Ultrasonographic evaluation of fetlock annular ligament constriction in the horse.

The diagnosis of restriction of free movement of the flexor tendons through the fetlock canal usually rests on the characteristic clinical appearance of this condition, or airtendography. In a series of seven normal Warmblood horses and 16 diseased horses of various breeds, the efficacy of ultrasonography in the diagnosis of this condition was determined. In normal limbs, the annular ligament is a very thin structure usually not visible on sonograms. In diseased limbs, ultrasonography outlined flexor tendon injury, distension and thickening of the digital sheath, peritendovaginal tissue proliferation and thickening of the annular ligament. Four different types of constriction syndrome were noticed. The first type (nine cases), was characterised by thickening of the annular ligament and distension of the digital sheath; the second type (three cases) was dominated by distension of the digital sheath; the third type (three cases) was characterised by superficial digital flexor tendon injury and thickening of the annular ligament and in the fourth type (one case), the constriction resulted from distension of the digital sheath and extensive peritendovaginal tissue proliferation.