CASE REPORT

Veterinary Surgery 24:396-401. 1995

Use of Intraoperative Ultrasonography in Six Horses

PATRICIA L. ROSE, D V M , MS, Diplomate ACVS and DOMINIQUE PENNINCK, DVM, Diplomate ACVR

Intraoperative ultrasonography was used in six horses to aid localization and removal of bone fragments ( 3 horses) and foreign bodies ( 3 horses). The ultrasound transducer was enclosed in a sterile sleeve containing sterile aqueous gel and the examination was performed after aseptic preparation of the surgical site. Using ultrasound guidance a needle was placed in contact with the bone fragment or foreign body and an incision was made along the path of the needle to expose and remove the object. This technique resulted in decreased operative time and minimal tissue dissection. OCopjwghr 1995 by The American College of Veterinary Surgeons

HE INTRAOPERATIVE use of ultrasound has T been accepted in human surgery since the early 1970s.' The development of real-time B-mode equipment with dedicated high-frequency, high-res- olution intraoperative probes in the late 1970s and early 1980s led to markedly improved image quality. At the same time, ultrasonographers became in- creasingly familiar with the technique and gained expertise. Diagnostic ultrasound is a commonly used method of diagnostic imaging in horses2 Reports of the use of intraoperative ultrasonography in horses have been limited.3-5 We describe our experience with use of intraoperative ultrasound in six horses.

TECHNIQUE

Ultrasonography was performed after induction of general anesthesia and routine aseptic preparation of the surgical site. Either a 7.5 MHz (ATL Ultra- mark 8 Ultrasound System: Advanced Technology Laboratories; Bellevue, WA) or a 3.5 MHz trans- ducer (GE RT 2800; Milwaukee, WI) was used. The transducer was placed within a sterile plastic sleeve (Sterile Ultrasound Transducer Cover Set, Echo U1-

trasound, Reedsville, PA) or within sterilized plastic rectal examination sleeves. Sterile aqueous contact gel was used within the sleeve and on the horses skin.

CASE REPORTS

Horse I

A 3-year-old Thoroughbred-cross mare that had fallen in the pasture 2 weeks earlier was admitted for lameness. A grade 2 of 4 right rear lameness was improved about 50% by intra-articular administration of local anesthetic solution into the metatarsophalangeal joint. A 4 mm by 4 mm bone fragment that appeared to arise from the proximal plantaromedial surface of the proximal phalanx was identified on radiographs (Fig 1A). Penosteal new bone was identified on the medial surface of the proximal phalanx near the area of attachment of the medial col- lateral ligament but it was unclear whether the fragment was intra- or extra-articular in location.

Intraoperative ultrasonography was used to locate the fragment and to guide placement of the incision. The bone fragment, which was easily identified in relation to the medial structures of the third metatarsal bone and prox- imal phalanx, appeared as a hyperechoic structure with

From the Tufts New England Veterinary Medical Center, North Grafton, MA. Address reprint requests to Dominique Penninck, DVM, Tufts New England Veterinary Center, 200 Westboro Road, North

@Copyright 1995 by The American College of Vetennary Surgeons Grafton, MA 01536.

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396

ROSE AND PENNINCK 397

Horse 2 A 6-year-old Holsteiner gelding was admitted with right

hindlimb lameness that occurred 1 day after a dressage clinic 1 month earlier. The horse was grade 3 of 4 lame and had a swollen right metatarsophalangeal joint. Bone fragments were identified on radiographs of the right metatarsophalangeal joint. One fragment was dorsal to the condyles of the third metatarsal bone and a second larger fragment was identified in the medial aspect of the plantar pouch (Fig 2A). Dorsoplantar radiographs taken with the joint in flexion and extension indicated mobility of this fragment, however, it was unclear if the fragment was loose within the joint or attached to and moving with the joint capsule.

