (2.5 cm) of IR to extend beyond each joint space; half of a 14- × 17-inch (35- × 44-cm) IR placed lengthwise should be adequate. To ensure that the IR extends beyond the elbow joint, palpate the medial epicondyle, which is located approximately 0.75 inch (2 cm) proximal to the elbow joint. To ensure that the IR extends beyond the wrist joint, palpate the base of the first metacarpal; the wrist joint is located just proximal to this base. Digital imaging requires tight collimation without overlapping of individual exposures.

• Central ray centering and collimation. Once the forearm is accurately positioned in relation to the IR, center the central ray with the midpoint of the forearm and open the longitudinal collimation field until it extends just beyond the elbow and the wrist. If the collimation does not extend beyond the joints, adjust the centering point of the central ray until both the elbow and the wrist joint are included within the collimated field without demonstrating an excessive field beyond them. Transverse collimation should be within 0.5 inch (1.25 cm) of the forearm skin line.

Distal Forearm Positioning

The distal and proximal forearm is positioned in an AP projection. The radial styloid is demonstrated in profile laterally, and superimposition of the metacarpal bases and of the radius and ulna is minimal.

The ulnar styloid is projected distally to the midline of the ulnar head.

The anterior and posterior carpal articulating surfaces of the distal radius are superimposed, and the radioscaphoid and radiolunate joint spaces are open.

Proximal Forearm Positioning

The proximal forearm is positioned in an AP projection. The radial head is superimposed over the lateral aspect of the proximal ulna by approximately 0.25 inch (0.6 cm). If included on the IR, the medial and lateral humeral epicondyles are demonstrated in profile at the extreme medial and lateral edges of the distal humerus.

The capitulum-radius joint is either partially or completely closed, and the radial head articulating surface is demonstrated. The olecranon process is situated within the olecranon fossa, and the coronoid process is visible on end.

The radial tuberosity is demonstrated in profile medially, and the radius and ulna appear parallel.

Anteroposterior Forearm Projection Analysis

• Anode heel effect. To use the anode heel effect to obtain uniform density across the forearm, position the thinner wrist (distal forearm) at the anode end of the tube and the thicker elbow (proximal forearm) at the cathode end. Set an exposure (mAs) that will adequately demonstrate the midpoint of the forearm.

• Soft tissue structures on lateral forearm projection. Soft tissue structures of interest are the anterior and posterior fat pads and the supinator fat stripe at the elbow and pronator fat stripe at the wrist (Figure 4-62). The elbow's anterior fat pad is situated anterior to the distal humerus, and the elbow's supinator fat stripe is visible parallel to the anterior aspect of the proximal radius. A change in the shape or placement of these fat structures indicates joint effusion and elbow injury. The elbow's posterior fat pad is normally obscured on a negative lateral forearm image because of its location within the olecranon fossa. On elbow injury, joint effusion pushes this pad out of the fossa, allowing it to be visualized proximally and posterior to the olecranon process. The wrist's pronator fat stripe is demonstrated parallel to the anterior surface of the distal radius. Bowing or obliteration of this fat stripe may be the only indication of subtle radial fractures.

• A perpendicular central ray is centered to the midpoint of the forearm to place the forearm in the center of the image.

• IR length for the forearm. Choose an IR that is long enough to allow at least 1 inch (2.5 cm) of IR to extend beyond each joint space; half of a 14- × 17-inch (35- × 44-cm) screen-film or computed radiography IR placed lengthwise should be adequate. To ensure that the IR extends beyond the elbow, palpate the medial epicondyle, which is located 0.75 inch (2 cm) proximal to the elbow joint. To ensure that the IR extends beyond the wrist joint, palpate the base of the first metacarpal; the wrist joint is located just proximal to this base.

• Central ray centering and collimation. Once the forearm is accurately positioned in relation to the IR, center the central ray to the midpoint of the forearm, and open the longitudinal collimation field until it extends just beyond the elbow and wrist joints. If collimation does not extend beyond the joints, adjust the centering point of the central ray until both the elbow and the wrist joint are included within the collimated field without demonstrating an excessive field beyond them. Transverse collimation should be within 0.5 inch (1.25 cm) of the forearm skin line.

Distal Forearm Positioning

The distal forearm is in a lateral projection. The anterior aspects of the distal scaphoid and pisiform are aligned with each other, and the distal scaphoid is demonstrated slightly distal to the pisiform. The distal radius and ulna are superimposed.

