Incomplete Ossification of Tarsal and Carpal bones in Foals

Christina Copple, DVMRadiology Resident

NCSU CVM-VTHAccession #s: 109113

Skittles

• 12 hours old at 316 days gestation• Stood, suckled, passed meconium, but not seen to

urinate• Fluctuant swelling around umbilicus and prepuce,

irregular, well circumscribed mass that was increasing in size

• Dribbling from prepuce, small skin defect (necrotic area) at prepuce and petechia at sight of mass

• Mild laxity of both hind limbs, slight dome-shaped head• Blood work unremarkable

Skittles cont’d

• US of preputial area: patent urachus up to but not including the body wall, no abdominal fluid noted

• Swelling gradually decreased with evidence of skin sloughing in affected area

• Began urinating normally

• Carpal and tarsal radiographs

Left Carpus- Incomplete ossification Grade 3+ Accession #109113

OssificationCarpal and Tarsal bones

• Begins in last 2 months of gestation

• Usually rapid in last 2 weeks of gestation and continues for ~ 1 month after birth

• Ossification center is spherical, surrounded by cartilaginous precursors; ossification occurs radially until it reaches the cartilaginous extremity

• Degree of ossification at birth is varied, regardless of gestational age

• Carpal ossification precedes tarsal ossification

http://img.dailymail.co.uk/i/pix/2007/05_02/FoalsSolent_468x572.jpg

Dutton et al, JAVMA1998

Skeletal Ossification Index

• Adams and Poulos, Veterinary Radiology, 1988• 52 neonatal foals and fetuses, reviewed radiographs of

carpi and tarsi as well as postmortem findings• Evaluated shape and degree of ossification of cuboidal

bones• Index created consists of four grades• Applied index to 24 neonatal foals of various gestational

ages, radiographed within first 3 days of life– Two high risk groups of foals: <320 days gestation or “small for

gestational age”– Degree of ossification is thought to be incomplete in these foals– Recommend radiographic assessment of ossification

Grade 1• Some of the cuboidal bones

had no radiographic evidence of ossification

Grade 2• Some radiographic

evidence of ossification of all cuboidal bones– Did not include 1st

carpal or 1st tarsal bones

• Proximal epiphysis of 3rd MC or MT were present and physis open

• Lateral styloid process of distal radius and/or malleoli of tibia were absent or barely visible

Grade 3• All cuboidal

bones ossified but are small with rounded edges

• Joint spaces appear overly wide

• Lateral styloid process and malleoli are distinct

• Proximal physes of 3rd MC and MT are radiographically closed

Grade 4 - Normal• Most advanced

degree of ossification

• Met criteria of grade 3 but shape of bones were that of an adult and joint space width was normal

Incomplete Ossification-Causes and Associated Risks

• Congenital hypothyroidism?• Aseptic necrosis due to infarction?• Skeletal immaturity at birth-current thought

– Premature = gestation <320 days– Dysmature– Twins

• Can lead to deformation of bones (excess load on immature bones compresses cartilage canal vessels = ischemia, chondromalacia, dystrophic calcification and irregular-shaped centers of ossification)

• May develop degenerative joint disease and angular limb deformities-poor prognosis for athletic performance

Dutton et al, JAVMA1998

Incomplete Ossification of Tarsal Bones

• Retrospective, 22 foals between 1 day to 10 months of age

• Severity of radiographic lesions were associated with outcome

• Tarsal bones most often affected were central or 3rd tarsal bones

Dutton et al, JAVMA1998

Incomplete Ossification of Tarsal Bones

• Type I: incomplete ossification with <30% collapse of affected bones

• Type II: incomplete ossification with >30% collapse of and pinching or fragmentation of affected bones– Guarded prognosis for athletic soundness

• Continued collapse can be decreased with early recognition and treatment– Treatment aimed at maintaining true longitudinal axis

= ossification continues without further distortion of cartilaginous models

– Stall rest vs splint or tube cast

Dutton et al, JAVMA1998

References

• Dutton, David M., DVM, Jeffrey P. Watkins, DVM, MS, Michael A. Walker, DVM, and Clifford M. Honnas, DVM. Incomplete Ossification of the Tarsal Bones in Foals: 22 cases (1988-1996). JAVMA 1998 (213):11 1590-1594.

• Adams, Ragan, MA, DVM and Paul Poulos, DVM, PhD. VetRadUS 1988 (29):29 217-222.