EQUINE VETERINARY EDUCATION / AE / FEBRUAry 2008 93

Original Article A technique for computed tomography (CT) of the foot in the standing F. G. D ESBROSSE, J.-M. E. F. VANDEWEERD*, R. A. R. PERRIN, P. D. CLEGG†, M. T. LAUNOIS, L. BROGNIEZ AND S. P. GEHIN Clinique Equine Desbrosse, 18, rue des Champs, La Brosse, 78470, St Lambert des Bois, France; and †Department of Veterinary Clinical Science and Animal Husbandry, The University of Liverpool, Leahurst, Neston, Cheshire CH64 7TE, UK. Keywords: horse; computed tomography; standing; foot

Summary fracture lines within the (Rose et al. 1997; Martens et al. 1999). Computed tomography has proved to be valuable in Computed tomography (CT) in equine orthopaedics is the diagnosis of associated with distal limb currently limited because of the price, availability, pathology in the horse (Whitton et al. 1998; Tucker and Sande impossibility to transport the scanner into surgical 2001; Nowak 2002; Puchalski et al. 2007). Though CT has theatre, and the contraindications of general anaesthesia traditionally been perceived as an inferior soft tissue imaging in some patients. A pQCT (peripheral quantitative modality compared to MRI, a recent abstract indicated that it computerised tomography) scanner was designed by the may be a useful modality for soft tissue injury of the equine authors to image the limbs of the horse, both in standing foot (Eliashar et al. 2006). or recumbent position. Standing computed tomography However, the use of CT in equine orthopaedics is currently of the foot with a pQCT scanner is feasible and well limited because of the expense, availability and logistic tolerated by the horse. It enables good visualisation of problems associated with performing the procedure with large bony structures but is not suitable to evaluate soft animals. The contraindications of general anaesthesia in some tissues. The technique can also assist surgery by patients have to be considered when using CT in clinical cases. assessing the 3D configuration of bone lesions. CT imaging of the distal extremities of the standing, sedated horse would be desirable if diagnostic quality images could be Introduction obtained.

There is a growing interest in the use of computed tomography (CT) and magnetic resonance (MR) imaging in equine orthopaedic patients. The highly detailed cross- sectional images obtained with these 2 modalities can often demonstrate pathological changes undetected with other common imaging techniques (Barbee 1996; Tucker and Sande 2001). The use of CT imaging has been reported to adequately detect and characterise bone injury (Lischer et al. 2005; Morgan et al. 2006; Waselau et al. 2006), and to evaluate subchondral osseous lesions (Hanson et al. 1996) and occult osteochondral defects (Barbee et al. 1987). Where the complex nature of comminuted fractures makes radiographic interpretation difficult, computed tomography allows the production of cross-sectional images with spatial separation of structures that are superimposed on survey radiographs. This allows accurate assessment of the number and direction of Fig 1: Preparation of scanning. Five persons are required: one at the head, 2 at the forelimbs, one at the scanner and one at the *Author to whom correspondence should be addressed. computer. 94 EQUINE VETERINARY EDUCATION / AE / FEBRUAry 2008

In 2002, a pQCT (peripheral quantitative computerised tomography) scanner (Equine XCT 3000, Norland-Stratec Medical Sys.)1 was designed by the authors to specifically image the distal limbs of the horse both in standing or recumbent position. It is a translate-rotate multidetector system used for peripheral quantitative computerised tomography in man. pQCT is a method of assessing bone mineral density that uses multiple cross-sectional x-rays to reconstruct a volumetric model of the bone density distribution. The x-ray tube is operated at 60 kV maximum at an anode current of 0.3 mA. The mean energy is 45 keV. The fan beam detector consists of 6 CdTe detectors with amplifiers, rotating in a gantry with an opening of 300 mm. In the longitudinal direction, the minimal step width for scans is 0.01 mm over a full length of 350 mm (Braun et al. 1998). The system was modified by the authors to allow horizontal and vertical use. It was mounted on a frame that is moved with Fig 2: Positioning the limbs for standing CT of the left fore foot. electric motors. Wheels and brake have been added to the structure. This resulted in a scanner of 200 kg that was Patient selection mobile, could be moved within the hospital and transported in a small car (Fig 1). The system uses software to control the The criterion for inclusion for standing CT was that had scan, display the images and measure bone densities. clinical disease isolated to the foot by physical examination, Additional software (VolView)2 was used in more recent cases local anaesthesia or radiography, but further imaging was to obtain 3D images. required to identify lesions, measure their extent, monitor the The aim of the current study was to evaluate and progress or assist surgical treatment. Only horses with a good demonstrate the feasibility of CT scan in the standing horse temperament that would tolerate front limb manipulation and and to discuss some of the applications of the technique. distal flexions were selected for the procedure. All horses that underwent the procedure (n = 51) in the standing position Material and methods tolerated the examination without incident.

