A 7-year-old Quarter Horse gelding, which weighed 524 kg (1,153 lb) and was used for general-purpose riding, was evaluated at the University of Georgia Veterinary Teaching Hospital because of a 4-day history of sudden onset of severe left forelimb lameness (grade 4/51). The lameness was first noticed when the horse was brought in from pasture. Prior to referral, the left forefoot shoe had been removed and the foot had been pared; after a poultice had been applied, there was no evidence of discharge or improvement in lameness. However, treatment with phenylbutazonea (4.4 mg/kg [2 mg/lb], IV, q 12 h) resulted in reduction in lameness severity. The horse had no known previous history of lameness.
Signs of a mild diffuse pain were elicited in response to hoof testers, with a focal area of intense pain response on the lateral quarter of the affected forefoot. Administration of an abaxial sesamoid nerve block with 2% mepivacaine hydrochlorideb markedly improved the lameness (estimated reduction in severity, 80%). Further paring of the lateral aspect of the sole was performed; no purulent material was found, but severe profuse hemorrhage developed as the sensitive tissues were approached. A well-padded foot bandage was applied for hemostasis.
Once hemostasis was achieved, standard radiographic views of the foot were obtained. These included the following: lateromedial, weight-bearing dorsopalmar, 45° dorsoproximal-palmarodistal oblique, 45° dorsoproximomedial-palmarodistolateral oblique, and 45° dorsoproximolateral-palmarodistomedial oblique.2 Subsequently, the foot was placed in a water bath to displace gas artifact, and a dorsoproximal-palmarodistal oblique radiographic view was obtained. Assessment of the images revealed a radiolucent line that extended transversely across the distal phalanx approximately halfway between the extensor process of the distal phalanx and the dorsal solar border (Figure 1). To better define the radiographic abnormality, additional dorsoproximal-palmarodistal oblique views were obtained at multiple angles of obliquity ranging from 40° to 70°. The radiolucent line appeared to extend from the medial and lateral solar margins of the distal phalanx. The radiographic interpretation was a nondisplaced transverse fracture of the distal phalanx.
A rim cast was placed on the left forefoot.3 After placing orthopedic feltc across the heel bulbs, one 3-inch roll of fiberglass cast materiald was placed around the hoof of the left forelimb circumferentially. A cuff was formed over the heel bulbs, and the cast material was wrapped around the distal aspect of the foot so that approximately 1.5 inches of material covered the solar surface and 1.5 inches of material covered the distal hoof wall, thereby molding the material to the shape of the foot. Each sequential wrap was placed directly on top of the first. The hoof of the right forelimb was supported by packing the sole with impression material.e Treatment with phenylbutazonea (3.3 to 4.4 mg/kg [1.5 to 2 mg/lb], PO, q 12 h) was initiated. Over the following 24-hour period, improvement was marginal with persistence of grade 4/5 lameness. To create an approximately 12° heel elevation, wedge padsf were subsequently attached to the rim cast by use of standard 2-inch drywall screws drilled proximally to distally through the hoof wall, rim cast, and wedge pads. There was immediate improvement in the lameness with elimination of the lameness during walking. The horse was discharged from the hospital the following day; it was maintained in the elevated rim cast with strict stall rest and received a gradually tapering dosage of phenylbutazonea (2.2 to 1.1 mg/kg [1 to 0.5 mg/lb], PO, q 12 to 24 h) over a period of 3 weeks after injury, at which time administration of the drug was discontinued.
The horse appeared to remain comfortable, and on day 28, the rim cast was removed. There were no complications associated with the cast except for development of some mild cast sores over the heel bulbs (Figure 2). Follow-up radiographic views were obtained, which revealed a more radiographically apparent fracture line with no displacement (Figure 3). The foot was shod in a manufactured elevated heel shoe with 5 toe and quarter clips. The palmar half of an egg-bar shoe was welded to the palmar half of a full eggbar shoe to create a sagittally supported heel wedge of approximately 10° elevation. The horse was reevaluated at 14-day intervals, and progressive improvement in the lameness was evident. At 2 months, the cast sores had resolved and the horse had grade 2/5 lameness1 of the left forelimb. The horse was allowed controlled hand walking for 2 weeks, at which time it was allowed access to a small paddock. At 3 months after injury, the horse was no longer lame; the elevated heel shoe was removed, and the foot was shod in a flat steel bar shoe with a 3° wedge pad. At 4 months after injury, repeated radiographic examination did not reveal the presence of a fracture line. The horse was allowed a slow reintroduction to light work with increasing durations of walking and trotting. At 6 months, there was no detectable lameness under regular work at the horse's previous level of performance, including cantering and jumping fences up to 3 feet in height.
The horse was readmitted to the hospital 6 months after the injury because of severe colic that was unresponsive to analgesia. Financial limitations prohibited surgical intervention, and the horse was euthanized via IV injection of an overdose of pentobarbital sodium solution.g The forelimbs were removed immediately and frozen at −20°C. The limbs were subsequently defrosted and underwent MR imaging (by use of a 3.0-T magneth) in transverse, sagittal, and frontal (dorsal) planes in PD, T2-weighted, and STIR sequences. In PD, T2-weighted, and STIR sagittal images, a thin, moderate- to high-intensity signal through the solar surface of the distal phalanx at the distal aspect of the insertion of the DDFT of the left forefoot was visible. This was surrounded by a narrow area of low signal intensity on PD and T2-weighted images (Figure 4). Additionally, there was a region of moderately increased signal intensity approximately halfway between the extensor process and solar aspect of the dorsal surface of the distal phalanx. Signal changes were difficult to interpret through the body of the distal phalanx on sagittal images. There was a reproducible high-intensity signal on PD, T2, and STIR frontal sequences through the solar surface of the distal phalanx of the left forelimb.
After MR imaging, the cadaveric limbs were dissected and photographed. Gross dissection revealed transverse linear disruption (most evident in the sagittal plane) of the normal appearance of the distal phalanx of the left forelimb (Figure 5). Histologic examination of this area after acid decalcification and staining with H&E stain revealed trabeculae that were broader and more irregular than those more distant from the fracture site. These trabeculae were composed of a large amount of central woven bone surrounded by a smaller layer of lamellar bone; the trabeculae further from the fracture site were composed of lamellar bone exclusively. The associated cortical bone was also composed of woven bone and lamellar bone. These findings were consistent with a healing fracture.
Deep digital flexor tendon
Distal sesamoidean impar ligament
Short tau inversion recovery
Phenylbutazone, Butler Schein Animal Health, Dublin, Ohio.
Mepivacaine hydrochloride, Pfizer Inc, New York, NY.
Orthopedic felt, 1/4 × 36 × 21 inches, Hartmann-Conco Inc, Rock Hill, SC.
Fiberglass casting tape, BSN Medical Inc, Rutherford College, NC.
SciCan Select Polysil, SciCan Inc, Canonsburg, Pa.
Nanric Ultimate Pads, Nanric, Lawrenceburg, Ky.
Pentobarbital sodium solution, Virbac AH, Fort Worth, Tex.
16-channel fixed site SignaHDx, GE Health Care, Chalfont St Giles, Buckinghamshire, England.
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