We concluded that the dorsal fragment could be re- moved arthroscopically but were concerned that the frag-

Fig 1. (A) Dorsoplantar radiograph. A bone fragment is ob- served adjacent to the medial aspect of the proximal phalanx. (B) Ultrasound image. The bone fragment (arrow) appears as a hyperechoic structure with shadowing. It is surrounded by poorly echoic synovial fluid and lies adjacent to the proximal phalanx (PI). The skin surface is in the near field.

acoustic shadowing surrounded by a poorly echoic area that was believed to be synovial fluid (Fig 1B). This ap- pearance confirmed an intra-articular location. Using 111-

trasound guidance, a needle was placed in contact with the bone fragment and a incision made alongside the needle, was extended to the fragment. It was attached by fibrous tissue to the proximal phalanx and involved a Small portion of its articular Surface. The fragment was removed by sharp dissection.

Fig 2. (A) Dorsomedial-plantarolateral oblique radiograph. A large bone fragment is observed in the medial aspect of the plan- tar pouch of the right metatarsophalangeal joint. (B) Ultrasound image. The bone fragment is observed as a hyperechoic structure (between calipers) Hith a strong acoustic shadow. The skin sur- face is located in the near field and the third metatarsal bone (MT3) and proximal phalanx (PI) are deep to the fragment.

398 INTRAOPERATIVE ULTRASONOGRAPHY IN HORSES

ment in the plantar pouch was free and that its position could change substantially after the horse was anesthe- tized. Intraoperative ultrasonography was planned to lo- cate this fragment which was identified as a hyperechoic structure with acoustic shadowing surrounded by anechoic synovial fluid (Fig 2B). The fragment was in close prox- imity to the medial proximal sesamoid bone and the me- dial aspect of the distal third metatarsal bone and was believed to be attached to the joint capsule. Thickened synovium and joint effusion were also evident. Real-time ultrasonographic guidance was used to position a needle in contact with the bone fragment and a stab incision was made to remove the fragment, using the needle as a guide.

Horse 3

An 8-year-old Thoroughbred gelding was referred for surgical removal of a bone chip in the left metacarpo- phalangeal joint. A 1 cm by 0.3 cm ovoid, mineral opacity, adjacent to the abaxial border of the medial proximal sesamoid bone was identified on radiographs. It was sus- pected that this bone fragment originated from the sesa- moid bone or was an avulsion fracture at the insertion of the medial collateral sesamoidean ligament. An ultra- sound examination was performed with the horse standing and the fragment was observed only with the joint in full flexion. This positioning limited the thoroughness of the examination and it could not be determined if the frag- ment was intra- or extra-articular.

The horse had a grade IV to V systolic ejection murmur and second degree atrioventricular block. On echocardi- ography, an acquired moderately severe mitral valve in- sufficiency with left atrial enlargement and left ventricular dilatation was identified. Despite the horse’s severe cardiac problem the owner requested surgical removal of the bone fragment. lntraoperative ultrasound was planned to help decrease the anesthesia time. With the metacarpophalan- geal joint in full flexion the fragment was identified as a hyperechoic structure surrounded by anechoic synovial fluid, confirming an intra-articular location. A needle was placed in contact with the fragment to guide the surgical approach. Unfortunately the horse had a cardiac arrest before the surgery was completed. Necropsy confirmed enlargement of the left atrium and ventricle, and mitral insufficiency.

HOVSP 4

An 1 I-year-old Thoroughbred-cross gelding had hit a fence with his right carpus while hunting 1 month before admission. Sixteen days after the injury the carpus became hot and swollen and mucopurulent drainage occurred from a small wound on the dorsal aspect of the carpus. On admission, there was swelling over the dorsal surface

of the right carpus. Marked soft tissue swelling dorsal and medial to the distal row of carpal bones was identified on radiographs. No osseous abnormalities were noted. On ultrasound examination, a discrete linear foreign body with a strong acoustic shadow was identified between the tendon of the common digital extensor muscle and the tendon of the long digital extensor muscle. The foreign body was approximately 1 cm in length and was sur- rounded by an ill-defined poorly echoic area. This ultra- sound appearance was consistent with abscess formation around a foreign body.

