Avascular necrosis caused by pressure in heavy birds that are down because of lameness or leg deformity is seen occasionally and occurs most frequently in the breast muscle. On gross examination, the tissue is firm and pale. Histologic examination reveals swelling, hyalinization, and necrosis of fibers with edema, heterophils, and macrophages at the periphery.

Rupture of the gastrocnemius tendon is common in meat-type chickens, particularly roasters and breeders, and rare in turkeys. The rupture is due to application of excess weight to tendons that have been previously damaged (most frequently by reoviral or staphylococcal tendinitis) or can be spontaneous. The intra- and peritendinous fibroplasias that occur following infectious tendinitis make the tendon larger but weaker due to replacement of normal strong, dense tendon connective tissue with weak, dense, irregular tissue. Synechial connections between the tendon and its sheath may also be produced, limiting the tendon's range of motion. Application of normal or excess weight to these previously damaged tendons results in partial or complete tearing or rupture. Rupture of the tendon of one leg puts stress on the other tendon, and bilateral rupture is frequent. Affected birds are lame or “down on their hocks” (creepers). Hemorrhage from the injury is visible as red, blue, or green discoloration in the tissue above the hock on the back of the leg and results in condemnation of the affected part at processing (red-leg, green-leg). The ruptured tendon can be palpated as a hard mass on the back of the leg above the hock.

Last full review/revision March 2012 by Arnaud J. Van Wettere, DVM, MS, DACVP