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Perosis, Slipped Hock, Luxation Of The Achilles (gastrocnemius) Tendon
Slipped tendon, also known as perosis, occurs when the duck's Achilles (gastrocnemius) tendon pops off the side of the bone, resulting in pain and reluctance to put weight on the leg. Affected ducks may be seen having a difficult time walking, and will have a limp to their walk--or they may continuously land with one foot on top of the other. There is often a variable amount of swelling around the hock joint. If the duck's tendon is completely ruptured, they may even walk "flat-footed" or "dropped", with their toes in that leg curled downward in a crab claw stance, like they are trying to grip the floor or perch on a roosting bar.
If identified early enough when ducks are still growing, and action is swiftly taken, sometimes the condition can be reversed, or at least improved through providing support and stabilization of the hock through splinting. It may easily be confused with splay leg, however with splay leg, the whole leg deviates rather than just at the hock. Rickets may also be mistaken for slipped tendon in ducklings, however with rickets, it is caused by the long bone deformity, not tendon displacement.
Hong, Cai, and Feng Zeguang Experimental Pathology of Manganese (Mn) deficiency and effects of higher phosphorus upon manganese deficiency in broiler ducks ACTA Veterinaria et Zootechnica sinica (1997)