Cardinal errors in bone radiology

Cardinal Errors in Bone Radiology

w. P.

Butt

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Diagnostic errors in bone radiology tend to recur and there is some virtue in trying to classify the causes so that future errors can be prevented. Most errors result from reporting an inadequate or imcomplete examination, or from ignoring the fundamental deficiencies of standard radiography-. Standard radiographic examinations were designed to permit a diagnosis of normal and not to demonstrate specific disease processes or specific entities. Additional exposures and special forms of investigation were designed to demonstrate specific points or specific entities. It follows that a diagnosis of normal, or the other quaint terms beloved by radiologists which mean normal, cannot be made on an incomplete or inadequate examination and a different examination or a different projection cannot be substituted for an inadequate or incomplete standard examination. For example, .In oblique film of the spine (Fig. 1) cannot be substituted for a lateral. In general. a positive diagnosis can be made on poor films but one must not accept that abnormalities have been excluded. Certain examinations have been accepted traditionally as complete even though they are not and the adage against diagnosing normal applies. Among them are those studies which are routinely single projections such as ‘pelvis to show the hips’ and ‘shoulder’. Figures 2 and 3 show that neither is a complete examination and neither excludes abnormalities which are quite clear on the views that should be a routine part of the examination of these structures. Any single view examination of the skeleton for initial assessment should be abandoned. Some studies are routinely non-frontal or non-lateral when structures which have an oblique inclination to the standard body planes are obliquely inclined to an W. P. Butt MD, FRC’R, FRCP(C), Department of Radiology. Jame\‘\ I’nibcwty Hwpit:il. Beckctt Street. Leeds LS9 7TF

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X-ray beam which is perpendicular to the table top on which the patient lies. For example, it is accepted that a single frontal film will demonstrate all the lumbar vertebral bodies even though that it is never the case. Pedicle destruction of L5 (Fig. 4) may not be seen on a routine frontal film and one hesitates to accept the diagnosis normal of a lumbar spine examination which does not include an inclined frontal film of that vertebra. The sacrum is a diagnostic trap partially because it is not seen en ,fia on any routine radiograph of pelvis or spine. In the cervical spine it is a frequent occurrence that no vertebral body is visualised on a standard frontal film and deformities which increase the tilt of the spine may result in a film which shows no vertebral bodies at all even in the thoracic spine (Fig. 5). Films of the spine that are not centrcd on the area of interest will frequently hide diagnostic findings even though the film appears. at first glance, to be a reasonable projection (Fig. 6). Some examinations are routinely underpenetrated because the resulting X-ray looks prettier. The ‘pelvis to show the hips’ is a common example of this flau. Textural changes in the bones of the hips may be extraordinarily difficult to appreciate in slightly underpenetrated films (Fig. 7). In general terms the adequately exposed bone film is not pretty. It seems strange to me that the more difficult the diagnosis is, the more frequent it is that no-one tries to improve the X-rays before making it. There has been almost universal disregard of recent advances in improving radiographic quality such as processor compatible mammographic film and commercially available microfocus X-ray tubes. This type of combination can demonstrate microscopic pathological changes in living bone. Less expensive techniques are available to produce high quality radiographs with no increase in cost or work time. Ignoring the basic flaws of diagnostic radiography

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Fig. l-Oblique films (C and D) cannot compensate for an inadequate lateral film (A) and the inadequate film must be repeated (E). Note how a vertebral body is simulated on the Frontal film (B) by an intact posterior arch. From Butt W. P. 1967 Standard Radiographic Examination in Orthopaedic Radiology. Park W. M. and Hughes S. P. F. (eds) Blackwell Scientific Publications.

Fig. Z-A

frontal film of the hip joint (A) is not adequate for diagnosis. From Orthopaedic

Radiology

with permission.