The ulnar styloid is demonstrated in profile posteriorly.

Proximal Forearm and Distal Humerus Positioning

Elbow is flexed 90 degrees.

The distal humerus is in a lateral projection. The distal humerus demonstrates three concentric (having the same center) arcs, formed by the trochlear sulcus, capitulum, and medial aspect of the trochlea. The elbow joint space is open, and the radial head is superimposed over the coronoid process.

Lateral Forearm Projection Analysis

• An AP projection of the elbow is obtained by supinating the patient's hand and externally rotating the forearm and humerus until an imaginary line drawn between the humeral epicondyles is parallel with the IR (Figure 4-67). This positioning places the proximal radius anterior to the ulna.

• Detecting elbow rotation. Rotation of the elbow is a result of poor humeral epicondyle positioning and can be identified on an image when (1) the epicondyles are not visualized in profile, (2) the radial head is demonstrated with more or less than 0.25 inch (0.6 cm) superimposition of the ulna, and (3) the coronoid process is seen in profile. The smaller, lateral humeral epicondyle is more sensitive to rotation, moving out of profile with only a slight degree of elbow rotation. If the epicondyles are not demonstrated in profile, evaluate the degree of radial head superimposition of the ulna to determine how to reposition for an AP projection. If more than 0.25 inch (0.6 cm) of radial head is superimposed over the ulna, the elbow has been internally rotated (see Image 74). If less than 0.25 inch (0.6 cm) of the radial head is superimposed over the ulna, the elbow has been externally rotated (see Images 75 and 76).

• The alignment of the radius and ulna is determined by the position of the humerus and the wrist. When the humerus is positioned with the humeral epicondyles parallel with the IR, the radial and ulnar relationship can be adjusted with wrist rotation. For an AP projection of the elbow, the hand and wrist should also be positioned in an AP projection by supinating the hand. This positioning places the radial tuberosity medially in profile and eliminates crossing of the radius and ulna. As the hand and wrist are pronated, the radius crosses over the ulna, and the radial tuberosity is rotated posteriorly, out of profile (see Image 77).

• You must use accurate central ray placement and position the forearm parallel with the IR to obtain an open capitulum-radius joint space. When the central ray is centered proximal to the elbow joint space, the capitulum is projected into the joint; when the central ray is centered distal to the elbow joint, the radial head is projected into the joint space (see Image 78). Poor central ray placement also distorts the radial head, causing its articulating surface to be demonstrated. The degree of joint closure depends on how far the central ray is positioned from the elbow joint. The farther away from the joint the central ray is centered, the more the capitulum-radial joint space is obscured and the more the radial head articulating surface is demonstrated.

• Effect of elbow flexion. Flexion of the elbow joint also distorts the AP elbow projection. With elbow flexion, the capitulum-radial joint closes, the olecranon process moves away from the olecranon fossa, and the coronoid process shifts proximally. How a flexed elbow is positioned with respect to the IR determines which elbow structures are distorted on the image. If a flexed elbow is resting on the posterior point of the olecranon, with the proximal humerus and the distal forearm elevated as shown in Figure 4-68, both the humerus and the forearm are foreshortened and the capitulum-radial joint is obscured (see Image 79). Foreshortening of the proximal humerus is indicated on the image by an oval olecranon fossa that is clearly demonstrated, without the olecranon within it. Foreshortening of the distal forearm is demonstrated if the radial head articulating surface is imaged partially on end. The severity of the distortion increases with increased elbow flexion.

• Compensating for a nonextendable elbow. An elbow that cannot be fully extended should be imaged using separate exposures to image the distal humerus and the proximal forearm. Figure 4-69demonstrates how the patient should be positioned for an undistorted AP distal humerus image to be obtained. Note that the humerus is placed parallel with the IR. The resulting image demonstrates an undistorted image of the distal humerus, whereas the proximal forearm is severely distorted and the capitulum-radial joint space is obscured (see Image 80). Figure 4-70 demonstrates how the patient should be positioned for an undistorted AP proximal forearm projection to be obtained. Note that the forearm is placed parallel with the IR. The resulting image demonstrates an undistorted image of the proximal forearm and an open capitulum-radial joint, but the distal humerus is severely distorted (see Image 81). The capitulum-radial joint space is visible on the image only if the forearm is positioned parallel with the IR.

