Radiography of Horses and Cattle

Brit. vet. J. (1962), liB, 359

RADIOGRAPHY OF HORSES AND CATTLE By W. D. TAVERNOR and L. C. VAUGHAN Department of Surgery, Royal Veterinary College, Hawkshead Lane, North Mymms, Hatfield, Hertfordshire

Page Equipment 360 Dark-room technique 364 Protection against radiation 366 Radiography 371 Exposure factors 376 Radiology 378 Discussion 382 The use of radiography in veterinary practice has increased considerably in comparatively recent times. There is little doubt that modern advances in surgery, especially in the orthopaedic field, along with the desire of both veterinary surgeons and .owners to make the fullest possible investigation of cases have contributed substantially to the increased application of radiography as a diagnostic aid. The prosperity of veterinary practice is also a contributory factor in that a greater number of people have been able to afford the capital outlay required for the purchase of the equipment. The main increase in radiography has been in small animal practices or mixed practices with a high proportion of small animal work. In large animal practice the need for radiography has in the past been largely governed by the amount of horse work undertaken, when X-rays are invaluable in the investigation of many cases of lameness. Consequently only those people engaged in thoroughbred practice or working in hunting areas judged the possession of an X-ray machine necessary. Since the Second World War, however, a gradual increase in the volume of horse work in both town and country practices has been brought about by the resurgence of interest shown in the horse by the general public. As a result many practitioners have found it necessary to provide X-ray facilities. Radiography has also been extended in recent years to further the investigation of orthopaedic problems in farm animals, and hence the X-ray machine has become an instrument of considerable importance to all branches of veterinary practice. Radiography in horses and cattle on the one hand and the dog and cat on the other requires two entirely different techniques, largely on account of the disparity in body size. With small animals, radiography is undertaken in the comfort of the surgery; nervous or fractious patients may be sedated or anaesthetized to allow for accurate positioning; relatively low exposures are required; D

BRITISH VETERINARY JOURNAL, 118, 9

and personnel can be protected against the hazards of radiation if comparatively simple measures are adopted. In general practice radiography of horses and cattle is mostly carried out at the farm or stable, where the machine has to be operated from an often inconveniently positioned power point. The co-operation of the patient is not always readily achieved and sedation or anaesthesia is not easy without obtaining much extra help. High exposures are needed even for the extremities, and protection against radiation from these exposures is more difficult to ensure. British veterinarians have made notable contributions to the literature on the use of radiography in horses. The renowned pioneering efforts of Pryer (1934) and Oxspring (1935) on the radiography of the hoof for the diagnosis of navicular disease and the studies of Jones (1936) are outstanding examples. In more recent times Hickman (1953, 1954) has described various aspects of clinical radiography in horses and Drury, Dyce & Merlen (1954) demonstrated in experimental studies the feasibility of obtaining radiographs of even the thicker parts of horse limbs by employing improved X-ray materials and techniques. More recently there has also been published an American textbook on veterinary radiology (Carlson, 1961) which includes some sections on radiography of large animals. Apart from these contributions there does not exist in this country any composite article on radiography in large animals which is readily available to the practising veterinary surgeon. In the present monograph the authors have endeavoured to go some way towards making good this deficiency. The study is related to two X-ray machines, one a portable model (Newton-Victor) that is commonly employed in practice, and the other a more powerful mobile unit (Philips DX5). Particular attention has been paid to the way in which exposure times can be reduced by using the new types of fast film and intensifying screens, and also to the most important topic of protection against radiation. EQ.UIPMENT

X-rqy machines Two machines have been used by the authors. The larger of these, a Philips DX5 unit (Fig. I), is freely mobile within the department and has a kilovoltage range of 45-100. At the lower end of this range the maximum exposure obtainable is 50 rnA for 8 seconds and at the upper part of this range 35 rnA for 8 seconds. The unit is sufficiently powerful to give reasonable pictures of subjects such as the thorax and abdomen of adult sheep and it will produce good radiographs of the limbs of cattle and horses up to the shoulder and stifle joints. The machine has been fitted with a light beam diaphragm protective device which will be described under a later heading. The smaller machine is an A.E.!. (Newton-Victor) Model K.5 (Fig. 2) which is portable. It is packed in a case and can be easily carried by car to the farm. The output of this unit is less than the DX5 unit and the effective kilovoltage varies according to the kilovolt stud setting and the milliamperage used.

RADIOGRAPHY OF HORSES AND CATTLE

Approximate effective kilovoltages are as shown below: k V Stud Setting 2

3

lIlA

kV

kV

kV

5 10 15

65 60 55

70 65 60

75 70 65

The X-ray head may be fitted to a portable stand as shown in Fig. 2 for use on the farm or in the surgery. For more permanent use in the surgery it may be fitted into a larger mobile stand. This machine is effective for most small animal radiography and also for the extremities of large animals. These machines are limited in their capabilities, but when used with the appropriate film and screens it is possible to obtain reasonable pictures of most parts of the limbs of adult cattle and horses.

X-ray film X-ray film consists of a cellulose acetate or plastic support, both sides of which are coated with an emulsion consisting of silver bromide crystals suspended in gelatin. The size and arrangement of these silver bromide crystals determines the speed and contrast of the film. The emulsion may be sensitized during manufacture by various methods, such as the addition of suitable dyes or by using different methods of ripening, to enable the manufacturer to control the characteristics of the film. X-ray film is usually classified according to speed, and by using the faster types X-ray exposure may be reduced. This is a point of great importance when radiographs are required of thick or dense parts of animals and an X-ray apparatus of low output is being used. The use of fast film will extend the versatility of the X-ray unit to include subjects previously excluded and will reduce both the risk of exposure to the operator and the amount of possible movement blur in the radiograph. There are two main types of X-ray film : screen type film intended for exposure between X-ray intensifying screens in a suitable cassette; and non-screen X-ray film intended for exposure to direct X-rays and usually contained in a lightproof paper envelope. The screen films are available in three types: standard; ultraspeed (Kodak Blue Brand, Ilford Red Seal); and extra fast (Kodak Royal Blue; Ilford Gold Seal). The ultraspeed films are approximately twice the speed of standard films and the extra fast films are approximately 75 per cent faster than the ultraspeed films. The use of high-speed screen film is indicated where possible movement of the subject is a hazard, or for any other reason where the exposure time must be kept to an absolute minimum. When the faster films are used great care should be taken in their handling, particularly in respect of safelight illumination, as their extreme speed renders them very liable to fogging. Processing conditions must also be strictly adhered to; failure in this respect may cause

BRITISH VETERINARY JOURNAL, 118, 9

the films to appear somewhat coarse in grain with consequent loss of image quality. Non-screen fihn is recommended for examinations where fine bone detail is of importance. Because of the limited speed of this film, and the lower contrast achieved, its use is generally restricted to the extremities of small animals. It should always be appreciated that X-ray fihn is a delicate material and it should be handled accordingly. Film should be kept in a cool, dry place, and ordered in such quantities that the supply is renewed frequently.

Intensifying screens Intensifying screens are employed to reduce exposure time to a fraction of that required for direct, non-screen exposures. The screens consist of a cardboard support coated with a fluorescent salt such as calcium tungstate or barium lead sulphate. When excited by X-rays the grains of fluorescent salt emit visible blue and ultraviolet light, thereby exposing the film. The X-ray film is sensitized to the spectral emission of the screens to ensure the maximum photographic effect. Because the grains of fluorescent salt are somewhat larger than the silver bromide grains of the emulsion, and for other technical reasons, such as the thickness of the layer of salt, the use of intensifying screens may involve a slight loss of definition as compared with the non-screen image. However, the greatly reduced exposure time and consequent reduction of movement unsharpness, plus the increased contrast -of the image, more than offset the slight loss of definition produced by the screens. They also vastly increase the versatility of low output X-ray machines. Screens are supplied in pairs and should be permanently mounted in the cassette with the active face in close contact with the film. Any lack of screen/ film contact will greatly increase the unsharpness in the radiograph. Most screens in common use are of the calcium tungstate type and they are available in different speeds. As the speed of a salt screen is almost a direct function of its grain size, it will be seen that the faster (coarse grain) screens will produce relatively more unsharpness than the slower (fine grain) screens. New types of calcium tungstate screens have been recently introduced by both Kodak and Ilford where the speed has been increased without a resultant increase in unsharpness. The most widely used screens in the past have been Kodak Ultraspeed and Ilford Standard, but the new screens, Kodak Regular and Ilford Fast Tungstate, enable exposures to be reduced to half that previously required. Even further reductions in exposure may be obtained with Kodak High Speed screens. These screens reduce the exposure required with the old Ultraspeed screens to approximately one-third and their use in conjunction with extra fast film gives the fastest possible combination. The efficiency of screens depends to a marked degree upon the cleanliness and condition of their surfaces. It is important that the screens should be periodically examined in white light and any signs of soiling removed by cleaning with water and good quality soap, using a cotton wool swab. Grease may

RADIOGRAPHY OF HORSES AND CATTLE

be removed by the careful application of carbon tetrachloride. Dust and dirt will cause artifacts on the film and chemical splashes may cause permanent stains.