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Fig. 3--Rotated bone, Orthopaedic Radiology

Fig. Q-An permisslon

inclined

here a depressed with permission.

frontal

film of L5 (B)

fracture,

will disappear

is necessary

if the incident

to demonstrate

is so ingrained in experienced observers that they no longer realise that they are doing so. There are a number ofthings that standard radiography, including standard tomography. cannot do. The destruction of medullary bone by any process that does not, itself. calcify cannot be appreciated on standard radiography no matter how good, and that includes standard tomography. Lodvic explored this subject thoroughly and his original work should be read in toto by all who work with bone radiographs. Two examples from his work (Fig. 8) illustrate that medullarq bone destruction cannot be demonstrated

pedicle

beam is not parallel

destruction.

ORTHOPAEDIC‘S ~___~__._~

to the tilted

From Orthopaedic

cortex.

Radiology

185

From

with

in the adult. All the observations that one makes on standard radiographs of a destructive lesion of bone are due to the cortical component of that destruction. The margins of the cortical destruction are due to an advancing edge of osteoporosis which is always somewhat separated from the actual destructive lesion. The radiological ‘tumour edge’ is, therefore, never the tumour and is often not its edge. Several conclusions are inescapable. Any small ‘central’ radiolucency in a bone shaft must be cortical or endo-cortical in location. The size of a medullary lesion cannot be determined from an X-ray and a relatively small radiological

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Fig. ~--NO thoracic vertebral body is visible on this frontal film. The posterior arches simulate bodies in this patient with kyphosis. From Orthopaedic Radiology with permission.

lesion may in fact extend throughout the entire medullary cavity. The size of a purely destructive medullary lesion Will almost always be underestimated by the radiologically visible destruction. Trabeculation which crosses a lesion is much more likely to be due to residual uneroded endo-cortical bone between areas of erosion than to actual bony bridges. Axial imaging such as CT scanning has demonstrated how frequently fractures are invisible on standard frontal and lateral radiographs due to the inability of radiography to demonstrate a fracture unless the X-ray beam is parallel to a plane of that fracture. The corollary of that observation is that

standard radiography cannot verify that bone is continuous. Apparent trabecular continuity can be mimicked by overlap (Fig. 9). Radiological attempts to demonstrate bone continuity, or bone union, should be attempts to exclude discontinuity and the approach is to obtain films parallel to the plane of discontinuity. Figure 10 exemplifies the technique of using oblique films of unusual angulation to parallel planes of discontinuity in order to establish that bone union has not occurred. Situations where it is difficult or impossible to establish discontinuity without CT scanning are stress fractures in all bones, fractures of the vertebrae, and fractures of the femoral neck. There is a regrettable tendency to assume that all skeletal structures which are difficult to visualise on standard radiographs must be normal. One’s clinical judgement must not be ignored in situations exemplified by an unusual injury of the carpus (Fig. 11). Those of us who spend most of our time viewing static radiographic images tend to forget that those images may only be a brief glimpse of a changing process and conclude that they represent things as they were, as well as as they are. The time at which a radiological film is obtained does not alter the process that is occurring but may alter the ease of making a diagnosis. For example, the clinical significance of the sequence; dislocation-reduction-X-ray is no different than the sequence; dislocation-X-ray-reduction but the radiological diagnosis may be much more difficult in the former. Frequently it is necessary to consider dynamic factors in interpreting a static XP ray, particularly in the injured patient. If a fracture is undisplaced it will be invisible radiologically. The scaphoid fracture is well known but karate injuries and subcapital femoral fractures may also be invisible. Ultrasonic demonstration of an effusion in the hip joint is a useful diagnostic tool if a suspect subcapital fracture is not visible and bone scintigraphy has been used to demonstrate if a fracture, which is usually ‘undisplaced’ (e.g. a scaphoid). is obviously displaced. If that occurs (Fig. 12) there must be disruption of those structures which normally resist that displacement-the intercarpal ligaments in the case of the scaphoid. Displacement of the scaphoid fracture indicates that the intercarpal ligaments are torn and therefore that one is viewing a trans-scaphoid carpal dislocation. Because these fracture dislocations

Fig. 6-An antero-posterior film of the cervical spine (A) does not demonstrate the occiput to C2. A lateral film (B) is not adequate to assess this region. The correct frontal film (C) demonstrates the metastasis in the right side of C2.