• The elbow joint is located 0.75 inch (2 cm) distal to the easily palpable medial epicondyle. To obtain an image of the elbow joint with the least amount of distortion, place a perpendicular central ray at this level and centered to the midelbow. Open longitudinal collimation to include one fourth of the proximal forearm and distal humerus. Transverse collimation should be within 0.5 inch (1.25 cm) of the elbow skin line.

• Half of a 10- × 12-inch (24- × 30-cm) detailed screen-film IR placed crosswise or an 8- × 10-inch (18- × 24-cm) computed radiography IR placed lengthwise should be adequate to include all the required anatomic structures.

Anteroposterior Elbow Projection Analysis

• To obtain open capitulum-radial and trochlear-coronoid process joint spaces, you must use accurate central ray placement and position the elbow with the forearm parallel with the IR. When the central ray is centered proximal to the elbow joint spaces, the structures of the distal humerus are projected into the joint; when the central ray is centered distal to the elbow joint, the structures of the proximal forearm are projected into the joint space. Poor central ray positioning also distorts the radial head and coronoid process, causing their articulating surface to be visualized. The degree of joint closure and radial head and coronoid process distortion depends on how far the central ray is positioned from the elbow joint. The farther away from the joint the central ray is centered, the more the joint spaces will be obscured, and the more the articulating surfaces of the radial head and coronoid process will be demonstrated.

• Effect of elbow flexion. Flexion of the elbow joint also distorts the AP oblique elbow projection. With elbow flexion, the olecranon process moves away from the olecranon fossa and the coronoid process shifts proximally. How the flexed elbow is positioned with respect to the IR determines which elbow structures are distorted on the image. If a flexed elbow is resting on the posterior point of the olecranon, with the proximal humerus and the distal forearm elevated, both the humerus and the forearm are foreshortened and the capitulum-radial and trochlear-coronoid process joints are obscured. Foreshortening of the proximal humerus is demonstrated on an image by an oval olecranon fossa that is clearly shown but without the olecranon process within it. Foreshortening of the distal forearm is demonstrated on the image if the radial head and trochlear articulating surfaces are visualized.

The severity of the distortion depends on the degree of elbow flexion. If the humerus is positioned parallel with the IR and the distal forearm is elevated, the image shows an undistorted distal humerus, but the proximal forearm is severely distorted and the capitulum-radial joint is obscured (see Image 82). If the forearm is positioned parallel with the IR and the proximal humerus is elevated, the image shows an undistorted proximal forearm and open capitulum-radial and trochlear-coronoid process joints, but the distal humerus is severely distorted.

• Positioning of the nonextendable elbow. For AP oblique elbow projections, if the patient's condition prevents full elbow extension, the anatomic structure (forearm or humerus) of interest should be positioned parallel with the IR. If the radial head or coronoid process is of interest, position the forearm parallel with the IR (Figure 4-73). If the capitulum or medial trochlea is of interest, position the humerus parallel with the IR. The degree and direction of elbow obliquity are the same as those used for an extended elbow.

Internally Rotated AP Oblique Projection

The elbow has been internally rotated 45 degrees. The coronoid process, the trochlear notch, and the medial aspect of the trochlea are demonstrated in profile. The trochlear-coronoid process articulation is open, and the radial head and neck are superimposed over the ulna.

Externally Rotated Oblique Projection

The elbow has been externally rotated 45 degrees. The capitulum and radial tuberosity are demonstrated in profile, the radial head, neck, and tuberosity are visualized without superimposing the ulna, and the radioulnar articulation is demonstrated.

The elbow joint is at the center of the exposure field. The elbow joint, one fourth of the proximal forearm and distal humerus, and surrounding soft tissue are included within the collimated field.

AP Oblique Elbow Projection Analysis

• Fat pads on lateral elbow projection. To evaluate a lateral elbow projection, the reviewer not only analyzes the bony structure, but also studies the placement of the soft tissue fat pads. Three fat pads of interest are present on a lateral elbow projection, the anterior and posterior fat pads and the supinator fat stripe. The anterior fat pad should routinely be seen on all lateral elbow projections when adequate exposure factors are used. This pad is formed by the superimposed coronoid process and radial pads and is situated immediately anterior to the distal humerus (Figure 4-77). A change in the shape or placement of the anterior fat pad may indicate joint effusion and elbow injury. The posterior fat pad is normally obscured on a negative lateral elbow projection because of its location within the olecranon fossa. When an injury occurs, joint effusion pushes this pad out of the fossa, allowing it to be visualized proximal and posterior to the olecranon fossa. The supinator fat stripe is visible parallel to the anterior aspect of the proximal radius (see Figure 4-77). Displacement of this fat stripe is useful for diagnosing fractures of the radial head and neck.