Cassettes It is important that the cassettes used are of good quality and that the film is kept in close and uniform contact with the intensifying screens inside the cassette. If the cassette becomes bent, dented or otherwise damaged faulty contact between film and screens occurs, and this results in the fluorescence of the screen spreading to neighbouring areas of the film, thereby causing a Jack of definition in the region of poor contact. There is no effective way of repairing damaged cassettes so it is most advisable to treat them carefully. All good cassettes have a lead back which prevents fogging of the film by back-scattered radiation from the table top and apparatus. There are two main methods of fastening cassettes, either with two spring bands or two clips on the edge of the cassette. The authors consider the former method better.

Grids An X-ray stationary grid is a wafer-thin flat plate consisting of a series of fine strips oflead foil separated by wood or plastic. This may be laid in close contact with the cassette. Grids are used to prevent the scattered radiation which occurs in thicker objects, particularly at high kilovoltages, from reaching the film. This considerably improves the contrast and thereby the definition of the film. The primary X-rays pass between the strips oflead, but the obliquely scattered rays are absorbed by the lead. Most modern grids are focused, usually for an anode-film distance of36 in. It is essential that a focused grid is used the correct way up and at the correct distance, or there will be a lack of density at the edges of the film and a poor peripheral picture. When a stationary grid is used the strips oflead show up as a series offine lines on the film. The main beam should be at right angles to the grid or else the grid lines will appear more marked. To eliminate these lines a moving grid or Potter-Bucky diaphragm may be used, but this equipment does not usually lend itself to large animal radiography. When a stationary grid is pJaced between the cassette and the object the exposure usually needs to be doubled and if a moving grid is used the exposure must be increased as much as four times. Film marking Any radio-opaque object may be used to mark a film, and sets of lead letters are available which give permanent records when they are placed on the cassette in a holder during the exposure. It is, of course, most important to mark right and left sides of an object when taking an X-ray, otherwise it becomes impossible to orientate the'radiograph for interpretation. Inadvertent bending or kinking may result in light or dark marks on the film. The film will also be marked by being splashed with developer or fixer, by being handled after copper objects have been touched, or simply by a small piece of f'aper or other small object being left inside the cassette.

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Recording exposures To get the best radiographic results from an X-ray machine it is essential to use the optimum exposure for the particular object in the particular circumstances. In order to get uniformity of results all exposures should be recorded and details of the patient, such as breed, age, size or weight, and position and area X-rayed should be given. To this should be added details of the exposure in the form of kilovoltage, milliamperage, time and anode-film distance, along with type of film and screens, and whether or not a grid was used. If this information is kept in a book with columns ruled for the various headings it takes very little time to complete, and if the final column is used for remarks concerning the quality of the resultant radiograph it forms a very valuable reference book. Mter a time it becomes possible to look up the necessary exposure for almost any subject and if necessary the results may be analysed in a simple tabular form. Such records result in improved radiography and prevent wastage of film. DARK-ROOM TECHNIQ.UE

The procedures carried out in the dark room consist of unloading and reloading the cassette and processing the exposed film by developing, rinsing, fixing and washing. It is essential that there should be sufficient illumination to carry out these procedures efficiently and this should be in the form of an approved safelight containing a bulb of the correct wattage. If the safelight is too bright it will cause fogging, particularly of the newer fast films. The walls of the dark room should be white or light-coloured to make the most use of the subdued lighting. A dark room need not be in any way elaborate as long as it is light-proof and has a sink with running hot and cold water. It is preferable to mount the developing, fixing and rinsing tanks in a wooden frame in order to prevent them being knocked over. It will be seen .from the previous section that there are very many variable factors in the taking of a radiograph. In order to standardize as far as possible so that the end-results are consistent it is most important to make the dark-room technique an established routine.

The developer Once the film has been removed from the cassette and placed in a hanger it should be put into the developing tank. X.ray developer basically consists of reducing agents which reduce the silver bromide in the emulsion to black metallic silver. There is an optimum temperature of 68°F for the developing solution and every effort should be made to keep solutions at this temperature. This can be achieved by using a thermostat or a simple immersion heater. Below 60°F the action is slow and results in a thin image of low contrast, and above 75 OF it becomes too active and causes chemical fogging of the film. The commonly used X-ray developers require a development time of four minutes at 68°F and this is known as standard time and temperature for development.

RADIOGRAPHY OF HORSES AND CATTLE

If these two factors are kept constant it goes a long way towards standardizing the result. During the time the film is in the developer it should be agitated occasionally to avoid flow marks on the film. The activity of the developer gradually diminishes by exhaustion in a busy hospital X-ray department, but in a veterinary practice it is far more likely to deteriorate because of oxidation. In busy X-ray departments the developer is regenerated by the use of replenishers but in veterinary practice it is probably best to throwaway the developer and replace it with new solution at least once a month. Ifold developer is used it is necessary to increase the development time considerably to obtain an image. The developer tank should be covered by a lid to keep out light and dust. After the film has been developed it should be well drained and then rinsed in a water bath in order to remove the surface portion of the considerable amount of developer solution that is retained in the gelatin. If this rinse is omitted the alkalinity of the retained developer tends to neutralize the acid fixer and as a result subsequent radiographs may become stained. Usually fresh water is used for rinsing but occasionally a weak acid stop bath is used to · arrest development immediately by neutralizing the alkaline developer. The minimum recommended rinsing time is ten seconds, after which the film should be well drained before being put into the fixer. The fixer When the film has been developed only the exposed silver bromide crystals form the radiographic image and the unexposed crystals are left unaffected by the developer. To complete the processing of the film the unexposed crystals must be cleared so that after it is washed the film will no longer be sensitive tQ light. The gelatin coating of the film must also be hardened. The fixing solution carries out these processes and contains a clearing agent (usually in the form of sodium thiosulphate-"hypo") and a hardening agent (usually an alum). The optimum temperature for the fixer is 68°F. The film when taken from the developer has a milky appearance and after being placed in the fixer this milky opacity is removed. The time taken for this to occur is known as the clearing time and when the fixer is fresh this will be less than one minute. The film should not be exposed to white light during this time. As the fixer becomes older this time becomes progressively longer. This is due to dilution of the fixer by water carried over from the rinse on the film surfaces, the formation of complex fixer salts and loss of fixer by adequate drainage not being allowed before the final wash. The fixing solution should be renewed when the clearing time has doubled. In veterinary practice it is usual to make up new solutions periodically rather than to regenerate the old solution. The time that the film must remain in the fixing solution to remove all the undeveloped silver salts is generally about twice the clearing time and the total time required to harden the emulsion is known as the fixing time. This is in the region of ten minutes. If the film is left in the fixer for too long the image may lose density. The method of fixing is to place the film in the fixer and to move it up and

BRITISH VETERINARY JOURNAL, 118, 9

down several times. This movement allows uniform fixation. Care should be taken to avoid splashing the fixer solution about the room. Hypo solutions are . corrosive and can badly damage brick walls and cement floors.

Wasking and drying These two steps in the processing of an X-ray film are most important. Washing is carried out to remove the residual processing chemicals and proper washing ensures the permanence of radiographs as records. If the chemicals are not removed the image will discolour and fade. Washing should be carried out in running water so circulated that the entire emulsion area receives frequent changes. Where the water flow is such that the water is changed four times in an hour the washing time should be fifteen minutes. Where the water change is at half this rate the washing time should be doubled. The film should never be left to wash for less than fifteen minutes. To obtain a good-quality radiograph proper drying of the film is essential. The film may first of all be immersed for a few seconds in a final bath containing a wetting agent to avoid the formation of drying marks. The use of wetting agents also speeds up the drying time. Drying should be carried out without causing any mechanical damage to the emulsion, or marks from uneven drying, and without exposing the film to dust or dirt. The after-treatment and storage of the film is also of importance if good records are to be kept. The sharp corners of the film should be trimmed off and the film placed in the folder from the original pack of film and then stored in an envelope bearing the relevant references. If washed and stored properly radiographs may be kept for many years. PROTECTION AGAINST RADIATION

The dangers of exposure to radiation are in the minds of most people nowadays. Many papers have been published on methods of protection against excessive exposure, but unfortunately tp.ere are many people who do not take these precautions seriously. The biological basis for these precautions has been dealt with in a most excellent manner by Mole (1961). He brings home quite forcibly the reasons for taking precautions both as a safeguard for individuals and for the community as a whole. Lawson (1960) lists a number of important practical measures to minimize exposure in small animal radiography. It is not easy, however, to compare methods used in large animal radiography to those used in small animals. It is common sense that the main beam should be limited to the area to be X-rayed and that personnel should be kept out of this beam. -

Large animal radiography It is easy to anaesthetize small animals for radiography but to anaesthetize a horse to take an X-ray of a digit is, to say the least, making life difficult. Most radiography in large animals is confined to the limbs. Owing to the density of the structures in the extremities of horses and cattle, high kilovoltages and

PLATE I

o'-

U

C: o

;> ~
Tavernor & Vaughan, Brit. vet. ] ., 11 8,9.

