Radiographic investigation Special imaging procedures

3.2.1 Standard radiographic examination

3.2.1.1 Conventional radiographs in two planes

In instances of fresh fractures a.-p. and lateral radiographs are usually sufficient for a proper diagnosis and planning for emergency surgery (Böhler, 1963; Williams et al, 1992). The ultimate fate of the patient depends foremost on the quality of the radiographs. Radiologists and traumato-logists are equally responsible for their correct execution. Therefore both must be familiar with the technique and responsible for their proper execution.

The a.-p. film is taken with the patient supine and the limbs placed parallel to the midline of the body in 10 to 20° of internal rotation. Thus the lesser trochanter is projected over the diaphysis, it overlaps the diaphyseal edge; exceptionally its tip can be seen. Films taken in external rotation lead to an erroneous interpretation as the hip is seen in valgus; Pauwels-II fractures appear as Pauwels-III fractures and the greater trochanter is projected over a "shortened" neck. As a result the fracture is not recognized or fracture type and displacement are wrongly interpreted (Fig. 75).

Internal rotation must be done slowly to avoid unnecessary pain. It is advisable to hold this position with a support or sandbag. The film-focus distance should be 1 m. A Bucky or Lysholm grid is re-

Radiographic Grid

Fig. 75. A.-p. fine grain radiograph of a proximal femoral specimen taken in four different degrees of rotation.

a. Proper a.-p. film taken in 10 to 20° of internal rotation: the lesser trochanter is almost invisible and the femoral neck seen in full length;

b. Film in neutral position of the leg barely acceptable for proper assessment: the lesser trochanter is seen but the neck is already foreshortened, the fracture cannot be definitely recognized in every instance; c. Film taken in external rotation, poor radiographic technique: the greater trochanter is projected over the neck, the neck markedly foreshortened, the picture is almost useless; d. Film taken in marked external rotation, very poor radiographic technique: the greater trochanter is projected also over the femoral head, the neck is extremely foreshortened and seems to be in valgus position, the fracture cannot be assessed, the film is useless. Such films often lead to an erroneous diagnosis followed by a wrong decision and treatment quired. The cassette of 24 x 30 cm is placed longitudinally under the hip, its center should be 3 cm below the center of a line between symphysis and anterosuperior iliac spine. This point corresponds to the center of the femoral head. The X-ray beam must be centered at this point (Fig. 76).

For lateral radiographs the limb remains in the same position as for a.-p. films but it is slightly abducted. The film-focus distance is again 1 m. An 18 x 24 cm cassette with the Bucky grid is pressed laterally over the soft tissues at the level of the iliac crest and its long side parallel to the longitudinal axis of the femoral neck; it is supported by a sandbag. The center of the femoral head (as described in the instructions for a.-p. films) is projected over the midpoint between middle and cranial third of the cassette. The horizontally placed X-ray tube is turned in direction of the neck so that the central beam forms an angle of 40° with the longitudinal axis of the thigh. It thus points to the midpoint of the neck (Fig. 77).

The patient bends the opposite leg at the hip and either holds it there or places it on the case of the X-ray tube (Fig. 78). If the patient is unable to lift the leg, the tube can be placed in an opposite direction and the cassette between the thighs. The femoral head is often missed on these films, because the cassette has not been placed sufficiently cranial.

Internal Rotation LegInternal Fixator Image

(internal rotation)

(internal rotation)

Perpendicular Lines Brain Mri

Fig. 76. Determination of the center of the femoral head in average sized subjects.

a. Schema; b. Seen in the a.-p. projection and c. lines drawn on the body. With the leg in internal rotation of 10 to 20° a line is drawn between pubic tubercle and anterosuperior iliac spine. From its midpoint a 3 cm long perpendicular line is made in a caudal direction. It ends over the center of the femoral head c

Fig. 76. Determination of the center of the femoral head in average sized subjects.

a. Schema; b. Seen in the a.-p. projection and c. lines drawn on the body. With the leg in internal rotation of 10 to 20° a line is drawn between pubic tubercle and anterosuperior iliac spine. From its midpoint a 3 cm long perpendicular line is made in a caudal direction. It ends over the center of the femoral head

If the beam has not been pointed perpendicular to the femoral neck, the greater trochanter is projected over the femoral head and the neck is barely or not at all seen or foreshortened. Useless are also lateral films taken with the limb in external rotation (Fig. 79).