• When the elbow is flexed 90 degrees, the forearm can be elevated to align the anatomic structures of the distal humerus properly, and displacement of the anterior and posterior fat pads can be used as signs to determine diagnosis. If the elbow is not adequately flexed, these fat pads can be displaced by poor positioning instead of joint pathology, interfering with their diagnostic usefulness. When the arm is extended, nonpathologic displacement of the anterior fat pad results from intraarticular pressure placed on the joint. Nonpathologic displacement of the posterior fat pad is a result of positioning of the olecranon within the olecranon fossa, which causes proximal and posterior displacement of the pad (see Image 87).

• A lateral elbow projection is obtained when the humeral epicondyles are positioned directly on top of each other, placing an imaginary line drawn between them perpendicular to the IR. To obtain this humeral epicondyle positioning, place the humerus parallel with the IR and elevate the distal forearm until the palpable medial and lateral epicondyles are superimposed (Figure 4-78). This positioning aligns the trochlear sulcus, capitulum, and medial trochlea into three concentric (having the same center) arcs (Figure 4-79). The trochlear sulcus is the small center arc. It moves very little when a positional change is made and works like a pivoting point between the capitulum and medial aspect of the trochlea. The largest of the arcs is the medial aspect of the trochlea. It is demonstrated very close to and slightly superimposed on the curve of the trochlear notch. The intermediate-sized arc is the capitulum. When these three arcs are in accurate alignment, the elbow joint is visualized as an open space and the anterior and proximal surfaces of the radial head and coronoid process are aligned.

• Importance of accurate positioning. The distal humerus, radial head, and coronoid process are misaligned when the proximal humerus and distal forearm are inaccurately positioned. Proximal humerus positioning determines the alignment of the distal surfaces of the capitulum and medial trochlea, whereas distal forearm positioning determines the AP alignment of the capitulum and medial trochlea. Proximal humerus and distal forearm positioning also determines the alignment of the radial head and coronoid process. Depression or elevation of the proximal humerus moves the radial head anteriorly or posteriorly on the coronoid process, respectively. Depression or elevation of the distal forearm shifts the radial head distally or proximally, respectively, to the coronoid process. To help understand how the distal humerus and radial head move together, remember that ligaments connect the capitulum and the radial head, so any movement in one causes an equal amount of movement in the other. Precise positioning is a must to obtain a true lateral elbow projection. It takes only a small amount of inaccurate positioning to misalign the distal humerus and close the elbow joint space.

• Mispositioning of the proximal humerus. If the proximal humerus is elevated (Figure 4-80), the radial head is positioned too far posteriorly on the coronoid process, and the distal capitulum surface is demonstrated too far distal to the distal surface of the medial trochlea (see Image 88). If the proximal humerus is positioned lower than the distal humerus (Figure 4-81), the radial head is positioned too far anteriorly on the coronoid process and the distal capitulum surface is demonstrated too far proximal to the distal medial trochlear surface (see Images 89, 90, and 96).

• Mispositioning of the distal forearm. When the distal forearm is positioned too low (Figure 4-82), the image shows the radial head distal to the coronoid process and the capitulum too far anterior to the medial trochlea (Images 91 and 92). When the distal forearm is positioned too high (Figure 4-83), the image shows the radial head proximal to the coronoid process and the capitulum too far posterior to the medial trochlea (see Images 93 and 96). Carefully evaluate images that show poor positioning. Often, both forearm and humeral corrections are needed to obtain accurate positioning.

• Visibility of the radial tuberosity is determined by the position of the wrist and hand. When the wrist and hand are placed in a lateral position, the radial tuberosity is situated on the medial aspect of the radius. Because a lateral elbow projection is taken in a lateromedial projection, the radius is superimposed over the radial tuberosity. If the wrist and hand are not placed in a lateral position, placement of the radial tuberosity changes. When the wrist and hand are supinated (externally rotated), the radial tuberosity is demonstrated in profile anteriorly (see Image 94). Pronation (internal rotation) of the wrist and hand shows the radial tuberosity in profile posteriorly (see Image 95).

