Equis ISSN 2398-2977

Foot: subsolar abscess/infection

Contributor(s): Olin Balch, Simon Curtis, Vetstream Ltd, Graham Munroe

Introduction

  • Very common.
  • Focal accumulation of purulent exudates, usually between the germinal and keratinized epithelium of the hoof.
  • Usually due to defects in the sole or white line, or less commonly, a penetrating foreign body which leads to ingress of bacteria through the insensitive sole or frog of the foot; the pathology is in the deeper sensitive tissue where there is an abscess formed. Rarely, infection may extend to the deeper structures when pedal bone periosteum, the digital cushion, navicular bursa, palmar/plantar partition of the coffin joint and insertion of the deep digital flexor tendon (DDFT). When such deeper tissues are involved the condition can become potentially life-threatening. 
  • Signs: lameness of varying severity, but generally unilateral, acute and severe Musculoskeletal: gait evaluation, forelimb > hindlimb.
  • Diagnosis: foot examination Foot / shoe: examination, foot trimming may reveal point of abscess; in some cases may be difficult even with radiography Digit: radiography.
  • Treatment: local drainage, and control of infection, pain and inflammation.
  • Prognosis: dependent on extent of initial damage, adequate treatment and rest, but generally good.
Print off the Owner factsheets on Caring for your horse's feet and Subsolar abscess - pus in the foot to give to your clients.

Pathogenesis

Etiology

  • The cause is not always identifiable.
  • Most commonly, the bacteria appear to enter the hoof capsule through small defects in the horn, such as microfractures or separation of the white line, or through hoof cracks.
  • Less commonly a penetrating foreign body, most likely through the sole or frog, eg nails, screws, wire, stones, glass or even wood.
  • May be iatrogenic, associated with nail misplacement during shoeing - nail prick or nail bind.

Predisposing factors

General

  • Exercise in poor conditions such as wet muddy areas and hard rough ground can increase the incidence.
  • Poor foot shape, structure and balance are common predisposing causes, most particularly the long toe/low heel conformation and poor mediolateral foot balance Foot: trimming and balancing.
  • Chronic laminitic foot Foot: laminitis.

Pathophysiology

  • Infection into the foot → inflammation → migration of white cells and fluid from the dermal vessels to form an abscess which leads to increased pressure on sensitive hoof laminae → pain and lameness. This is exacerbated by the low compliance of the hoof capsule restricting any swelling and increasing the pressure within the sensitive laminae.
  • As an abscess develops it separates the germinal layer of the epithelium from the hoof capsule extending further under the sole, frog or proximally under the wall.
  • Abscessation may develop from previous bruise or hematoma Foot: sole bruising.
  • Pus develops and may discharge through the penetrating site, elsewhere through the sole or proximally around the coronet (gravel), typically opposite to the site of the infection.
  • Lameness diminishes with either natural or induced drainage.
  • If drainage occurs at the coronet (the junction of the hairline and the wall), short horizontal defects (cracks) may appear in the hoof wall and slowly move distally as the hoof grows out.
  • Forelimbs are more commonly affected than hindlimbs.
  • Chronic discharge may lead to sinus and fistula development.
  • Infection may extend deeper to any or all of the structures in the region, eg pedal bone, coffin joint, navicular bursa, DDFT.
  • Chronic abscessation may occur in chronic laminitis Foot: laminitis, immunocompromise, keratoma Foot: keratoma or septic osteitis Bone: osteitis - septic.

Timecourse

  • If infection becomes established the disease is likely to be protracted.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Cole S D et al (2019) Factors associated with prolonged treatment days, increased veterinary visits and complications in horses with subsolar abscesses. Vet Rec 184 (8), 251 PubMed.
  • Redding W R & O’Grady S E (2012) Septic diseases associated with the hoof complex: abscesses, punctures wounds, and infection of the lateral cartilage. Vet Clin North Am Equine Pract 28 (2), 423-440 PubMed.
  • Milner P I (2011) Diagnosis and management of solar penetrations. Equine Vet J 23 (3), 142-147 VetMedResource.
  • Stephenson R (2011) Presenting signs of foot abscessation - A practice based survey of 150 cases. UK Vet 16, 4-7 VetMedResource.
  • Carmalt J L (2009) What is your diagnosis? Subsolar abscess with secondary distal interphalangeal joint synovitis. JAVMA 235 (4), 377-378 PubMed.
  • Cullimore A (2009) Clinical aspects of the equine foot. Part 4: Sole penetrations. UK Vet 14 (5), 8-13 VetMedResource.
  • Leonard J M et al (1990) What is your diagnosis? Hoof abscesses and cellulitis extending along the palmar aspect of the pastern of the left forelimb. JAVMA 196 (1), 1791-1794 PubMed.
  • DeBowes R M et al (1989) Penetrating wounds, abscesses, gravel and bruising of the equine foot. Vet Clin North Am Equine Pract 5 (1), 179-194 PubMed.
  • Fessler J F (1989) Hoof injuries. Vet Clin North Am Equine Pract 5 (3), 643-664 PubMed.
  • Jamison J M et al (1983) What is your diagnosis? Sole abscess involving the lateral and plantar aspects of the foot. JAVMA 182 (6), 625-626 PubMed.


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