Hoof disorders can cause lameness, a reduction in a horse’s durability, as well as economic losses for its owners (1,4,6). In a study in the Netherlands, in 85% of the horses, at least one hoof problem was found during regular foot trimming, with hoof wall cracks representing 54.7% (quarter cracks 2.7%) (2). Various causes for quarter cracks such as coronet injuries, inappropriate farrier management, hoof wall quality (due to genetics, nutrition, or environment), white line disease, hoof capsule distortion have been reported. Quarter cracks would lead to the hoof capsule structural integrity loss and may result in lameness. The healing process is primarily replacement by new growth originating from the coronet which may take 4 to 12 months depending on the region of the crack. The management of the underlying causes and appropriate rest are essential to reducing the likelihood of recurrence of cracks (11).

In Korea, there have been no previous prevalence studies of hoof disorders, however, case reports related to white line disease (12), quarter cracks (9,13) in 3 or 4-year-old Thoroughbred racehorses and navicular syndrome (5) in an 18-year-old Warmblood gelding have been reported.

In this report we report on a quarter crack caused by the dam accidentally stepping on the left hind foot of a 5 day-old Warmblood foal, which lacked adequate hoof wall thickness for the repair with stainless steel wire and hoof size for a reinforcing fabric to be applied. Polymethyl methacrylate (PMMA) composites treated the quarter crack successfully with a reshaped plastic gluing shoe.

A 5 day-old, 60 kg, male Warmblood foal who was born on 1st June, 2021 at the Cheju Halla University farm was presented to the authors (licensed vets) of Cheju Halla University for the evaluation of a left hind medial quarter crack. According to the witness who was working at Cheju Halla University farm, the crack had happened due to dam accidentally stepping on it in their box, leading to sudden lameness and bleeding from an avulsion wound above the newly formed crack. The hoof crack showed that the vertical crack originated at the coronary band which opened and extended obliquely distally almost to the sole. There was strong digital arterial pressure, heat and swelling up to metacarpophalangeal joint area. The medial side crack inclusive of blood stained coronary band displacement and associated with a lower pastern avulsion wound (Fig. 1A) and bruised coronary band area at the lateral side of left hind hoof (Fig. 1B), indicated abnormal strain on the foot at the time of accident.

Figure 1. Blood stained medial side of left hind quarter crack associated with lower pastern avulsion wound (A) and bruised lateral side of the left hind hoof (B). (C, D) Applied composites over the cracked area with a reshaped gluing shoe to protect the skin of the lower pastern, and to reduce the loading pressure on the medial side, and to spread the pressure to other parts of the hoof when bearing the weight. (E) Functionally recovered hoof 4 months after the crack accident. (F) Follow-up 8 months after the accident revealing successful outcomes without hoof shape distortion and unbalanced hoof/ limb growth.

The cracks can only be healed by new and healthy growth from the coronary band, and stabilization of the edges of the cracked wall was required during the healing period. Different from adult horses, the foot of the 5 day-old foal lacked adequate hoof wall thickness for the repair with stainless steel wire insertion, and therefore we decided to stabilize the edges of the cracked wall only by the PMMA composites (Equilox^®, Equilox International, Pine Island, Minn.) without wiring.

The surface of the hoof crack was pared away. The cracked area was thoroughly cleaned out and disinfected with a topical disinfect agent (2% tincture of Iodine, Betadine^®, Mundiphama Co. Ltd.; Seoul, Korea) before application of the composites. Generally, the composites are applied over the composites smeared reinforcing fabric bridged across the crack area, however, the left area of the hoof in this foal was too small for the composites to be applied if a reinforcing fabric was bridged. The decision was taken not to bridge a reinforcing fabric as it could be a contributory factor for unstable bonding, and to apply only the composites to the cracked edges of the hoof. The composites were applied according to the manufacturer’s instruction. Disinfection and bandage were applied once daily for 2 weeks for the prevention of infection and exuberant granulation of the avulsion wound. The foal was given an injection of gentamicin (5 mg/kg, IM, Gentamicin inj., Samu Median Co., Ltd.; Seoul, Korea) and phenylbutazone (10 mg/kg, IV, Arthridine, Virbac; Seoul, Korea) daily for 5 days. Intravenous infusion of phenylbutazone was performed slowly in conjunction with close monitoring for signs of toxicity and the response to therapy. The foal improved gait at 3 days after the repair.