• Lateral elbow projections obtained with the different hand and wrist positions just described are often taken to study the circumference of the radial head and neck for fractures; they are referred to as radial head images.

• The elbow joint is located 0.75 inch (2 cm) distal to the lateral epicondyle. To obtain an undistorted image of the elbow joint, place a perpendicular central ray at this level and centered to the midelbow. Open longitudinal collimation to include one fourth of the proximal forearm and distal humerus. Transverse collimation should be within 0.5 inch (1.25 cm) of the elbow skin line.

• Half of a 10- × 12-inch (24- × 30-cm) detailed screen-film IR placed crosswise or an 8- × 10-inch (18- × 24-cm) computed radiography IR placed lengthwise should be adequate to include all the required anatomic structures.

Lateral Elbow Projection Analysis

• If the elbow is flexed 90 degrees, the forearm can be elevated to align the anatomic structures of the distal humerus properly.

• The axiolateral elbow projection is obtained by placing the patient's elbow in a lateral projection, with the humeral epicondyles aligned perpendicular to the IR and placing a 45-degree proximal (toward the shoulder) angle on the central ray (Figure 4-85). It is this humerus and central ray positioning that accurately separates the capitulum and trochlea of the distal humerus and positions the radial head anteriorly to the coronoid process. The combination of positioning and angulation projects the anatomic structures (radial head and capitulum) situated farther from the IR proximal to those structures (coronoid process and medial trochlea) situated closer to the IR.

• Effects of errors in positioning or angulation. If the central ray is angled accurately but the proximal humerus is depressed lower than the distal humerus, the medial trochlea and capitulum cortices are not clearly defined, the coronoid process is free of radial head superimposition, and the radial neck and tuberosity are superimposed by the ulnar supinator crest (a sharp, prominent ridge running along the lateral margin of the ulna that divides the ulna's anterior and posterior surfaces; see Image 97). The same image can result if the patient is accurately positioned but the central ray is angled more than 45 degrees.

    If the central ray is accurately angled but the proximal humerus is elevated, the medial trochlea demonstrates some capitular superimposition and the radial head is superimposed over a greater portion of the coronoid process (see Image 98). The same image can result if the patient is accurately positioned but the central ray is angled less than 45 degrees.

• An accurately aligned radial head and coronoid process and an open capitulum-radial head joint is obtained when the elbow is in a lateral projection. A lateral elbow projection is accomplished when the humeral epicondyles are positioned directly on top of each other, placing them perpendicular to the IR (see Figure 4-85).

• Effect of distal forearm mispositioning. The alignment of the proximal surfaces of the radial head and coronoid process is affected when the distal forearm is positioned. Precise positioning is necessary to obtain accurate alignment. It takes only a small degree of inaccurate positioning to close the capitulum-radius joint. If the distal forearm is positioned too low, the image shows a closed capitulum-radius joint space and shows the capitulum too far anterior to the medial trochlea and the radial head distal to the coronoid process (see Image 99). If the distal forearm is positioned too high, the image shows the capitulum too far posterior to the medial trochlea and the radial head proximal to the coronoid process.

• The position of the wrist determines which surface of the radial head is placed in profile.

• Effect of wrist position. When the patient's elbow is placed in a lateral projection, wrist rotation causes the radius to rotate around the ulna. This rotation places different radial head surfaces in profile. To determine which surfaces are in profile, one should become familiar with the relationship between the wrist position and visualization of the radial tuberosity. The radial tuberosity is adjacent to the medial aspect of the radius. If the tuberosity is demonstrated, the medial aspect of the radial head is also shown on that same surface and the lateral aspect of the radial head is visible on the opposite surface. If the patient's wrist is positioned in a PA projection, the radial tuberosity and medial radial head are demonstrated posteriorly and the lateral radial head appears in profile anteriorly (see Image 98). If the wrist is in a lateral projection, the radial tuberosity is not demonstrated in profile but is superimposed by the radius. In this position, the anterior radial head is demonstrated in profile anteriorly and the posterior surface is shown in profile posteriorly (see Image 93).

