History
A 6-year-old Appaloosa mare that was used for general riding purposes was evaluated because of a firm swelling and intermittently draining tract over the medial aspect of the coronary band of the right hind foot. The horse had been purchased by the current owner as a yearling. The owner indicated there had been no signs of lameness in this hind limb until 2 months prior to evaluation. At that time, the horse was found to be lame in the right hind limb while coming in from pasture. The initial clinical signs described by the referring veterinarian included diffuse swelling of the proximal phalangeal (pastern) region and a painful response to palpation over the medial aspect of the coronary band. A large draining tract subsequently developed above the medial aspect of the coronary band within a few days of examination. The horse was treated with trimethoprim-sulfamethoxazole (22 mg/kg [10 mg/ lb], PO, q 12 h) and phenylbutazone (2.2 mg/kg [1.0 mg/lb], PO, q 12 h) for 14 days and was rested in a box stall with access to a small paddock. The lameness and drainage resolved only to recur on several occasions.
At the time of admission, the horse had a grade 1 of 5 lameness in the right hind limb. Circumferential swelling of the pastern area with focal enlargement and a tract draining purulent material above the medial aspect of the coronary band were present. This area was painful on palpation. An increased pain response was observed when pressure was applied with hoof testers over the medial quarter, bar, and body of the sole of the foot. The sole and frog were pared with a hoof knife, but no tracts were identified. No other abnormalities were detected on physical examination. Radiographic views of the right hind foot were obtained (Figure 1).
Lateromedial (A) and 65° dorsoproximal-plantarodistal oblique (B) radiographic views of the right hind foot (RH) of a 6-year-old Appaloosa horse with a history of intermittent swelling and a draining tract over the medial aspect of the coronary band of the foot with right hind limb lameness of 2 months' duration.
Citation: Journal of the American Veterinary Medical Association 236, 1; 10.2460/javma.236.1.37
Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →
Radiographic Findings and Interpretation
An oval, radiolucent lesion surrounded by an illdefined sclerotic margin in the medial aspect of the distal phalanx in close proximity to the soft tissue swelling and draining tract of the coronary band is evident (Figure 2). Communication between the fistula and the lucency was confirmed by introducing a metal teat cannula into the draining tract and injecting water-soluble iodinated positive contrast material. These findings are consistent with advanced septic osteitis of the foot with drainage to the medial aspect of the coronary band.
Same 65° dorsoproximal-plantarodistal oblique radiographic view as in Figure 1 (A). A 30° dorsoproximal-plantarodistal oblique radiographic view (B) of the RH was taken when the limb was not bearing weight; a metal teat cannula that was attached to a syringe containing contrast material was introduced through the fistula. Note (A) the oval-shaped, radiolucent lesion surrounded by ill-defined sclerosis in the medial aspect of the distal phalanx (black arrowheads) in close proximity to the soft tissue swelling of the medial aspect of the coronary band (white arrowheads). Furthermore, the distal interphalangeal joint space is absent in both views and the outline of the hypoplastic distal sesamoid bone is obscure. A screw (B) was placed as a marker to indicate the area of the sole where surgical drainage was provided.
Citation: Journal of the American Veterinary Medical Association 236, 1; 10.2460/javma.236.1.37
Additionally, absence of the distal interphalangeal joint space of the right hind limb is evident and the outline of a hypoplastic distal sesamoid bone is obscure. By comparison, radiographic images of the left hind foot reveal normal conformation (Figure 3). On the basis of the historical information and lack of reactive bony changes, a presumptive diagnosis of a unilateral congenital ankylosis of the distal interphalangeal joint with hypoplasia of the distal sesamoid bone was made. This was considered to be an incidental finding. It was speculated that the conformational anomaly may have contributed to the unusual progression of septic osteitis in the affected right hind foot as a result of altered mechanical properties within the hoof capsule.
Lateromedial radiographic views of the RH (same view as in Figure 1) and left hind foot (LH). Notice the absence of the distal interphalangeal joint space without associated reactive bony changes and the hypoplastic, abnormally shaped distal sesamoid bone incorporated within the plantar aspect of the fused distal and middle phalanx of the RH.
Citation: Journal of the American Veterinary Medical Association 236, 1; 10.2460/javma.236.1.37
Comments
Septic or severe traumatic arthritis that occurred prior to skeletal maturity cannot be ruled out as a possible pathogenesis for the observed distal interphalangeal joint ankylosis and distal sesamoid bone hypoplasia. The historical information provided and absence of reactive bony changes associated with the ankylosis are more supportive of a presumptive diagnosis of congenital malformation.
Congenital bony ankylosis of the distal interphalangeal joint in both hind limbs with concurrent dysplasia of the distal sesamoid bone in all 4 limbs has been reported for a 2-year-old Arabian horse.1 As with the horse reported here, the condition remained clinically silent until the horse sustained a traumatic injury of the proximal phalanx of its left hind limb. The authors suggested that the abnormal conformation may have served as a predisposing factor to the traumatic injury by causing increased stress on the proximal phalanx.1
Speculation about a possible hereditary etiology for congenital ankylosis of the distal interphalangeal joint has been made in case series of clinically affected Simmental and Fleckvieh cattle, in which this condition has been more commonly recognized than in equidae.2,3 In the pedigrees available for the affected cattle, however, no common lineage was detected that would support this theory.
The sole and bar overlying the subsolar abscess were resected to permit curettage of the cavity and debridement of the draining tract. A Penrose drain was placed through the draining tract from the opening in the coronary band and exited through the sole. The drain was removed after 3 days, and the tract was left to heal by second intention. The foot was maintained in a clean, waterproof bandage until the defect in the sole had filled in with healthy tissue. The horse made a full recovery.
- 1.↑
Rosenstein DS, Nickels FA, Moore EA, et al. Congenital bony ankylosis of the distal interphalangeal joint and distal sesamoid bone in a horse. Vet Rec 2000;146:736–737.
- 2.
Martig J, Riser WH, Germann F. Deforming ankylosis of the coffin joint in calves. Vet Rec 1972;91:307–310.
- 3.
Nuss K, Roth M, Schaeffer EH. Deformierende idiopathische Ankylose der Klauengelenke beim Jungrind. Tierarztl Prax 1994;22:312–318.
