a.k.a. Ballerina Syndrome. One of the Angular Limb Deformity syndromes and a part of the Developmental Orthopaedic Disease complex, these flexural abnormalities may be present at birth (congenital) or acquired by young foals usually from 1 to 4 months of age and can involve either hyperflexion (up on toes / ballerina to knuckling over) or hyperextension (down on their bumpers) affecting the fetlock, pastern, or knee joints alone or in combination. Front or hind limbs can be affected, forelimb involvement being more common, and the hock joint rarely involved.
Congenital forms are believed to be due to mare factors including malpositioning of the foetus, influenza during pregnancy, thyroid problems, and lathyrism (poisoning by members of the pea family like Sweet Pea).
Acquired deformity is generally encountered in rapidly growing foals or in conjunction with other painful conditions affecting a limb or foot such as fracture or hoof abscess limiting normal exercise. Growth spurts triggered by excess energy consumption may cause the problem as the long bones grow faster than can be accommodated by the flexor tendons. Treatment depends on type and includes limb splinting, corrective shoeing, restricting, or encouraging exercise, and surgical intervention by check ligament desmotomy (sectioning a supporting ligament).