• To place the radial head in the center of the collimated field, center the central ray 0.75 inch (2 cm) distal (toward the wrist) to the lateral epicondyle. Open the longitudinally and transversely collimated fields to within 0.5 inch (1.25 cm) of the posterior elbow skin line.

• An 8- × 10-inch (18- × 24-cm) detailed screen-film or computed radiography IR placed lengthwise should be adequate to include all the required anatomic structures.

Axiolateral Elbow (Coyle Method) Projection Analysis

• If the patient's upper arm AP thickness measures less than 4 inches (10 cm), a grid is not required. For such a patient, a high-contrast, low-kVp (below 60) technique sufficiently penetrates the bony and soft tissue structures of the humerus without causing excessive scatter radiation to reach the IR and hinder image contrast. If the upper arm measures more than 4 inches (10 cm), a grid should be used, because this thickness would produce enough scatter radiation to affect the image contrast negatively. When a grid is used, increase the kVp to above 70 to penetrate the thicker humerus and provide an adequate scale of contrast. If the technique is manually set, increase the exposure (mAs) by the standard density conversion factor for the grid ratio (number used to express a grid's scatter-eliminating ability) being used to compensate for the scatter and the primary radiation that the grid will absorb.

• Anode heel effect. To take advantage of the anode heel effect, position the thinner elbow (distal humerus) at the anode end of the tube and the thicker (proximal humerus) at the cathode end. Set an exposure (mAs) that will adequately demonstrate the midpoint of the humerus.

• An AP projection is obtained by placing the patient in a supine or upright AP projection, with the affected arm extended. Supinate the hand and externally rotate the elbow until an imaginary line drawn between the palpable humeral epicondyles is aligned parallel with the IR (Figure 4-88). This positioning places the proximal radius anterior to the ulna, causing the radial head and tuberosity to be superimposed over the lateral ulna by approximately 0.25 inch (0.6 cm), and places the greater tuberosity in profile.

• Detecting humeral rotation. Rotation of the humerus is a result of poor humeral epicondyle positioning. When the humeral epicondyles and the greater tuberosity are not demonstrated in profile, measure the amount of radial head and tuberosity superimposition of the ulna to determine how the patient should be repositioned. If less than 0.25 inch (0.6 cm) of the radial head and tuberosity are superimposed over the ulna, the elbow and humerus have been excessively externally rotated (see Image 100). If more than 0.25 inch (0.6 cm) of the radial head and tubercle are superimposed over the ulna, the elbow and humerus have been internally rotated (see Image 101).

• Positioning for humeral fracture. When a fracture of the humerus is suspected or a follow-up image is being taken to assess healing of a humeral fracture, the patient's arm should not be externally rotated to obtain the AP projection because external rotation of the forearm increases the risk of radial nerve damage. For such an examination, the joint closer to the fracture should be aligned in the true AP projection. If the fracture site is situated closer to the shoulder joint and the arm cannot be externally rotated, the greater tuberosity is placed in profile by rotating the patient's body toward the affected humerus 35 to 40 degrees (Figure 4-89). Depending on the amount of humeral rotation at the fracture site, the distal humerus may or may not be an AP projection (see Image 102). If the fracture is situated closer to the elbow joint, extend the arm and rotate the patient's body toward the affected humerus until the humeral epicondyles are aligned parallel with the IR. Depending on the amount of humeral rotation at the fracture site, the greater tubercle may or may not be in profile.

• If the humerus can remain aligned with the long axis of the IR while including the elbow and shoulder joints, align the long axis of the collimated light field with the long axis of the humerus to allow for tight transverse collimation.

• For many adult humeral projections, it may be necessary to position the humerus diagonally on the IR to include the elbow and shoulder joint. If using screen-film or DR systems for this positioning, the collimator head or tube column should be turned or rotated to align the long axis of the collimated light field with the long axis of the humerus. If a grid is used, the collimator head may be rotated, but do not rotate the tube column or grid cutoff will result. This is not recommended with computed radiography (CR) systems. If the collimator head or tube column cannot be adjusted for a diagonal positioning, leave the transversely collimated field open enough to include the shoulder joint and elbow. With this setup the collimated field includes a large portion of the patient's thorax. Therefore the thorax is exposed to unnecessary radiation but can be protected by use of a contact shield across it. Remember to leave at least 3 inches (7.5 cm) of space between the humeral head and the shield to allow for magnification, so that the shoulder joint is not obscured by the shield (Figure 4-90).

