INNOVATIVE IMAGING TECHNIQUES TO ENHANCE THE QUALITY OF YOUR PRACTICE


an assistant. In this position, the final surgical scrub is applied, and the area copiously doused in alcohol as an ultrasound coupling agent. A 7.5 to 10 Mhz linear or curvilinear probe is


placed inside a sterile sleeve with sterile lube be- tween the transducer and the glove. The probe is placed over the medial condyle in


both parasagittal and transverse planes to deter- mine the best needle trajectory. A 3.5 inch 18Gspinal needle is placed through the


skin adjacent to the transducer and advanced, in the ultrasound beam, towards the SBC. It is prefera- ble to perform this freehand, rather than with a biopsy guide. The needle will appear as a hyper- echoic line, which may cast an acoustic shadow (Fig. 5). The needle should be advanced into the far wall of the cyst, which may not be visible on ultrasound if the cyst is wider than the cloacal opening. The needle should contact bone and be fairly


Fig. 4. Ultrasound images of a MFC SBC obtained in parasag- ittal (A) and transverse (B) orientations in the flexed stifle. The normal smooth convex hyperechoic subchondral bone is disrupted by the SBC defect (arrows). (A: distal is to the left. B: medial is to the left).


firmly placed prior to removal of the stylette and injection of 10 to 15 mg of sterile triamcinolone acetonide. It has been recommended that injection in multiple sites within the cyst lining may be ben- eficial,7 and this can be attempted with ultrasound depending on patient compliance. The total dose of triamcinolone should not exceed 18 mg. In less cooperative horses, the technique can be performed under general anesthesia. Following premedication with xylazine (0.8mg/kg bwt i.v.) and butorphanol (0.04 mg/kg bwt i.v.), anesthesia is in- duced with diazepam (0.05 mg/kg bwt i.v.) and ket- amine (2.2 mg/kg bwt i.v.). The horse is then placed in dorsal recumbency, a sterile rectal sleeve placed over the foot on the affected limb, and the limb flexed to allow evaluation of the medial con- dyle. The surgical technique is similar to that de- scribed in the standing patient, with the stifle held in a 90° flexed position by the assistant (Fig. 6). An adhesive bandage strip should be placed to pre- vent contamination during recovery from anesthe- sia. This procedure can be performed under short acting intravenous general anesthesia of 20-minutes duration. Following the procedure, the patient should be


Patient Preparation


Following a thorough ultrasonographic examination of the stifle, the area from the base of the patella to the tibial crest is surgically prepared with the horse fully weight-bearing on all 4 limbs. The patient should be resedated if necessary to ensure complete compliance. With the horse weight-bearing, a subcutaneous


line block using mepivicaine should be placed at the level of the base of the proximal patella. This should be sufficiently proximal to avoid gas artifact appearing in the ultrasound image. The limb is then lifted and the foot placed on the hoof jack and stabilized throughout the procedure by


stall rested for several days, provided with systemic anti-inflammatory medications, and observed for any negative sequalae to joint injection.


3. Results


The authors have successfully performed this tech- nique in over 45 horses (2011–2013). For the pur- poses of this manuscript, however, case selection was limited to juvenile Thoroughbred horses in race training presenting with sudden-onset unilateral hindlimb lameness within the first 6 months of commencement of training. The source of lame- ness being localized to the medial femorotibial joint by a positive response to intra-articular anesthesia of the medial femorotibial joint with radiologic confirmation of a MFC SBC with no additional ul- trasonographic abnormalities. Twelve cases met


AAEP PROCEEDINGS  Vol. 60  2014 351


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