PLATE II

Fig. 4. Cassette ho lder with cassette and grid being slipped into position.

Fig. 3. Rad iograph of ox foot, with shadow of finger at top left.

f

•

Fig. 5. Use of cassette holder during radio- Fig. 6. Use of cassette holder during radiography of horse-'s graphy of horse's foot. hock. Tavernor & Vaughan, Brit. vet. J., 118, 9.

RADIOGRAPHY OF HORSES AND CATTLE

exposures are required and the use of a grid is essential. Although the exposure may be cut down by use of the newer types of fast film and fast intensifying screen it still remains quite high and it is not possible to dispense with a grid. This means that a bulky cassette, a grid and possibly a marking device must be held steadily in the correct position and the correct plane behind the part to be X-rayed. Quite apart from possible movements by the animal it can be quite difficult to hold the grid and cassette together in a steady manner in the correct position. It also means that the person holding these objects is very close to and possibly in the area covered by the direct beam. In fact without some device to show the exact area irradiated it is highly likely that some part of the person holding the cassette will be exposed to radiation. This is illustrated by Fig. 3, such radiographs being all too frequent for peace of mind. When a higher part of the limb is to be X-rayed the procedure is even more hazardous, as it is not possible to steady the grid and cassette on the ground. This often means that the person holding these objects must use both hands to keep them steady.

Device for holding cassette and grid To overcome these problems a frame has been designed which will hold a standard cassette and grid (Fig. 4). This frame has two fittings into which it is possible to screw a! in. metal tube. A series of tube lengths are used. One piece 3 ft. long is used as a handle and a set of five varying from 3 in. to 15 in. in length may be used as supports. The frame may be used to support the cassette either horizontally or vertically. In actual fact two frames are in use: one to hold a 10 by 8 in. cassette and grid, and another to hold a 12 by 15 in. cassette and grid. Marking devices are easily clipped or stuck on to the edge of the frame. With this device the appropriate size of cassette and grid may be held steadily for X-rays of the foot, and with the support tube of appropriate size the cassette may be held in position for radiographs of the fetlock, carpal, elbow, hock and stifle joints (Figs. 5 and 6). Not only is it possible to hold the cassette and grid steadily but by using the 3 ft. handle the person holding the device is well outside the main beam and gloves and aprons may be used as protection against scatter. Limitation of the main beam The main X-ray beam may be limited by the use of a cone or a beam-limiting device. All X-ray machines are supplied with a cone and most machines have a variety of cones that are interchangeable. Each cone has a cone factor, the use of which may be illustrated by Fig. 7. Using different sizes of cones the effective area of the main beam can be altered to suit the size of film used. It is obvious that only the smallest area necessary should be exposed and that the operator should be aware of the size of this area. With the beam-limiting device the main beam is shut down by means of a series of sliding shutters and using a light source it is possible to illuminate the

BRITISH VETERINARY JOURNAL, 118, 9

~~---'-O-.~------301·_---------'~l

! --...-1-

ANODE,

..

IS-

1

Fig. 7. Cone factor= IO =~ .'. area of plate exposed at distance of 30 in. will be a circle of 15 in. diameter. 5 2

exact area exposed. Such a device is shown fixed to the head of the Philips DX5 unit (Fig. I) and is a most efficient means of cutting down the effective size of the main beam to exact limits. Further protection to the individual may be afforded by lead rubber gloves and aprons and the judicious placing of sheets of lead rubber. Such protective clothing should always be worn when there is any danger of personnel being exposed to scattered radiation. More effective still are mobile lead-lined screens. These are, however, expensive and are only mobile within the surgery.

Continuation of main beam and scattered radiation Most modern cassettes are backed with about 0'1-0'2 mm. oflead, which forms an effective means of terminating the main beam for the quaJity of radiation considered, and when used in conjunction with a beam-limiting device this backing may act as a fairly complete stop to the main beam. With most cones, however, it must be remembered that some of the main beam will pass around the edges of the cassette. In order to assess the danger of the radiation continuing as the main beam, and as scatter, radiation measurements have been made while radiographs of a horse's foot were being taken. A heavy hunter was used as a subject and measurements were made using both the Philips and the NewtonVictor machines. With the Philips DX5 unit the machine setting used was 80 kV for 0'26 seconds, giving an exposure of 17 milliampere-seconds (rnA-sec.). The radiation in the primary beam was measured first of all at varying distances from the anode and the results are shown below: Distance from atWde (metres)

ArnolDlt of radiation (mr,*)

1'25 1' 75 2 '5 5'5

40 20 10 2

• Milliroentgen

The horse's hoof was then positioned in the wooden hoof block 36 in. from the anode and the grid and cassette in their holder were placed behind the

RADIOGRAPHY OF HOR'iES AND CATTLE

animal's foot. The main beam was cut down, using the limiting device, to the size of the cassette and the following measurements were taken: Position of measuring device

Amount of radiation (mr.)

metre at right angles to cassette ·5 metres behind the cassette 4·5 metres behind the cassette

I

0·3

I

0 ·2 0·2

\

The horse's hoof was then held by an assistant in the position that is normally adopted for radiography of the navicular bone and measurements taken at the position of the assistant's knee (approximately 1 ft. lateral to the cassette) and at the position of his hand on the horse's leg just above the carpus (approximately I ft. above the cassette). The exposure was the same as described above and the results were as follows: mr. I I

foot lateral to cassette foot above cassette

0·8 0·4

Similar measurements were then made using the Newton-Victor machine fitted with the standard cone (cone factor=-l). Here the machine setting was 15 mA for 2 seconds at stud 3 (approximately 65 kV), giving an exposure of 30 mA-sec. The measurements for the primary beam were as follows: Distance from anode

Amount of radiation

(metres)

(mr. )

1·25 1·75

The measurements made with the horse's hoof and cassette in place 36 in. from the anode were as follows: Amount of radiation Positioning of measuring device

(mr.)

I metre at right angles to cassette 1·5 metres behind the cassette 4:5 metres behind the cassette

With the assistant holding the horse's leg as described for the Philips machine, the measurements were as follows: mr. I I

foot lateral to cassette foot above cassette

2·5 2·5

One further series of measurements were made using the Philips DX5 unit to X-ray the stifle joint of a heavy hunter. The machine setting was 92 kV for 0·7 seconds, giving an exposure of 35 rnA-sec. The cassette and grid were held in place in the cassette holder with a supporting leg of suitable length fitted. Measurements were then taken at the position of the assistant's hand on the

370

BRITISH VETERINARY JOURNAL, 118, 9

handle of the cassette holder (approximately 18 in. to the right of and at right angles to the cassette) and at the horse's hind quarters (approximately I ft. to the left and at right angles to the cassette) where a groom may well stand to steady the horse. The results were as follows: mr. 18 inches to the right of the cassette 12 inches to the left of the cassette

2·0

3·5

The use of a lead-backed cassette gives a reduction factor of about twenty to the main beam radiation and where the beam-limiting device was used to restrict the beam to the size of the cassette the radiation behind the cassette was reduced to negligible proportions. The same fact was apparent for the Newton-Victor machine, except that here a circular cone was used and some of the main beam was passing round the edge of the cassette. Also here the amount of radiation at right angles to the cassette (probably just at the periphery of the main beam) was higher. Where a higher exposure with the DX5 machine was used for a thick part of the horse, there was obviously more radiation in the form of scatter at right angles to the cassette. It is apparent from these results that the main danger lies in the main beam in front of and around the edges of the cassette (depending on how effectively the main beam is limited) and if adequate precautions are taken by holding the cassette by some device other than the hands, andby using gloves and aprons, the danger from radiation assumes negligible proportions. If these precautions are not taken, however, it is possible that radiation in significant doses may be picked up, especially when using long exposures as in the case ofthe NewtonVictor machine.