• To place the humeral midpoint in the center of the image, palpate the coracoid process and the medial epicondyle and position the central ray halfway between these two palpable landmarks. When the elbow and shoulder joints are included on the image, the degree of radiation beam divergence used for a long body part needs to be considered.

• IR length and positioning: Choose an IR that is long enough to allow at least 1 inch (2.5 cm) of IR to extend beyond each joint space; a 14- × 17-inch (35- × 44-cm) screen-film or computed radiography IR placed lengthwise should be adequate. For a patient with a long humerus, it may be necessary to position the humerus somewhat diagonally on the IR to obtain the needed IR length. For the computed radiography system, it is not advisable to position the part diagonally unless the system is set to handle this alignment. Palpate the two joints to ensure that the IR extends beyond them. The elbow is located approximately 0.75 inch (2 cm) proximal to the medial epicondyle. The shoulder joint is located at the same level as the palpable coracoid.

• Central ray centering and collimation. Once the humerus is accurately positioned with the IR, center a perpendicular central ray to the humeral midpoint, and open the longitudinal collimated field until it extends 1 inch (2.5 cm) beyond the elbow and shoulder joint. If the collimation does not extend beyond both joints, adjust the centering point of the central ray until both the elbow and the shoulder joint are included within the collimated field without demonstrating an excessive light field beyond them. Transverse collimation should be to within 0.5 inch (1.25 cm) of the skin line laterally and the coracoid medially.

Anteroposterior Humeral Projection Analysis

• If the patient's upper arm AP thickness measures less than 4 inches (10 cm), a grid is not required, but a grid is required if the patient's upper arm measures more than 4 inches (10 cm). When a grid is used, increase the penetration to above 60 kVp to penetrate the thicker humerus and provide an adequate scale of contrast. If the technique is manually set, increase the exposure (mAs) by the standard density conversion factor for the grid ratio used to compensate for the absorption of the scatter and primary radiation that occurs.

• Anode heel effect. To take advantage of the anode heel effect, position the thinner elbow (distal humerus) at the anode end of the tube and the thicker (proximal humerus) at the cathode end. Set an exposure (mAs) that will adequately demonstrate the midpoint of the humerus.

• Two methods can be used to position the patient for a lateral humerus projection, mediolateral and lateromedial. The first method positions the patient's body in an upright PA projection, with the elbow flexed 90 degrees and the forearm and humerus internally rotated until an imaginary line connecting the humeral epicondyles is perpendicular to the IR; this is termed a mediolateral projection (Figure 4-93). Have the patient rotate the humerus internally while the body maintains a PA projection. Do not allow the patient to rotate the body toward the affected humerus instead. Such body obliquity would cause a decrease in density of the proximal humerus compared with the distal humerus (see Image 103), because the shoulder tissue would be superimposed over the proximal humerus. If body rotation cannot be avoided, an increase in exposure (mAs) is required to demonstrate the upper humerus adequately.

• The second method positions the patient's body in an AP projection. The hand is positioned against the patient's side, the elbow is slightly flexed, and the forearm and humerus are internally rotated until an imaginary line connecting the humeral epicondyles is perpendicular to the IR; this is termed a lateromedial projection (Figure 4-94). If the patient's forearm is positioned across the body in an attempt to flex the elbow 90 degrees and the distal humerus is not brought away from the IR enough to position the humeral epicondyles perpendicular to the IR (Figure 4-95), the image demonstrates the capitulum posterior to the medial trochlea, a distorted proximal forearm, and the lesser tubercle in partial profile (see Image 104). The difference in the anatomic relationship of the distal humerus between the mediolateral and lateromedial projections is a result of x-ray beam divergence. For a lateral humerus projection, the central ray is centered to the midhumeral shaft, which is located approximately 5 inches (13 cm) from the elbow joint. Because the elbow joint is placed so far away from the central ray, diverged x-ray beams are used to image the elbow joint. This causes the anatomic structures positioned farthest from the IR to be diverged more distally than the anatomic structures positioned closest to the IR. In the mediolateral projection, the medial trochlea is placed farther from the IR than the capitulum. Consequently, x-ray beam divergence will project the medial trochlea distal to the capitulum. In the lateromedial projection the capitulum is situated farther from the IR; therefore, the x-ray beam divergence will project it distally to the medial trochlea.

