Page 88 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Musculoskeletal system: 1.3 The foot 63

VetBooks.ir and excessive granulation tissue on the surface of the antibiotic in physiological solutions are excellent for
maintaining an optimal environment on the surface
foot is uncommon.
The tetanus vaccination history of all horses with
wounds should be ascertained and if inadequate, teta- of the wound for healing and controlling surface
infection, but they may need to be replaced with dry-
nus antitoxin should be administered. The use of anti- to-dry dressings if the adjacent hoof capsule shows
microbial drugs depends on the nature of the wound. evidence of maceration from excessive moisture.
Wounds that only involve the superficial layers of the
integument (e.g. abscesses) are usually satisfactorily ABSCESSES
treated with topical antibiotics or antiseptics, and
systemic antibiotics are seldom warranted. Topical Definition/overview
antiseptics should be used at appropriate concentra- Foot abscesses are a focal accumulation of purulent
tions to inhibit bacterial growth without affecting exudate that most commonly occurs between the
fibroplasia and epithelialisation. Systemic antibiotics germinal and keratinised epithelium of the hoof.
are usually used in wounds that extend deep to the
dermis in conjunction with topical antimicrobials. Aetiology/pathophysiology
Systemic antibiotics should be continued until there The cause is not usually specifically identifiable,
is a healthy layer of granulation tissue across the but most cases of foot abscessation are presumed
surface of the wound; diffuse infection is unlikely to follow small defects in the hoof capsule, such
after this occurs. In wounds that involve a synovial as microfractures or separation of the white line,
structure, antibiotics are continued until 1–2 weeks which permit bacterial access to the underlying tis-
after the communication between the wound and the sues. Less frequently, they follow puncture wounds
synovial structure has closed and the clinical signs or hoof cracks. Some horses are prone to recurrent
have resolved. The choice of antibiotics is related to abscess formation because of concurrent disease (e.g.
spectrum of activity, ease of administration and cost. laminitis) or poor hoof structure (e.g. dropped or
Penicillin or trimethoprim–sulphonamide are com- thin soles) that predisposes to bruising. Abscesses
monly used for more superficial wounds, whereas within the foot are particularly painful because
combinations with a broader spectrum (e.g. penicillin the low compliance of the hoof capsule results in a
and gentamicin) are frequently used when more vital more rapid increase in pressure. The pressure will
structures are affected. Regional perfusion of the with time cause separation of the hoof capsule from
distal limb with antibiotics via a superficial vein has the germinal layer of the epithelium to extend fur-
been shown to achieve antibiotic concentrations in ther under the sole or frog or proximally under the
joint fluid that persist above the minimum inhibitory wall. Abscesses that extend proximally deep to the
concentration for various bacteria for over 24 hours, wall and cause separation at the coronary band are
although this is subject to variability depending on called a ‘gravel’. Abscesses may also extend through
the ability to maintain an effective tourniquet. the germinal layers of the integument and dermis to
Bandaging for foot injuries requires two or three affect deeper structures.
layers. The primary layer or surface dressing should
be adherent if debridement is required and non- Clinical presentation
adherent if epithelialisation and fibroplasia are to The clinical picture of a horse with a foot abscess
be encouraged. The secondary padding layer is fre- is that of a horse acutely and severely lame in one
quently omitted but is useful to protect and support limb, sometimes evident after exercise or turnout.
the distal limb for heel bulb lacerations and hoof Most horses with abscesses are found with a severe
wall avulsions. The tertiary layer holds the underly- lameness, usually 4–5/5, although the lameness
ing layers in place, but care should be taken to avoid may be seen to develop over 12–48 hours if they
excessive pressure and contact with adhesive around are observed closely. Distal limb swelling and/or
the coronary band. Both dry-to-dry and wet-to-dry cellulitis may be present in some cases. Swelling or
dressings are used. Wet-to-dry dressings containing a discharging sinus may occur at the coronary band.