X-ray monitoring A service is offered by a number of bodies for the personal monitoring of individuals engaged in radiography. This takes the form of a small badge containing a film that is worn in the lapel or other suitable place whenever X-rays are taken. The film is changed and developed at fixed intervals and from an assessment of the degree of exposure of the film a report may be given of the amount of radiation picked up by the individual during the period in question. A little common sense must be used, however, as to the best place to wear the badge and for a person who is mostly taking X-rays of horses' feet probably the best place to wear the badge is on the trouser turn-up. The cost of this service is quite reasonable and any person who takes a number of X-rays would be sensible in making use of such a service. The other point that should be borne in mind is that in older machines there may be faults in the lead screening of the X-ray tube, resulting in leaks of primary radiation in any direction. The only way of knowing about such leaks is by checking the X-ray head. This may be done in two ways: either by enlisting the help of someone with a radiation measuring device and going all round the X-ray head with it whilst exposures are made, or by fastening X-ray film all

RADIOGRAPHY OF HORSES AND CATTLE

37 1

round the X-ray head and taking an ,exposure. The films should be numbered and their positions recorded before development. Any leaking radiation will show by blackening of the films at the site ofleakage; this may then be covered by a piece of lead or similar protective covering. RADIOGRAPHY

Restraint The decision as. to whether the horse or cow is to be X-rayed in the standing position or cast is largely dependent on the temperament of the animal and the part of the body to be examined. The penetration of thick, dense regions such as the shoulder, stifle, head and neck requires protracted exposure during which the standing animal would in all probability move. In these instances, therefore, the requisite immobility can only be achieved when the patient is restrained on the ground and in some cases only under narcosis. On the other hand, for the hoof and distal parts of the limbs shorter exposures are needed and the procedure is con,veniently undertaken with the patient standing. Horses vary greatly in their reaction to positioning for X-ray examination while standing and also to the sight and sound of the apparatus employed. Experience has shown that hunters, hacks and show jumpers co-operate the best on average, prc;>bably because they are already accustomed to a varied environment. The procedure is resented most by highly strung thoroughbreds, especially when young, and ponies may also be difficult to position because of their extreme mobility. All horses should be bridled for the examination because control of the head is essential for accurate positioning. Measures such as tempting with food, the application of blinds, and twitching, each prove effective in certain instances but the most important factors by far are patience and gentle persuasion. When management methods fail resort may be made to sedation, .preferably with agents such as promazine hydrochloride administered parenterally. Care, however, has to be taken not to render the patient inco-ordinate, more particularly when a limb has to be raised as for radiography of the hoof. Cattle are generally more co-operative and consequently radiography in this species is less exacting than in horses. Positioning and Radiographic Anatomy Phalanges (a) Horse. The shoe should be removed and the hoof trimmed. With the aid of a drawing knife and a stiff brush the foot should be thoroughly cleaned. Particular attention must be paid to the removal of the debris that accumulates in the frog lacunae as much of this material is radio-opaque and will produce artifacts on the film. If the hoof is very muddy it should be washed. It is imperative to obtain antero-posterior and lateral views of the implicated digit and it may be desirable to X-ray the opposite limb for purposes of comparison. For an antero-posterior view of the front extremity the hoof is tilted so that I.

BRITISH VETERINARY JOURNAL, 118, 9

the wall at the toe is vertical, the cassette is placed close behind the heels~ and the beam directed horizontally at the centre of the coronet. With the machines generally used it is not possible to direct a beam at ground level and the hoof has to be raised. The procedure is greatly facilitated by supporting the hoofin a wooden block (Fig. 8) similar to that advocated by Oxspring (1935). The block consists of a stout wooden base to which are screwed two 3 in. cu bes. The inner half of each cube is sectioned diagonally in order to provide a slope at an angle of 45°, which accommodates the hoof. A strong cross-member is screwed to the front of the cubes, thereby limiting any possibl~ forward movement of the foot. The distance between the cubes has to be such that only I in. of the hoof rests on each slope, otherwise the X-ray beam would be obstructed. Hoof size varies considerably with the type and size of horse but it is usually sufficient to construct two blocks, one for ponies and light hunters (distance between cubes 4 in.) and another for heavy hunters and draught horses (distance between cubes 5 in.).

I I

~.

12'

\

I--

0

0 0

o

I I ').

I

rl\",

I

n ......... 1·-

I

Fig. 8. Diagrams showing a top view and side view of wooden block used to aid radiography of the hoof in horses and cattle,

The horse is led towards the machine and its foot is advanced slightly before being placed in the block. With the hoof in this position the front wall automatically approximates the vertical. Minor adjustments for the tube-film distance and alignment of the beam are made by moving the machine or the tube head. Some horses will take weight on the limb that is supported in the block

RADIOGRAPHY OF HORSES AND CATTLE

373

and this is of considerable assistance in overcoming tremor. With others it is necessary to steady the limb by holding it just above the carpus (Fig. 9). In order to produce a similar view of a hind digit the tube head would have to be placed between the fore and hind legs, which is too hazardous to be practical with most horses. It is preferable to employ the postero-anterior approach in which the beam is directed from behind. It is nearly always necessary to steady the limb by holding it at the hock (Fig. 10). For a lateral view of the fore and hind phalanges the beam is directed at coronet level from the lateral side, while the hoof is balanced on the stout crossmember of the block (Fig. II). ' By using a 10 by 8 in. cassette placed with the longer side upright, an X-ray of the entire phalanx is obtained. In the antero-posterior and postero-anterior views (Fig. 12) the navicular bone shadow is superimposed near the middle of the second phalanx, which is the best position possible radiologically. Faulty positioning technique, however, will cause the navicular either to be superimposed on the corono-pedal joint or even to be indiscernible, thus making interpretation impossible. The view obtained of the fetlock joint in these positions is too cramped and when a clear plate of this articulation is required it is advisable to adjust the alignment so that the beam is centred on the joint and the cassette is raised to the requisite level. The thickness and density of the phalanx varies at different levels and consequently it is not always possible to demonstrate each component part clearly on 'one exposure. For example, a plate in which the navicular bone is perfectly outlined is usually over-exposed for the distal border of the os pedis. It follows that exposures have to be varied to suit the particular requirements. The thickness of the hoof in the dorso-ventral direction is considerably reduced at the level of the central and lateral lacunae of the frog. This loss of density is demonstrated in antero-posterior views of the hoof by three wide, dark lines which cross the corono-pedal joint and navicular bone. These artifacts tend to interfere with interpretation but it is possible to eliminate them by filling the lacunae prior to X-ray with a paste of horn filings mixed in lard. The authors do not adopt this measure as a routine but use it whenevei a particularly wide or dense "frog shadow" has confused the interpretation. The horny excrescence or ergot which lies in the skin posterior to the fetlock joint is responsible for the production of another artifact. It is visible in anteroposterior views as a small circular opacity in the midline immediately below the groove in the proximal articular surface of the first phalanx. The outline of the first, second and third phalanges is irregular at the sites of insertion of certain ligaments and tendons. These eminences on X-ray are not infrequently misinterpreted as osteophytic outgrowths and hence careful note should be made of their situation and relative size. In the antero-posterior plane confusion is most notably caused by the eminences on the medial and lateral borders of the distal extremity of the first phalanx (Fig. 12) and in the lateral view by the ridge on the posterior aspect of the first phalanx, the eminences on the anterior surface of the second phalanx and the extensor process of the third phalanx (Fig. 13). It has also to be remembered that the development of

374

BRITISH VETERINARY JOURNAL, 118, 9

osteophytes at or near these sites is not unusual but the outline of the bone in these instances becomes more markedly raised and irregular. (b) Ox. In the majority of cases the claws require to be scrubbed and washed, special attention being paid to the interdigital cleft. X-rays of the front and hind digits in the antero-posterior and lateral projections are obtained with the animal in the standing position, precisely the same technique being used as for the horse (Fig. 14). Difficulty with the positioning of a hind foot is occasionally experienced and it may become necessary in these circumstances to cast the animal. Films of the extremity are complicated by the presence of four digits. The third and fourth are fully developed and each comprises three phalanges, two sesamoids and a navicular. The second and fifth are vestigial; they are made up of one or two bones, and lie behind the fetlock joint (Fig. 15). It is important to attach a marker to the film in order to distinguish between the right and left claws. Lateral views are of limited value because in this position the bones of the two main claws are superimposed.

Metacarpus and carpus In both species X-rays in the antero-posterior and lateral plane are readily achieved with the animal in the standing position. The cassette is raised to the requisite levels with the aid of extension rods attached to the cassette holder (Figs. 16 and 17). The small metacarpal bones in the horse are masked by superimposition but it is possible to outline them for the detection of fractures or exostosis formation ("splints") with oblique views taken at an angle of 60° to the cannon (Fig. 18). There are substantial differences in the structure of the carpus and metacarpus between the species (Figs. 19. and 20). Outstanding disparities include the number of carpal bones (horse seven, ox siX), the absence of small metacarpal bones in the ox except for a minute lateral vestige, and participation of the ulna in the carpal articulation in the ox. 2.

3. Elbow joint In order to include the entire joint in a lateral view in the standing horse or ox the cassette has to be raised as high as possible into the musculature medial to the elbow (Fig. 21). This is a difficult position for an animal to maintain during the process of alignment because the pressure of the cassette in the axilla causes the animal such discomfort that it is liable to fidget. The antero-posterior view presents even more difficulty because the joint is closely applied to the chest wall and its shape precludes close apposition to the cassette. The cassette has to be thrust well into the thoracic musculature immediately behind the olecranon, and the beam directed from the front (Fig. 22). In this plane the joint is considerably thicker than laterally and consequently good-quality antero-posterior films are difficult to obtain. Positioning for views of the elbow is greatly facilitated when it is possible to cast and narcotize the animal. This applies especially to the antero-posterior view since the leg can be abducted and extended to allow room for the cassette and also to bring the latter into closer contact with the limb.

