Unilateral phalangeal dysgenesis and navicular bone agenesis in a foal.

This research journal article documents a rare case of a five-day-old foal suffering from a congenitally malformed hoof and the associated lameness. The disorders studied were unilateral navicular bone agenesis and distal phalangeal hypoplasia.

Case History

• The foal was admitted to the hospital due to acute lameness in its left forelimb. It was noticed when the foal was allowed to exercise in the pasture with its mare.
• Physical examinations had earlier shown no abnormalities. The foal’s serum gamma globulin concentrations indicated adequate immune response through passive transfer of immunoglobulins.

Clinical Examination

• The foal was found to show severe lameness during walk and had a noticeably smaller left forelimb.
• The deformities of the left forelimb included laxity of the deep digital flexor tendon and distal interphalangeal joint. Sensitivity was also detected over the toe of the left forefoot.
• Anæsthetisation noticeably improved the foal’s gait, reducing lameness.
• Radiography revealed the absence of the navicular bone and abnormality in the third phalanx. A fracture was also identified in the anterior part of the third phalanx.

Prognosis and Further Developments

• A follow-up on the foal’s progress showed an increase in lameness despite confinement and analgesic administrations. Furthermore, the size discrepancy between the forelimbs became more pronounced.
• Subsequent radiographs showed no improvements, and even revealed a progressive distal displacement of the fracture and overgrowth of the hoof. A gas-filled tract, namely a subsolar abscess, was noticed that extended from the sole.
• It was decided to euthanize the foal due to insufficient improvements.

Postmortem Examination

• The postmortem examination revealed the absence of the navicular bone and a fused deep digital flexor tendon to the third phalanx.
• The hoof was also found to be deformed, and the sole three times thicker than normal. Hemorrhage and bruising were evidently present.
• The abnormalities mainly focussed on the third phalanx, while the first and second phalanges appeared normal.

Discussion

• It is determined that the abnormalities were congenital in nature, although the exact cause is undetermined. Routine vaccinations and anthelmintics administered during the dam’s pregnancy are denied to have any contribution to such organ anomalies.
• The lameness in the foal is believed to have been triggered by the fracture upon physical exercise. The hoof deformation might have been present at birth but went unnoticed until lameness occurred.
• The study insisted on including congenital anomalies of the skeletal system as differential diagnoses in lame foals.
• Diagnosis of phalangeal hypoplasia and navicular bone agenesis needs to be supported by radiographic evaluation.