Morphometric and radiographic characteristics of tibial bone of broiler chickens with twisted leg disorders.

Tibiae from normal broiler chickens were compared with those from broilers displaying twisted leg in an attempt to develop a pattern recognition for the disorder. Qualitative differences were determined using conventional radiography, and quantitative differences were determined using sequential morphometry. Sequential radiography revealed that twisted leg developed from a slight deviation or torsion of the distal tibiae. Progressive bowing of the tibiae and compensatory thickening of the cortex on the weight-bearing side were characteristic radiographic features of twisted leg and were most likely a functional adaptation to the disorder. Sequential morphometry suggests that the development of twisted leg in broilers may be related to a structural abnormality in the distal tibiae, namely shallow distal condyle grooves. Shallow distal condyle grooves may predispose the distal tibiae to a slight displacement of the gastrocnemius tendon and hence uneven strain on the distal condyles. Other changes in tibial morphology (diameter at midshaft, condylar width, cortical thickness) appeared to be functional adaptations to the deformation rather than the primary cause.