Introduction

• Cause: poorly understood condition; ? excessive over-extension strain on the accessory ligament (ALDDFT) during exercise, plus evidence of age-related degeneration; more common in show jumpers and hunters, especially older athletic horses and ponies; less frequently reported in racehorses and eventers.
• Signs:
  • Acute cases: local heat, pain, swelling in the palmar proximal third of the metacarpus Musculoskeletal: physical examination - adult  ; forelimb lameness Musculoskeletal: gait evaluation.
  • Chronic cases: less swelling, possible adhesion formation and subsequent flexural deformities.
• Diagnosis: palpation, ultrasonography Ultrasonography: musculoskeletal.
• Treatment: rest for up to 6-12 months, gradual re-introduction of exercise, monitor with ultrasonography, anti-inflammatories Therapeutics: anti-inflammatory drugs (phenylbutazone Phenylbutazone, flunixin meglumine Flunixin meglumine, ketaprofen/vedaprofen Ketoprofen).
• Prognosis: guarded, especially in chronic cases or where adhesions and flexural deformities are present. Recurrence is possible.

Pathogenesis

Etiology

• Unclear at present.
• The ALDDFT is loaded during the late stance phase of the stride, during extension of the digital joints, or when the animal lands over a fence. Thus the ALDDFT prevents overstretching of the DDFT and as the mechanical properties of the ALDDFT are inferior to that of the DDFT, the former is more likely to breakdown earlier then the latter.

Pathogenesis

• Excessive mechanical forces acting on the ALDDFT may cause acute damage to the ligament.
• More commonly fibrillar failure is caused by deterioration in the material properties of ligament, ie age-related degenerative changes in the fibers which cause them to fail at lower mechanical loads. It is also possible that repetitive microtrauma to these compromised ligaments may also lead to clinical desmitis.

Predisposing factors

General

• Previous or concurrent SDFT injury may increase the stress on the ALDDFT.

Specific

• Degenerative changes in the ALDDFT related to increasing age leads to decreasing amount of fibrillar collagen and number of large collagen fibers, which decreases the mechanical properties of the ligament and predisposes to injury.

Diagnosis

Treatment

Outcomes