PLATE III

Fig. 9. Position for antero-posterior radiograph of horse's fore foot.

Fig. 10. Position lor postero-anterior radiograph of horse's hind foot.

Fig. I I. Position for lateral radiograph of horse's fore foot. Tavernor & Vaughan, B rit . vet.

E

J., 118,9.

PLATE IV

Fig. 12. Antero-posterior radiograph of horse's fore foot, illustrating radiographic anatomy. I, first phalanx; 2, second phalanx; 3, navicular; 4, third phalanx; 5, eminence for collateral ligament.

Fig. 13. Lateral radiograph of horse's fore foot, illustrating radiographic anatomy. I, 2 and 3, first, second and third phalanges; 4, ridge for attachment of distal sesamoid ligament; 5, eminence for collateral ligament; 6, extensor process; 7, navicular.

Tavernor & Vaughan, Brit. vet. ]., 118,9.

'"d

r

~ -< ttl

>-l ~ < (1)

...,

::l

o...,

R'

-< ~

c ::r ~ ?

(JQ

g:; ~.

~ ~ "Ci:)

'!'

Fig. 14. Position for antero-posterior radiograph of cow's fore foot.

Fig. 15. Antero-posterior radiograph of cow's fore foot , illustrating radiographic anatomy. I, metacarpus; 2, sesamoid; 3, first phalanx; 4, second phalanx; 5, navicular ; 6, third phalanx.

PLATE VI

Fig. 16. Position for lateral radiograph of horse's metacarpus and carpus.

Fig. 17. Position for antero-posterior radiograph of horse's metacarpus and carpus.

Fig. 18. Oblique rad iograph of horse's metacarpus to demonstrate splint bone. Tavernor & Vaughan, Brit. vet. ]., 118, 9.

RADIUS

'"d

t-<

~

-< ...... ......

>--l P>

..,< o o.., <1>

R"

~

c

aq

::r

S>l

?

t:xl ~:

~ ~ ~CP

'P

Fig. 19. Antero-posterior radiograph of horse's carpus, illustrating radiographic anatomy. I, radial carpal ; 2, intermediate carpal ; 3, ulnar carpal; 4, accessory carpal ; 5, second carpal ; 6, third carpal; 7, fourth carpal.

Fig. 20. Antero-posterior radiograph of cow's carpus, illustrating radiographic anatomy. I, radial; 2, intermediate; 3, ulnar; 4, accessory carpal ; 5, fused second and third carpals; 6, fourth carpal; 7, small metacarpal.

PLATE VIII

HUMERUS

Fig. 2 I. Position for lateral radiograph of horse's elbow joint.

Fig.

22.

Fig. 23. Lateral radiograph of horse's elbow joint. I, processus anconeus.

Position for antero-posterior radiograph of horse's elbow joint. Tavernor & Vaughan, Brit. vet.]., 118, 9.

PLATE IX

Fig. 24. Position for postero-anterior radiograph of horse's hock.

Fig. 25. Position for lateral radiograph of horse's hock.

Fig. 26. Lateral radiograph of horse's hock, illustrating radiographic anatomy. I, fibular tarsal; 2, tibia; 3, tibial tarsal; 4, central tarsal; 5, third tarsal; 6, fourth tarsal; 7, splint; 8, metatarsus; 9, sustentaculum.

Fig. 27. Lateral radiograph of cow's hock, illustrating radiographic anatomy. I, tibia; 2, fibular tarsal; 3, tuber calcis; 4, tibial tarsal; 5, fused central and fourth tarsal; 6, fused second and third tarsal; 7, metatarsus; 8, small metatarsal; 9, sustentaculum. Tavernor & Vaughan, Brit. vet. ]., 118,9.

PLATE X

Fig. 28. Position for lateral radiograph of cow's stifle joint.

Fig. 2g. Lateral radiograph of cow's stifle joint, illustrating radiographic anatomy. I, tibial spine; 2, fibula; 3, condyle. Tavernor & Vaughan, Brit. vet. ]., 118, g.

RADIOGRAPHY OF HORSES AND CATTLE

37.'>

Radiographically the ulna presents an uncomplicated picture but it should be noted that the olecranon process is derived from a separate centre of ossification and it does not unite with the rest of the bone until the horse and cow are 3i-4 years old (Fig. 23).

4. Shoulder In both species the shoulder region because of its thickness and awkward situation is beyond the range of these machines in animals over 9 cwt. It is possible in young stock, however, to obtain a medio-Iateral view of the joint by holding the cassette at an angle on the lateral side of the shoulder, while the beam is directed from the other side of the animal. By pulling the leg being . X-rayed forwards the shoulder can be brought into better relief. S. Metatarsus and tarsus In all except the most intractable horses and cattle it is most convenient to X-ray the hind cannon and hock in th.e standing position. The postero-anterior approach is adopted in the sagittal plane just as for the extremity of the hind leg (Fig. 24). The concave shape of the hock anteriorly makes it difficult to obtain a close application with the cassette and so an allowance for this has to be made in the exposure. For the lateral view the cassette is situated medial to the hock and the beam directed from the lateral aspect (Fig. 2S). Differences in the structure of the tarsus and metatarsus between the species a:re many. Attention is especially drawn to the presence of two small bones in the bovine tarsus which have on occasion been mistaken for fracture fragments, namely the I in. long small metatarsal bone which articulates with the upper end of the large metatarsus, and the distal end of the fibula which forms the lateral malleolus. Other differences concern the number of tarsal bones (horse six to seven, ox five), their shape and mode of articulation (Figs. 26 and 27).

6. Stijlt joint In the standing animal the lateral view is obtained by thrusting the cassette high into the tissues medial to the joint (Fig. 28). This causes the animal discomfort and often leads to movements that repeatedly spoil the alignment. In the other plane the postero-anterior approach is used, for which the cassette is pushed hard into the flank just anterior to the stifle and the beam is directed from behind. Except in light animals it is difficult to produce adequate plates in the postero-anterior direction ,because in this plane the joint is extremely thick and its shape prevents the cassette from being placed in close apposition. Positioning is simpler when the animal is recumbent and narcotized but even then the thickness of the region is such that the' plates produced are seldom clear enough for the detection of anything but gross lesions. Lateral views of the joint (Fig. 29) are complicated in the horse and ox by superimposition in the anterior section of the prominent medial trochlear ridge and the patella. In the postero-anterior film unless it is exceptionally clear the patella is completely masked by the femur. The fibula in the two species differs markedly; in the ox it is a short blunt prolongation ·whereas in the horse it continues from half to two-thirds of the way down the lateral border of the tibia. p

BRITISH VETERINARY JOURNAL, 118, 9

7. Head and neck The density of the skull and cervical spine demands the use of exposures at or near the maximum output of the machine. Positioning is, therefore, best carried out with the horse or ox cast, both from the point of view of establishing immobility and also to provide protection from radiation. For the lateral projection there is no difficulty with regard to alignment but for the dorso-ventral view the animal has to be placed on its back with its head fully extended. E~POSURE

FACTORS

The following exposure factors have been prepared for the radiography of the limbs of cattle and horses using the Philips DX5 and the Newton-VictorK.5 machines. As X-ray machines show slight individual variations and different people have varying requirements as to the density and contrast 'of the final radiograph, these factors should only. be used as a guide. Different factors are given for certain film-screen combinations but it is not possible to give all possible combinations.

Philips DX5 Machine All exposures were made at a focus-film distance of 36 in., using a stationary grid.

Cattle These factors are for a milking cow of 1,000 lb. body weight. Film A

\

&gum Foot Foot Foot Carpus Carpus Carpus Hock Hock Hock Elbow Elbow Stifle Stifle

Position A.P. A.P. Lat. A.P. A.P. Lat. A.P. A.P. Lat. Lat. Lat. Lat. Lat.

kV

Time (sec.)

0 '26 0 ·06 0'26 0'33 0·08 0'26 0'33 0·08 0'26 0'26 0·06 0'42 92 0'12 92 • Kodak Ltd.

73 73 76 76 76 76 76 76 76

a. a.

Horses I. Heavy Hunter approximately

1,200

BIUl! Brand·

Royal BIIII·

•

•

•

•

•

•

• •

•

lb. body weight. Sere",

A

\

Foot (os pediJ) Foot (navicular and fetlock) Foot (navicular and fetlock) Foot (navicular and fetlock) Foot (navicular and fetlock)

•

•

Film Region

•

•

•

•

Regular·

• • • • • •

•

•

A

Ultra SjHed·

•

• •

ScrIm

,

BIUl! Brand

Position

kV

Time (sec. )

A.P.

88

0'26

A.P.

