History
A 15-year-old Quarter Horse gelding was referred with a 5-day history of lameness. Clinical examination revealed that the horse had a grade 3 of 5 lameness of the right forelimb. Signs of pain were evident when pressure was applied with hoof testers to the medial aspect of the frog. There was palpable effusion of the dorsal pouch of the distal interphalangeal joint (coffin joint), and the distal aspect of the forelimb to the level of the metacarpophalangeal joint (fetlock joint) was also mildly swollen and edematous.
Synovial fluid acquired by arthrocentesis of the distal interphalangeal joint was slightly cloudy and had a low viscosity. Cytologic examination of synovial fluid revealed a nucleated cell count of 4.4 × 109 cells/L (81.5% nondegenerative neutrophils and 18.5% small and large mononuclear cells) and a total protein concentration of 44 g/L. Intra-articular analgesic administration did not result in an improvement in lameness. Radiographic views of the right forefoot were obtained (Figure 1).
Lateromedial (A) and 60° dorsoproximal-palmarodistal oblique (B) radiographic views of the distal portion of the right forefoot of a 15-year-old Quarter Horse with a 5-day history of lameness.
Citation: Journal of the American Veterinary Medical Association 235, 4; 10.2460/javma.235.4.377
Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →
Radiographic Findings and Interpretation
On the lateromedial radiographic view, a rounded bony opacity indicative of an osteochondral fragment is seen in the region of the extensor process of the distal phalanx (Figure 2). A similar view of the left forefoot did not reveal similar findings. The joint space of the distal interphalangeal joint is wide. On the 60° dorsoproximal-palmarodistal oblique radiographic view, a focal radiolucent region suggestive of gas is evident superimposed over the medial aspect of the distal interphalangeal joint.
Same radiographic views as in Figure 1. On the lateromedial radiographic view, notice the rounded, smooth, bony opacity indicative of an osteochondral fragment in the region of the extensor process of the distal phalanx (dotted white arrow) and the wide distal interphalangeal joint space (black arrows). On the 60° dorsoproximal-palmarodistal oblique radiographic view, a well-circumscribed radiolucent region (arrows) is evident that is suggestive of a gas pocket.
Citation: Journal of the American Veterinary Medical Association 235, 4; 10.2460/javma.235.4.377
On the basis of the lack of improvement in lameness in response to intra-articular analgesic administration, the fragment of the extensor process was deemed to be an old lesion and not the current cause of pain. Joint sepsis was considered a possibility because of the degree of lameness, palpable distal interphalangeal joint effusion, and findings on cytologic examination of synovial fluid.
A uniaxial medial palmar digital nerve block was performed immediately proximal to the collateral cartilage of the coffin bone. This resulted in a substantial improvement in lameness. On the basis of this finding, a diagnosis of a subsolar abscess with secondary distal interphalangeal joint synovitis was made.
Comments
The sole was pared away from the medial bars of the foot. No abscess was found, and the foot was poulticed with a combination of Epsom salts and povidone-iodine solution. Phenylbutazone (4.4 mg/kg [2 mg/lb], IV, q 24 h) and procaine penicillin (22,000 U/kg, [10,000 U/lb], IM, q 12 h) were also administered. Two days later, the abscess ruptured at the coronary band on the medial aspect of the foot; lameness improved dramatically. All medications were stopped on day 5 of hospitalization. Bacterial culture of the synovial fluid obtained by arthrocentesis prior to antimicrobial treatment did not result in aerobic or anaerobic bacterial growth.
Hoof abscesses have a myriad of clinical manifestations.1 Most hoof abscesses are the result of a stone bruise or solar penetration from a rock or other foreign body. Most horses with a hoof abscess have a sudden onset of lameness, in which some horses are almost non–weight-bearing.1 There can also be a variable amount of swelling and edema in the limb proximal to the hoof.
In the horse of this report, the smooth, well-defined, rounded fragment of the extensor process of the distal phalanx was incidental. Although the bony lesion may have resulted in joint effusion, it would not have resulted in the inflammatory nature of the synovial fluid; furthermore, the lameness did not improve after analgesia of the joint.
The well-circumscribed radiolucent area observed on the 60° dorsoproximal-palmarodistal oblique radiographic view of the forefoot was indicative of gas rather than a bone cyst of the distal phalanx because it extended beyond the margins of the distal phalanx. The response to uniaxial perineural analgesia supported a nonarticular cause of pain. The horse of this report represented a case in which lameness, distal interphalangeal joint effusion, periarticular limb edema, and visibly and cytologically abnormal synovial fluid were all attributable to a periarticular infection in the form of a hoof abscess.
Furst AE, Lischer CJ. Foot. In: Auer JA, Stick J, eds. Equine surgery. 3rd ed. St Louis: WB Saunders Co, 2006;1184–1217.
