- Definition
- Pathophysiology
- Systems Affected
- Genetics
- Incidence/Prevalence
- Geographic Distribution
- Signalment
- Signs
- Causes
- Risk Factors
BASICS
- FLD is a conformational limb abnormality that can be defined as a deviation of the limb in the sagittal plane, described as either persistent hyperflexion or persistent hyperextension of the joint region.
- The flexural deformity is named according to the joint involved. Joints commonly involved include distal interphalangeal, metacarpophalangeal/metatarsophalangeal, and carpus.
- Flexural limb deformities may be congenital or acquired
Present at birth. Thought to involve genetic predisposition, intrauterine malpositioning, and teratogens (i.e. ingestion of locoweed and hybrid sudangrass by the mare, maternal influenza infection, collagen cross-linking abnormality, and equine goiter).
- Nutrition—excessive intake and abrupt changes in quality and quantity of feed can lead to accelerated growth in foals. It is believed that, during the rapid growth phase, the longitudinal growth rate of the bone exceeds the ability of the tendons to lengthen passively, pulling the respective joint into flexion.
- Polyarthritis and trauma—both are painful conditions that result in the “flexion result reflex,” leading to an acquired hyperflexural deformity
Musculoskeletal—FLD is commonly found in the distal interphalangeal joint, metacarpophalangeal joint, metatarsophalangeal joint, and carpus.
Any. Glycogen branching enzyme deficiency may cause transient flexural deformities in Quarter Horses.
- Congenital deformity—present at birth.
- Acquired deformity—flexural deformities at the distal interphalangeal joint usually occur at 1–4 months of age; deformities at the metacarpophalangeal joint usually occur at 12–14 months of age
- Dystocia in the mare may occur secondary to flexural deformity in the foal.
- The foal may have difficulty rising or ambulating. There is sometimes a history of failure to stand and nurse
- Congenital
- Digital hyperextension—toes lift off the ground due to flaccidity of the flexor tendons and the foot may rock back on the heel. More severe cases result with the foal walking on the palmar/plantar surface of the phalanges, especially in the hind limbs, which can result in severe skin abrasions.
- Hyperflexural deformities—foals with hyperflexion usually have no voluntary extension of the affected limb. Often occurs bilaterally. If the deformity is located at the distal interphalangeal joint, the foals walk on their toes. If the metacarpophalangeal joint is involved, the foal will often have difficulty standing and will knuckle over at the fetlock. If the carpus is affected, the foals can be observed to buckle forward.
- Acquired
- Hyperflexural deformity of the distal interphalangeal joint—short toe and steep dorsal hoof wall angle. Over time, a “boxy” appearance is observed as the heel increases in length relative to the toe. Stage I—angle of the dorsal hoof wall is less than 90°. Stage II—angle of the dorsal hoof wall is >90°.
- Hyperflexural deformity of the metacarpophalangeal/metatarsophalangeal joint—characterized from a straight angle to “knuckled-over” appearance at the fetlock. More common in the front limbs but can occur in the hindlimbs.
- Hyperflexural deformity of the proximal interphalangeal joint. Dorsal subluxation with audible click heard as the foal walks
- Genetic predisposition.
- Uterine malpositioning.
- Teratogens.
- Multifactorial.
- Prematurity/dysmaturity (hyperextension/laxity)
DIAGNOSIS
TREATMENT
MEDICATIONS
FOLLOW-UP
MISCELLANEOUS