• Positioning for a humeral fracture. When a fracture of the humerus is suspected or a follow-up image is being taken to assess healing of a fracture, the patient's forearm or humerus should not be rotated to obtain a lateral position. Rotation of the forearm and humerus would increase the risk of radial nerve damage and displacement of the fracture fragments. Because the forearm should not be rotated for a trauma examination, a lateral image of the proximal and distal humerus must be obtained by positioning the patient differently.

• Distal humeral fracture. Obtain a lateral distal humerus projection by gently sliding an IR between the patient and the distal humerus. Adjust the IR until the epicondyles are positioned perpendicularly to the IR. Place a flat contact protecting shield between the patient and the IR to absorb any radiation that would penetrate the IR and expose the patient. Finally, center the central ray perpendicularly to the IR and distal humerus (Figure 4-96). This positioning should demonstrate a true lateral projection of the distal humerus with superimposition of the epicondyles and of the radial head and coronoid process (see Image 105).

• Proximal humeral fracture. A lateral projection can be achieved by positioning the patient in one of two ways. The first method is best done with the patient in an upright position, a position known as the scapular Y, PA axial projection. Begin by placing the patient in a PA upright projection with the humerus positioned as is, and then rotate the patient toward the affected humerus (approximately 45 degrees) until the scapular body is in a lateral position (Figure 4-97; see Image 106). Precise positioning and evaluating points for this image can be studied by referring to the discussion of the PA oblique (scapular Y) projection (see page 270).

• If the patient's humerus can remain aligned with the long axis of the IR while the elbow and shoulder joints are included on the IR, align the long axis of the collimated light field with the long axis of the humerus to allow for tight transverse collimation. For many adult humeral images, it may be necessary to position the humerus diagonally on the IR to include the elbow and shoulder joint. If using screen-film or digital radiography (DR) systems for this positioning, the collimator head or tube column should be turned or rotated to align the long axis of the collimated light field with the long axis of the humerus. If a grid is used, do not rotate the tube column or grid cutoff will result. This is not recommended with CR systems. If the collimator head or tube column cannot be adjusted for diagonal positioning, leave the transversely collimated field open enough to include the elbow and shoulder joint. With this setup the collimated field includes a large portion of the patient's thorax. Therefore the thorax is exposed to unnecessary radiation but can be protected by laying a flat contact shield across it. Remember to leave at least 3 inches (7.5 cm) of space between the humeral head and the shield to allow for magnification, so that the shoulder joint is not obscured by the shield.

• To place the humeral midpoint in the center of the image, palpate (1) the acromion angle (Figure 4-99) for a mediolateral projection or (2) the coracoid process for a lateromedial projection and the medial epicondyle. Position the central ray with the humeral midpoint at a level halfway between the two palpable landmarks. To include the elbow and shoulder joints on the image, the degree of radiation beam divergence used when imaging a long body part needs to be considered.

• IR length and positioning. Choose an IR that is long enough to allow at least 1 inch (2.5 cm) of IR to extend beyond each joint space; a 14- × 17-inch (35- × 44-cm) screen-film or computed radiography IR placed lengthwise should be adequate. On a patient with a long humerus, it may be necessary to position the humerus somewhat diagonally on the IR to obtain the needed IR length. For the CR system, it is not advisable to position the part diagonally unless the system is set to handle this alignment. Palpate the joints to ensure that the IR extends beyond them. The elbow is located approximately 0.75 inch (2 cm) distal to the medial epicondyles. The shoulder joint is located at the same level as the palpable coracoid and acromion angle.

• Central ray centering and collimation. Once the humerus is accurately positioned with the IR and the central ray is centered to the humeral midpoint, open the longitudinal collimated field until it extends 1 inch (2.5 cm) beyond the elbow and shoulder joint. If the collimation does not extend beyond both joints, adjust the centering point of the central ray until both the elbow and shoulder joint are included within the collimated field without demonstrating an excessive light field beyond them. Transverse collimation should be within 0.5 inch (1.25 cm) of the skin line laterally and to (1) the lateral scapular border for the mediolateral projection or (2) the coracoid for the lateromedial projection.

Lateral Humeral Projection Analysis

1. Epner, R.A., Bowers, W.H., Guilford, W.B. Ulnar variance—the effect of wrist positioning and roentgen filming techniques. J Hand Surg. 1982;7:298–305.