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Fig.

7-Underpenetrated

films of the pelvis

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(A) are a trap. Significant

pathology

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may well be hidden

A Fig. ~-TWO examples of bivalved specimens and radiographs of those specimens demonstrate that medullary cannot be appreciated radiologically. From Lodwick G. S 1964 Radio1 Clin N Amer 2 and Lodwick G. S. 1965 andSoft Tissue (Ed M D. Anderson Hospital) Chicago Year Book Medical Publishers.

Fig.

9-Bone

‘union’

(A) can be simulated

by overlap.

From Qrthopaedic

Radiology

with

permission.

bone destructron in: Turnours of Bone

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Fig. lo-Tomography to assess union (6) often does no more than make a sharp picture (A) blurry. On the other hand, a film (D) with its central beam parallel to the plane of the fracture (as determined from other views (C)) will demonstrate non-union.

Fig. II-It Tomography

is tempting to consider all radiographically complex areas to be normal but one’s clinical suspicion should not be ignored. should be used in these complex areas to remove overlying bone to reveal the injury.

__-_cause rotation in the midcarpus a lateral projection of both the wrist and the hand are not obtained on the same exposure and the resultant oblique film of the carpus (Fig. 12) hides the dislocation. The avulsions of the insertions of tendons, ligaments, capsules and periosteum to bone are commonly seen as flake or chip fractures. If this is the only radiological observation one tends to lump them all together and consider that the injury is minor. Muscle contraction can avulse a tendon insertion to bone and there need not be any other injury and such an in.jury may well be minor. On the other hand, a fibrous tissue insertion such as periosteum, ligament, or capsule cannot be avulsed by muscle contraction but requires forceful displacement of the bone away from its fibrous tissue attachment. If the attachment is at a joint margin the chip fracture almost always indicates that the joint was dislocated. In Figure 13A one has no difficulty in accepting that the chip fracture is associated with a dislocation of the humeral head, but would one consider the chip equally significant on the film (Fig. 13B) taken 2 minutes later’? The two elbows in Figure I4 might easily be considered similar in that both have chip fractures following injury the one posteriorly, the other anteriorly. Further consideration will indicate, however, that the posterior chip is due to avulsion of a portion of the triceps insertion to the olecranon and therefore is an injury of little consequence. whereas the anterior chip is due to avulsion of the capsular insertion of the elbow to the coronoid process and must, therefore, indicate a spontaneously reduced elbow dislocation. Other examples of the chip fracture uncovering an occult dislocation are given in Figure 15. It must be emphasised that the siLe of the chip that is avulsed is irrelevant. Subluxation in the sense of‘a ‘little bit of dislocation’

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is something that is difficult to accept in the acutely injured patient and it is usually the result of partial spontaneous reduction of a complete dislocation. Subluxation following injury may also be due to muscle spasm alone and may not indicate an injury of the joint that is subluxed. If a joint is held at the extreme of normal motion by a process outside that joint (Fig. 16) it will appear subluxed and the inference of injury to that joint will distract one from looking for a lesion elsewhere. One of the dynamic factors often ignored in the assessment of static radiographs is blood supply. It is tempting to interpret Figure 17A as demonstrating a destructive process involving the tarsus and extending into the bases of the metatarsals. until one looks at the clinical specimen (Fig. 17B) after which it is apparent that the ‘destruction’ is a normal bone response contrasted with the failure of the distal bones to respond. If this process were hidden and not easily viewed one would be forgiven for not realising that the ‘normal’ bone was dead. Nevertheless, this is the only dependable radiological sign of bone death. namely the inability to respond to normal stimuli such as growth or osteoporosis. The other signs considered diagnostic of bone death such as increased density. sclerosis. and fragmentation are all signs of metabolic process. trauma or bone repair rather than bone death. Finally one must consider errors that arise from ignoring the effect of deformity. One tends to forget that :I static radiographic image is a two dimensional projection of a three dimensional structure and that any type of deformity from rotation to scoliosis will alter the final static image and can easily mimic disease or hide disease. Examples range from inaccurate leg length measurement due to joint contraction. to universal acceptance of ;i nonentity such a$