The medical records of all horses undergoing standing foot Patient preparation and handling CT at The Clinique Vétérinaire Équine Desbrosse between February 2002 and May 2007 were reviewed to report on: Before scanning, the shoes were removed and the feet were the selection of the patients; the CT scan procedure; the trimmed and cleaned. An indwelling catheter was placed in image acquisition and the number of valid slices that could the jugular vein. The horse was tranquilised with i.v. be performed; and the clinical usefulness. The procedure administration of 0.02 mg/kg bwt of acepromazine was considered clinically useful when it answered the clinical (Vetranquil)3 30 min before scanning. A fly repellent question by confirming or excluding a diagnosis, or (Emouchine)4 was sprayed on the horse. providing helpful information for the treatment or surgical Once in the scanning room, the horse was positioned in procedure. stocks, with the head either supported by 2 ropes or held by a handler at a height of 1.3 m (Fig 1). The gantry was moved Results up and down a few times to accustom the animal to the noise of the engine. Sedation was achieved by i.v. administration of Between February 2002 and March 2007, 56 CT scans of the 0.01 mg/kg bwt of detomidine (Domosedan)5. ‘Top up’ foot were performed. In 5 cases, standing CT was not sedation was administered in one case only. Cotton wool was considered applicable either due to the temperament of the placed in the ears of the horse. When the animal was quiet horse or because the scan was performed for presurgical and accustomed to the environment, both feet were planning and thus the images were acquired under general positioned a few times on the pads until the horse accepted anaesthesia. Fifty-one standing scans were obtained of the procedure. The scanner was then brought forward, the forelimbs. There were 26 left fore feet and 29 right fore feet. feet were placed on the pads with the foot to be examined The 51 horses in this study included 33 Selle Français, within the gantry (Fig 2). The limb was centred in the gantry 14 Standardbred Trotters, 1 , 1 Belgian and maintained as immobile as possible during acquisition. Warmblood and 2 Oldenburgs. The age ranged from 3–13 years (mean 7 years). They were 19 mares, 19 stallions Images acquisition and 13 geldings. Four horses were clinically normal and used to test and develop the technique, and 47 scans were The site of interest was first determined by a pilot scan of the performed on clinically abnormal horses. foot (taking approximately 1 min). The pilot sequence was also EQUINE VETERINARY EDUCATION / AE / FEBRUAry 2008 95

used to check positioning and set the position and angle of horse, no diagnostic images could be obtained due to a subsequent scans. The number of slices performed was software problem. Images that were considered clinically determined by the clinician. Ten slices were taken when 3D useful were identified in 26 of the 47 clinical cases. The reconstruction was requested. Generally, the procedure time indication for CT and clinical details are reported in Table 1 was about 90 s per slice and the entire scan protocol took and illustrated in Figure 3. 20 min to obtain 10 slices. The number of slices performed ranged from 1–11 (mean 6). Eleven percent of slices were Discussion invalid due to movement of the limb or inadequate targeting. In 4 cases, 3D images were created. The main disadvantages of the standing CT scan are the risk to the equipment and the problem of motion that need to be Clinical usefulness addressed to achieve successful, diagnostic quality images. In the current study, the CT scan was well tolerated by the horses On the 47 scans performed on clinically abnormal horses, that were selected. No adverse incident occurred during 2 cases were seen for assessment of a keratoma, 5 for scanning due to the horses reacting adversely to the diagnosis of P3 fracture, one for investigation of chronic technique. This indicates both good case selection based on lameness subsequent to previous pedal bone fracture, 4 for assessment of the horses’ behaviour as well as tolerance of the evaluation of foot abscess and seedy toe, 7 for assessment of procedure by horses. Total acquisition time is about 90 s per bone cysts, one for internal fixation of a sagittal fracture of slice, which limits the time spent with the limb through the the distal phalanx and one for confirmation of fragmentation gantry. More slices of higher quality were obtained with of . The other 26 cases were seen for lameness increasing experience. More slices might be captured with investigations for foot pain. In these, in addition to the full improvement of speed of acquisition. series of conventional radiographs, special projections of the Although the system has no movement correction features, foot (dorsal 60° latero-medial oblique view, dorsal 30° latero- diagnostic quality images were obtained in 89% of cases. medial oblique view) had been performed previously. No Random wobbling motions in the standing sedated horse can abnormality was seen in 17 of the 26 cases, and, in one be several centimetres in magnitude for more proximal regions