Postoperatively, standard films in two planes are mandatory for control of reduction and internal fixation. These postoperative films must be compared to the follow-up radiographs for proper assessment. We check our patients regularly after start of weight bearing (before discharge) and at predetermined intervals (4 months, 1, 3 and 5

years after injury). In the presence of symptoms, clinical and radiologic examinations have to be done more frequently.

The first postoperative films are usually taken while the patient is still under anesthesia. This allows proper positioning of the tube. Also the follow-up radiographs must be taken in the same position as the original ones. The required internal rotation must be done carefully to avoid pain. We recommend placing the limb temporarily on a splint in optimal rotation.

A comparison of the vascular supply to the femoral head on radiographs taken at different time intervals can be problematic. On one hand, it is often impossible to achieve identical radiographic quality. On the other hand, the positioning of the leg, changes in the general condition of the patient (weight gain), changes in bone density (osteoporosis) or atrophy of the gluteal muscles may render comparison difficult.

Spect Schema

Fig. 77. Schema of the correct positioning of the X-ray tube for lateral films.

The proper direction of the beam (1) forms an angle of 30 to 40° to the longitudinal axis of the femur. It runs perpendicular to the femoral neck axis and to the cassette (2). To find the proper direction of the beam a triangular template (3) easily made from Styro-foam is placed on the inner side of the thigh, it is particularly useful in obese patients

Fig. 77. Schema of the correct positioning of the X-ray tube for lateral films.

The proper direction of the beam (1) forms an angle of 30 to 40° to the longitudinal axis of the femur. It runs perpendicular to the femoral neck axis and to the cassette (2). To find the proper direction of the beam a triangular template (3) easily made from Styro-foam is placed on the inner side of the thigh, it is particularly useful in obese patients

Fig. 78. Standard lateral film: schema and fine grain radiograph of a specimen.

a, b. In internal rotation of 10 to 20° the neck axis shows the physiologic anteversion, it is inclined anteriorly; c, d. A more marked internal rotation abolishes the anteversion, longitudinal axes of neck and diaphysis form a straight horizontal line. This projection is familiar during surgery, it also shows a proper position of a guide wire d c

Fig. 78. Standard lateral film: schema and fine grain radiograph of a specimen.

a, b. In internal rotation of 10 to 20° the neck axis shows the physiologic anteversion, it is inclined anteriorly; c, d. A more marked internal rotation abolishes the anteversion, longitudinal axes of neck and diaphysis form a straight horizontal line. This projection is familiar during surgery, it also shows a proper position of a guide wire

Poor Radiographic Images

Fig. 79. Poor technique of a lateral film: schema and fine grain radiograph of a specimen.

a, b. The beam has not been centered perpendicular to the femoral neck, the greater trochanter is projected over the femoral head; c, d. With external rotation the picture looks like an a.-p. film. Course of the fracture line as well as reduction and internal fixation cannot be properly seen with this faulty technique

Fig. 79. Poor technique of a lateral film: schema and fine grain radiograph of a specimen.

a, b. The beam has not been centered perpendicular to the femoral neck, the greater trochanter is projected over the femoral head; c, d. With external rotation the picture looks like an a.-p. film. Course of the fracture line as well as reduction and internal fixation cannot be properly seen with this faulty technique

3.2.1.2 Supplementary radiographs

The diagnosis of displaced fractures is unambiguous on standard radiographs. If the presence of an undisplaced fracture is suspected, we recommend additional films in internal and external rotation. Radiographs in two planes of the opposite hip in similar positions may also be of help. These additional films may assist in clarifying the degree of displacement in instances of coxa vara or valga and in assessing the reduction.

A.-p. radiographs of both hips together can be taken using the same cassette 15 x 40 cm. Radiographs of the entire pelvis are not well suited as the central beam will be directed to the midline and both hips seen on the edges of the radiograph. Preferable is a more caudally placed cassette. In this position the radiograph will show both coxofemoral joints.

Occasionally magnified radiographs can be useful to establish the diagnosis. Fine grain films used together with intensifying screens allow analyzing the bone structure.

Completely undisplaced fractures can be difficult to diagnose (Pathak et al, 1997) but their pres ence can be suspected by a kinking of Shenton-Menard's line (a.-p. film) or a straightened or interrupted S-shape of the head-neck-junction

Suspicions can be raised in certain forms of fatigue fractures that may appear as small folds of the anterior cortex, an interruption of the contours or a minimal axial deviation. Fine grain films may show an interruption in the course of trabeculae. Furthermore, the presence of osteoarthritis may present problems in interpretation in the a.-p. and lateral films, if the marginal osteophytes are erroneously interpreted as a fracture (see Fig. 98).