Fig. 12---Displacement of the usually undisplaced fracture frequently indicates an associated dislocation. film goes a long way in hiding the midcarpal dislocation. From Orthopaedic Radiology with permission.

A slightly imperfect

lateral

Fig. 13-The ‘chip’ fracture as a sign of dislocation is readily appreciated on a film obtained before the dislocation its significance may not be appreciated after reduction (6). From Orthopaedic Radiology with permission.

is reduced (A) but

Fig. l&The X-rays of the elbows of two patients following injury demonstrate the importance of careful assessment of ‘chip’ fractures. The partial avulsion of a tendon insertion (A) is relatively minor in comparison with avulsion of a ligament or capsule insertion (B) because the latter indicates a spontaneously reduced dislocation. From Orthopaedic Radiology with permission.

Fig. 15.-Other examples of avulsion indicating major displacements in; a tarsometatarsal dislocation (A); and in epiphyseal separation (B and C). The size of the flake fracture is not important. From Orthopaedic Radiology with permissron.

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kyphoscoliosis (Fig. 18 A and B). Conclusions that one normally draws from a radiological observation must be rethought if there is an anatomical deformity. Some principles need re-affirming. Rotation of an angled structure will alter its radiographic projection and make measurements of that angulation meaningless. If a patient with a scoliosis is rotated the measured angle can be made more obtuse than it is, i.e. the scoliosis can be ‘improved’ but cannot be made worst than it truly is (Fig. 18 C and D). If a patient with a scoliosis bends forward the scoliosis can be made

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‘worse’ but cannot be improved. If the same patient both rotates and bends forward (a not uncommon occurrence) his curve can be made either better or worse depending on which influence is stronger. Rotated bone becomes smaller, whiter and more distinct or larger, greyer and less distinct depending entirely on how the central beam strikes the rotated bone (Fig. 19). The practical significance of this is that the signs of rotated bone may disappear entirely from one projection to another and the lesion may be missed (Fig. 3!.

Fig. 16-With C l/C2 rotation the spmous process of C2 (closed arrow) is turned to the same side as the midline of the face (open arrow). This rotation causes the lateral masses of C 1 to have different sizes, shapes, radiodensities and relationships to C2. It must be emphasised that these joints are normal and that the posture is due to muscle spasm caused by a lesion somewhere else. One must not be mislead into considering that the Cl ‘C2 region is abnormal and look no further.

Fig. 17-Dead bone does not respond to stirnull. The demarcation between can mlrnlc bone destruction. From Orthopaedic Radiology with permission

normal

osteoporotic

bone and dead unresponsive

--

bone

_--.

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Fig. Is-Deformities can cause misleading radiographs. The lateral view of a patient with scoliosis (A) suggests that he is also kyphotic. A lateral film of his spine (B) reveals that he is actually lordotic. A frontal film of a patient (C) reveals a curve measuring 90 degrees whereas a frontal film of his spine (D) indicates the curve is much worse. Clearly, the easiest way to ‘cure’ a scoliosis radiologically is to rotate the patient.

(‘URRENI.

Fig. 19---Rotated See also Figures

bone becomes smaller, denser and more clearly demarcated 3 and 16. From Orthopaedic Radiology with permission

as IS well

Illustrated

ORTHOPAFDIC

by the tilted

facets

S

in this patlent

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