Intraoperative ultrasonography was used to locate the foreign body and a needle was placed in contact with the foreign body to guide location of the incision. A 1 cm by 0.5 cm fragment of wood was removed. An abscess mea- suring 3 cm by 3 cm surrounded the wood; this was de- brided and a drain was placed.

Horse 5

A 12-year-old Percheron gelding was admitted with a 1 week history of increased salivation, decreased appetite, and discomfort while eating. Treatment with antibiotics and flunixin meglumine had not improved the clinical signs. On admission, the horse was salivating excessively. Submandibular lymph nodes were enlarged and there was ulceration of the tongue. A linear metallic foreign body approximately 17 cm in length was identified, on radio- graphs, in the submandibular area slightly to the left of the midline (Fig 3A). It was unclear from the radiographs if the wire was in the tongue or sublingual tissues. The wire could not be palpated on oral examination. Ultra- sound examination between the mandibular rami located the wire within the left side of the tongue and extending into the sublingual tissues. Cystic structures containing echoic fluid were also identified and were considered to be abscesses.

Ultrasonography was used to facilitate location of the wire during surgery (Fig 3B). A biopsy guide was used to pass a 20 cm, 20 gauge needle into one of the cystic cavities for fluid collection for microbial culture. Ultrasound guidance was then used to position a needle in contact with the wire. An incision was made along the path of the needle to the wire that was then grasped with forceps and removed. The incision was enlarged to provide drain- age, a drain was sutured in position and the incision was left open to heal by second intention.

Horse 6

A 3-year-old quarter horse filly was admitted with a history of dysphagia and passage of water out of the nos- trils when drinking. There was no nasal discharge but a foul odor was detected at the nares; a guttural pouch in-

ROSE AND PENNINCK 399

fection was suspected. On radiographs, a fluid line was identified in one guttural pouch and an approximately 7 cm piece of small gauge wire was noted within the soft tissues ventral to the guttural pouches and dorsal to the larynx. On the dorsoventral projection the wire was iden- tified on the midline and extending to the left.

Intraoperative ultrasound was planned to aid localiza- tion of the wire. A 1 cm hyperechoic object, with strong acoustic shadowing, believed to be a section of the wire was identified about 5 cm from the caudal angle of the left mandibular ramus at a depth of 8.5 cm; this location corresponded well with the radiographic location. A modified Whitehouse approach6 which extended rostrally, to include the area where the wire was believed to lie. was made to the level of the guttural pouch. The incision was then filled with sterile saline to provide an acoustic window and the area was reexamined with ultrasound. The strongly echoic object previously identified was visible at the same location approximately 1 cm below the surface of the dissected tissue. Blunt dissection was used to locate and remove the wire. The left guttural pouch was then opened and lavaged. A Penrose drain was placed into the pouch and exited adjacent to the incision which was closed.

DISCUSSION

Successful application of intraoperative ultraso- nography requires the availability of appropriate equipment. Although specially designed transducers for intraoperative use in human surgery are available, they are not essential for equine surgery. Because of the large size of horses and the superficial location of the probe, size and shape of the transducer is not a limiting factor. The frequency of transducer re- quired will depend on the anticipated depth to be scanned.' In general, 5 and 7.5 MHz transducers will be adequate because they provide 5 to 10 cm of tissue penetration. Structures u p to 20 cm in depth can be imaged with a 3.5 MHz transducer, whereas very superficial structures will require a 10 MHz probe.'

An ultrasound unit with guided biopsy capability is helpful but not necessary for intraoperative ultra- sound. Such units permit the use of a specially de- signed biopsy guide which attaches to the transducer. The region of interest can be viewed in real-time and markers appear on the screen to indicate the needle path. The needle can be viewed between the markers as it enters the tissue. This technique permits precise localization of structures deeper than 2 cm from the

Fig 3. (A) Dorsoventral radiograph. A linear metallic foreign body (wire) is identified between the mandibular rami slightly to the left of midline. lt is not clear if the wire is in the tongue or sublingual tissues. (B) Ultrasound image. Wire is visible in the center of the image as a hyperechoic linear structure with shadowing deep to it. To the right of the wire is a cystic cavity containing echoic material. A second cystic structure is observed at the upper left of the image. Both cystic structures were ab- scesses.

surface. More superficial structures cannot be ob- served between the markers.

