The peroneus muscle originates on the proximal end of the tibiotarsus and patellar tissue, with attachments to other muscles in that area. In turkeys, the insertion appears to be in 3 places. A small band of tissue from the medial side of the muscle runs to the lateral tibial condyle. The main muscle tendon crosses the lateral side of the hock and joins other tendons that extend the hock and may affect foot and toe movement. The muscle is thin and wide, covering the anterior and lateral surface of the leg. It has a heavy aponeurosis in which the tendon is embedded. Rupture of the aponeurosis and muscle occurs as a 1–2 cm horizontal wound on the anterior surface of the muscle. It occurs above the middle of the tibiotarsus at the top of the ossifying tendon where the tendon attaches to the muscle. Rupture occurs at 10–14 wk, the age at which turkey leg tendons become ossified, reducing the elasticity of the tissue in that location.

Fig. 1
Rupture of the peroneus (fibularis) longus muscle in the turkey. Illustration by Dr. Gheorghe Constantinescu.

Incidence appears to be increasing. It is most frequent in females and may affect up to 5% of the flock. The separation of the muscle likely occurs slowly, caused by activity such as repeated springing, in turkeys that are becoming heavier and maturing earlier. The attachments of this muscle suggest that antagonistic activity is possible. Affected birds are not lame, but the resulting hemorrhage causes a red, blue, or green discoloration under the skin on the anterior of the drumstick ventral to the rupture. The affected portion is trimmed at processing.

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