If a definite diagnosis is still uncertain, special imaging procedures have to be requested. As a basic rule any suspicion of a fracture must be cleared during the first hospital visit. Standard radiographs in two planes are sufficient for emergency procedures of fresh displaced fractures. Examination of circulation and other imaging procedures will not change the necessity for surgery and should therefore not be ordered.

Functional films (in ab-/adduction, internal and external rotation) are foremost desirable for surgical planning in instances of avascular necrosis (flexion-, extension-, valgus-, varus-, rotational osteotomies).

3.2.2 Special imaging procedures

3.2.2.1 Conventional tomography

Conventional tomography used to be an important tool in the classic radiologic diagnosis. This technique was done to demonstrate, detect and localize suspected abnormalities that could not or only poorly be seen on standard radiographs. A refined image was obtained on thin slices using a specially designed equipment. This technique has lost its place in the age of modern CT.

Where this method is still available, it is of help to assess delayed healing and pseudarthrosis. It is as reliable as scintigraphy and single-photon-emissions-computer-tomography (SPECT) but less invasive.

3.2.2.2 MRI (Magnetic Resonance Imaging)

The phenomenon of nuclear magnetic resonance was described by Bloch et al (1946) and Purcell et al (1946). Up to the end of the seventies and the beginning of the eighties it has been used for chemical analysis of structures in high frequency spec-troscopy. Inspired by the success of the Fourier transformation the computer tomography was developed by Lauterbur (2004) and others and initially called "zeumatography".

Prerequisites are atom nuclei with angular momentum, a spin and a magnetic dipole moment. All atoms with an uneven number of protons show these characteristics. In biologic tissue the most frequently found atom is hydrogen. Its atom nucleus having only one proton is perfectly suited for imaging on account of its high dipole moment. The principle of this method is the fact that these atoms align in a strong magnetic field with a almost similar probability parallel or antiparallel to the field strength and form their circular movements in the direction of the outer magnetic field. This thermo-dynamic distribution of equilibrium can be markedly disturbed by a high radiofrequency stimulating impulse, when its frequency corresponds exactly with precession frequency of the preceding protons. The nucleus turns into a high-energy state. The temporal signal decrease is captured quantitatively. The time the system needs to return to the preexisting distribution of equilibrium is termed the longitudinal or Spin-Lattice-Relaxation time (T1). Other interactions exist inside the MR system. Precession movements occur in the same phase during the initial impulse. After abatement of the impulse the preexisting state returns (phase loss). The time constant is termed transversal or Spin-Spin-Relaxation Time (T2). The T2 relaxation is determined by the interference of proton signals. The object to be examined is divided into cuts for localization of the captured signals; they are successively stimulated by the nuclear resonance. The traced stationary proton signals are analyzed by computers and transformed into a picture by complex mathematical calculations (Fourier transformation).

Permanent magnets (horse shoe or rod magnets) are used for the generation of magnetic fields. They are very heavy and their magnetic field strength is limited. They are, however, relatively inexpensive and horse shoe magnets with great openings or open rod magnets can be manufactured. Their advantage lies in the fact that contact with patients during the examination is easy, the video surveillance is facilitated, invasive procedures are possible and claustrophobic reactions are limited. For the examination of limbs as in orthopedics and sport medicine the use of specialized magnets (coils) is easy. Only one limb can be placed in its opening.

Two types of electromagnets exist: resistive and superconducting magnets. The disadvantage of the resistive magnets is the fact that a major part of the electrical input is converted into heat due to the electric resistance of the coil and the ferromagnetic loss of the magnet nucleus. For that reason the newer generation employs low temperature, superconductive coils to generate the magnetic field (4K). The maximal field strength of these magnets for use in humans amounts to 2 Tesla, a tenfold of that of the resistive magnets. More recently, devices have been developed with an even greater field strength thanks to Blood Oxygen Level Dependant (BOLD technique, 3 Tesla) for the functional examination of the brain. Magnets with a field strength between and 6 and 9 Tesla have been used for ex perimental purposes investigating specimens, their opening being only a few inches.

MRI cannot be used in patients with implants consisting of ferromagnetic metals (such as several stainless steels), as the strong magnetic field will cause heating and displacement. Moreover, they influence markedly the distribution of field strength of the outer magnetic field and thus distort the cross-sectional images. If after implant removal microscopic ferromagnetic particles remain, they may cause extensive artifacts and thus render impossible an assessment of their surroundings (Fig. 80). Non-ferromagnetic metals such as gold,

Mri Artifact

Fig. 80. MRI artifacts.