Alternatively, one of two freehand guidance tech- niques for needle placement can be used. In one method, the transducer is placed so that the structure

INTRAOPERATIVE ULTRASONOGRAPHY IN HORSES

of interest is viewed and the needle is inserted from a second location and observed in real-time until it contacts the structure. An incision is then made along the path of the needle. In general, for the needle to be visible, the transducer and the needle need to be separated by an angle of between 45 and 90 de- grees. In the other method, which was used in horse 6, the structure of interest is identified before incision and again periodically as the incision is deepened. The direction of the incision can be adjusted as needed. Isotonic fluid or sterile aqueous gel can be placed within the incision to function as a "stand- off" and provide a clear image of the near field. In a deep incision fluid is preferred; gel is better if the incision is too shallow to allow pooling of fluid. If gel is used care must be taken to remove all the gel before closure. The first method is preferred but re- quires enough space that the transducer and needle can be separated from each other. The second method is suited to small areas and regions sur- rounded by hyperreflective structures such as bone and gas-containing structures.

Most transducers cannot be sterilized so sterile transducer covers are n e c e s ~ a r y . ~ ~ ' ~ The commer- cially available kits that we used provide both sterile aqueous gel and a sterile plastic sleeve. This sleeve is seamless and of heavy-gauge plastic so leakage is of little concern. These sleeves will not fit all trans- ducers so, if necessary, sterile rectal sleeves and any sterile aqueous gel can be used. Rectal sleeves may be more prone to leakage so it is best to enclose the transducer in two sleeves with contact gel between each sleeve.

One study of intraoperative ultrasound in humans reported that the technique was useful in 9 1.5% of patients and provided the following benefits: allowed the acquisition of new information; complemented or replaced intraoperative radiography; guided sur- gical procedures; and confirmed the completion of the operation.' In the reported cases, the advantages of intraoperative ultrasound were similar. Use of ul- trasonography allowed the acquisition of new infor- mation, especially in the three horses with bone fragments whose location could not be definitively determined by standard radiographic techniques. Although arthroscopic examination of the affected joints may have allowed location of the fragments it is an invasive procedure and takes longer to per- form than an ultrasound examination. Further, ul- trasonography replaced the use of intraoperative ra-

diographs as a method for location of the bone fragments and foreign objects. This exact location provided a guide for necessary surgical manipula- tions. In horses 1 to 3 , this resulted in minimal size of the arthrotomy incisions and in horse 6 a very small wire was located and removed with minimal trauma to adjacent vascular and neural structures.

The benefits of intraoperative ultrasonography included a decrease in operative time, a decrease in tissue dissection and a reduction in radiation ex- posure to the patient and operating room personnel. In equine surgery, the potential decrease in operating time may be the single greatest advantage and, therefore, the greatest indication for the use of op- erative ultrasonography. Although objective mea- surements were not obtained, it was believed that the use of ultrasonography shortened the surgical time in all cases. This reduction in surgical time more than offset the time required to perform the ultra- sound examination.

Use of intraoperative ultrasonography does have some limitation^.'.'^ Planned use of ultrasonography before starting the surgical procedure is important if reductions in operative time are to be realized." Secondly, knowledge of regional anatomy and ex- perience in interpretation of ultrasound images is important for accurate interpretation. Ideally the surgeon and ultrasonographer should be the same person. When this is not the case, the surgeon and ultrasonographer must work together to achieve a good outcome.' I

Current reported use of intraoperative ultrasound in the horse has been limited to examination of su- perficial structure^.^,^ This is in contrast to human surgery where ultrasound is most commonly used to examine deep organs that have been surgically e~p0sed.I .~ Increased awareness of the uses of intra- operative ultrasonography may expand applications in equine surgery.

ACKNOWLEDGMENT

The authors wish to acknowledge Drs. Emily Butler and Grant Myhre of Rochester Equine Clinic, Rochester, NH for the inclusion of horse 6.

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