88

0'33

• •

A.P.

88

0'16

•

A.P.

88

0'16

A.P.

88

0 ·08

Royal Blue

A

f

Ultra SjHed

Regular

• •

• • •

• •

RADIOGRAPHY OF HORSES AND CATTLE 2.

377

Light Hunter approximately goo lb. body weight. Film

IUgum Foot (os pedis) Foot (navicular and fetlock) Foot Fetlock Fetlock Fetlock Fetlock Hock Hock Hock Hock Carpus Carpus Carpus Carpus Elbow Elbow Elbow Elbow Stifle Stifle Stifle

Position

kV

A.P.

80

Time (sec.) 0·26

A.P. Lat. Lat. Lat. Lat. A.P. P.A. P.A. Lat. Lat. A.P. A.P. Lat. Lat. P.A. P.A. Lat. Lat. P.A. Lat. Lat.

80 80 76 76 76 76 84 84 80 80 80 80 80 80 96 96 88 88 100 92 92

0·33 0·26 0·26 0·12 0·06 0·33 0·33 0·08 0·33 0·08 0·26 0·08 0·26 0·08 0·42 0·1 0·33 0·08 0·55 0.42 0·12

,

Screen

Royal Blue

Blue Brand

10.

I

Ultra SPeed

•

IUgular

•

•

•

• •

• • • • •

•

•

• • •

•

•

• •

• •

•

• •

•

•

• •

• •

•

•

•

•

•

•

• •

• • •

•

Newton- Victor K.5 Machine All exposures were taken using a kilovolt stud setting of 3 with focus-film distance of 30 in. and a stationary grid.

15

• rnA at a

Cattle These factors are for a milking cow of 1,000 lb. body weight. Film

Screen

,--A---,

IUgion

Position

Foot Foot Foot Carpus Carpus Carpus Hock Hock Hock Hock Elbow Elbow Stifle Stifle

A.P. A.P. Lat. A.P. A.P. Lat. A.P. A.P. Lat. Lat. Lat. Lat. Lat. Lat.

Horses I. Heavy Hunter approximately

1,200

Time (sec. ) 1·0 0·25 1·25 1·5 0·375 1·25 1·5 0·375 1·25 0·375 2·5 0·75 4.0 1·0

Blue Brand

Royal Blue

•

•

•

• •

Foot Foot Foot Foot

(os pediS) (navicular and fetlock) (navicular and fetlock) (navicular and fetlock)

A.P. A.P. A.P. A.P.

•

•

• •

•

•

•

• • •

IUgular

•

•

•

•

• •

•

•

•

•

•

•

lb. body weight.

,

A

Position

Ultra SPeed

•

Film IUgion

,--A---,

Time (sec.) 2·0 2·5 1·25 0·75

Blue Brand

Royal Blue

• •

•

Screen

,

A

Ultra Speed

•

•

•

IUgullJr

• •

378 2.

BRITISH VETERINARY JOURNAL, 118,9

Light Hunter approximately goo lb. body weight.

.

Screen

.

Film I .

&gion

Foot (os pedis) Foot (navicular and fetlock) Foot Fetlock Fetlock Fetlock Fetlock Carpus Carpus Carpus Carpus Elbow Elbow Elbow Elbow Hock Hock Hock Hock Stifle

Position

A.P. A.P. Lat. A.P. Lat. Lat. Lat. A.P. A.P. Lat. Lat. P.A. P.A. Lat. Lat. P.A. P.A. Lat. Lat. Lat.

Time (sec.)

1'5 2'0 1'5 1' 75 1'5 0'75 0 '375 1'5 0 '375 1'5 0 '375 4'0 1'25 4 '0 1'0 2 '5 0'75 2'0 0 '5 5'0

Blue Brand

\

Royal Blue

• •

• •

•

• • •

&gular

Speed

•

•

•

Ultra

• • • •

•

•

•

I

• •

• • • • •

•

• • • • • •

•

•

• • • • • •

RADIOLOGY

The accurate interpretation of radiographs is largely dependent on a sound knowledge of the radiographic anatomy of the normal subject. When the radiographer is able to recognize the normal contour and structure of each bone and joint on X-ray plates taken in the two usual planes, it is then a relatively simple matter for him to detect deviations from the normal. The inexperienced person will find it extremely helpful in this respect to have to hand a set of normal plates which can be used for reference when any problem of interpretation arises. These are most easily prepared from the limbs of cadavers, and furthermore the exercise will also provide an opportunity to obtain a set of standard exposures for each structure. Radiographs should for preference be examined on a fluorescent illuminator rather than be held at arms' length against a hanging light or against a window. An illuminator supplies an equal distribution of light to all parts of the film at the same time and this facilitates the detection of variations in bone density because the comparison of different areas is more straightforward. Occasionally it is helpful to examine specific parts of the film, particularly ifit is slightly overexposed, against a 100 watt light bulb in order that minute osteophytic growths may be detected. As far as possible all extraneous light should be eliminated, and if a small plate is to be viewed the surrounding part of the illuminator screen should be blacked out. This will result in greatly improved contrast. A standard technique must be adopted for the scrutiny of the films in order to ensure that a thorough examination is made in each instance. The films should always be viewed in the same position and are more easily observed about 3 ft. from the screen. To the trained eye any obvious defects will be noted in the first glance at the plate but the prompt detection of an abnormality must

RADIOGRAPHY OF HORSES AND CATTLE

379

not prevent a detailed examination. Each bone and joint must be examined systematically, for contour, structure, density and position, and at the same time the type oflesion that the clinical examination of the patient has suggested must be kept in mind. The abnormalities that are commonly encountered in large animal radiographyare:

(I) Changes in the density of bone A portion of a bone may become less opaque to X-rays than is normal, due to a localized reduction in the amount of bone matrix. On X-ray the lesion is detected as a dark focus, to which the term rarefaction is applied. One of the most common examples offocal rarefaction is that encountered in the advanced stages of navicular disease in horses (Fig. 30). A rarefactive area can also be the consequence of an infective process either in the form of an osteomyelitis (Fig. 3 I) or following the penetration of a bone by a foreign body (Figs. 4 1, 42 and 43). It is not unusual for an area of bone resorption, such as that seen in osteomyelitis, to be circumscribed by a narrow band of extremely dense bone which appears to wall off the' abscess. This change is termed sclerosis and since the sclerotic bone is more opaque to X-rays it appears very much lighter on the plate (Fig. 32). (2) Osteophyte formation The development of osteophytes inevitably leads to a disturbance in the normal outline of the bone involved. Large formations of new bone are instantly recognizable on X-ray (Figs. 45 and 49) but when the exostosis is small considerable care has to be exercised to ensure its detection. In the latter instance there may be merely an unevenness in the cortical outline or a small focus of ray-like prolongations emanating from the surface of the bone. Osteophytes may develop on any bone as a result of a periostitis of traumatic or infective origin. The proliferation of.new bone at the periphery of a joint is a characteristic feature of osteoarthritis, a condition to which the interphalangeal (ringbone) and intertarsal (spavin) joints in horses are particularly prone. (3) Changes in joints Apart from the peripheral osteophyte formation, the other radiographic changes to be looked for in joints are alteration in the outline of the articular surfaces of the component bones, variation in the distance between the components and the presence of opaque bodies ("joint mice") within the joint capsule. For example, as a result of a suppurative arthritis affecting the coronopedal joint the articular surfaces of the second and third phalanges become severely distorted and the distance between the bones greatly changed (Figs. 44 and 47). In the more chronic forms of arthritis, such as in spavin in the horse, the joint space may be imperceptible on X-ray as a result of an ankylosis between the involved bones (Fig. 56).

BRITISH VETERINARY JOURNAL, 118, 9

(4) Fractures and dislocations Generally speaking X-rays of complete fractures of the long bones offer little difficulty in interpretation because the fracture line is wide and the usually occurring displacement of the fragments obvious. The distortion that accompanies the dislocation of a joint is also usually readily apparent. Some fractures, however, are not so readily observed, as in the case of fissures (e.g. first phalanx), the separation of relatively small fragments (e.g. sesamoid) and when there is superimposition (e.g. navicular, sesamoid). When displacement is minimal the fracture line is identified as a narrow, dark shadow which can nearly always be followed to a perceptible break in the cortical outline. Described below are some of the conditions which commonly occur in horses and cattle and in which the radiographic changes just described are found.