11-year-old girl. Fracture/dislocation of the left hip treated by internal fixation. Eight months after the injury on account of avascular necrosis and deformity a Chiari osteotomy was performed and fixed with Kirschner wires. After removal of the Kirschner wires, small metallic particles (arrow) remain in the acetabulum. They interfere markedly with the interpretation of the MRI (see Fig. 218)

silver, amalgam and titanium are only seen as localized metallic artifacts.

In patients with a pacemaker (or any other electronic device) MRI may not be used as it may cause damage to the device. Moreover, the metallic electrode implanted in the right chamber may act as an antenna for radio waves. If the electrode forms a loop, a currency can be induced here.

Patients in whom the limb has been immobilized in a particular position may only be examined with appropriately opened or with open magnets. Plaster casts or fiber glass splints do not interfere with MRI. In patients with claustrophobia a slight sedation or anti-claustrophobic techniques are recommended to prevent an attack.

MRI does not show the cortical bone itself as it does not contain hydrogen in sufficient quantities. MRI visualizes, however, very well bone marrow: the red marrow having a higher water content gives dark signals in T1 weighted images and bright signals in T2 weighted images. The fatty bone marrow shows bright signals in T1 weighted images and dark signals in T2 weighted images. If the goal of the examination is to diagnose bone marrow pathologies, such as traumatic edema, suffusion, inflammatory edema, changes accompanying deposition of edematous cells, it is recommended to use fat-suppressing sequences allowing the strong signals of water to predominate and fat to be saturated.

T1 weighted images are advantageous for the demonstration of anatomic details and T2 weighted images for pathologic conditions.

MRI is the preferred choice for the earliest possible and the least invasive documentation of a fresh, undisplaced femoral neck fracture (Poulsen et al, 1996; Sernbo et al, 1997b; Pandey et al, 1998) On T1 weighted coronal images one can recognize already within the first 24 hours after

Fig. 80. MRI artifacts.

11-year-old girl. Fracture/dislocation of the left hip treated by internal fixation. Eight months after the injury on account of avascular necrosis and deformity a Chiari osteotomy was performed and fixed with Kirschner wires. After removal of the Kirschner wires, small metallic particles (arrow) remain in the acetabulum. They interfere markedly with the interpretation of the MRI (see Fig. 218)

Fig. 81. Undisplaced fracture documented by MRI.

67-year-old woman, fell and hit her right hip; a. The standard a.-p. radiograph does not reveal a fracture; b. The T1 weighted image shows a radiolucent line corresponding to an edema of a trochanteric fracture (arrow) (film supplied by Dr. Kinga Karlinger)

Fig. 81. Undisplaced fracture documented by MRI.

67-year-old woman, fell and hit her right hip; a. The standard a.-p. radiograph does not reveal a fracture; b. The T1 weighted image shows a radiolucent line corresponding to an edema of a trochanteric fracture (arrow) (film supplied by Dr. Kinga Karlinger)

Internal Fixation

Fig. 82. Early MRI after internal fixation of a neck fracture.

This 31-year-old patient was injured during a traffic accident. His condition was judged serious enough to transport him to our institute by helicopter; a, b. Radiographs show a left Garden-IV femoral neck fracture and an undisplaced acetabular fracture; c. d. An internal fixation was done within 4 hours: proper reduction and fixation with cannulated titanium screws; e. 3 weeks later T1 weighted films taken after contrast injection show a good blood supply to the head. The patient has not been positioned symmetrically; consequently, to allow comparison of the accumulation of the contrast agent in the intact and injured head two sequential images were needed. Little interference by the titanium screws; f, g. 4.5 years later the patient is symptom-free, the head contour preserved. Cysts lying anterior to the screws indicate the previous presence of circulatory disturbances

Fig. 82. Early MRI after internal fixation of a neck fracture.

This 31-year-old patient was injured during a traffic accident. His condition was judged serious enough to transport him to our institute by helicopter; a, b. Radiographs show a left Garden-IV femoral neck fracture and an undisplaced acetabular fracture; c. d. An internal fixation was done within 4 hours: proper reduction and fixation with cannulated titanium screws; e. 3 weeks later T1 weighted films taken after contrast injection show a good blood supply to the head. The patient has not been positioned symmetrically; consequently, to allow comparison of the accumulation of the contrast agent in the intact and injured head two sequential images were needed. Little interference by the titanium screws; f, g. 4.5 years later the patient is symptom-free, the head contour preserved. Cysts lying anterior to the screws indicate the previous presence of circulatory disturbances

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    What is supplementary radiographic technique?
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