15-Days-Old Female Thoroughbred

Signalment & History

  • This patient presents to your clinic for recumbence and frequent attempts to stand, difficulties to keep weight-bearing.
  • You order right tarsus radiographs.

 

Findings

  • The talus has irregular margins and is incompletely mineralized.
  • The distal epiphysis of the tibia is smoothly marginated but severely small.  A proximal epiphysis of the calcaneus and trochlear ridges of the talus are not present.
  • There is a round, focal, 6mm mineral opacity present in the presumed location of the distal row of tarsal bones.  There are two focal, faint mineral opacities also present in the presumed location of the distal row of tarsal bones.
  • The soft tissues surrounding the tarsus are mildly thickened.

Diagnosis

  • Incomplete ossification of the tarsal bones, with soft tissue edema or fibrosis. The findings are due to prematurity.

Incomplete ossification of the cuboidal bones

  • Incomplete ossification of the carpal and tarsal bones is a common sequela to premature, dysmature and twin foals and, possibly, foals with hypothyroidism.
  • In normal foals, all carpal and tarsal bones and their respective joint spaces are visible radiographically by approximately 300 days gestation.
  • Ossification of the carpal and tarsal bones begins in the last 2 months of gestation and continues through the first 4 weeks after birth, undergoes faster between the las 2 weeks of gestation and the first month of life.
  • In the carpus, the third, fourth and ulnar carpal bones are the last to ossify and are the most likely bones to become deformed.
  • In the tarsus, the third and central tarsal bones ossify last with the third tarsal bone being slightly less ossified than the central tarsal bone at birth.
  • The third, fourth and ulnar carpal bones are the last to ossify in the carpus and are the most likely bones to become deformed.
  • In the tarsus, the third and central tarsal bones ossify last with the third tarsal bone being slightly less ossified than the central tarsal bone at birth.
  • Factors that can delay or impede normal ossification include prematurity related to short gestational age (<320 days), dysmaturity secondary to placentitis, placental insufficiency, fetal infection, and/or severe prolonged metabolic disturbances Intrauterine growth retardation, such as decreased uteroplacental blood flow and increased uterine and fetal vascular resistance, have been described as a common factor that may inhibit normal growth of the fetus.
  • Hypothyroidism has also been described as a possible cause of incomplete ossification of cuboidal bones. Congenital goiter in foals has been associated with diets that have either excessive or deficient levels of iodine fed to the dam.
  • This deficit may generate musculoskeletal deformities, including flexural deformities of the forelimbs, rupture of the common digital extensor tendon, mandibular prognathia and immature carpal and tarsal bones
  • Better radiographic views for assessing the degree of ossification are dorsopalmar and lateromedial views of the carpus and the tarsus.
  • The presence of collapse of the cuboidal bones is recognized radiographically as prominent wedging or fragmentation of the dorsal aspect of the bones.
  • It is suggested make radiographs after birth in those foals considered in risk of incomplete ossification.
  • Ultrasonography has been used to evaluate the tarsal development and can be used to monitor the ossification process.
  • Incomplete ossification can subsequently predispose the foal to limb deformities or degenerative joint disease that may limit future athletic soundness
  • Due to the inherent susceptibility of the third, fourth and ulnar carpal bones and third and central tarsal bones to incomplete ossification, the majority of limb deformities observed are carpal valgus of the forelimbs and tarsal valgus and/or tarsal flexural deformities.

Skeletal Ossification Index (SOI for Neonatal Foals

From Adams and Poulos (1988)

  • Grade 1: Some cuboidal bones have no radiographic signs of ossification.
  • Grade 2: Some radiographic evidence of ossification is present in all cuboidal bones (excluding the first carpal and first tarsal bones).
  1. Proximal epiphysis of either the third metacarpal or metatarsal bones is present, and the physics is radiographically open.
  2. Lateral styloid process of the distill radius is absent or barely visible.
  3. Malleoli of the tibia absent or barely visible.
  • Grade 3: All cuboidal bones appear ossified but are small with rounded edges.
  1. Joint spaces appear wide.
  2. Lateral styloid process and malleoli are distinct.
  3. Proximal physic of either the third metacarpal bone or metatarsal bone is radiographically closed.
  • Grade 4: 
  1. All cuboidal bones are shaped like the corresponding bones in the adult.
  2. Joint spaces are of expected width.

References

  • Wong et al. Incomplete ossification in the dysmature foal. Equine Veterinary education (2003 15 (2) 72-81
  • Ruohiniemi et al. Monitoring the progression of tarsal ossification with ultrasonography and radiography in three immature foals. VRUS Vol. 36 No.5, 1995, pp 402-410.