( I) Phalanges (a) Navicular disease (horse). The existence of this disease can be established radiographically by the demonstration on films taken in the antero-posterior plane of small, dark, circular areas of rarefaction in the navicular bone which are mostly to be found at or close to the central ridge (Fig. 33). The nutrient foramina are enlarged and a few may be confluent with the rarefied area. In some cases osteophytes are present on the dorsal border and at the extremities of the bone. These positive findings indicate a disease process of relatively prolonged duration and the clinician is not often fortunate enough to have the opportunity of examining the horse at this stage. In the early stages the disease is not demonstrable by X:ray even though there may well be substantial changes in the posterior surface of the bone and the adjacent portion ofthe deep flexor tendon. As the disease progresses, however, there is a tendency for the nutrient foramina to become enlarged and on X-ray the ventral edge of the bone appears very irregular or "comb-like". (b) Fractures (horse). Fracture of the navicular bone most frequently occurs a short distance medial or lateral to the central ridge. The fracture on X-ray appears as a vertical or slightly oblique fissure and displacement is usually minimal (Fig. 34). The lateral and medial angles of the third phalanx are prone to fracture (Fig. 35), but it is not unusual for the bone to be virtually bisected by a fracture through its median line. There is a tendency to comminution in fractures of the second p~alanx, the fragments becoming widely displaced due to impaction from the first phalanx (Fig. 36). Simple fissures ("splits") commonly occur in the first phalanx, the fracture line extending from the proximal articular surface for three-quarters of the length of the bone. Such fissures may be visible in only one view and it is therefore imperative to take X-rays in both the antero-posterior and lateral planes. Comminuted fractures of the first phalanx also occur and displacement of the fragments is usually relatively slight on account of attachment of the inferior sesamoidean ligaments (Fig. 37). Occasionally the bone is merely chipped (Fig. 38).

RADIOGRAPHY OF HORSES AND CATTLE

Fractures which bisect the sesamoid bone horizontally or vertically are not difficult to detect by X-ray but when, as occasionally happens, small fragments become detached from the apex or base (Figs. 39 and 40) superimposition can mask their presence in both antero-posterior and lateral views. (c) Pedal necrosis (horse, ox). Foreign bodies, especially nails, which penetrate the sole of horses and cattle sometimes damage the solar aspect of the third phalanx. The injury, in conjunction with the almost inevitable infection, produces a focus of necrosis. On X-ray the lesion is recognized as an area ofrarefaction (Figs. 41, 42 and 43). (d) Suppurative arthritis of interphalangeal Joints (horse, ox). In cattle suppurative arthritis of the corono-pedal joint is well recognized as a possible sequel to the commonly occurring condition "foul-in-the-foot". The infection initially affects the interdigital cleft, but in neglected cases and in those which have not responded to therapy it tracks to the joint which is only a short distance away. Gross damage to the articulation rapidly follows. In the antero-posterior view the joint space appears to be wider on account of cartilage loss, pitting of the subchondral bone, and in many cases partial or complete destruction of the navicular bone (Fig. 44). In long-standing cases there is extensive osteophyte formation around the joint which may involve the other phalanges (Fig. 45). Suppurative arthritis of the fetlock joint usually results from an infection introduced directly via a penetration of the joint (Fig. 46). This condition is met less frequently in horses but it has been known for infection to spread to the corono-pedaljoint following the introduction of sepsis into the hoof by a foreign body (Fig. 47). (e) Sidebone (horse). The extent to which the lateral cartilages ossify in the horse varies greatly. Sometimes only the area adjacent to the angle of the third phalanx is affected whereas in other instances the entire cartilage becomes ossified (Fig. 48). Sidebones are best demonstrated in the antero-posterior plane. Interpretation in the lateral view is complicated by superimposition. (f) Periostitis "ringbone" (horse). Exostoses may form at virtually any point in the phalanges. When the outgrowths are large their demonstration by X-ray offers little difficulty but minute lesions are not always readily detectable and may be visible in only ORe plane (Fig. 49).

Metacarpus and carpus (a) Periostitis (horse). The osteophytes, known as "splints", that form on the small metacarpal bones vary greatly in size. When they are small they can only be seen on oblique views of the cannon but the larger formations can be seen protruding beyond the border of the cannon bone in antero-posterior and lateral views (Fig. 50). Periostitis may also occur in the metacarpal bones (Fig. 51). Osteophytes may also form on the carpal bones and are usually the consequence of particularly severe damage to the front of the knee. The anterior surface of the carpus is especially affected and the exostoses are therefore most likely to be detected by lateral exposures. Antero-posterior views should also 2.

BRITISH VETERINARY JOURNAL, 118, 9

be obtained, however, in order to reveal spurring on the interarticular facets (Fig. 52). (b) Fractures (horse). The cannon is so readily palpable that fractures of the metacarpus rarely require confirmation by X-ray. Radiography is essential, however, in the diagnosis of carpal fractures, more particularly when the injury involves the separation of a small fragment (Fig. 53).

3. Elbow (horse, ox) Fractures of the olecranon process or avulsion of its terminal epiphysis are best seen in lateral projections (Fig. 54). 4. Metatarsus and tarsus

(a) Fracture (horse, ox). Recourse to X-ray is seldom needed for the diagnosis of metatarsal fractures as the cannon bone is readily palpable. Generally speaking tarsal fractures are rare, but fracture of the os calcis is not an uncommon occurrence especially in cattle (Fig. 55). (b) Spavin (horse). Exostosis formation on the medial aspect of the large metatarsal, scaphoid and cuneiform bones and a varying degree of ankylosis between these bones is a characteristic feature of bone spavin in the horse. The lesion is best detected on antero-posterior films although both views of the hock should be obtained (Figs. 56 and 57).

5. Stifle Arthritis (horse, ox). Irregularities in the outline of the femoral and tibial articular surfaces and the presence of "joint mice" are best detected in lateral views of the stifle joint (Fig. 58). Postero-anterior views, except in smaller animals, are usually not of good enough quality for an accurate evaluation of joint space but on occasion it has been possible to detect fracture of the tibial spine in this plane. DISCUSSION

Very many difficulties arise when radiographs are required oflarge animals and these difficulties are accentuated under field conditions when portable machines are used. Even under hospital conditions when higher output X-ray units are used many areas of large animals are beyond the scope of radiography, but as veterinary hospitals and equipment improve it should be possible to extend considerably the scope of large animal radiography. A major disadvantage is the noise made by timing devices. This is particularly noticeable in portable machines using a clockwork timer. In the meanwhile the most should be made of existing equipment and the newer materials at the disposal of the radiographer. The use of the extra fast type of film combined with the new faster tungstate intensifying screens allows a considerable reduction in the exposure required. This has two applications: firstly, it allows reduction in exposure times, so reducing the danger of movement by the patient during the exposure; and secondly, it allows radiography by low output machines of thick parts that were previously beyond their scope.

PLATE XI

Fig. 30. Antero-posterior radiograph of horse's navicular bone after removal from hoof, d emonstrating a large central rarefaction .

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Fig. 32. Antero-posterior of a metacarpus in a h eifer, d emonstrating a seques trum with accompanying sclerosis.

Fig. 3 I. Lateral radiograph of the proximal ex tremity of a tibia in a young heifer, demonstrating an osteomyelitis.

T avernor & Vaughan, Brit. vet. ] ., 11 8,9.

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Fig. 34. Antero-posterior radiograph of a horse's fore foot, with a fracture of the navicular bone.

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Fig. 35. Antero-posterior radiograph of a horse's fore foot, with a fracture of the third phalanx .

Fig. 36. Lateral radiograph of a horse's fore limb, with a comminuted fracture of the second phalanx.

Fig. 37. Antero-posterior radiograph of a horse's fore limb, with a comminuted fracture of the first phalanx.

Fig. 38. Antero-posterior radiograph of a horse's fore limb, with the separation of a frag ment from the first phalanx.

Sesamoid Bones

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Fig. 39. Lateral radiograph of a horse's fetlock, with a fracture of a sesamoid bone.

Fig. 40. Antero-posterior radiograph of same limb as in Fig. 39.

Fig. 41. Lateral radiograph of a horse's fore foot, with a focal necrosis of the third phalanx.

Fig. 42 . Antero-posterior radiograph of same hoof as in Fig. 41.

PLATE XVII

Fig. 43. Antero-posterior radiograph of a cow's Fig. 44. Antero-posterior radiograph of a fore foot, with a focal necrosis of the third cow's hind foot, with a suppurative arthritis phalanx. of the corono-pedal joint.

Tavernor & Vaughan, Brit. vet. ]., 118, g.

PLATE XVIII

Af~ected I J

Fig. 45. Antero-posterior radiograph of a cow's hind foot, with a suppurative arthritis of the corono-pedal joint and extensive osteophyte formation.

Fig. 46. Antero-posterior radiograph of a cow's hind limb, with a suppurative arthritis of the metacarpophalangeal joints.

Tavernor & Vaughan, Brit. vet.

J.,

118, 9.

PLATE XIX

Fig. 47. Lateral radiograph of a foal's fore limb, with a suppurative arthritis of the corona-pedal joint and a necrosis of the third phalanx.

F ig. 48. Antero-posterior radiograph of a horse's fore foot, with sidebone.

Metacarpus

First

Fig. 49. Lateral radiograph of a horse's hind foot, with ringbone affecting the first/second phalangeal joint.