TABLE 1: Reasons for computed tomography (CT) scan and findings for the 47 clinical cases included in this study

Reasons for CT scan No. of cases Clinical usefulness

Assessment of chronic foot abscess 4 Exclusion of new bone formation or osteolysis in 3 cases. Significant pedal osteitis diagnosed in one case. Assessment of keratoma 2 The direction and extent of keratoma was identified in both cases. Results of scans were used for surgery. Suspicion of wing fracture of P3 3 A fracture line was found in 2 cases. No abnormality was seen in one case. on radiographs Suspicion of fracture of P3 on the basis of 2 No abnormality was seen in either case. Horses were treated conservatively and clinical signs. No radiographic abnormality. the lameness resolved after one month. Investigation of chronic lameness 1 The fracture line appeared to involve the insertion site of the collateral . subsequent to previous pedal bone fracture Assessment of cyst-like lesions 7 Confirmation of communication of a cyst in distal P2 with the in one case. A radiolucency in P2 in another case was not identified as a cyst with CT. The cyst-like lesions identified in 3 cases in P3 did not communicate with the joint. A radiolucency in the navicular bone was a cyst in one case and was not identified as a cyst in another. Sagittal fracture of P3 1 Preparation of surgery (evaluation of direction and length of implant). Suspicion of radiopaque body on the distal 1 A fragment was clearly identified with CT. border of navicular bone Foot pain investigation after positive palmar 26 No diagnostic image in one case due to a software problem. No abnormality was digital nerve block found in 16 cases. In these, no significant abnormalities were observed on a full series of radiographs including special projections. In 4 cases, the lesions identified on radiographs (enlargement of synovial fossae of navicular bone) were confirmed. In 5 cases, images were found clinically significant. Remodelling suspected on radiographs was confirmed in 2 cases at the insertion of the DDFT and in one case at the insertion of the impar ligament. Remodelling of palmar processes and insertion of the DDFT, which did not appear clearly on radiographs, was visualised with CT in 2 other cases. 96 EQUINE VETERINARY EDUCATION / AE / FEBRUAry 2008

12 3 4

56 7 8

9101112

Fig 3: Clinical applications of CT on the standing horse. White arrows show: enlarged synovial fossae (1); loss of contour of P3 due to keratoma (2); fracture line in palmar process (3); cystic lesion in P3 (4); seedy toe (5); bone cyst in P2 (6); wing fracture of P3 (7); osteolysis and new bone formation of P3 after subsolar abscess (8); new bone formation on palmar process (9); fragmentation of navicular bone (10); modelling of site of insertion of the deep digital flexor (11); and cystic lesion of P3 (12).

(McKnight et al. 2004) and might restrict the application of Sagittal articular fractures of the distal phalanx are standing CT scan only to the distal regions where there is much candidates for single lag screw fixation and accurate less movement in the standing sedated horse. preoperative radiographs are required to identify the location In this study, we report different clinical situations where where the screw should be placed. The length of the screw the technique appeared to be useful. In horses with a should be determined but this cannot be done accurately from suspected injury of the distal phalanx, a definitive diagnosis dorso-palmar radiographs because of the dome shape of the may not be reached on initial radiographic examination. This distal phalanx (Bertone 1996). In one case in the current study, may be due to insufficient time for resorption of bone, or those essential steps were performed with the use of standing inappropriate projections to identify fracture lines. The value of CT scan the day before the surgery, which reduced surgical computed tomography in diagnosing a geometric complicated time. However, further research work will be necessary to oblique fracture of the pedal bone has been shown (Martens assess if CT provides superior presurgical information for screw et al. 1999). In 5 cases in this study, CT was successfully used insertion in fractures of the distal phalanx. to confirm or exclude a fracture of the third phalanx. Another For keratoma removal, it was shown recently that partial issue is the assessment of healing of pedal bone fractures. A hoof wall resection resulted in fewer post operative significant correlation has not been made between the complications and a more rapid return to athletic activity than radiographic appearance of healing and potential soundness complete resection (Boys Smith et al. 2006). Accurate (Honnas et al. 1988). In our study, CT scan was used to assess anatomical definition of the affected area might be better the healing process in one case, and identify the cause for with the use of CT scan to identify the location and extent of persisting lameness, and fracture was identified by CT to the lesion, and preserve as much of the hoof wall as possible involve the site of insertion of collateral ligament. Those at surgery. In 2 of our clinical cases, the proximal extent of the findings led to a change in corrective shoeing, which resulted keratoma was assessed and a small window could be in improvement of lameness. Standing pQCT might be a useful trephined in the hoof wall to allow minimal invasive curettage noninvasive tool for the quantification of the fracture repair of the lesion. process in the horse and for treatment decisions in particular Septic osteitis of the distal phalanx may follow foot clinical situations, but this will require further research work. abscess with focal bone lysis being the most common EQUINE VETERINARY EDUCATION / AE / FEBRUAry 2008 97