A commercial gluing shoe (Dalric Lateral/Medial EXT1: Fits foals 1 to 6 weeks, Max foot width 3") with medial side removed and slightly extended caudally to cover the skin of the enlarged lower pastern (Fig. 1C) was applied with the PMMA composites to prevent the avulsed lower pastern from contacting the ground, and to reduce the loading pressure on the medial side from contacting the bearing surface of the shoe (floating) and, therefore, to spread pressure to other parts of the hoof when bearing the weight (Fig. 1D). Considering the fast growth rate in foals of this age, a reshaped gluing shoe was removed so as not to unbalance the growth of the limb after 3 weeks of fitting. After a week of re-evaluating the limb growth and healthy new hoof growth, new composites were reapplied over the cracked edges of the hoof with a reshaped gluing shoe. A month after the hoof crack accident, lameness had diminished. The movement of this foal was restricted in the stall with a stall size paddock with its dam for the inflammation to be resolved and the crack to be replaced by new wall. After a month when the avulsion wound was recovered, this foal was hand-walked for 10 minutes daily. This was to prevent habitual disproportionate loading as it would change the hoof shape over time, which may result in the hoof wall to be predisposed to injuries, such as repetitive quarter cracks. The quarter crack in this foal presented a successful functional recovery by the application of the composites three times with a reshaped gluing shoe with approximately a month interval over the 4 months and needed no further treatment (Fig. 1E). When followed up 8 months after the accident, it revealed successful outcomes without hoof shape distortion and unbalanced hoof/limb growth (Fig. 1F).

Hoof cracks are classified by their location in the hoof, such as a toe, quarter, or heel crack (7). Most hoof cracks are considered multifactorial and of management origin (3) while some could have happened by an accident such as stepping on a nail, etc. Limb conformation directly affects hoof loading, which affects the mechanical behavior of the hoof wall, predisposing it to a hoof wall crack. In general, quarter cracks occur more often in the fore feet as they bear more weight than the hind feet (11).

However, the present case was the rare accidental quarter crack case caused by the dam stepping on the medial side of left hind foot when this foal left laterally recumbent. There was an imbalance between the load applied by the dam accidentally stepping on left hind foot, and the capacity of the hoof wall of a 5 day-old foal to withstand that load. As the hoof wall stress/strain was excessive, a full-thickness hoof wall crack resulted.

The treatment of quarter cracks involves the identification, correction and management of balance, hoof wall stabilization, and follow-up management (11). The use of the composites (with a fabric bridge) alone may not be enough for sufficient stability, and an implant such as wire is usually combined with the composites in the repair to increase the strength and durability of the quarter crack repair (8). In this case, the cracked foot of 5 day-old foal lacked adequate hoof wall thickness for stainless steel wire insertion, and the authors were left with no option but to stabilize the edges of cracked wall only by the PMMA without wiring.

It was concerning that the location of the avulsion wound was at the lower pastern adjacent to the opened coronet where there could be high risk of contamination and/or infection. If either or both happen(s), it would most probably affect the cracked coronet and an uneventful recovery would be jeopardized as the healing process is primarily replacement by growth which originates from the coronet.

The foal’s active lifestyle was also of concern, and an applied plastic shoe was utilized to protect possible inadvertent impact over the cracked side of the hoof. Movement was restricted to the stall with a stall size paddock with its dam until the foal showed soundness of the affected hoof which took 4 months. The authors were of the opinion that a shoe, with the medial side removed and slightly extended caudally to cover the skin of the enlarged lower pastern, may not only reduce the pressure on crack but also spread the pressure to other parts of the hoof when bearing weight. It is well accepted that growth of the hoof wall is negatively related to pressure on the coronary band. Hoof wall growth tends to be slower where more weight is borne while faster where less weight is borne (10). The authors were also of the opinion that the applied shoe may have contributed to protect the skin of the lower pastern from contacting the ground, and at the least did not retard the hoof wall growth over the cracked area.

Artificial composites such as the PMMA, etc. have been utilized to treat a compromised hoof wall with or without application of gluing shoes, and their adhesiveness lasts up to 2 months. However, in the present case, care was taken as it was used on the immature foot of a foal, and from the perspective of achieving the right balance between fast growing hoof /limb and stabilization of the cracked hoof wall, based on the understanding that uneven weight bearing may produce uneven growth of the hoof and deviation in the limb. Feet were trimmed and the composites applied monthly with a gluing shoe to achieve a parallel hoof pastern axis of the cracked foot, bisecting the hoof sole, and the heels of the hoof capsule were extended to the base of the frog appropriately. The authors have not been able to find a successfully treated quarter crack case report in Korea where veterinarians were left with no option but to stabilize the edges of cracked wall only by the PMMA composites with a reshaped plastic gluing shoe in treating accidental quarter crack in a foal. The authors expect that the equine clinicians will find this report a reference when establishing a treatment strategy for a foal with a quarter crack in the future.

In the present case report, we approached this quarter crack in a foal from the perspective of stabilization with care for balanced growth. The combination of the stabilization of the foot with the composites and a reshaped gluing shoe to reduce the loading pressure on this area of the hoof was considered effective, and this approach could be an alternative when treatment options are limited. However, successful treatment should also involve controlled movement in the stall and committed follow-up to prevent infection, reoccurrence and unbalanced growth.

The authors would like to thank Yang-Nam Kim, farrier for his assistance.

The authors have no conflicting interests.