Fig. 50. Antero-posterior radiograph of a horse's fore cannon, with a large "splint". Tavernor & Vaughan, Brit. vet. ]., 118, g.

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Fig. 51. Antero-posterior radiograph of a horse's fore cannon, with an extensive periostitis.

Fig. 52. Antero-posterior radiograph of a horse's carpus, with periostitis.

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Fig. 54. Lateral radiograph of a horse's elbow joint, with fracture of the olecranon process.

PLATE XXII

Fig. 55 . Lateral radiograph of a cow's hock with a fracture of the os calcis.

Fig. 56. Postero-anterior radiograph of a horse's hock, with spavin.

Fig. 57. Lateral radiograph of same limb as in Fig. 56.

Fig. 58. Lateral radiograph of a cow's stifle, with osteoarthritis. Tavernor & Vaughan , Brit. vet.

J.,

118, g.

RADIOGRAPHY OF HORSES AND CATTLE

There is no doubt that the manufacturers of radiographic materials have these points in mind and are actively engaged in research to improve upon existing materials and equipment. There are so many variables in the production of radiographs that it is absolutely essential to standardize wherever possible. This may be translated into terms of dark-room procedure by developing the film under constant conditions and conforming to the use of standard time and temperature for development. The age of developer and fixer solutions should also be recorded and replenishment or renewal carried out at regular intervals. Under the conditions of use in veterinary practice where the number of X-rays taken may be small, this latter point must not be overlooked. If the radiographs are to be kept as permanent records the after-treatment and storage of the film is most important. Good radiographs can only be produced under good working conditions. This does not involve the use of elaborate equipment or premises but a little thought and the application of common sense will result in the improvement of the radiographic facilities of most establishments. Good film storage, care of cassettes and intensifying screens, secure blackout arrangements for dark rooms and the use of correct safelights are just a few of the points that have been considered. For individuals new to the field of large animal radiography it is essential to have some starting point from which to work as far as exposure factors are concerned. As an aid in this matter a chart of exposure factors for the different areas of cattle and horses that may require to be X-rayed has been prepared for both the machines that have been considered here. These factors should be used only as a guide, as they are only for average subjects and exposures may vary from animal to animal, but with their use and the recording of exposures as already described it should be possible to produce good radiographs and to improve greatly the resu1ts obtained over a period of time. Protection against radiation poses special problems where large animals are concerned, but once again a little thought and common sense combined with a strict discipline will result in the elimination of most dangers associated with radiography. Measurements of the actual radiation risk, in terms of milliroentgens during radiography of certain areas, have been made in order to show the extent of the hazard to the operator and his assistants. If the precautions that have been described are adhered to and attendants positioned away from the main beam and sources of scattered radiation the danger is negligible. The importance of this aspect of radiography cannot be overemphasized and adequate precautions and monitoring facilities are essential whenever X-rays are used. The more powerful the X-ray unit and the thicker the part radiographed the stricter are the precautions that must be taken. It cannot be too strongly stressed that meticulous positioning of the patient is an absolute essential for the production of radiographs of the high quality required for accurate diagnosis. Correct exposure is of little value if the resultant X-ray defies interpretation because the view of the structure under examination is oblique, foreshortened, or confused by superimposition. As a rule it is possible,

BRITISH VETERINARY JOURNAL, 118, 9

and indeed a lot more convenient, to X-ray the distal parts of the extremities with the horse or cow standing. The co-operation of the patient, especially horses, is not always forthcoming at first but with patience and perseverance a successful outcome is generally achieved. The procedure should be conducted in an unhurried manner and preferably in a quiet place free from distractions. For radiography of the head and neck, and also for the stifle, shoulder and elbow joints, in the case oflarge or extremdy fractious animals, the positioning is more accuratdy and easily accomplished with the animal restrained in recumbency or even anaesthetized. Views in both the antero-posterior (or postero-anterior) and lateral directions should be obtained as a matter of routine. Vital information may be missed if in an attempt to economize in time or materials an X-ray is taken in only one plane. For example, an exostosis on the anterior aspect of the second phalanx may well not be apparent on an antero-posterior plate but will be readily detected in a lateral view. Neither should the finding of a defect on the first plate deflect the operator from taking others since it is not uncommon for more than one condition to occur concurrently and the analysis of the findings should be left until "the completion of the examination. Frequently it is most hdpful to obtain plates of the opposite limb for comparison and this is especially true when examining the structures within the hoof. For antero-posterior and 1ateral views the X-ray beam should be focused at the centre point of the structure under review in order to avoid foreshortening and also to minimize superimposition which can be especially troublesome when complex joints such as the carpus and tarsus are X-rayed from an angle. Occasionally, as for the depiction of the small metacarpal hones in horses, or for an exostosis in an antero-Iateral situation, oblique views of the limb are required. As an aid to diagnosis a radiographic examination can be extremely valuable. The radiographic findings, however, must always be considered in relation to the information that has been gained from the history of the case and from a physical examination of the patient. For instance, in a lame horse, the seat of the lameness has first of all to be located, by means of palpation, manipulation and nerve block, before it is even known what part of the limb to X-ray. In some cases radiography is employed merdy to confirm the diagnosis whereas in others it is the ultimate and vital stage in the process of differentiating between a number of possible causes. The location and identification of an abnormality on a radiograph is only part of the problem of interpretation. It still remains to be decided what significance, if any, ought to be attached to the finding. In some instances (e.g. fractures, dislocations, gross structural changes in joints) the conclusions are obvious. Others (e.g. rarefactions, minimal osteophyte formation) are not as easily solved and can only be interpreted accuratdy if the radiologist has a clear understanding of the pathology of the conditions he is likdy to meet. If the changes detected at the initial examination are minimal or indefinite it is a wise precaution to repeat the examination at some later date should the lameness persist. This is particularly true of progressive conditions such as navicular disease and also when there are osteophyte formations.

RADIOGRAPHY OF HORSES AND CATTLE

Diagnostic radiology in horses and cattle is limited to the examination of the extremities, head and neck because the X-ray units within the financial scope of practitioners and, indeed, of most veterinary hospitals, are not of sufficient power to penetrate the thicker body regions. It means, therefore, that the spinal column, pelvis, thorax and abdomen of these species are virtually unexplored radiologically and there is little doubt that clinical research on conditions associated with these body regions has suffered severely as a result. The problem, however, is by no means insoluble, as has been demonstrated by Alksnis (1943), Bolz (1936), Spurrell and Kernkamp (1952) and Kralj (1954) who with more powerful machines have found it possible to obtain radiographs of the pelvis, thorax, abdomen and scapula of both species. With the advent of ultra-powerful X-ray units specially designed and housed to meet the requirements of large animal radiography the scope for advancement in the field would be virtually unlimited. Amongst other things it would undoubtedly lead to the use of special diagnostic techniques using contrast media, e.g. myelography, pyelography and bronchography, which are now employed as a matter of routine in the dog and which would considerably improve on present methods of diagnosis. It may well be that within the next decade the clinical departments of the teaching colleges and other veterinary establishments dealing with the treatment of large animals will be provided with the equipment which will enable the investigation oflarge animal diseases to be advanced by these diagnostic aids. ACKNOWLEDGEMENTS

The authors wish to express their gratitude to Professor C. Formston for providing the facilities for this work, and for advice on its preparation for publication. Grateful thanks are also extended to Dr. W. A. Jennings and Mr. B. E. Godfrey of the Royal Northern Hospital for technical aid with the investigation into radiation hazards. Thanks are due to Kodak Ltd. for the help readily provided by their staff, particularly Mr. S. A.J. Marshall and Mr. D. S. Cox, and for Figs. 30-57. The authors are also indebted to Associated Electrical Industries Ltd. and Philips Ltd. for technical aid and to Messrs. J. Boag and A. Wagstaff for photographic assistance. REFERENCES

A. (1943). Dtsch. tieriirztl. Wschr., 51, 301. BoLZ (1936). Dtsch. tierarztl. Wschr., 44t 394. CARLSON, W. D. (1961). Veterinary Radiology. London: Bailliere, Tindall & Cox. DRURY, F. S., DYCE, K. M., and MERLEN, R. H. A. (1954)' Vet. Rec., 66, 593. HICKMAN, j. (1953). J. rtry. Army vet. Cps, 240 44. HICKMAN, j . (1954), Vet. Rec., 66, 805. JONES, V. B. (1936). Vet. J., 92, 170. KRALj,J. (1954), Veterinaria (Sarajevo), 3, 81. LAWSON, D. D. (1960). Vet. Rec., 72, 1102. MOLE, R . H. (1961). Vet. Rec., 73, 1140. OXSPRlNG, G. E. (1935). Vet. Rec., 150 1433. PRYER, A. A. (1934). Vet. Rec., 140 253. SPURRELL, F. A., and KERNKAMP, H. C. H. (1952). Proc. 89th Amer. vet. med. Ass. CongT. ALlCSNlS,

(Received for publication,

1

May, 1962)