radiographic finding. Sequestra frequently are present (Cauvin a diameter of 0.2 x 0.2 mm. The low energy portion of the x- and Munroe 1998). However early lesions may be difficult to ray spectrum is absorbed by a special filter so that a small-band detect even with high quality radiographs (Butler et al. 2000). x-ray line at 42 keV with a half-value of 19 keV is emitted. In 4 of our cases, computed tomography was used to assess Therefore, the technique could be used easily and safely for complications of subsolar abscess and seedy toe. clinical and research purposes in hospital and practice situations. Subchondral bone cysts can occur in multiple sites in In conclusion, we have shown that CT scanning of the foot horses and cause lameness. Administration of intralesional in the standing horse is possible using a pQCT scanner. The long-acting corticosteroids has been reported as an efficient technique is easy to perform and provides an alternative to the treatment (Vandekeybus et al. 1999) with optimal results more established technique performed under general being obtained where there is no communication with the anaesthesia. This increases both patient safety and the joint. The current technique was used to accurately identify convenience of CT scan, allowing wide application and easy the full extent and articular involvement of cases of cyst-like follow-up of cases. Such a system to safely accommodate the lesions in distal P2, in P3 and in the navicular bone. standing horse may gain increasing popularity for both A CT scan was also useful to identify an avulsion fragment research studies and clinical applications. It allows good on the distal flexor margin of the navicular bone that could visualisation of bony structures including the third phalanx, not be visualised radiographically. Those radiopaque bodies the navicular bone and the distal aspect of the second are usually difficult to demonstrate clearly on any radiographic phalanx, but is not suitable to evaluate soft tissues. However, view (Butler et al. 2000 ). further studies comparing the results of standing CT with the The other cases were seen for lameness investigations or technique on the recumbent horse and with other diagnostic follow-up. Clinically useful information was obtained in procedures (such as MRI, radiology and diagnostic local comparison to radiology in a limited number of cases (n = 5). anaesthesia) are required before the sensitivity and specificity The XCT 3000 is used to measure bone density and of the technique can be assessed. geometrical parameters of bone with pQCT. The machine has not been tested for other purposes and is currently Manufacturers’ addresses inappropriate for diagnosis of soft tissue injury. Based on current thinking regarding foot lameness, it would be 1Stratec Medizintechnik GmbH, Pforzheim, Germany. uncommon for 26 horses blocking to the foot not having 2Kitware, New York, USA. several cases with a significant soft tissue injury. Only bony 3CEVA, Libourne, France. 4Audevar, Clichy, France. structures can be identified, which may limit the applications 5Pfizer, Paris cedex 14, France. and explain our results in lameness investigations. Abnormalities (remodelling) were identified at the insertion of References the deep digital flexor tendon and impar ligament. For those sites, CT provided information complementary to specific Barbee, D.D. (1996) Computed tomography (CT): a dip into the radiographic projections used by the authors. Much variation future. Equine vet. J. 28, 92. was also found at the insertion of collateral of the Barbee, D.D., Allen, J.R., Grant, B.D., Riggs, M.W., Crawley, G.R. and distal interphalangeal joint. Further in vitro and in vivo Sande, R.D. (1987) Detection by computed tomography of occult research, comparing the technique with other imaging osteochondral defects in the of a horse. Equine vet. J. modalities, is therefore necessary to assess the clinical 19, 556-558. significance of those abnormalities. Interpretation might have Bertone, A.L. (1996) Fractures of the distal phalanx. In: Equine been improved by a larger number of slices, especially in the Fracture Repair, Ed: A.J. Nixon, W.B. Saunders, Philadelphia. pp 150-151. cases seen in the development phase of the technique. It is our Boys Smith, S.J., Clegg, P.D., Hughes, I. and Singer, E.R. (2006) opinion that 3D reconstructions might allow better Complete and partial hoof wall resection for keratoma removal: identification of the size and location of the lesion. A means post operative complications and final outcome in 26 horses of generating a 3D model of the foot has recently been (1994-2004). Equine vet. 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