Angular limb deformity:

Deviations that occur in the frontal plane (medial or lateral).  May be congenital or 
acquired.  Includes
1) Laxity of the periarticular supporting structures
2) Incomplete ossification of the carpal or tarsal bones
3) Assymetric growth of the metaphysis or epiphysis

Possibly involving valgus or varus deformity.  Most malformations are tarsal valgus 
deformities.

Laxity of the periarticular supporting structures:
Associated with tarsal valgus deformities due to the laxity of the periarticular supporting 
structures.  Excessive loading on the angled limbs causes pathologic compression of the 
tarsal bones and adjacent physes resulting in the progression of the deformities and 
possibly permanent damage.  PVC pipe splint bandages have been shown to stabilize the 
joint disorder.

Incomplete ossification of the tarsal bones

Problem associated with prematurity or dysmaturity, but may involve normal foals as 
well.  Ossification of the tarsal bones starts in the center and progresses toward the 
periphery of the future bones.  Ossification should have progressed nearly to the 
periphery at the time of birth and should be complete by one month of age.  However, in 
foals with incomplete ossification, the centers of tarsal bones are smaller and more 
spherical than normal.  Stresses of normal weight bearing usually results in angular limb 
deformity.  Deformities are best based via radiographic findings.  It is important to 
correct this early within the first few days of life because it may result in abnormal 
wedge-shaped configurations.

Assymetric growth of the metaphysis or epiphysis
Present at birth and develop within the first few weeks or months of life.  Trauma in the 
form of assymetric nonphysiologic compressive forces on the growth cartilages has been 
implicated as the major cause of assym. Growth.  Other causes include osteochondrosis, 
intrauterine malpositioning (was there any problems asssociated with birth (dystocia)?), 
physeal fractures, and physeal infections.  Radiographs will demonstrate asymmetric 
longitudinal growth of the metaphysis or epiphysis.  Within a physiologic range, 
compression accelerates chrondral growth.  When a compression becomes pathologic, 
condral growth is markedly decreased.

Congenital contracture deformity
Can affect fetlock.  Cause is not known.  Suggested etiologies include uterine 
malpositioning, teratogenic insults (influenza, locoweed), hypothyroidism, 
neuromuscular disorder, genetic factors, and nutritional imbalances in the pregnant mare.